Xu Xin, Goddard William A
Materials and Process Simulation Center, Beckman Institute (MC 139-74), California Institute of Technology, Pasadena 91125, USA.
Proc Natl Acad Sci U S A. 2002 Nov 26;99(24):15308-12. doi: 10.1073/pnas.202596799. Epub 2002 Nov 18.
The recent observation [Wentworth, P., Jones, L. H., Wentworth, A. D., Zhu, X. Y., Larsen, N. A., Wilson, I. A., Xu, X., Goddard, W. A., Janda, K. D., Eschenmoser, A. & Lerner, R. A. (2001) Science 293, 1806-1811] that antibodies form H(2)O(2) from (1)O(2) plus H(2)O was explained in terms of the formation of the H(2)O(3) species that in the antibody reacts with a second H(2)O(3) to form H(2)O(2). There have been few reports of the chemistry for forming H(2)O(3), but recently Engdahl and Nelander [Engdahl, A. & Nelander, B. (2002) Science 295, 482-483] reported that photolysis of the ozone-hydrogen peroxide complex in argon matrices leads to significant concentrations of H(2)O(3). We report here the chemical mechanism for this process, determined by using first-principles quantum mechanics. We show that in an argon matrix it is favorable (3.5 kcal/mol barrier) for H(2)O(2) and O(3) to form a [(HO(2))(HO(3))] hydrogen-bonded complex [head-to-tail seven-membered ring (7r)]. In this complex, the barrier for forming H(2)O(3) plus (3)O(2) is only 4.8 kcal/mol, which should be observable by means of thermal processes (not yet reported). Irradiation of the [(HO(2))(HO(3))-7r] complex should break the HO-OO bond of the HO(3) moiety, eliminating (3)O(2) and leading to [(HO(2))(HO)]. This [(HO(2))(HO)] confined in the matrix cage is expected to rearrange to also form H(2)O(3) (observed experimentally). We show that these two processes can be distinguished isotopically. These results (including the predicted vibrational frequencies) suggest strategies for synthesizing H(2)O(3) and characterizing its chemistry. We suggest that the [(HO(2))(HO(3))-7r] complex and H(2)O(3) are involved in biological, atmospheric, and environmental oxidative processes.
最近的观察结果[温特沃思，P.，琼斯，L. H.，温特沃思，A. D.，朱，X. Y.，拉森，N. A.，威尔逊，I. A.，徐，X.，戈达德，W. A.，詹达，K. D.，埃申莫泽，A. & 勒纳，R. A.（2001年）《科学》293，1806 - 1811]表明抗体能使单线态氧（¹O₂）和水生成过氧化氢（H₂O₂），这一现象可通过过氧化氢根（H₂O₃）物种的形成来解释，即在抗体中，一个H₂O₃与另一个H₂O₃反应生成H₂O₂。关于生成H₂O₃的化学过程报道较少，但最近恩达尔和内兰德[恩达尔，A. & 内兰德，B.（2002年）《科学》295，482 - 483]报道在氩气基质中臭氧 - 过氧化氢复合物的光解会产生显著浓度的H₂O₃。我们在此报告通过第一性原理量子力学确定的该过程的化学机制。我们表明在氩气基质中，过氧化氢（H₂O₂）和臭氧（O₃）形成[（HO₂）（HO₃）]氢键复合物[头对尾七元环（7r）]是有利的（势垒为3.5千卡/摩尔）。在这个复合物中，生成H₂O₃和三线态氧（³O₂）的势垒仅为4.8千卡/摩尔，这应该可以通过热过程观察到（尚未报道）。对[（HO₂）（HO₃） - 7r]复合物进行辐照应会断裂HO₃部分的HO - OO键，消除³O₂并生成[（HO₂）（HO）]。预计被困在基质笼中的[（HO₂）（HO）]也会重排形成H₂O₃（实验已观察到）。我们表明这两个过程可以通过同位素进行区分。这些结果（包括预测的振动频率）为合成H₂O₃及其化学性质的表征提供了策略。我们认为[（HO₂）（HO₃） - 7r]复合物和H₂O₃参与了生物、大气和环境中的氧化过程。
