Fluorescence of organic dyes in lipid membranes: Site of solubilization and effects of viscosity and refractive index on lifetimes

The fluorescence decay of several organic dye molecules intercalated in egg phosphatidylcholine lipid membrane vesicles is consistent with the existence of two or three prominent lifetime components rather than a single continuous distribution of lifetimes. The major lifetime components are identified with different sites of solubilization in the membrane. The variation of the lifetime of the membrane-bound dye was studied as a function of the sucrose concentration, which varied the viscosity and refractive index of the aqueous solution. The combined effect of viscosity and refractive index on the lifetime of the dye was used to identify the site of solubilization of the dye in the membrane. The study was useful to identify dye molecules on the surface which are exposed to the aqueous phase, for which the fluorescence lifetime increased systematically with sucrose (viscosity effect). More importantly, it was possible in a few cases to identify the dye molecules which are oriented in the membrane phase, and the fluorescence lifetime decreased systematically with sucrose (refractive index effect). Anomalous values of order parameters determined from the refractive index effect are explained in terms of an orientational distribution of the linear dye molecule weighted in favor of mutually orthogonal orientations.     

Conversion of propargyl alcohols to chloroallenes and arylalkynes using the TiCl4/R3N reagent system

Whereas the reaction of certain propargyl alcohols with TiCl4 in the presence of tertiary alkylamines gives the corresponding chloroallenes in 37-58% yields, reaction with the tertiary arylamines gives the corresponding arylalkynes in 68-77% yields.     

Excited state complex and electroluminescence in TPD-based single layer device

N-N′-diphenyl-N,N′-(bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine) (TPD), was used to fabricate single layer devices (ITO/TPD/Ca/Al). A near-white emission (CIE coordinate of 0.25, 0.24) is observed in electroluminescence (EL) of the single layer device with prominent emission bands at 400, 475 and 670 nm. Steady state and time-resolved emission spectra of spin-coated and annealed TPD films and TRES and TRANES analysis confirmed that emission at 400 and 475 nm are due to monomer and excimer emission, respectively. The origin of the red emission at 670 nm in EL is discussed.     

Toward homogeneity of chirality via selective formation of homochiral or heterochiral aggregates

[reaction: see text] A new method of achieving homogeneity of chirality via purification of nonracemic (partially resolved) amino alcohols 1a-d and the C2 chiral diamine 2 to obtain samples of higher ee, through preparation of homochiral and heterochiral aggregates using oxalic and fumaric acids, is described.     

Binuclear bis(β-diketonato) complexes of ruthenium(III) containing triphenylphosphine or triphenylarsine

Stable bis(-diketonato) bridged binuclear complexes prepared by reacting [RuX₃(EPh₃)₃] (X = Cl or Br; E = P or As) with (RCO)(MeCO)CH–Y–CH(COR)(COMe) [R = Me or Ph; Y = (CH₂)₆, (CH₂)₁₀] in a 2:1 molar ratio in benzene, have been characterised by elemental analyses, i.r., electronic, e.p.r. and cyclic voltammetry. The oxidation state of the metal ion in these complexes is confirmed as + 3 by electrochemical and by e.p.r. measurements. The complexes belong to a low-spin d⁵ configuration. An attempt has been made to ascertain the effect of the length of the bridging ligand on the electron transfer processes by cyclic voltammetry in these binuclear complexes. Based on the above studies an octahedral geometry has been tentatively proposed. The new complexes have been subjected to the antifungal activity studies.     

Triboluminescence,a new tool to investigate fracture-initiation time of crystals under stress

The present paper reports that triboluminescence (TBL) does not appear at the instant of impact of the load but a certain time lag is required for its appearance which depends on the value of the stress applied to the crystal. Since TBL appears in sugar crystals during the creation of new surfaces, the fracture-initiation time of the crystal has been taken to be the delay time in observing TBL pulse after the application of stress. The dependence of fracture-initiation time,t _f ^σ , of crystals on the stress, σ, may be expressed ast _f ^σ =t _o exp (− ασ), wheret _o and α are constants. The values of the lattice energy, and the change in lattice energy per unit stress, of sugar crystals have been calculated from TBL measurements and they have been found to be 21·2 kcal mole⁻¹ and 0·41 × 10⁻⁸ kcal mole⁻¹ dyne⁻¹ cm² respectively.     

Two-photon excitation spectrum of benzonitrile vapour

The two-photon excitation spectrum of benzonitrile in the gas phase at about 1 torr has been recorded and analysed in the total energy region of 36300 to 40500 cm⁻¹ using both linearly and circularly polarised light from a Nd-YAG pumped dye laser. The two-photon spectrum consists of strong Franck Condon (fc) transitions bearing a good resemblance to the one-photon spectrum and also vibronic coupling (vc) transitions essentially arising out of the analogue of the benzeneν ₁₄. By a comparative study of thetp spectra of various other monosubstituted benzenes, it has been inferred that the strongtp spectrum of benzonitrile should be ascribed to a considerableπ charge delocalization over the phenyl and nitrile groups.     

Ruthenium(III) complexes with tetradentate Schiff bases containing triphenylphosphine or triphenylarsine

Ruthenium(III) complexes of Schiff bases derived from the condensation of salicylaldehyde or o-vanillin with diamines have been prepared and characterised. The complexes are of the type [RuX(EPh₃)(L)] [X=Cl or Br; E=P or As; L=bis(salicylaldehyde)tetramethylenediimine, bis(salicylaldehyde)o-phenylenediimine, bis(o-vanillin)ethylenediimine, bis(o-vanillin)propylenediimine, bis(o-vanillin)tetramethylenediimine or bis(o-vanillin)o-phenylenediimine]. The Schiff bases behave as dibasic tetradentate ligands.     

New methods of resolution and purification of racemic and diastereomeric amino alcohol derivatives using boric acid and chiral 1,1'-bi-2-naphthol

Resolution of the racemic amino alcohol derivatives 1-6 is readily achieved to obtain enantiomerically enriched compounds using chiral 1,1'-bi-2-naphthol and boric acid in solvents such as CH(3)CN, THF, and MeOH. Purification of the diastereomeric mixture 7 has also been carried out following this method. The corresponding intermediate ammonium borate complexes were also characterized by X-ray diffraction methods.