Kinetic study of the interaction of three glycine‐containing dipeptides with diaquaethylenediamineplatinum(II) in aqueous medium

The kinetics of the interaction of three glycine‐containing dipeptides, namely, glycine‐L‐leucine (Gly‐Leu), glycine‐L‐isoleucine (Gly‐Ile), and glycine‐valine (Gly‐Val) with [Pt(en)(H₂O)₂](ClO₄)₂ has been studied spectrophotometrically as a function of [substrate complex], [dipeptides] and temperature at a particular pH(4.0), where the substrate complex exists predominantly as the diaqua species and the dipeptides as a zwitterion. The substitution reaction shows two consecutive steps; the first is the ligand‐assisted anation and the second is the chelation step. The activation parameters for both the steps were evaluated using Eyring's equation. The low ΔH₁^≠ and large negative value of ΔS₁^≠ as well as ΔH₂^≠ and ΔS₂^≠ indicate an associative mode of activation for both the aqua ligand substitution processes. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 498–506, 2011     

Fluorescence quenching of 9-cyanoanthracene in presence of zinc tetraphenylporphyrin in a polar liquid medium

Steady-state and time-resolved techniques are used to study photoinduced electron and/or excitational energy transfer processes involved within a novel donor (zinc tetraphenylporphyrin)-acceptor (9-cyanoanthracene) system in a polar liquid medium (acetonitrile) at the ambient temperature (300 K). After photoexcitation of 9-cyanoanthracene, its fluorescence emission as well as lifetime are found to be quenched in presence of zinc tetraphenylporphyrin. The fluorescence quenching is ascribed to be due to the combined effect of electron transfer from zinc tetraphenylporphyrin to 9-cyanoanthracene and energy transfer (radiative as well as non-radiative) from 9-cyanoanthracene to zinc tetraphenylporphyrin. The highly exergonic values of Gibbs free energy change for both forward electron transfer reaction (−1.15 eV) and charge recombination reaction (−1.94 eV) indicate the possibilities of occurrences of these two processes in the Marcus inverted region. The fluorescence quenching rate due to photoinduced electron transfer reaction is found to be close to the diffusion-controlled limit within the present donor-acceptor system upon excitation of the acceptor molecules.     

Thermochemical studies on organic eutectics and molecular complexes

The phase diagrams of the binary systems of picric acid with naphthalene, anthracene and phenanthrene, and of -naphthol withp-toluidine, determined by the thaw-melt method, show the formation of a molecular complex and two eutectics in each system. The heats of the pure components, eutectics and molecular complexes were determined by differential scanning calorimetry. Comparison of the experimental heats of fusion with the theoretical values calculated via the mixture law suggests cluster formation in the melts. The entropy of fusion, enthalpy of mixing and excess thermodynamic functions were also calculated from the heat of fusion data.

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Zusammenfassung Die Phasendiagramme der binären Systeme von Pikrinsäure mit Naphthalin, Anthrazen und Phenanthren sowie von -Naphthol mit p-Aminotoluol wurden bestimmt. In jedem System zeigt sich die Bildung eines Molekülkomplexes sowie je zwei Eutektika. Mittels DSC wurden die Schmelzwärmen der reinen Komponenten, der eutektischen Mischungen und der Molekülkomplexe ermitteis. Der Vergleich der experimentell ermittelten Schmelzwärmen mit den mittels der Mischungsregel errechneten Werten läßt auf eine Clusterbildung in der Schmelze schließen. Weiterhin wurden aus den Schmelzwärmen auch Werte für Schmelzentropie und Mischungsenthalpie errechnet.

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Thanks are due to Prof. I. S. Ahuja, Head, Chemistry Department, Banaras Hindu University, for providing research facilities. Thanks are also due to CSIR, New Delhi, for financial assistance.     

Equation of motion approach to the plasmon-plasmon interaction in a many-electron system

Using the Bohm-Pines hamiltonian we present a method for calculating the effective interaction between two plasmons by solving the equation of motion of a double-time retarded commutator defined to represent the propagation of two plasmons. This is achieved by using a decoupling procedure for the higher-order plasmon Green functions which is based on the conservation of frequency moments. The effective interaction between two plasmons is found to be repulsive, in contrast with the results obtained earlier.     

Non-Static Local String in Higher-Dimensional Gravity

We analyze the space-time structure of local gauge string with a phenomenological energy–momentum tensor, as prescribed by Vilenkin, in an arbitrary number of space-time dimensions with a non-zero cosmological constant Λ. A set of solutions of the full non-linear Einstein's equations for the interior region of such a string is presented.     

The first regioselective palladium-catalyzed indolization of 2-bromo- or 2-chloroanilines with internal alkynes: a new approach to 2,3-disubstituted indoles

[reaction: see text] The first practical and economical process for synthesis of 2,3-disubstituted indole compounds has been developed with high regioselectivity by palladium-catalyzed indolization of 2-bromo- or chloroanilines and their derivatives with internal alkynes.