(350f) Understanding Solvation Effects On Biomass Derived Platform Chemicals: A Combined Spectroscopic and Theoretical Approach
Understanding solvation effects on biomass derived platform chemicals: A combined spectroscopic and theoretical approach
G. Tsilomelekis, C. Bagia, T.R. Josephson, S. Caratzoulas, V. Nikolakis, D.G. Vlachos
Catalysis Center for Energy Innovation & Department of Chemical and Biomolecular Engineering, University of Delaware, Newark, DE 19716
The dehydration of carbohydrates, and especially fructose to 5- hydroxymethylfurfural (HMF), has attracted increasing interest since HMF is considered as a “top value-added chemical” because it can be transformed to non-petroleum based building blocks for chemicals and fuels [1,2]. Even though it is well established that the HMF selectivity of fructose dehydration reactions can be significantly affected by using organic co-solvents or by carrying out the reaction in organic solvents or in ionic liquids, the reasons behind these observations remain elusive[3,4]. Furthermore, studies correlating the effect of different solvents in HMF molecular structure in solution with HMF stability are lacking.
With the ultimate goal to unravel structure-activity relationships using insights from solvation, the present work focuses on the understanding the structural as well as the vibrational properties of dissolved HMF in DMSO-D2O mixtures in a wide range of binary and ternary compositions by employing ATR/FTIR spectroscopy and ab-initio DFT calculations. Solvent effects, such as the formation of hydrogen bonds (HBs), are investigated by probing both HMF as well as DMSO and D2O vibrational modes of specific functional groups under different conditions. The HMF conformational equilibrium is considered too, for the first time. HMF rehydration experiments are also carried out starting with HMF/DMSO/D2O ternary mixtures of different compositions.
The analysis of the HMF ATR/IR spectra focused mainly on the change of the vibrational behavior of HMF functional groups, C=O and OH, located at ~1670 and ~3300-3450 cm-1 respectively. The position, the width as well as the shape of the bands are analysed by exploring all the plausible reasons such, vibrational coupling, formation of hydrogen bonds and –cis/-trans HMF conformational equilibrium. The latter is also studied for the first time using ab-initio calculations. Calculations indicate that the trans-HMF is the more stable conformer. The predicted IR spectra are in very good agreement with our experiments. The effect of solvent composition on the C=O and OH vibrational modes of HMF, reveals significant differences which are ascribed to intermolecular interactions between HMF and DMSO or/and water. The C=O stretching vibration appears clearly in higher frequency in the case of HMF/DMSO mixtures than in HMF/water. In contrary, the OH stretching vibration of HMF appears in lower wavenumbers in DMSO compared to water, indicating that the hydrogen bonds between the H of the HMF OH and the oxygen of DMSO to be stronger. The experimental observations are confirmed with our ab-initio calculations. In the case of HMF/DMSO/D2O ternary mixtures, the addition of D2O molecules around HMF seems to affect significantly the frequency of the HMF OH group while, the C=O stretching band is affected only when the D2O molar fraction is higher than 0.3. More specifically, as the D2O content increases a shift to lower wavenumbers is observed. This effect is ascribed to a perturbation in bond length (elongation) and strength (weakening) of the C=O band caused by the formation of C=O…D hydrogen bonds between HMF and D2O molecules. The implications of spectroscopic analysis for solvent selection and improved biomass processes will also be discussed.
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