School of Chemistry, Seoul National University, NS60, Seoul 151-742, Korea.
Phys Chem Chem Phys. 2011 Mar 7;13(9):3730-6. doi: 10.1039/c0cp01977a. Epub 2010 Dec 20.
The ground-state proton transfer (GSPT) of 7-hydroxyquinoline along a hydrogen-bonded alcohol chain has been investigated in n-alkanes using time-resolved transient-absorption spectroscopy with variation of alcohols, media, isotopes, and temperatures. As a 7-hydroxyquinoline molecule associates with two alcohol molecules via hydrogen bonding to form a cyclic complex in a nonpolar aprotic medium, the intrinsic GSPT dynamics of the cyclic complex in a n-alkane has been observed directly without being interfered with by solvent association to form the cyclic complex. GSPT occurs concertedly without accumulating any reaction intermediate and yet asymmetrically with a rate-determining tunneling process. Both the rate constant and the kinetic isotope effect of GSPT increase rapidly with the proton-donating ability of the alcohol but decrease greatly with the molecular size of the alcohol. The reorganization of the hydrogen-bond bridge to form an optimal precursor configuration for efficient proton tunneling takes place prior to intrinsic GSPT, and configurational optimization becomes more important as the molecular size of the alcohol increases. Consequently, the larger contribution of configurational optimization to GSPT leads to the weaker asymmetric character of GSPT.
使用时间分辨瞬态吸收光谱法，研究了氢键醇链上 7-羟基喹啉的基态质子转移（GSPT），考察了醇、介质、同位素和温度的变化。由于 7-羟基喹啉分子通过氢键与两个醇分子结合，在非极性非质子介质中形成环状络合物，因此可以直接观察到 n-烷烃中环状络合物的固有 GSPT 动力学，而不会受到溶剂缔合形成环状络合物的干扰。GSPT 协同发生，没有积累任何反应中间体，但却是不对称的，具有速率决定的隧道过程。GSPT 的速率常数和动力学同位素效应都随着醇的供质子能力迅速增加，但随着醇的分子尺寸的增加而大大降低。形成有效质子隧穿的最佳前体构型的氢键桥的重组发生在固有 GSPT 之前，随着醇分子尺寸的增加，构象优化变得更加重要。因此，构象优化对 GSPT 的贡献越大，GSPT 的不对称性就越弱。
