coordinate transfer (CCT) or molecules in molecules (MIM) methodology enable to
predict ROA spectra of much bigger structures, for instance cyclodextrins [28],
globular proteins [29] or even protein fibrils [23].
6.1.3 Sophisticated Applications of the ROA Techniques
The development of new ROA techniques and applications has been recently
entering a higher and higher level. New techniques, such as surface-enhanced
Raman optical activity (SEROA) [30] and coherent anti-Stokes Raman spectroscopy–Raman optical activity (CARS-ROA) [31], were performed in biomedical applications, e.g., cancer detection [32] and sophisticated measurements like
chirality induction of solvent, [33] ROA of gas phase samples [34], diamagnetic
ROA of iodine and bromine gases [35], paramagnetic ROA of NO x gases [36], and
much more, shedding a new light on the analysis of molecular systems and their
interactions. Moreover, ROA spectrometers recently become useful also for circularly polarized light (CPL) measurements [37].
Another sophisticated methods are related to the attempts of ROA signal
enhancement. As ROA signal is very weak, measurements of low concentrated or
unstable chiral samples are very demanding, and therefore ROA signal enhancement methods are of interest. One of the attempts to enhance the ROA signal is
resonance Raman optical activity (RROA). Similar to resonance Raman (RR),
strong enhancement of the RROA intensity is observed when the incident laser
wavelength coincides with one of the electronic transitions of a molecule. In case of
RROA, an absorbing chromophore needs to be chiral or in chiral environment;
therefore, the presence of rotatory strength of related electronic transition, characterized by electronic circular dichroism (ECD) intensity, is necessary. Single
electronic state (SES) limit theory of Nafie [38] predicts monosigned RROA spectra
and with the opposite sign to the corresponding ECD band. What is more, relative
intensity of RROA bands is the same as in the parent RR spectrum and CID value
equals to −g/2 in the ICP and SCP-ROA strategy, where g is UV–Vis/ECD ratio of
relevant electronic transition [38]. First, RROA spectra were recorded for small
organic molecules [39] and metal complexes [40], however, the newest attempts
demonstrated that it is also possible for proteins [41] and carbon nanotubes [42].
Another technique of RROA is aggregation-induced resonance Raman optical
activity (AIRROA) observed recently by Zajac et al. in induction of strong RROA
signal after aggregation of carotenoids [43]. AIRROA spectra are monosigned and
opposite in sign to the relevant ECD band, in agreement with the SES theory—
however, CID values are rather comparable to the UV–Vis/ECD ratio; hence, twice
the value is predicted by the SES theory [38]. As carotenoid monomers do not
possess pronounced ECD signal in the spectral region of polyene chain chromophore absorption, measurements of RROA in use of a 532-nm laser line are
rather impossible. After aggregation, in mixed water and organic solvent solutions,
strong induction of ECD signal in the discussed region is observed due to the chiral
6 Small and Large Molecules Investigated by Raman Spectroscopy
165
predict ROA spectra of much bigger structures, for instance cyclodextrins [28],
globular proteins [29] or even protein fibrils [23].
6.1.3 Sophisticated Applications of the ROA Techniques
The development of new ROA techniques and applications has been recently
entering a higher and higher level. New techniques, such as surface-enhanced
Raman optical activity (SEROA) [30] and coherent anti-Stokes Raman spectroscopy–Raman optical activity (CARS-ROA) [31], were performed in biomedical applications, e.g., cancer detection [32] and sophisticated measurements like
chirality induction of solvent, [33] ROA of gas phase samples [34], diamagnetic
ROA of iodine and bromine gases [35], paramagnetic ROA of NO x gases [36], and
much more, shedding a new light on the analysis of molecular systems and their
interactions. Moreover, ROA spectrometers recently become useful also for circularly polarized light (CPL) measurements [37].
Another sophisticated methods are related to the attempts of ROA signal
enhancement. As ROA signal is very weak, measurements of low concentrated or
unstable chiral samples are very demanding, and therefore ROA signal enhancement methods are of interest. One of the attempts to enhance the ROA signal is
resonance Raman optical activity (RROA). Similar to resonance Raman (RR),
strong enhancement of the RROA intensity is observed when the incident laser
wavelength coincides with one of the electronic transitions of a molecule. In case of
RROA, an absorbing chromophore needs to be chiral or in chiral environment;
therefore, the presence of rotatory strength of related electronic transition, characterized by electronic circular dichroism (ECD) intensity, is necessary. Single
electronic state (SES) limit theory of Nafie [38] predicts monosigned RROA spectra
and with the opposite sign to the corresponding ECD band. What is more, relative
intensity of RROA bands is the same as in the parent RR spectrum and CID value
equals to −g/2 in the ICP and SCP-ROA strategy, where g is UV–Vis/ECD ratio of
relevant electronic transition [38]. First, RROA spectra were recorded for small
organic molecules [39] and metal complexes [40], however, the newest attempts
demonstrated that it is also possible for proteins [41] and carbon nanotubes [42].
Another technique of RROA is aggregation-induced resonance Raman optical
activity (AIRROA) observed recently by Zajac et al. in induction of strong RROA
signal after aggregation of carotenoids [43]. AIRROA spectra are monosigned and
opposite in sign to the relevant ECD band, in agreement with the SES theory—
however, CID values are rather comparable to the UV–Vis/ECD ratio; hence, twice
the value is predicted by the SES theory [38]. As carotenoid monomers do not
possess pronounced ECD signal in the spectral region of polyene chain chromophore absorption, measurements of RROA in use of a 532-nm laser line are
rather impossible. After aggregation, in mixed water and organic solvent solutions,
strong induction of ECD signal in the discussed region is observed due to the chiral
6 Small and Large Molecules Investigated by Raman Spectroscopy
165