The Usefulness of Infrared Microspectroscopy for IR Spectroscopic Measurements of Solid Proteins

Abstract

IR spectroscopic measurements of solid proteins are very important because their IR data mediate between x-ray crystallographic data and IR spectra of the proteins in aqueous solutions. Thus far, the solid film method, the diffuse reflectance (DR) method, and the KBr disc method have usually been employed for the IR measurements of solid proteins. However, these three methods have their respective disadvantages. The solid film method is a very reliable method in terms of the protection of protein samples, but a fairly large amount of sample (~0.1 mg) is needed for this approach. The DR method, which is probably the most often used, suffers from two problems. One is the occurrence of effect from the mixture with KBr (or KCl) powder and the other is interference by regular reflection. The KBr disc method requires a fairly large amount of sample (~0.1mg) and may cause the proteins to be denatured because of the effects of mixing with KBr powder and adding high pressure.