271
9 Qualitative and Quantitative FT-Raman Analysis of Plants
polyacetylenes occurring in the plant tissue can be detected by means of Ft-Raman spectroscopy even in comparatively low amounts of 0.01–0.1 g/100 g fresh
matter. Raman spectra of diacetylenes show a very strong and polarized band due
to -C≡C-C≡C- symmetric stretching vibration in the region of 2,200–2,300 cm
−1
[71, 107, 108]. It has been observed that both, the number of conjugated -C≡C-
bonds in polyacetylenes and substituents contribute to the number of Raman signals, their frequencies and intensities [71]. therefore, the individual shape of the
region around 2,200 cm
−1
provides first informations with regard to the individual
polyacetylene type. thus, the diacetylene substances falcarinol, falcarindiol, and
panaxydol present similar characteristic bands which are shifted by only a few cm
−1
.
the band maximum for falcarinol appears at 2,258 cm
−1
and for falcarindiol at
2,252 cm
−1
(caused by the additional -OH group in α-position of the diacetylenic
system), whereas the Raman spectrum of panaxydol shows the corresponding band
at 2,260 cm
−1
[71]. Contrary to that, Raman spectra of unsubstituted triacetylenes
show two strong bands in the region between 2,190 and 2,120 cm
−1
, due to in-phase
and out-of phase stretching vibrations of all triple bonds [71]. It has been found
that tetraacetylenes show two symmetric and antisymmetric -C≡C- modes, whereas
diacetylenes substituted by a group with a similar mass as that of the -C≡C- moiety,
several additional couplings occur and the spectral shape in the ν(C≡C) region becomes more complicated [109].
generally, polyacetylenes can be reliably quantified even if they occur in lower
concentration in plant tissue. this observation is mainly due to the high scatter induced by -C≡C- bonds in a frequency region not interfering with other vibrational
modes. Furthermore, it has to be mentioned here that the presence of polyacetylenes
in plant tissues can be clearly illustrated by in situ Raman mapping.
It has been proved that apart from easy detection of polyacetylenic compounds,
Ft-Raman spectroscopy is also very useful to distinguish several polyacetylenes
[71]. two similar polyacetylenes, i.e. falcarinol and falcarindiol, usually co-existing in several plants, present a significant wavenumber shift of their characteristic
polyacetylene band. Also other polyacetylenes can be distinguished in a similar
way. the spectrum taken from the roots of the high-carotene orange carrot ( Daucus
carota) shows a few overlapping bands in the region of 2,260 and 2,250 cm
−1
. It has
been found that the main part of polyacetylenes is located in the outer section of the
root, i.e. in the secondary phloem tissue close to the vascular cambium as well as
in pericyclic parenchyma tissue close to the periderm [110]. It has been found that
the accumulation of polyacetylenes correlates very well with a high concentration
of carotenes, but both polyacetylenes and carotenoids occurred at different areas in
the investigated plant material.
Wild carrot species ( D. carota ssp. maritimus, D. carota ssp. gummifer, D. carota
ssp. commutatus) have been also investigated regarding the accumulation of polyacetylenes. Raman spectra prove that mainly falcarindiol is present in the individual
wild species. Recently, differences in the Raman spectra of two wild carrot species
have been described more detailed ( D. carota ssp. gummifer, D. carota ssp. maximus) [111]. generally, the Raman band at 2,258 cm
−1
characteristic for falcarinol
was missing in the spectra obtained from wild carrot roots implying that falcarinol
9 Qualitative and Quantitative FT-Raman Analysis of Plants
polyacetylenes occurring in the plant tissue can be detected by means of Ft-Raman spectroscopy even in comparatively low amounts of 0.01–0.1 g/100 g fresh
matter. Raman spectra of diacetylenes show a very strong and polarized band due
to -C≡C-C≡C- symmetric stretching vibration in the region of 2,200–2,300 cm
−1
[71, 107, 108]. It has been observed that both, the number of conjugated -C≡C-
bonds in polyacetylenes and substituents contribute to the number of Raman signals, their frequencies and intensities [71]. therefore, the individual shape of the
region around 2,200 cm
−1
provides first informations with regard to the individual
polyacetylene type. thus, the diacetylene substances falcarinol, falcarindiol, and
panaxydol present similar characteristic bands which are shifted by only a few cm
−1
.
the band maximum for falcarinol appears at 2,258 cm
−1
and for falcarindiol at
2,252 cm
−1
(caused by the additional -OH group in α-position of the diacetylenic
system), whereas the Raman spectrum of panaxydol shows the corresponding band
at 2,260 cm
−1
[71]. Contrary to that, Raman spectra of unsubstituted triacetylenes
show two strong bands in the region between 2,190 and 2,120 cm
−1
, due to in-phase
and out-of phase stretching vibrations of all triple bonds [71]. It has been found
that tetraacetylenes show two symmetric and antisymmetric -C≡C- modes, whereas
diacetylenes substituted by a group with a similar mass as that of the -C≡C- moiety,
several additional couplings occur and the spectral shape in the ν(C≡C) region becomes more complicated [109].
generally, polyacetylenes can be reliably quantified even if they occur in lower
concentration in plant tissue. this observation is mainly due to the high scatter induced by -C≡C- bonds in a frequency region not interfering with other vibrational
modes. Furthermore, it has to be mentioned here that the presence of polyacetylenes
in plant tissues can be clearly illustrated by in situ Raman mapping.
It has been proved that apart from easy detection of polyacetylenic compounds,
Ft-Raman spectroscopy is also very useful to distinguish several polyacetylenes
[71]. two similar polyacetylenes, i.e. falcarinol and falcarindiol, usually co-existing in several plants, present a significant wavenumber shift of their characteristic
polyacetylene band. Also other polyacetylenes can be distinguished in a similar
way. the spectrum taken from the roots of the high-carotene orange carrot ( Daucus
carota) shows a few overlapping bands in the region of 2,260 and 2,250 cm
−1
. It has
been found that the main part of polyacetylenes is located in the outer section of the
root, i.e. in the secondary phloem tissue close to the vascular cambium as well as
in pericyclic parenchyma tissue close to the periderm [110]. It has been found that
the accumulation of polyacetylenes correlates very well with a high concentration
of carotenes, but both polyacetylenes and carotenoids occurred at different areas in
the investigated plant material.
Wild carrot species ( D. carota ssp. maritimus, D. carota ssp. gummifer, D. carota
ssp. commutatus) have been also investigated regarding the accumulation of polyacetylenes. Raman spectra prove that mainly falcarindiol is present in the individual
wild species. Recently, differences in the Raman spectra of two wild carrot species
have been described more detailed ( D. carota ssp. gummifer, D. carota ssp. maximus) [111]. generally, the Raman band at 2,258 cm
−1
characteristic for falcarinol
was missing in the spectra obtained from wild carrot roots implying that falcarinol