The Formation of Carbonyl Groups during Irradiation of Wool and Its Relevance to Photoyellowing

Abstract

The carbonyl contents of wool fabrics have been determined by colorimetric analysis after partial acid hydrolysis. Irradiation of dry wool fabrics with simulated sunlight causes an increase in carbonyl content. The rate of production is approximately the same for unbleached, bleached, and fluorescently whitened fabrics, even though these fabrics yellow at markedly different rates. In contrast, irradiation of the same fabrics in water results in few additional carbonyl groups, although extensive yellowing occurs. Thus it seems unlikely that carbonyl groups are directly responsible for yellowing. However, the observation that hydrothermal yellowing of dry-irradiated wool is accompanied by a loss in carbonyl content leads us to suggest that carbonyl groups could be involved indirectly in yellowing. The keto acids present in partial acid hydrolysates of irradiated wool have been identified by reductive amination with sodium 3H-borohydride in ammonia solution, a reaction which converts keto acids to the corresponding 3H-amino acids. The formation of radiolabeled alanine, glycine, proline, serine, threonine, glutamic acid, and tyrosine provides evidence for the photo-oxidation of a number of amino acid residues during irradiation of wool.