Guerra Anderson, Gaspar Armindo R, Contreras Sofía, Lucia Lucian A, Crestini Claudia, Argyropoulos Dimitris S
Organic Chemistry of Wood Components Laboratory, Department of Forest Biomaterials Science and Engineering, North Carolina State University, Raleigh, NC 27695-8005, USA.
Phytochemistry. 2007 Oct;68(20):2570-83. doi: 10.1016/j.phytochem.2007.05.026. Epub 2007 Jun 27.
Despite evidence that lignin associates under both aqueous and organic media, the magnitude and nature of the underlying driving forces are still a matter of discussion. The present paper addresses this issue by examining both solution properties and size exclusion behaviour of lignins isolated from five different species of softwoods, as well as from the angiosperms Eucalyptus globulus and wheat straw. This investigation has used the recently described protocol for isolating enzymatic mild acidolysis lignin (EMAL), which offers lignin samples highly representative of the overall lignin present in the wood cell wall. The molecular weight distributions of these EMALs were found to be dependent upon the wood species from which they were isolated and upon the incubation conditions used prior to size exclusion chromatography. While the chromatograms of EMALs isolated from softwoods displayed a bimodal behaviour, the elution profiles of EMAL from E. globulus and straw were nearly unimodal. A marked tendency to dissociate prevailed under incubation at room temperature for all examined species with the exception of the straw lignin preparation; furthermore, lignin solutions incubated at 4 degrees C showed an associative behaviour manifested by an increase in the weight and number average molecular weights for some species. The extent of such association/dissociation, as well as the time needed for the process to reach completion, was also found to depend upon the wood species, i.e. lignins from softwoods were found to associate/dissociate to a greater extent than lignins from E. globulus and straw. The origin of such effects within the lignin structure is also discussed.
尽管有证据表明木质素在水性和有机介质中都会缔合，但其潜在驱动力的大小和性质仍存在争议。本文通过研究从五种不同软木树种以及被子植物蓝桉和小麦秸秆中分离出的木质素的溶液性质和尺寸排阻行为来解决这个问题。这项研究采用了最近描述的分离酶促温和酸解木质素（EMAL）的方法，该方法提供的木质素样品能高度代表木材细胞壁中存在的整体木质素。发现这些EMAL的分子量分布取决于它们所分离的木材种类以及尺寸排阻色谱分析之前使用的孵育条件。虽然从软木中分离出的EMAL的色谱图呈现双峰行为，但从蓝桉和秸秆中分离出的EMAL的洗脱曲线几乎是单峰的。除了秸秆木质素制剂外，所有受试物种在室温孵育下都有明显的解离倾向；此外，在4℃下孵育的木质素溶液表现出缔合行为，某些物种的重均分子量和数均分子量增加。这种缔合/解离的程度以及该过程达到完成所需的时间也被发现取决于木材种类，即发现软木中的木质素比蓝桉和秸秆中的木质素缔合/解离程度更大。本文还讨论了木质素结构中这种效应的起源。
