Happs Renee M, Addison Bennett, Doeppke Crissa, Donohoe Bryon S, Davis Mark F, Harman-Ware Anne E
Renewable Resources and Enabling Sciences Center, National Renewable Energy Laboratory, Golden, CO, 80401, USA.
Biosciences Center, National Renewable Energy Laboratory, Golden, CO, 80401, USA.
Biotechnol Biofuels. 2021 Mar 6;14(1):58. doi: 10.1186/s13068-021-01897-y.
Multiple analytical methods have been developed to determine the ratios of aromatic lignin units, particularly the syringyl/guaiacyl (S/G) ratio, of lignin biopolymers in plant cell walls. Chemical degradation methods such as thioacidolysis produce aromatic lignin units that are released from certain linkages and may induce chemical changes rendering it difficult to distinguish and determine the source of specific aromatic lignin units released, as is the case with nitrobenzene oxidation methodology. NMR methods provide powerful tools used to analyze cell walls for lignin composition and linkage information. Pyrolysis-mass spectrometry methods are also widely used, particularly as high-throughput methodologies. However, the different techniques used to analyze aromatic lignin unit ratios frequently yield different results within and across particular studies, making it difficult to interpret and compare results. This also makes it difficult to obtain meaningful insights relating these measurements to other characteristics of plant cell walls that may impact biomass sustainability and conversion metrics for the production of bio-derived fuels and chemicals.
The authors compared the S/G lignin unit ratios obtained from thioacidolysis, pyrolysis-molecular beam mass spectrometry (py-MBMS), HSQC liquid-state NMR and solid-state (ss) NMR methodologies of pine, several genotypes of poplar, and corn stover biomass. An underutilized approach to deconvolute ssNMR spectra was implemented to derive S/G ratios. The S/G ratios obtained for the samples did not agree across the different methods, but trends were similar with the most agreement among the py-MBMS, HSQC NMR and deconvoluted ssNMR methods. The relationship between S/G, thioacidolysis yields, and linkage analysis determined by HSQC is also addressed.
This work demonstrates that different methods using chemical, thermal, and non-destructive NMR techniques to determine native lignin S/G ratios in plant cell walls may yield different results depending on species and linkage abundances. Spectral deconvolution can be applied to many hardwoods with lignin dominated by S and G units, but the results may not be reliable for some woody and grassy species of more diverse lignin composition. HSQC may be a better method for analyzing lignin in those species given the wealth of information provided on additional aromatic moieties and bond linkages. Additionally, trends or correlations in lignin characteristics such as S/G ratios and lignin linkages within the same species such as poplar may not necessarily exhibit the same trends or correlations made across different biomass types. Careful consideration is required when choosing a method to measure S/G ratios and the benefits and shortcomings of each method discussed here are summarized.
已经开发了多种分析方法来测定植物细胞壁中木质素生物聚合物的芳香族木质素单元的比例，特别是紫丁香基/愈创木基（S/G）比例。诸如硫代酸解等化学降解方法会产生从某些键释放的芳香族木质素单元，并可能引发化学变化，使得难以区分和确定所释放的特定芳香族木质素单元的来源，硝基苯氧化法也是如此。核磁共振（NMR）方法提供了用于分析细胞壁中木质素组成和连接信息的强大工具。热解-质谱方法也被广泛使用，特别是作为高通量方法。然而，用于分析芳香族木质素单元比例的不同技术在特定研究内部和不同研究之间经常产生不同的结果，这使得难以解释和比较结果。这也使得难以获得将这些测量结果与植物细胞壁的其他特征相关联的有意义的见解，而这些特征可能会影响生物衍生燃料和化学品生产的生物质可持续性和转化指标。
作者比较了通过硫代酸解、热解-分子束质谱（py-MBMS）、HSQC液态NMR和固态（ss）NMR方法获得的松树、几种杨树基因型和玉米秸秆生物质的S/G木质素单元比例。采用了一种未充分利用的解卷积ssNMR光谱的方法来推导S/G比例。不同方法得到的样品S/G比例不一致，但趋势相似，py-MBMS、HSQC NMR和解卷积ssNMR方法之间的一致性最高。还讨论了S/G、硫代酸解产率以及由HSQC确定的连接分析之间的关系。
这项工作表明，使用化学、热学和非破坏性NMR技术来测定植物细胞壁中天然木质素S/G比例的不同方法，可能会因物种和连接丰度的不同而产生不同的结果。光谱解卷积可应用于许多以S和G单元为主的木质素的阔叶树，但对于一些木质素组成更多样化的木本和草本物种，结果可能不可靠。鉴于HSQC提供了关于其他芳香族部分和键连接的丰富信息，它可能是分析这些物种中木质素的更好方法。此外，同一物种（如杨树）内木质素特征（如S/G比例和木质素连接）的趋势或相关性不一定与不同生物质类型之间的趋势或相关性相同。选择测量S/G比例的方法时需要仔细考虑，本文总结了每种方法的优缺点。
