Electrocatalytic efficiency of polyaniline by cyclic voltammetry and electrochemical impedance spectroscopy studies

Electrochemical redox reactions of ferrous/ferric (Fe2+/Fe3+) and hydroquinone/quinone (H(2)Q/Q) were studied on Pt and polyaniline (PANI)-deposited Pt electrodes in 0.5 M H2SO4-supporting electrolyte by cyclic voltammetry and ac impedance spectroscopy. A comparison of the experimental data obtained with the Pt and PANI/Pt electrodes suggested that the reactions were catalyzed by the PANI. Based on a relative increase in peak currents of cyclic voltammograms, catalytic efficiency (gamma(cv)) of the PANI was defined. There was an increase in gamma(cv) with an increase of scan rate and a decrease of concentration of Fe2+/Fe3+ or H(2)Q. The complex plane impedance spectrum of the electrode consisted of a semicircle in high frequency range and a linear spike in low frequency range. The exchange current density (i(0)) calculated using the semicircle part of the impedance showed Butler-Volmer kinetics with respect to concentration dependence. From a relative increase of i(0) on the PANI/Pt electrode, catalytic efficiency (gamma(eis)) was evaluated. (C) 2002 Elsevier Science B.V. All rights reserved.

DNA recognition by the first tail-to-tail linked distamycin-like oligopeptide dimers

Sequence-specific bidentate binding to double-stranded (ds)-DNA by 'tail-to-tail' linked dimeric, distamycin analogues is described; compared to their monomeric analogues, these dimers exhibit greater affinity and longer binding site size and open up a novel avenue in the design of minor groove binders that overcome the phasing problem.

Analytical solutions for heat transfer during cyclic melting and freezing of a phase change material used in electronic or electrical packaging

In this paper we develop an analytical heat transfer model, which is capable of analyzing cyclic melting and solidification processes of a phase change material used in the context of electronics cooling systems. The model is essentially based on conduction heat transfer, with treatments for convection and radiation embedded inside. The whole solution domain is first divided into two main sub-domains, namely, the melting sub-domain and the solidification sub-domain. Each sub-domain is then analyzed for a number of temporal regimes. Accordingly, analytical solutions for temperature distribution within each subdomain are formulated either using a semi-infinity consideration, or employing a method of quasi-steady state, depending on the applicability. The solution modules are subsequently united, leading to a closed-form solution for the entire problem. The analytical solutions are then compared with experimental and numerical solutions for a benchmark problem quoted in the literature, and excellent agreements can be observed.

Conformational basis for substrate recognition and regulation of catalytic activity in Staphylococcus aureus nucleoside di-phosphate kinase

Nucleoside diphosphate kinases (NDK) are characterized by high catalytic turnover rates and diverse substrate specificity. These features make this enzyme an effective activator of a pro-drug an application that has been actively pursued for a variety of therapeutic strategies. The catalytic mechanism of this enzyme is governed by a conserved histidine that coordinates a magnesium ion at the active site. Despite substantial structural and biochemical information on NDK, the mechanistic feature of the phospho-transfer that leads to auto-phosphorylation remains unclear. While the role of the histidine residue is well documented, the other active site residues, in particular the conserved serine remains poorly characterized. Studies on some homologues suggest no role for the serine residue at the active site, while others suggest a crucial role for this serine in the regulation and quaternary association of this enzyme in some species. Here we report the biochemical features of the Staphylococcus aureus NDK and the mutant enzymes. We also describe the crystal structures of the apo-NDK, as a transition state mimic with vanadate and in complex with different nucleotide substrates. These structures formed the basis for molecular dynamics simulations to understand the broad substrate specificity of this enzyme and the role of active site residues in the phospho-transfer mechanism and oligomerization. Put together, these data suggest that concerted changes in the conformation of specific residues facilitate the stabilization of nucleotide complexes thereby enabling the steps involved in the ping-pong reaction mechanism without large changes to the overall structure of this enzyme. (C) 2011 Elsevier B.V. All rights reserved.

Effect of non-plastic fines on cyclic behaviour of sandy soils

This paper presents the results of the detailed studies on stress - controlled cyclic triaxial tests on sandy soils from Ahmedabad, Gujarat, India subjected to a loading frequency of 0.1 Hz in cyclic triaxial equipment. Undrained stress controlled cyclic triaxial tests were carried out on cylindrical samples of size 50 mm diameter and height 100 mm with different cyclic stress ratios. Laboratory evaluations were carried out to compare the cyclic resistance of clean sand to that of sand with various fines contents at a constant gross void ratio. The gross void ratio considers the voids formed by sand particles and fines. The effects of gross void ratio with and without fines on pore water pressure build up and liquefaction potential of sandy soils in stress controlled tests are presented. The results obtained from this study provide direct evidence that the limiting silt content plays an important role in the cyclic resistance of sandy soils. Below the limiting silt content the cyclic resistance decreases until the limiting silt content is reached and then the cyclic resistance increases.

Complexes of rare-earth perchlorates with ditbutyl amides of di, tri and tetraglycolic acids

New complexes of lanthanide perchlorates with di-t-butyl amides of di, tri and tetraglycolic acids have been synthesised. The complexes have the general formula Ln(DiGA)3(ClO4)3; Ln(TriGA)2 (ClO4)3 and Ln(TetGA)2 (C1O4)3, where Ln = La-Yb and Y and DiGA = N,N′, di-t-butyl diglycolamide, TriGA N,N′, di-t-butyl triglycolamide and TetGA = N,N′ di-t-butyl tetraglycolamide, respectively. The complexes have been characterized by analysis, electrolytic conductance, infrared,1H and13C nuclear magnetic resonance and electronic spectral data.Infrared spectra indicate the coordination of all the available ether oxygens and the amide carbonyls in each of the ligands, to the metal ions. IR and conductance data show that the perchlorate groups in all the complexes are ionic.1H and13C NMR data support the IR data regarding the mode of coordination of ligands to the metal ions. Electronic spectral shapes have been interpreted in terms of nine, eight and ten coordination in DiGA, TriGA and TetGA complexes respectively.

Efficient space-time codes from cyclic division algebras

An overview of space-time code construction based on cyclic division algebras (CDA) is presented. Applications of such space-time codes to the construction of codes optimal under the diversity-multiplexing gain (D-MG) tradeoff, to the construction of the so-called perfect space-time codes, to the construction of optimal space-time codes for the ARQ channel as well as to the construction of codes optimal for the cooperative relay network channel are discussed. We also present a construction of optimal codes based on CDA for a class of orthogonal amplify and forward (OAF) protocols for the cooperative relay network

Increased glycosidic bond stabilities in 4-C-hydroxymethyl linked disaccharides

Three new hydroxymethyl-linked non-natural disaccharide analogues, containing an additional methylene group in between the glycosidic linkage, were synthesized by utilizing 4-C-hydroxymethyl-alpha-D-glucopyranoside as the glycosyl donor. A kinetic study was undertaken to assess the hydrolytic stabilities of these new disaccharide analogues toward acid-catalyzed hydrolysis, at 60 degrees C and 70 degrees C. The studies showed that the disaccharide analogues were stable, by an order of magnitude, than naturally-occurring disaccharides, such as, cellobiose, lactose, and maltose. The first order rate constants were lower than that of methyl glycosides and the trend of hydrolysis rate constants followed that of naturally-occurring disaccharides. alpha-Anomer showed faster hydrolysis than the beta-anomer and the presence of axial hydroxyl group also led to faster hydrolysis among the disaccharide analogues. Energy minimized structures, derived through molecular modeling, showed that dihedral angles around the glycosidic bond in disaccharide analogues were nearly similar to that of naturally-occurring disaccharides. (C) 2011 Elsevier Ltd. All rights reserved.

Functional regulation of PVBV Nuclear Inclusion protein-a protease activity upon interaction with Viral Protein genome-linked and phosphorylation

Regulation of NIa-Pro is crucial for polyprotein processing and hence, for successful infection of potyviruses. We have examined two novel mechanisms that could regulate NIa-Pro activity. Firstly, the influence of VPg domain on the proteolytic activity of NIa-Pro was investigated. It was shown that the turnover number of the protease increases when these two domains interact (as: two-fold; trans: seven-fold) with each other. Secondly, the protease activity of NIa-Pro could also be modulated by phosphorylation at Ser129. A mutation of this residue either to aspartate (phosphorylation-mimic) or alanine (phosphorylation-deficient) drastically reduces the protease activity. Based on these observations and molecular modeling studies, we propose that interaction with VPg as well as phosphorylation of Ser129 could relay a signal through Trp143 present at the protein surface to the active site pocket by subtle conformational changes, thus modulating protease activity of NIa-Pro. (C) 2011 Elsevier Inc. All rights reserved.

Gap model of one-way cyclic lateral load on vertical files in soft clay

For the analysis and design of pile foundation used for coastal structures the prediction of cyclic response, which is influenced by the nonlinear behavior, gap (pile soil separation) and degradation (reduction in strength) of soil becomes necessary. To study the effect of the above parameters a nonlinear cyclic load analysis program using finite element method is developed, incorporating the proposed gap and degradation model and adopting an incremental-iterative procedure. The pile is idealized using beam elements and the soil by number of elastoplastic sub-element springs at each node. The effect of gap and degradation on the load-deflection behavior. elasto-plastic sub-element and resistance of the soil at ground-line have been clearly depicted in this paper.

Nonlinear cyclic load analysis for lateral response of batter piles in soft clay with a rigorous degradation model

Nonlinear analysis of batter piles in soft clay is performed using the finite element technique. As the batter piles are not only governed by lateral load but also axial load, the effect of P- Delta moment and geometric stiffness matrix is included in the analysis. For implementing the nonlinear soil behavior, reduction in soil strength (degradation), and formation of gap with number of load cycles, a numerical model is developed where a hyperbolic relation is adopted for the soil in static condition and hyperbolic relation considering degradation and gap for cyclic load condition. The numerical model is validated with published experimental results for cyclic lateral loading and the hysteresis loops are developed to predict the load-deflection behavior and soil resistance behavior during consecutive cycles of loading. This paper highlights the importance of a rigorous degradation model for subsequent cycles of loading on the pile-soil system by a hysteretic representation.