Pranati K. Bose

Evidence for covalent binding between copper ions and cyclodextrin cavity: a vibrational circular dichroism study

Vibrational absorption and circular dichroism (VCD) spectra were obtained for parent cyclodextrins, hydroxyl deuterated alpha-cyclodextrin, cyclodextrin-copper complexes, and for the cyclodextrin inclusion complexes with Methyl Orange, methyloxirane, 1-propanol, and substituted cyclohexanones, in the solution phase. Changes in the VCD spectra, reflecting perturbations of cyclodextrin cavity, were found in the case of an inclusion complex with Methyl Orange, but for the remaining inclusion complexes measurable changes in VCD were not found. Significant changes observed in the VCD spectra of cyclodextrin-copper complexes suggest that the covalent binding of copper ions to the hydroxyl groups of cyclodextrin is involved.

Ab initio and experimental vibrational Raman optical activity in (+)-(R)-methylthiirane

Experimental and theoretical vibrational Raman optical activity (ROA) spectra of (+)-(R)-methylthiirane are presented. The vibrational origin of the observed bands is discussed and the predictive capabilities of the theoretical calculations are evaluated in relation to the experimental observations. The ROA spectral sign patterns predicted with the 6-31G* basis set are in good agreement with those in the experimental spectra. For most of the vibrations the predicted magnitudes of the normalized ROA quantities are larger than those experimentally observed.

Vibrational circular dichroism of monosaccharides

Abstract Vibrational absorption and circular dichroism spectra of several monosaccharides in the 1500–1180 cm −1 region are presented. The spectra are analyzed for similarities and differences among anomeric, homomorphic and epimeric pairs of sugars. Among the anomeric sugars, distinct bands characteristic of anomers are present that can be used to characterize the anomers. The homomorphic sugars are found to give rise to similar vibrational circular dichroism (VCD) sign patterns provided that the substituents do not have interfering VCD bands, or those interfering bands can be identified and properly accounted for. The epimeric sugars have markedly different VCD spectra, indicating that VCD is sensitive to the chirality at individual chiral centers.

ACETATE GROUPS AS PROBES OF THE STEREOCHEMISTRY OF CARBOHYDRATES: A VIBRATIONAL CIRCULAR DICHROISM STUDY

Abstract Vibrational absorption and circular dichroism spectra of five different monosaccharide pentaacetates were measured. These spectra were found to be dominated by the contributions from the acetate groups. In the carbonyl region, α- and β- d -glucose pentaacetates do not show measurable vibrational circular dichroism (VCD), but α- and β- d -galactose pentaacetates and α- d -mannose pentaacetate show significant VCD, with mannose pentaacetate giving opposite signs to those of α- and β- d -galactose pentaacetates. These observed features are interpreted to reflect the orientation of carbonyl groups around the carbohydrate ring.

Counter observations on the practice of scaling individual ab initio force constants: Vibrational spectra of methylthiirane

Abstract Ab initio Raman and infrared spectra were computed for methylthiirane and compared to the corresponding experimental spectra. An excellent qualitative agreement is present between theoretical predictions and experimental results. When the ab initio force constants were scaled as suggested in the literature, the quality of the resulting theoretical Raman spectrum deteriorated.

Ab initio Raman spectra of oxirane

Abstract Raman spectra of oxirane computed with different basis sets are compared with the corresponding experimental spectra. The polarized nature of the experimental Raman bands permits unambiguous symmetry assignments for some of the observed bands. The frequency ordering determined in this manner is somewhat different from that obtained in different calculations. The calculations performed at the experimental geometry with 6-31G(E) basis set appeared to reproduce the experimental Raman spectrum satisfactorily.

Vibrational absorption and circular dichroism in 2,3-d2-oxirane. Interpretation of the observed intensities

Abstract Vibrational absorption and circular dichroism intensities due to the CH stretching vibrations of 2,3-d2-oxirane are interpreted by deriving semi-classical expressions involving the charge reorganization.

Development and Evaluation of a Polarization-Division Interferometer with Cube Corner Mirrors

The use of cube corner mirrors in conventional Fourier transform infrared (FT-IR) spectrometers has led to increased stability and enhanced signal-to-noise ratio. Polarization-division interferometers for the mid- and far-infrared regions, however, were based on either the Martin–Puplett design, which utilizes roof-top mirrors, or the Michelson interferometer design, which utilizes the plane mirrors. In this paper, we report the development of a polarization-division interferometer with cube corner mirrors. In this design, two different wire-grid beamsplitters are used for the division and recombination of polarized light. The performance of this new instrument has been evaluated by measuring the linear dichroism of oriented films and the circular dichroism of isotropic samples. This development facilitates the adaptation of commonly used FT-IR spectrometers with cube corner mirrors for polarization-division configuration.

Circular dichroism of the benzene group vibrations and molecular stereochemistry

Circular dichroism (CD) in the vibrational transitions of three different series of molecules-namely, phenylcarbinols, carboxylic acids, and oxiranes-containing the benzene group is measured. It is found that a benzene-group vibration, where the hydrogen atoms in the meta and para positions vibrate in a concerted semicircular path, gives rise to CD that is consistent with the molecular stereochemistry. This observation provides a practical approach to the use of the benzene group as a probe of molecular chirality.