Liquid-liquid extraction of osmium thiocyanate with hexamethylphosphoramide and direct spectrophotometric determination in the organic phase

The use of hexamethylphosphoramide (HMPA) in the osmium-thiocyanate system makes the method more sensitive and selective. The blue colour formed by osmium(VIII) with thiocyanate in 1.5M hydrochloric acid is intensified in the presence of HMPA and the complex becomes readily extractable into chloroform. The colour system has its absorption maximum at 595 nm and obeys Beer's law over the range 0.5-16 mug of Os per ml. The optimum range is 2-10 mug/ml. The molar absorptivity is 2.09 x 10(4)l.mole(-1).cm(-1). The method is simple, sensitive and free from interference from many metal ions, including ruthenium and other platinum metals.     

Solution of the problem of a concentrated torque on a semi-space by similarity transformations

Similarity transformations are constructed and used to obtain an exact solution for the axisymmetric boundary value problem of a homogeneous isotropic elastic semi-space subjected to a concentrated torque normal to its surface.     

On the gate-controlled surface capacitance of MOS structures of Si having n-channel inversion layers

An attempt is made to work out a simple theory of gate-controlled MOS capacitance based on the triangular potential-well approximation. The predicted dependence of the capacitance on gate voltage is in excellent qualitative agreement with the recent experimental observation reported elsewhere.On leave of absence fromthe Dept. of Physics, University of Patna, Patna, India.     

Non-linear compatibility equations and Bianchi-type identities for elastic dielectrics

Using an elimination technique, the non-linear compatibility equations for the theory of elastic dielectrics including polarization gradient effects are established. The corresponding Bianchi-type identities are constructed and used to establish the number of independent compatibility conditions consistent with the number of unknown field variables for a stress-like boundary value problem.     

Spectra of K3Mn(CN)6

The polarised optical spectra of single crystal of K₃Mn(CN)₆ is reported at liquid nitrogen temperature. A new system of transition is located along with its hot components which is verified by temperature variation studies. The crystal field parameters to reproduce the bands are given.     

Generation of fluorescent adducts of malondialdehyde and amino acids: toward an understanding of lipofuscin

Lipofuscin is a yellow-brown, highly fluorescent pigment that undergoes an age-related progressive accumulation in animal cells, mainly in postmitotic cells. It is a heterogeneous, high-molecular weight material associated with proteins, lipids and nucleic acids. Lipofuscin is implicated in many aspects of human health, including aging, oxidative stress, macular degeneration, lipid peroxidation, atherosclerosis, dementia (Alzheimer's Disease) and diseases associated with prions. Although the fluorescent properties of lipofuscin have long been recognized, neither histologists nor chemists have yet isolated the pigments themselves or characterized their optical properties. We have prepared lipofuscinlike species by reacting malondialdehyde (MDA) with cysteine (Cys). MDA:Cys adducts 3:2 and 2:2 are two of those that have been identified among the many that were present in the reaction. Whereas previous attempts to synthesize lipofuscinlike species resulted in compounds that were either nonfluorescent or emitted principally in the blue, the MDA:Cys adducts reported in this study are not only fluorescent but also emit over a broader range.     

Synthesis of fused pyrimidines with N‐, S‐heterocyclic moieties by double‐annelation reaction

A variety of tri‐ and tetracyclic hetero systems were obtained by reaction of heteroaromatic ortho‐aminoesters or ortho‐aminonitriles with iminothioether, yielding double‐annelation of a thiazolo[3,2‐a]‐pyrimidine, pyrimido[2,l‐b]thiazine, imidazo[1,2‐a]pyrimidine, and pyrimido[1,2‐a]pyrimidine moieties in a one‐pot process.     

Computer simulations of history of life: speciation, emergence of complex species from simpler organisms, and extinctions

We propose a generic model of eco-systems, with a hierarchical food web structure. In our computer simulations, we let the eco-system evolve continuously for so long that we can monitor extinctions as well as speciations over geological time scales. Speciation leads not only to horizontal diversification of species at any given trophic level but also to vertical bio-diversity that accounts for the emergence of complex species from simpler forms of life. We find that five or six trophic levels appear as the eco-system evolves for sufficiently long time, starting initially from just one single level. Moreover, the time intervals between the successive collections of ecological data is so short that we could also study “micro”-evolution of the eco-system, i.e., the birth, ageing and death of individual organisms.     

Vibration of ZnO nanotubes: a molecular mechanics approach

We investigate the vibrational properties of two kinds of single-wall ZnO nanotubes. The simulations are carried out for three types of zigzag nanotubes (5,0), (8,0), (10,0) and armchair nanotubes (3,3), (4,4), (6,6). The natural frequencies are determined by means of the molecular mechanics approach with the universal force field potential. The first four natural frequencies are obtained for length/diameter ratio of about 5–20. The vibration modes associated with these frequencies have been computed. Closed-form analytical expressions have been derived using the continuum shell theory for the physical explanations of the simulations results. We observe that the natural frequencies decrease as the aspect ratios increase. The results follow similar trends with results of previous studies for carbon nanotubes (CNT). However, the magnitudes of the frequencies are lower from the corresponding CNT counterparts, indicating that ZnO nanotubes are comparatively less stiff.     

Isomeric complexes of [RuII(trpy)(L)Cl] (trpy=2,2':6',2'-terpyridine and HL=quinaldic acid): preference of isomeric structural form in catalytic chemoselective epoxidation process

The present work deals with the isomeric complexes of the molecular composition [Ru(II)(trpy)(L)Cl] in 1 and 2 (trpy = 2,2':6',2'-terpyridine, L = deprotonated form of quinaldic acid, HL). Isomeric identities of 1 and 2 have been established by their single-crystal X-ray structures, which reveal that under the meridional configuration of trpy, O(-) and N donors of the unsymmetrical L are in trans, cis and cis, trans configurations, respectively, with respect to the Ru-Cl bond. Compounds 1 and 2 exhibit appreciable differences in bond distances involving Ru-Cl and Ru-O1/Ru-N1 associated with L on the basis of their isomeric structural features. In relation to isomer 2, the isomeric complex 1 exhibits a slightly lower Ru(II)-Ru(III) oxidation potential [0.35 (1), 0.38 (2) V versus SCE in CH(3)CN] as well as lower energy MLCT transitions [559 nm and 417 nm (1) and 533 nm and 378 nm (2)]. This has also been reflected in the DFT calculation where a lower HOMO-LUMO gap of 2.59 eV in 1 compared to 2.71 eV in 2 is found. The isomeric structural effect in 1 and 2 has also been prominent in their (1)H NMR spectral profiles. The relatively longer Ru-Cl bond in 1 (2.408(2) ?) as compared to 2 (2.3813(9) ?) due to the trans effect of the anionic O(-) of coordinated L makes it labile, which in turn facilitates the transformation of [Ru(II)(trpy)(L)(Cl)] (1) to the solvate species, [Ru(II)(trpy)(L)(CH(3)CN)](Cl) (1a) while crystallizing 1 from the coordinating CH(3)CN solvent. The formation of 1a has been authenticated by its single-crystal X-ray structure. However, no such exchange of "Cl(-)" by the solvent molecule occurs in 2 during the crystallization process from the coordinating CH(3)CN solvent. The labile Ru-Cl bond in 1 makes it a much superior precatalyst for the epoxidation of alkene functionalities. Compound 1 is found to function as an excellent precatalyst for the epoxidation of a wide variety of alkene functionalities under environmentally benign conditions using H(2)O(2) as an oxidant and EtOH as a solvent, while isomer 2 remains almost ineffective under identical reaction conditions. The remarkable differences in catalytic performances of 1 and 2 based on their isomeric structural aspects have been addressed.