Twisted Intramolecular Charge Transfer Emission of 2-(4'-N,N-dimethylaminophenyl)benzimidazole in Micelles

Spectral characteristics of 2-(4'N,N-dimethylaminophenyl)benzimidazole have been studied as a function of surfactant concentration and as a function of acid concentration in three surfactants. Dual fluorescence is observed in all the micelles. Fluorescence intensities of the local emission (B band) and twisted intramolecular charge transfer (A band, TICT) increase by an 17-30% and 38 to 64% respectively. When dissolved in micelles lifetimes of both the states also increase in the presence of micelles. The increase in the fluorescence intensities is attributed to the decrease in the non-radiative decay constant. cmc of the surfactants can be determined from the variation in the fluorescence intensity and the lifetime data. The equilibrium constants are determined for the prototropic reactions of the fluorophore in all the micelles in S0 and S1 states and the values obtained are discussed. Copyright 1999 Academic Press.     

Grafting onto wool. III. Graft copolymerization of poly(vinyl acetate) by use of fenton's reagent as initiator

In an attempt to modify fibrous protein, poly(vinyl acetate) has been graft copolymerized onto Himachali wool in an aqueous medium by using Fenton's reagent as redox initiator. Graft copolymerizations were carried out at 25, 30, 35, 40, and 45°C for a period of 3 hr. Percentage grafting was found to be dependent upon reaction temperature, concentration of monomers, and the molar ratio of [H₂O₂]/[Fe⁺²]. Maximum grafting occurred at 45°C with a molar ratio of [H₂O₂]/[Fe⁺²] = 1.43. A small amount of grafting (2.6–2.8%) occurred when grafting was effected at 45°C in the presence of Fe⁺² alone.     

Effect of micelles on the spectral characteristics of the prototropic species of 2-(2'-aminophenyl)benzimidazole

The absorption and fluorescence spectra of 2-(2'-aminophenyl)benzimidazole (2-APBI) have been studied in anionic (sodium dodecylsulphate, SDS), cationic (cetyltrimethylammonium bromide, CTAB) and non-ionic micelles (Tween-80, TritonX-100) at different acid-base concentrations. Spectral characteristics of 2-APBI at various acid concentrations have established only one kind of monocation (MC) in Tween-80 and TritonX-100 (TX-100), whereas two kinds of MCs are present in SDS. Above study has further shown that there is a strong hydrogen bonding interaction between the polar polyoxyethylene groups of non-ionic micelles and the MCs of 2-APBI. This interaction is responsible for the stabilization of the MC III to MC III' which is more planar than either MC II or MC III, which is otherwise less stable in water. This is substantiated by the lifetime data, fluorescence excitation spectra and the pKa values of the monocation-neutral (MC-N) equilibrium.     

Hyperfine Interactions of Pm in Nd and Gd Hosts

Time differential perturbed angular correlation measurements were carried out using short lived isomeric 5/2⁺ state in ¹⁴⁷Pm to investigate the magnetic and electric hyperfine interactions in Nd and Gd hosts at different temperatures. At 10 K the magnetic hyperfine fields at ¹⁴⁷Pm in Nd and Gd hosts are 361(42) kG and 256(30) kG, respectively, and are very low as compared to the free-ion value while the electric field gradients are of comparable order. The magnetic hyperfine field in Gd is constant with temperature. The results are interpreted in terms of singlet ground state of Pm ion. This revised version was published online in September 2006 with corrections to the Cover Date.     

SOLVENT EFFECTS ON THE ELECTRONIC ABSORPTION AND FLUORESCENCE SPECTRA OF INDOLE-4-CARBOXYLIC ACID: PROTOTROPIC EQUILIBRIA IN AQUEOUS SOLUTIONS

Abstract— The absorption and fluorescence spectra of indole-4-carboxylic acid in various solvents have indicated that the -COOH group is more planar with respect to the indole ring in the first excited singlet state (S₁) than in the ground (S₀) state. Relatively large Stokes' shifts indicate that polarisability and dipole moment of the molecule are increased predominantly upon excitation. Prototropic reactions in the S₀ and S₁ states are the same. The -COO^- and -COOH+₂ groups are not coplanar in the S₀, but coplanar in the S₁ state. pH-dependent fluorescence spectra have revealed that both protonation and deprotonation of the -COOH group increase the basicity of the molecule upon excitation.     

Quadrupole Interaction of 99Ru in Pr,Nd and 100Rh in Tb Hosts

The electric field gradient at transition element impurities ⁹⁹Ru and ¹⁰⁰Rh in metallic rare earth hosts Pr, Nd and Tb has been investigated by time differential perturbed angular correlation (TDPAC) technique at room temperature. The electric field gradients, calculated from the measured quadrupole interaction frequencies at room temperature, are; RuPr: 6.06×10¹⁷ V/cm², RuNd: 5.83×10¹⁷ V/cm² and RhTb: 5.40×10¹⁷ V/cm². The electronic enhancement factors (α) for RuPr and RuNd are about 2.5 times the value observed in RuGd and RhTb (it is found to be more than 40 as in RhGd). The results cannot be explained in terms of the existing models based on charge transfer or volume mismatch of the impurity and the host. This revised version was published online in September 2006 with corrections to the Cover Date.     

Synthesis of (-)-Delta9-trans-tetrahydrocannabinol: stereocontrol via Mo-catalyzed asymmetric allylic alkylation reaction

[reaction: see text] Delta9-THC is synthesized in enantiomericaly pure form, where all of the stereochemistry is derived from the molybdenum-catalyzed asymmetric alkylation reaction of the extremely sterically congested bis-ortho-substituted cinnamyl carbonate in high regio- and enantioselectivity.     

Grafting onto Cellulose. VI. Graft Copolymerization of Vinyl Acetate by Use of Metal Chelates as Initiators

Graft copolymerization of vinyl acetate (VAc) onto cellulose has been studied in an aqueous medium in the presence of Fe(acac)₃, Al(acac)₃, and Zn(acac)₂ as initiators. Percentage of grafting has been determined as a function of concentration of initiators and monomer, reaction time, and temperature. The reactivities of different metal chelates toward grafting of VAc on cellulose have been determined and were found to follow the order: Zn(acac)₂ > Al(acac)₃ > Fe(acac)₃. A plausible mechanism for grafting involving complex formation between metal chelates and vinyl monomer has been suggested. Several grafting experiments were carried out in presence of CCl₄, CHCl₃, CH₃CH₂CH₂SH and Et₃N. All these additives with the exception of Et₃N were found to suppress grafting.