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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >C_α?H Carries Information of a Hydrogen Bond Involving the Geminal Hydroxyl Group: A Case Study with a Hydrogen-Bonded Complex of 1,1,1,3,3,3-Hexafluoro-2-propanol and Tertiary Amines
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C_α?H Carries Information of a Hydrogen Bond Involving the Geminal Hydroxyl Group: A Case Study with a Hydrogen-Bonded Complex of 1,1,1,3,3,3-Hexafluoro-2-propanol and Tertiary Amines

机译：C_α？H携带涉及Gemmal羟基的氢键信息：以1,1,1,3,3,3-六氟-2-丙醇和叔胺的氢键复合物为例

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Experimental measurement of the contribution of H-bonding to intermolecular and intramolecular interactions that provide specificity to biological complex formation is an important aspect of macromolecular chemistry and structural biology. However, there are very few viable methods available to determine the energetic contribution of an individual hydrogen bond to binding and catalysis in biological systems. Therefore, the methods that use secondary deuterium isotope effects analyzed by NMR or equilibrium or kinetic isotope effect measurements are attractive ways to gain information on the H-bonding properties of an alcohol system, particularly in a biological environment. Here, we explore the anharmonic contribution to the C?H group when the O?H group of 1,1,1,3,3,3-hexafluoro-2-propanol (HFP) forms an intermolecular H-bond with the amines by quantum mechanical calculations and by experimentally measuring the H/D effect by NMR. Within the framework of density functional theory, ab initio calculations were carried out for HFP in its two different conformational states and their H-bonded complexes with tertiary amines to determine the ~(13)C chemical shielding, change in their vibrational equilibrium distances, and the deuterium isotope effect on ~(13)C2 (secondary carbon) of HFP upon formation of complexes with tertiary amines. When C2?OH was involved in hydrogen bond formation (O?H as hydrogen donor), it weakened the geminal C2?H bond; it was reflected in the NMR chemical shift, coupling constant, and the equilibrium distances of the C?H bond. The first derivative of nuclear shielding at C2 in HFP was ?48.94 and ?50.73 ppm ?~(-1) for anti and gauche conformations, respectively. In the complex, the values were ?50.28 and ?50.76 ppm ?~(?1), respectively. The C?H stretching frequency was lower than the free monomer, indicating enhanced anharmonicity in the C?H bond in the complex form. In chloroform, HFP formed a complex with the amine; δC2 was 69.107 ppm for HFP?triethylamine and 68.766 ppm for HFP-d2?triethylamine and the difference in chemical shift, the ΔδC2 was 341 ppb. The enhanced anharmonicity in the hydrogen-bonded complex resulted in a larger vibrational equilibrium distance in C?H/D bonds. An analysis with the Morse potential function indicated that the enhanced anharmonicity encountered in the bond was the origin of a larger isotope effect and the equilibrium distances. Change in vibrational equilibrium distance and the deuterium isotope effect, as observed in the complex, could be used as parameters in monitoring the strength of the H-bond in small model systems with promising application in biomacromolecules.
机译：H键对分子间和分子内相互作用的贡献的实验测量，其对生物复合物的形成提供特异性，是大分子化学和结构生物学的重要方面。但是，几乎没有可行的方法来确定单个氢键对生物系统中结合和催化的能量贡献。因此，使用通过NMR或平衡或动力学同位素效应测量分析得到的次级氘同位素效应的方法是吸引人的方法，尤其是在生物环境中，该方法可获取有关醇系统H键合性质的信息。在这里，我们探索当1,1,1,1,3,3,3-六氟-2-丙醇（HFP）的O？H基团与胺形成分子间H键时，对C？H基团的非谐贡献。量子力学计算以及通过NMR实验测量H / D效应。在密度泛函理论的框架内，对处于其两种不同构象状态的HFP及其与叔胺的H键复合物进行了从头算，以确定〜（13）C化学屏蔽，其振动平衡距离的变化以及与叔胺形成配合物时，氘同位素对HFP的〜（13）C2（仲碳）的影响。当C2？OH参与氢键的形成（O？H作为氢供体）时，它减弱了双键的C2？H键。它反映在NMR化学位移，偶合常数和C？H键的平衡距离上。对于HFP和Cauche构象，HFP中C2处的核屏蔽作用的一阶导数分别为？48.94和？50.73 ppm？〜（-1）。在该络合物中，该值分别为〜50.28ppm和〜50.76ppmδ〜（δ1）。 C 2 H的拉伸频率低于游离单体，表明在复合形式的C 2 H键中增强了非谐性。在氯仿中，HFP与胺形成络合物。 HFP→三乙胺的δC2为69.107ppm，HFP-d2→三乙胺的δC2为68.766ppm，化学位移之差ΔδC2为341ppb。氢键配合物中增强的非谐性导致C 2 H / D键的振动平衡距离更大。用摩尔斯电势函数进行的分析表明，键中遇到的增强的非谐性是较大的同位素效应和平衡距离的起源。如在复合物中观察到的，振动平衡距离的变化和氘同位素效应可作为监测小模型系统中氢键强度的参数，并有望在生物大分子中应用。

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