Michael W. Nolte

Sodium Ion Interactions with Aqueous Glucose: Insights from Quantum Mechanics, Molecular Dynamics, and Experiment

In the last several decades, significant efforts have been conducted to understand the fundamental reactivity of glucose derived from plant biomass in various chemical environments for conversion to renewable fuels and chemicals. For reactions of glucose in water, it is known that inorganic salts naturally present in biomass alter the product distribution in various deconstruction processes. However, the molecular-level interactions of alkali metal ions and glucose are unknown. These interactions are of physiological interest as well, for example, as they relate to cation-glucose cotransport. Here, we employ quantum mechanics (QM) to understand the interaction of a prevalent alkali metal, sodium, with glucose from a structural and thermodynamic perspective. The effect on β-glucose is subtle: a sodium ion perturbs bond lengths and atomic partial charges less than rotating a hydroxymethyl group. In contrast, the presence of a sodium ion significantly perturbs the partial charges of α-glucose anomeric and ring oxygens. Molecular dynamics (MD) simulations provide dynamic sampling in explicit water, and both the QM and the MD results show that sodium ions associate at many positions with respect to glucose with reasonably equivalent propensity. This promiscuous binding nature of Na(+) suggests that computational studies of glucose reactions in the presence of inorganic salts need to ensure thorough sampling of the cation positions, in addition to sampling glucose rotamers. The effect of NaCl on the relative populations of the anomers is experimentally quantified with light polarimetry. These results support the computational findings that Na(+) interacts similarly with α- and β-glucose.

Hydrodeoxygenation of cellulose pyrolysis model compounds using molybdenum oxide and low pressure hydrogen

A molybdenum oxide catalyst in a low pressure hydrogen atmosphere was used for the hydrodeoxygenation (HDO) of pulsed injections of cellulose pyrolysis model compounds to examine reaction products. Higher catalyst loadings (≥20 : 1 catalyst : cellulose injection) in the HDO reactor were found to preferentially produce alkanes, while at lower loadings (≤10 : 1 catalyst : cellulose injection) alkene selectivity was increased. However, as the amount of catalyst was decreased, the pyrolysis vapors were not completely deoxygenated. The HDO of monofunctional oxygenated C4 compounds found hydroxyl groups to be the most readily reacted and ether linkages to be the most recalcitrant. In general, the reactivity towards deoxygenation of the tested oxygen-containing functional groups was observed to be C–OH > CO > C–OC. Several cellulose pyrolysis model compounds were also tested, including methyl glyoxal, glycolaldehyde, furfural, 5-hydroxymethylfurfural, and levoglucosan, and found the same general trend to occur, except for levoglucosan, which was totally reacted and did not yield any oxygenated low molecular weight compounds despite containing two ether linkages. Across the compounds, the general reaction pathway was observed to include carbonyl/alcohol hydrogenation/dehydrogenation, deoxygenation, and alkene isomerization and hydrogenation.