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Abstract: The results of a FTIR microspectroscopy analysis performed on the mixed gelling system of a protein (gelatin) and a polysaccharide (maltodextrin) are presented. A series of spectra were acquired consecutively by raster scanning the surface over a region of interest. The analysis has been carried out on three mixed-biopolymer samples prepared following different temperature paths, to study the effects of kinetics and thermodynamics on the texture of the final product. The chemical mapping has revealed to be very sensitive to composition, physical structure and hydration of the biopolymers. The results are critically discussed in reference to the band assignments and to protocols of sample preparation on the microtexture of the thin film.

Tyrosines can be selectively nitrated in a protein and the resultant chromophore can be used as an in situ probe of the tyrosine environment. Resonance Raman scattering could have specific advantages as a detection method because of the inherent selectivity of the technique and because shifts in the intensity and frequency of the nitro stretch can be detected and related to the form and environment of the nitrotyrosine. To evaluate this possibility the internal residue Tyr67 of cytochrome c was nitrated and resonance Raman scattering was recorded. With 413.1-nm excitation the resonance scattering from the heme protein dominates, but with 457.9-nm excitation intense bands due to nitrostretching vibrations are readily observed. The frequency of the internal Tyr67 indicates an aqueous environment that suggests that on nitration this residue becomes exposed on the protein surface or that water enters the active pocket. pH dependent measurements can be used to follow the protonation of the residue. A pKa of approximately 7 also indicates an aqueous environment. This initial study indicates that resonance Raman scattering does have unique advantages as an in situ probe of the local structure of nitrated tyrosine residues. © 1999 John Wiley & Sons, Inc. Biospectroscopy 5: S71–S76, 1999

Raman scattering is a sensitive and selective probe of the environment of nitro groups in nitrated proteins. As a model study to aid the interpretation of the changes observed, the spectra of 2-nitrophenol in solvents with different hydrogen bonding characteristics were recorded. An intramolecularly hydrogen-bonded and an intermolecularly hydrogen-bonded form of the molecule were identified from the wavenumber and intensity of the symmetric stretching vibration of the nitro group. In addition, the wavenumber of the mode is sensitive to the strength of the hydrogen-bonding interactions. The application of the conclusions to two nitrated proteins shows that in one case where the nitro group is on the surface intermolecular hydrogen bonding occurs, whereas in the other where the nitro groups is on an internal residue intramolecular hydrogen bonding occurs. Copyright © 1999 John Wiley & Sons, Ltd.