COLLABORATIVE RESEARCH EAGER: Sum-frequency generation (SFG) vibration study of structure and enzymatic hydrolysis activities of crystalline cellulose in biomass

摘要：为了有效地将生物质转化为其他有用的化学品，有必要了解和克服其对酶解构过程的抵抗。生物量研究中的一个关键问题是酶活性和纤维素结构之间的相关性。尽管之前已经尝试了许多实验研究来回答这个基本问题，但答案仍然难以捉摸。困难在于，它需要对含有相同有机官能团的无定形基质中的结晶碳水化合物聚合物(纤维素)进行分子分析。目前的分析方法不能提供关于木质纤维生物质中结晶纤维素的足够细节。在这个EAGER项目中，北卡罗来纳州立大学的Pis Sunkyu Park和宾夕法尼亚州立大学的Seong H.Kim将探索和频产生(SFG)振动光谱的应用，以发现纤维素晶体结构对酶解构过程的影响。纤维素独特的晶体结构使其能够表现出其他生物质成分所没有的非线性光学性质，如SFG。SFG是无光学中心对称性的系统在高强度激光脉冲作用下的二阶非线性光学响应。基于这种独特的非线性光学选择规则，生物质中的半纤维素和木质素等无定形成分不能产生SFG信号。因此，SFG可以检测生物质中结晶纤维素的结构，而不需要对纤维素进行任何化学分离和修饰。此外，结构和酶活性之间的关系的问题可以通过以下纤维素SFG响应的变化来监测。这项研究产生了许多更广泛的技术影响。通过这项研究获得的分子洞察力将是了解生物质顽抗和开发更有效的生物质转化过程的宝贵信息。具体来说，预期成果包括：(1)朝着理解纤维素的结晶结构迈出了重要的一步；(2)开发了无需分离的纤维素表征的新工具，该工具只对木质纤维素生物质中的结晶纤维素敏感；(3)对纤维素结晶结构和酶解之间的关系的分子洞察；以及(4)跨学科领域的学生教育。这种名为SFG光谱的工具有望用于其他生物质应用，如纤维素溶解、生物质热转化、纤维素生物合成等。

Abstract: In order to efficiently convert biomass to other useful chemicals, it is necessary to understand and overcome its recalcitrance to enzymatic deconstruction processes. One key question involved in a biomass study is the correlation between the enzymatic activity and the cellulose structure. Although many experimental studies have been attempted previously to answer this fundamental question, the answer still remains elusive. The difficulty is that it requires molecular analysis of crystalline carbohydrate polymers (cellulose) in an amorphous matrix containing the same organic functional groups. Current analytical methods cannot provide sufficient details about crystalline cellulose in lignocellulosic biomass. In thisEAGER project, the PIs Sunkyu Park from North Carolina State University and Seong H. Kim from Pennsylvania State University will explore the application of sum-frequency generation (SFG) vibration spectroscopy to find the influence of cellulose crystal structure on the enzymatic deconstruction process. The unique crystal structure of cellulose allows it to demonstrate non-linear optical properties such as SFG which are absent in other biomass components. SFG is a second-order nonlinearoptical response of a system without optical centrosymmetry when it is irradiated withhigh-intensity laser pulses. Based on this unique non-linear optical selection rule, amorphous components such as hemicellulose and lignin in biomass cannot generate SFG signals. Thus, SFG can detect the structure of crystalline cellulose in biomass without any chemical isolation and modification of the cellulose. Furthermore, the question of the relation between structure and enzymatic activity can be monitored by following changes in the cellulose SFG response. There are a number of Broader technical impacts that result from this study. The molecular insights that will be obtained through this research will be valuable information to understand the biomass recalcitrance and develop more efficient biomass conversion processes. Specifically the expected outcomes include: (1) a significant step toward understanding of the crystalline structure of celluloses, (2) new tool development for cellulose characterization without separation, which is sensitive only to crystalline cellulose in lignocellulose biomass, (3) a molecular insight into the relationship between cellulose crystalline structure and enzymatic hydrolysis, and (4) student education in cross-disciplinary areas. This tool, SFG spectroscopy, is expected to be useful for other biomass applications such as cellulose dissolution, biomass thermal conversion, cellulose biosynthesis, etc.