Internal stresses and chemical binding in the H molecule

Following an interpretive formalism presented earlier, chemical binding in the H molecule has been studied in terms of the variations, with respect to R, of electrostatic field and stress components at five selected points on the interuclear axis. At three points phenomena analogous to those recorded earlier for H₂ have been observed. In particular, the existence of extremal relationships for the difference density field and the total field, as well as for the corresponding stresses, at R ? R_eq for certain specific points on the internuclear axis has been confirmed. As in the case of H₂, chemical binding in H occurs due to local variations of electrostatic pressure from point to point in such a manner as to cause the vanishing of either the total electrostatic force density or the difference force density at certain points on the internuclear axis.     

Patterned polyfluorene surfaces by functionalization of nanoimprinted polymeric features

A new procedure is described for surface grafting polymer brushes by step-growth polymerization from initiator-embedded polymeric thin films and micron- and nanometer-scale patterns. An imprint lithographic process, nanocontact molding, was used to prepare thin patterned cross-linked polyacrylate network films on silicon wafers that incorporated 4-bromostyrene in the networks. These networks present reactive 4-bromophenyl functionality at the surface that act as attachment sites for the subsequent Ni(0)- mediated step-growth condensation polymerization of 2,7-dibromo-9,9-dihexylfluorene The step-growth polymerization medium consisted of 2,7-dibromo-9,9-dihexylfluorene, Ni(0)-catalyst, and bipyridine in a toluene/dimethylformamide solvent mixture. The resulting growth of polydihexylfluorene brushes from the patterned surface was monitored by contact angle, optical spectrometry, surface profilometry and AFM. Brush growth was conducted from patterned features ranging from 100 microm to 100 nm in width and 50 nm in height. The optical and fluorescence behavior of the polyfluorene brushes was similar to that of thin polyfluorene films made by spin coating.     

A link between the second-order Jahn-Teller effect and the highest occupied molecular orbital postulate for molecular shapes

For a closed-shell molecule, a connection is drawn between two recent models for molecular shapes, namely, those based on the second-order Jahn-Teller (SOJT) effect and the highest occupied molecular orbital (HOMO) postulate respectively. Two necessary and sufficient conditions are derived within the molecular orbital framework for the approximation inherent in the SOJT model to be valid. One of these conditions is akin to the HOMO postulate.     

Internal stresses in molecules

Earlier work on internal stresses in one-electron systems is now extended to many-electron systems. The expressions for local stresses and local force densities involve electrostatic fields arising from given electronic and nuclear charge distributions and, therefore, the stress at any point in 3-D space again assumes a maxwellian form. As an illustration of the stress formalism, the interaction between two many-electron systems has been considered, taking the formation of the hydrogen molecule from its constituent atoms as a simple example. Using the double-zeta gaussian wavefunctions of Snyder and Basch, the stresses and fields experienced by an observer at three points on the internuclear axis are evaluated as functions of the internuclear distance R, and their respective variations are rationalized by means of classical arguments. The most interesting observation is that, depending on the location of the point considered, the interaction stress or the total stress or both may either vanish or pass through an extremum at an R value close to R _eq. The consequences of a charge build-up in the binding region are clearly apparent. The picture of chemical binding in the H₂ molecule that emerges from these calculations is a local one in which binding occurs due to variations of electrostatic pressure from point to point in such a manner as to cause the vanishing of either the total electrostatic force density or the difference force density or both at certain points on the internuclear axis; this complements the existing viewpoints on binding in the molecule. It may not be too early to say that the stress formalism which includes the Hellmann-Feynman force viewpoint as a special case has the potential to develop into a powerful interpretive tool for understanding molecular phenomena.     

Dynamics of the two-dimensional melting transition of a liquid crystal confined in Anopore membranes

Dielectric measurements on a liquid crystal exhibiting the smectic A-crystal B transition and confined to Anopore membranes having 20 and 200 nm pore sizes are reported. The studies reveal that compared with the bulk, the confined material shows a decrease in transition temperature. More importantly, the confinement leads to a slowing of the relaxation mechanism by about three orders of magnitude.     

Isolation of a Decavanadate Cluster [H2V10O28][4-picH]4·2H2O (4-pic = 4-picoline): Crystal Structure,Electrochemical Characterization,Genotoxic and Antimicrobial Studies

The studies on polyoxovanadate clusters have received considerable attentions due to their interesting structures and extensive applications in material science and medicinal chemistry. A novel decavanadate cluster with composition [H₂V₁₀O₂₈][4-pic]₄·2H₂O has been synthesized in aqueous solution and characterized by spectral (FTIR, ⁵¹V NMR, EPR and Mass) and electrochemical studies. Single crystal X-ray crystallographic investigations indicate that decavanadate anion [H₂V₁₀O₂₈]^4? and the protonated counter cations (4-picH⁺) stabilize the crystal lattice giving a 2D sheet consolidated via extensive H-bonding interactions. Cyclic voltammetric studies indicate formation of stable quasi-reversible redox couple \( \left( {{\text{V}}^{\text{V}} \overset {} \rightleftharpoons {\text{V}}^{\text{IV}} } \right) \) in solution. The genotoxic studies employing single cell gel electrophoresis and plasmid nicking assay ascertained the non toxic nature of the compound. The complex has also been tested for in vitro antimicrobial activities against gram +ve and gram ?ve bacteria and fungi. The compound can thus be exploited as antimicrobial agent since it does not cause any toxicity or damage to DNA.     

A Cryptic Polyene Biosynthetic Gene Cluster in Streptomyces calvus Is Expressed upon Complementation with a Functional bldA Gene

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