Dynamics of bound dyes in a nonpolymeric aqueous gel derived from a tripodal bile salt

Rotational dynamics of polarity sensitive fluorescent dyes (ANS and DPH) in a nonpolymertic aqueous gel derived from tripodal cholamide I was studied using ultrafast time-resolved fluorescence technique. Results were compared with that of naturally occurring di- and trihydroxy bile salts. ANS in the gel showed two rotational correlation time (phi) components, 13.2 ns (bound to the hydrophobic region of the gel) and 1.0 ns (free aqueous ANS), whereas DPH showed only one component (4.8 ns). In the sol state, faster rotational motion was observed, both for ANS and DPH. Our data revealed that dyes get encapsulated more tightly in the gel network when compared to the micellar aggregates. ANS has more restrained rotation compared to DPH. This was attributed to the interaction of the sulfonate group of ANS with water molecules and hydrophilic parts of the gelator molecule. No restricted rotation was observed for DPH in the gel state unlike when it is in the gel phase of lipid bilayer.

Phase transitions in the anchored organic bilayers of long-chain alkylammonium lead iodides (CnH2n+1NH3)(2)PbI4; n=12, 16, 18

The single perovskite slab alkylammonium lead iodides (CnH2n+1NH3)(2)PbI4, n = 12, 16, 18, display two phase transitions, just above room temperature, associated with changes in the alkylammonium chains. We have followed these two phase transitions using scanning calorimetry, X-ray powder diffraction, and IR and Raman spectroscopies. We find the first phase transition to be associated with symmetry changes arising from a dynamic rotational disordering of the ammonium headgroup of the chain whereas the second transition, the melting of the chains in two dimensions, is characterized by an increased conformational disorder of the methylene units of the alkyl chains. We examine these phase transitions in light of the interesting optical properties of these materials, as well as the relevance of these systems as models for phase transitions in lipid bilayers.

Synthesis of electrically conducting copolymers of o-/m-toluidines and o-/m-amino benzoic acid in an organic peroxide system and their characterization

Copolymers of o-lm-toluidine with o-lm-amino benzoic acid have been synthesized by chemical polymerization using inverse emulsion pathway and characterized by a number of techniques including UV-Vis, FT-IR, FT Raman, EPR and NMR spectroscopies, thermal analysis and conductivity. The solubility of the copolymers in organic solvents increases with increase in the amount of amino benzoic acid in the feed. The copolymers synthesized at room temperature show relatively higher conductivity and are obtained in higher yield compared to those synthesized at 0 and 60 degreesC. The spectral studies have revealed restricted conjugation along the polymer chain. The effect of -COOH substituent on the copolymer structure is discussed. (C) 2003 Elsevier Science B.V All rights reserved.

Weak interactions involving organic fluorine: analysis of structural motifs in Flunazirine and Haloperidol

The crystal structure of Flunazirine, an anticonvulsant drug, is analyzed in terms of intermolecular interactions involving fluorine. The structure displays motifs formed by only weak interactions C–H⋯F and C–H⋯π. The motifs thus generated show cavities, which could serve as hosts for complexation. The structure of Flunazirine displays cavities formed by C–H⋯F and C–H⋯π interactions. Haloperidol, an antipsychotic drug, shows F⋯F interactions in the crystalline lattice in lieu of Cl⋯Cl interactions. However, strong O–H⋯N interactions dominate packing. The salient features of the two structures in terms of intermolecular interactions reveal, even though organic fluorine has lower tendency to engage in hydrogen bonding and F⋯F interactions, these interactions could play a significant role in the design of molecular assemblies via crystal engineering.

Synthesis and DNA binding studies of Ni(II), Co(II), Cu(II) and Zn(II) metal complexes of N(1),N(5)-bis[pyridine-2-methylene]-thiocarbohydrazone Schiff-base ligand

The thiocarbohydrazone Schiff-base ligand with a nitrogen and sulphur donor was synthesized through condensation of pyridine-2-carbaldehyde and thiocarbohydrazide. Schiff-base ligands have the ability to conjugate with metal salts. A series of metal complexes with a general formula [MCl(2)(H(2)L)]center dot nH(2)O (M=Ni, Co, Cu and Zn) were synthesized by forming complexes of the N(1),N5-bis[pyridine-2-methylene]thiocarbohydrazone (H2L) Schiff-base ligand. These metal complexes and ligand were characterized by using ultraviolet-visible (UV-Vis), Fourier Transform Infrared (FT-IR), (1)H and (13)C NMR spectroscopy and mass spectroscopy, physicochemical characterization, CHNS and conductivity. The biological activity of the synthesized ligand was investigated by using Escherichia coli DNA as target. The DNA interaction of the synthesized ligand and complexes on E. coli plasmid DNA was investigated in the aqueous medium by UV-Vis spectroscopy and the binding constant (K(b)) was calculated. The DNA binding studies showed that the metal complexes had an improved interaction due to trans-geometrical isomers of the complexes than ligand isomers in cis-positions. (C) 2011 Elsevier B.V. All rights reserved.

Structural Variability in the Monofluoroethynylbenzenes Mediated through Interactions Involving ``Organic'' Fluorine

Competition among weak intermolecular interactions can lead to polymorphism, the appearance of various crystalline forms of a substance with comparable cohesive energies. The crystal structures of 2-fluorophenylacetylene (2FPA) and 3-fluorophenylacetylene (3FPA), both of which are liquids at ambient conditions, have been determined by in situ cryocrystallization. Both compounds exhibit dimorphs, with one of the forms observed in common, P2(1), Z = 2 and the other form being Pna2(1), Z = 4 for 2FPA and P2(1)/c, Z = 12 for 3FPA. Variations in the crystal structures of the dimorphs of each of these compounds arise from subtle differences in the way in which weak intermolecular interactions such as C-H center dot center dot center dot pi and C-H center dot center dot center dot F are manifested. The interactions involving ``organic'' fluorine, are entirely different from those in the known structure of 4-fluorophenylacetylene (4FPA), space group P2(1)/c, Z = 4. The commonalities and differences in these polymorphs of 2FPA and 3FPA have been analyzed in terms of supramolecular synthons and extended long-range synthon aufbau module (LSAM) patterns. These structures are compared with the three polymorphs of phenylacetylene, in terms of the T-shaped C-H center dot center dot center dot pi interaction, a feature common to all these structures.

Influence of the highest occupied molecular orbital energy level of the donor material on the effectiveness of the anode buffer layer in organic solar cells

Efficiency of organic photovoltaic cells based on organic electron donor/organic electron acceptor junctions can be strongly improved when the transparent conductive Anode is coated with a Buffer Layer (ABL). Here, the effects of a metal (gold) or oxide (molybdenum oxide) ABL are reported, as a function of the Highest Occupied Molecular Orbital (HOMO) of different electron donors. The results indicate that a good matching between the work function of the anode and the highest occupied molecular orbital of the donor material is the major factor limiting the hole transfer efficiency. Indeed, gold is efficient as ABL only when the HOMO of the organic donor is close to its work function Phi(Au). Therefore we show that the MoO(3) oxide has a wider field of application as ABL than gold. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Ferromagnetism Exhibited by Nanoparticles of Noble Metals

Gold nanoparticles with average diameters in the range 2.515 nm, prepared at the organic/aqueous interface by using tetrakis( hydroxymethyl) phosphonium chloride (THPC) as reducing agent, exhibit ferromagnetism whereby the saturation magnetization M(S) increases with decreasing diameter and varies linearly with the fraction of surface atoms. The value of M(S) is higher when the particles are present as a film instead of as a sol. Capping with strongly interacting ligands such as alkane thiols results in a higher M(S) value, which varies with the strength of the metal-sulfur bond. Ferromagnetism is also found in Pt and Ag nanoparticles prepared as sols, and the M(S) values vary as Pt > Au > Ag. A careful study of the temperature variation of the magnetization of Au nanoparticles, along with certain other observations, suggests that small bare nanoparticles of noble metals could indeed possess ferromagnetism, albeit weak, which is accentuated in the presence of capping agents, specially alkane thiols which form strong metal-sulfur bonds.

Perfluoroalkyl bile esters: a new class of efficient gelators of organic and aqueous-organic media

A new class of fluorinated gelators derived from bile acids is reported. Perfluoroalkyl chains were attached to the bile acids through two different ester linkages and were synthesized following simple transformations. The gelation property of these derivatives is a function of the bile acid moiety, the spacer and the fluoroalkyl chain length. By varying these parameters, gels were obtained in aromatic hydrocarbons, DMSO and DMSO/DMF-H(2)O mixtures of different proportions. Several derivatives of deoxycholic and lithocholic acids were found to be efficient organogelators, while the reported bile-acid based organogelators are mostly derived from the cholic acid moiety. The efficient gelators among these compounds formed gels well below 1.0% (w/v) and hence they can be termed as supergelators. The mechanical properties of these gels could be modulated by changing either the bile acid moiety or by varying the length of the fluoroalkyl segment. The presence of CO(2)-philic perfluoroalkyl groups is also expected to enhance their solubility in supercritical CO(2) and hence these compounds are promising candidates for making aerogels.

Perfluoroalkyl bile esters: a new class of efficient gelators of organic and aqueous-organic media

A new class of fluorinated gelators derived from bile acids is reported. Perfluoroalkyl chains were attached to the bile acids through two different ester linkages and were synthesized following simple transformations. The gelation property of these derivatives is a function of the bile acid moiety, the spacer and the fluoroalkyl chain length. By varying these parameters, gels were obtained in aromatic hydrocarbons, DMSO and DMSO/DMF-H(2)O mixtures of different proportions. Several derivatives of deoxycholic and lithocholic acids were found to be efficient organogelators, while the reported bile-acid based organogelators are mostly derived from the cholic acid moiety. The efficient gelators among these compounds formed gels well below 1.0% (w/v) and hence they can be termed as supergelators. The mechanical properties of these gels could be modulated by changing either the bile acid moiety or by varying the length of the fluoroalkyl segment. The presence of CO(2)-philic perfluoroalkyl groups is also expected to enhance their solubility in supercritical CO(2) and hence these compounds are promising candidates for making aerogels.

Fluorescent metal-organic framework for selective sensing of nitroaromatic explosives

Highly luminescent micrometre-sized fine particles of a Zn(II) metal-organic framework (MOF) of a new pi-electron rich tricarboxylate dispersed in ethanol is demonstrated as a selective sensory material for the detection of nitroaromatic explosives via a fluorescence quenching mechanism.

An eight-connected metal organic framework based on Cu(5) clusters: Synthesis, structure, magnetic and catalytic properties

A reaction of copper acetate, 5-nitroisophthalic acid in a water-methanol mixture under solvothermal condition results in a new metal-organic framework compound, [Cu(5)(mu(3)-OH)(2)(H(2)O)(6){(NO(2))-C(6)H(3)-(COO)(2)}(4)]center dot 5H(2)O, (1). The compound contains Cu5 pentameric cluster units connected by 5-nitro isophthalate (NIPA) moieties forming a CdCl(2)-like layer, which are further connected by another NIPA moiety forming the three-dimensional structure. The water molecules in (1) can be reversibly adsorbed. The removal of water accompanies a change in the colour as well as a structural re-organization. Magnetic studies suggest strong antiferromagnetie correlations between the Cu5 cluster units. The compound (1) exhibits heterogeneous Lewis acid catalysis for the cyanosilylation of imines with more than 95 % selectivity. Compound (1) has been characterized by IR, UV-vis, TGA, powder XRD studies.