2-Pyrones have been identified as potential platform molecules derived from biomass to produce high-value chemicals. Theoretical studies utilizing density functional theory (DFT) simulations have shown the partially saturated form of these molecules undergoing a retro Diels–Alder (rDA) reaction in both vapor and solvent conditions. Developing an understanding of the effect of solvent media is crucial to improve the processing of these biomass-derived compounds. In this context, DFT simulations had shown limited access due to either implicit solvent or static explicit solvent environment applied in the model, which did not account for the contribution from the dynamics. Herein, Car–Parrinello molecular dynamics (CPMD) simulations, in conjunction with metadynamics, were performed to understand the effect of dynamics of the solvent on the rDA reaction of partially saturated 2-pyrones. For this, compounds containing both electron-donating and -withdrawing groups as substituent were studied. It was observed that, in the vapor phase, the results from CPMD simulations were in agreement with our previous DFT results. However, in water, a relative lowering in calculated activation barriers (by ∼10 kJ/mol) was observed, due to the dynamic behavior of solvent, differentially interacting with the reactant and the activated complex, along the minimum energy path. For hydroxyl substituted 2-pyrones, computed activation free energy of 63 ± 7 kJ/mol was in agreement with the apparent activation energy measured experimentally (42 ± 18 kJ/mol). CPMD-metadynamics simulations were further applied to study the reaction energetics of complex 2-pyrone molecule undergoing a similar rDA reaction.

中文翻译：

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水中部分饱和2-吡喃酮的逆Diels-Alder反应的Car-Parrinello分子动力学模拟

2-吡喃酮已被确定为源自生物质的潜在平台分子，可产生高价值的化学物质。利用密度泛函理论（DFT）模拟进行的理论研究表明，这些分子的部分饱和形式在蒸汽和溶剂条件下都经历了逆Diels-Alder（rDA）反应。了解溶剂介质的作用对于改善这些生物质衍生化合物的加工至关重要。在这种情况下，DFT仿真显示由于模型中应用了隐式溶剂或静态显式溶剂环境而导致访问受限，这没有考虑动力学的影响。在此，Car-Parrinello分子动力学（CPMD）模拟与元动力学相结合，进行了研究以了解溶剂动力学对部分饱和的2-吡喃酮的rDA反应的影响。为此，研究了同时具有供电子基团和吸电子基团作为取代基的化合物。据观察，在气相中，CPMD模拟的结果与我们以前的DFT结果一致。然而，在水中，由于溶剂的动态行为，沿着最小的能量路径与反应物和活化的络合物发生不同的相互作用，观察到计算的活化势垒相对降低（约10 kJ / mol）。对于羟基取代的2-吡喃酮，计算的63±7 kJ / mol的活化自由能与实验测得的表观活化能（42±18 kJ / mol）一致。