Banoub Joseph, Delmas Guo-Hua, Joly Nicolas, Mackenzie Grahame, Cachet Nadja, Benjelloun-Mlayah Bouchra, Delmas Michel
Department of Chemistry, Memorial University of Newfoundland, St John's, Newfoundland, A1C 5X1, Canada; Science Branch, Special Projects, Fisheries and Oceans Canada, St John's, NL, A1C 5X1, Canada.
J Mass Spectrom. 2015 Jan;50(1):5-48. doi: 10.1002/jms.3541.
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.
本综述致力于质谱（MS）在软电离方法中的应用，特别强调电喷雾电离、大气压光电离以及基质辅助激光解吸/电离质谱和串联质谱（MS/MS），以阐明天然和改性木质素的化学结构。我们描述并批判性地评估了这些软电离方法如何促进了当今对木质素结构的认识。在此，我们将引入有关木质素化学状态的新术语，即原始释放木质素（VRLs）和加工改性木质素（PMLs）。VRLs是通过化学水解和/或酶水解降解植物物质来释放木质素而获得的。PMLs是通过使VRL进行一系列进一步的化学转化和纯化而产生的，这些转化和纯化可能会改变其原始化学结构。我们提出，存在于木质纤维素生物质中的天然木质素聚合物并非如经常报道的那样由与纤维素纤维相连的大分子组成。相反，我们认为木质素由大量线性相关的低聚物组成，这些低聚物具有不同的长度，以交叉模式共价连接到纤维素和半纤维素纤维上形成植物物质网络结构。因此，对VRLs的结构解析可能反映天然木质素的结构，因为VRLs大概未经过任何其他类型的额外化学处理和纯化。在本综述中，我们介绍了一种用于木质素测序的MS/MS自上而下的概念，以及该技术如何用于应对表征VRLs结构的挑战。最后，我们提出这样一种情况，尽管据报道木质素具有非常高或较高的分子量，但基于现代质谱中使用的温和电离技术从未鉴定出此类聚合物这一事实，它们可能并不存在。
