Fabrication and fundamental understanding of cellulase-mimetic bifunctional solid acids for hydrolyzing cellulose

利用碳水化合物/糖平台将木质纤维素生物质资源转化为燃料的第一步是将生物质中的纤维素转化为糖。然而，从生物质中高效地生产糖仍然是一个巨大的挑战。生物质中的纤维素的化学转化使用酶(纤维素酶)和均质酸(如硫酸)来产生葡萄糖，通常分两步进行。目前所需的酶价格昂贵；它们需要严格的操作条件(温度和pH)，并且需要更长的时间(天)才能实现令人满意的纤维素转化。均相酸存在设备腐蚀、回收和废水处理等问题。本项目旨在设计一种新型的仿生聚合物固体酸催化剂，它结合了目前顺序使用的酶和无机酸所提供的功能。通过模拟纤维素酶/酶，该研究项目将包括基础研究，以设计和制造双功能仿生固体酸催化剂，用于水解纤维素以生产所需的单糖。该项目的综合教育计划将针对不同层次的学生，包括高中、本科生和研究生。将特别关注STEM中代表性不足群体(少数民族和妇女)的高中生和本科生。新概念、研究成果、所获得的知识和创新技术将通过出版物、演讲和课堂教学/学习向学术界、产业界、学生和公众传播。所有这些都将直接和/或间接地有利于生物能源和生物产品领域的研究、生产、教育和政策制定。该研究项目将涉及高效、坚固和低成本的纤维素酶仿酶固体酸催化剂的基础研究，用于从生物质的主要成分之一纤维素生产糖。该项目的成功将促进从生物质糖中生产生物燃料。通过分子设计和结构设计，固体酸催化剂将含有两类官能团。第一类是酸性官能团，如磺酸，负责水解纤维素。第二个基团是结合官能团，将使用羟基、羧基、卤素和硼酸基等官能团。这种结合作用在固体酸催化剂上的作用是将催化剂的酸性作用带给纤维素，从而增强固体酸-纤维素的相互作用。这种新型催化剂的两个功能分别模拟了纤维素水解酶(纤维素酶)的纤维素水解区和纤维素结合区。预计，固体酸的仿生功能化将显著改善其在纤维素降解中的性能。具体地说，双功能和纤维素酶模拟的固体酸将通过两步法制备。在第一步中，精选含有所需纤维素结合基团的芳香族单体(S)，通过傅克聚合法合成聚合物，这将导致具有多孔结构(较大比表面积)和纤维素结合基团的主链聚合物。在第二步中，将生成的聚合物磺化以引入磺酸作为纤维素水解基。将对所得到的纤维素酶模拟固体酸的性能进行评估。研究的重点是从根本上了解模拟纤维素酶的固体酸的结构性质(如比表面积、孔结构和官能团)与其在纤维素降解中的性能之间的关系。将特别关注纤维素酶模拟固体酸与纤维素之间的相互作用(亲和力、吸附或吸引力)，以及纤维素酸在纤维素水解过程中的机理和动力学。

The first step in converting lignocellulosic biomass resources to fuels using the carbohydrate/sugar platform is to form sugars from the cellulose in the biomass. However, efficiently producing sugars from biomass remains a significant challenge. Chemical conversion of the cellulose in the biomass uses enzymes (cellulases) and homogenous acids (e.g. sulfuric acid) to produce glucose, usually in a 2-step process. The required enzymes are currently expensive; and they need restrictive operating conditions (temperature and pH) and take longer time (days) to achieve satisfactory conversion of the cellulose. Homogenous acids have issues such as equipment corrosion, recycling, and wastewater treatment. This project aims to design a novel biomimetic polymeric solid acid catalyst that combines the functions served by the enzymes and inorganic acids currently used in sequence. By mimicking the cellulase/enzyme, the research project will involve fundamental research to design and fabricate bifunctional biomimetic solid acid catalysts for hydrolyzing cellulose to produce the required simple sugars. The integrated education plan of the project will target different levels of students, including high school, undergraduate, and graduate students. Special attention will be paid to high school students and undergraduate students from underrepresented groups in STEM (minorities and women). New concepts, research findings, acquired knowledge, and innovative technologies will be disseminated to academia, industry, students, and the Public through publications, presentations, and classroom teaching/learning. All these will directly and/or indirectly benefit research, production, education, and policy-making in the area of bioenergy and bioproducts.The research project will involve fundamental research of efficient, robust, and low-cost cellulase-mimetic solid acid catalysts for producing sugars from cellulose, one of the major components of biomass. The success of the project would promote the production of biofuels from biomass sugars. Using molecular and structural design, the solid acid catalysts will contain two types of functional groups. The first group, the acidic function, such as sulfonic acid, is responsible for hydrolyzing cellulose. The second group, the binding function, will use functional groups such as hydroxyl, carboxylic, halogen, and boronic acid groups. The role of this binding function on the solid acid catalyst is to bring the acidic function of the catalyst to cellulose to enhance the solid acid-cellulose interaction. The two functions of the new catalyst mimic the cellulose-hydrolytic domain and the cellulose-binding domain of cellulose-hydrolytic enzymes (cellulases), respectively. It is expected that the biomimetic functionalization of the solid acids would significantly improve their performance in cellulose hydrolysis. Specifically, the bifunctional and cellulase-mimetic solid acids will be fabricated via a two-step approach. In the first step, a polymer is synthesized from carefully selected aromatic monomer containing the desired cellulose-binding group(s) by Friedel-Crafts polymerization, which will lead to a backbone polymer with porous structure (larger surface area) and cellulose-binding groups. In the second step, the resultant polymer is sulfonated to introduce sulfonic acid as the cellulose-hydrolytic group. The performance of the resultant cellulase-mimetic solid acids in hydrolyzing cellulose will be evaluated. The research focus is to fundamentally understand the relationships between the structural properties (e.g., surface area, porous structure, and functional groups) of the cellulase-mimetic solid acids and their performance in cellulose hydrolysis. Special attention will be paid to the interactions (affinity, adsorption or attraction) between the cellulase-mimetic solid acids and cellulose and the mechanisms and kinetics of the solid acids in cellulose hydrolysis.