Publications

Hydrogen bonding: A molecular orbital treatment by the EHT and the CNDO/2 methods of methanol and of formic acid

No abstract is provided for this article.

Effect of curcumin and Cu2+/Zn2+ ions on the fibrillar aggregates formed by the amyloid peptide and other peptides at the organic–aqueous interface

Characteristic features of a perilous neuro-degenerative disease such as the Alzhiemer’s disease is fibrillar plaque formation by the amyloid (Aβ) peptide. We have modelled the formation and disintegration of fibrils by studying the aggregate structures formed by Aβ structural motif diphenylalanine as well as insulin and bovine serum albumin at the organic–aqueous interface. Even small concentrations of curcumin in the organic medium or Cu2+ and Zn2+ ions in the aqueous medium are found to break down the fibrillar structures.

Adsorption of oxygen on (100), (110) and (111) surfaces of Ag, Cu and Ni: An electron spectroscopic study

Adsorption of oxygen has been studied on (111), (110) and (100) surfaces of Ag, Cu, and Ni employing XPS and UPS. Besides atomic species with an O(1s) binding energy of ~ 530 eV, molecular adsorption is found on all the three Ag surfaces associated with a characteristic O(1s) binding energy of 532 eV. He II spectra show a feature around 2.5 eV due to the molecular species. Molecular adsorption is also found on all the three surfaces of Cu with a characteristic binding energy of 533 eV. He II spectra show characteristic features due to molecular adsorption on these surfaces at 100 K. The proportion of molecular species is maximum on the (111) surfaces and least on the (110) surfaces of both Ag and Cu. On Ni surfaces, there is no molecular adsorption; a unique O(1s) feature ascribed to O1− species is found at 531 eV. The intensity of this feature does not vary significantly with temperature in contrast to the O(1s) feature due to the molecular species on Ag and Cu surfaces.

Supramolecular Organization in Lead Bromide Salts of Imidazolium-Based Ionic Liquids

By heating imidazolium bromide-based ionic liquids with lead(II) salts under ionothermal conditions, we have been able to obtain two imidazolium bromoplumbates, (EMIm)PbBr3, I, and (BMIm)2PbBr4, II, where EMIm and BMIm stand for 1-ethyl-3-methyl and 1-butyl-3-methyl imidazolium cations respectively. Interestingly, both these compounds exhibit unusual supramolecular organization wherein dialkylimidazolium cations arrange themselves in a cylindrical fashion giving rise to channel structures. The bromoplumbate anions reside in the channels. The lead(II) cation exhibits either hemi- or holodirected coordination geometry.

Carbon Nanotubes from Organometallic Precursors

For Abstract see ChemInform Abstract in Full Text.

Metal Auger intensity ratios as a probe for change-transfer effects in aluminum-covered transition metal surfaces

Marked changes in the LVV/LMV and LVV/LMM Auger intensity ratios of Co, Ni and Cu are observed on depositing Al on their surfaces. These changes, ascribed to charge-transfer or hybridization effects, are accompanied by changes in the intensity of the satellites next to the core levels of the transition metals.

Influence of "Aging" on the Characteristics of an Electrodeless Discharge

No abstract is provided for this article.

Notable Effects of Aliovalent Anion Substitution on the Electronic Structure and Properties of Metal Oxides and Sulfides

Although it is customary to substitute cations in metal oxides, sulfides, and other materials to modify their structure and properties, effects of anion substitution have not been investigated sufficiently. This is particularly true of materials cosubstituted by two anions (such as N3– and F– in place of O2– or P3– and Cl– in place of S2–). Substitution of a trivalent anion along with a monovalent anion helps to eliminate defects, the three anions being isoelectronic and of nearly the same size. Furthermore, such aliovalent anion substitution gives rise to marked changes in the electronic structure and properties. Isovalent anion substitution (e.g., S2– in place of O2– or Se2– in place of S2–) does not bring about such changes. In this Perspective, we examine the electronic structures and properties of several oxides involving cosubstitution of N and F for oxygen. The oxides discussed are TiO2, ZnO, Cr2O3, and BaTiO3. Aliovalent anion substitution decreases the band gaps of the oxides and affect the magnetic and ferroelectric transitions. Sulfides such as CdS and ZnS where sulfur is substituted by P and Cl also show a large decrease in band gaps. Unlike in cation substitution where the conduction band is mainly affected, in the aliovalent anion-substituted materials the p-states of the trivalent anions (N3– and P3–) dominate the top of the valence band, with the metal-trivalent anion (N, P) bond being shorter and the metal–halogen bond longer. Such materials with high visible absorption extending to long wavelengths may indeed find uses.

Influence of "Aging" on the Characteristics of an Electrodeless Discharge

No abstract is provided for this article.

Role of the Cu-O charge-transfer energy in the superconductivity of cuprates: Evidence from Cu 2<i>p</i>core-level spectroscopy and theory

Based on Cu 2p core-level spectroscopy and theoretical calculations, it has been demonstrated that the Cu-O charge-transfer excitation energy which determines the Cu 2p satellite intensity also plays a crucial role in the superconductivity of cuprates. The relative intensity of the satellite generally decreases with an increase in the ${\mathit{T}}_{\mathit{c}}$ or in the hole concentration in a given series of cuprate superconductors. In the case of ${\mathrm{Bi}}_{2}$${\mathrm{Ca}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathit{R}}_{\mathit{x}}$${\mathrm{Sr}}_{2}$${\mathrm{Cu}}_{2}$${\mathrm{O}}_{8+\mathrm{\ensuremath{\delta}}}$ (R=rare earth), the satellite intensity goes through a minimum around the same composition where the hole concentration as well as the ${\mathit{T}}_{\mathit{c}}$ show maxima.

Size-dependent changes in the electronic structure of metal clusters as investigated by scanning tunneling spectroscopy

Pd, Ag, Cd and Au clusters of varying sizes have been investigated by scanning tunneling spectroscopy under ultra-high vacuum. The conductance of the clusters decreases markedly when the cluster diameter is ≤1 nm. A plot of the density of states at the Fermi level against the cluster volume varies nearly linearly up to a cluster volume of 4 nm3 (diameter ∼2 nm). Below a cluster diameter of 1 nm, an energy gap occurs, the value of which increases with the decrease in cluster size, reaching values up to 70 meV at small sizes. Clearly, the very small clusters tend to become non-metallic.

Chemistry of Nanomaterials

The chemistry of Nanomaterials , The chemistry of Nanomaterials , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

L3/L2 white-line intensity ratios in the electron energy-loss spectra of 3d transition-metal oxides

The L3/L2 white-line intensity ratio in transition-metal oxides deviates widely from the statistical value of 2 : 1 but shows interesting systematics. In a series of oxides of a given metal, the ratio reaches a maximum for the d5 configuration (e.g. MnO) and a minimum for the d0 configuration (e.g. KMnO4). In a series of monoxides, sesquioxides and dioxides of different metals, the ratio is again a maximum at the d5 configuration and decreases as the configuration changes towards d0 or d10. Our results, obtained by electron energy-loss spectroscopy, carried out in an electron microscope, are interpreted on an atomic mechanism involving spin-spin coupling. According to this model, the L2 transition probability decreases in the progression d0 to d5 whereas the L3 transition probability decreases beyond d5.

CCDC 267379: Experimental Crystal Structure Determination

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Semiconductor-metal transition in v-doped Ti3O5

The semiconductor-metal transition in Ti3O5 is significantly affected by vanadium doping. The unit cell volume, ΔH, Δϱ as well as ΔχM decrease markedly up to 0.1% V3O5 and gradually thereafter until at ∼ 10% V3O5, the transition disappears.

Satyendra Nath Bose Medal Lecture -1980: Studies of Surfaces by Electron Spectroscopy

CCDC 224286: Experimental Crystal Structure Determination

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Promotion of the metal–oxide support interaction in the Ni/TiO₂catalyst. Crucial role of the method of preparation, the structure of TiO₂and the NiTiO₃intermediate

Based on in situ X-ray diffraction and EXAFS studies, it is shown that NiTiO3 formed by the reaction of TiO2(anatase) with Ni2+ during the calcination of Ni/TiO2, gives rise to Ni metal and TiO2(rutile) on reduction, a process that may be responsible for the strong interaction between the metal and the oxide support.