Photophysical and Electrochemical Studies of 4-Dicyanomethylene 2,6-Dimethyl-4H-Pyran (DDP) Dye with Amides in Water

Photophysical and electrochemical studies of DDP dye with Formamide and alkyl substituted amides were carried out in water. Addition of Formamide (F), Acetamide (ACM), N,N-Dimethylformamide (DMF), Dimethylacetamide (DMAC) to DDP dye result in an isosbestic point. A fluorescence enhancement of DDP dye is observed on the addition of amides. Apart from the fluorescence enhancement, the addition of formamide result in no significant shift in the position of emission maxima of DDP dye whereas addition of ACM and DMF result in a shift towards the blue and red region respectively. DDP dye exhibits three lifetime components which are unique in lifetime and amplitude. The fluorescence lifetime and relative amplitude of DDP dye varies significantly by addition of amides in aqueous solution which are influenced by amidewater hydrogen-bonding network and hydrophobic influences of the alkyl substituted amides. The nature of interaction between dye and amide be predominantly through hydrogen-bonding wherein the carbonyl oxygen (C=O) of amides are bonded to N-H hydrogen of DDP dye through water molecule. The existence of more than one microenvironment of DDP dye in aqueous phase is elucidated by Electrochemical Impedence Spectroscopy (EIS) through Nyquist plots wherein it signifies that there exist at least three different micro environments which support the existence of different fluorescence lifetimes. Fluorescence spectral technique is used as an efficient tool to elucidate the nature of interaction of water soluble probe with hydrogen-bonding solutes is established in our studies.     

Catalytic activity of a supported palladium–benzimidazole complex toward alkene hydrogenation

A polymer anchored palladium complex was synthesized by sequential attachment of benzimidazole and palladium chloride to chloromethylated polystyrene divinyl benzene co-polymer with 6.5 % cross-linking. The product was characterized by XPS, UV–vis. spectrophotometry, FTIR and TGA. Various physico-chemical properties such as bulk density, surface area and swelling behavior in different solvents were also measured. The polymer anchored complex was tested as a catalyst for reduction of olefins. The kinetics of hydrogenation of 1-hexene was studied by varying the temperature, catalyst concentration and substrate concentration. The energy and entropy of activation were evaluated from the kinetic data. The catalyst could be recycled a number of times and no leaching of metal from the catalyst surface was observed.     

Polymer immobilized Fe(III) complex of 2-phenylbenzimidazole: An efficient catalyst for photodegradation of dyes under UV/Visible light irradiation

Fe(III) complex of 2-phenylbenzimidazole has been covalently anchored on polymer and characterized by elemental analysis, FT-IR, far-IR, BET surface area measurements, UV–Vis/DRS spectroscopy, thermo-gravimetric analysis and magnetic moment measurements by VSM which confirmed an octahedral environment around Fe(III) in the bound complex. The photocatalytic performance of this complex was evaluated in the photodegradation of dyes in presence of H₂O₂ as an oxidizing agent. Suitable reaction conditions have been optimized by considering the effects of various reaction parameters such as pH, oxidants, concentration of dye, H₂O₂ and catalyst for the maximum degradation of dye. The photodegradation was found to be 100% with complete mineralization in 150?min. The comparison of photocatalytic efficiency of the catalyst under visible light, sunlight and dark conditions are accomplished. Comparison between catalytic activity of the polymer-supported complex and unbound complex demonstrated that the polymer-supported complex was more active. Photocatalytic performance of PS-Fe(III)PBMZL was also compared with commercial TiO₂ (P25). This heterogeneous complex retained its activity up to 8 runs. A tentative mechanism has been proposed.     

A simple gamma-backbone modification preorganizes peptide nucleic acid into a helical structure

Peptide nucleic acid (PNA) is a synthetic analogue of DNA and RNA, developed more than a decade ago in which the naturally occurring sugar phosphate backbone has been replaced by the N-(2-aminoethyl) glycine units. Unlike DNA or RNA in the unhybridized state (single strand) which can adopt a helical structure through base-stacking, although highly flexible, PNA does not have a well-defined conformational folding in solution. Herein, we show that a simple backbone modification at the gamma-position of the N-(2-aminoethyl) glycine unit can transform a randomly folded PNA into a helical structure. Spectroscopic studies showed that helical induction occurs in the C- to N-terminal direction and is sterically driven. This finding has important implication not only on the future design of nucleic acid mimics but also on the design of novel materials, where molecular organization and efficient electronic coupling are desired.     

Designed alpha-helical barrels for charge-selective peptide translocation

Synthetic alpha-helix based pores for selective sensing of peptides have not been characterized previously. Here, we report large transmembrane pores, pPorA formed from short synthetic alpha-helical peptides of tunable conductance and selectivity for single-molecule sensing of peptides. We quantified the selective translocation kinetics of differently charged cationic and anionic peptides through these synthetic pores at single-molecule resolution. The charged peptides are electrophoretically pulled into the pores resulting in an increase in the dissociation rate with the voltage indicating successful translocation of peptides. More specifically, we elucidated the charge pattern lining the pore lumen and the orientation of the pores in the membrane based on the asymmetry in the peptide-binding kinetics. The salt and pH-dependent measurements confirm the electrostatic dominance and charge selectivity in controlling target peptide interaction with the pores. Remarkably, we tuned the selectivity of the pores to charged peptides by modifying the charge composition of the pores, thus establishing the molecular and electrostatic basis of peptide translocation. We suggest that these synthetic pores that selectively conduct specific ions and biomolecules are advantageous for nanopore proteomics analysis and synthetic nanobiotechnology applications.

Synthetic alpha-helix based pores for selective sensing of peptides have not been characterized previously.     

Infrared spectra of 1.3-dithiole-2-thione and its selenium analogues — frequency assignment and molecular force constants

Infrared spectra of 1,3-dithiole-2-thione (DTT) and its four selenium analogues have been studied in the region 4000 to 20 cm^?1. Assignment of all the fundamental frequencies was made by noting the band shifts on progressive selenation. Normal coordinate analysis procedures have been applied for both in-plane and out-of-plane vibrations to help the assignments. The Urey—Bradley force function supplemented with valence force constants for the out-of-plane vibrations was employed for coordinate calculations. A correlation of the infrared assignments of DTT with its different selenium analogues is accomplished. Further, the infrared assignments are compared with those of trithiocarbonate ion and its selenium analogues and other structurally related heterocyclic molecules.     

Metal-insulator transition in Ni-doped Na0.75CoO2: Insights from infrared studies

Nickel substitution at the cobalt site in Na_0.75CoO₂ induces an upturn in the resistivity on lowering the temperature, with the metal-to-insulator transition temperature (T _MIT) increasing with the Ni content. Low temperature far infrared measurements on polycrystalline samples of Na_0.75CoO₂ and Na_0.75Co_0.95Ni_0.05O₂, the latter having T _MIT ∼ 175 K, have been carried out. Dramatic changes in the Na mode frequencies, and relative intensities of the out-of-plane modes corresponding to the two Na sites are observed, coincident with the MIT in Na_0.75Co_0.95Ni_0.05O₂. It is argued that these changes are associated with a charge ordering of the CoO₂ layer, associated with the metal-insulator transition.     

Synthesis and characterisation of a polymer-bound rhodium-benzimidazole complex as catalyst for the hydrogenation of nitroarenes

A polymer-anchored rhodium complex was synthesised by sequential attachment of benzimidazole (BzlH) and RhCl₃ to chloromethylated poly(styrene–divinylbenzene) co-polymer (PSDVB) with 6.5% cross-linking. The catalyst was characterised by X-ray photoelectron spectroscopy, far-IR, UV–Vis, FTIR, SEM and thermogravimetric analysis. Various physico-chemical properties such as bulk density, surface area and swelling behaviour in different solvents were also studied. The polymer-anchored complex was tested as a catalyst for reduction of nitroarenes, namely o,m,p-nitrobenzoic acid, nitroaniline, nitrophenol and nitrotoluene. Kinetic measurements were carried for o-nitroaniline and p-nitrophenol by varying temperature, catalyst concentration and concentration of substrates. The rate of the reaction was found to be first order with respect to catalyst concentration and also with substrate concentration at low concentrations, becoming independent of substrate at higher concentrations. A plausible mechanism for the reaction is proposed. The energy and entropy of activation calculated from Arrhenius plots indicate high activity of the catalyst on the support. The recycling efficiency of the catalyst has been studied and there was no leaching of metal from the catalyst surface.     

Growth,crystal perfection,optical and electrical properties of organic crystal: Brucinium 5-sulfosalicylate trihydrate

Single crystals of brucinium 5-sulfosalicylate trihydrate (B5ST) were grown from ethanol–water (1:1) mixed solvent by slow evaporation method. Structure and crystallinity of the grown crystal were confirmed by single-crystal X-ray diffraction analysis. Presence of functional groups and coordination of brucine and 5-sulfosalicylic acid (5SSA) were confirmed by FT-IR and FT-Raman analyses. Optical transmittance spectrum shows the crystal having 90% transmittance in the visible region. The laser-induced surface damage threshold for the grown crystal was measured as 13.64 GW cm⁻² with Nd:YAG laser assembly. Dielectric study was performed on the single crystal to study the power dissipation of the material in the presence of alternating electric field. Crystal defects and surface morphology are studied by dissolution solvent technique and it reveals the layer growth mechanism for B5ST compound.