Computational and Experimental Studies of Cellulose Degradation for the Production of Biofuels

从植物等生物质中提取的纤维素为生产生物燃料乙醇提供了一种有吸引力的可再生原料。天然存在的纤维素是一种长链聚合物分子，主要以半结晶形式存在。在纤维素酶解生产乙醇的过程中，聚合纤维素分子在第一阶段被分解成较短的片段。这些片段在酶的作用下进一步分解成更短的片段，形成双糖纤维素二糖，最后形成单糖葡萄糖；这些糖分子发酵产生乙醇。在初始阶段形成的短纤维素碎片被认为附着在结晶纤维素的表面，并且假设这种现象减慢了酶解过程的总体速度。本提案的目的是确定纤维素碎片从纤维素晶体表面分离过程的能量学。从长远来看，本研究获得的基本认识将有助于提高纤维素酶解的速度，从而提高纤维素乙醇生产的速度。拟议的工作将包括一种方法，将分子模拟研究与使用原子力显微镜（AFM）进行的实验相结合。分子模拟解释了详细的化学相互作用以及系统的特定分子结构。这些模拟将用于表征纤维素低聚物碎片从纤维素晶体表面分离的过程的分子途径以及该过程所需的能量。模拟结果将通过AFM测量从纤维素表面分离纤维素碎片所需的力来验证。纤维素低聚物从纤维素晶体表面分离的详细机理将在这项工作中得到发展。如果成功，在提议的工作中获得的基础知识将导致提高纤维素生物质酶水解率的新策略，从而提高从纤维素中经济生产乙醇的能力。这将对消除目前日益增长的对化石燃料的依赖产生重大影响。提议的工作将涉及界面热力学、有机化学和替代能源领域的多学科研究。参与该项目的研究生将接受分子模拟、原子力显微镜测量和化学合成技术的跨学科培训。

CBET-0854463KhareCellulose that is derived from biomass such as plant material provides an attractive renewable feedstock for the production of the biofuel ethanol. The naturally occurring cellulose is a long chain polymeric molecule that is predominantly in semi-crystalline form. In the process of enzymatic hydrolysis of cellulose for the production of ethanol, the polymeric cellulose molecule is broken down into shorter fragments in the first stage. These fragments are further broken down by the action of enzymes to even shorter fragments leading to the disaccharide cellobiose and finally to the monosaccharide glucose; fermentation of these sugar molecules yields ethanol. The short fragments of cellulose that are formed in the initial stage have been suggested to be attached to the surface of the crystalline cellulose and it is hypothesized that this phenomenon slows down the overall rate of enzymatic hydrolysis process. The objective of this proposal is to determine the energetics of the process of separation of such cellulose fragments from the cellulose crystal surface. The fundamental understanding gained in this study will be useful in the long term for increasing the rate of enzymatic hydrolysis of cellulose and thus increasing the rate of ethanol production from cellulose. The proposed work will consist of an approach that will combine molecular simulation studies with experiments performed using atomic force microscopy (AFM). Molecular simulations account for the detailed chemical interactions as well as the specific molecular structure of the system. These simulations will be used to characterize the molecular pathway of the process of separating the cello-oligomer fragments from the surface of a cellulose crystal and the energy required for this process. The simulation results will be validated against AFM measurements of the force required for separating cellulose fragments from the cellulose surface. A detailed mechanistic understanding of the process of cello-oligomer separation from a cellulose crystal surface will be developed in this work. If successful, the fundamental knowledge gained in the proposed work will lead to new strategies for increasing the rate of enzyme hydrolysis of cellulosic biomass and hence the ability for economical production of ethanol from cellulose. This will have significant implications on removing the current, ever increasing dependence on fossil fuels. The proposed work will involve multidisciplinary research in the areas of interfacial thermodynamics, organic chemistry and alternate energy sources. The graduate students working on the project will receive interdisciplinary training in the techniques of molecular simulations, AFM measurements and chemical synthesis.