Biological Applications of IR Spectroscopy

These infrared spectral data of representative biological samples are underlying to the figures in chapter 17 of Encyclopedia of Spectroscopy and Spectrometry, 2nd edition, Vol 1. Oxford: Elsevier; 2010. pp. 142–152 (John Lindon, George Tranter and David Koppenaal, editors) # All biological processes occur in an aqueous environment. The strong absorption by water can be reduced by performing measurements in deuterium oxide or by using attenuated total reflection (ATR) IR spectroscopy. The spectra in the introduction folder demonstrate the effect on the spectra when applying these techniques. # Biological samples mainly consist of proteins, lipids and carbohydrates. The spectra in the folder microbiological focus on the distinct peaks that can be observed for proteins (bacteriophage Pf1). lipids (dipalmitoyl phosphatidyl choline) and carbohydrates (glucose) # Cell membranes mostly consist of phospholipid bilayers, providing a selective barrier between the cytoplasm and the environment. Fluidity of the membrane is determined by the lipid composition in terms of headgroup, length of the acyl chains and degree of unsaturation. A higher fluidity is associated with a lower gel to liquid crystalline transition temperature. The data in the botanical folder contain methylene stretching band position versus temperature for typical phospholipids with different composition. The transition temperature is found halfway on the S-shaped curve # In order to demonstrate the sensitivity of infrared vibrational bands towards molecular structure, the biomedical directory shows that selected point mutations in a protein result in small but relevant changes in the amide I and amide II region of a protein infrared spectrum, as visible in a small set of mutants of the muscle fatty acid binding protein. It is quite difficult to detect selected proteins in complex samples such as complete cell suspensions. Chemically labeling a protein with stable isotopes such as carbon-13, nitrogen-15 or oxygen-18. result in selective band shifts for molecular fragments, containing those atoms. This effect is illustrated in infrared spectra of a Spodoptera frugiperda cell line, with and without nitrogen-15 label. ATR IR spectroscopy is a convenient technique for in situ biotechnological process monitoring. It can differentiate whole milk, semi-skimmed milk and soy light drink without any special sample preparation.