The reaction mechanism of nucleophilic aromatic substitution of 1-chloro-2,4-dinitrobenzene by glutathione (as modeled by a thiomethoxide ion) in the gas phase and in solution was elucidated using ab initio molecular orbital theory in combination with a continuum solvent model at the HF/6-31G*, HF/6-31+G**, and MP2/6-31+G** levels of theory. Two ion−molecule complexes were located in the gas phase at the HF level, but only one exits at the MP2/6-31+G** level, while neither exits in aqueous solution. In aqueous solution, there is a large free energy barrier and C−S bond formation is the rate-determining step, which is in agreement with experimental observation. The calculated free energy barrier (30.2 kcal/mol) at the HF/6-31+G** level of theory seems to be in good agreement with experiment (23.8 kcal/mol), while the MP2/6-31+G** barrier is too low, indicating that the MP2/6-31+G** level of theory probably overestimates the stability of the transition state for C−S bond formation. Implications for the mode of action of glutathione S-transferases (GSTs) and a related enzyme are discussed in light of the results of the current study.

No abstract

No abstract

We study the ergodic control problem for a class of jump diffusions in R d , which are controlled through the drift with bounded controls. The Lévy measure is finite, but has no particular structure-it can be anisotropic and singular. Moreover, there is no blanket ergodicity assumption for the controlled process. Unstable behavior is 'discouraged' by the running cost which satisfies a mild coercive hypothesis (i.e., is near-monotone). We first study the problem in its weak formulation as an optimization problem on the space of infinitesimal ergodic occupation measures, and derive the Hamilton-Jacobi-Bellman equation under minimal assumptions on the parameters, including verification of optimality results, using only analytical arguments. We also examine the regularity of invariant measures. Then, we address the jump diffusion model, and obtain a complete characterization of optimality.