Structures in Solutions from Joint Experimental-Computational Analysis: Applications to Cyclic Molecules and Studies of Noncovalent Interactions

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• 作者：Abil E. Aliev ; Zakirin A. Mia ; Harmeet S. Khaneja ; Frank D. King
• 刊名：The Journal of Physical Chemistry A
• 出版年：2012
• 出版时间：January 26, 2012
• 年：2012
• 卷：116
• 期：3
• 页码：1093-1109
• 全文大小：1220K
• 年卷期：v.116,no.3(January 26, 2012)
• ISSN：1520-5215

文摘

The potential of an approach combining nuclear magnetic resonance (NMR) spectroscopy, molecular dynamics (MD) simulations, and quantum mechanical (QM) calculations for full structural characterizations in solution is assessed using cyclic organic compounds, namely, benzazocinone derivatives 1鈥?b>3 with fused five- and eight-membered aliphatic rings, camphoric anhydride 4, and bullvalene 5. Various MD simulations were considered, using force field and semiempirical QM treatments, implicit and explicit solvation, and high-temperature MD calculations for selecting plausible molecular geometries for subsequent QM geometry optimizations using mainly B3LYP, M062X, and MP2 methods. The QM-predicted values of NMR parameters were compared to their experimental values for verification of the final structures derived from the MD/QM analysis. From these comparisons, initial estimates of quality thresholds (calculated as rms deviations) were 0.7鈥?.9 Hz for ³J_HH couplings, 0.07鈥?.11 脜 for interproton distances, 0.05鈥?.08 ppm for ¹H chemical shifts, and 1.0鈥?.1 ppm for ¹³C chemical shifts. The obtained results suggest that the accuracy of the MD analysis in predicting geometries and relative conformational energies is not critical and that the final geometry refinements of the structures selected from the MD simulations using QM methods are sufficient for correcting for the expected inaccuracy of the MD analysis. A unique example of C(sp³)鈥擧路路路N(sp³) intramolecular noncovalent interaction is also identified using the NMR/MD/QM and the natural bond orbital analyses. As the NMR/MD/QM approach relies on the final QM geometry optimization, comparisons of geometric characteristics predicted by different QM methods and those from X-ray and neutron diffraction measurements were undertaken using rigid and flexible cyclic systems. The joint analysis shows that intermolecular noncovalent interactions present in the solid state alter molecular geometries significantly compared to the geometries of isolated molecules from QM calculations.