Low-frequency Raman optical activity provides insight into the structure of chiral liquids

Abstract

Vibrational frequencies of modes involving intermolecular motions in liquids are relatively small, in the Raman scattering close to the excitation frequency, and the bands may merge into a diverging uninterpretable...

Molecular dynamics and Raman optical activity spectra reveal nucleotide conformation ratios in solution

“…Similar ROA bands were previously observed for sugars, 63 peptides 64 and chiral liquids, 65 and seems to provide interesting, although still relatively unexplored, possibility to expand ROA structural studies.…”

“…34,62 Interesting is also the large lowfrequency ROA, close to the 50 cm À1 instrumental limit, where the parent Raman spectra are virtually featureless and start to diverge towards the Rayleigh line. Similar ROA bands were previously observed for sugars, 63 peptides 64 and chiral liquids, 65 and seem to provide interesting, although still relatively unexplored, possibility to expand ROA structural studies. The fitted ROA spectra (red in Fig.…”

“…We did not attempt to analyze the lowest-frequency (<100 cm −1 ) ROA signal, because of its complexity and extensive computer demands needed. 65 Nevertheless, the experimental spectra plotted in the full range (Fig. S9, ESI†) also show in this region significant differences between the nucleotides; this signal is particularly strong for rAMP, stronger than in any other wavenumber region.…”

“…We did no attempt to analyze the lowest-frequency (< 100 cm -1 ) ROA signal, because of its complexity and extensive computer demands needed. 65 Nevertheless, the experimental spectra plotted in the full range (Figure S9) show also in this region significant differences between the nucleotides; this signal is particularly strong for rAMP, stronger than in any other wavenumber region. Also the CH stretching Raman and ROA bands (~2900 cm -1 ) provide so far limited information, as they are weak and prone to error in experiment, and eventual simulation would require rather expensive computations involving anharmonic corrections.…”

Conformational analysis of amphetamine and methamphetamine: a comprehensive approach by vibrational and chiroptical spectroscopy

“…The VCD spectral region was limited by the D 2 O absorption bands. Although we were able to measure Raman and ROA spectra in the much wider spectral range of 50–4500 cm −1 , the low-frequency region of 50–300 cm −1 is strongly affected by intermolecular interactions 63 that can bias the conformer population determination. On the other hand, CH stretching vibrations have a relatively low ROA signal, they are highly anharmonic and a different wavenumber scaling factor will be needed.…”