Water in a Biomembrane by Infrared Spectrometry

This article is the first one of a series aimed at determining the numerous interaction configurations adopted by H2O molecules in macromolecular systems, using infrared spectrometry. These configurations are important for understanding the role of water in such systems, particularly biosystems. This article concerns H2O molecules at low concentration in an isolated plant cuticle. The analysis of quantitative variations of the entire spectrum due to modifications of chosen parameters such as stage of growth, humidity of the surrounding atmosphere, and temperature shows that two types of interaction configurations exist for H2O molecules hydrogen bonded to surrounding molecules: There are "volatile" molecules held by one hydrogen bond they formed with receptor sites of the cuticle and "embedded" molecules held by two stronger or three hydrogen bonds which are part of the hydrogen bond network of the cuticle. Embedded molecules do not evaporate, even at 100 °C. We emphasize the conditions which should be fulfilled in order to extend such a method to other macromolecular systems.