Discovery of aggregative chirality of surfactants

Abstract

166 Although both surface activity and optical activity follow from the molecular structure of matter, they reflect different aspects of the structure and need not be related to each other. Surface activity requires the presence of hydrophilic and hydrophobic parts in a molecule. If these parts are particularly pronounced, which is characteristic of colloidal surfactants, then, with increasing concentration, aggregation processes occur in solution, which finally lead to micelle forma� tion (at a temperature above the Kraft point). Optical activity requires the absence of either a center or plane of symmetry. A chiral substance consisting of such molecules rotates the light polarization plane by angle α (optical rotation) according to the Biot law where l is the length of the transmitted sample, с is the concentration (or, for individual substances, density) of the optically active substance, and [α] is a propor� tionality constant (specific rotation)—a tabulated characteristic of optical activity of the substance. The quantity [α] is usually measured, like α, in degrees, which is inconsistent with the dimension of [α]. In this case, it is meant that the length l is measured in milli� meters for solids and in decimeters for solutions (in accordance with the optical cell sizes) and the con� centration is measured in grams per 100 mL (if the number of moles of substance is used instead of grams, then the specific rotation is replaced by molar rota� tion). Most probably, such contrivances were aimed at always dealing with rotation angles within 360°; however, they were in vain because chiral substances with specific rotation 400° and more are already known.