KINETIC STUDIES OF THE REACTION OF FORMALDEHYDE WITH PLASMA ALBUMIN IN WATER AND ETHANOL - WATER MIXTURES
KINETIC STUDIES OF THE REACTION OF FORMALDEHYDE WITH PLASMA ALBUMIN IN WATER AND ETHANOL - WATER MIXTURES
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Date
2015-09
Authors
UGYE, JOSEPH TORSHIAN
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Abstract
Formaldehyde is a simple member of the aldehyde family and one of the simplest organic molecules. It is known to be ubitiquious in nature in foods, domestic air, cigarette smoke etc and has been found to be toxic over certain doses. The chances of harmful effects are reported to increase under room temperature because of its volatility and have also been reported as occupational and environmental toxicant. In spite of these claims, there is paucity of knowledge of the reaction kinetics and mechanisms of this organic molecule with carrier proteins, common non-foods and food materials in the literature. In this study an investigation of formaldehyde levels in some selected foods, non-foods, cosmetics, human milk and urine samples based on spectrophotometric method of Hantzsch by formation of a derivative for separation was carried out using acetylacetone and acetoacetanilide reagents. A 3,5-diaphenyl-1,4-dihydropyridine adduct was also prepared from acetoacetanilide, formaldehyde and plasma albumin and was characterized by measuring its melting point, IR analysis, Uv spectra as well as the antimicrobial activity. The stoichiometry and the kinetic measurements were carried out at constant conditions with the concentrations of the formaldehyde in excess of 0.27 x10-1 mol dm-3 while that of plasma albumin was kept constant at 0.51 x10-4 mol dm-3. The effect of dielectric constant, added ions , pH and ionic strength and acidity constant (pKa) on the rate of reaction were all monitored by varying their concentrations while keeping the concentration of the aqueous formaldehyde and all the other conditions constant The kinetic of the reaction of plasma albumin with formaldehyde in water and ethanol-water mixtures was also investigated using bronsted-type plot model. Both the acetylacetone and acetoacetanilide reagents methods found formaldehyde levels in the studied samples at a non significant amount with a (p > 0.0001) at 95% degree of confidence. Also the
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prepared 3,5-diaphenyl-1, 4-dihydropyridine adduct was found to have a melting temperature range of 179.5 - 180.4o indicating that it was a labile schiff base and a protein with glycol protein (lectin) properties. The stoichiometric data showed a mole ratio of 1:2 for formaldehyde to plasma albumin and the reaction was found to be pseudo-first order with respect to formaldehyde and overall second order at constant conditions in both systems. The rate of the reaction in water medium and ethanol water-mixtures was found to increase with increased pH, ionic strength and the added ions. The results of the activation parameters in water and ethanol-water mixtures showed a large negative entropy, small positive values of activation energy, negative values of enthalpies of reaction and a small positive Gibbs free energies. This shows that the reaction was not spontaneous and thermodynamically hindered or unfavourable but can take place by a collision or activated complex mechanism. The values of rate constants of the reaction between plasma albumin and formaldehyde were found to decrease with the increase in the concentration of ethanol and the reaction. The corresponding values of the Brønsted-type plots proportionality constants (β) for the reaction in water solution and ethanol-water mixtures were found to be β = 0.059 and 0.0021 respectively. The second order rate constant values of 0.099 (±0.034) dm3 mol-1 s-1 in water and 0.06 (±0.028) dm3 mol-1s-1 ethanol-water mixtures respectively were obtained. Also appropriate mechanistic proposals were made for the reaction in water and ethanol-water systems. The proposals showed that one mole of formaldehyde binds two moles of plasma albumin forming Schiff bases slowly and reaction was found to operate by binding/ associative mechanism
Description
A THESIS SUBMITTED TO THE SCHOOLOF POSTGRADUATE STUDIES, AHMADU BELLO UNIVERSITY, ZARIA, NIGERIA IN PARTIAL FULFILLMENT FOR THE AWARD OF DOCTOR OF PHILOSOPHY IN CHEMISTRY DEPARTMENT OF CHEMISTRY, AHMADU BELLO UNIVERSITY, ZARIA, NIGERIA
Keywords
KINETIC STUDIES,, REACTION,, FORMALDEHYDE,, PLASMA ALBUMIN,, WATER,, ETHANOL - WATER MIXTURES,