(437c) Investigating the Influence of Co-Solvents on Acid Catalyzed, Condensed Phase Biomass Reactions Using Molecular Dynamics and Metadynamics.

One of the challenges in catalytic, condensed phase biomass to chemicals conversion is the formation of humins. Solvent environment and the presence of co-solvents have shown to modify the kinetics and thermodynamics of biomass conversion reactions, and hence the formation of humins^1,2. The objective of this research is to investigate the role of the co-solvent in the presence of a Bronsted acid catalyst in inhibiting the formation of humins. The reaction chosen is the dehydration of fructose to HMF.

The simulation systems consisted on fructose/HMF in water-DMSO acid solutions. Five concentrations of DMSO from 0 to 80 % wt. were simulated at 1 % wt. of substrate concentration and 0.1 M of hydronium ion to simulate the acidic environment. Molecular dynamics simulations were performed to analyze the preferential configuration of hydronium ion, DMSO and water molecules solvating fructose/HMF. Additionally, well-tempered metadynamics simulations were performed to evaluate the relative stability the hydronium ion in bulk and near fructose/HMF, as a function of solvent composition.

Radial distribution functions (RDF) and 3-D probability distribution maps show that the interaction between hydronium ion and fructose is enhanced by increasing the concentration of DMSO. While for HMF systems, DMSO inhibits the interaction between HMF and hydronium ion. Free energy surfaces (FES) were reconstructed from the metadynamic simulations as function of coordination number of water & DMSO and that of the hydronium ion with the substrates. FES’s show that increasing DMSO concentration provides higher stability to the hydronium ion near fructose than in the bulk. Conversely, DMSO destabilizes the hydronium ion in the vicinity of HMF molecules, as compared to the bulk. This is the first research that quantitaively compares the relative stability of the hydronium ion in bulk and near the functional groups in fructose and HMF, as a function of solvent composition.

1.ChemSusChem,4,1166,2011.

2.JACS,26,5281,2012.