ChemNews - Department of Chemistry - University of Minnesota

Force fields for complex reactionsRecent research from the group of Professor Don TruhlarCombined quantum mechanical and molecular mechanical (QM/MM) methods have provided powerful means forstudying chemical reactions in condensed phases such as liquids, enzymes, and solids. In these approaches, the reactioncenter is described quantum mechanically, while the surroundings are treated by using a molecular mechanicsforce field. However, the high computational cost of quantum mechanical (QM) calculations prevents carryingout QM/MM molecular dynamics simulationswith reliable accuracy and adequate sampling.In order to reduce the computationalcost of the QM calculation,postdoctoral research associateMasahiro Higashi and Regents Professor DonaldG. Truhlar* have developed a new method calledelectrostatically embedded multi-configurationmolecular mechanics (EE-MCMM) for generatingglobal potential energy surfaces (PESs) in thepresence of an electrostatic potential. MCMMdescribes the global PES of a condensed-phasereaction with electronic structure information, inparticular energies and partial chargedistributions, obtained in the gas phase at selectedgeometries. Because this new method is efficient,high-level QM calculations can be usedin QM/MM methods. The result is a key step towardstudying chemical reactions in condensedphases with high accuracy.Methyl anion dethroned as themost basic speciesRecent research from the group of Professor StevenKassAfter decades as the champion of proton acceptors, the methyl anionis finally playing second fiddle to the gas-phase lithium monoxideanion. In a joint effort between University of Minnesota researchersZhixin Tian and Prof. Steven R. Kass and collaborators at the Universityof Sydney, the LiO- species was prepared and its acid-base propertieswere measured to verify calculations that predicted its chemicalprowess. Their work was reported in The Proceedings of the NationalAcademy of Sciences (Proc. Natl. Acad. Sci. USA 2008, 105, 7647) andhighlighted in Chemical and Engineering News (C&EN June 9, 2008).Page 23