Observing the water molecule in macromolecules and aqueous media using infrared spectrometry

The H2O molecule is a molecule which takes on crucial importance when it is embedded in macromolecules. It is, however, difficult to observe and to determine the interactions it establishes with hydrophylic groups of macromolecules. It has consequently for long been ignored. IR spectroscopy, the most powerful tool to look at hydrogen bonds, has up to recently been disregarded to look at these molecules. After explaining the reasons of this situation, we describe the two set-ups which have recently been proposed to overcome the corresponding difficulties: ATR and absorption of a thin macromolecular film in a controlled atmosphere. We more particularly describe the material and procedures used with this last set-up which allows to precisely determine hydration mechanisms of macromolecules and the hydrogen-bond configurations that H2O molecules adopt when they are embedded in these macromolecules. In the conclusion we indicate how IR spectrometry appears a potentially precious tool to precise the fundamental role we suspect these water molecules play in the reactivity of aqueous media, particularly bio-media. (C) 2003 Elsevier Science B.V. All rights reserved.