A.R. Gargaro

Experimental and ab initio theoretical vibrational Raman optical activity of alanine

The vibrational Raman optical activity (ROA) spectra of l-alanine in water, 1 N NaOH and 1 N HCl between 720 and 1500 cm−1 measured in backscattering are reported. Unlike the associated vibrational circular dichroism (VCD), the main ROA features are relatively insensitive to pH changes. Ab initio Raman and ROA intensities were evaluated using 6-31G and 6-31G* basis sets and found to agree remarkably well with the experimental parameters in the lower-frequency region.

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.

Experimental and ab initio theoretical vibrational Raman optical activity of tartaric acid

Abstract The vibrational Raman optical activity (ROA) spectra of (2 R ,3 R )-(+) tartaric acid- d 0 in H 2 O and (2 R ,3 R )-(+) tartaric acid- d 4 in D 2 O between 300 and 1800 cm −1 measured in backscattering are reported. Ab initio Raman intensifies were evaluated using basis sets at 6-31G, 6-31G* and double zeta plus polarization (DZP) levels. Ab initio ROA intensities were obtained at two levels: in one calculation both the normal coordinates and the polarizability and optical activity tensor derivatives were evaluated with the 6-31G basis set; in a second calculation normal coordinates obtained with the DZP basis set were used to evaluate the normal coordinate derivatives of polarizability and optical activity tensors from the corresponding Cartesian derivative tensors obtained with the 6-31G basis set. Sufficiently good correlation was found between many of bands in the theoretical and experimental Raman and ROA spectra for both the - d 0 and - d 4 species to confirm that the absolute configuration of the ( + )-enantiomer is indeed (2 R ,3 R ) and to suggest that the trans COOH and trans COOD conformations are dominant. Tartaric acid- d 4 shows very similar ROA to tartaric acid itself in the range 300–800 cm −1 but quite different in the range 800–1450 cm −1 , which provides insight into the influence of normal mode composition on ROA spectra. It was found that the normal mode compositions are much more sensitive to the level of basis set used than the polarizability and optical activity tensor derivatives.

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 CCD detector have now enhanced the sensitivity to the level necessary to provide vibrational ROA spectra of biological molecules in aqueous solution. Preliminary results on peptides and proteins show features originating in coupled Ca-H and N-H deformations of the peptide backbone which appear to be sensitive to the secondary conformation. Also carbohydrates show many features that appear to be characteristic of the central aspects of carbohydrate architecture with effects from the glycosidic link in di- and oligosaccharides particularly prominent. 1.

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.