A critique on the structural analysis of lignins and application of novel tandem mass spectrometric strategies to determine lignin sequencing

Abstract

This review is devoted to the application of MS using soft ionization methods with a special emphasis on electrospray ionization, atmospheric pressure photoionization and matrix-assisted laser desorption/ionization MS and tandem MS (MS/MS) for the elucidation of the chemical structure of native and modified lignins. We describe and critically evaluate how these soft ionization methods have contributed to the present-day knowledge of the structure of lignins. Herein, we will introduce new nomenclature concerning the chemical state of lignins, namely, virgin released lignins (VRLs) and processed modified lignins (PML). VRLs are obtained by liberation of lignins through degradation of vegetable matter by either chemical hydrolysis and/or enzymatic hydrolysis. PMLs are produced by subjecting the VRL to a series of further chemical transformations and purifications that are likely to alter their original chemical structures. We are proposing that native lignin polymers, present in the lignocellulosic biomass, are not made of macromolecules linked to cellulose fibres as has been frequently reported. Instead, we propose that the lignins are composed of vast series of linear related oligomers, having different lengths that are covalently linked in a criss-cross pattern to cellulose and hemicellulose fibres forming the network of vegetal matter. Consequently, structural elucidation of VRLs, which presumably have not been purified and processed by any other type of additional chemical treatment and purification, may reflect the structure of the native lignin. In this review, we present an introduction to a MS/MS top-down concept of lignin sequencing and how this technique may be used to address the challenge of characterizing the structure of VRLs. Finally, we offer the case that although lignins have been reported to have very high or high molecular weights, they might not exist on the basis that such polymers have never been identified by the mild ionizing techniques used in modern MS.

Organosolv Wheat Straw Lignin as a Phenol Substitute for Green Phenolic Resins

“…The structure of wheat straw BL has been widely studied (Banoub and Delmas 2003;Banoub et al 2007Banoub et al , 2015Delmas et al 2011a). A model of the structure is proposed in Fig.…”

“…The selected lignin was extracted from wheat straw using a mixture of acetic and formic acids, according to the organosolv pretreatment developed by CIMV (Paris, France) (Delmas and Avignon 2000;Delmas 2008;Delmas et al 2009). Its high purity, low molecular weight, high hydroxyl groups content, and especially its linear fragments make this lignin unique and particularly interesting for this application (Banoub and Delmas 2003;Banoub et al 2007Banoub et al , 2015. In addition to its qualities, this particular lignin, named Biolignin TM , is valuable since CIMV is building its first pre-industrial demonstration plant as part of the European project 2G-BIOPIC (Horizon 2020, Grant Agreement n°657867).…”

Identification of lignin oligomers in Kraft lignin using ultra-high-performance liquid chromatography/high-resolution multiple-stage tandem mass spectrometry (UHPLC/HRMSn)

“…Different depolymerisation and biological conversion methods for Kraft lignin have been investigated to produce new valuable molecules [1, 7]. For an easier classification of different types of lignin samples, Banoub et al introduced the terms virgin released lignins (VRLs), for lignin obtained by chemical hydrolysis and/or enzymatic hydrolysis, and processed modified lignins (PMLs) obtained by techniques like the Kraft lignin process that cause more chemical transformations of the lignin biopolymer [8].

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“…However, with techniques like Py-GC/MS and NMR, it is difficult to identify and characterise single lignin oligomers (LOs) in complex Kraft lignin samples. In recent years, several methods based on atmospheric pressure ionisation (API) in combination with tandem mass spectrometry (MS/MS) or multiple-stage tandem mass spectrometry (MS n ) have been established for the investigation of LOs in different types of lignin samples [8, 13]. …”

A Fundamental Tandem Mass Spectrometry Study of the Collision‐Activated Dissociation of Small Deprotonated Molecules Related to Lignin

“…[22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37] Most of these previouss tudies relied on two [23-26, 28, 29, 31, 34, 35, 38] (MS 2 )o rt hree [22,27,36] (MS 3 )s tages of mass spectrometry,t hat is, only the fragment ions of the deprotonated molecules and their fragment ions were examined. [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37] Most of these previouss tudies relied on two [23-26, 28, 29, 31, 34, 35, 38] (MS 2 )o rt hree [22,27,36] (MS 3 )s tages of mass spectrometry,t hat is, only the fragment ions of the deprotonated molecules and their fragment ions were examined.…”