Study of the sedge (Cárex) lignin by high-resolution mass spectrometry and NMR spectroscopy

Features of the Chemical Composition and Structure of Birch Phloem Dioxane Lignin: A Comprehensive Study

“…The yields of the obtained DL-P, DL-P-AH and DL-X lignin preparations recalculated to Klason lignin were 30.3%, 24.7% and 25.0%, respectively. Weight-average (M w ), number-average (M n ) molecular weights and polydispersity index (PDI) determined by size-exclusion chromatography [ 15 ], as well as hydroxyl and carboxyl group contents determined by the conventional wet chemistry methods [ 28 ] for the obtained lignin preparations are presented in Table 2 .…”

“…Analytical pyrolysis was performed as described previously [ 15 ] using a GCMS-QP2010 Plus gas chromatography–mass spectrometry system (Shimadzu, Kyoto, Japan) equipped with an EGA/PY-3030D pyrolyzer (Frontier Lab, Koriyama, Japan) with a liquid nitrogen cooled cryo-trap. Lignin sample (~100 μg) was subjected to the thermal decomposition at 450 °C for 30 s in inert (6.0 grade helium) atmosphere with cryo-focusing of the formed products.…”

“…The latter can be condensed tannins and high-molecular polyphenolic acids (HPA), which are extracted from plant tissues along with lignin and can be effectively removed with only an alkali solution [ 13 ]. Polyphenols can participate in the formation of phloem lignin macromolecules due to covalent binding during lignin biosynthesis by analogy with cinnamic acids, which play an important role in the structure of grass lignins [ 14 , 15 ]. Another issue is the possibility of condensation of HPA with lignin to form new covalent bonds during a lignin isolation procedure [ 16 ].…”

“…The first one provides information regarding the different lignin units and inter-unit linkages and is considered now as a most powerful tool for lignin structural studies [ 17 ]. Typically, it involves the most popular HSQC (Heteronuclear Single Quantum Coherence) experiments with recording of additional diagnostic 2D NMR spectra, for example, HMBC (Heteronuclear Multiple Bond Correlation) techniques to identify unknown cross-peaks [ 4 , 5 , 7 , 8 , 14 , 15 , 16 , 17 , 18 ]. An additional way to increase the reliability of identification is by using expert systems for the prediction of spectra and computer-assisted structure elucidation [ 18 ].…”

“…One of the most promising analytical tools for molecular characterization of lignin is an orbital ion trap (Orbitrap) HRMS with atmospheric pressure photoionization (APPI) demonstrating a high efficiency of ionization of biopolymers in the wide range of molecular weights (up to 2 kDa) and a capability to simultaneously detect several thousands of oligomers [ 19 , 20 ]. This technique has been successfully used to characterize extremely complex mixtures of lignin depolymerization products [ 21 , 22 ], as well as to study the structure of nettle and sedge grass lignins [ 15 , 23 ].…”