Jagannadh Bulusu, Reddy Surasani Sumathi, Thangavelu Ramagounder P
Division of Organic Chemistry III, Indian Institute of Chemical Technology, 500 007 Hyderabad, India.
J Mol Model. 2004 Feb;10(1):55-9. doi: 10.1007/s00894-003-0166-5. Epub 2003 Nov 22.
Conformational preferences of 1,4,7-trithiacyclononane were studied using a highly efficient sampling technique based on local nonstochastic deformations and the MM2(91) force field. The results show that conformers that the molecule adopts in the crystal state were found to be low-energy conformers (LECs) within 5 kcal mol(-1) of the global minimum. A conformation with C1 symmetry was the global minimum and the C3 and C2 conformations were calculated to be 0.03 and 1.78 kcal mol(-1) higher in energy, respectively. The structures were further minimized using Density Functional Theory (DFT) calculations with two different functionals. The C2 and the C1 conformations were found to be LECs with the C3 conformation more than 4.0 kcal mol(-1) above the global minimum. The relative energies and structural ordering obtained using the BP86 functional are in agreement with the previously reported relative energies calculated using second-order Moller-Plesset (MP2) ab initio calculations. With the energy ordering being dependent on the molecular mechanics force field used, the approach of MM-->DFT (searching exhaustively the available conformational space at the MM level followed by generating the energy ordering through DFT calculations) appears to be appropriate for thiacrown ethers.
使用基于局部非随机变形和MM2(91)力场的高效采样技术，研究了1,4,7-三硫杂环壬烷的构象偏好。结果表明，该分子在晶体状态下所采取的构象异构体是全局最小值5千卡摩尔（-1）范围内的低能量构象异构体（LECs）。具有C1对称性的构象是全局最小值，计算得出C3和C2构象的能量分别高0.03和1.78千卡摩尔（-1）。使用两种不同的泛函通过密度泛函理论（DFT）计算进一步优化结构。发现C2和C1构象是LECs，C3构象比全局最小值高4.0千卡摩尔（-1）以上。使用BP86泛函获得的相对能量和结构排序与先前报道的使用二阶Moller-Plesset（MP2）从头算计算得出的相对能量一致。由于能量排序取决于所使用的分子力学力场，MM→DFT方法（在MM水平上详尽搜索可用的构象空间，然后通过DFT计算生成能量排序）似乎适用于硫杂冠醚。
