Identification of inhibitors of DNA topoisomerase II from a synthetic library of glycoconjugates

A library of 24 glycoconjugates related to glycosylated beta-amino acid derivative (I) was been prepared and screened against DNA topoisomerase-II of the filarial parasite S. cervi. Among these, compound 6 was found to be a potent inhibitor of DNA topoisomerase-II with 95% inhibition at 1.09 microM. Furthermore, compound 6 was at least three times more potent than the lead compound, glycosylated beta-amino acid derivative I.     

Protection of poly(2,6-dimethyl-1,4-phenylene oxide) against u.v. irradiation

The photo-oxidative degradation and stabilization of poly(2,6-dimethyl-1,4-phenylene oxide) films have been examined in the temperature range 263–313 K in air with u.v. light of 253.7 nm. The changes in weight-average molecular weight, quantum efficiencies, carbonyl index, hydroperoxide concentration and i.r. spectra have been followed in the absence and presence of the stabilizer. The heats of activation of the systems have been calculated and the mechanism of stabilization has been postulated. A saturation limit in photostabilization of the polymer was achieved beyond 0.6 wt% of zinc di-n-hexyl dithiophosphate.     

Efficient oxidizing methods for the synthesis of oxandrolone intermediates

Mild, efficient and eco-friendly oxidation of 17alpha-methylandrostan-3beta-17beta-diol (1) has been studied with three different reagents viz. pentavalent iodine reagent 2-iodoxy benzoic acid (IBX) in DMSO at 65 degrees C, sodium hypochlorite and H2O2/Na2WO4 under phase transfer conditions to give 17beta-hydroxy-17alpha-methylandrostan-3-one (mestanolone 2), a drug intermediate as oxidized product. The H2O2/Na2WO4/PTC gave mestanolone in high yield and purity whereas sodium hypochlorite/PTC system yielded some chlorinated material along with the mestanolone. However, 1 with 2.5 equivalent of IBX gave 17beta-hydroxy-17alpha-methyl-Delta1-androsten-3-one (3) under the similar reaction conditions in good yield and single step reaction.     

Modeling of transient electroluminescence overshoot in bilayer organic light-emitting diodes using rate equations

When a voltage pulse is applied under forward biased condition to a spin-coated bilayer organic light-emitting diode (OLED), then initially the electroluminescence (EL) intensity appearing after a delay time, increases with time and later on it attains a saturation value. At the end of the voltage pulse, the EL intensity decreases with time, attains a minimum intensity and then it again increases with time, attains a peak value and later on it decreases with time. For the OLEDs, in which the lifetime of trapped carriers is less than the decay time of the EL occurring prior to the onset of overshoot, the EL overshoot begins just after the end of voltage pulse. The overshoot in spin-coated bilayer OLEDs is caused by the presence of an interfacial layer of finite thickness between hole and electron transporting layers in which both transport molecules coexist, whereby the interfacial energy barrier impedes both hole and electron passage. When a voltage pulse is applied to a bilayer OLED, positive and negative space charges are established at the opposite faces of the interfacial layer. Subsequently, the charge recombination occurs with the incoming flux of injected carriers of opposite polarity. When the voltage is turned off, the interfacial charges recombine under the action of their mutual electric field. Thus, after switching off the external voltage the electrons stored in the interface next to the anode cell compartment experience an electric field directed from cathode to anode, and therefore, the electrons move towards the cathode, that is, towards the positive space charge, whereby electron–hole recombination gives rise to luminescence. The EL prior to onset of overshoot is caused by the movement of electrons in the electron transporting states, however, the EL in the overshoot region is caused by the movement of detrapped electrons. On the basis of the rate equations for the detrapping and recombination of charge carriers accumulated at the interface expressions are derived for the transient EL intensity I, time t_m and intensity I_m corresponding to the peak of EL overshoot, total EL intensity I_t and decay of the intensity of EL overshoot. In fact, the decay prior to the onset of EL overshoot is the decay of number of electrons moving in the electron transporting states. The ratio I_m/I_s decreases with increasing value of the applied pulse voltage because I_m increases linearly with the amplitude of applied voltage pulse and I_s increases nonlinearly and rapidly with the increasing amplitude of applied voltage pulse. The lifetime τ_t of electrons at the interface decreases with increasing temperature whereby the dependence of τ_t on temperature follows Arrhenius plot. This fact indicates that the detrapping involves thermally-assisted tunneling of electrons. Using the EL overshoot in bilayer OLEDs, the lifetime of the charge carriers at the interface, recombination time of charge carriers, decay time of the EL prior to onset of overshoot, and the time delay between the voltage pulse and onset time of the EL overshoot can be determined. The intense EL overshoot of nanosecond or shorter time duration may be useful in digital communication, and moreover, the EL overshoot gives important information about the processes involving injection, transport and recombination of charge carriers. The criteria for appearance of EL overshoot in bilayer OLEDs are explored. A good agreement is found between the theoretical and experimental results.     

On Some Properties of (Θ+) Excited States

The mass splitting and the decay width of pentaquark (Θ⁺) at the higher angular momentum states have been investigated in the framework of flux tube model considering the diquark-diquark-antiquark configuration for Θ⁺ along with statistical model. A quasi particle model for diquark has been considered. The Regge trajectory of Θ⁺ has also been investigated with interesting some observations.     

Chemoselective Alkylation of Thiols: A Detailed Investigation of Reactions of Thiols with Halides

Arylthiols, aralkylthiols and alkane thiols can be readily alkylated by alkyl/aralkyl halides in presence of K₂CO₃DMF to yield unsymmetrical sulphides in nearly quantitative yields. 2-Mercaptoethanol gave the thioether chemoselectively.     

Synthesis,spectroscopic evaluation,molecular modelling,thermal study and biological evaluation of manganese(II) complexes derived from bidentate N,O and N,S donor Schiff base ligands

Manganese(II) complexes having the general composition Mn(L)₂X₂ (where L = 3‐bromoacetophenone semicarbazone, 3‐bromoacetophenone thiosemicarbazone, 1‐tetralone semicarbazone, 1‐tetralone thiosemicarbazone, flavanone semicarbazone or flavanone thiosemicarbazone and X = Cl^? or ½SO₄^2?) were synthesized. All the complexes were characterized using elemental analyses, molar conductance and magnetic moment measurements, and mass, ¹H NMR, infrared, electron paramagnetic resonance and electronic spectral studies. The molar conductance of the complexes in dimethylsulfoxide lies in the range 10–20 Ω^?1 cm² mol^?1 indicating their non‐electrolytic nature. All the complexes show magnetic moments corresponding to five unpaired electrons. The possible geometries of the complexes were assigned on the basis of electron paramagnetic resonance, electronic and infrared spectral studies. Some of the synthesized ligands and their complexes were screened for their antifungal activities against fungi Macrophomina phaseolina, Botrytis cinerea and Phoma glomerata using the food poison technique and their antibacterial activities against Xanthomonas campestris pv. campestris and Ralstonia solanacearum using the paper disc diffusion method. They showed appreciable activities.     

Valence bond calculations of vicinal proton coupling constants in cyclopropane

Vicinal proton couplings in cyclopropane have been calculated using Dirac-Van Vleck and variational methods in valence bond formalism. The couplings may be considered as taking place along a path comprising either three or four intervening bonds. Inclusion of all exchange integrals in the appropriate fragment models leads to a satisfactory ratio of J_cis/J_trans . In this respect valence bond results appear to be superior to those obtained using a molecular orbital approach. The present valence bond results on couplings in cyclopropane are not affected by the choice of models for bonding in cyclopropane, namely the Coulson-Moffitt model or the Walsh model.