The effects of the spin and lattice degrees of freedom on the electronic structure of M1 vanadium... more The effects of the spin and lattice degrees of freedom on the electronic structure of M1 vanadium dioxide are explored using a quasiparticle description. Contraction of the inter-vanadium spacing of the Peierls pairings stabilizes bonding electrons, reducing polarizability and thus widening the band gap. Increases of this inter-vanadium spacing of as little as 1 \% reduce this stabilization, resulting in a crossover to ferromagnetic behaviour accomplished by half of the valence electrons inhabiting the leading edge of the conduction band in localized atomic-like orbitals, as the antiferromagnetic order becomes unstable with respect to rearrangement according to Hund's first rule. The data indicates that the magnetic structure of M1 vanadium dioxide may be finely balanced; the antiferromagnetic order is a consequence of the overlapping nuclear potential of the Peierls pairs, and input which disrupts this will have a significant effect on magnetic properties.
A common method of adjusting the metal-insulator transition temperature of M1 VO2 is via disrupti... more A common method of adjusting the metal-insulator transition temperature of M1 VO2 is via disruption of the Peierls pairing by doping, or inputting stress or strain. However, since adding even small amounts of dopants will change the band structure, it is unclear how doped VO2 retains its insulating character observed in experiments. While strong correlations may be responsible for maintaining a gap, theoretical evidence for this has been very difficult to obtain due to the complexity of the many-body problem involved. In this work we use GW calculations modified to include strong local k-space interactions to investigate the changes in band structure from tungsten doping. We find that the combination of carrier doping and the experimentally observed structural defects introduced by inclusion of tungsten are consistent with a change from band insulating to Mott insulating behaviour.
It is demonstrated that Mott physics can be reproduced by using the GW approximation, if the calc... more It is demonstrated that Mott physics can be reproduced by using the GW approximation, if the calculation of the polarizability matrix is suitably modified. These modifications, when applied to the Mott insulator CuO, result in the opening of the Mott gap by the splitting of states at the Fermi level into upper and lower Hubbard bands, and exhibit a giant transfer of spectral weight upon electron doping. The method is also employed to clearly illustrate that the M1 and M2 forms of vanadium dioxide are fundamentally different types of insulator. Standard GW calculations are sufficient to open a gap in M1 VO2, which arise from the Peierls pairings filling the valence band, creating homopolar bonds. The valence band wavefunctions therefore overlap poorly with the conduction band, reducing polarizability and pushing the conduction band eigenvalues to higher energy. The M2 structure however opens a gap from strong local correlations in k-space; a Mott insulator. The data suggest a computa...
Protoporphyrin IX species bearing highly branched alkyl chains were self-assembled into well-defi... more Protoporphyrin IX species bearing highly branched alkyl chains were self-assembled into well-defined nanostructures such as rod-like in CHCl3–cylcohexane (1:9, v/v) and a honeycomb-like morphology in a polar solvent dimethyl sulfoxide (DMSO). The rod-like morphologies observed in the atomic force microscopy (AFM) and transmission electron microscopy (TEM) suggest that the lamellar phase self-organises into multilamellar vesicles. The X-ray diffraction (XRD) results indicate molecular arrangements resulting from longitudinal and transverse stacking of the porphyrin head groups in the lamellar structure. The typical nanostructures were derived from a high level of cooperativity between the porphyrin cores via π–σ interactions and supported by hydrogen bonding and van der Waals interactions. The nanostructures were characterised by means of UV–vis, fluorescence, AFM, TEM and XRD analysis. Our methodology confirms the potential of protoporphyrin IX derivatives in supramolecular chemistry.
The effects of the spin and lattice degrees of freedom on the electronic structure of M1 vanadium... more The effects of the spin and lattice degrees of freedom on the electronic structure of M1 vanadium dioxide are explored using a quasiparticle description. Contraction of the inter-vanadium spacing of the Peierls pairings stabilizes bonding electrons, reducing polarizability and thus widening the band gap. Increases of this inter-vanadium spacing of as little as 1 % reduce this stabilization, resulting in a crossover to ferromagnetic behaviour accomplished by half of the valence electrons inhabiting the leading edge of the conduction band in localized atomic-like orbitals, as the antiferromagnetic order becomes unstable with respect to rearrangement according to Hund's first rule. The data indicates that the magnetic structure of M1 vanadium dioxide may be finely balanced; the antiferromagnetic order is a consequence of the overlapping nuclear potential of the Peierls pairs, and input which disrupts this will have a significant effect on magnetic properties.
The Protein Kinase C family of enzymes is a group of serine/threonine kinases that play central r... more The Protein Kinase C family of enzymes is a group of serine/threonine kinases that play central roles in cell-cycle regulation, development and cancer. A key step in the activation of PKC is translocation to membranes and binding of membrane-associated activators including diacylglycerol (DAG). Interaction of novel and conventional isotypes of PKC with DAG and phorbol esters occurs through the two C1 regulatory domains (C1A and C1B), which exhibit distinct ligand binding selectivity that likely controls enzyme activation by different co-activators. PKC has also been implicated in physiological responses to alcohol consumption and it has been proposed that PKCα (Slater et al. J Biol Chem 272(10):6167-6173, 1997; Slater et al. Biochemistry 43(23):7601-7609, 2004), PKCε (Das et al. Biochem J 421(3):405-413, 2009) and PKCδ (Das et al. J Biol Chem 279(36):37964-37972, 2004; Das et al. Protein Sci 15(9):2107-2119, 2006) contain specific alcohol-binding sites in their C1 domains. We are in...
The solid state and lyotropic phase behavior of 10 new nonionic urea-based surfactants has been c... more The solid state and lyotropic phase behavior of 10 new nonionic urea-based surfactants has been characterized. The strong homo-urea interaction, which can prevent urea surfactants from forming lyotropic liquid crystalline phases, has been ameliorated through the use of isoprenoid hydrocarbon tails such as phytanyl (3,7,11,15tetramethyl-hexadecyl) and hexahydrofarnesyl (3,7,11-trimethyl-dodecyl) or the oleyl chain (cis-octadec--9-enyl). Additionally, the urea head group was modified by attaching either a hydroxy alkyl (short chain alcohol) moiety to one of the nitrogens of the urea or by effectively "doubling" the urea head group by replacing it with a biuret head group. The solid state phase behavior, including the liquid crystal-isotropic liquid, polymorphic, and glass transitions, is interpreted in terms of molecular geometries and probable hydrogen-bonding interactions. Four of the modified urea surfactants displayed ordered lyotropic liquid crystalline phases that were stable in excess water at both room and physiological temperatures, namely, 1-(2-hydroxyethyl)-1-oleyl urea (oleyl 1,1-HEU) with a 1D lamellar phase (L R ), 1-(2-hydroxyethyl)-3-phytanyl urea (Phyt 1,3-HEU) with a 2D inverse hexagonal phase (H II ), and 1-(2-hydroxyethyl)-1-phytanyl urea (Phyt 1,1-HEU) and 1-(2-hydroxyethyl)-3-hexahydrofarnesyl urea (Hfarn 1,3-HEU) with a 3D bicontinuous cubic phase (Q II ). Phyt 1,1-HEU exhibited rich mesomorphism (Q II 1 , Q II 2 , L R , L U , and H II ), as did one other surfactant, oleyl 1,3-HEU (Q II 1 , Q II 2 , L R , L U , and H II ), in the study group. L U is an unusual phase which is mobile and isotropic but possesses shear birefringence, and has been very tentatively assigned as an inverse sponge phase. Three other surfactants exhibited a single lyotropic liquid crystalline phase, either L R or H II , at temperatures >50°C. The 10 new surfactants are compared with other recently reported nonionic urea surfactants. Structureproperty correlations are examined for this novel group of self-assembling amphiphiles.
In the quest to rationally design novel mesophase systems the challenge remains to deconvolute th... more In the quest to rationally design novel mesophase systems the challenge remains to deconvolute the relationship between structure, composition, and function. In the current study, novel glycerol-derived surfactants with high negative interfacial areas and a preference for inverse phase behavior have been targeted and synthesized. This has been achieved by application of the rule-of-thumb afforded by the critical packing parameter (CPP), namely, that inverse phase behavior is favored by wedge-shaped molecules with relatively small head group versus chain volume. Highly splayed hydrophobes with exaggerated cross section such as oleyl (cis-octadec-9-enyl) hexahydrofarnesyl (3,7,11-trimethyl-dodecyl) and phytanyl (3,7,11,15-tetramethyl-hexadecyl) were particularly successful for this purpose across many variations of head group. The phase behavior of the binary system in water of many of these surfactants is relatively simple. Typically, cubic or inverse hexagonal phases exist at the interface with water with the inverse micellar phases present at lower hydration. The inverse liquid crystalline phases were present for a broad range of temperatures and compositions.
Voltammetric techniques have been introduced to monitor the formation of gold nanoparticles produ... more Voltammetric techniques have been introduced to monitor the formation of gold nanoparticles produced via the reaction of the amino acid glycyl-L-tyrosine with Au(III) (bromoaurate) in 0.05 M KOH conditions. The alkaline conditions facilitate amino acid binding to Au(III), inhibit the rate of reduction to Au(0), and provide an excellent supporting electrolyte for voltammetric studies. Data obtained revealed that a range of timedependent gold solution species are involved in gold nanoparticle formation and that the order in which reagents are mixed is critical to the outcome. Concomitantly with voltammetric measurements, the properties of gold nanoparticles formed are probed by examination of electronic spectra in order to understand how the solution environment present during nanoparticle growth affects the final distribution of the nanoparticles. Images obtained by the ex situ transmission electron microscopy (TEM) technique enable the physical properties of the nanoparticles isolated in the solid state to be assessed. Use of this combination of in situ and ex situ techniques provides a versatile framework for elucidating the details of nanoparticle formation.
Protoporphyrin IX species bearing highly branched alkyl chains were self-assembled into well-defi... more Protoporphyrin IX species bearing highly branched alkyl chains were self-assembled into well-defined nanostructures such as rod-like in CHCl 3 -cylcohexane (1:9, v/v) and a honeycomb-like morphology in a polar solvent dimethyl sulfoxide (DMSO). The rod-like morphologies observed in the atomic force microscopy (AFM) and transmission electron microscopy (TEM) suggest that the lamellar phase self-organises into multilamellar vesicles. The X-ray diffraction (XRD) results indicate molecular arrangements resulting from longitudinal and transverse stacking of the porphyrin head groups in the lamellar structure. The typical nanostructures were derived from a high level of cooperativity between the porphyrin cores via p-s interactions and supported by hydrogen bonding and van der Waals interactions. The nanostructures were characterised by means of UV -vis, fluorescence, AFM, TEM and XRD analysis. Our methodology confirms the potential of protoporphyrin IX derivatives in supramolecular chemistry.
Anisotropic Structure Deformation in the VO2 Metal-Insulator Transition
Physical Review Letters, 2009
X-ray absorption fine structure data of tungsten (VI)-doped vanadium dioxide in the insulating ph... more X-ray absorption fine structure data of tungsten (VI)-doped vanadium dioxide in the insulating phase, and during the metal-insulator transition, are presented for the first time. Tungsten L(III)- and vanadium K-edge data suggest that significant expansion in the [110] and [110] directions occurs across the phase transition from low to high temperature. This distortion breaks the bonds between Peierls-paired vanadium ions, opening a band gap, and reveals the nature of the mechanism by which tungsten doping lowers the transition temperature and enthalpy.
Gold Nanoparticle Formation during Bromoaurate Reduction by Amino Acids
Langmuir, 2005
The synthesis and characterization of water-soluble dispersions of gold nanoparticles by the redu... more The synthesis and characterization of water-soluble dispersions of gold nanoparticles by the reduction of a potassium tetrabromoaurate precursor solution using the amino acids L-tyrosine, glycyl-L-tyrosine, and L-arginine using alkaline synthesis conditions are reported. The particle sizes determined by small-angle X-ray scattering (SAXS) and high-resolution transmission electron microscopy (HRTEM) measurements are found to be inversely proportional to the rate of particle formation, which was determined by time-resolved UV-visible spectrophotometry measurements, and vary very slowly at intermediate gold concentrations and rapidly at the extremes. Dispersions produced with a mixture of the two amino acids glycyl-L-tyrosine and L-tyrosine showed particle sizes and particle size distributions which were directly proportional to the ratio of the two L-amino acids, thus offering the possibility for control over the properties of the gold nanoparticle dispersions.
Periodic mesoporous Lix(Mn1/3Ni1/3Co1/3)O2 spinel
Dalton Transactions, 2010
A monoclinic periodic mesoporous Li(x)(Mn(1/3)Ni(1/3)Co(1/3))O(2) spinel has been successfully pr... more A monoclinic periodic mesoporous Li(x)(Mn(1/3)Ni(1/3)Co(1/3))O(2) spinel has been successfully prepared for the first time using a 'two solvents' pore infiltration methodology on hard silica templates. More commonly used synthetic techniques are not applicable to this complex material. This important battery cathode has a surface area of over 180 m(2)g(-1) and a pore size of 5.5 nm.
Production of VO 2 M 1 and M 2 Nanoparticles and Composites and the Influence of the Substrate on the Structural Phase Transition
ACS Applied Materials & Interfaces, 2009
A two-step, high-purity, high-yield synthesis of nanoparticulate vanadium dioxide, which has a gr... more A two-step, high-purity, high-yield synthesis of nanoparticulate vanadium dioxide, which has a greater than 10-fold potential cost reduction is reported. This consists of a short reflux of V2O5 with aspartic acid, followed by calcination at 600 degrees C or above. The particles produced have a mean diameter of approximately 90 nm with phase change characteristics of transition temperature and enthalpy that compare favorably with a commercial standard. In cases where the reduction reaction has progressed too far and a mixture of vanadium(III) and -(IV) is formed, redispersion and aging of the particulate product in water preferentially oxidizes the vanadium(III) component to vanadium(IV), thus allowing a versatile route to achieving a high-purity material. The synthesis was also used to deposit high-purity phases of VO2 onto the surfaces of other particles, and significant differences in the structural phase transition behavior and even the crystal structure were found for deposited samples. The data suggest that substrate properties may affect the characteristics of the structural phase transition, and this has significant implications for measurements on, and applications of, deposited VO2 layers and films.
This essay will provide the reader with a critical analysis of not only the generally accepted th... more This essay will provide the reader with a critical analysis of not only the generally accepted theories, but some of the more contentious issues that arise when determining why in fact the Luftwaffe failed in their quest for air superiority over Britain, in prelude to invasion that never came. Of particular importance one will
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