Al-Jallal Nada A, El-Azhary Adel A
Chemistry Department, Faculty of Science, King Saud University, P.O. Box 2455, Riyadh 11451, Saudi Arabia.
Chemistry Department, Faculty of Science, Cairo University, Giza, Egypt.
J Mol Graph Model. 2017 Jan;71:257-267. doi: 10.1016/j.jmgm.2016.10.016. Epub 2016 Nov 10.
Crown ethers are an important class of molecules with wide applications. Crown ethers are large ring flexible molecules with a large number of possible conformations. In the current manuscript, we report the conformational analysis results of one of the smallest crown ether systems, namely, 9-crown-3, 9c3, 9-thiacrown-3, 9t3, and 9-azacrown-3, 9a3. The conformational search is performed using the CONFLEX conformational search method utilizing the MMFF94s force field. 8, 11 and 62 conformations were predicted for 9c3, 9t3 and 9a3, respectively. The ab initio computations were performed at B3LYP and MP2 levels using the 6-311G** basis set. For the accurate prediction of the ground state conformation and the energy order of the low-lying energy conformations, the computations were performed at the G4 level for some selected conformations. Factors affecting the stability of different conformations of 9c3, 9t3 and 9a3 are discussed. These factors are also discussed with respect to larger crown ether systems. The ab initio computations were performed also for water and chloroform as solution phases. The same ground state predicted in the gas phase was also predicted in the solution water and chloroform phases.
冠醚是一类具有广泛应用的重要分子。冠醚是大环柔性分子，具有大量可能的构象。在当前的手稿中，我们报告了最小的冠醚体系之一，即9-冠-3（9c3）、9-硫杂冠-3（9t3）和9-氮杂冠-3（9a3）的构象分析结果。构象搜索使用CONFLEX构象搜索方法并利用MMFF94s力场进行。分别预测出9c3、9t3和9a3的构象数为8、11和62个。从头算计算在B3LYP和MP2水平上使用6-311G**基组进行。为了准确预测基态构象和低能构象的能量顺序，对一些选定的构象在G4水平上进行了计算。讨论了影响9c3、9t3和9a3不同构象稳定性的因素。还针对更大的冠醚体系讨论了这些因素。也对水和氯仿作为溶液相进行了从头算计算。在气相中预测的相同基态在溶液水相和氯仿相中也被预测到。
