Hydrogen-Binding-Initiated Activation of O-H Bonds on a Nitrogen-Doped Surface for the Catalytic Oxidation of Biomass Hydroxyl Compounds.

Hydrogen binding of molecules on solid surfaces is an attractive interaction that can be used as the driving force for bond activation, material-directed assembly, protein protection, etc. However, the lack of a quantitative characterization method for hydrogen bonds (HBs) on surfaces seriously limits its application. We measured the standard Gibbs free energy change (ΔG0 ) of on-surface HBs using NMR. The HB-accepting ability of the surface was investigated by comparing ΔG0 values employing the model biomass platform 5-hydroxymethylfurfural on a series of Co-N-C-n catalysts with adjustable electron-rich nitrogen-doped contents. Decreasing ΔG0 improves the HB-accepting ability of the nitrogen-doped surface and promotes the selectively initiated activation of O-H bonds in the oxidation of 5-hydroxymethylfurfural. As a result, the reaction kinetics is accelerated. In addition to the excellent catalytic performance, the turnover frequency (TOF) for this oxidation is much higher than for reported non-noble-metal catalysts.

Binding Energy as Driving Force for Controllable Reconstruction of Hydrogen Bonds with Molecular Scissors.

Hydrogen bonds are one of the most important directional intermolecular interactions and play key roles in chemical and biochemical systems, but there is still a lack of prediction and understanding of their control. Herein, hydrogen-binding energy (EHB) acted as a driving force for controllably reconstructing hydrogen bonds with molecular scissors. We related hydrogen-binding energies of the donor-acceptor couple (EHB,2) and the donor itself (EHB,1) and ΔG based on ΔG = a1EHB,1 + a2EHB,2 + a3. When EHB,1 and EHB,2 satisfy the condition ΔG < 0, the acceptor is predicted as molecular scissors with sufficient reconstruction capacity in breaking the initial hydrogen bonds and forming new ones. Remarkably, we developed an experimental method to determine the EHB values by a linear equation as a function of chemical shifts (δ) ([Formula: see text]), which is innovational since in the former research EHB can only be deduced from empirical formulas and DFT calculation. On that basis, the hydrogen bonds of α-cellulose were broken and re-formed in molecular scissors-consisting deep eutectic solvents, leading to the white powder transforming into a hydrogel and colorless and transparent thin film materials with distinct crystalline structure, surface flatness, and morphology.

Understanding and Measurement for the Binding Energy of Hydrogen bonds of Biomass-Derived Hydroxyl Compounds.

Experimental measurement for the binding energy of hydrogen-bonds (HBs) has long been an attractive and challenging topic in chemistry and biochemistry. In the present study, the binding energy of OH···O HBs can be determined by 1H NMR technique using a set of model biomass-derived hydroxyl compounds, including furfuryl alcohol, isosorbide, tetrahydrofurfuryl alcohol, and (S)-3-hydroxytetrahydrofuran. By performing concentration- and temperature-variation experiments, we put forward a modified Arrhenius-type equation, in which the compensated natural logarithm of the chemical shift (ln δ + Δδ) is linearly correlated with 1/T. HBs energies can be directly determined by the slope of the plot, and are substantiated by density functional theory (DFT) theoretical calculations. This study provides a reliable method to measure the binding energy of OH···O HBs in hydroxyl-containing biomass-derived feedstocks.

Hydrogen bond distinction and activation upon catalytic etherification of hydroxyl compounds.

An excellent linear correlation between ln δ (OH chemical shift) and 1/T (temperature) is discovered for the first time for hydroxyl compounds. The derived slope (A) provides information as an index not only for distinguishing different types of H-bonds, but also for predicting their reactivities. This finding can be extended to other H-bond-containing molecules.

Catalytic selective etherification of hydroxyl groups in 5-hydroxymethylfurfural over H4SiW12O40/MCM-41 nanospheres for liquid fuel production.

5-Hydroxymethylfurfural (HMF) is an important biomass-derived building block, but production and sustainable utilization of HMF remain challenging due to reactions of the highly reactive functional groups of this compound. H(4)SiW(12)O(40)/MCM-41 nanospheres were developed that exhibit 84.1% selectivity to 5-ethoxymethylfurfural (EMF) when HMF conversion reaches 92.0%, during etherification of 5-hydroxymethylfurfural (HMF) with ethanol under mild conditions. The catalyst could be reused, and its activity remained unaffected over five cycles. The strong acidity of the catalyst significantly enhanced etherification. The acetalized byproducts, 5-(diethoxymethyl)-2-furanmethanol and the HMF-dimer (5,5'(oxy-bis(methylene))bis-2-furfural), can be converted into HMF and then transformed to the main product, EMF, by using this catalyst to shift the reaction equilibrium.