HMB体系分子内质子传递的量子化学计算研究

Quantum Chemistry Calculation Research on Hypomycin B's Intramolecular Proton Transfer on Ground State

首次利用量子化学半经验AM1方法和从头算HF/6 31G 方法对一种新型的醌类光敏剂 (PQP)———菌生素 (HMB)的结构及其分子内质子传递 (IPT)进行了理论计算研究 ,并采用逐步增加侧链的方法设计了一系列模型化合物以考虑各侧链对HMBIPT的影响 ,结果和醌 (PQ)的IPT作了对比 .由于HMB只有一个分子内氢键 ,此项研究对解释PQP的光敏活性有十分重要的意义 .本研究主要结论 :(1)基态时HMB的IPT势垒只有 2 0 .0 180kJ/mol(反式 )和 37.9819kJ/mol(顺式 ) ,分子中存在着快速的IPT .(2 )侧链对HMB的IPT势垒影响较小 ,IPT主要受它的大共轭结构和共振模式的影响 .(3)过渡态时质子的电荷增加 ,质子传递势垒与它的电荷变化成线性关系 ,此关系可推广到其它质子传递体系 .(4 )HMB的IPT势垒和IPT过程中羟基氧氢键以及氢键的键长变化均成较好的线性关系 .(5 )虽然只有一个IPT模式 ,HMB的IPT以及共振模式仍然和PQ十分相似 ,这是HMB保持光敏活性的基础 .

A study on the structure and intramolecular proton transfer (IPT) of hypomycin B (HMB), a novel type of perylenequinonoid photosensitizer (PQP), with semiempirical method AM1 and HF ab inito method,with 6-31G** basis sets has been performed for the first time in this paper, We designed nine model compounds to study the effect of the sidechain and made comparison with perylenequinonoid (PQ). The most important results are: (1) On the ground state, the barrier of HMB's IPT is only 20.0180 kJ/mol (for versa conformer) and 37.9819 kJ/mol (for parallel conformer), so the rate of LPT is fast. (2) The side-chain has a little influence on the barrier of HMB's IPT, and the IPT barrier is mostly determined by the conjugation structure or the resonance mode. (3) The charge of the proton transferred increases on it's transition state. The IPT's barrier is linear to the change of the atom's charge for most similar systems. (4) The barrier of HMB's IPT is linear to the change of the H-bond length or hydroxyl O-H bond length. (5) Comparing with PQ, with only one IPT mode, the IPT and the resonance mode of HMB is still similar to PQ, which is die basis of HMB's photosensitization.