This book aims to provide an insight into some of the key areas where infrared spectroscopy has been successfully applied to understand important biological and biomedical processes. It highlights the latest advances and the directions for the future. The book provides a historical framework for the development of biological infrared spectroscopy. Key methodologies that are in current use and latest advances, in both theoretical and practical aspects, are discussed. Examples of applications, ranging from characterisation of individual macromolecules (DNA, RNA, lipids, proteins) to complex systems such as human tissues, cells and whole organisms are covered. The main focus is in the mid-infrared region as the vast majority of studies are conducted in this region. However, there is increasing use of the near-infrared region for biomedical application and hence a chapter is devoted to this part of the infrared spectrum.

Biological spectroscopy is a highly interdisciplinary field of research requiring involvement of life scientists and analytical chemists. Advances in instrumentation technology and methods for analysis and interpretation of the spectroscopic data require input from multiple disciplines including Chemistry, Physics, Mathematics, Computer Science and Engineering. It is this cooperation between scientists from diverse disciplines that ultimately results in the utilisation of a physical technique for understanding the molecular details of biological processes and systems. Such cooperation is vital if spectroscopists are to play a significant role in the analysis of the vast number of genes and proteins that are being identified by the various genome sequencing projects. Currently, it is not impossible for a gene sequencing laboratory to produce as much data in less than a week as was produced by Shakespeare in his entire life-time. However, an understanding of the molecular details of the genes and proteins identified, and their diverse interactions, require application of biophysical techniques such as infrared spectroscopy. Continued technological development in spectroscopic methods is vital to keep pace with the breathtaking advances in the field of molecular biology.

Nearly 400 years ago Shakespeare described the “seven ages” of life in the following manner:

“All the world's a stage, And all the men and women merely players: They have their exits and their entrances; And one man in his time plays many parts, His acts being seven ages.”

Using this as an analogy, Laitinen in 1973 wrote an editorial in Analytical Chemistry describing the seven ages of an analytical method (H.A. Laitinen, Anal. Chem. 45 (1973) 2305). He used infrared spectroscopy as an example to illustrate how it has reached its “seventh age”. His description of this “seventh age” is as follows:

“Seventh, a period of senescence occurs as other methods of greater speed, economy, convenience, sensitivity, selectivity, etc., surpass the method under consideration.”

It is surprising that Laitinen chose infrared spectroscopy as his example, since at that time the first commercial Fourier transform infrared spectrometers were being delivered to laboratories around the world. As such it was a very exciting time for infrared spectroscopy. Indeed, a year earlier, in 1972, Peter Griffiths published a letter in the same journal entitled “Trading rules” in infrared Fourier transform spectroscopy" (P.R. Griffiths, Anal. Chem., 44 (1972), 1909). As an editor of the journal, Laitinen must have been aware of the revolution taking place in infrared spectroscopy. The widespread availability of FT instruments and the use of computers for recording and analysis of infrared spectra, heralded a new era in infrared spectroscopy. Now it was possible to analyse biological molecules, in aqueous media, at fast speeds and at high resolutions that was virtually impossible with dispersive instruments.

Far from reaching its “seventh age” infrared spectroscopy is a vibrant methodology playing a central role in some of the latest discoveries in biology and medicine, including some recent Nobel Prize winning work. For example, Stanley Prusiner was awarded the Nobel Prize for Physiology or Medicine in 1997 and infrared spectroscopy played an important role in his work. In a section of his Nobel lecture (S.B. Prusiner, Proc. Natl. Acad. Sci. USA, 95 (1998), 13363-13383) he states the following:

“For more than 25 years, it had been widely accepted that the amino acid sequence specifies one biologically active conformation of a protein…. Yet in scrapie we were faced with the possibility that one primary structure for PrP might adopt at least two different conformations to explain the existence of both PrPC and PrPSc. When the secondary structures of the PrP isoforms were compared by optical spectroscopy, they were found to be markedly different…. Fourier-transform infrared (FTIR) and circular dichroism (CD) studies showed that PrPC contains about 40% α-helix and little β-sheet, whereas PrPSc is composed of about 30% α-helix and 45% β-sheet…). Nevertheless, these two proteins have the same amino acid sequence!”

It is noteworthy that the abnormal form of the prion protein (PrPSc) misfolds and forms aggregates that are virtually impossible for characterisation using X-ray crystallography, NMR and CD spectroscopy. In order to overcome this problem, Prusiner and coworkers used infrared spectroscopy to obtain direct evidence for an increase in betasheet structure in the PrPSc aggregates.

In recent years infrared spectroscopy is going through a renaissance catalysed by some exciting developments in technology. This includes the use of the bright synchrotron radiation for recording infrared spectra. Latest breakthroughs also include the development of two-dimensional infrared spectroscopy and the ability to record infrared spectra at ultrafast speeds. There are also some major advances in theoretical analysis that is enabling a better interpretation of the infrared spectra of biological molecules. Considering these advances, we felt it would be timely to produce a book that brings together some of the key developments in the field. The book is intended for both experts and those who are new to the field of biological infrared spectroscopy. It would be particularly beneficial for graduate students and research scientists in both industry and academia.

Finally, we would like to thank all the authors who have contributed in this volume. Without their cooperation it would not have been possible to accomplish this task.

Andreas Barth (Stockholm University, Stockholm, Sweden), Parvez I. Haris (De Montfort University, Leicester, UK)