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

Abstract

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 B-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 a-and B-glucose. ABSTRACT: 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 g...

Fast pyrolysis of glucose‐based carbohydrates with added NaCl part 1: Experiments and development of a mechanistic model

“…30 Moreover, Patwardhan et al, 11 and other researchers 40,41 reported that the cations had a much greater effect on the product distribution of fast pyrolysis of cellulose than the anions did. With NaCl present in fast pyrolysis of glucose-based carbohydrates at 500 8C in this study, chloride would be efficiently volatilized while sodium would stay in the melt phase, based on the experimental findings from the literature.…”

“…14,21,22 Furthermore, Na 1 would be likely to bind with oxygen atoms in the reactive species. 26,[28][29][30] In this work, Na 1 ions were assumed to be able to bind with all the neutral species including polymeric chains and LMW species and form Na 1 -complex species (Na 1 -complexes). Once these complexes are formed, they can undergo the same reactions as their neutral counterparts, but with different kinetics.…”

“…17,26,27 It has been postulated that sodium in the melt phase probably exists as ions bound to oxygen functionalities within the organic matrix during fast pyrolysis of biomass or cellulose. 26,[28][29][30] Experimental work of Wu and coworkers on investigating reaction intermediates during fast pyrolysis of NaCl-loaded cellulose suggested that Na 1 interacted with ring oxygen atoms and catalyzed ring-opening, dehydration, decarboxylation and decarbonylation reactions, and hence, the destruction of sugar ring structures in cellulose pyrolysis was greatly promoted. 28 Yu et al 28 also concluded that char formation was favored by the addition of NaCl in two ways.…”

The Alpha–Bet(a) of Salty Glucose Pyrolysis: Computational Investigations Reveal Carbohydrate Pyrolysis Catalytic Action by Sodium Ions

“…20,56,57 Several previous studies have found that the cation of an inorganic salt such as NaCl interacts more closely with carbohydrates than do anions such as Cl − , 47,58,59 justifying continued focus on the effects of the cation on carbohydrate pyrolysis reactions. Our previous simulation work indicates that cations directly interact with the nucleophilic oxygens, 58 which are central in the dominant reactions in carbohydrate pyrolysis, dehydration, and isomerization. [23][24][25]29,30 In contrast, the counterion, Cl − , was preferably located farther from the carbohydrate reaction centers, interacting instead with the partially positively charged hydrogen atoms.…”

Dependence of enthalpic pairwise self-interactions on ionic strength: Some 2-deoxy and N-acetyl monosaccharides in aqueous NaCl solutions at T=298.15K

“…Apart from its theoretical importance, the study is of biological or physiological interests as well, for example, its possible relation to cation-monosaccharide co-transport [45,46].…”