Molecular association of K-vitamins with biologically occurring molecules. Part 1. A study of the association properties of the quinone moiety

Abstract

The p-benzoquinone (pBQ) moiety is known to be involved in many biochemical processes and since this moiety occurs in the structure of the K-vitamins, it was felt necessary to study the molecular association of the pBQ moiety. This paper deals with the stability constants and the nature of the binding in some molecular associations of pBQ with carboxylate ions in an aqueous medium and of 1,4-naphthaquinone with resorcinol in dioxane. We observed that pBQ in water is strongly hydrated and that carboxylate ions slowly displace the water molecules in the hydration sphere and bind to pBQ in a 1 : 1 stoichiometry. The n–π* band of pBQ in water is shown to be blue-shifted (from the Franck–Condon principle) when a pBQ–carboxylate association is formed. 1,4-Naphthaquinone, which is sparingly soluble in water (like the K-vitamins) forms a 1 : 1 π–CT complex with resorcinol in a dioxane medium. The stoichiometries have been determined spectrophotometrically using the Benesi–Hildebrand equation and Job's continuous variation method. The formation constants of the ion–molecule and molecule–molecule associations are reported.