337
Threonine Except for minor relative intensity variations, our spectra are very similar to those reported by Zhu [3], as well as to the data published by other workers
[7, 58].
Phenylalanine our spectrum agrees with the spectrum published previously for a
somewhat smaller wavenumber range [3].
Proline Quite a few papers discussed the Raman spectra of solid proline [3, 7,
59–62]. our data are in good agreement with previously published results regarding peak positions, but the relative intensities are significantly different from those
reported by Zhu et al [3].
Serine Literature data on solid serine are quite extensive [3, 7, 37, 63–67]. our
spectra compare satisfactorily with those of Culka et al. [7], whereas the spectra
reported by Zhu et al. [3] are quite different with regard to intensities.
Tryptophan Raman spectra of solid tryptophan have been reported in several papers
[3, 7, 68–70]. our spectra are in very good agreement with those published recently
[3, 7].
Tyrosine three recent papers reported the Raman spectra of solid tyrosine [3, 7,
71]. these data correspond well to our spectra. It is to be noted, though, that the
relative intensities differ from those shown in the work by Zhu et al. [3]. In particular, in the region of 1100–1400 cm
−1
the dominant peak is located at 1328 cm
−1
,
whereas in our spectra the most intense band is observed in this range at 1198 cm
−1
.
Valine different groups have studied Raman spectra of valine in the solid state [3,
52, 66, 72, 73]. our spectra agree well with frequencies detected for the crystals,
but the intensities follow a different pattern, very similar to that observed by Zhu
et al [3]. Interestingly, in one case, for the spectra recorded in nujol mulls [52],
the measured frequencies are completely different from those reported for all other
solid samples.
It should be stressed that, due to polarization effects, the relative intensities of
the band may change when the crystalline sample is pulverized. our data refer to
finely ground powders, for which these effects should be minimized. this may be
the reason for discrepancies in relative intensities between our measurements and
other works in the spectra discussed above.
12.3.1 Similarity Analysis Using Pearson Correlation Coefficient
We start the analysis using Pearson correlation coefficients between the template
spectra of single amino acids in the range from 300 to 1700 cm
−1
. the values of the
correlation coefficients for all pairs are presented in Fig. 12.3. It is easy to see that
they have a tendency to increase towards the lower-right part of the table. this is a
consequence of sorting amino acids according to the mean value of the coefficient
for a given template spectrum and the rest of the spectra. Let us also note that this
12 Raman Spectra of Solid Aminoacids: Spectral Correlation Analysis …
Threonine Except for minor relative intensity variations, our spectra are very similar to those reported by Zhu [3], as well as to the data published by other workers
[7, 58].
Phenylalanine our spectrum agrees with the spectrum published previously for a
somewhat smaller wavenumber range [3].
Proline Quite a few papers discussed the Raman spectra of solid proline [3, 7,
59–62]. our data are in good agreement with previously published results regarding peak positions, but the relative intensities are significantly different from those
reported by Zhu et al [3].
Serine Literature data on solid serine are quite extensive [3, 7, 37, 63–67]. our
spectra compare satisfactorily with those of Culka et al. [7], whereas the spectra
reported by Zhu et al. [3] are quite different with regard to intensities.
Tryptophan Raman spectra of solid tryptophan have been reported in several papers
[3, 7, 68–70]. our spectra are in very good agreement with those published recently
[3, 7].
Tyrosine three recent papers reported the Raman spectra of solid tyrosine [3, 7,
71]. these data correspond well to our spectra. It is to be noted, though, that the
relative intensities differ from those shown in the work by Zhu et al. [3]. In particular, in the region of 1100–1400 cm
−1
the dominant peak is located at 1328 cm
−1
,
whereas in our spectra the most intense band is observed in this range at 1198 cm
−1
.
Valine different groups have studied Raman spectra of valine in the solid state [3,
52, 66, 72, 73]. our spectra agree well with frequencies detected for the crystals,
but the intensities follow a different pattern, very similar to that observed by Zhu
et al [3]. Interestingly, in one case, for the spectra recorded in nujol mulls [52],
the measured frequencies are completely different from those reported for all other
solid samples.
It should be stressed that, due to polarization effects, the relative intensities of
the band may change when the crystalline sample is pulverized. our data refer to
finely ground powders, for which these effects should be minimized. this may be
the reason for discrepancies in relative intensities between our measurements and
other works in the spectra discussed above.
12.3.1 Similarity Analysis Using Pearson Correlation Coefficient
We start the analysis using Pearson correlation coefficients between the template
spectra of single amino acids in the range from 300 to 1700 cm
−1
. the values of the
correlation coefficients for all pairs are presented in Fig. 12.3. It is easy to see that
they have a tendency to increase towards the lower-right part of the table. this is a
consequence of sorting amino acids according to the mean value of the coefficient
for a given template spectrum and the rest of the spectra. Let us also note that this
12 Raman Spectra of Solid Aminoacids: Spectral Correlation Analysis …