The COMP Division is excited to announce the OpenEye Award winners for the New Orleans ACS meeting (spring 2013). Please visit the COMP award winners and the other excellent COMP posters at the COMP Poster Session on Tuesday, April 9, 2013 from 6pm to 8pm at a location to be determined.
Molecular Simulation of Biomolecules in Non-Aqueous Media
The potential for non-aqueous solvents to endow biological catalysts with improved or previously unknown properties is exciting and could transform their use in industry. In spite of this great promise, our incomplete understanding of the relationship between solvent, enzyme structure, and reactivity has hampered significant scientific technological development in this arena. Specifically, we lack the ability to relate molecular features of the solvent to its effect on enzyme stability and activity. This poster describes our efforts to study biomolecular structure and dynamics of two enzymes (Candida Rugosa Lipase A and glycoside hydrolase 11) in four different solvents. We use classical MD simulations to probe the solvent structure and equilibrium fluctuations. These results are used to understand enzyme deactivation that was observed in our lab with various experiments. Additionally, we apply the metadynamics method to study the thermodynamics of protein folding in ionic liquids on the model system tryptophan cage.
Partition Energy Functionals: Avoiding the Delocalization Error of Approximate Density Functionals
We show how the delocalization error that plagues density-functional calculations of bond stretching processes can be avoided by approximating the partition energy of Partition Density Functional Theory (PDFT) via simple functionals of the set of fragment densities. These functionals involve the overlap between the relevant fragment densities, and can be used in combination with any approximate exchange-correlation functional. I also describe our progress understanding the behavior of the fragment energies as a function of fragment occupations, the formulation of the partition energy as an implicit functional of the total spin-densities, derivative discontinuities, practical implementation, and application of PDFT to small molecules.
Dissecting electrostatic potentials: Understanding anion/π interactions and the nature of electron-deficient arenes
Although strong interactions between cations and the faces of aromatic systems have long been recognized (i.e.: cation/π interactions), only in the last decade have favorable interactions between anions and electron deficient arenes been reported. That is, arenes heavily substituted with electron-withdrawing substituents, as well as N-heteroaromatic systems, have been shown computationally and experimentally to exhibit strong avidities for anions, with important applications in biology, supramolecular chemistry, and crystal engineering. Previously, we showedd that prototypical anion/π interactions between halide ions and the faces of substituted benzenes arise from the direct interactions of the anion with the local multipole moments associated with the substituents; the interaction of the anion with the phenyl ring itself remained repulsive regardless of the substituents. Here, we examine the interaction of anions with a number of heteroaromatic systems using symmetry-adapted perturbation theory (SAPT) and electrostatic potentials (ESPs). Notably, we introduce dissected ESPs, which enable the rigorous division of electrostatic potentials of planar arenes into contributions from the σ- and π-systems. These dissected ESPs provide critical insight into the factors that govern the strength of prototypical anion/π interactions and the nature of electron-deficient aromatic systems in general. They also provide, indirectly, a means of quantifying the contribution of the σ- and π-electron systems to Hammett substituent constants.