259
9 Qualitative and Quantitative FT-Raman Analysis of Plants
After cellulose, lignin is the second most abundant organic material on earth. In
the past, numerous techniques have been used to characterise the lignin structure in
the context of cell plant lignification and biodegradation processes [36]. Contrary
to IR, Raman analysis of lignin have been performed quite recently [37–39]. the
distribution of lignin and cellulose in the cell walls of black spruce wood ( Picea
mariana) was investigated using a Raman spectrometer equipped with a confocal
microscope and 633 nm laser excitation [37]. the Raman spectra obtained from
sections of black spruce show cellulose bands at 380, 1,098 and 2,900 cm
−1
, whereas lignin contributed signals at 1,600 as well as 1,650 cm
−1
[40]. Based on these
spectral features the ratio of lignin to cellulose concentration was calculated across
the double cell wall. the authors stress that Raman imaging permits analyzing plant
cell walls without the necessity to use stain, dye and contrast agents. Recently, the
same group developed a new SERS Raman method to increase sensitivity and selectivity of lignin in various lignin-containing materials [41]. they mixed the wood
samples in presence of ethanol with silver particles (100–150 nm and 2–3.5 µm)
and observed that Raman spectra of milled-wood-lignin were surface-enhanced
when compared to the normal Ft-Raman spectra. Furthermore, a number of Raman
signals are shifted to lower wavenumbers suggesting a complexation with silver
particles and consequently a change of frequency in the SERS spectra. Contrary to
that, silver-adsorbed cellulose samples did not produce a SERS spectrum. It is assumed that π-electrons of the aromatic ring system interact with the silver particles.
therefore, the signals observed in the SERS spectrum of spruce wood can be predominantly related to lignin vibrational modes [41].
various plant species used as bioenergy feedstocks (pine, oak, poplar, kenaf,
miscanthus, pampas gras, switchgrass, alfalfa, orchard grass, and red clover) were
analysed for their lignin guaiacyl and syringyl monomer content applying Ft Raman spectroscopy [42]. the interpreted Raman data were correlated with the
13
CNmR spectral dataset; furthermore PCA as well as PCR models were developed for
classifying plant samples and quantifying lignin components.
Numerous organic colouring substances belong to the chemical class of flavonoids. Beside anthraquinones and indigoids they were the main source of textile
colour until the mid- to late 19th century. the most important plants containing
yellow dyes include weld ( Reseda luteola), old fustic ( Chlorophora tinctoria) and
dyer’s greenweed ( Genista tinctoria) [43]. Several vibrational studies have been
performed with flavonoids [44–47] but only a limited number of Raman spectra of
natural dyes are available in literature [48–50] (natural dyes will be also discussed
in the next chapter Chemometric analysis of Raman and IR spectra of natural
dyes). Surprisingly, only few applications of in situ and in vivo Raman measurements of anthocyanins have been described [51–53]. Recently, model systems containing anthocyanins, metals (aluminium and iron) and pectins were investigated
to analyse the interactions in the individual metal chelate complexes [50]. In this
context two marker bands were identified (at approx. 1,510 and 1,330/1,350 cm
−1
)
being responsible for the formation of metal chelates with cyaninidin-3-glycoside
and delphinidin-3-glycoside as ligands. Pelargonidin-3-glycoside did not form metal chelates, which was clearly proved by missing marker bands (Fig. 9.1).
9 Qualitative and Quantitative FT-Raman Analysis of Plants
After cellulose, lignin is the second most abundant organic material on earth. In
the past, numerous techniques have been used to characterise the lignin structure in
the context of cell plant lignification and biodegradation processes [36]. Contrary
to IR, Raman analysis of lignin have been performed quite recently [37–39]. the
distribution of lignin and cellulose in the cell walls of black spruce wood ( Picea
mariana) was investigated using a Raman spectrometer equipped with a confocal
microscope and 633 nm laser excitation [37]. the Raman spectra obtained from
sections of black spruce show cellulose bands at 380, 1,098 and 2,900 cm
−1
, whereas lignin contributed signals at 1,600 as well as 1,650 cm
−1
[40]. Based on these
spectral features the ratio of lignin to cellulose concentration was calculated across
the double cell wall. the authors stress that Raman imaging permits analyzing plant
cell walls without the necessity to use stain, dye and contrast agents. Recently, the
same group developed a new SERS Raman method to increase sensitivity and selectivity of lignin in various lignin-containing materials [41]. they mixed the wood
samples in presence of ethanol with silver particles (100–150 nm and 2–3.5 µm)
and observed that Raman spectra of milled-wood-lignin were surface-enhanced
when compared to the normal Ft-Raman spectra. Furthermore, a number of Raman
signals are shifted to lower wavenumbers suggesting a complexation with silver
particles and consequently a change of frequency in the SERS spectra. Contrary to
that, silver-adsorbed cellulose samples did not produce a SERS spectrum. It is assumed that π-electrons of the aromatic ring system interact with the silver particles.
therefore, the signals observed in the SERS spectrum of spruce wood can be predominantly related to lignin vibrational modes [41].
various plant species used as bioenergy feedstocks (pine, oak, poplar, kenaf,
miscanthus, pampas gras, switchgrass, alfalfa, orchard grass, and red clover) were
analysed for their lignin guaiacyl and syringyl monomer content applying Ft Raman spectroscopy [42]. the interpreted Raman data were correlated with the
13
CNmR spectral dataset; furthermore PCA as well as PCR models were developed for
classifying plant samples and quantifying lignin components.
Numerous organic colouring substances belong to the chemical class of flavonoids. Beside anthraquinones and indigoids they were the main source of textile
colour until the mid- to late 19th century. the most important plants containing
yellow dyes include weld ( Reseda luteola), old fustic ( Chlorophora tinctoria) and
dyer’s greenweed ( Genista tinctoria) [43]. Several vibrational studies have been
performed with flavonoids [44–47] but only a limited number of Raman spectra of
natural dyes are available in literature [48–50] (natural dyes will be also discussed
in the next chapter Chemometric analysis of Raman and IR spectra of natural
dyes). Surprisingly, only few applications of in situ and in vivo Raman measurements of anthocyanins have been described [51–53]. Recently, model systems containing anthocyanins, metals (aluminium and iron) and pectins were investigated
to analyse the interactions in the individual metal chelate complexes [50]. In this
context two marker bands were identified (at approx. 1,510 and 1,330/1,350 cm
−1
)
being responsible for the formation of metal chelates with cyaninidin-3-glycoside
and delphinidin-3-glycoside as ligands. Pelargonidin-3-glycoside did not form metal chelates, which was clearly proved by missing marker bands (Fig. 9.1).