Effect of solvent environment on the Photophysics of a newly synthesized bioactive 7-oxy(5-selenocyanato-pentyl)-2H-1-benzopyran-2-one

The synthesis and solvatochromic behavior of the compound, 7-oxy(5-selenocyanato-pentyl)-2H-1-benzopyran-2-one (PCM), a pervasive, bioactive coumarin derivative, which is expected to possess antioxidative properties and other important therapeutic activities of significant potency with low systematic toxicity, have been reported employing steady state and time resolved fluorescence techniques. Spectroscopic studies reveal that the solvatochromic behavior of the probe depends not only on the polarity of the medium but also on the hydrogen bonding properties of the solvents. Specific hydrogen bonding interaction of PCM in polar solvents modulated the order of the two close-lying lowest singlet states. The photophysical response of PCM in different solvents has been explained considering solute-solvent interactions. To corroborate these results, we performed the ground-state geometry, lowest energy transition and the UV–vis spectrum of PCM using the density functional theory (DFT) and the time-dependent density functional theory (TD–DFT) at B3LYP/6-31G^? level. We found excellent correlation between the predicted and experimental spectral data, providing a useful tool in the design of new fluorogenic probes having potential therapeutic activity.     

Influence of the nanofiller type and content on permeation characteristics of multifunctional NR nanocomposites and their modeling

Along with other properties, superior gas permeation behavior would impart an extra dimension to multifunctional natural rubber (NR) nanocomposites used in various applications, like tires. For the first time, the impact on thermodynamics and kinetics of oxygen transport has been evaluated for nano, micro, and dual filler based multifunctional NR nanocomposites through oxygen permeation studies at three different temperatures. It is seen that, the kinetics is less affected by platelet like nanofillers, while the thermodynamics and eventual permeability are not altered much by fibrous nanofillers. The permeability of the nanocomposites decreased in the presence of nanofillers due to high aspect ratio and exquisite dispersion, as ascertained from morphological studies, which caused increment in tortuosity and the reduction in free volume. Relative permeabilities were compared to predictions of existent permeation models and a novel function was successfully introduced to address deviations in a model. Finally, nearly 60% decrement in permeability of dual filler based nanocomposites explained by the formation of zeta potential driven filler associations indicate potency in development of thinner, but stronger and more durable multifunctional materials with longer air retention capabilities. These could be applied in tire research to reduce material, energy costs and increase fuel efficiencies. Copyright © 2011 John Wiley & Sons, Ltd.     

First principles prediction of the third conformer of hydrogenated BN sheet

We report, using first principles density functional calculations, the relative stabilities, structural and electronic properties of various conformers of hydrogenated BN sheet (BHNH). The already known chair and boat BHNH conformers are structurally similar to those of graphane. We propose a third BHNH conformer called ‘stirrup’ which turns out to be the most stable one, as also verified by frequency analysis. In this conformer, the B–H and N–H bonds of a hexagon alternate in 3‐up and 3‐down fashion on either side of the sheet. We also explore that any other alternative hydrogenation of the BN sheet disrupts its periodic puckered geometry and turns out to be energetically less stable. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The relation between a microscopic threshold-force model and macroscopic models of adhesion

This paper continues our recent work on the relationship between discrete contact interactions at the microscopic scale and continuum contact interactions at the macroscopic scale(Hulikal et al., J. Mech. Phys. Solids 76,144–161, 2015). The focus of this work is on adhesion. We show that a collection of a large number of discrete elements governed by a threshold-force based model at the microscopic scale collectively gives rise to continuum fracture mechanics at the macroscopic scale. A key step is the introduction of an efficient numerical method that enables the computation of a large number of discrete contacts. Finally,while this work focuses on scaling laws, the methodology introduced in this paper can also be used to study roughsurface adhesion.     

Interface of AOT/Brij mixed reverse micellar systems: conductometric and spectrophotometric investigations

Solubilization and conductivity studies are carried out with AOT/Brijs (Brij-30, Brij-35, Brij-52, Brij-56, Brij-58, Brij-72, Brij-76, Brij-78)/isooctane/water mixed reverse micellar systems. Replacement of AOT molecules with large head group Brij molecules (Brij-30, Brij-35, Brij-56, Brij-58, Brij-76, Brij-78) decreases the solubilization capacity, whereas those with smaller polar head groups (Brij-52 and Brij-72) increases it. The former blends assist the conductance percolation whereas the latter retard it. An attempt has been taken to obtain more insight on the interfacial composition of the mixed interface with the help of spectrophotometric studies using 7-hydroxycoumarin as the fluorophore. The results obtained from the solubilization and conductometric studies have been correlated with those obtained from the spectroscopic studies.     

Stability and conformation of the complexes of riboflavin with aromatic hydroxy compounds in an aqueous medium

Overall equilibrium constants K' for the formation of molecular complexes of riboflavin with the conjugate forms of different aromatic hydroxy compounds are greater in magnitude than those involving the protonated forms of the hydroxy compounds. There is good agreement between the K(B) values determined by using absorption and emission methods. Based on the magnitude of K(B), it is possible to differentiate between the donor capacities of the hydroxy compounds in the charge transfer complexes with riboflavin. Molecular modeling studies indicate stacking interactions for all the systems in an aqueous medium.     

Composite magnetic particles as carriers for laccase from Trametes versicolor

In this paper we report a study of laccase immobilisation on different kinds of carrier particles. The immobilisation of enzyme on the particle surface with respect to the immobilisation efficiency and the properties of the immobilised enzymes is discussed. The immobilisation of laccase on polystyrene particles bearing reactive beta-diketone groups is characterised by high efficiency, but grafting of the enzyme increases the stability of the colloidal system, which makes the separation/purification procedure difficult. Additionally, the extreme colloidal stability of the immobilisates hinders the application of such particles with immobilised enzymes in some applications where the recycling of the enzyme should be performed. It has been found that hybrid PS-AAEM particles equipped with maghemite show similar immobilisation efficiency to that of their analogues without maghemite and can additionally be manipulated in magnetic fields. The activity of the immobilised laccase is much higher in the pH region 5-7 and the temperature range 50-70 degrees C as compared with that of the free enzyme. Immobilised enzymes also exhibit much better storage stability.     

Size-controlled synthesis and characterization of polyvinyl alcohol coated palladium nanoparticles

In order to synthesize stable, catalytically active palladium nanoparticles with low polydispersity, a one-pot synthesis by the facile reduction of palladium chloride with citric acid in an aqueous solution of steric stabilizer polyvinyl alcohol (PVA) has been developed. The resulting nanoparticles are highly water-dispersible, excellent electro-catalysts, and have long shelf life. The palladium nanoparticles have been characterized by physico-chemical, spectroscopic, microscopic, and CV studies. The average size of the nanoparticles can be readily tuned from 8.1 to 53 nm by controlling the extent of reflux for mixtures containing suitable concentrations of metal ion, reducing agent and capping polymer, which also influence the size. Despite the surface-protecting action of PVA, the palladium nanoparticles are electro-catalytically active and exhibit size-dependent electro-catalytic behavior.     

Catechol oxidase activity of dinuclear copper(II) complexes of Robson type macrocyclic ligands: Syntheses, X-ray crystal structure, spectroscopic characterization of the adducts and kinetic studies

Five dinuclear copper(II) complexes, [Cu₂L¹(N₃)₂·2H₂O] (1), [Cu₂L²(N₃)₂·2H₂O] (2), [Cu₂L³(N₃)₂·2H₂O] (3), [Cu₂L⁴(N₃)₂·2H₂O] (4) and [Cu₂L⁵(N₃)₂·2H₂O] (5) of Robson type macrocyclic Schiff-base ligands derived from [2 + 2] condensation of 4-methyl-2,6-diformylphenol with 1,3-diaminopropane (H₂L¹), 1,2-diaminoethane (H₂L²), 1,2-diaminopropane (H₂L³), 1,2-diamino-2-methylpropane (H₂L⁴) and 1,2-diaminocyclohexane (H₂L⁵), respectively have been synthesized and characterized. Catecholase activity of those complexes using 3,5-di-tert-butylcatechol as substrate has been investigated in two solvents, methanol and acetonitrile. The role of the solvent and of the steric properties of the macrocyclic ligand of these complexes on their catecholase activity has been examined thoroughly. Acetonitrile is observed to be a better solvent than methanol as far as their catalytic activity is concerned. However, methanol reveals to be a better choice to identify the enzyme–substrate adduct. The investigation also prompted that chelate ring size does affect on the catalytic efficiency: 6-membered ring (as in H₂L¹) exhibits better activity than its 5-membered counterpart (as in H₂L²). The activity of the 5-membered counter parts also depend upon the steric factor. Moreover, the catalytic activity of the complexes is enhanced to a significant extent by increasing the bulkiness of the substituents on the backbone of macrocyclic H₂L² ligands.