First-principles Calculations of InS-based Nanotubes

We employed first-principles simulations using a hybrid exchange-correlation density functional PBE0 within an LCAO approximation to investigate the properties of InS single layers and nanotubes constructed from its stable orthorhombic and hypothetical hexagonal phases. We have found two types of 4-plane layers with relatively low formation energy, Rec4 and Hex4, which have been extracted from the orthorhombic and hexagonal phases, respectively. By rolling up Rec4 and Hex4 layers, the initial structures of single- and double-walled nanotubes have been generated. The nanotube formation and strain energies calculated after atomic relaxation show that the most stable structures can be obtained from the rectangular Rec4 nanosheets. At the same time, the double-walled nanotubes folded from the Rec4 nanosheets may be potentially useful for photocatalytic water splitting if they can really be synthesized.     

First-principles Studies of the Electronic and Thermoelectric Properties of Misfit Layered Phases of Calcium Cobaltite

The electronic and thermoelectric properties of two phases of calcium cobaltite, a misfit layered compound, are investigated and compared using first-principles DFT calculations. The two phases considered here include the conventional bulk phase that consists of alternating layers of Ca₂CoO₃ and CoO₂, and a new phase that consists of alternating layers of CaCoO₂ and CoO₂, which was recently discovered in nanotubes. Electronic structure calculations reveal that both phases are ferrimagnetic materials with one important difference: the bulk phase is metallic, whereas the nanotubular phase is semiconducting. The metal-to-semiconductor transition that accompanies the Ca₂CoO₃ to CaCoO₂ structural transition is shown to arise from the depletion of free carriers from the donor Ca atoms. The implications of the difference in electronic structure for the thermoelectric performance of these two phases are further examined with Boltzmann transport calculations. Relative to the metallic phase, the semiconducting phase displays appreciably higher Seebeck coefficients at minimal doping levels; these increased Seebeck coefficients compensate for the reduced conductivity and result in large power factors. In conjunction with the fact that the semiconducting phase is peculiar to 1D nanotubes, it is expected that additional effects from quantum confinement could render these low-dimensional materials as promising thermoelectric materials.     

Reactivity of the V2O5–TiO2-anatase catalyst: role of the oxygen sites

A theoretical DFT-based study combining cluster and periodic models has been performed to elucidate the role of the oxygen sites in the reactivity of the vanadia/titania catalyst. We have focused on the coordination of the oxygen sites that has been directly related to reactivity. First, the reactivity of the active phase vanadia is studied by means of a V₂O₅ cluster model. The support TiO₂-anatase is then modeled by periodic conditions. Finally, a complex model containing vanadia units dispersed on anatase surfaces (100) and (001) is explored. According to our results, reactivity of the catalyst is associated to the presence of V–O–Ti bonds, the vanadyl V = O bonds being too stable to react.     

The missing link in COS metabolism: a model study on the reactivation of carbonic anhydrase from its hydrosulfide analogue

Carbonic anhydrase (CA) is known to react with carbonyl sulfide, an atmospheric trace gas, whereby H(2)S is formed. It has been shown that, in the course of this reaction, the active catalyst, the His(3)ZnOH structural motif, is converted to its hydrosulfide form: His(3)ZnOH+COS-->His(3)ZnSH+CO(2). In this study, we elucidate the mechanism of reactivation of carbonic anhydrase (CA) from its hydrosulfide analogue by using density functional calculations, a model reaction and in vivo experimental investigation. The desulfuration occurs according to the overall equation His(3)ZnSH+H(2)O right harpoon over left harpoon His(3)ZnOH+H(2)S. The initial step is a protonation equilibrium at the zinc-bound hydrosulfide. The hydrogen sulfide ligand thus formed is then replaced by a water molecule, which is subsequently deprotonated to yield the reactivated catalytic centre of CA. Such a mechanism is thought to enable a plant cell to expel H(2)S or rapidly metabolise it to cysteine via the cysteine synthase complex. The proposed mechanism of desulfuration of the hydrosulfide analogue of CA can thus be regarded as the missing link between COS consumption of plants and their sulfur metabolism.     

Tautomerism and Magnesium Chelation of HIV‐1 Integrase Inhibitors: A Theoretical Study

The tautomerism and corresponding transition states of four authentic HIV‐1 integrase (IN) inhibitor prototype structures, α,γ‐diketo acid, α,γ‐diketotriazole, dihydroxypyrimidine carboxamide and 4‐quinolone‐3‐carboxylic acid, were investigated at the B3LYP/6‐311++G(d,p) level in vacuum and in aqueous solvent models. To study the possible chelating modes of these tautomers with two magnesium ions—a process important for inhibition—we modeled an assembly of three formic acids, four water molecules and two Mg²⁺ ions as a template mimicking the binding site of IN. The DFT calculation results show that deprotonated enolized or phenolic hydroxy groups of specific tautomers in water lead to the most stable complexes, with the two magnesium ions separated by a distance of approximately 3.70 to 3.74 Å, and with each magnesium ion at the center of an octahedron. The drug candidate GS‐9137 (Gilead), based on the 4‐quinolone‐3‐carboxylic acid scaffold, and its analogues form similar but different chelating modes. When one water molecule in the complex is replaced by a methanol molecule, which mimics the terminal 3′‐OH of viral DNA, a good chelating complex is retained. This supports the hypothesis that, in the binding site of IN after 3′‐processing, the terminal 3′‐OH of viral DNA interacts with one Mg²⁺ by chelation.     

Functionalization of carbon nanomaterials for advanced polymer nanocomposites: A comparison study between CNT and graphene

The allotropes of carbon nanomaterials (carbon nanotubes, graphene) are the most unique and promising substances of the last decade. Due to their nanoscale diameter and high aspect ratio, a small amount of these nanomaterials can produce a dramatic improvement in the properties of their composite materials. Although carbon nanotubes (CNTs) and graphene exhibit numerous extraordinary properties, their reported commercialization is still limited due to their bundle and layer forming behavior. Functionalization of CNTs and graphene is essential for achieving their outstanding mechanical, electrical and biological functions and enhancing their dispersion in polymer matrices. A considerable portion of the recent publications on CNTs and graphene have focused on enhancing their dispersion and solubilization using covalent and non-covalent functionalization methods. This review article collectively introduces a variety of reactions (e.g. click chemistry, radical polymerization, electrochemical polymerization, dendritic polymers, block copolymers, etc.) for functionalization of CNTs and graphene and fabrication of their polymer nanocomposites. A critical comparison between CNTs and graphene has focused on the significance of different functionalization approaches on their composite properties. In particular, the mechanical, electrical, and thermal behaviors of functionalized nanomaterials as well as their importance in the preparation of advanced hybrid materials for structures, solar cells, fuel cells, supercapacitors, drug delivery, etc. have been discussed thoroughly.