Mixed ligand palladium(II) complexes of oxalate and malonate with vitamin-B6 molecules: synthesis,crystal structure and kinetics

The synthesis of six mononuclear palladium complexes of general formula [Pd(ox)/(mal)L₂] and [Pd(ox)/(mal)L] (ox = oxalate, mal = malonate, both L and L are vitamin-B₆ molecules (I), L = pyridoxine, pyridoxal and L = pyridoxamine) has been achieved. The structures of these compounds were established by elemental analysis, i.r. and ¹³C-n.m.r. [Pd(oxalate)(pyridoxine)₂] was analyzed by single crystal X-ray diffraction. It exhibits square planar coordination with bond lengths 2.015 (2) Å for Pd—N and 2.010 (2) Å for Pd—O. The interaction of [Pd(ox)₂]^2– and [Pd(mal)₂]^2– with L has been followed kinetically in order to look into the nature of products and the mechanism of formation under the conditions [Pd^II-chelate] [L] and [L].     

Charge transfer to helium ions from metastable helium

The cross section for charge transfer in He⁺He(2³S) collisions is calculated using the asymptotic theory of ion-atom interactions, including the effects of polarization and momentum transfer. The results agree well with recent measurements by the merged beam technique.     

Silver(II) Complexes of Tetraazamacrocycles: Studies on e.p.r. and Electron Transfer Kinetics with Thiosulfate Ion

The e.p.r. studies of Ag^II complexes of three tetraazamacrocycles, 1,4,8,11-tetraazacyclo-tetradecane (cyclam)(I), 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclo-teradecane-4,11-diene (Me₆CD)(II) and 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclo-teradecane (Me₆Cy)(III) and the electron transfer between [Ag^II(cyclam)]²⁺ and thiosulfate ion are described. The e.p.r. studies reveal that the spectra are almost the same as those reported earlier, particularly, for polycrystalline material and are typical of a d ⁹ planar Ag^II complexes. Previous e.p.r. studies on these square planar polycrystalline complexes showed no ligand hyperfine splitting. Reinvestigation of the e.p.r. spectra of these complexes in both the solid state and in solution at room (T 297 K) and at low (T= 120 K) temperature reveals resolved hyperfine structures in solution for [Ag(Me₆CD)]²⁺ and [Ag(Me₆Cy)]²⁺ complexes. Surprisingly, such a structure was not observed in solutions of [Ag(cyclam)]²⁺. Computer simulations of the hyperfine structure observed in solutions are in good agreement with structural formulae proposed. The oxidation of thiosulfate ion by [Ag(cyclam)]²⁺ follows the rate law:–d/dt[Ag^II(cyclam)²⁺]=(k ₁ Q ₁[H+]+k ₂ Q ₂ K _a2)/([H+]+K _a2)[Ag^II(cyclam)²⁺][S₂O₃ ^2–] and an inner-sphere mechanism is proposed, based on the spectral and kinetic evidence.     

Kinetics and mechanism of dissociation of some tri- and tetra-dentate complexes of copper(II) in acid media

Summary Kinetics of the dissociation ofm-phenylene-dibiguanidecopper(II) ion,N-salicylideneglycyl-glycinatocuprate(II) ion andN-salicylideneglycinato-aquocopper(II) in acid media, forming aquo-copper(II) ion, have been studied by the stopped-flow spectrophotometric technique. Dissociation of the complexes occurs in two consecutive steps, the first being faster than the second. For them-phenylenedibiguanide complex each step exhibits second order acid dependance,k _x=k _x [H⁺]² wherek _x is the observed pseudo-first order rate constant. However, the Schiff base complexes show first order acid dependance,k _x=k _x [H⁺], for both steps. The results, with relatively low H and highly negative S values, are consistent with a solvent-assisted dissociative process.     

Thermodynamics of Black Holes and the Symmetric Generalized Uncertainty Principle

In this paper, we have investigated the thermodynamics of Schwarzschild and Reissner-Nordström black holes using the symmetric generalised uncertainty principle which contains correction terms involving momentum and position uncertainty. The mass-temperature relationship and the heat capacity for these black holes have been computed using which the critical and remnant masses have been obtained. The entropy is found to satisfy the area law upto leading order logarithmic corrections and corrections of the form A² (which is a new finding in this paper) from the symmetric generalised uncertainty principle.     

Electrochemical Properties of Carbon Nanoparticles Entrapped in Silica Matrix

Carbon-based electrode materials have been widely used for many years for electrochemical charge storage, energy generation, and catalysis. We have developed an electrode material with high specific capacitance by entrapping graphite nanoparticles into a sol-gel network. Films from the resulting colloidal suspensions were highly porous due to the removal of the entrapped organic solvents from sol-gel matrix giving rise to high Brunauer-Emmett-Teller (BET) specific surface areas (654 m(2)/g) and a high capacitance density ( approximately 37 F/g). An exponential increase of capacitance was observed with decreasing scan rates in cyclic voltammetry studies on these films suggesting the presence of pores ranging from micro (< 2 nm) to mesopores. BET surface analysis and scanning electron microscope images of these films also confirmed the presence of the micropores as well as mesopores. A steep drop in the double layer capacitance with polar electrolytes was observed when the films were rendered hydrophilic upon exposure to a mild oxygen plasma. We propose a model whereby the microporous hydrophobic sol-gel matrix perturbs the hydration of ions which moves ions closer to the graphite nanoparticles and consequently increase the capacitance of the film.     

A study on natural coral stone—a fractal solid

This present research work contains the study of natural fractal material, coral stone. X-ray diffraction, FTIR, optical, DC and AC electrical characteristics are studied. The study includes Arrhenius like plots for both wafer and powder form of the material. Measurements show a possible partially irreversible phase transition occurs when coral is heated for a long time at an about 115?°C. From the XRD data it has been also established that coral stone contains nano sized clusters which is supported by DC electrical measurement. The variation of AC conductivity of coral with thickness of the sample is studied and found exhibit an interesting feature of fractal solid. A scaling relation between AC conductivity and thickness has also been proposed here. The overall behavior of the specimen is like that of a fractal system.     

Hawking radiation from black holes in de Sitter spaces via covariant anomalies

We apply the covariant anomaly cancellation method to compute the Hawking fluxes from the event and cosmic horizons of the Schwarzschild–de Sitter black hole. The derivation is new from the existing ones as we split the space in three different regions (near to and away from the event and cosmic horizons) and write down the covariant energy–momentum tensor using three step functions which covers the whole region leading elegantly to the conditions required to compute the Hawking fluxes from the event and cosmic horizons.