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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Hydrogen-bonding interactions in cinchonidine-2-methyl-2-hexenoic acid complexes: A combined spectroscopic and theoretical study
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Hydrogen-bonding interactions in cinchonidine-2-methyl-2-hexenoic acid complexes: A combined spectroscopic and theoretical study

机译：辛可尼定-2-甲基-2-己酸复合物中的氢键相互作用：光谱学和理论研究相结合

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摘要

Molecular interactions between cinchonidine (CD) and 2-methyl-2-hexenoic acid (MHA) have been studied by means of NMR, ATR-IR MES, DFT, and ab initio molecular dynamics. These interactions are of particular interest due to their pivotal role in the chiral induction occurring in the heterogeneous catalytic asymmetric hydrogenation of alpha,beta-unsaturated acids. The population density of the Open(3) conformer of CD, the most populated one at room temperature in apolar solvents, considerably increased to a maximum by addition of MHA to CD in toluene. The CD-MHA complex showed prominent symmetric and asymmetric carboxylate stretching vibrations in the regions of 1350-1410 and 1520-1580 cm(-1), respectively. DFT calculations revealed that these vibrational frequencies are expected to significantly shift depending on the chemical surrounding of MHA, that is, the hydrogen bond network. Earlier postulated 1:1 binding between CD and MHA was considered unlikely; instead, a dynamic equilibrium involving, the MHA monomer and dimer, the 1:3 and possibly 1:2 CD-MHA complexes, were rationalized. Stable CD-MHA structures suggested by DFT calculations are the 1:3, halfN, cyclic" and the "13, halfN, cyclic tilted" complexes, where three MHA molecules are connected in wire by hydrogen bonding, two having direct interaction with CD. The confinement of CD's torsional motions in the complexes, leading to a slightly distorted Open(3) conformer via specific hydrogen-bonding interactions, was clearly reproduced by ab initio molecular dynamics, and the stable and flexible nature of the interaction was verified. Theoretical IR spectra of the complexes reproduced the characteristic vibrational frequencies of the complexes observed experimentally, supporting the stability of the 1:3 and implying the possibility of even higher molecular weight CD-MHA complexes.
机译：辛可尼定（CD）和2-甲基-2-己酸（MHA）之间的分子相互作用已通过NMR，ATR-IR MES，DFT和从头算分子动力学的方法进行了研究。由于它们在α，β-不饱和酸的非均相催化不对称氢化中发生的手性诱导中起关键作用，因此这些相互作用特别受关注。 CD的Open（3）构象异构体的人口密度是室温下在非极性溶剂中密度最高的种群，通过将MHA添加到甲苯中的CD中，其人口密度大大增加到最大值。 CD-MHA复合物分别在1350-1410和1520-1580 cm（-1）的区域中显示出明显的对称和不对称的羧酸盐拉伸振动。 DFT计算表明，根据MHA的化学环境，即氢键网络，预期这些振动频率会发生显着变化。早先假定CD和MHA之间没有1：1的结合;相反，合理的动态平衡涉及MHA单体和二聚体，1：3和可能的1：2 CD-MHA配合物。 DFT计算表明，稳定的CD-MHA结构是1：3，半N环状”和“ 13，N环状倾斜”复合物，其中三个MHA分子通过氢键连接成线，两个分子直接与CD相互作用。 CD扭转运动在复合物中的局限性，通过特定的氢键相互作用导致Open（3）构象异构体轻微扭曲，从头算分子动力学就清楚地再现了这种相互作用，并验证了相互作用的稳定和灵活。配合物的光谱再现了实验观察到的配合物的特征振动频率，支持了1：3的稳定性并暗示了更高分子量CD-MHA配合物的可能性。

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