The structure of surface films. Part XIII.—Sterols and their derivatives

Abstract

In this paper the results of the examination of mono-molecular surface films of numerous sterols, and of compounds simply related to them, are reported. The work is a continuation of Part XII of this series of papers, and was undertaken in the first place to provide results on a number of derivatives of sterols, whose constitution is known in its main features, for comparison with those obtained on surface films of various irradiation products of ergosterol. The results on irradiated ergosterol will be given in a separate paper. The results of this paper are of considerable interest, as showing how different substituents in the complex ring system of cholesterol affect the behaviour of the molecules on water surfaces. It has appeared that a very great, and unexpected, variety exists in the character of the surface films, although nearly all the substances studied have practically the same ring system; that is, the bulk of the molecules is the same in all cases. A change in the position of a substituent group may make a profound alteration in the compressibility of the films and their area; this is perhaps not surprising, as the water-soluble groups in the molecule will naturally be directed downwards, being anchored to the water, and the position of these will affect the tilt of the molecules and consequently their mode of packing. It is more surprising that quite a small change in the nature of one group only, such as the transformation of CHOH into CO, without change of position of the group, may also have a great effect on the structure of the film.