Efficient cleavage of ribonucleoside 3',5'-cyclic phosphates and deoxyribonucleoside 3',5'-cyclic phosphate by lanthanides

The cleavage of 3',5'-cAMP, 3',5'-cGMP and 3',5'-dcAMP by lanthanides has been investigated by HPLC and H-1 NMR. Rapid cleavage of cAMP, cGMP and dcAMP by Ce(III) under air at pH 8 and 37 degrees C has been observed. Regioselective cleavage of P-O(5') bond in cAMP, cGMP and dc;aMP tu give the corresponding 3'-AMP, 3'-GMP and 3'-dAMP by lanthanide chlorides has been achieved, and 3'-AMP and 3'-GMP are cleaved to adenosine(A) and guanosine(CT) more slowly, respectively, The notable difference in reactivity between Ce(III) and the other lanthanide ions under air has also been studied. The cleavage is enhanced with the increase in the molar fraction of Ce(IV). The fast cleavage of cAMP by Ce(III) under air at pH 8 is ascribed to the resultant Ce(IV) in the reaction mixture.

Isolation and X-ray crystallographic structure of cyclic tetramer based on bisphenol A and o-phthaloyl dichloride

The polycrystalline powder of the cyclic tetramer based on bisphenol A and o-phthaloyldichloride has been prepared by recrystallization from nitrobenzene and its crystal structure has been determined by Wide-Angle X-ray Diffraction (WAXD). The unit cell is orthorhombic and its dimensions a = 0.967 6 nm, b = 0.869 9 nm, c = 2.085 9 nm, Space group belongs to Pmmm, With two tetramers per unit cell,the crystal density is 1.36 g . cm(-3), Indices of crystal diffraction peaks are also detailed in the present work.

X-ray crystallographic structure of cyclic tetramer ester based on bisphenol-A and o-phthaloyldichloride

The polycrystalline powder of the cyclic tetramer ester based on bisphenol-A and o-phthaloyldichloride has been prepared by recrystallization from nitrobenzene and its crystal structure determined by wide-angle X-ray diffraction. The unit cell is orthorhombic and has dimensions a=0.967 nm, b=0.8699 nm, c = 2.0859 nm. With two tetramers per unit cell, the crystal density is 1.36 g cm(-3). Indices of crystal diffraction peaks are also detailed in the present work. Copyright (C) 1996 Elsevier Science Ltd.

CYCLIC VOLTAMMETRIC STUDY OF QUININE DERIVATIVES TRANSFER ACROSS THE WATER NITROBENZENE INTERFACE

Quinine derivatives, quinine hydrochloride and 8-hydroxyquinoline, transfer across the water/nitrobenzene interface was studied by cyclic voltammetry. The effect of solution acidity on the transfer behaviour was observed. Transfer mechanism was discussed

EFFECTS OF DOPANT AND SOLVENT ON THE PROPERTIES OF POLYPYRROLE - INVESTIGATIONS WITH CYCLIC VOLTAMMETRY AND ELECTROCHEMICALLY INSITU CONDUCTIVITY

A new method for electrochemically in situ conductivity measurements based on a reusable glassy carbon disc carbon fibre array double electrode is described. Using this technique and cyclic voltammetry, we have investigated the effects of the doping anion and solvent on the electrochemical properties of polypyrrole film. The electroactivity and potential dependent conductivity of polypyrrole film are strongly affected by solvent and the doping anion's solubility in the solvent, and also by the history of electrochemical treatments in different electrolyte solutions. It is very interesting that NO3-doped polypyrrole can completely keep its conducting state (doped state) at a reasonably negative potential (eg -0.8 V vs. sce) in acetonitrile solutions.

CYCLIC VOLTAMMETRIC AND SPECTROELECTROCHEMICAL STUDIES OF COPPER IN ALKALINE-SOLUTION

The behaviour of the electroplated copper film electrode on tin oxide/glass or glassy carbon surface was studied in potassium hydroxide medium by cyclic voltammetry and in situ transmission spectroelectrochemistry. The results indicate that the electroplated copper film electrode is similar to a copper electrode and cyclic voltammetry with this electrode affords more resolution. The anodic peaks were found to correspond successively to the adsorption of oxygen, the formation of a surface layer of Cu2O, the formation of a surface layer of Cu(OH)2 or CuO and formation of a thick multilayer film of CuO. This is the first time it has been proposed that a surface layer of Cu(OH)2 or CuO is formed from the oxidation of the surface layer of Cu2O. Similarly, a clear interpretation is presented that the cathodic peaks correspond successively to the reduction of CuO to Cu2O, the reductions of Cu2O to Cu and the soluble Cu(II) species to Cu. On the other hand, a shoulder peak related to the chemical transformation of Cu(OH)2 to CuO was first observed.

A NOVEL METAL THIAMINE COMPLEX WITH A CYCLIC DIMER FORMED BY METAL-BRIDGED 2 THIAMINE LIGANDS - CRYSTAL-STRUCTURE OF [MN(THIAMINE)CL2(H2O)]2[THIAMINE]2CL4.2H2O

The crystal structure of [Mn(thiamine)Cl2(H2O)]2[thiamine]2Cl4.2H2O has been determined by X-ray diffraction methods. The compound contains a cyclic dimer of a complex cation with two thiamine ligands bridged by two Mn(II) ions across a crystallographic center of symmetry. Each Mn(II) is coordinated by two chloride atoms, a water molecule, a N(1') atom of the pyrimidine from a thiamine and an O(53) atom of the hydroxyethyl side chain from another thiamine. There are two free-base thiamine molecules related by a center of symmetry in the unit cell, which form a base-pair through the hydrogen bonds. Both the independent thiamine molecules in the asymmetric unit assume the common F conformation with phi-T = 10.0(9) and 3.6(10) and phi-P = 85.6(7) and 79.6(7), respectively. The compound provides a possible model for a metal-bridged enzyme-coenzyme complex in thiamine catalysis. Crystallographic data: triclinic, space group P1BAR, a = 12.441(4), b = 13.572(4), c = 11.267(3) angstrom, alpha = 103.15(2), beta 89.03(3), gamma = 115.64(2)-degrees, Z = 1, D(calc) = 1.524 g cm-3, and R = 0.050 for 3019 observed reflections with I > 3-sigma(I).

COMPARISON OF THE BEHAVIOR OF CYCLIC AND LINEAR POLYSTYRENE IN DILUTE-SOLUTION

Using a low angle laser light scattering photometer, the second virial coefficients (A2) of both cyclic and linear polystyrene were determined in cyclohexane, toluene and methyl ethyl ketone (MEK) solutions. From the data obtained in cyclohexane solution the theta-temperature of cyclic polystyrene was determined to be 30-degrees-C. In toluene solution A2 of cyclic polystyrene is smaller than that of linear polystyrene with the same molecular weight, but in MEK the values are similar.

MOLECULAR-WEIGHT DEPENDENCE OF THE GLASS-TRANSITION OF CYCLIC POLYSTYRENE

The glass transition temperature (T(g)) of cyclic polystyrene was measured by differential scanning calorimetry. There was a marked difference in the glass transition behaviour between cyclic and linear polystyrene. In the low molecular weight region (M(n) < 5 x 10(3)), the T(g) of the cyclic polystyrene increased with decreasing M(n), contrary to that of linear polystyrene. With M(n) higher than 5 x 10(3), the T(g) of cyclic polystyrene increased with increasing M(n). The T(g) of cyclic and linear polystyrene approached the same constant value when the M(n) was high enough (M(n) > 10(5)). Combining the results of specific volume, it is believed that the variation of T(g) with molecular weight does not depend only on free volume effects but that configurational entropy is also an important factor.

CYCLIC VOLTAMMETRIC STUDY ON THE TRANSFER MECHANISM OF ALKALI-METAL IONS ACROSS LIQUID LIQUID INTERFACE FACILITATED BY TRITON X-100

The transfer behavior of alkali motal ions K~+ and Na~+ across the interfaces of water/nitrobenzene and water/1, 2-dichloroethane facilitated by Triton X-100 is investigated by cyclic voltammetry with four electrodes. The equations of interfacial half-wave potential derived in terms of the mechanism proposed isverified by the experimental data and consistent with the practical △_0~wφ_p-pM curves.

Hydrogen permeation and corrosion behaviour of high strength steel 35CrMo under cyclic wet-dry conditions

Hydrogen permeation behaviours of high strength steel 35CrMo under different cyclic wet-dry conditions have been investigated by using Devanathan-Stachurski's technique. Four electrolytes were used: distilled water, seawater, seawater containing 1500 ppm H2S and seawater containing 0.03 mol L-1 SO2. The corrosion weight loss of 35CrMo in the wet-dry cycles was measured simultaneously. The experimental results show that hydrogen can be detected at the surface opposite to the corroding side of the specimen during wet-dry cycles and the permeation current density during a wet-dry cycle showed a maximum during the drying process. The hydrogen permeation was obviously promoted by Cl- ions, H2S and SO2. The hydrogen permeation in the real marine atmosphere has also been investigated. There is a clear correlation between the amount of hydrogen permeated and the corrosion weight losses. Results show the importance of hydrogen permeation that merits further investigation.

Hydrogen permeation behavior and corrosion monitoring atmospheric of steel in cyclic wet-dry environment

Hydrogen permeation of 16Mn steel under a cyclic wet-dry condition was investigated by Devanathan-Stachurski's electrolytic cell with a membrane covered on the exit side by a nickel layer and the weight loss was measured for each wet-dry cycle. The results show that hydrogen permeation current change with different atmospheric environment: distilled water, seawater, and seawater containing 100 ppm H2S. The results show that seawater can induce an increase in the hydrogen permeation current due to the hydrolyzation reaction. And after the increase, equilibrium is reached due to the equilibrium of hydrolyzation reaction effect and the block of the rust layer. On the other hand, H2S contamination also can induce an increase in the maximum hydrogen permeation current due to the hydrolyzation reaction. And H2S contamination delays the time that hydrogen permeation is detected because of the formation of the FeS(1-x) film. The FeS(1-x) film can block the absorption of hydrogen onto the specimen surface. The surface potential change and the pH change of the metal surface control the hydrogen permeation current. And a clear linear correlation exists between the quantities of hydrogen permeated through the 16Mn steel and the weight loss. Based on the linear correlation, we monitored the corrosion rate by monitoring the hydrogen permeation current by a sensor outside. Good coherences were shown between results in laboratory and outside.