V. Carunchio

Using thermoanalytical data: Part 1. The power of kinetic parameters determined from thermogravimetry to describe the experimental behaviour of the sample

Abstract Sources of misunderstandings when evaluating kinetic parameters from thermogravimetric (TG) curves are discussed. A simple method for calculating Arrhenius parameters, suitable for implementation on a PC connected to the TG apparatus, is presented. The results obtained with calcium oxalate are discussed with respect to their ability to predict thermal behaviour in several experimental conditions: agreement with experimental data is satisfactory. This is not so when using some literature-cited kinetic parameters, which fail to represent the same TG curves from which they are extracted. Suggestions are derived for design of a modern TG apparatus connected to a PC.

Determination of the urease activity and the relative inhibition in the presence of some metal ions: a microcalorimetric study

Abstract Batch microcalorimetry has been employed to obtain a calibration curve for the enzymatic activity of urease in solution. This method is simplier, more reliable and easier to handle than the more common techniques (spectrophotometry and potentiometry), because it is based on direct investigation of the enzymatic reaction. By comparison with calorimetric studies employing the thermistor combined with the immobilized, enzyme, this method also allows the catalytic activity to be measured. Variations in the urease activity in the presence of nine metal ions [Hg(II), Ag(I), Cu(II),Zn(II), Cd(II), Ni(II), Co(II), Mn(II) and Mg(II)] are also described. A graphic method has been devised for immediate identification of the minimum inhibitor concentration,determining the start, 50% and complete inhibition of ureasic activity.

Complex formation equilibria of some β-amino-alcohols with lead(II) and cadmium(II) in aqueous solution

A study of complex formation equilibria of some beta-amino-alcohols with lead(II) and cadmium(II) ions at 25 degrees C and in 0.5 M KNO(3) is reported. The amino-alcohols considered are 2-amino-1-propanol, 2-amino-1-butanol, 2-amino-1-pentanol and 2-amino-1,3-propanediol. sec-Buthylamine and 2-amino-1-methoxy-propane have been also considered for comparison. The results are discussed in terms of ligand structure, paying attention to the number of hydroxyl groups and to the length of the alkyl residual. A weak contribution of the alcoholic oxygen in the coordination of cadmium(II) and the presence of a mixed hydroxyl species in lead(II) containing systems are hypothesized.

Solvent effects on the formation equilibria of cobalt(II)-chloride system in acetone-water mixture

The data about cobalt(II) - chloride complexes in acetone solution have been completed by recent spectrophotometric methods (K3=4.5 107; K4=6.1 102). Furthermore, the influence of water addition on the system has been pointed out by considering the dielectric and donor properties of the solvent mixture. The results show a linear correlation of the complex species distribution with the reciprocal dielectric constant of the simple binary system, so that a possible explanation of the present data and of those of some oher authors has been discussed in terms of DEC influence on dissociation reactions. Donor number equality for water and acetone has made it possible to minimize the solvent influence on the ionization processes when varying water-acetone ratio.

Chitosan-coated silica gel as a new support in high-performance liquid chromatography

SummaryA new stationary phase was prepared by immobilizing the chitosan, a natural hydrophilic polymer, on microparticolate silica gel. The effect of the polarity, pH and ionic strength of the mobile phase has been studied in order to find optimal conditions for the separation of nucleotides and aminoacids. The influence of the properties of the mobile phase on the retention was examined, allowing to employ the chitosan-coated silica gel both to anion exchange and adsorption, depending on the pH and the polarity of the eluent used.

Complex formation between copper(II) and several β-amino alcohols in aqueous solution: a potentiometric and spectrophotometric study

Abstract The behaviour of solutions containing copper(II) and several β-amino alcohols was examined by potentiometric and spectrophotometric techniques. The potentiometric results at 25°C and KNO3 0.5 M, indicates in all the examined systems the formation of four main species with M:L:H stoichiometry 1:1:0, 1:1:−1, 1:2:−1 and 1:2:−2, respectively. The deprotonated species have been demonstrated to be alkoxo chelates formed by the loss of alcoholic hydrogen. No evidence of formation of ternary hydroxy or polynuclear complexes have been found in the examined experimental conditions, and the absence of dimeric alkoxo-bridged species have been confirmed by the analysis of the UV charge-transfer bands. The dependence of complex stability on the ligand structure is discussed with particular regard to the influence exherted by the number of hydroxyl groups. Also, the comparison with the behaviour of other metal ions is discussed.

A new microcalorimetric method for the determination of lipase activity and substrate concentration in aqueous medium

Abstract The lipase activity and the triglyceride concentration have been determined for the first time in a simple and direct way. The heat quantity involved in the main enzymatic hydrolysis reaction has been measured by means of batch microcalorimetry. The heat quantity measured was related linearly to the substrate concentration, and the heat change rate has been directly related to the enzymatic activity of lipase. No ancillary reactions were necessary. For the first time the lipolytic reaction has been directly studied in an aqueous medium, without organic solvents and/or emulsifying agents. The described calorimetric method has been applied to milk samples.

Determination of aspartate aminotransferase activity by high-performance liquid chromatography

A sensitive and reproducible assay of aspartate aminotransferase activity based on UV detection of the reaction products after their separation by HPLC is described. The main advantage is the direct measurement of the enzyme activity as micromoles of product (glutamate) formed within a known period of time without any coupled reaction. Further, with the chromatographic method, all components of the reaction mixture are identified, allowing the reaction course to be controlled and the possible presence of side-reactions to be monitored.

Protonation and silver(I) complex-formation equilibria of some amino-alcohols

Formation constants of the silver(I) complexes with some amino-alcohols have been determined at 25 degrees C in 0.5 M KNO(3) by means of two independent potentiometric measurements employing glass and silver electrode. The ligands considered are: sec-butylamine, 2-amino-1-propanol, 2-amino-1-methoxy-propane, 2-amino-2-methyl-1-propanol, 2-amino-1-butanol, 2-amino-1-pentanol, 2-amino-1-hexanol, 2-amino-1,3-propanediol, 2-amino-1,3-hexandiol, 2-amino-2-methyl-1,3-propanediol and Tris(hydroxymethyl)-aminomethane. Protonation constants of the selected ligands have also been determined. Calculations were made using HYPERQUAD computer program. The influence exerted by the introduction of hydroxy groups and by the presence of alkyl residuals in the ligand structure on the formation equilibria, is discussed.

High performance liquid chromatography assay for alanine amino transferase

SummaryAn improved method of alanine-amino transferase determination is proposed. The reaction is carried out with alanine and 2-oxoglutarate as substrates and analysis is by HPLC on a reversed-phase chromatographic system using a C18 column and tetrabutylammonium phosphate in phosphate buffer (pH 7.0)-acetonitrile as mobile phase. The enzyme activity was determined by directly following the formation of pyruvic acid without employing any secondary reaction, which is necessary in the spectrophotometric method. The detection limit of pyruvic acid is 10 pmole μl−1 and the standard deviation for the enzymatic activity of standard solutions is 5.4%. Furthermore under the chromatographic conditions selected it is possible to detect the presence of some intermediate species.