Title

Development and application of Raman optical activity

Date of Award

1994

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

Advisor(s)

Teresa Freedman

Second Advisor

Lawrence Nafie

Keywords

Raman optical activity

Subject Categories

Analytical Chemistry | Biological and Chemical Physics | Chemistry

Abstract

Following steady development over the past two decades, the theory and measurement of Raman optical activity (ROA) have both reached a sophisticated level. This dissertation presents advances in ROA in the areas of artifact control, experimental measurements, theoretical intensity computation, isolation of pre-resonance behavior and observation of surfaced-enhanced phenomena.

Backscattering incident circular polarization (ICP) and in-phase dual circular polarization (DCP$\sb{\rm I}$) ROA have been demonstrated theoretically and experimentally to be the best configurations for routine ROA studies on biological molecules in the far-from-resonance limit. Since DCP$\sb{\rm I}$ ROA provides better signal-to-noise ratios and artifact control when both methods are available on the same ROA instrument, backscattering DCP$\sb{\rm I}$ ROA spectra were recorded for terpene molecules, (($-$)-trans-pinane, ($-$)-cis-myrtanylamine, ($-$)- -pinene, ($-$)- -pinene, (+)-nopinone, ($-$)-verbenone, ($-$)-myrtenol, ($-$)-nopol, ($-$)-myrtenal, ($-$)-fenchone, (+)-limonene, and ($-$)-carvone as neat liquids, and ($-$)-camphor and ($-$)-camphene in CCl$\sb4$), ephedrine molecules, ((1S,2R)-ephedrine, (1S,2R)-norephedrine, (1S,2S)-pseudoephedrine and (1S,2S)-norpseudoephedrine in HCl aqueous solution), an amino acid, (L-alanine in H$\sb2$O and D$\sb2$O solution), four peptides, (glycyl-L-alanine, L-alanylglycine, L-alanyl-L-alanine and L-alanyl-L-alanyl-L-alanine in H$\sb2$O and D$\sb2$O solution), and two proteins, (lysozyme and albumin).

Theoretical Raman and ROA intensities for L-alanine, L-alanine-2-d$\sb1$ and L-alanine-3,3,3-d$\sb3$ in H$\sb2$O and D$\sb2$O solution were calculated by using ab initio methods with a 6-31G* basis set. A self-consistent-field calculation with the inclusion of an Onsager reaction field to simulate solvent effects was found necessary to stabilize properly the zwitterionic form of alanine. A high level of agreement was found between experiment and calculation for both Raman and ROA spectra.

By comparing backscattering ICP and DCP$\sb{\rm I}$ ROA and right-angle ICP and scattered circular polarization (SCP) ROA spectra, pre-resonance ROA behavior was observed. The gradual breakdown of the far-from-resonance approximation was observed by comparing ROA spectra for ($-$)-trans-pinane, ($-$)- -pinene, ($-$)-verbenone and (+)-quinidine. The differences between backscattering ICP and DCP$\sb{\rm I}$ ROA spectra also resulted in an indirect observation of out-of-phase dual circular polarization (DCP$\sb{\rm II}$) ROA signal.

Possible observation of surface-enhanced ROA phenomena for quinidine in an AgCl colloid is reported here for the first time. The experiment was carried out by using a backscattering DCP$\sb{\rm I}$ ROA configuration. This may open a new frontier for ROA studies.

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