S Ynchrotron Infrared Spectroscopy in B Iology and B Iochemi Stry

Introduction The absorption of near infrared light by materials provides information about the chemistry and structure of those materials by probing their molecular vibrations. The infrared spectra of biological macromolecules have distinct absorbances that allow Fourier Transform InfraRed (FTIR) spectroscopy to monitor macromolecular changes. FTIR can be carried out in aqueous solution, organic solvents, thin films, deposits, flow cells and membrane environments using μg quantities. Moreover, protein secondary structure can be determined, individual bonds in an enzyme can be monitored and processed on time scales of μs or a few ns with rapid scanor step scan-based instruments. Lipid polymorph structure and lipid phase transitions can be studied along with the physical states and conformational transitions of nucleic acids. Carbohydrates and glyco-conjugates and the interactions between these molecules and proteins or lipids can also be monitored. Membranes can be studied as model systems, as isolated membranes, in cells or as subcellular fractions. The macromolecular structure and composition of tissue, whole cells and bacteria can be used to follow disease. Until the 1980s, infrared spectroscopy was generally carried out using dispersive instruments and the time taken to record spectra of adequate sensitivity precluded easy investigation of biological systems. With the advent of fast computing, the Fast Fourier Transform, new detectors and the earlier development of the helium/neon laser for calibration, commercial FTIR spectroscopy became available. With a sensitivity some three orders of magnitude greater than dispersive instruments, FTIR rapidly became the instrument of choice. This increased sensitivity led to an upsurge in techniques that were previously marginal. The techniques that arose with particular relevance to biological and biochemical systems include reflectance methods, attenuated total (internal) reflectance (ATR), microscopy, difference spectroscopy, time-resolved spectroscopy and surface-based techniques. For a recent review of the techniques involved and their detailed applications see the Handbook of Vibrational Spectroscopy (1).