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31.
The potential energy surface for the [CH5N]+˙ system has been investigated using ab initio molecular orbital calculations with large, polarization basis sets and incorporating valence-electron correlation. Two [CH5N]+˙ isomers can be distinguished: the well known methylamine radical cation, [CH3NH2]+˙, and the less familiar methylenammonium radical cation, [CH2NH3]+˙. The latter is calculated to lie 8 kJ mol?1 lower in energy. A substantial barrier (176 kJ mol?1) is predicted for rearrangement of [CH2NH3]+˙ to [CH3NH2]+˙. In addition, a large barrier (202 kJ mol?1) is found for loss of a hydrogen radical from [CH2NH3]+˙ via direct N—H bond cleavage to give the aminomethyl cation [CH2NH2]+. These results are consistent with the existence of the methylenammonium ion [CH2NH3]+˙ as a stable observable species. The barrier to loss of a hydrogen radical from [CH3NH2]+˙ is calculated to be 140 kJ mol?1. 相似文献
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Moumita Majumder Samuel E. Hegger Richard Dawes Sergei Manzhos Xiao-Gang Wang 《Molecular physics》2015,113(13-14):1823-1833
A data-set of nearly 100,000 symmetry unique multi-configurational ab initio points for methane were generated at the (AE)-MRCI-F12(Q)/CVQZ-F12 level, including energies beyond 30,000 cm?1 above the minimum and fit into potential energy surfaces (PESs) by several permutation invariant schemes. A multi-expansion interpolative fit combining interpolating moving least squares (IMLS) fitting and permutation invariant polynomials (PIP) was able to fit the complete data-set to a root-mean-square deviation of 1.0 cm?1 and thus was used to benchmark the other fitting methods. The other fitting methods include a single PIP expansion and two neural network (NN) based approaches, one of which combines NN with PIP. Full-dimensional variational vibrational calculations using a contracted-iterative method (and a Lanczos eigensolver) were used to assess the spectroscopic accuracy of the electronic structure method. The results show that the NN-based fitting approaches are able to fit the data-set remarkably accurately with the PIP–NN method producing levels in remarkably close agreement with the PIP–IMLS benchmark. The (AE)-MRCI-F12(Q)/CVQZ-F12 electronic structure method produces vibrational levels of near spectroscopic accuracy and a superb equilibrium geometry. The levels are systematically slightly too high, beginning at ~ 1–2 cm?1 above the fundamentals and becoming correspondingly higher for overtones. The PES is therefore suitable for small ab initio or empirical corrections and since it is based on a multi-reference method, can be extended to represent dynamically relevant dissociation channels. 相似文献
34.
Özge Pala Dirk J Vriens Jac AM Vennix 《The Journal of the Operational Research Society》2015,66(4):593-601
Escalation of commitment, the tendency of decision makers to keep on investing in losing courses of action, has been shown to be a costly decision bias that affects many areas of decision making. Even though escalation is a widely studied phenomenon, there has been comparatively little research on how to avoid this bias. The present study focuses on de-escalation of commitment and proposes that causal loop diagrams (CLDs) can help to decrease escalating commitment to a failing course of action. By means of an experiment, this study shows that using a CLD decreases escalation tendencies. 相似文献
35.
It is shown that neural networks (NNs) are efficient and effective tools for fitting potential energy surfaces. For H2O, a simple NN approach works very well. To fit surfaces for HOOH and H2CO, we develop a nested neural network technique in which we first fit an approximate NN potential and then use another NN to fit the difference of the true potential and the approximate potential. The root-mean-square error (RMSE) of the H2O surface is 1 cm(-1). For the 6-D HOOH and H2CO surfaces, the nested approach does almost as well attaining a RMSE of 2 cm(-1). The quality of the NN surfaces is verified by calculating vibrational spectra. For all three molecules, most of the low-lying levels are within 1 cm(-1) of the exact results. On the basis of these results, we propose that the nested NN approach be considered a method of choice for both simple potentials, for which it is relatively easy to guess a good fitting function, and complicated (e.g., double well) potentials for which it is much harder to deduce an appropriate fitting function. The number of fitting parameters is only moderately larger for the 6-D than for the 3-D potentials, and for all three molecules, decreasing the desired RMSE increases only slightly the number of required fitting parameters (nodes). NN methods, and in particular the nested approach we propose, should be good universal potential fitting tools. 相似文献
36.
Y. Kawaguchi M.L. Dawes S.C. Langford J.T. Dickinson 《Applied Physics A: Materials Science & Processing》1999,69(7):S621-S624
We have investigated KrF excimer-laser-induced positive ion desorption from single-crystal brushite (CaHPO4·2H2O), a model biomineral containing water, and we show the effect of heat treatment on ion desorption. Time-of-flight peaks of Ca+ desorption from the heated-cleaved surface are similar to those from as-cleaved ones, but the ion intensity is 2 to 4 orders of magnitude larger. In addition to Ca+, desorption of CaO+, PO+, and P+ from the heated surface is also strongly enhanced. The heated-cleaved surface shows rough, platelet-like fine structures due to recrystallization. Surface defects created during recrystallization strongly couple with the 5 eV photons and dramatically enhance ion desorption. 相似文献
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James D. Grayson Matthew P. Baumgartner Cleide Dos Santos Souza Samuel J. Dawes Imane Ghafir El Idrissi Jennifer C. Louth Sasha Stimpson Emma Mead Charlotte Dunbar Joanna Wolak Gary Sharman David Evans Anastasia Zhuravleva Margarita Segovia Roldan Nicola Antonio Colabufo Ke Ning Claire Garwood James A. Thomas Benjamin M. Partridge Antonio de la Vega de Leon Valerie J. Gillet Amlia P. Rauter Beining Chen 《Chemical science》2021,12(10):3768
Amyloid β oligomers (Aβo) are the main toxic species in Alzheimer''s disease, which have been targeted for single drug treatment with very little success. In this work we report a new approach for identifying functional Aβo binding compounds. A tailored library of 971 fluorine containing compounds was selected by a computational method, developed to generate molecular diversity. These compounds were screened for Aβo binding by a combined 19F and STD NMR technique. Six hits were evaluated in three parallel biochemical and functional assays. Two compounds disrupted Aβo binding to its receptor PrPC in HEK293 cells. They reduced the pFyn levels triggered by Aβo treatment in neuroprogenitor cells derived from human induced pluripotent stem cells (hiPSC). Inhibitory effects on pTau production in cortical neurons derived from hiPSC were also observed. These drug-like compounds connect three of the pillars in Alzheimer''s disease pathology, i.e. prion, Aβ and Tau, affecting three different pathways through specific binding to Aβo and are, indeed, promising candidates for further development.A new approach combining virtual screening, 19F and STD NMR, and biochemical assays using hiPSC and targetting multiple pathways involving Aβ, PrPC and Tau provides a more effective strategy for Alzheimer''s disease drug discovery than Aβ only approach. 相似文献
40.
García Ruano JL Gamboa AE Gutiérrez LG Martín Castro AM Rodríguez Ramos JH Yuste F 《Organic letters》2000,2(6):733-736
A new kind of chiral dienophiles, cyclic vinyl-p-tolylsulfilimines (2a and 2b), were obtained from the corresponding (Z)-sulfinylacrylonitriles with HBF(4) and methanol. The asymmetric Diels-Alder reaction of optically pure 2a with cyclopentadiene under mild thermal or catalyzed conditions afforded only the endo-4a adduct with complete endo and pi-facial selectivities. The ability of the sulfilimine moiety to enhance the dienophilic reactivity of the double bond is similar to that of the sulfinyl group. 相似文献