(534d) Plant Biopolymer Structure during Plant Cell Wall Deconstruction and Biopolymer Separations.

Non-food plants are an excellent renewable resource for production of biofuels and bioproducts. The plant cell wall is a complex hierarchical structure, consisting of multiple biopolymers arranged in an intricate organization. It is mainly composed of cellulose and hemicellulose as the main plant carbohydrates and lignin as the only phenolic hydrophobic polymer which functions as the barrier to the external elements. The complex structure of the plant cell wall has made it difficult to efficiently deconstruct the cell wall in a manner that allows to utilize all plant biopolymer components- cellulose and hemicellulose for biofuels and lignin for bioproducts. Plant carbohydrates are an excellent resource for biofuels, converted through thermochemical pretreatment followed by enzymatic hydrolysis to bioethanol. And, lignin biopolymer, obtained from mild processes are more suitable to use for synthesis and fabrication of bioproducts. The traditional approaches for biopolymer separation and extraction have been particularly designed to optimize cellulose and hemicellulose utilization for bioenergy at the cost of lignin, which is usually highly degraded. Therefore, understanding the plant cell wall organization is critical for selecting developing optimal approaches to deconstruct the plant cell wall and subsequent biopolymer separation methods.

Plant cell wall organization ranges over multiple length scales with structural elements most difficult to observe and understand in the nanometer scale. Small-angle neutron scattering (SANS) is a technique particularly suited to study hierarchical systems like the plant cell wall. Neutrons have excellent properties- highly penetrating, non-destructive and ability to modify contrast through hydrogen-deuterium replacement. The foremost property affords the use of bulky equipment in the beam like pressure cells to mimic thermochemical reactions and follow these reactions in real-time. Non-destructive property allows to monitor reaction studies that span several hours without the concern of structural deterioration by the probe (neutron beam). The ability to vary contrast allows to selectively highlight specific biopolymer structure of the complex in its native environment and process.

In this talk, I will present results of different kinds of reaction studies for deconstruction of plant cell wall: dilute acid (acidic), aqueous sodium hydroxide (basic), ionic liquid and co-solvents (acidic water/THF) as well as organic solvents (catalytic super-critical methanol) reactions required to breakdown plant biosystems. These reactions take several hours to complete and not ideally suited for synchrotron X-ray studies. A reaction pressure cell with a specification of 300 °C and 1 kbar was used for these studies. In-situ dilute acid pretreatment SANS studies showed for the first time a direct evidence of lignin aggregation during the pretreatment heating phase triggered just above the lignin glass transition temperature. Until then, the common knowledge was that lignin aggregation was triggered due to the quenching process necessary to retrieve samples for studies. This result highlighted the limitation of dilute acid pretreatment and the need for co-solvent based pretreatments. On similar lines, this presentation will cover new in-sights gained by these experiments that were not possible by the ex-situ based techniques highlighting the paradigm shift in the thinking of biotechnologists pursuing biomass deconstruction strategies for the production of bioenergy and bioproducts. Finally, I will discuss recent promising results of growing partially deuterated plants for introducing a neutron contrast between plant polymers- polysaccharides and lignin.