期刊
CHEMISTRY-A EUROPEAN JOURNAL
卷 18, 期 30, 页码 9405-9414出版社
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.201200443
关键词
computational chemistry; isotope effects; molecular dynamics; solvent effects; transition states
资金
- EPSRC [EP/E019455/1]
- Juan de la Cierva subprogramme of the Spanish Ministry of Science
- General Secretariat of the Spanish Ministry for Education [SAB2010-0116]
- Engineering and Physical Sciences Research Council [EP/E019455/1] Funding Source: researchfish
- EPSRC [EP/E019455/1] Funding Source: UKRI
The existence of solvent fluctuations leads to populations of reactant-state (RS) and transition-state (TS) configurations and implies that property calculations must include appropriate averaging over distributions of values for individual configurations. Average kinetic isotope effects < KIE > for NC-+EtCl -> NCEt+Cl- in DMSO solution at 30 degrees C are best obtained as the ratio < f(RS)>/< f(TS)> of isotopic partition function ratios separately averaged over all RS and TS configurations. In this way the hybrid AM1/OPLS-AA potential yields < KIE > values for all six isotopic substitutions (2 degrees alpha-H-2(2), 2 degrees beta-H-2(3), alpha-C-11/C-14, leaving group Cl-37, and nucleophile C-13 and N-15) for this reaction in the correct direction as measured experimentally. These thermally-averaged calculated KIEs may be compared meaningfully with experiment, and only one of them differs in magnitude from the experimental value by more than one standard deviation from the mean. This success contrasts with previous KIE calculations based upon traditional methods without averaging. The isotopic partition function ratios are best evaluated using all (internal) vibrational and (external) librational frequencies obtained from Hessians determined for subsets of atoms, relaxed to local minima or saddle points, within frozen solvent environments of structures sampled along molecular dynamics trajectories for RS and TS. The current method may perfectly well be implemented with other QM or QM/MM methods, and thus provides a useful tool for investigating KIEs in relation to studies of chemical reaction mechanisms in solution or catalyzed by enzymes.
作者
我是这篇论文的作者
点击您的名字以认领此论文并将其添加到您的个人资料中。
推荐
暂无数据