Journal of the Iranian Chemical Society
Volume:1 Issue: 2, Dec 2004

In this review the characteristics of the prosthetic group and the role of copper in amine oxidase purified from lentil seedlings are compared with the corresponding features of the amine oxidase isolated from bovine serum. Although both enzymes contain the same organic cofactor, the 6-hydroxydopa (2,4,5-trihydroxyphenethylamine) quinone, the catalytic cycle of lentil seedling amine oxidase operates through a Cu(I)-free-radical intermediate of the cofactor, whereas in bovine serum enzyme the radical form was not observed. The role of the metal in the catalytic mechanism of the two enzymes is also discussed. Moreover, the energetic domains and the effect of the temperature on activity, for both enzymes, are examined using differential scanning calorimetry.

A method is suggested to determine valid and authentic values of thermodynamic stability parameters of proteins from their heat-induced conformational transition curves. We show (a) that the estimate of ΔHmvan, the enthalpy change on denaturation at Tm, the midpoint of denaturation, is significantly less than ΔHmcal, the value obtained by the calorimetric measurements, if the analysis of the conformational transition curve uses the conventional method which assumes a linear temperature-dependence of the pre- and post-transition baselines; and (b) that there exists an excellent agreement between ΔHmvan and ΔHmcal values of proteins, if the analysis of thermal denaturation curves assumes that the temperature-dependence of pre- and post-transition baselines is described by a parabolic function. The latter analysis is supported by our observations that the temperature-dependencies of the absorption and circular dichroism properties of protein groups are indeed nonlinear. It is observed that the estimate of ΔCp, the constant-pressure heat capacity change is independent of the model used to describe the temperature-dependence of the pre- and post-transition baselines. An important conclusion is that for proteins which exhibit a two-state character, all stability parameters are measured with the same error as that observed with a calorimeter.

Three simple, selective and cost-effective procedures for the determination of captopril in bulk drug and in tablets are described. All the procedures make use of silver nitrate as a reagent and involve titrimetry and spectrophotometry as measurement techniques. In titrimetry (Method A), the aqueous solution of the drug is titrated directly with the standard silver nitrate solution to a potassium chromate end-point. In one spectrophotometric method (Method B), the sample solution is treated with excess of silver nitrate and a known amount of methyl orange and the increase in absorbance at 520 nm, caused by a decrease in pH due to release of nitric acid, is measured and related to drug concentration. The other spectrophotometric method (Method C) involves the addition of a measured excess of silver nitrate to the sample solution followed by the determination of residual silver ion by an ion-associate complex formation reaction involving eosin and 1,10-phenanthroline. The decrease in absorbance at 550 nm, which corresponds to Ag+ reacted with the drug, is measured and is found to be linearly related to drug concentration. All experimental variables involved in the methods were investigated and optimized. Stoichiometry of the reaction that forms the basis for titrimetry is found. Method A is applicable in the range of 1.0-20.0 mg of drug while methods B and C can be conveniently used in the concentration ranges of 2.5-50.0 and 0.25-4.0 µg ml-1, respectively. Several optical characteristics such as molar absorptivity, Sandell sensitivity, limits of detection and quantification, and correlation coefficient were calculated. The methods were applied to the analysis of tablets containing captopril. Statistical treatment of the results indicates that the procedures are precise and accurate. The excipients used as additives in tablets did not interfere in the proposed procedures as revealed by the recovery studies.

The kinetics of substitution of chloride ion in trans-dichlorobis(ethylenediamine) cobalt(III) cation by five organic bases (diethylamine, triethylamine, benzylamine, t-butylamine and n-propylamine) in dimethylacetamide (DMA) at ionic strength of 0.80 M NaClO4 is reported. The activation parameters for the second-order path lie on a good isokinetic line. The linear plots of kobs vs. [B], the large negative values of ΔS2‡ and the span of k2 values signify an associative mechanism.

In order to gain an insight into the mechanism of reduction of Mn(III) heteropoly ions, and also to establish the conditions for use of some of these ions as oxidizing agent, following measurements have been made. The pseudo-first order rate constants, kobs, have been determined and specific rate constants, k, were calculated from the plots of kobs against SO32- concentrations. A plot of ln(k2/T) against inverse temperature gives enthalpy of activation as 10.67 kJ mol-1 and entropy of activation as -237.90 J K-1 mol-1. Effects of ionic strength and pH have also been studied over a limited range.

Cyclic voltammetry and potentiometry were used to investigate the electrochemical behavior of cysteine at a chemically modified electrode prepared by incorporating cobalt(II) phthalocyanine [Co(II)Pc] into carbon paste matrix. The modified electrode showed high electrocatalytic activity toward cysteine; the overpotential for the oxidation of cysteine was decreased by more than 100 mV, and the corresponding peak current increased significantly. The electrocatalytic process was highly dependent on the pH of the supporting electrolyte. The peak currents decreased when the pH was raised to 6 and totally disappeared at pH≥ 7, resulting from the autocatalytic oxidation of cysteine by Co(II)Pc at the electrode surface. Therefore, at pH values of 6 to 8, the modified electrode was used as a potentiometric sensor for quantitative measurement of cysteine in the presence of oxygen in air saturated solutions. In fact, the Co(II)Pc/Co(I)Pc couple acts as a suitable mediator for indirect oxidation of cysteine by dissolved oxygen at approximately neutral pH values. Under the optimized conditions, the potentiometric response of the modified electrode was linear against the concentration of cysteine in the range of 0.6 µM to 2 mM. The limit of detection was found to be 0.5 µM. The potentiometric response time was £15 s. The electrode showed long term stability; the standard deviation of the slope obtained after repeated calibration during a period of two months was 2.8% (n = 7). Application of the electrode in a recovery experiment for the determination of cysteine added to a synthetic serum sample is described.

Iodine, was found to be a practical and novel catalyst for the reaction of aminal and trimethylsilyl cyanide under mild and neutral reaction condition to afford the corresponding α-aminonitriles in high yields and short reaction times. Trimethylsilyl iodide derived in situ from elemental iodine and trimethylsillyl cyanide catalyzed this conversion.

New aromatic poly(amide-imide)s with high inherent viscosities were prepared by direct polycondensation reaction of diimide-diacid (I) and aromatic diamines using triphenyl phosphite in N-methyl-2-pyrrolidone (NMP)/pyridine solution containing dissolved CaCl2. The bis(3-trimellitimidophenyl) phenyl phosphine oxide (I) was readily obtained by the condensation reaction of bis(3-aminophenyl) phenyl phosphine oxide (BAPPO) with trimellitic anhydride. The resulting poly(amide-imide)s showed high thermostability. Their decomposition temperatures at 10% weight loss in nitrogen atmosphere were above 532 ºC and the anaerobic char yield at 800 ºC ranged from 56% to 74%. Almost all the poly(amide-imide)s showed high glass transition temperature above 233 ºC by differential scanning calorimetry (DSC) measurements. These polymers were readily soluble in various organic solvents and by their casting into transparent, tough and flexible films can be easily achieved.

The adsorption of Triton X-100 in aqueous solution on the granite sand has been investigated to evaluate its ability as an adsorbent. Various parameters such as agitation time, adsorbent dose, adsorbent size, initial concentration of adsorbate, pH, temperature, and effect of interference ions were studied on the laboratory scale to establish optimum conditions for the removal of TX-100 from the effluents of different industries. Isotherm data were analyzed for possible agreement with the Langmuir and Frendlich adsorption isotherm equations. The first order rate equation by Lagergren was tested on the kinetic data. The rate of adsorption was conformed a pseudo first order kinetics with good correlation coefficient. The value of activation energy of sorption (Ea) was obtained as 44.6 kJ mol-1. Results showed that granite sand exhibit reasonably good surfactant removals for non-ionic types. The possible role of the adsorbent in a chromatographic column was also worked out.

Wet silica-supported potassium permanganate was used as an inexpensive and efficient reagent for conversion of α-sulfinyl oximes 1 and α-sulfinyl hydrazones 2 to the corresponding α-keto sulfoxides (3) in high yields and high enantiomeric purity under solvent-free conditions.