High pressure X-ray diffraction study of CdAl2Se4 and Raman study of AAl2Se4 (A=Hg, Zn) and CdAl2X4 (X=Se, S)

We report the results of an X-ray diffraction study of CdAl₂Se₄ and of Raman studies of HgAl₂Se₄ and ZnAl₂Se₄ at room temperature, and of CdAl₂S₄ and CdAl₂Se₄ at 80 K at high pressure. The ambient pressure phase of CdAl₂Se₄ is stable up to a pressure of 9.1 GPa above which a phase transition to a disordered rock salt phase is observed. A fit of the volume pressure data to a Birch-Murnaghan type equation of state yields a bulk modulus of 52.1 GPa. The relative volume change at the phase transition at ∼9 GPa is about 10%. The analysis of the Raman data of HgAl₂Se₄ and ZnAl₂Se₄ reveals a general trend observed for different defect chalcopyrite materials. The line widths of the Raman peaks change at intermediate pressures between 4 and 6 GPa as an indication of the pressure induced two stage order-disorder transition observed in these materials. In addition, we include results of a low temperature Raman study of CdAl₂S₄ and CdAl₂Se₄, which shows a very weak temperature dependence of the Raman-active phonon modes.     

Selective quenching of tryptophanyl fluorescence in bovine serum albumin by the iodide ion

Modified Stern-Volmer equation is obeyed by bovine serum albumin (BSA)-iodide system showing selective quenching of tryptophanyl fluorescence of BSA. The fraction of accessible protein fluorescence is 0.56 and the effective Stern-Volmer constant is 290 M^-1 at pH 7.4 in 0.005 M phosphate buffer at 25°C. Collisional quenching is operative both in the BSA -I⁻¹ system and the model system, tryptophan-I⁻¹. It is supported by the observed relationship between the ratio of quenching rate constants (k _q ) and diffusion coefficients and alsok _q with bulk viscosity.     

On algebras of Toeplitz fuzzy matrices

In this paper, necessary and sufficient conditions are given for a product of Toeplitz fuzzy matrices to be Toeplitz. As an application, a criterion for normality of Toeplitz fuzzy matrices is derived and conditions are deduced for symmetric idempotency of Toeplitz fuzzy matrices. We discuss similar results for Hankel fuzzy matrices. Keywords: Fuzzy matrix, Toeplitz and Hankel matrices.     

Amine-templated metal squarates

Two layered amine-templated cobalt squarates, [C₆N₂H₁₄]₂[Co₂(C₄O₄)₃(H₂O)₄], I, and [C₃N₂H₅]₂[Co₂(C₄O₄)₃(H₂O)₄], II, have been prepared under hydrothermal conditions. Both I and II contain chains formed by dimers comprising two cobalt atoms bound to the squarate units, the chains being connected through hydrogen bond interactions. An amine-templated cobalt squarate of the formula [C₄N₂H₁₂][Co(C₄O₄)₂(H₂O)₄][H₂O]₂, III, as well as its Ni, Zn and Cd analogues have been prepared by room temperature reactions. III has a layered architecture wherein the cobalt-squarate monomers are linked by the amine molecules. Co and Zn analogues of [Ni(C₄O₄)(H₂O)₂(C₃N₂H₄)] with ligating imidazole units have also been prepared and characterized.     

Impact of micelles on the biocidal efficiency in a diesel–water interface

Biodegradation occurs in the diesel/water interface in petroleum product pipelines. The microbial contamination can result in inhibitor/fuel degradation, leading to unacceptable levels of turbidity, filter plugging, storage tank corrosion and stored product souring. Therefore, selection of the biocide/inhibitor plays an important role in the transportation of petroleum products through pipelines. Three biocides (cationic and nonionic) were employed to study the biodegradation in a diesel‐water interface. The biocidal efficiency against degradation of diesel was examined by employing Fourier‐transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy and gas chromatography mass spectrometry (GC‐MS) techniques. Bronopol (2‐bromo‐2‐nitro‐propane‐1, 3‐diol) was found to have higher bactericidal efficiency than N‐cetyl‐N,N, N‐trimethyl ammonium bromide (CTAB) and cetyl pyridinum bromide (CPB). But the cationic biocides (CTAB and CPB) showed good biocidal efficiency at the interface. The data are explained in terms of a model that postulates the formation of a ‘micelle’ at the diesel‐water interface. Copyright © 2007 John Wiley & Sons, Ltd.     

Syntheses of mixed ligands complexes of Ru(II) with 4,4′-dicarboxy-2,2′-bipyridine and substituted pteridinedione and the use of these complexes in electrochemical photovoltaic cells

The synthesis, spectral and photoelectrochemical studies of mixed ligand complexes of [Ru(dcbpy)₂(LL)]Cl₂, where LL=2,4-(1,3-N,N′-dimethyl)pteridinedione (DMP), 6,7-dimethyl-2,4-(1,3-N,N′-dimethyl)pteridinedione (MDMP), 6,7-diphenyl-2,4-(1,3-N,N′-dimethyl)pteridinedione (PhDMP), dibenzo[h,j]-(1,3-N,N′-dimethyl)isoalloxazine (BIAlo), 6,7-bis(pyrid-2-yl)-2,4-(1,3-N,N′-dimethyl) pteridinedione (PyDMP) were carried out. These complexes were attached to sol–gel processed TiO₂ electrodes and the photocells fabricated were illuminated with polychromatic radiation in the presence of I₂/I₃⁻ as redox electrolyte. The incident photon to current conversion efficiency determined was found to be 20–48%.     

Investigation on the formation and decay of the N,N,N′,N′-tetramethylbenzidine radical cation using various oxidants and reductants by stopped-flow spectrophotometry

N,N,N′,N′-Tetramethylbenzidine (TMB) is an aromatic amine that undergoes oxidation by various oxidizing agents such as Ce⁴⁺, MnO⁻₄, Cr₂O²⁻₇; HSO⁻₅, S₂O⁻₈, H₂O₂, Cl₂, Br₂ and I₂, thereby serving as a reducing substrate. One-electron oxidation of TMB results in a radical cation (TMB^˙+), and on further oxidation leads to the product dication (TMB⁺⁺) were monitored by stopped-flow spectrophotometer at the absorption wavelength of TMB^˙+(λ_max; 460 nm). ESR data was also provided to confirm the formation of radical cation. The rates of both the formation and decay of TMB^˙+ have been followed by a total second-order kinetics, a first-order dependence each on [TMB] (or) [TMB^˙+] and [oxidant]. The kinetic and transition state parameters have been evaluated for the effects of pH and temperature on the formation and decay of TMB^˙+ and discussed with suitable reaction mechanisms. Also, the rate constants for the reactions of the radical cation with various reducing agents such as sulfite (SO²⁻₃), thiosulfate (S₂O²⁻₃), dithionite (S₂O²⁻₄) and disulfite (S₂O²⁻₅) and ascorbic acid (vitamin C, AH₂ were determined. Besides these, this article also explains how TMB acts as a better electron relay than unsubstituted benzidine, even though both of them undergo one-electron oxidation and are used in the chemical routes to solar energy conversions. The observed rate constants for electron transfer were correlated theoretically using Marcus theory. The observed and calculated rate constants have good correlation.     

A novel method for the determination of synthetic colors in ice cream samples

A simple method has been developed for the extraction, separation, and determination of synthetic colors in ice cream samples. The process involves the breakdown of emulsion by neutral detergents (Triton X-100 and Tween 20) followed by extraction with petroleum ether for removal of fat. The aqueous colored solution obtained is treated with 5% acetic acid, and the uptake of color is carried out by a wool-dyeing technique. The color is eluted from the wool with 5% ammonia solution, the solution is evaporated to dryness, and the residue is dissolved in 60% ethanol for paper chromatography using trisodium citrate-ammonia-water (2 + 5 + 95, w/v/v) as the mobile phase. The colored spots from the paper chromatogram are cut and eluted with 60% ethanol, and the absorbance is measured at the respective lambda maximum corresponding to the Rf value of the appropriate standard. The recoveries of 6 colors, including sunset yellow FCF (SSYFCF), tartrazine, carmoisine, ponceau 4R, brilliant blue FCF (BBFCF), and fast green FCF from spiked samples with either detergent were found to be >90%. However, recoveries of erythrosine were 21 and 65% with Triton X-100 and Tween 20, respectively. Indigo carmine could not be recovered at all because of its fugitive property in 5% ammonia solution, which is used to strip the color from the wool. The sensitivity of the method with the use of Tween 20 is 1 ppm (1 microg/g) for the colors in spiked ice cream samples. With this method, we analyzed samples of 20 branded colored ice cream. The results showed the presence of tartrazine (8.4-43.3 ppm), SSYFCF (23.5-117.6 ppm), carmoisine (traces-53.2 ppm), erythrosine (3.5 ppm), and BBFCF (4.1 ppm) in the ice cream samples. Apart from 2 samples of tuttifruity, all of the ice cream samples showed the presence of permitted synthetic colors below the permissible level of 100 ppm established by the Prevention of Food Adulteration Act of India.     

Purification and Characterization of Tyrosine Phenol Lyase from Citrobacter freundii

The purification and characterization of intracellular tyrosine phenol lyase from Citrobacter freundii has been carried out. The enzyme was purified 35-fold to homogeneity by ammonium sulphate precipitation and hydrophobic interaction chromatography. Its subunit molecular weight was found to be 52 kDa on sodium dodecyl sulphate polyacrylamide gel electrophoresis. The purified tyrosine phenol lyase showed maximum activity in borate buffer (0.05 M at pH 8.5) at 45 °C after 20 min of incubation. The K _m and V _max values of purified enzyme were found to be 0.446 mm and 0.342 mM/min/mg. This enzyme exhibits t _1/2 of 10, 52 and 130 min at 55, 45 and 35 °C, respectively. The N-terminal amino acid sequence was determined as MET-ASN-TYR-PRO-ALA-GLU-PRO-PHE-ARG-ILE-TRP-TRP-VAL-GLY.     

Conductivity relaxation in Ag+ ion conducting PEO–PMMA–PEG polymer blends

In this paper, the electrical conductivity and relaxation studies in two different temperature regions (T?<?T _m and T?>?T _m) on plasticized PEO–PMMA blend polymer electrolyte system with AgNO₃ salt are reported. The polymer electrolyte system has been prepared by solution cast technique and characterized by X-ray diffraction and differential scanning calorimetry. The conduction and relaxation processes at various temperatures have been investigated in the framework of modulus formalism. The distribution of relaxation times is discussed using Argand plot. Variation in ionic conductivity of polymer blends is discussed with the increase of PEO as well as with temperature.