J. C. Dobrowolsk et al.
116
spectra was concluded. the authors emphasised that the RoA and vCd spectra did
not resemble one another and are complementary in content. however, it was argued
that RoA has greater potential than vCd for the study of biological molecules in
aqueous solution because RoA can be measured in all spectral regions for light and
heavy water while this is not possible for vCd. For example, the spectral region between 1500 and 1700 cm
−1
in vCd spectra has to be measured in d 2 o because of the
strong absorbance of hoh bending vibrations in liquid h 2 o. on the other hand, RoA
in aqueous solution can be measured without hindrance down to 100 cm
−1
[179].
Backward scattering in-phase dual circular polarisation (dCP I ) Raman optical
activity (RoA) spectra of L-alanine and its -2-d 1 and -3,3,3-d 3 isotopomers were
measured in light and heavy water in the 1700–800 cm
−l
frequency region by Yu et al.
in 1995 [195]. the registration of RoA for deuterated isotopomers followed by theoretical interpretation of the spectra enabled the authors to evaluate the contributions
from the motion of deuterated C*h and Ch 3 groups as well as Co 2
−
and Nh 3
+
in generating large RoA signals. the spectra were also calculated at the SCF/6-31g* level
with the onsager reaction field used for stabilisation of the zwitterionic forms. Excellent agreement was found between experiment and calculation for both Raman and
RoA spectra, except for alanine -2-d 1 . the disagreement was assumed to be an effect
of too low a level of calculations applied in the study. the experimental and theoretical RoA spectra of a 1.6 m solution of L-alanine in neutral h 2 o were also shown to
be in fair agreement in the range of 1300–750 cm
−1
if the SCF/6-31g* method was
applied, even without additional SCRF simulations in the water medium [196].
the RoA spectra of L-alanine in aqueous solution were next predicted by Jalkanen et al. using the hF and B3LYP methods and the 6-31g* basis set [197]. however, the electric dipole–magnetic dipole polarisability derivatives (EdmdPd) and
electric dipole-electric quadrupole polarisability derivatives (EdEQPd) required to
obtain the RoA spectra, at that time, had to be obtained at the RhF/6-31g*/Sto3g level. the L-alanine structures optimised earlier with and without the explicit
presence of four water molecules [182] were used to calculate the RoA spectra,
whereas the mixed basis set approach was used for those surrounded by nine water
molecules; the L-alanine zwitterion was calculated with the 6-31g** basis set while
the water molecules were calculated with the Sto-3g set [197]. the onsager model
was considered for the studied structures, but the influence of bulk water on EdmdPd and EdEQPd was ignored. In conclusion, the L-alanine zwitterion surrounded
by nine water molecules and the bulk water modelled in the frame of the onsager
model appeared to be the best for reproduction of the experimental spectra obtained
by Barron et al. [156, 194] and Yu et al. [195]. In the next article, modelling the RoA
spectra of the L-alanine zwitterion in water was performed by the supramolecular
approach using four water molecules for the first solvation sphere and the PCm continuum model for the bulk water [144]. this study, performed at the B3LYP/aug-ccpvdZ basis set, led to better compatibility with newly measured experimental RoA
spectra (Fig. 5.5) than those previously obtained using the 6-31g* basis set [154].
the role of the rotation of Ch 3 , Nh 3
+
, and Co 2
−
groups on the RoA spectrum was
estimated by Kapitán et al. [198] using the B3LYP/CPCm/6-31 + + g** level of theory for structural details and the hF/6-31 + + g** method for the intensity tensors for
a zwitterion in a vacuum (Fig. 5.6a). the band shapes were obtained by Boltzmann
116
spectra was concluded. the authors emphasised that the RoA and vCd spectra did
not resemble one another and are complementary in content. however, it was argued
that RoA has greater potential than vCd for the study of biological molecules in
aqueous solution because RoA can be measured in all spectral regions for light and
heavy water while this is not possible for vCd. For example, the spectral region between 1500 and 1700 cm
−1
in vCd spectra has to be measured in d 2 o because of the
strong absorbance of hoh bending vibrations in liquid h 2 o. on the other hand, RoA
in aqueous solution can be measured without hindrance down to 100 cm
−1
[179].
Backward scattering in-phase dual circular polarisation (dCP I ) Raman optical
activity (RoA) spectra of L-alanine and its -2-d 1 and -3,3,3-d 3 isotopomers were
measured in light and heavy water in the 1700–800 cm
−l
frequency region by Yu et al.
in 1995 [195]. the registration of RoA for deuterated isotopomers followed by theoretical interpretation of the spectra enabled the authors to evaluate the contributions
from the motion of deuterated C*h and Ch 3 groups as well as Co 2
−
and Nh 3
+
in generating large RoA signals. the spectra were also calculated at the SCF/6-31g* level
with the onsager reaction field used for stabilisation of the zwitterionic forms. Excellent agreement was found between experiment and calculation for both Raman and
RoA spectra, except for alanine -2-d 1 . the disagreement was assumed to be an effect
of too low a level of calculations applied in the study. the experimental and theoretical RoA spectra of a 1.6 m solution of L-alanine in neutral h 2 o were also shown to
be in fair agreement in the range of 1300–750 cm
−1
if the SCF/6-31g* method was
applied, even without additional SCRF simulations in the water medium [196].
the RoA spectra of L-alanine in aqueous solution were next predicted by Jalkanen et al. using the hF and B3LYP methods and the 6-31g* basis set [197]. however, the electric dipole–magnetic dipole polarisability derivatives (EdmdPd) and
electric dipole-electric quadrupole polarisability derivatives (EdEQPd) required to
obtain the RoA spectra, at that time, had to be obtained at the RhF/6-31g*/Sto3g level. the L-alanine structures optimised earlier with and without the explicit
presence of four water molecules [182] were used to calculate the RoA spectra,
whereas the mixed basis set approach was used for those surrounded by nine water
molecules; the L-alanine zwitterion was calculated with the 6-31g** basis set while
the water molecules were calculated with the Sto-3g set [197]. the onsager model
was considered for the studied structures, but the influence of bulk water on EdmdPd and EdEQPd was ignored. In conclusion, the L-alanine zwitterion surrounded
by nine water molecules and the bulk water modelled in the frame of the onsager
model appeared to be the best for reproduction of the experimental spectra obtained
by Barron et al. [156, 194] and Yu et al. [195]. In the next article, modelling the RoA
spectra of the L-alanine zwitterion in water was performed by the supramolecular
approach using four water molecules for the first solvation sphere and the PCm continuum model for the bulk water [144]. this study, performed at the B3LYP/aug-ccpvdZ basis set, led to better compatibility with newly measured experimental RoA
spectra (Fig. 5.5) than those previously obtained using the 6-31g* basis set [154].
the role of the rotation of Ch 3 , Nh 3
+
, and Co 2
−
groups on the RoA spectrum was
estimated by Kapitán et al. [198] using the B3LYP/CPCm/6-31 + + g** level of theory for structural details and the hF/6-31 + + g** method for the intensity tensors for
a zwitterion in a vacuum (Fig. 5.6a). the band shapes were obtained by Boltzmann