title: Determination of the carbonyl groups in native lignin utilizing Fourier transform Raman spectroscopy.
abstract: A near-infrared Fourier transform Raman (NIR-FTR) spectroscopic technique was utilized to determine the chemical structure of lignin in a woody matrix. In the NIR-FTR spectra of coniferaldehyde and coniferyl alcohol, the Raman bands for the carbonyl group and the alpha, beta unsaturated bond were detected at 1620 and 1660 cm(-1), respectively. These peaks were also found in the NIR-FTR spectra of chemically synthesized lignins, isolated lignin from conifer wood, and conifer wood meal. Upon the reduction of carbonyl groups in the lignin samples and wood meal, the band at 1620 cm(-1) disappeared; on the other hand, the band at 1660 cm(-1) remained unchanged. However, upon the oxidation of reduced lignin at the benzyl hydroxyl group using dicyanodichrolobenzoquinone, the band at 1620 cm(-1) clearly appeared, strongly suggesting that the band at 1620 cm(-1) can be assigned as a carbonyl marker band. The hydrogenation reaction optimized for the reduction of the unsaturated bond in lignin caused the disappearance of the band at 1660 cm(-1), indicating that the band at 1660 cm(-1) is an alpha, beta unsaturated bond marker band. The change in carbonyl content during the wood decay process was also shown to be monitored using the Raman intensity of the carbonyl marker band. It was indicated that the NIR-FTR spectroscopic techniques were suitable analytical method for a rapid and nondestructive analysis of wood samples.
authors.affiliation: Department of Forest and Forest Products Sciences, Kyushu University, Fukuoka, Japan.
authors.forename: Momoko
authors.initials: M
authors.lastname: Kihara
authors.forename: Miyuki
authors.initials: M
authors.lastname: Takayama
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Wariishi
authors.forename: Hiroo
authors.initials: H
authors.lastname: Tanaka
mesh_terms: D028203:Cedrus / Q000737:chemistry; D008031:Lignin / Q000737:chemistry* / Q000302:isolation & purification; D008968:Molecular Conformation; D015394:Molecular Structure; D017550:Spectroscopy, Fourier Transform Infrared / Q000379:methods; D013059:Spectrum Analysis, Raman / Q000379:methods
chemical_list: D008031:Lignin