Amperometric determination of organic isothiocyanates

An amperometric titration method is described for the determination of 1-5 mg of organic isothiocyanates, based on their quantitative reaction with n-butylamine in dimethylfonnamide to form N,N-disubstituted thioureas which are then titrated amperometrically in aqueous ammonia-ammonium nitrate buffer with silver nitrate (dropping mercury electrode at -0.56V). The end-point corresponds to a silver:thiourea ratio of 2:1, with precipitation of silver sulphide. The method is simple, accurate, widely applicable, and gives reproducible results.     

Indicators in non-aqueous cerimetric titrations of thioureas and xanthates

The use of some chemical indicators in the non-aqueous cerimetric determination of thioureas and xanthates in acetonitrile medium is described.     

Electronic, cyclic voltammetry, IR and EPR spectral studies of copper(II) complexes with 12-membered N4, N2O2 and N2S2 donor macrocyclic ligands

A new series of copper(II) complexes have been synthesized with macrocyclic ligands having three different donating atoms in the macrocyclic ring. It has been shown that the stereochemistry of complexes is dependent on the coordinated anions. These complexes are characterized by various physicochemical techniques, viz. elemental analysis, molar conductance, magnetic susceptibility measurements, IR, electronic, 1H NMR and EPR spectral studies. Cyclic voltammetric behavior of the complexes has also been discussed. The observed anisotropic g-values indicate that the chloro and acetato complexes are six-coordinate tetragonal. Whereas the sulfato and nitrato complexes are found to have five-coordinate square-pyramidal and four-coordinate square-planar geometry, respectively.     

Oxidation of cyclohexane with molecular oxygen using a Schiff base cobalt complex bonded to carbamate-modified silica gel

The Schiff base [1,2-bis(salicylidene amino)phenylene]cobalt(II) complex, chemically bonded to a carbamate-modified silica gel catalyst, has been prepared by a four step procedure. The oxidation of cyclohexane was studied in the presence of this catalyst under relatively mild conditions (150–200 °C, 15–20 atm) using molecular oxygen. The catalyst was found to be very selective for the production of cyclohexanol, with cyclohexanone formed in only a small amount (45:1). This is in contrast to the commercially available processes in which cyclohexanol and cyclohexanone are both formed in appreciable amounts. The t.g.a. analysis shows the catalyst to be stable up to 211 °C and atomic absorption spectroscopy indicated negligible metal loss during 50 h use of the catalyst up to 180 °C.     

Synthesis of a novel cis-proline-derived cyclic type VI beta-turn mimic via ring-closing metathesis

A cis-proline derived cyclic mimic of a type VI beta-turn is synthesized via a ring-closing metathesis reaction. The solution NMR conformational study indicates that the major conformer of the cyclic peptide adopts a type VIa beta-turn in CDCl(3) and a type VIb beta-turn in DMSO-d(6).     

INDUCIBLE POSTREPLICATION REPAIR IS RESPONSIBLE FOR MINIMAL MEDIUM RECOVERY IN UV-IRRADIATED Escherichia coliK–12

Abstract— Ultraviolet (UV)-irradiated Escherichia coli K–12 uvrA cells showed higher survival if plated on minimal growth medium rather than on rich growth medium, i.e., they showed minimal medium recovery (MMR). A 2-hour treatment of UV-irradiated cells with rifampicin inhibited the subsequent expression of MMR, and produced a large reduction in survival. We have recently isolated a new mutant ( mmrA1 ) that does not show MMR. The mmrA mutation protected UV-irradiated uvrA cells from the effect of rich growth medium on survival, but not from the effect of rifampicin on survival. DNA daughter-strand gap (DSG) repair in UV-irradiated (4 J/m²) uvrA cells was inhibited to the same degree whether rich growth medium was added immediately after irradiation or after 10 min of postirradiation incubation in minimal growth medium. However, chloramphenicol added immediately after irradiation greatly reduced this repair; there was less reduction if it was added 10 min after UV irradiation. These findings suggest that MMR is an inducible repair phenomenon, and that rich growth medium inhibits this repair process itself rather than its induction.     

Iron(III) complexes of 2-acetylpyridine-4-phenyl-3-thiosemicarbazones: Magnetic,E.s.r. and spectral studies

Summary Iron(III) complexes of 2-acetylpyridine-4-phenyl-3-thiosemicarbazone (LH) with the general formulae FeLX₂ (X = Cl, Br, NO₃ or SCN) and FeLSO₄ have been prepared and characterised by elemental analysis and by magnetic measurements in the polycrystalline state in the 77–298 K range and by electronic, i.r. and e.s.r. spectra. The FeLX₂ species (X = Cl, NCS or NO₃) are square pyramidal of intermediate spin-state (S=3/2) with an⁴ A ₂ ground state. The magnetic behaviour of FeLSO₄ is commensurate with high order effects coupled with antiferromagnetic exchange interactions. FeLBr₂ is a spin-free dimer involving bromine bridging between two FeLBr₂ square pyramids. However, the low-spin species [FeL(DMF)₃]²⁺ exists in dimethylformamide solution.     

A Polarographic Study of ϵ-Caprolactam Complexes of Uranium and Tellurium

The polarographic behaviour of uranium and tellurium has been studied in the presence of increasing concentration of complex forming agent viz. ?-caprolactam at pH 4.4 for U(VI) and at pH 10.0 for Te(IV) at μ=0.1 M KNO₃. In both cases the waves have been found to be diffusion controlled and irreversible. The values of kinetic parameters (σπ_a and K°_f,h) have been calculated as a function of the ligand concentration. Method is suitable for the quantitative determination of these metals individually and simultaneously with the effect of diverse ions.     

Polarographic reduction of some guanylpyrazoline nitrates and the effect of double layer structure on E1/2 values

Polarographic reduction of 4-arylhydrazono-1-guanylnitrate-3-methyl-2-pyrazoline-5-ones takes place in a single 4-electron transfer, giving a diffusion controlled irreversible wave in B.R. buffers of pH range 2.0–10.0. The reduction in these compounds takes place at the ?NH?N=C-bond. Effect of various cations, anions and solvent percentage on the reduction has been discussed. The effect of substituents and its correlation with the Hammett substituent constant (δ) have also been studied.