Reaction of glutaraldehyde with amino and thiol compounds

Abstract

Stoichiometry, pH dependence, and reversibility of the reaction of glutaraldehyde with various amino and thiol compounds were investigated to elucidate the chemical nature of glutaraldehyde. For glutaraldehyde, three commercial samples were examined. They have different spectral characteristics probably due to the difference in the content of α, β-unsaturated aldehyde polymers formed by aldol condensations of glutaraldehyde, but the amount of such unsaturated structures is very small, and the chemical reactivity of these samples are almost the same. Therefore, the chemical reactivity characteristic of glutaraldehyde is not due to the α, β-unsaturated aldehydes. Glutaraldehyde reacts with the amino group in a wide pH range ( ≧ pH 3 ). The reactions at pH 7 and 9 are almost irreversible, though a little reversibility is observed. The reaction rate becomes very slow after the initial rapid phase. The average molar ratio of the amino and aldehyde groups consumed during the reaction of glutaraldehyde with the amino group is in a range of 0.3-0.2. Glutaraldehyde reacts with cysteine with a stoichiometric relationship of one mol of the thiol and amino groups of cysteine per mol of glutaraldehyde. Glutaraldehyde does not react with the thiol group without the presence of the primary amino group; the average stoichiometric relationship is 0.5–0.6 mol of the thiol group, about 0.4 mol of the amino group, and 1 mol of glutaraldehyde, under the conditions of excess in the thiol and amino groups. These results indicate the complex nature of the glutaraldehyde reaction.