Z. Q. Wen

Vibrational Raman optical activity of carbohydrates.

Vibrational Raman optical activity (R.o.a.) spectra of a range of carbohydrates in aqueous solution, measured in back-scattering between 700 and 1500 cm-1, are presented. Features were revealed that appear to be characteristic of details of the stereochemistry. Effects associated with the glycosidic linkage in di- and oligo-saccharides are prominent.

Vibrational Raman optical activity of cyclodextrins

Vibrational Raman optical activity spectra of aqueous solutions of α−, β− and γ-D-cyclodextrin in the range 700–1500 cm−1 are reported. As well as showing features characteristics of D-glucose, the ROA spectra all show remarkably intense features between 890 and 960 cm−1 originating in coupled C(1)-H deformations and glycosidic C-O stretches delocalized around the cyclodextrin ring and which reflect the stereochemistry of the glycosidic links.

Vibrational Raman optical activity of enzymes

Advances in Raman optical activity (ROA) instrumentation, based on the employment of a backscattering geometry together with a back-thinned CCD detector and a single-grating spectrograph with a holographic edge filter, have now enhanced the sensitivity to the level necessary to provide vibrational ROA spectra of proteins in aqueous solution. Early results show at least four separate regions in protein ROA spectra associated with vibrations of the backbone which appear to characterize the alpha-helix, beta-sheet, reverse turn and random-coil secondary conformation content. Side-group ROA features also appear, with tryptophan particularly prominent in lysozyme and alpha-lactalbumin. ROA should become a sensitive new probe of protein folding and ligand-induced conformational change in aqueous solution.

Vibrational Raman optical activity of peptides and proteins

Vibrational Raman optical activity spectra in the range 1100–1500 cm–1 of aqueous solutions of L-alanyl-L-alanine, D-alanyl-D-alanine, lysozyme, and α-chymotrypsin show features originating in coupled Cα–H and N–H deformations of the peptide backbone and appear to be sensitive to the details of the secondary conformation.

Vibrational Raman optical activity of proteins

Recent advances in optical technology have led to the development, at Glasgow, Scotland of a backscattering incident circular polarization (ICP) Raman optical activity (ROA) instrument. The higher S/N ratio and the greater control of polarization artifacts has allowed the study of protein samples to become almost routine. The advantage of ROA, over conventional Raman, is the far more prominent stereochemical sensitivity. In the case of the Glasgow instrument ROA is achieved by measuring the small difference between the Raman intensities in incident circularly right polarized and circularly left polarized light. We hope to utilize this chiroptical extension of conventional Raman to gain new insights into protein conformation and dynamics.

Vibrational Raman optical activity of biological molecules

Advances in Raman optical activity (ROA) instrumentation based on the employment of a backscattering geometry together with a cooled backthinned CCD detector, a holographic notch filter, and a high-efficiency single-grating spectrograph have now enhanced the sensitivity to the level necessary to provide vibrational ROA spectra of most biological molecules in aqueous solution. Results on peptides and proteins show features originating in coupled C(alpha )-H and N-H deformations of the peptide backbone which appear to be sensitive to the secondary conformation including loop and turn structures. Also carbohydrates show many features characteristic of the central aspects of carbohydrate architecture, with effects from the glycosidic link in oligosaccharides particularly prominent. Preliminary ROA spectra of pyrimidine nucleosides appear to reflect the mutual orientation of the sugar and base rings and the dominant furanose conformations.