J. C. Dobrowolsk et al.
106
were registered. Since then, the Nafie group have studied this problem in more and
more detail [148–150]. In 1985, they explained the positive sign of the C-*h band
by the formation of intramolecular hydrogen bonds between the Nd 3
+
and Co 2
−
groups [148]. In 1988, they observed a characteristic negative/positive band vCd
pattern in the 1200–1400 cm
−1
range of the vCd spectra of L-alanine, L-proline,
and selected dipeptides dissolved in water [149]. the negative and positive band
were assigned to two orthogonal bending modes of the C*h(Co 2
−
) group of Lamino acids and peptides. In 1989, the vCd spectra of L-alanine and its deuterated
isotopomers, L-serine, L-cysteine, and β-chloro-L-alanine were again analysed in
the C*h stretching vibrations region [150]. the vCd spectra were examined as a
function of ph and it was found that at neutral and high ph, the spectra exhibited a
large positive vCd intensity bias associated with the C*h stretching mode, whereas at low ph, the bias was absent and only very weak vCd signals were detected.
At that time, the interpretation of the vCd intensity could only be supported by a
general consideration of amino acid conformation but not confirmed by quantum
chemical calculations.
vCd analysis of amino acids in aqueous solution in the mid-IR region is difficult to undertake since (1) high concentrations and short path lengths should be
used because of the strong absorption of water and (2) amino acid solubilities in
water at neutral ph are usually not sufficient for vCd measurements. A small experimental breakthrough in the registration of the vCd spectra of amino acids in
water was achieved in 2005 by the innovation of a film technique by Shanmugam
and Polavarapu [151]. the technique consists of the formation of aqueous films of
water-soluble α-cyclodextrin as a matrix. In this way, the strong interference of water absorption is eliminated, enabling the vCd technique to be applied to biologically important compounds which are poorly soluble in water. the innovation lies
in the fact that, even though moderately absorbing α-cyclodextrin provides a chiral
environment, its interaction with amino acids is weak [152] and the vCd spectra of
amino acids are practically unperturbed. In 2006, the vCd spectra of L-alanine, Lproline, L-methionine, L-histidine, L-phenylalanine, and L-tryptophan in the form
of aqueous films with α-cyclodextrin were registered by Zhang and Polavarapu [38,
153]. A wide spectral region of the vCd spectra of L-methionine and L-histidine, as
well as poorly soluble in water L-phenylalanine and L-tryptophan, were registered
for the first time [151]. For moderately soluble L-alanine, L-proline, L-methionine,
and L-histidine, the VCD spectra of films with α-cyclodextrin were compared with
those obtained in the solution state and good agreement was found. For L-tyrosine,
neither absorption nor vCd spectra could be obtained in the solution state because
of extremely low solubility.
In 2006 Jalkanen et al. published complex, combined computational research
on IR, vCd, Raman, RoA, and SERS spectroscopy of L-alanine, L-tryptophan,
L-histidine, some model peptides, and a variety of small molecules of relevance to
protein systems [154]. A variety of computational methods including molecular mechanics, SCC-dFtB (self-consistent charge density functional tight binding) [155],
RhF, mP2, and dFt methods were combined with continuous and discrete solvation by several water molecules. the discrete hydration model (four water molecules
106
were registered. Since then, the Nafie group have studied this problem in more and
more detail [148–150]. In 1985, they explained the positive sign of the C-*h band
by the formation of intramolecular hydrogen bonds between the Nd 3
+
and Co 2
−
groups [148]. In 1988, they observed a characteristic negative/positive band vCd
pattern in the 1200–1400 cm
−1
range of the vCd spectra of L-alanine, L-proline,
and selected dipeptides dissolved in water [149]. the negative and positive band
were assigned to two orthogonal bending modes of the C*h(Co 2
−
) group of Lamino acids and peptides. In 1989, the vCd spectra of L-alanine and its deuterated
isotopomers, L-serine, L-cysteine, and β-chloro-L-alanine were again analysed in
the C*h stretching vibrations region [150]. the vCd spectra were examined as a
function of ph and it was found that at neutral and high ph, the spectra exhibited a
large positive vCd intensity bias associated with the C*h stretching mode, whereas at low ph, the bias was absent and only very weak vCd signals were detected.
At that time, the interpretation of the vCd intensity could only be supported by a
general consideration of amino acid conformation but not confirmed by quantum
chemical calculations.
vCd analysis of amino acids in aqueous solution in the mid-IR region is difficult to undertake since (1) high concentrations and short path lengths should be
used because of the strong absorption of water and (2) amino acid solubilities in
water at neutral ph are usually not sufficient for vCd measurements. A small experimental breakthrough in the registration of the vCd spectra of amino acids in
water was achieved in 2005 by the innovation of a film technique by Shanmugam
and Polavarapu [151]. the technique consists of the formation of aqueous films of
water-soluble α-cyclodextrin as a matrix. In this way, the strong interference of water absorption is eliminated, enabling the vCd technique to be applied to biologically important compounds which are poorly soluble in water. the innovation lies
in the fact that, even though moderately absorbing α-cyclodextrin provides a chiral
environment, its interaction with amino acids is weak [152] and the vCd spectra of
amino acids are practically unperturbed. In 2006, the vCd spectra of L-alanine, Lproline, L-methionine, L-histidine, L-phenylalanine, and L-tryptophan in the form
of aqueous films with α-cyclodextrin were registered by Zhang and Polavarapu [38,
153]. A wide spectral region of the vCd spectra of L-methionine and L-histidine, as
well as poorly soluble in water L-phenylalanine and L-tryptophan, were registered
for the first time [151]. For moderately soluble L-alanine, L-proline, L-methionine,
and L-histidine, the VCD spectra of films with α-cyclodextrin were compared with
those obtained in the solution state and good agreement was found. For L-tyrosine,
neither absorption nor vCd spectra could be obtained in the solution state because
of extremely low solubility.
In 2006 Jalkanen et al. published complex, combined computational research
on IR, vCd, Raman, RoA, and SERS spectroscopy of L-alanine, L-tryptophan,
L-histidine, some model peptides, and a variety of small molecules of relevance to
protein systems [154]. A variety of computational methods including molecular mechanics, SCC-dFtB (self-consistent charge density functional tight binding) [155],
RhF, mP2, and dFt methods were combined with continuous and discrete solvation by several water molecules. the discrete hydration model (four water molecules