The development of new low-molecular-weight gelators for organic solvents is motivated by several potential applications of gels as advanced functional materials. In the present study, we developed simple dipeptide-based organogelators with a minimum gelation concentration (MGC) of 6-0.15 %, w/v in aromatic solvents. The organogelators were synthesized using different L-amino acids with nonpolar aliphatic/aromatic residues and by varying alkyl-chain length (C-12 to C-16). The self-aggregation behavior of these thermoreversible organogels was investigated through several spectroscopic and microscopic techniques. A balanced participation of the hydrogen bonding and van der Waals interactions is crucial for efficient organogelation, which can be largely modulated by the structural modification at the hydrogen-bonding unit as well as by varying the alkyl-chain length in both sides of the hydrophilic residue. Interestingly, these organogelators could selectively gelate aromatic solvents from their mixtures with water. Furthermore, the xerogels prepared from the organogels showed a striking property of adsorbing dyes such as crystal violet, rhodamine 6G from water. This dye-adsorption ability of gelators can be utilized in water purification by removing toxic dyes from wastewater.

A series of heteroleptic tridentate ruthenium(II) complexes of composition [(H(2)pbbzim)Ru(tpy-X)](PF(6))(2) (1-7), where H(2)pbbzim = 2,6-bis(benzimidazole-2-yl)pyridine and tpy-X = 4'-substituted terpyridine ligands with X = H, p-methyl phenyl (PhCH(3)), p-bromomethylphenyl (PhCH(2)Br), p-dibromomethylphenyl (PhCHBr(2)), p-cyanomethylphenyl (PhCH(2)CN), p-triphenylphosphonium methylphenyl bromide (PhCH(2)PPh(3)Br), and 4'-phenylformyl (PhCHO) groups, has been synthesized and characterized by using standard analytical and spectroscopic techniques. These compounds were designed to increase the excited-state lifetime of ruthenium(II) bisterpyridine-type complexes. The X-ray crystal structure of a representative compound 2, which crystallized with monoclinic space group P2(1)/c, has been determined. The absorption spectra, redox behavior, and luminescence properties of the ruthenium(II) complexes have been thoroughly investigated. All of the complexes display moderately strong luminescence at room temperature with lifetimes in the range of 10-58 ns. Correlations have been obtained for the Hammett sigma(p) parameter with their MLCT emission energies, lifetimes, redox potentials, proton NMR chemical shifts, etc. The anion binding properties of all the complexes as well as the parent ligand H(2)pbbzim have been studied in acetonitrile using absorption, emission, and (1)H NMR spectral studies, and it has been observed that the metalloreceptors act as sensors for F(-), AcO(-), and to some extent H(2)PO(4)(-). At a relatively lower concentration of anions, a 1:1 H-bonded adduct is formed; however, in the presence of an excess of anions, stepwise deprotonation of the two benzimidazole N-H fragments occurs, an event which is signaled by the development of vivid colors visible with the naked eye. The receptor-anion binding constants have been evaluated. Cyclic voltammetric (CV) measurements carried out in acetonitrile-dimethylformamide (9:1) provided evidence in favor of anion (F(-), AcO(-)) concentration dependent electrochemical responses, enabling 1 - 7 to act as suitable electrochemical sensors for F(-) and AcO(-) ions.

Cell-free extracts (CFEs) of chromium-resistant bacterium Bacillus sphaericus AND 303 isolated from serpentine soil of Andaman, India reduced Cr(VI) in in vitro condition, and the reductase activity was solely localized in the soluble cell-fractions (S12, S32, and S150). The enzyme was constitutive as the CFEs from cells grown in Cr(VI)-free and Cr(VI)-containing media reduced a more or less equal amount of Cr(VI). Optimum Cr(VI) reductase activity was obtained at an enzyme (S150) concentration equivalent to 4.56 mg protein/mL, 300 microM: Cr(VI) and pH 6.0 after 30 min incubation at 30 degrees C. The enzyme was heat labile; 80% of its activity was lost when exposed at 70 degrees C for 15 min. Kinetics of Cr(VI) reductase activity fit well with the linearized Lineweaver-Burk plot and showed a V(max) of 1.432 micromol Cr(VI)/mg protein/min and K(m) of 158.12 microM: Cr(VI). The presence of additional electron donors accelerated Cr(VI) reductase activity of CFE, and an increase of 28% activity over control was recorded with 1.0 microM: NADH. Heavy metal ions such as Ni(II), Cu(II), and Cd(II) were strong inhibitors of Cr(VI) reductase unlike that of 100 microM: Co(II), which retained 93% activity over control.

With the growing importance of hydrogels in scientific applications, the search for low molecular weight hydrogelators (LMWH), with simultaneous logical structural correlation is continuously increasing. In the present work, counterion variation of amino acid based amphiphiles was done to qualitatively evaluate its contribution towards hydrogelation. Further changes in the molecular skeleton of the amino acid amphiphile were done along with counterion variation to establish the importance of p-p interactions of aromatic planar ring in hydrogelation. An efficient conversion of a non-gelator to gelator molecule was achieved simply by changing the counterions to aromatic carboxylates. Role of the counterion in the mechanism of gelation process through the self-assembly of amino acid based amphiphiles has been discussed. The formation of supramolecular structures during hydrogelation was investigated by FESEM, CD, FT-IR, luminescence, 2D-NOESY and rheological studies. Interestingly, the L-tryptophan containing amphiphile hydrogelators were further utilized for synthesis of Ag nanoparticles under mild conditions without any need for high temperature, alkaline medium and external reducing agent. The nanoparticles obtained were characterized by UV-Vis, TEM, AFM and XRD experiments.

The gelation of ionic liquids is attracting significant attention because of its large spectrum of applications across different disciplines. These 'green solvents' have been the solution to a number of common problems due to their eco-friendly features. To expand their applications, the gelation of ionic liquids has been achieved by using amino acid-based low-molecular-weight compounds. Variation of individual segments in the molecular skeleton of the gelators, which comprise the amino acid and the protecting groups at the N and C termini, led to an understanding of the structure-property correlation of the ionogelation process. An aromatic ring containing amino acid-based molecules protected with a phenyl or cyclohexyl group at the N terminus were efficient in the gelation of ionic liquids. In the case of aliphatic amino acids, gelation was more prominent with a phenyl group as the N-terminal protecting agent. The probable factors responsible for this supramolecular association of the gelators in ionic liquids have been studied with the help of field-emission SEM, (1)H NMR, FTIR, and luminescence studies. It is the hydrophilic-lipophilic balance that needs to be optimized for a molecule to induce gelation of the green solvents. Interestingly, to maximize the benefits from using these green solvents, these ionogels have been employed as templates for the synthesis of uniform-sized TiO(2) nanoparticles (25-30 nm). Furthermore, as a complement to their applications, ionogels serve as efficient adsorbents of both cationic and anionic dyes and were distinctly better relative to their organogel counterparts.