Calendar Details

For more information about item submission and attendance, see About the Technical Calendar.

Monday, March 18

Chemistry in silico: Tautomerization Thermodynamics,
Ionic Liquids, N-chlorohydantoins

Billy W. McCann, Auburn University, Auburn, Alabama
Chemical Sciences Division Seminar
11:00 AM — 12:00 PM, Chemical and Material Sciences Building (4100), Room C-201
Contact: Benjamin Hay (haybp@ornl.gov), 865.574.6717

Abstract

Three distinct areas of chemistry shall be presented: (1) the free energy of tautomerization in solution, (2) pairwise alternatives to the Ewald summation for room temperature ionic liquids, (3) the reactivity of UVA irradiated N-chlorohydantoins. The accurate calculation of solution phase ΔG of tautomerization remains a challenge to computational chemistry, especially in cases where tautomers have small free energy differences and their equilibrium constants change in different solvents. QM/MM calculations in many cases fail to calculate ΔG of tautomerization to chemical accuracy. Implicit solvation models in combination with different solute cavity sizes have been benchmarked against experimental free energy differences in order ascertain the most appropriate model to attain chemical accuracy. Use of this same method in calculating base-induced tautomerization is also explored to ascertain the applicability to free energies of activation. QM/MM calculations are also employed for comparison. Interest in ionic liquids has exploded in the past decade due to their plethora of use cases, from enhancing the rates and selectivity of organic reactions to drug delivery agents. Simulating ionic liquids, however, requires extensive sampling of configuration space due to the high degree of localized structuring. Hence, a large amount of computer time is required for the convergence of physico-chemical properties, much of which is spent evaluating long range electrostatic interactions via the Ewald summation. Recently developed pairwise alternatives have been investigated and a new methodology has been developed which is highly accurate compared to the Ewald summation yet at one-sixth the computational cost. N-chlorohydantoins have been shown to possess excellent antimicrobial properties and are used as aqueous disinfectants. They also have the advantage of regeneration in situ. However, UVA irradiation of certain N-chlorohydantoins leads to a change in chlorine bonding arrangement, and hence loss of regenerative capability. All possible reactive pathways have been explored and reveal that rearrangement occurs through intermolecular hydrogen atom transfer reactions. This finding will lead to new hydantoins which avoid the possibility of such reactions.