Department of Chemistry, University of Calcutta, 92 A. P. C. Road, Kolkata 700009, India.
J Phys Chem A. 2010 Feb 25;114(7):2618-27. doi: 10.1021/jp909029c.
Study of intra- and intermolecular hydrogen-bonding interaction and excited state proton transfer reaction has been carried out in 4-hydroxyacridine (4-HA) and its hydrated clusters theoretically. Density functional theory [B3LYP/6-311++G(d,p)] has been exploited to calculate structural parameters and relative energies of different conformers of 4-HA and its hydrates. The substantial impact of solvent reaction field on hydrogen-bond energies, conformational equilibrium, and tautomerization reaction in aqueous medium have been realized by employing Onsager and PCM reaction field methods, and the stability of the conformers of 4-HA is found to be profusely modulated by the electrostatic influence of the solvent. A deeper insight into the nature of H-bonding in 4-HA and its hydrated clusters has been achieved under the provision of natural bond orbital and atoms in molecule analysis. Elucidation of potential energy curves for proton transfer reaction reveals that an intrinsic and two-water-molecule-assisted proton transfer (PT) reaction in 4-HA is hindered by high energy barrier in the S(1) surface, whereas single-water-assisted PT reaction is practically rendered barrierless. At the same time, the appreciably high barrier height of the ground state potential energy curve in all the cases unambiguously rules out the possibility of ground state proton transfer reaction.
本研究采用理论计算的方法，对 4-羟基吖啶（4-HA）及其水合团簇的分子内和分子间氢键相互作用以及激发态质子转移反应进行了研究。利用密度泛函理论（B3LYP/6-311++G(d,p)）计算了 4-HA 及其水合物不同构象的结构参数和相对能量。采用 Onsager 和 PCM 反应场方法，研究了溶剂反应场对氢键能、构象平衡和水介质中互变异构反应的重要影响，结果表明，溶剂的静电影响极大地调节了 4-HA 构象的稳定性。通过自然键轨道和原子分子分析，深入了解了 4-HA 及其水合团簇中氢键的性质。质子转移反应势能曲线的阐明表明，在 S(1)表面，4-HA 中存在固有和两个水分子辅助的质子转移（PT）反应，其能垒较高，而单水分子辅助的 PT 反应实际上是无势垒的。同时，所有情况下基态势能曲线的显著高势垒高度，明确排除了基态质子转移反应的可能性。
