Measurement of protein in heavy water by FT-IR

Analyzing protein sequences consisting of 30 peptides or fewer has become very common. The number of peptide hormones that have been produced by peptide synthesis has become very large. As a result, the need to evaluate these hormones using analytical instruments has increased rapidly.
This application bulletin demonstrates FT/IR measurements of several types of protein in heavy water. It is well-known that in the IR spectrum of a protein, the characteristic vibration peaks of the principal chain appear in the range of 1700 - 1600 cm-1 (approximately 6 um) for amide I, and in the 1600 - 1500 cm-1 range (approximately 6.45 um) for amideⅡ. If IR measurement of protein is conducted in an aqueous solution, the strong absorption band of normal water occurring at 6 µm prevents meaningful date acquisition. In order to overcome this problem, it is necessary to measure the protein in heavy water. When the protein is immersed in heavy water, the sample can be measured in affixed cell of 50 - 100 µm in width. In this case, a waterproof cell window must be sued. In transmittance mode, CaF2 or BaF2 are typically used; ZnSe, which is typically employed for ATR, can be used as well. These window materials are transparent, offering the advantage of easy detection of air bubbles.