Monitoring of the metal displacement from the recombinant mouse liver metallothionein Zn(7)-complex by capillary zone electrophoresis with electrospray MS detection

A solution of a Zn-complex of recombinant mouse MT-1 isoform (Zn(7)-MT-1) was prepared and titrated with Cd(2+) ions. A method based on the coupling of capillary zone electrophoresis (CZE) with electrospray MS detection was developed for the analysis of the stoichiometry of the species formed during the titration. The method offered the possibility of the on-line removal of up to 100 mM Tris or phosphate buffer solutions that would otherwise suppress the electrospray signal. By allowing the determination of the metal stoichiometry of the complex species present in solution the method was shown to be complementary to circular dichroism and UV-VIS spectrophotometry conventionally used for similar studies. The titration of the Zn(7)-MT complex with Cd(II) showed the sequential displacement of the Zn by Cd. The unusually high stability of the Cd(6)Zn(1)-MT species was observed which suggests a structural role of the remaining Zn(II) ion.     

Cyclic chronocoulemetry: Disproportionation and dimerization reactions coupled to electron transfer

An extension of double-potential-step chronocoulemetry to multiple or cyclic techniques has been developed, and its potential applications in the study of coupled chemical reactions in electrochemistry are discussed. Disproportionation and dimerization mechnisms are considered. Wroking curves have been calculated with the use of the finite difference digital simulation method. It is shown that better resolution for disproportionation and dimerization reactions can be obtained with cyclic chronocoulometry than with double-potential-step chronocoulemetry. The method has been experimentally verified measuring the disproportionation reaction U(V) in 1 mol dm^?3 sodium hydrogen carbonate solutions. A rate coefficient of 15.6 dm³ mol^?1 was calculated for this reaction.     

Complete 1H and 13C NMR spectral assignment of cis- and trans- 3-(2-[2-(4-methylphenyl)ethenyl]phenyl])sydnones

1H and 13C NMR spectra of cis- and trans-3-(2-[2-(4-methylphenyl)ethenyl]phenyl])sydnones, the first stilbene-substituted mezoionic oxadiazolium rings, were fully assigned combining the information in various solvents, such as deuterated benzene, acetone and chloroform, using 2D NMR techniques.     

Atomic walk counts of negative order

Atomic walk counts (awc's) of order k (k > or = 1) are the number of all possible walks of length k which start at a specified vertex (atom) i and end at any vertex j separated by m (0 < or = m < or = k) edges from vertex i. The sum of atomic walk counts of order k is the molecular walk count (mwc) of order k. The concept of atomic and molecular walk counts was extended to zero and negative orders by using a backward algorithm based on the usual procedure used to obtain the values of mwc's. The procedure can also be used in cases in which the adjacency matrix A related to the actual structure is singular and therefore A(-1) does not exist. awc's and mwc's of negative order may assume noninteger and even negative values. If matrix A is singular, atomic walk counts of zero order may not be equal to one.     

Corrosion of Cu-xZn alloys in slightly alkaline chloride solutions studied by stripping voltammetry and microanalysis

The mechanism of corrosion of Cu-xZn alloys (x = 10-40 wt %) in slightly alkaline chloride solutions was investigated by analysing solid reaction products by energy dispersive X-ray analysis (EDS) and dissolved reaction products by differential anodic pulse stripping (DAPS) voltammetry. The corrosion process was studied under open circuit and under potentiostatic conditions at selected potentials. Pure metals were studied comparatively so that an interacting effect of particular metal components in the alloy could be determined. All four Cu-xZn alloys show an improved behaviour compared to pure metals. Under open-circuit condition both components dissolve simultaneously in the solution. With increasing immersion time the preferential, dissolution of zinc in the solution becomes pronounced. It is the highest for Cu-10Zn and the lowest for Cu-30Zn alloy. Under potentiostatic control the dissolution mechanism depends on the electrode potential and changes from exclusive dissolution of zinc to simultaneous dissolution of both components with preferential dissolution of zinc. The latter decreases, as the electrode potential becomes more positive.     

The kinetics of water desorption from porous glasses

The kinetics of water desorption from porous glasses silica gel and porous aluminosilicates were followed through the TG and DTG methods. In all cases only one thermodesorption peak appeared. The kinetic parameters were determined by standard nonisothermal methods. The activation energy is constant and independent of the coverage degree and pore diameter in the system porous glass-water. The functionE(θ) were determined for the silica gel and porous aluminosilicatesE=E ₀+a exp (-bθ). The parametersE ₀,a andb depend on the SiO₂/Al₂O₃ ratio and on the distribution of active centers on the surface.     

Determination of pefloxacin in serum and pharmaceutical forms by derivative spectrophotometry

A method for the direct determination of pefloxacin in serum and pharmaceutical forms (tablets and ampoules) has been developed, based on the use of second-order derivative ultraviolet spectra. Spectrophotometric assay of pefloxacin in tablets and ampoules was carried out in 0.1 mol/L NaOH, while in serum it was performed in 0.1 mol/L NaOH with the addition of sodium dodecylsulfate, in 337–347 nm wavelength range. Linear calibration curves were obtained in the concentration ranges 2–30g/mL pefloxacin for tablets and ampoules and 0.12–5 g/ mL for serum samples. Relative error of determination, as criterion for accuracy, was less than 1%, while the precision was better than 4 ng/ml. The minimum detectable concentration of pefloxacin in serum was 15 ng/mL.     

Kinetics of the alizarine red S surface redox reaction

Kinetics of the surface redox reaction of alizarine red S adsorbed on mercury is measured by square-wave voltammetry. In 1 mol/l KNO₃ buffered to pH 9.22, the standard reaction rate constant of the redox couple anthraquinone/anthrahydroquinone in the adsorbed alizarine red S molecule is k_s=100 ±10 s^-1 and the cathodic transfer coefficient is =0.4. At pH 2 in this medium k_s is greater than 500 s^-1.     

Parametric analysis of the inductively coupled plasma

A systematic parametric study of an LTE (local thermodynamic equilibrium) mathematical model of pure inductively coupled argon plasma (ICAP) used for spectrochemical purposes was performed by means of computer simulations. The spatial distributions of temperature, gas velocity, magnetic field and energy losses were investigated under typical plasma operating conditions as function of the ICAP geometrical dimensions and dynamic parameters. These theoretical calculations can be used to predict the properties of the applied plasma in the course of practical work, to choose the optimal conditions by changing the operating parameters and to interpret existing analytical results.