RAMAN-SPECTROSCOPIC STUDIES OF SOME BIOCHEMICALLY RELEVANT MOLECULES

Near-infrared (NIR) Raman spectra of the protein aprotinin, in both po wder form and aqueous solutions, are presented. The amide I and amide III bands give information about the secondary structure. The conforma tion around the sulphur bridges and the environment of tyrosine were a lso studied. Due to the low scattering efficiency, only aqueous soluti ons in the concentration range 2-20% (w/w) were used. Use of a windowl ess cell improved the quality of the spectra, as compared to spectra o btained with quartz cells. Fluorescence can be a serious problem in Ra man studies of biologically relevant molecules. Some examples are show n, which illustrate that the use of NIR excitation can frequently elim inate this fluorescence. Heating effects give rise to serious problems with excitation at 1064 nm in the NIR-FT-Raman spectrum of some stron gly coloured macromolecules, like haemoglobin. In order to avoid compl ications due to both heating and fluorescence, an excitation wavelengt h around 800 nm is suggested. A preliminary surface enhanced Raman (SE R) spectrum of a peptide nucleic acid (PNA) in aqueous silver colloid solution is shown. Low-frequency Raman spectra of aprotinin in aqueous solution are presented. The low-frequency limit in the NIR-FT-Raman s pectrum is similar to 80 cm(-1). Several models are used to describe t he bands assigned to hydrogen bonding in the systems. The low-frequenc y modes can be of importance for the formation and breaking of hydroge n bonds, and thus may be of importance for biological activity.