Interfacial tension and hydrogen-ion concentration

Abstract

The object of this communication is to extend our knowledge of the relation between the interfacial tension of long chain carbon compounds dissolved in benzene and the hydrogen-ion concentration of the aqueous phase with which they may be placed in contact. To this extent, it forms an extension of earlier work by Hartridge and Peters. The stimulus of the work was in large part the desire to throw light upon the question of ionisable interfaces in the living cell. Historical . It is well known in a general way that the Hydrion concentration (C H ) of the aqueous phase influences the interfacial tension between solutions of a fatty substance dissolved in a lipoid solvent and an aqueous solution, and that the fall in interfacial tension which takes place with increasing alkalinity is produced by the presence of soap. The first experimental indication that there was a direct relation between (C H ) and the interfacial tension (I. T.) of such a system appears to have been given by Reinders. This relation, highly significant so far as biochemical processes are concerned, seems to have attracted little attention. Though it is mentioned by Freundlich, interest has been concerned in the main with emulsification. In 1920-22, Hartridge and Peters found a direct relation between p H and interfacial tension in the system olive oil in benzene-aqueous buffered solution. A fall in I. T. commenced to the alkaline side of p H 4.5, which started rather abruptly and appeared to pursue an almost straight line to p H 9•0, the degree of fall being independent of the buffer used. The drop weight method was used for most of the experiments, but was checked against a ripple method. In accordance with expectation, with a series of pure substances, the only ones showing a change of I. T. were those containing a —COOH group, but a change also appeared with —COOH combined in a triglyceride. The relation was not quite simple, because the strength of the buffer solution influenced the results. Below a certain concentration of phosphate for instance, 0•005 M. in the case of a buffered solution of p H 7.6, no lowering of I. T. took place. In explanation it was suggested that the effects only appeared when sufficient alkali was present to form alkali salts of the fatty acids at the interface.