Quenching of nucleotide-derived radicals by bis benzimidazole derivative Hoechst-33258 in aqueous solution

The pulse radiolysis technique has been employed to investigate the reaction of DNA-minor-groove ligand bisbenzimidazole Hoechst 33258 with pyrimidine and purine nucleotide-derived radicals. Formation of an N-centred Hoechst-33258 radical is observed. Bimolecular rate constants and the yields of Hoechst-33258 radical have been evaluated. While the rate constant for the reaction of pyrimidine-derived radicals with Hoechst-33258 remained the same (1–2) × 10⁹ dm³ mol⁻¹ s⁻¹, the yields of the Hoechst-33258 radical varied from 25% (5′-cytidine monophosphate) to 75% (5′-guanosine monophosphate) under anoxic conditions. The rate constant values for the reaction of purine-derived radicals with Hoechst-33258, under oxic and anoxic conditions, remained the same whereas with pyrimidine-derived radicals, the rate constant value under oxic conditions was about two orders of magnitude lower than under anoxic conditions. The difference in the yields of Hoechst-33258 radical with various nucleotide-derived radicals suggest the formation of different types of radicals and that the reaction mainly occurs by electron transfer from Hoechst-33258 to the nucleotide radicals.     

Radiation induced crosslinking of poly(vinyl methylether) in aqueous solutions

Radiation induced crosslinking of poly(vinyl methylether) (PVME) has been investigated in aqueous solutions. The spectral and kinetic features of the transients involved in the crosslinking reaction have been studied by pulse radiolysis of dilute PVME solutions. H atoms reacts with PVME, like OH radicals, by abstracting an H atom predominantly from β-position with respect to ---OCH₃ group, but the rate of reaction of H atom is an order of magnitude slower than that of OH reaction. The PVME radicals formed by H attack have been found to decay by usual 2nd-order kinetics unlike PVME radicals produced by OH attack that are reported to decay by a complex time-dependent kinetics that deviates strongly from 2nd-order kinetics. The rate constant of e⁻_aq with PVME at pH 5.5 has been found to be 1.2×10⁸ dm³ mol⁻¹ s⁻¹. From the decay behaviour of the transient species formed by reaction of e⁻_aq with PVME, it has been shown that the transient initially reacts with solvent protons by a fast reaction to yield radical species which subsequently recombine by a slow mode. The dependence of gelation dose and radiation yields of crosslinking (Gx) of PVME on various factors such as polymer concentration, dose rate, pH, presence of oxygen and crosslinking agent has also been studied by steady-state radiolysis using an electron-beam accelerator.     

Macrocyclic Bis(phenanthroline‐pyrrole): A Convenient One‐Pot Synthesis,Structure(s), Spectroscopic,and Redox Properties,and the Binding of Amine Guests,Protons, and Lanthanide Ions

This paper reports a convenient, one‐pot, easily scalable and readily modifiable synthesis of a novel large‐ring bis(1,10‐phenanthrolinyl‐2,5‐pyrrole) macrocycle, H₂L_MC and describes its spectroscopic and electrochemical properties, protonation, cooperative amine binding, electrocatalysis of the oxidation of primary amines, photosensitization of the decomposition of dichloromethane, and the first lanthanide complexes of the hexaaza‐dianion L_MC ^2? including the novel dimer, [(NO₃)( L_MC )Eu(μ‐OH)Eu( L_MC )(H₂O)₂]?2py.     

Enantioselective Synthesis of (−)-5-Deoxyjuglomycin A+

Abstract

Starting from methyl 1, 4-dimethoxynaphthalene-2- acetate (4), (?)-5-deoxy juglomycin A (3) has been prepared in 6 steps; the overall yield is 79%. The key step in the synthesis is the asymmetric hydroxylation of the β, γ-unsaturated ester (8), leading to the hydroxylactone (9) having 96% ee.     

Fluorescence characteristics of Dy ions in calcium fluoroborate glasses

Calcium fluoroborate (CFB) glasses doped with different concentrations of trivalent dysprosium ions were prepared and investigated by the FTIR, optical absorption, photoluminescence and decay analysis. Free-ion Hamiltonian model and Judd-Ofelt theory have been used to analyze the energy level scheme and the spectral intensities of Dy³⁺ ions in CFB glasses. From the emission spectra it is observed that the samples emit intense light yellowish color which is nearer to white light. Chromaticity color coordinates have been calculated and the dominant emission wavelength has also been indicated. Decay curves of ⁴F_9/2 level for the samples with different concentrations have been analyzed using the Inokuti-Hirayama model and the energy transfer and non-radiative decay rates have been determined.     

A study of field induced transitions (FiT) in the nematic phase of an inter hydrogen bonded ferroelectric liquid crystal

A novel series of hydrogen bonded ferroelectric liquid crystals (HBFLC) have been isolated. Hydrogen bond is formed between non mesogen chiral ingredient (S)-1, 2–cholo-3-(4-hydroxy) phenyl propionic acid and mesogenic p-n alkoxy benzoic acids. Phase diagram is constructed from the transition temperatures obtained by differential scanning calorimetry (DSC) and polarizing optical microscopic (POM) studies. Thermal and electrical properties exhibited by a hydrogen bonded complex namely (S)-1,2–cholo-3-(4-hydroxy)phenyl propionic acid with octyloxy benzoic acid (CTy + 8BA) are discussed. Observation of dielectric hysteresis in CTy + 8BA makes it more suitable for device applications. Salient feature of the present work is observation of a field induced transitions in nematic phases pertaining to the above complex designated as FiT. This phenomenon has been confirmed by optical textures of POM, helicoidal measurements, optical intensity and dielectric studies. Four threshold electrical field values are noticed which in turn contributed to four new phases (E₁, E_2, E₃ and E₄) induced by electric field and helical pitch measurements supports the above observation. FiT is reversible in the sense that when applied field is removed the original texture is restored.     

A Novel,Simple and Rapid Regeneration of Alcohols from Their Allylic Ethers Using NaCNBH3 / TMSCl

A Novel, Simple and efficient method for the regeneration of alcohols from their allylic ethers using NaCNBH₃/TMSCl is described.     

Bismuth (III) Acetate: A New Catalyst for Preparation of Azlactones via the Erlenmeyer Synthesis

Bismuth(III) acetate catalyzes the synthesis of azlactones from aromatic aldehydes in moderate to good yields via the Erlenmeyer synthesis. The relatively low toxicity and low cost of bismuth(III) acetate make this procedure particularly attractive.     

Dual fluorescence of Methylene Blue encapsulated in silica matrix

Dynamics related to the optical effect of Methylene Blue (MB) dye molecules in solid host has been investigated. MB doped silica samples of varying concentrations are prepared by the sol–gel technique in acidic environment. Absorption and laser induced fluorescence spectra have been recorded for the samples. Interesting result of dual fluorescence at lower concentrations is explained. Attempt is done to study the dynamics of the dual fluorescence. These results may be useful for designing and developing solid-state optoelectronic devices.