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 this EAGER 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 nonlinear optical response of a system without optical centrosymmetry when it is irradiated with high-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.
Intellectual merits: The key question involved in the 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, it still remains elusive. The difficulty in this study is that it requires molecular analysis of crystalline carbohydrate polymers (cellulose) in amorphous matrix containing the same organic functional groups. Current analytical methods cannot provide sufficient details about crystalline cellulose in lignocellulose biomass. In this EAGER project, we proposed to explore the application of sum-frequency generation (SFG) vibration spectroscopy to find the influence of cellulose crystal structure on enzymatic deconstruction process. SFG is a non-linear spectroscopy that can selectively detect crystalline cellulose microfibrils and their packing inside lignocellulosic biomass. XRD analyses of cellulose retrieved from enzymatic hydrolysis showed that cellulose polymorph (I-alpha and I-beta) and crystallinity in nanoscale did not change. However, SFG analyses found changes in packing or assembly of crystalline cellulose microfibrils in the sample. Broader impacts: Two graduate students and one undergraduate student were trained with SFG spectroscopy. The course outcome was discussed in graduate level materials characterization courses. The principles and application examples of XRD, NMR, IR, Raman, and SFG for cellulose characterization were taught to engineers. Scientists at National Renewable Energy Laboratory were involved in the project discussion. This led a collaborative project with them to study the effect of biomass pretreatment on enzymatic hydrolysis using SFG.
