PH Nanosensor

A novel solid-state pH sensor technology invented at the University of Oxford is to be further developed and commercialised by San Francisco Bay Area based company Phathom Nanosensors Inc.

The University’s technology transfer company, Isis Innovation has licensed the technology – originally developed for monitoring pH in oil wells – to Phathom, who will adapt it for other industries. The first industrial segment will be pharmaceutical, but measurement and control of pH is also vital in other industries such as water, food & beverage and chemical manufacturing.

The technology was developed by Prof Richard Compton at Oxford’s Physical and Theoretical Chemistry Laboratory. Compton’s group is a world leader in developing electrochemical sensors for extremely precise detection. A previous invention able to measure the amount of 'drugs of impairment' such as cannabis and amphetamines, by rapidly analysing a small sample of saliva is being developed by Oxford spin-out Oxtox Ltd.

“This is an exciting project because this technology has the potential to disintermediate a market worth nearly a billion dollars annually, that is dominated by a 70 year old technology,” said Lee Leonard, CEO of Phathom. “Introduction of these sensors will be analogous to replacement of vacuum tubes with solid-state transistors. With that comes the opportunity not only to improve existing processes already using pH measurement and control, but to address new opportunities where the existing technology cannot be used due to calibration, drift and mechanical limitations.”

Phathom has assembled a team of experienced scientists, executives and entrepreneurs, each of whom has started and grown highly successful multinational companies.

“Our pH sensor technology has several key advantages over the glass electrode technology still widely used in industry,” said Compton. “They are more accurate, enabling tighter control of pH-critical manufacturing processes. Co-inventor Dr Greg Wildgoose added: “The sensors are also self-calibrating, eliminating the problem of reading drift over time experienced with glass pH electrodes.”

Isis licenses pH sensor technology to Phathom Nanosensors
http://www.isis-innovation.com/news/news/PhantomNanosensors.html

Technology transfer from Oxford University

Iron based superconductor

Fig. 1. Schematic crystal structure of α-FeSe. Four unit cells are shown to reveal the layered structure.


Although superconductivity exists in alloy that contains the element Fe, LaOMPn (with M = Fe, Ni; and Pn = P and As) is the first system where Fe plays the key role to the occurrence of superconductivity. LaOMPn has a layered crystal structure with an Fe-based plane. It is quite natural to search whether there exists other Fe based planar compounds that exhibit superconductivity. Here, we report the observation of superconductivity with zero-resistance transition temperature at 8 K in the PbO-type α-FeSe compound.

A key observation is that the clean superconducting phase exists only in those samples prepared with intentional Se deficiency.



Fig. 2.

Powder x-ray diffraction patterns of FeSe0.82 and FeSe0.88. The patterns show that the resulting sample with starting composition of Fe (53%)/Se (47%) composes of primarily PbO-type tetragonal FeSe1−x (P4/nmm), the α-phase, and partly of NiAs-type hexagonal FeSe (P63/mmc), the β-phase. The sample with higher initial iron content, Fe (55%)/Se (45%), shows no β-phase but trace amounts of possible impurity phases including elemental selenium, iron oxide, and iron silicide (marked with an asterisk). Question marks in the figure represent unknown phases.

FeSe, compared with LaOFeAs, is less toxic and much easier to handle. What is truly striking is that this compound has the same, perhaps simpler, planar crystal sublattice as the layered oxypnictides. Therefore, this result provides an opportunity to better understand the underlying mechanism of superconductivity in this class of unconventional superconductors.



Superconductivity in the PbO-type structure α-FeSe, Sept 2008
http://www.pnas.org/content/105/38/14262.full
PNAS September 23, 2008 vol. 105 no. 38 14262-14264



SUPERCONDUCTOR SYNTHESIS


Theory
________________________________________
Electrical resistance in metals arises because electrons propagating through the solid are scattered due to deviations from perfect translational symmetry. These are produced either by impurities (giving rise to a temperature independent contribution to the resistance) or the phonons (lattice vibrations in a solid - the temperature dependent occupancy of these boson states produces a temperature dependent resistivity p = p0 + AT5 in a metal at low temperature.
In a superconductor below its transition temperature Tc, there is no resistance because these scattering mechanisms are unable to impede the motion of the current carriers. The current is carried in all known classes of superconductor by pairs of electrons known as Cooper pairs. The mechanism by which two negatively charged electrons are bound together is still controversial in "modern" superconducting systems such as the copper oxides or alkali metal fullerides, but well understood in conventional superconductors such as aluminium in terms of the mathematically complex BCS (Bardeen Cooper Schrieffer) theory.
The essential point is that below Tc the binding energy of a pair of electrons causes the opening of a gap in the energy spectrum at Ef (the Fermi energy - the highest occupied level in a solid), separating the pair states from the "normal" single electron states.
The size of a Cooper pair is given by the coherence length which is typically 1000Å (though it can be as small as 30Å in the copper oxides). The space occupied by one pair contains many other pairs, and there is thus a complex interdependence of the occupancy of the pair states. There is then insufficient thermal energy to scatter the pairs, as reversing the direction of travel of one electron in the pair requires the destruction of the pair and many other pairs due to the nature of the many-electron BCS wavefunction. The pairs thus carry current unimpeded.
BCS theory applies directly to superconductors such as Nb3Ge (Tc = 23K) in which the electrons are bound together by their interaction with the vibrations of the underlying lattice: one electron in the pair polarises the lattice by attracting the nuclei towards it, leaving a region of excess positive charge (a potential well) into which a second electron is attracted - the positively charged nuclei thus mediate an attraction between the negatively charged electrons. Only electrons within the vibrational frequency of EF can be paired by this interaction, and so only a small fraction of the electrons become superconducting.
The most obvious experimental signature of superconductivity is the observation of zero D.C. electrical resistance, and the possibility for low loss power transmission and large fast computers is one of the main reasons for technological interest in breakthroughs in superconductivity.
Zero resistance is hard to measure, and the most definitive evidence for superconductivity in fact arises from d.c. magnetic measurements. Persistent currents on the surface of the superconductor make it a perfect diamagnet below Tc i.e. it expels all magnetic flux. The difference between superconducting diamagnetism and that of benzene is both its larger size and more complex history dependence. This is illustrated by the effect of the cooling procedure on the measured superconducting diamagnetism:
Cooling in zero applied magnetic field and measurement of the magnetisation on warming in a measuring field applied below Tc (zero field cooled (ZFC) measurement). The superconductor displays perfect diamagnetism (flux exclusion)
Cooling in the measuring field through Tc followed by measurement on warming (field cooled or FC measurement). Magnetic flux present inside the sample above Tc is trapped inside by the shielding currents on the surface below Tc . The FC susceptibility is still diamagnetic (flux expulsion) but reduced in magnitude compared to the ZFC susceptibility.
This hysteresis of the diamagnetic susceptibllity below Tc is known as the Meissner effect and is definitive proof of superconductivity. The magnetic behaviour of a superconductor below Tc as a function of field is also more complex than that of a simple para- or diamagnet. The magnetisation initially varies linearly with applied field, but its behaviour above a critical field allows the division of superconductors into Type I or the more common Type II.
Type I superconductors lose their superconductivity above a critical field Hc as the field penetrates the material. In type II superconductors, the field penetrates the superconductor partially to form the Abrikosov flux lattice above the lower critical field Hc1. Above Hc1 the diamagnetism decreases with increasing applied field until superconductivity is quenched at the upper critical field Hc2, returning to the normal metallic state.
The value of HC2 is very important as it partially determines the current carrying capacity of the superconductor and its uses e.g. to produce high field superconducting magnets. In the copper oxides, Hc2 is of the order of 40T at liquid helium temperatures.
Copper oxide superconductors
The YBa2Cu307 sample made in this experiment was the first material ever to have a superconducting transition temperature above the boiling point of liquid nitrogen (BCS based predictions had suggested a limit to Tc of about 30-40K). It is important to note that superconductivity only occurs for copper oxidation states either greater or less than, but not equal to, two e.g. La2CuO4 is an antiferromagnetic insulator whereas La1.85Sr0.15CuO4 is a metal and superconductor. Question 6 asks you to account for the insulating nature of the Cu(II) compounds.
The binding mechanism leading to the formation of Cooper pairs in the copper oxides is thought to be related to the extremely strong superexchange interactions between the copper spins and not to result from the electron-vibration interaction which produces the lower Tc's.
The variation of electronic properties with copper oxidation state is well illustrated in the La2-xSrxCuO4 series. For 0>x>0.03, the Neel temperature TN decreases from 250K at x=0 to zero at 0.03, and a transition to a superconducting metal occurs at x = 0.06, with Tc rising to a maximum of 42K at 0.15. Beyond x=0.2, the superconductivity disappears and the compounds are non-superconducting metals. The importance of the copper oxidation state and the chemical environment of the copper cations in controlling the properties is shown by the very wide variation in Tc in the compounds listed in Table I. The influence of applied pressure on superconductivity is also remarkable, and suggests the likely influence of possible chemical substitutions. The highest superconducting transition temperature yet achieved reproducibly is 150K under 23.5 GPa of hydrostatic pressure in HgBa2Ca2Cu3O8+d.

Transition temperatures in inorganic superconductors

Compound Tc (K)
PbMo6S8 12.6
SnSe2(Co(C5H5)2)0.33 6.1
K3C60 19.3
Cs3C60 40 (15 kbar applied pressure)
Ba0.6K0.4BiO3 30
Lal.85Sr0.l5CuO4 40
Ndl.85Ce0.l5CuO4 22
YBa2Cu3O7 90
Tl2Ba2Ca2Cu3O10 125
HgBa2Ca2Cu3O8+d 133


http://neon.chem.ox.ac.uk/vrchemistry/super/default.html

Protein corona

Nanoparticle size and surface properties determine the protein corona with possible implications for biological impacts

Nanoparticles in a biological fluid (plasma, or otherwise) associate with a range of biopolymers, especially proteins, organized into the “protein corona” that is associated with the nanoparticle and continuously exchanging with the proteins in the environment. Methodologies to determine the corona and to understand its dependence on nanomaterial properties are likely to become important in bionanoscience. Here, we study the long-lived (“hard”) protein corona formed from human plasma for a range of nanoparticles that differ in surface properties and size. Six different polystyrene nanoparticles were studied: three different surface chemistries (plain PS, carboxyl-modified, and amine-modified) and two sizes of each (50 and 100 nm), enabling us to perform systematic studies of the effect of surface properties and size on the detailed protein coronas. Proteins in the corona that are conserved and unique across the nanoparticle types were identified and classified according to the protein functional properties. Remarkably, both size and surface properties were found to play a very significant role in determining the nanoparticle coronas on the different particles of identical materials. We comment on the future need for scientific understanding, characterization, and possibly some additional emphasis on standards for the surfaces of nanoparticles.
Edited by H. Eugene Stanley, Boston University, Boston, MA, and approved August 7, 2008

http://www.pnas.org/content/105/38/14265



Probing the interactions of proteins and nanoparticles

......on development of methods for probing the association of proteins to nanoparticles: Such association is almost always a first step when nanoparticles enter a biological fluid, so that when we think of the interactions of nanoparticles with a living system, we are really speaking of protein-coated particles. Adsorption of the proteins onto the particle surface can lead to altered conformation, exposure of novel “cryptic” peptide epitopes, perturbed function (caused by structural effects or local high concentration), or avidity effects arising from the close spatial repetition of the same protein (10). Thus, although protein adsorption has been studied classically both on planar surfaces and in colloidal dispersions (11–13), the focus by Cedervall et al. on the specific binding rates and affinities of different plasma-related proteins to nanoparticles is a welcome development in this field. Proteins compete for the nanoparticle surface, leading to an adsorbed protein layer or “corona” that largely defines the biological identity of the particle. Underlying all of these effects is the fact that nanoparticles have a very large surface-to-volume ratio, so that even small amounts of particles present extremely large surface areas available for protein binding.

A better understanding of the biological effects of nanoparticles requires knowledge of the binding properties of proteins (and other molecules) that associate with the particles from realistic mixtures of proteins such as those in biological fluids. However, the isolation and identification of particle-associated proteins is not a simple task. The methods proposed by Cedervall et al. (9) are able to identify both major and minor particle-associated proteins and to study the competition between proteins that bind when the system is under kinetic or thermodynamic control. The challenge is to use nonperturbing methods that do not disrupt the protein–particle complex or induce additional protein binding.

Most of the methods applied by Cedervall et al. (9) have not been used before for studying nanoparticle–protein affinity but, happily, are nonetheless based on established techniques, including size-exclusion chromatography (SEC), isothermal titration calorimetry (ITC), and surface plasmon resonance (SPR), which should make them widely accessible. These approaches are applied to a set of model copolymer nanoparticles of two different sizes that allow for systematic investigation of the effect of the composition (hydrophobicity) and size of the particles on their interaction with proteins. In particular, a new approach (based on SEC-gel filtration; see below and Fig. 1) is introduced that can yield both the identity of the proteins on the nanoparticles and the rates of exchange with plasma proteins. This method is less perturbing of protein–particle complexes than centrifugation and other approaches (9). Cedervall et al. also show that ITC can be used to assess the stoichiometry and affinity of protein binding, and SPR studies (in which nanoparticles are linked to gold by a thiol anchor) yield additional data on protein association/dissociation from nanoparticles.

Nanoparticles have a very large surface-to-volume ratio.

The results indicate that many proteins form transient complexes with nanoparticles and that there is a clear dependence of the binding and dissociation parameters on protein identity and the particle surface characteristics. The resulting corona then effectively constitutes the new nanoparticle “surface,” while its shape and size also may play an important role in its interactions with cell surfaces. An important role of the nanoparticles also may be in giving a “ride” to the corona proteins across a cell or organelle membrane, where they are then dissociated.

A remarkable observation made by Cedervall et al. (9) is the large variation in dissociation rates for proteins on nanoparticles, implying that, depending on the experimental procedures and times, different sets of proteins may be identified as part of the particle–protein corona. Also, the concentrations of particles and biological fluid will influence the outcome of identification experiments. The total protein concentration in bodily fluids, especially in intracellular environments, can be up to 35% (0.35 g/ml), representing several thousand different proteins spanning a wide range of concentrations. As a result, there will be competition between the proteins for the available nanoparticle surface area in a typical biological environment. Human serum albumin (HSA) and fibrinogen may dominate on the particle surface at short times but will subsequently be displaced by lower abundance proteins with higher affinity and slower kinetics (in the case of the hydrophobic particles studied here, for example, apolipoprotein A-I is much more important). In contrast, when the available nanoparticle surface area is in excess over the total available protein, lower-affinity proteins such as albumin also may be found in isolation experiments. To identify a set of associated proteins that more closely reflects the situation in vivo will require the protein mixture (e.g., plasma) to be in excess over the available particle surface area, and at best that the particle concentration used reflects a true biological situation (such as a typical therapeutic or imaging particle concentration; see, e.g., ref. 14).

Another very interesting and, to my mind, unexpected observation is that for a given level of nanoparticle hydrophobicity, there is a distinct difference between the degrees of surface coverage of the nanoparticles depending on their size, with the larger degree of coverage on the larger particle. This finding suggests that as little as a 3-fold difference in nanoparticle sizes can result in a marked curvature-induced suppression of the protein adsorption [as pointed out by Cedervall et al. (9)], even when the nanoparticles themselves, of diameters 70 and 200 nm, are much larger than the adsorbing proteins (of order 10 nm for the globular HSA studied). One speculation is that the curvature of even smaller nanoparticles, say, 30 nm or so in diameter, may entirely suppress the adsorption of certain (presumably larger) proteins: thus, the nanoparticle size, and not only the chemical composition of its surface, may itself be an important parameter in determining the composition of the protein corona.

From a methodological point of view, the gel filtration approach looks promising. The simple, but effective, idea underlying this approach is that the nanoparticles, which are much larger than the proteins that attach to and detach from them, move through the gel faster and elute from it sooner than free proteins, which, en route to elution, sample many of the smaller gel cavities from which nanoparticles are excluded. Thus, proteins may hitch a fast ride on the nanoparticles as long as they are attached to them but migrate sluggishly once they dissociate, as illustrated in Fig. 1. A fraction-by-fraction comparison of the proteins eluting with and without particles allows the identification of both slowly and more rapidly dissociating proteins, and their exchange rates may be estimated from their elution profiles. With careful choice of column dimensions and relative concentrations of protein and particles, the technique isolates both major and minor particle-associated proteins, and modern methods of proteomics may be applied to identify them. Further development of the technique, using a wide range of column designs, lengths, and other parameters, could be expected to make the approach increasingly flexible and contribute significantly to our understanding of the particle–protein corona.

The novelty and importance of the work by Cedervall et al. (9) is that it imaginatively adapts familiar methodologies to examine the issue of nanoparticle–protein interactions and the resulting coating of the particles by a protein layer (so-called corona). This issue will be of increasing relevance to the fields of nanomedicine and, in particular, nanotoxicology, which recognizes the potential for harmful interactions between living tissues and submicrometer- or nanometer-scale objects in a way that may differ qualitatively from more familiar, larger-scale particles with which living organisms have evolved (15). Further advances in these fields will require not only a more quantitative and systematic study of the composition of the nanoparticle–protein corona but also a study of how that corona actually interacts with and affects the well-being of living cells, using, among other approaches, the highly sophisticated methodologies that have been developed to measure surface and intermolecular forces directly (16).

Klein J, Department of Physical and Theoretical Chemistry, Oxford University, 2007
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1892940


Understanding the nanoparticle–protein corona using methods to quantify exchange rates and affinities of proteins for nanoparticles, Tommy Cedervall,* Iseult Lynch et al, 2007

http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1892985

Sono-Electrochemistry

Sonoelectrochemistry - The Compton Group

Waves of ultra-sound (20-100 kHz) alternately compress and stretch the structure of the liquid. If a critical distance is exceeded then the liquid breaks down and voids are formed so creating bubbles. During the compression stage the cavities can collapse leading to huge local temperatures (~ 1000s of K) and pressures (~ 100s of atmospheres). Needless to say, this may have interesting chemical consequences! We use voltammetry to monitor ultrasonically induced radicals and other high energy species and are engaged in "dual activation" experiments in which electrolytically formed species are further transformed by ultrasound directed at the electrode surface with the aim of generating new chemistry and novel intermediates. In other experiments ultrasound is used to continuously activate an electrode ~ literally by stripping off surface atoms ~ so as to open up the electrochemistry of either otherwise passivating species.

The sono-activation of electrodes finds particular relevance in facilitating the use of electroanalytical methods (e.g. for trace metals) in real, "dirty" media where conventional voltammetry fails due to the adsorption of surface active species which inhibit or interfere with the intended analytical determination.

http://compton.chem.ox.ac.uk/home.html






dielectric material

A dielectric material is a substance that is a poor conductor of electricity, but an efficient supporter of electrostatic field s. If the flow of current between opposite electric charge poles is kept to a minimum while the electrostatic lines of flux are not impeded or interrupted, an electrostatic field can store energy. This property is useful in capacitor s, especially at radio frequencies. Dielectric materials are also used in the construction of radio-frequency transmission lines.

In practice, most dielectric materials are solid. Examples include porcelain (ceramic), mica, glass, plastics, and the oxides of various metals. Some liquids and gases can serve as good dielectric materials. Dry air is an excellent dielectric, and is used in variable capacitors and some types of transmission lines. Distilled water is a fair dielectric. A vacuum is an exceptionally efficient dielectric.

An important property of a dielectric is its ability to support an electrostatic field while dissipating minimal energy in the form of heat. The lower the dielectric loss (the proportion of energy lost as heat), the more effective is a dielectric material. Another consideration is the dielectric constant , the extent to which a substance concentrates the electrostatic lines of flux. Substances with a low dielectric constant include a perfect vacuum, dry air, and most pure, dry gases such as helium and nitrogen. Materials with moderate dielectric constants include ceramics, distilled water, paper, mica, polyethylene, and glass. Metal oxides, in general, have high dielectric constants.

The prime asset of high-dielectric-constant substances, such as aluminum oxide, is the fact that they make possible the manufacture of high-value capacitors with small physical volume. But these materials are generally not able to withstand electrostatic fields as intense as low-dielectric-constant substances such as air. If the voltage across a dielectric material becomes too great -- that is, if the electrostatic field becomes too intense -- the material will suddenly begin to conduct current. This phenomenon is called dielectric breakdown . In components that use gases or liquids as the dielectric medium, this condition reverses itself if the voltage decreases below the critical point. But in components containing solid dielectrics, dielectric breakdown usually results in permanent damage.

http://whatis.techtarget.com/definition/0,,sid9_gci211945,00.html

Deltahedral Zintl Ions

The categorisation of the elements as metals, semi-metals and non-metals is based fundamentally on the physical properties of the condensed elemental solids. While these labels offer a fair deal of information on the elements, they are not particularly useful in predicting their tendency to undergo oxidation and/or reduction or in assessing their ability to form small polyatomic cluster species. Thus, the relatively widespread belief that metals can exclusively be oxidized to monoatomic cationic species is a simplification which, while appropriate in the majority of cases, has several noteworthy exceptions (e.g. Au-, Bi22-, Sb73- and E9x- (E = Si, Ge, Sn, Pb; x = 2-4).

Figure 1.





a) [(Pd-Pd)@Ge18]4-: the largest single cage deltahedron isolated to date. The two palladium atoms form a dimer encapsulated within an eighteen-atom germanium cage (red).

b) [E9Zn(C6H5)]3- (E = Si, Ge, Sn, Pb): the nine-atom cluster cage (red) acts as a six-electron donor to the Zn atom (pictured in yellow).

Deltahedral Zintl Ions. Recent years have witnessed a renaissance of Zintl cluster chemistry as the reactivity of the deltahedral anions of group 14 towards a series of transition metal reagents has been explored. Incorporation of transition metals has resulted in the isolation of a series of novel species in which the transition metal atoms play an essential role in the stabilization of large, otherwise unattainable geometries (as pictured in Figure 1a). Also of interest are recent findings which show that nine-atom Zintl ions may act a 6 electron donors to electrophilic fragments such as Ni(CO), M(CO)3 (M = Cr, Mo, W) or ZnPh (Figure 1b). From a coordination chemist’s viewpoint these species are of interest as they are comparatively similar to the numerous organometallic species containing cyclic polyene ligands such as cyclopentadiene that have been the subject of great interest throughout the history of organometallic chemistry.

The ability of Zintl ions to undergo nucleophilic and electrophilic substitution may also allow for their integration as backbones within ligand and spacer group moieties, with the aim of employing them for the construction of molecular devices and larger frameworks. The unique physical properties of these Zintl clusters allows for the development of interesting new species with potential applications in sensors, molecular wires and photochemical systems. The clusters isolated to date represent the first steps in a nascent area of chemistry where many interesting new discoveries await.

(b) Metalloid Clusters. Metalloid cluster compounds are defined as metal cluster species where the number of metal-metal contacts outnumber metal-ligand contacts, and in which the metal atoms of the cluster core take on a close-packed arrangement reminiscent of the bulk metal. These species offer a unique insight into the rather ill-defined area of chemistry that spans between isolated molecular species and solid-state compounds with extended structures. Small, cage-like clusters have been relatively well studied and are found to generally follow established rules for electron counting and isolobal relationships. Their structures and bonding are fairly well understood and can be rationalized within the context of said rules. However, this is not the case for large clusters with high nuclearities (n>12) and dimensions beyond that of the nanometer. These species lack such a cohesive theoretical foundation and, furthermore, many of them seem to disobey traditional electron counting rules, which ultimately makes discussion of structure and bonding very difficult.



Figure 2. [Zn9Bi11]5- : Zn (yellow) and Bi (green) atoms arrange to form an intermetalloid cluster comprised of a Zn-centered, Zn8Bi4 icosahedron (blue), in which seven of the icosahedral faces are capped by bismuth atoms. The cluster represents a fragment of an otherwise unknown binary Bi/Zn alloy.


To date the chemistry of such clusters has been predominantly limited to the group 13 elements and to a few precious metals such as palladium and gold. However, recent findings show that controlled oxidation of negatively charged metal species such as the dimeric Bi22- molecule may be used as a viable synthetic route towards a series of novel metalloid species such as [Zn9Bi11]5- (Figure 2). These species prove that such nanometric species are available in other areas of the periodic table. Isolation of such compounds is paramount in establishing a library of cluster species which may be used for the development of a unified theory for bonding in solids.

(c) Nanoparticle synthesis. The aforementioned Zintl clusters and metalloid species represent intermediates in the oxidative transformation of negatively charged metal and semi-metal species to the bulk element. As such they are molecular ‘snap-shots’ of a synthetic procedure which may ultimately be used to obtain homo- and hetero-metallic colloids and nanoparticles. A similar approach involving the reduction of cationic metal complexes in the presence of strongly coordinating ligands has already been employed as a synthetic technique towards precious metal nanoparticles. However, this approach often suffers from poor polydispersities due to the kinetic nature of the reaction products. An inverse approach involving the mild oxidation of negatively charged species may be used as a synthetic alternative offering greater molecular control over the species synthesized as well as a wider gamut of available nanoparticle compositions.

Dept. of Chemistry, University of Oxford

http://www.chem.ox.ac.uk/researchguide/jmgoicoechea.html

DrugFinder: Providing Superior Inhibitors

InhibOx Limited announces the launch of a free hit identification service, devised by Professor Graham Richards of the Chemistry Department of the University. It will enable research groups in academia and biotechnology companies to exploit an increasingly important starting point for novel drug discovery, namely, crystal structures of target proteins with an inhibitor bound in the active site. The project follows on from the extremely successful screensaver project run from the University of Oxford Chemistry Department (http://www.chem.ox.ac.uk) by Professor Richards in collaboration with computational chemistry company InhibOx and the National Foundation for Cancer Research (NFCR), with sponsorship at various times from Intel Corporation, Microsoft and IBM. The screensaver project which ran from 2001‐2007 (http://www.chem.ox.ac.uk/curecancer) involved over 3.5 million personal computers in more than 200 countries and was the world’s biggest computational chemistry experiment. A database of some three billion molecules was screened and a number of predicted hits were subsequently synthesized and tested with very promising results. Virtual screening clearly works.

The NFCR and Inhibox have joined forces again to offer a service using InhibOx’s inhouse computing facilities and databases of molecular structures. By going to a web site (http://www.inhibox.com/drugfinder), researchers in universities or biotechnology companies will be able to submit a structure with a bound inhibitor. Inhibox will screen its small molecule database against the target and then provide to the academic or biotechnology company potentially superior inhibitors. Any intellectual property will be treated confidentially and results will belong to the group providing the crystal structure.

The screening service will be provided through three service levels: Bronze, Silver and Gold. The Bronze service will be entirely free of charge and will identify up to 100 compounds from the database which are similar to the bound inhibitor, but offer the possibility of new scaffolds and chemistry.

The Silver service mirrors the Bronze, but includes searching a larger database and will return a larger number (up to 1000) of novel potential inhibitors.

About InhibOx
InhibOx is a computational drug discovery company. The company’s primary objective is to develop novel and effective computational methods for drug discovery in order to improve the productivity of lead and candidate identification. InhibOx was founded in 2001 by Professor W. Graham Richards, chairman of Chemistry at the University of Oxford and world leading computational chemist. The company grew from the outstandingly successful screen saver project which involved some 3.5 million personal computers in over 200 countries: the world’s biggest computational chemistry experiment finding lead compounds to inhibit cancer targets, anthrax and smallpox. Subsequently, the company has built up a significant technology platform. Its main ongoing research activities comprise the development of entirely novel computational discovery methods and associated with this, the development of Scopius a very large database of chemical structures. For more information, please refer to (http://www.inhibox.com).

About NFCR
The NFCR was founded in 1973 to support basic science cancer research in the laboratory. The NFCR’s program of basic science cancer research conducted at both the cellular and molecular levels is leading to better prevention, earlier diagnostic techniques, new treatments, and eventually a cure for cancer. By supporting the best ideas of the best minds, and by facilitating collaboration among scientists, advances in one field contribute to discoveries in another. This is what NFCR’s “Laboratory Without Walls” makes possible. Since 1973 NFCR has provided more than $250 million to fund discovery‐oriented research that has played a key role in many current breakthroughs in the prevention, diagnosis and new treatments of all types of cancer. In 2000 the NFCR funded a virtual centre, the Centre for Computational Drug Discovery, directed from Oxford University’s Department of Chemistry by Professor Graham Richards. For more information, please refer to (http://www.nfcr.org).

http://www.chem.ox.ac.uk/news/DrugFinder.pdf

Viteomics

Introduction

Viteomics represents a group of scientists who are interested in the biosynthesis of a range of coenzymes and cofactors. The primary objective of the project is to gain molecular detail on the control, regulation and biosynthesis of vitamins B5 (pantothenate), B9 (folate), B12 (cobalamin), H (biotin) and the molybdenum cofactor (Moco) within a comprehensive research programme entitled Viteomics. We have outlined a multidisciplinary approach to investigate how these compounds are made and to develop methods for exploitation of the data. In so doing we aim to provide a Network promoting training through outstanding research.

http://www.kent.ac.uk/bio/viteomics/training/default.htm

Liquid Crystalline Phases

A material is defined as a crystalline solid (Cryst) when the structure has long-range order of the molecular positions in three dimensions. A fully ordered crystal will also have long-range orientational ordering of its constituent molecules. When a fully ordered molecular crystal is heated the thermal motions of the molecules within the lattice increase and eventually the vibrations become so intense that the regular arrangement of molecules is broken down with the loss of long-range orientational and positional order to give the disorganised isotropic liquid (Iso). The temperature at which this process occurs is called the melting point and the heat absorbed by the molecules is the latent heat of fusion. However, this process, which takes a compound from being very well ordered to being totally disordered in one step is a very destructive one, which is not universal for all compounds. For many compounds, this process occurs by way of one or more intermediate phases as the temperature is increased. These phases are called mesophases and some of these mesophases are liquid crystalline. Liquid crystalline phases have properties which are intermediate between those of the fully ordered crystalline solid and the isotropic liquid; liquid crystalline mesophases are fluids which, due to partial orientational ordering of the constituent molecules, have material properties such as permittivity, refractive index, elasticity and viscosity which are anisotropic (i.e., their magnitude will differ from one direction to another).


Mesogenic (i.e., mesophase-producing) compounds generally consist of long, narrow, lath-like and fairly rigid molecules (see Figure 1 and the examples on page 5). In the crystal state (Cryst), the molecules are held together by strong intermolecular forces of attraction which, due to the lath-like structure, are anisotropic. In simple terms, the smectic phase arises if the lateral intermolecular forces of attraction are stronger than the terminal forces and so, on heating, the terminal forces breakdown first, in-plane translational order is lost and this results in a lamellar arrangement of molecules in which the layers are not well defined (T2). Due to possible correlations within the layers and between the layers there are five true smectic modifications and a further six quasi-smectic disordered crystal mesophases. T3 illustrates the loss of both in-plane and out-of-plane translational order to leave a statistically parallel arrangement of molecules (orientational order) in the nematic phase. When the smectic phase is heated either out-of-plane translational ordering is lost (T4), which produces the nematic phase, or additionally orientational ordering is lost (T5), which gives the isotropic liquid. T6 represents the loss of orientational ordering of the nematic phase to give the isotropic liquid. No single liquid crystalline material exhibits all liquid crystal phase types but many compounds do exhibit two or three different types of liquid crystalline phase.

An important feature of mesophase-mesophase and mesophase-isotropic liquid phase transitions is that they are exactly reversible (to within ~0.5 ¡C), whereas crystal-crystal, crystal-mesophase and crystal-isotropic liquid phase transitions are not because supercooling occurs. This can be useful in determining the presence of a mesophase and since supercooling occurs on cooling to the crystal state then mesophases may be revealed on cooling and not on heating. Such mesophases are called monotropic and the temperatures at which they occur are given in round brackets (). Monotropic mesophases always occur below the melting point, whereas mesophases which occur above the melting point are formed on both heating and cooling and are called enantiotropic mesophases.

All of the compounds have the familiar long, lath-like structure but in many respects their structural composition is completely different and reflects the different applications for which the materials are intended. In the design of liquid crystal compounds the most important aspect is that they must exhibit the correct type of liquid crystalline phase over the desirable temperature, usually room temperature. Additionally liquid crystals must have a suitable combination of structural features to enable the generation of a rather subtle blend of physical properties. Clearly, to obtain everything from one material is not possible and so liquid crystals for commercial applications are all mixtures of appropriate materials that provide the best compromise of properties. A wide variety of synthetic organic chemistry techniques are used to prepare liquid crystal materials which must be of extremely high purity. An equally wide range of techniques are used to assess the materials both as single compounds and in mixtures. Compounds 2 and 3 were discovered at the University of Hull. Compound 3 was the first commercially viable, stable, room temperature liquid crystal that is suitable for use in watch and calculator type liquid crystal displays. Compound 2 is still the largest single component used in liquid crystal mixtures for displays. Compounds of types 4, 5 and 6 were also invented at the University of Hull and were designed to be used as ferroelectric host materials in fast-switching displays. Compound 9 is another compound from the wide variety synthesized at the University of Hull and this material has highly conjugated and polarizable structure; this material is used for specialist mixtures where a high birefringence is required. Compounds 10, 11 and 12 are chiral materials (see page 6) which are of great technological importance and are currently the subject of intense research. Many liquid crystalline materials are synthesized for fundamental reasons, i.e., to determine the relationship between the molecular structure and the physical properties; others are synthesized directly for applications (e.g., display devices and thermochromic devices).

The Nomenclature and Structure of Liquid Crystalline Phases

Liquid crystalline phases are named according to their degree of molecular ordering. For smectic phases there are various possible ways in which the constituent molecules can order and this enables the generation of six quasi-smectic crystal mesophases and five true smectic liquid crystal phases. The quasi-smectic crystal phases are given the letters B, J, G and E, K, H which are rather arbitrary but relate to the degree of ordering of the constituent molecules. True smectic liquid crystals are given the symbol S and a subscript which indicates the phase type (SA, SC and SB, SI, SF), again the nomenclature is rather arbitrary. The nematic phase is given the symbol N and there is only one nematic phase.

In smectic phases the molecules are arranged in layers which are not well defined and the different smectic phase types arise because of the different possibilities of molecular ordering within the phase structure. For example, in the B phase (disordered crystal) the molecules are arranged in a hexagonal arrangement and the positions of the hexagonal nets within each layer repeat in a regular manner throughout the phase, however, where the hexagonal nets do not regularly repeat throughout the structure a SB phase is generated. When the hexagonal ordering of the molecules becomes disrupted but the layer-like structure remains then the least ordered smectic liquid crystal phase (SA) is generated. In some of the phases (e.g., SC and SI) the molecules are tilted within the layers. Accordingly, the SC phase is the tilted analogue of the SA phase and the SI and SF phases are the tilted analogues of the SB phase. The layer ordering of the smectic liquid crystal phases confers a viscous nature but the material does flow. The nematic phase does not have a layered structure and the only degree of ordering is the statistically parallel arrangement of the molecules in one direction (director). Accordingly, the nematic phase is very fluid and much like a conventional liquid in nature except that a bulk example appears opaque. The opaque appearance is because of director fluctuations within a bulk sample; a fully aligned nematic sample would appear transparent.

Chirality (Handedness) in Liquid Crystals

In certain cases, organic molecules can be chiral or handed, i.e., there are two possible isomers associated with a particular structure and they are object and mirror image; rather like a left hand and a right hand. The isolation of one particular isomer gives a chiral material and this type of chirality is often described as molecular chirality. However, liquid crystals are ordered phases that are also fluid and when certain liquid crystal phases are composed of chiral molecules then the whole phase becomes chiral or handed; this type of chirality is often called form chirality where some macroscopic feature of the bulk phase has a handed structural feature. The most common liquid crystalline phase that exhibits form chirality is the chiral nematic (N*) phase. When composed of chiral molecules the nematic phase is called the chiral nematic (N*) phase and is also commonly referred to as the cholesteric phase (Ch). The term cholesteric is historical in that all early chiral nematic materials were derivatives of cholesterol. In the chiral nematic phase the chirality manifests itself in the form of a helical arrangement of molecules (see Figure 4a). The molecular alignment is identical to that found in the nematic phase except that the molecular chirality causes a slight, sequential change in the direction of the rod-like molecules through a section of material. This gradual change in molecular direction scribes a helix and the length over which this occurs is temperature dependent and is called the pitch. The pitch becomes shorter as the temperature is increased (see page 10). For a particular chiral material the direction of the helix is opposite for each isomer but the pitch length is the same.

The chiral smectic C (SC*) phase also exhibits form chirality as a helical macrostructure. In the achiral smectic C (SC) phase the constituent molecules are tilted with respect to the layer normal and the helix in the chiral variant is generated by a slight, sequential change in the direction of the tilt within each layer (see Figure 4b). The pitch of the helix of the SC* phase is also temperature dependent but at high temperatures the pitch is long and at low temperatures the pitch is short. The combination of chirality and tilt in the chiral smectic C phase reduces the symmetry of the system and the constituent molecules are spontaneously polarized; this phenomenon has great technological implications for very fast-switching ferroelectric light shutters and display devices.

http://www.hull.ac.uk/chemistry/research/LChistory.html#phases



Electrochromic devices

Self-contained, hermetically sealed, two-electrode electrolytic cells that change their ability to transmit (or reflect) light in response to a small bias (typically 1–2 V) applied across the two electrodes. The operation of electrochromic devices relies upon their electrochromic material content. These materials are organic or inorganic substances that are able to interconvert between two or more color states upon oxidation or reduction, that is, upon electrolytic loss or gain of electrons. The electrochromic materials that are appropriate for most practical applications are strong light absorbers in one redox state but colorless in another.

A typical electrochromic device is a sandwichlike structure with two glass plates and an electrolyte (see illustration). Each glass plate is coated on the inside with a transparent electrically conducting layer of indium-tin oxide, which operates as an electrode. Electrochromic mirrors include an additional reflective coating (for example, aluminum) on the outside of one of the glass plates. The electrolyte carries the ionic current inside the cell between the two electrodes, and it can be as simple as a salt (for example, sodium chloride, NaCl) dissolved in a dissociating solvent such as water. However, development has focused on gel and solid electrolytes, because they offer several advantages: they are easier to confine in the space between the electrodes; they function as laminators holding the two glass plates together; and their use minimizes the hydrostatic pressure that can cause substrate deformation and leakage problems, particularly in large-area devices such as smart windows.





State-of-the-technology electrochromic devices utilize two electrochromic materials with complementary properties: the first electrochromic material is normally reduced (ECM1red) and undergoes a colorless-to-colored transition upon oxidation (loss of electrons), while the second electrochromic material is normally oxidized (ECM2ox) and undergoes a similar transition upon reduction (gain of electrons). The electrochromic materials ECM1red and ECM2ox are selected so that they do not react with each other. The oxidation of ECM1red and the reduction of ECM2ox then are forced by the external power source (see illustration), which operates as an electron pump consuming energy in order to transfer electrons from one electrode to the other. Oxidation of ECM1red occurs at the positive electrode (anode) and is a source of electrons, while reduction of ECM2ox occurs at the negative electrode (cathode) and is a sink of electrons. This approach, known as complementary counterelectrode technology, has two distinct advantages. First, the long-term operating stability of the electrochromic cell is greatly enhanced, because providing both a source and a complementary sink of electrons within the same cell prevents any electrolytic decomposition of the electrolyte. Second, the reinforcing effect of two electrochromic materials changing color simultaneously enhances the contrast difference between the color states per unit charge consumed. Depending on the location of the two electrochromic materials within the electrochromic devices, three main types of such devices exist: solution, precipitation, and thin-film. See also Electrode; Electrolyte; Oxidation-reduction.

Electrochromic devices are analogous to liquid-crystal devices in that they do not generate their own light but modulate the ambient light. Liquid-crystal devices require use of polarizers; consequently, their viewing angle is limited, and lateral size limitations are imposed because the spacing between the electrodes (thickness) must be controlled within a few micrometers over the entire device area. Electrochromic devices do not require polarizers, thereby allowing a viewing angle approaching 180°, and contrast ratios similar to black ink on white paper (20:1 or better); moreover, control of the thickness is not important. Other desirable features of electrochromic devices include inherent color, continuous gray scale, and low average power consumption for the thin-film-type devices. Furthermore, it has been shown that electrochromic thin films can be patterned with a 2–5-μm resolution to form a large number of display elements that can be matrix-addressed. Nevertheless, even though there is no apparent intrinsic limitation, the best cycling lifetimes claimed for electrochromic materials are of the order of 10–20 million cycles, while the lifetime of liquid-crystal devices is of the order of several hundred million cycles. This long lifetime has made liquid-crystal devices a very successful technology in matrix-addressed, flat-panel displays.

The larger tolerance in thickness variation for electrochromic devices renders them better suited than liquid-crystal devices for large-area light modulation applications, such as smart windows, space dividers, and smart mirrors. Another possible application is in large-area displays that do not need frequent refreshing, such as signs and announcement boards. Reconfigurable optical recording devices (for example, disks) have been proposed as a high-resolution application that is within the presently available lifetimes of electrochromic materials.

http://www.answers.com/topic/electrochromic-device

Defects at the rutile TiO2

The total energy of periodic TiO2 slabs using a self-consistent ab initio method calculated show that the 110 surface shows the lowest surface energy, and the 001 surface the highest.001 direction (the crystallographic c-axis). A Ti interstitial located in these channels is in an octahedral configuration, similar to the regular Ti sites. Consequently, the diffusing species in oxidation reactions of reduced TiaOb surfaces (where a>b/2 but probably less than b) produced by sputtering and/or Ti deposition is the Ti atom and not the not the O vacancy, as has been shown in a series of elegant experiments with isotopically labeled 18O and 46 Ti ...The surface science of TiO2

The diffusion mechanism for the various types of defects is quite different; oxygen migrates via a site exchange (vacancy diffusion) mechanism, while excess Ti diffuses through the crystal as interstitial atoms. The interstitial diffusion happens especially fast through the open channels along the 001 direction (the crystallographic c axis. A Ti interstitial located in these channels is in an octahedral configuration, similar to the regular Ti sites. Consequently, the diffusing species in oxidation reacions of reduced Tia Ob surfaces (where a> b/2 but probably less than b) produced by sputtering and/or Ti deposition is the Ti atom and not the O vacancy, as has been shown in a series of elegant experiments with isotopically labeled 18O and 46Ti.

The rutile 110 surface is the most stable crystal face and simple guidelines can be used to essentially predict the structure and stability of TiO2 (110) - (1x1). Because these concepts are very useful for the other crystal faces of TiO2 as well as other oxide materials, they ar exemplified for this surface. Although the TiO2 (110) surface is very stable, it nevertheless reconstrucs and restructures at high temperatures under both oxidizing and reducing conditions.

Surface science of TiO2

The bulk structure of reduced TiO2-x crystals is quite complex with a various types of defects such as doubly charged oxygen vacancies, TiO3+ and TiO4+ interstitials, and planar defects such as CSPs. The defect structure varies with oxygen deficiency which depends on temperature, gas pressure, impurities, etc. despite years of research the question of which type of defect is dominant in which region of oxygen deficiency is still subject to debate. It was shown that the dominant type are Ti interstitials in the region from TiO 1.9999 (from 3.7x10^18 to 1.3x19^19 missing O atoms per cubic centimetre). CS planes precipitate on cooling crystals across the TiO2-x (0 ≤ x≤ 0.0035) phase boundary. They show a very strong dependence on the cooling history and are absent in quenched specimen.
E Yagi physics Review B 54 (1996)
TiO2 electric properties in dependence on the bulk defect concentration has been investigated as well!




Structure, defects, and impurities at the rutile TiO2(0 1 1)-(2 × 1) surface: A scanning tunneling microscopy study


The titanium dioxide rutile (011) (equivalent to (101)) surface reconstructs to a stable (2 × 1) structure upon sputtering and annealing in ultrahigh vacuum. A previously proposed model (T.J. Beck, A. Klust, M. Batzill, U. Diebold, C. Di Valentin, A. Selloni, Phys. Rev. Lett. 93 (2004) 036104/1) containing onefold coordinated oxygen atoms (titanyl groups, Tidouble bond; length as m-dashO) is supported by Scanning Tunneling Microscopy (STM) measurements. These Tidouble bond; length as m-dashO sites are imaged bright in empty-states STM. A few percent of these terminal oxygen atoms are missing at vacuum-annealed surfaces of bulk-reduced samples. These O vacancies are imaged as dark spots. Their number density depends on the reduction state of the bulk. Double vacancies are the most commonly observed defect configuration; single vacancies and vacancies involving several O atoms are present as well. Formation of oxygen vacancies can be suppressed by annealing a sputtered surface first in vacuum and then in oxygen; annealing a sputtered surface in oxygen results in surface restructuring and a (3 × 1) phase. Anti-phase domain boundaries in the (2 × 1) structure are active adsorption sites. Segregation of calcium impurities from the bulk results in an ordered overlayer that exhibits domains with a centered (2 × 1) periodicity in STM.


Surface Science, Volume 600, Issue 19, 1 October 2006, Pages 4407-4417

http://www.sciencedirect.com/




The surface science of titanium dioxide

…a better understanding and improvement of catalytic reactions is one main driving force for surface investigations on TiO2. because most heterogeneous catalysts consist of small metal clusters on an oxide support, many growth studies of metals on TiO2 were performed. These metal/TiO2 systems often serve as a model for other metal/oxide surfaces. Traditionally, TiO2 is a component in mixed vanadia/titania catalysts used for selective oxidation reactions…TiO2 is not suitable as a structural support material, but small additions of titania can modify metal-based catalysts in a profound way. The so called strong metal support interaction (SMSI) is, at least in part, due to encapsulation of the metal particles by a reduced TiO2 overlayer (see review by Haller and Resasco). Recently, this phenomenon was revisited using surface science techniques. The discovery that finely dispersed Au particles supported on TiO2 and other reducible metal oxides oxidize CO at low temperature has spurred some excitement in the surface science community.

The photoelectric and photochemical properties of TiO2 are another focus of active research. The initial work on the photolysis of water on TiO2 electrodes without an external bias, and the thought that surface defect states may play a role in the decomposition of water into H2 and O2, has stimulated much of the early work on TiO2. Unfortunately, TiO2 has alow quantum yield for the photochemical conversion of solar energy. The use of colloidal suspensions with the addition of dye molecules has been shown to improve efficiency of solar cells, and has moved TiO2-based photoelectrochemical converters into the realm of economic competitiveness.
By far, the most actively pursued applied research on titania is its use for photo assisted degradation of organic molecules. TiO2 is a semiconductor and the electron-hole pair that is created upon irradiation with sunlight may separate and the resulting charge carriers might migrate to the surface where they react with adsorbed water and oxygen to produce radical species. These attack any adsorbed organic molecule and can, ultimately, lead to complete decomposition into CO2 and H2O. The applications of this process range from purification of wastewaters; disinfection based on the bactericidal properties of TiO2, for example in operating rooms in hospitals; use of self-cleaning coatings on car windshields, to protective coatings of marble, eg. for preservation of ancient Greek statues against environmental damage. It was even shown that subcutaneous injection of a TiO2 slurry in rats, and subsequent near-UV illumination, could slow or halt the development of tumour cells.


Diebold U, The surface science of titanium dioxide, Surface Science Reports, Volume 48, Issues 5-8, January 2003, Pages 53-229
www.sciencedirect.com









Role of surface oxygen vacancies in photoluminescence of tin dioxide nanobelts

The role of surface oxygen vacancies in the optical properties of tin dioxide nanobelts is investigated in this paper. Using a first-principles approach, based on the density functional theory combined to a very accurate exchange correlation functional, we characterize SnO2 (1 0 1), that is the nanobelt largest surface. We show that the presence of surface oxygen vacancies leads to the appearance of (i) occupied states located at about 1 eV above the valence band and (ii) unoccupied states lying in resonance with the conduction band. Photoluminescence characterization performed on samples of SnO2 nanobelts at low temperature shows that the basic spectral features of luminescence are in excellent agreement with theoretical predictions.

Microelectronics Journal, In Press, Corrected Proof, Available online 27 September 2008





Stored energy, vacancies and thermal stability of ultra-fine grained copper

The stored energy and thermal stability of oxygen-free high conductivity copper processed by equal channel angular pressing up to 16 passes at room temperature was studied by differential scanning calorimetry. Stored energy increased with strain up to four passes, after which it saturated at 0.95 ± 0.05 J/g. This saturation value is 20% higher than from conventional cold rolling. The microstructure of the copper after eight passes was characterized by an average subgrain size of about 0.21 μm and high-angle boundary fraction of about 35%. The contributions to the stored energy from defects were calculated and compared, suggesting that the stored energy mainly originates from boundaries and vacancies. The restoration activation energy after eight passes was between 77 and 80 kJ/mol. The higher stored energy and lower activation energy compared to cold-rolled copper is attributed to excess vacancies.

Materials Science and Engineering: A, Volume 492, Issues 1-2, 25 September 2008, Pages 74-79




Electrochemical and photoelectrical properties of titania nanotube arrays annealed in different gases

Titania nanotube arrays fabricated by anodic oxidation of titanium foil were calcined in dry nitrogen, air, and argon at various temperatures for varied period of time. Changes in morphology and crystallinity of the nanotube arrays were studied by means of SEM and XRD. The influences of annealing conditions on the electrochemical and conductivity were investigated by electrochemical impedance spectroscopy (EIS), and the results showed that the electrical conductivities of TiO2 nanotube arrays calcined in nitrogen for 3 h were improved greatly as compared to the as-grown titania nanotube arrays or annealed in air or argon. Well defined oxidation and reduction peaks were observed during the cyclic voltammetric scan at 0.1 V/s in 10 mM K3[Fe(CN)6] solution. Photocurrent response in TiO2 nanotube arrays calcined in nitrogen was significantly enhanced. Reduction of tetravalent titanium cations and the formation of oxygen vacancies were ascribed to explain the improved electrochemical and photoelectrical properties of titania nanotube arrays.

Sensors and Actuators B: Chemical, Volume 134, Issue 2, 25 September 2008, Pages 367-372






An investigation of the thermal stability, crystal structure and catalytic properties of bulk and alumina-supported transition metal nitrides

The relationship between crystal structures and catalytic activities was investigated. The results indicated that metal nitrides with higher vacancy concentration exhibited higher activities for NO decomposition. There was a stronger interaction between the metal nitride phases and γ-Al2O3 support. It was suggested that Co4N/γ-Al2O3 exhibited thermal stability significantly higher than that of bulk counterpart, owing to the strong interaction between the Co4N phase and γ-Al2O3 support. We applied the XRD technique to examine the structural changes of Co4N/γ-Al2O3 catalysts during the reactions. The results indicated that the rapidly loss in catalytic activity was due to the bulk oxidation of Co4N/γ-Al2O3. In the NO–H2 reaction, the oxygen generated during NO dissociation was partly reduced by H2 and partly incorporated into the nitride lattice. By the addition of H2 in feed gas at 600 °C, one can retain the active Co4N/γ-Al2O3 phase by minimizing the presence of surface oxygen.

Journal of Alloys and Compounds, Volume 464, Issues 1-2, 22 September 2008, Pages 488-496



NOVEL OXIDE MBE




This work concentrates on the growth of novel epitaxial oxides in ultra-thin film form. The primary goal of this work is to learn how to use defects -- both point defects and extended defects such as surface and interfaces -- to modify the electronic structure of highly correlated oxides. To this end we study the physical structure using RHEED, LEED, x-ray diffraction, and STM as well as the electronic strucutre via high-resolution ARPES.

http://www.physics.ubc.ca/~quantmat/OxideMBE.html






Fe nanocrystal growth on SrTiO3„001…

We have investigated the structure and morphology of self-assembled iron nanocrystals supported on a SrTiO3(001)-c (4x2) substrate using scanning tunneling microscopy. Nanocrystals with a truncated pyramid shape were imaged, which result from the epitaxial growth of bcc Fe on SrTiO3(001).

Magnetic materials composed of densely packed nanocrystals are of interest because they exhibit different magnetic properties compared to the bulk solids. For example,
such materials can show different magnetization directions, have enhanced magnetic moments, or display lower Curie temperatures. Organized arrays of self-assembled magnetic nanocrystals also have possible applications in the area of high-density information storage media. Iron in the bcc structure is of particular interest because of its high magnetic moment and remnant magnetization. However, if iron is
grown in ultrathin film form it often adopts the fcc structure, where a small variation of the lattice constant or lattice distortion can result in drastic changes of magnetic phases including a low-moment ferromagnetic phase, an antiferromagnetic phase, a ferrimagnetic phase, and highmoment ferromagnetic phases. A description of the properties of nanocrystalline Fe therefore requires knowledge of the structure, size, shape, and distribution of the nanocrystals.
In this letter we report on the epitaxial growth of Fe nanocrystals on a SrTiO3 (001)substrate. Fe self-assembles into truncated pyramid nanocrystal domains. A precise analysis of the pyramidal cluster shape shows that Fe is bcc packed. The equilibrium nanocrystal shape is used to determine the adhesion energy of bcc Fe on SrTiO3. Interest in the SrTiO3 surface has emerged from its electronic properties and its use as a substrate for supported nanocrystal growth. The SrTiO3 (001) surface presents a multitude of different reconstructions8, depending on sample
preparation, which can be used for the growth of regular nanocrystals over macroscopic length scales. SrTiO3 crystallizes into the cubic perovskite structure with a 3.905 Å lattice parameter. In its pure form it has a 3.2 eV band gap that
would make it unsuitable for imaging in the scanning tunneling microscope (STM). To overcome this problem we use crystals doped with 0.5% weight Nb.

The STM images show that iron forms truncated pyramidnanocrystals on SrTiO3 (001). This crystal shape can only evolve from cubic packing. Cubic-packed Fe thin films
can exist in the fcc and bcc structures. The equilibrium truncated pyramid shape for the fcc structure has a _001_ top facet and four _111_ side facets, these being the lowest energy facets. On the other hand, in the bcc structure the lowest energy facets are the _001_ and the _011_ facets. This means that the equilibrium truncated pyramid shape for the bcc structure has a [001] top facet and four (011) side facets.
A truncated pyramid-shaped fcc Fe nanocrystal will have (111) side facets that have an angle of 54.7° with respect to the substrate and an angle of 70.6° between each other. The unit cell dimension for fcc Fe is afcc ~3.6 Å, and as the interplanar periodicity along the (001) direction is half the unit cell dimension, we would expect fcc nanocrystals to be quantized in heights of ~1.8 Å. However, if the Fe nanocrystals have bcc packing, their shapes are subtly different. The (011) side facets have a 45° angle with respect to the substrate and a 90° angle between each other. The unit cell dimension for bcc Fe is abcc=2.87 Å and the height quantization
is therefore ~1.44 Å. Our data show that the measured side facets angle is 90.8°±1.2°
and that the islands are quantized into heights of 1.4 Å multiples. We therefore conclude that the truncated pyramid nanocrystals reported on here have a bcc structure.

Fabien Silly and Martin R. Castella, Department of Materials, University of Oxford




Shape changes of catalytic RH nanoparticles during oxidation, reduction

Heterogeneous catalysts often consist of metal nanoparticles absorbed on oxide supports, and the size and shape of these nanoparticles are likely to be affected by conditions in the reactor such as temperature and oxidation state. However, such changes are not readily observed experimentally because many methods require vacuum conditions. A research team was able to examine the changes to rhodium nanoparticles on a MgO surface using high-resolution in situ x-ray diffraction, as well as transmission election microscopy. At elevated temperatures (570 K), these pyramid-shaped nanoparticles became flatter upon exposure to oxygen, which causes the formation of a surface oxide. The nanoparticles returned to their original shape after exposure to CO, which causes reduction of the surface.

[Shape Changes of Supported Rh Nanoparticles During Oxidation and Reduction Cycles, Science 19 September 2008:
Vol. 321. no. 5896, pp. 1654 - 1658 DOI: 10.1126/science.1160845]

Quantum confinement

Nanotechnology has yielded a number of unique structures that are not found anywhere in nature. Most demonstrate an essential quality of quantum mechanics known as quantum confinement. The idea behind confinement is all about keeping electrons trapped in a small area. The sizes we're talking about here for confinement have to be less than 30 nm for effective confinement. Quantum confinement comes in several flavors. 2-D confinement is only restricted in one dimension, and the result is a quantum well (or plane). These are what most lasers are currently built from. 1-D confinement occurs in nanowires. 0-D confinement is found only in the quantum dot.

Quantum confinement is so important for one thing, it leads to new electronic properties that are not present in today's semiconductor devices. Consider the quantum dot. The typical quantum dot is anywhere between 3-60 nm in diameter. That's still 30 to 600 times the size of a typical atom. A quantum dot exhibits 0-D confinement, meaning that electrons are confined in all three dimensions. The only things in nature that have 0-D confinement are atoms. So a quantum dot can be loosely described as an 'artificial atom'. This is vitally important because we can't readily experiment on regular atoms. They're too small and too difficult to isolate in an experiment. Quantum dots, on the other hand, are large enough to be manipulated by magnetic fields and can even be moved around with an STM or AFM. We can deduce many important atomistic characteristics from a quantum dot that would otherwise be impossible to research in an atom.


The size dependence of the bandgap is the most identifiable aspect of quantum confinement in semiconductors; the bandgap increases as the nanostructure size decreases.
Nature, Two- versus three-dimensional quantum confinement in indium phosphide wires and dots, Nature Materials 2, 517 - 520 (01 Aug 2003)



Effect of quantum confinement of surface electrons on adatom–adatom interactions

We demonstrate that the surface-state mediated interaction between adatoms can be significantly modified by the quantum confinement of surface electrons. We show that quantum corrals and quantum mirrors constructed on metal surfaces can be used to tailor the exchange interaction between magnetic adatoms at large distances. We discuss the self-organization of adatoms on metal surfaces caused by quantum confinement.http://www.iop.org/EJ/abstract/1367-2630/9/10/388










Even though electrostatically induced forces seem to be rather weak, the electrostatic force between e.g an electron and a proton, that together make up a hydrogen atom, is about 40 orders of magnitude stronger than the gravitational force acting between them.

Electrostatic phenomena include examples as simple as the attraction of plastic wrap to your hand after you remove it from a package, to the apparently spontaneous explosion of grain silos, to damage of electronic components during manufacturing, to the operation of photocopiers. Electrostatics involves the buildup of charge on the surface of objects due to contact with other surfaces. Although charge exchange happens whenever any two surfaces contact and separate, the effects of charge exchange are usually only noticed when at least one of the surfaces has a high resistance to electrical flow. This is because the charges that transfer to or from the highly resistive surface are more or less trapped there for a long enough time for their effects to be observed. These charges then remain on the object until they either bleed off to ground or are quickly neutralized by a discharge: e.g., the familiar phenomenon of a static 'shock' is caused by the neutralization of charge built up in the body from contact with nonconductive surfaces.


Gauss's law

Gauss' law states that "the total electric flux through a closed surface is proportional to the total electric charge enclosed within the surface". The constant of proportionality is the permittivity of free space.

Mathematically, Gauss's law takes the form of an integral equation:

ʃˢ ɛ E. dA = ʃ ρ.dV

Alternatively, in differential form, the equation becomes

∆ . ɛ E = ρ

Poisson's equation

The definition of electrostatic potential, combined with the differential form of Gauss's law (above), provides a relationship between the potential φ and the charge density ρ:

∆2 φ = - ρ / ɛ

This relationship is a form of Poisson's equation. Where ɛ is Vacuum permittivity.

Laplace's equation

In the absence of unpaired electric charge, the equation becomes

∆2 φ = O

Singlet and Triplet oxygen

Singlet oxygen is the common name used for the two metastable states of molecular oxygen (O2) with higher energy than the ground state triplet oxygen [1]. O2 is a common gas in the Earth's atmosphere, but it is typically found with its electrons in the "triplet" state. The molecule can absorb energy in order to change its electron configuration to one of the singlet configurations. Usually, "excited" electron configurations result in the immediate discharge of the extra energy in the form of a photon, but because of its unusual properties, singlet oxygen can persist for over an hour, depending on the environment. Because of the differences in their electron shells, singlet oxygen has different chemical properties than triplet oxygen, including absorbing and emitting light at different wavelengths.



Triplet oxygen

Triplet oxygen is the ground state of the oxygen molecule. The electron configuration of the molecule has two unpaired electrons occupying two degenerate molecular orbitals. These orbitals are classified as antibonding, so the O-O bond is weaker than the N-N bond in molecular nitrogen, where all bonding molecular orbitals are filled.

Unpaired electrons in degenerate orbitals can have the same spin, so the total spin S of the molecule is 1. This is known as a triplet configuration because the spin has three possible alignments in an external magnetic field.

Because the molecule has a non-zero spin magnetic moment, oxygen is paramagnetic; i.e., it can be attracted to the poles of a magnet. The Lewis structure O=O does not accurately represent the diradical nature of molecular oxygen; molecular orbital theory must be used to adequately account for the unpaired electrons.

The unusual electron configuration prevents molecular oxygen from reacting directly with many other molecules, which are often in the singlet state. Triplet oxygen will, however, readily react with molecules in a doublet state, such as radicals, to form a new radical. Conservation of spin quantum number would require a triplet transition state in a reaction of triplet oxygen with a closed shell (a molecule in a singlet state). The extra energy required is sufficient to prevent direct reaction at ambient temperatures with all but the most reactive substrates, e.g. white phosphorus. At higher temperatures or in the presence of suitable catalysts the reaction proceeds more readily. For instance, most flammable substances are characterised by an autoignition temperature at which they will undergo combustion in air without an external flame or spark.

Wikipedia

Making of the solar cell in ambient atmosphere

Dye Sensitized Solar Cells are by far the most popular type of organic solar cells in terms of the number of research papers, the documented attempts of commercialization, and the general awareness of the technology.....perhaps more disputable reason could be that they are quite simple to prepare using simple equipment and readily available materials. DSSCs have been prepared by school classes employing window glass, white paint, a kitchen oven, and some sort of colored dye from berries or wine.

In this work we demonstrate a nanostructured polymer hybrid solar cell with excellent operational stability that can be prepared in the ambient atmosphere by simple means. There is a requirement for materials with a certain level of complexity but there are no requirements for vacuum or inert processing conditions......this example can be used by school or university classes for the preparation and demonstration of the polymer and hybrid solar cell technology.....The manipulations were carried out at an ambient temperature of 20±2 ◦C and a relative humidity of 35 ± 5%.

Substrates
Conducting indium tin oxide (ITO) substrates were employed. Rigid glass substrates with a 100 nm layer of ITO and a sheet resistivity of 8–12 Ω square−1 were purchased from Lumtec and were cleaned by consecutive ultrasonication in acetone, water, and isopropanol for 5 min, followed by drying immediately prior to use. The flexible substrates were purchased from Delta Technologies and comprised 200 μm
polyethyleneterephthalate (PET) foil with an overlayer of ITO and a sheet resistivity of 25–35 Ω square−1.


The zinc oxide nanoparticles were prepared by a procedure similar... In a typical run starting from Zn(OAc)2·2H2O (29.7 g) in methanol (1250 ml) heated to 60 ◦C, KOH (15.1 g) dissolved in methanol (650 ml) heated to 60 ◦C was added over 30 s. The mixture became cloudy towards the end of the addition. The mixture was heated to gentle reflux, and after 2–5 min the mixture became clear and was stirred at this temperature for 3 h, during which time precipitation starts. The magnetic stirring bar was removed and the mixture left to stand at room temperature for 4 h. The mixture was carefully decanted, leaving only the precipitate. The precipitate was then resuspended in methanol (1 l) and allowed to settle for 16 h. The methanol was removed by decantation, making sure that the precipitate was drained as well as possible without letting it dry. Chlorobenzene (40 ml) was added immediately and the precipitated nanoparticles dissolved gradually over 15 min, giving a total volume
of 60 ml. The concentration was typically in the range 150–225 mg ml−1. After determination of the zinc oxide concentration, methoxyethoxyacetic acid (MEA) was added. The best range of MEA concentration was found to be 4–6% w/w with respect to zinc oxide. Concentrations as high as 20% w/w were employed and gave the highest stability for the zinc oxide nanoparticle solutions.


A simple nanostructured polymer/ZnO hybrid solar cell—preparation and operation in air, Krebs et al 2008 Nanotechnology 19 424013

The solar cell can be prepared entirely in the ambient atmosphere by solution processing without the use of vacuum coating steps, and it can be operated in the ambient atmosphere with good operational stability under illumination (1000 W m-2, AM1.5G, 72 ± 2 °C, 35 ± 5% relative humidity) for 100 h with a 20% loss in efficiency with respect to the initial performance. The dark storability (darkness, 25 °C, 35 ± 5% relative humidity) has been shown to exceed six months without notable loss in efficiency. The devices do not require any form of encapsulation to gain stability, while a barrier for mechanical protection may be useful. The devices are based on soluble zinc oxide nanoparticles mixed with the thermocleavable conjugated polymer poly-(3-(2-methylhexan-2-yl)-oxy-carbonyldithiophene) (P3MHOCT), which through a thermal treatment is converted to the insoluble form poly(3-carboxydithiophene) (P3CT) that generally gives stable polymer solar cells. The devices employed a solution based silver back electrode. One advantage is that preparation of the devices is very simple and can be carried out by hand under ambient conditions, requiring only a hot plate that can reach a temperature of 210 °C, and preferably also a spincoater. This type of device is thus excellently suited for teaching and demonstration purposes provided that the materials are at hand.

http://www.iop.org/EJ/abstract/0957-4484/19/42/424013

NMR Spectrum

The Nuclear Magnetic Resonance spectrum proves to be of great utility in structure elucidation because the properties it displays can be related to the chemist's perception of molecular structure. The chemical shift of a particular nucleus can be correlated with its chemical environment, the scalar coupling (or J-coupling) indicates an indirect interaction between individual nuclei, mediated by electrons in a chemical bond, and, under suitable conditions, the area of a resonance is related to the number of nuclei giving rise to it. Thus, when we speak of "assigning a spectrum" we are really trying to identify a chemical structure that is consistent with the spectrum; we may have a fairly good idea of what this structure is likely to be, or we may have very little. There are a number of techniques in common use that help with this aim.

The 1H nucleus is the most commonly observed nucleus in NMR spectroscopy. Hydrogen is found throughout most organic molecules and, fortunately for chemists, the proton has high intrinsic sensitivity as well as being almost 100% abundant in nature, all of which make it a favourable nucleus to observe. The proton spectrum contains a wealth of chemical shift and coupling information and is the starting point for most structure determinations.

In addition to these data, the area of a resonance, usually presented as its relative integral, relates to the number of protons giving rise to the signal, giving further information as to a possible structural fragment. However, for most routine acquisitions, the accuracy of such integrals is not high and may commonly show errors of 10% or more. This level of accuracy is usually sufficient if you wish to decide whether it is one or two protons that are giving rise to a particular resonance, but are unsuitable if you wish to get an accurate determination of, say, the relative proportion of two isomers in a mixture.


Homonuclear decoupling in 1H NMR
The appearance of multiplet fine structure on NMR resonances is due to the presence of scalar coupling with another nucleus. In proton spectroscopy, such coupling will usually occur over two or three bonds (geminal or vicinal coupling respectively) and its presence provides direct evidence of a bond within a structure; it indicates connectivity. If the connectivity between all atoms in a structure is known, the gross structure is, therefore, defined. Coupling partners can often be identified by direct analysis of multiplet fine structure; if proton A shows a coupling to proton B of 7 Hz, then the coupling from B to A is also 7 Hz. However, it is often not
possible to identify coupling partners in this way; the multiplet may be too complex to determine all coupling constants; one, or both, protons may be hidden under another resonance or many multiplets may display a coupling similar in magnitude to the one of interest. Homonuclear decoupling (which belongs to a class of
experiments known as double-resonance experiments) offers a simple and effective means to identify coupled protons. The idea is to selectively saturate one multiplet in the spectrum with a radio-frequency during acquisition. This causes a loss of all couplings with the saturated proton and, hence, the multiplet structure of its partners will change. The example below illustrates this point. The spectrum of compound [1] shows a double-doublet at 5.44 ppm due to H5 and its coupling to the C6 protons, which resonate in the 2-3 ppm region. The multiplet structures of the resonances in this area are quite complex and do not lend themselves to direct
analysis. A simple homonuclear decoupling experiment with saturation of the C5 proton unambiguously identifies the C6 protons by removal of the vicinal 5-6 couplings.

http://www.chem.ox.ac.uk/spectroscopy/nmr/nmrfacility.htm


NMR offers the perfect accompaniment to the other major structural determination technique, x-ray crystallography. As well as 3D structure determination NMR can be used to investigate solution dynamics and interaction interfaces. Although still limited to some extent by protein size it is now more and more plausible to look at large proteins using higher field magnets and selective labelling techniques. NMR can be used to investigate proteins, nucleic acids, carbohydrates, lipids and metabolites.

950Mhz Magnet

We currently house a 22.3 T (950 MHz 1H Larmor frequency) superconducting magnet. Delivery and installation of the magnet from Oxford Instruments took place in October 2005 and final field was reached in December. We have built and continue to refine an inverse 1H/15N/13C triple resonance probehead with actively shielded triple axis gradients; and a multichannel console capable of executing essentially all the available pulse sequences.

http://www2.bioch.ox.ac.uk/~rrnmr/NMR-life_2007.pdf

Alice's Adventures in a Microscopic Wonderland

The winners of the 2008 International Science and Engineering Visualization Challenge have been announced. The awards are given to the best photographs, illustrations and interactive media that visualize science and technology.




Mad Hatter's Tea, winner of the Informational Graphics award, is taken from a book called Alice's Adventures in a Microscopic Wonderland. Colleen Champ and Dennis Kunkel, at Concise Image Studios, carefully built scenes from Lewis Carroll's story using microscope images of insects and other small animals.







String Vibrations, awarded an Honorable Mention in Photography, shows the path described by a rapidly-spinning string. Andrew Davidhazy of the Rochester Institute of Technology used a relatively long camera exposure to make the moving string appear to be a 3D object.



http://technology.newscientist.com/article/dn14809

Connoisseur of wit

Winston Churchill's comment 'I have derived continued benefit from criticism at all periods of my life and I do not remember any time when I was ever short of it'.

Oxford Dictionary of Humorous Quotations

NANORODS

NANORODS

In nanotechnology, nanorods are one morphology of nanoscale objects. Each of their dimensions range from 1–100 nm. They may be synthesized from metals or semiconducting materials. Standard aspect ratios (length divided by width) are 3-5. Nanorods are produced by direct chemical synthesis. A combination of ligands act as shape control agents and bond to different facets of the nanorod with different strengths. This allows different faces of the nanorod to grow at different rates, producing an elongated object.

The applications of nanorods are diverse, ranging from display technologies (the reflectivity of the rods can be changed by changing their orientation with an applied electric field) to microelectromechanical systems (MEMS).

Direct chemical synthesis and a combination of ligands are all that are required for production and shape control of the nanorods. Ligands also bond to different facets of the nanorod with varying strengths. This is how different faces of nanorods can be made to grow at different rates, thereby producing an elongated object of a certain desired shape.

Nanorods have wide application.

* Prominent among them is in the use in display technologies. By changing the orientation of the nanorods with respect to an applied electric field, the reflectivity of the rods can be altered, resulting in superior displays. Picture quality can be improved radically. Each picture element, known as pixel, is composed of a sharp-tipped device of the scale of a few nanometres. Such TVs, known as field emission TVs, are brighter as the pixels can glow better in every colour they take up as they pass through a small potential gap at high currents, emitting electrons at the same time.
* Nanorod-based flexible, thin-film computers can revolutionise the retail industry, enabling customers to checkout easily without the hassles of having to pay cash.


http://www.articleworld.org/index.php/Nanorod

Amphoteric substance

In chemistry, an amphoteric substance is one that can react as either an acid or base. The word is derived from the Greek prefix ampho- (αμφί-) meaning "both". Many metals (such as zinc, tin, lead, aluminium, and beryllium) and most metalloids have amphoteric oxides. Other examples include amino acids and proteins, which have amine and carboxylic acid groups, and self-ionizable compounds such as water and ammonia.

Examples

Zinc oxide (ZnO) reacts differently depending on the pH of the solution:

In acids: ZnO + 2H+ → Zn2+ + H2O

In bases: ZnO + H2O + 2OH- → [Zn(OH)4]2-

This effect can be used to separate different cations, such as zinc from manganese.

There are many other examples of chemical compounds which are also amphoteric, for the simplest example water:

Base (proton acceptor): H2O + HCl → H3O+ + Cl−

Acid (proton donor): H2O + NH3 → NH4+ + OH−

(It can do both at once: 2H2O → H3O+ + OH−)

Aluminium hydroxide is as well:

Base (neutralizing an acid): Al(OH)3 + 3HCl → AlCl3 + 3H2O

Acid (neutralizing a base): Al(OH)3 + NaOH → Na[Al(OH)4]


Some other examples include:

* Beryllium hydroxide
o with Acid: Be(OH)2 + 2HCl → BeCl2 + 2H2O
o with Base: Be(OH)2 + 2NaOH → Na2Be(OH)4

* Lead oxide
o with acid: PbO + 2HCl → PbCl2 + H2O
o with base: PbO + Ca(OH)2 +H2O → Ca2+[Pb(OH)4]2-

* Zinc oxide
o with acid: ZnO + 2HCl → ZnCl2 + H2O
o with base: ZnO + 2NaOH + H2O → Na22+[Zn(OH)4]2-

Some elements not mentioned that are able to form amphoteric oxides: Si, Ti, V, Fe, Co, Ge, Zr, Ag, Sn, Au


Amphiprotic


In chemistry and physical sciences, a substance is described as amphiprotic if it can both donate or accept a proton, thus acting either like an acid or a base (according to Brønsted-Lowry theory of acids and bases: acids are proton donors and bases are proton acceptors. In Lewis theory of acids and bases; acids are electron pair acceptors and bases are electron pair donors). Water, amino acids, hydrogen carbonate ions and hydrogen sulfate ions are common examples of amphiprotic species. Since they can donate a proton, all amphiprotic substances contain a hydrogen atom. Also, since they can act like an acid or a base, they are amphoteric.

An amphoteric substance, however, is not necessarily amphiprotic. For example it may be a base and a Lewis acid, but not a Brønsted acid.

Example

A common example of an amphiprotic substance is the hydrogen carbonate ion, which can act as a base:

HCO3- + H2O → H2CO3 + OH-

Or as an acid:

HCO3- + H2O → CO32- + H3O+

Thus, it can effectively accept or donate a proton.

Water is the most common example:

Basic: H2O + HCl → H3O+ + Cl-

Acidic: H2O + NH3 → NH4+ + OH-



From Wikipedia, the free encyclopedia


A Lewis acid is a chemical compound, A, that can accept a pair of electrons from a Lewis base, B, that acts as an electron-pair donor, forming an adduct, AB.

A + :B → A—B

Gilbert N. Lewis proposed this definition, which is based on chemical bonding theory, in 1923[1] Brønsted-Lowry acid-base theory was published in the same year. The two theories are distinct but complementary to each other as a Lewis base is also a Brønsted-Lowry base, but a Lewis acid need not be a Brønsted-Lowry acid.