Optically active solvents, spectral effect

Mustillo and CiurczakP" presented a paper discussing the spectral effect of optically active solvents on enantiomer mixes. This information was used as a technique to screen for polar modifiers in normal-phase chromatography of racemic mixtures. In 2000, the enantiomeric composition of ibuprofen in solid-state mixtures was performed by Agatonovic-Kurstrin, Beresford, Razzak. ... 

Solute-solvent interactions can occasionally be put to good use, as in the spectral resolution of enantiomeric pairs. By themselves monostereoisomers have identical spectra but when dissolved in an optically active solvent such as D- (or L-)2-octanol (available commercially) yield slightly different spectra. This is because of the asymmetry of the respective interactions which effectively create diastereoisometric pairs. 

In the case of fluorescence spectra, it is the emission of the radiation from the excited state that is measured, rather than its absorption. This also provides valuable information. As an example, tetraethylorthosilicate (TEOS)-based gels were doped with two optically active organic indicators, thionin and nile blue A. Before trapping in a solgel host, thionin and nile blue A were both evaluated for solvent and protonation effects on their spectral properties. Only extreme pH values provided by HCl, NaOH, and NH4OH produced new absorption and/or fluorescence bands. The absorption and fluorescence spectra revealed a decrease in a pH 11 solution of NH4OH compared to neutral conditions (Krihak et al., 1997). 

The two main nuclear modes affecting electronic energies of the donor and acceptor are intramolecular vibrations of the molecular skeleton of the donor-acceptor complex and molecular motions of the solvent. If these two nuclear modes are uncoupled, one can arrive at a set of simple relations between the two spectral moments of absorption and/or emission transitions and the activation parameters of ET. The most transparent representation is achieved when the quantum intramolecular vibrations are represented by a single, effective vibrational mode with the frequency vv (Einstein model).15-17 If both the forward (absorption) and backward (emission) optical transitions are available, their first spectral moments determine the reorganization energies of quantum vibrations, Xv, and of the classical nuclear motions of the donor-acceptor skeleton and the solvent, Xci ... 

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