Open Access

Urs Peter Fringeli, Hans Heinrich Günthard

• Application of vibrational spectroscopy to the problem of structure determination of molecules of biological interest goes back to the early uses of raman and infrared spectroscopy in the study of organic molecules. For reviews of earlier work the reader is referred to compilations by Kohlrausch (1943) and by Jones and Sandorfy (1956), whereas more recently a comprehensive discussion has been presented by Bellamy (1975). These compilations accentuate the correlation of vibrational spectra with molecular structure from an essentially empirical point of view and culminate in the establishment of empirical correlation charts. For typical examples the reader is referred to Weast (1974) and Bellamy (1975). There have been many treatments of the theoretical basis of molecular vibrational spectroscopy. Among them the classical work by Herzberg (1945) and by Wilson et al. (1955) should be mentioned. Applications of infrared spectroscopy (IR) to structure problems of biological interest have been summarized by Susi (1969), Fraser and MacRae (1973), and Wallach and Winzler (1974). It was remarked quite eraly that relevant structural information about biological systems often requires study in aqueous solution, which forms the natural environment for most biologically important systems. Besides critical control of experimental conditions and samples the conventional methods of raman spectroscopy may be applied to aqueous solutions in a quite straightforward manner, cf. the contribution by Lord and Mendelson, Chapter 8. The condition of biological environment, i.e., the study in aqueous solutions, by IR spectroscopy is difficult to achieve by conventional absorption technique, since the high absorption coefficient of water in wide regions of the mid and far infrared implies use of thin layers and high concentrations. As a consequence the application of special techniques for measurement of IR spectra of biological material has been a necessity in many cases. This contribution covers the following topics: (1) specific spectroscopic techniques used in this field, in particular for membrane spectroscopy, (2) discussion of typical results derived from application of IR techniques to model and natural membrane systems and to important constituent molecules of such systems.