Lignin Chemistry: Biosynthetic Study and Structural Characterisation of Coniferyl Alcohol Oligomers Formed In Vitro in a Micellar Environment

Abstract

Model coniferyl alcohol lignin (the so-called dehydrogenative polymerisate, DHP) was produced in water under homogeneous conditions guaranteed by the presence of a micellised cationic surfactant. A complete study of the activity of the enzymatic system peroxidase/H(2)O(2) under our reaction conditions was reported and all the reaction products up to the pentamer were characterised by (1)H NMR spectroscopy and ESI mass spectrometry. Our system, and the molecules that have been generated in it, represent a closer mimicry of the natural microenvironment since an enzyme, under micellar conditions, reproduces the cell system better than in buffer alone. On the basis of the oligomers structures a new biosynthetic perspective was proposed that focused attention on a coniferyl alcohol dimeric quinone methide as the key intermediate of the reaction. A formal, strictly alternate sequence of a radical and an ionic step underlines the reaction, thus generating ordered oligolignols structures. Alternatively to other model lignins, our olignols present a lower degree of radical coupling between oligomeric units. This offers a closer biosynthetic situation to the observation of a low rate of radical generation in the cell wall.

Heterogeneous and Homogeneous Components in Gas-Phase Pyrolysis of Hydrolytic Lignin

“…The calculations show that the less favorite one was dimerization of coupling units of o -C// o -C, o -C// p -C, and p -C// p -C, leading to carbon–carbon bond formation . It is intriguing that all the couplings occur through the quinone methide (QM) structure, a well-known intermediate in lignin chemistry. − All these coupling/dimerization reactions are termination reactions by removing phenoxy type radicals from the reaction media. In other words, differently generated QM structures are very active and can be easily hydrogenated to form a mixture of dimers as well as high-mass oligomers through consecutive polymerization. , It is pertinent to mention that the activation energies of dimerization of substituted phenoxy radicals, such as the radical (B), can be changed from barrierless up to 20 kcal/mol , leading to selective formation of dimers at different experimental conditions.…”

A Comparative Study of Matrix‐ and Nano‐assisted Laser Desorption/Ionisation Time‐of‐Flight Mass Spectrometry of Isolated and Synthetic Lignin

“…In these methods, lignin is degraded into small fragments, which constitute a fingerprint of the starting sample and give some structural information on the phenylpropane structure. In recent years, electrospray ionisation mass spectrometry (ESI‐MS; Angelis et al , ; Evtuguin et al , ; Evtuguin and Amado, ; Önnerud et al , ; Morreel et al , , 2010a, b; Reale et al , ) and secondary ion mass spectrometry (SIMS) combined with TOF have been applied to the structural analyses of lignin (Saito et al , ). These methods may expand mass spectrometry to the analysis of non‐volatile phenylpropanoids and surface lignin molecules on plant tissues (Saito et al , ).…”

On the reactivity of the Melanocarpus albomyces laccase and formation of coniferyl alcohol dehydropolymer (DHP) in the presence of ionic liquid 1-allyl-3-methylimidazolium chloride

“…Authentic compounds were used to identify ˇ-5, ˇ-ˇ and ˇ-O-4 dimers (1-3). The structure of trimer 5 [41] was confirmed with HR-ESI-MS. It is also known, that near neutral pH, addition of phenol to ˇ-O-4 type quinone methide to form ą -O-4/ˇ-O-4 product is dominating, and at more acidic pH, water is added to the quinone methide to form a ˇ-O-4 product [44].…”

“…The structure of trimer 5 [41] was confirmed by analyzing a sample collected from HPLC using high-resolution electrospray ionization mass spectrometry (HR-ESI-MS …”