The hydrolysis reaction of sulfur trioxide to form sulfuric acid in small water clusters is investigated using density function theory and ab initio methods. The equilibrium geometries for the reactant clusters that contain SO3 and one to four water molecules, SO3⋅(H2O)n, n=1–4, as well as the corresponding transition state and product clusters, are calculated at the levels of B3LYP/6-31+G*, B3LYP/6-311++G**, and MP2/6-311++G**. The relative energies of the reactant, transition state, and product are determined for each of the four clusters. The energy barrier required to form H2SO4 from the reactant cluster is found to decrease sharply with the number of water molecules in the cluster. Most significantly, the SO3⋅(H2O)4 cluster is found to be unstable and to form the ion pair HSO4− and H3O+ with little or no energy barrier. This work reveals the possibility of more pathways for the formation of sulfuric acid than have been previously considered.
Two-layered and three-layered ONIOM calculations were performed to compare the binding energies of 8-Cl TIBO inhibitor when bound into the human immunodeficiency virus reverse transcriptase binding pocket and a Y181C variant. Both consisted of 20 residues within a radius of 15 A. A combination of different methods [MP2/6-31G(d), B3LYP/6-31G(d,p), and PM3] were performed to take advantage of ONIOM's layering strategy analysis. The obtained results clearly indicate that the Y181C mutation reduces the binding affinity and stability of the inhibitor by approximately 8-9 kcal/mol as obtained from different combined MO:MO methods. Analyses regarding the energetic components of the interaction and deformation energies for 8-Cl TIBO inhibitor upon binding were also examined extensively. Additional calculations involving the interaction energies between 8-Cl TIBO with individual residues surrounding the binding pocket were performed at MP2/6-31G(d,p) and B3LYP/6-31G(d,p) levels of theory to gain more insight into the energetic differences of wild-type and Y181C mutant type at the atomistic level.
Alkaloids U 0600 Ziziphine N, O, P and Q, New Antiplasmodial Cyclopeptide Alkaloids from Ziziphus oenoplia var. brunoniana. -Ziziphine N (Ia) and ziziphine Q (Id) exhibit significant antiplasmodial and weak antimycobacterial activities, whereas ziziphines O (Ib) and P (Ic) are found to be inactive in the same tests. -(SUKSAMRARN*, S.; SUWANNAPOCH, N.; AUNCHAI, N.; KUNO, M.; RATANANUKUL, P.; HARITAKUN, R.; JANSAKUL, C.; RUCHIRAWAT, S.; Tetrahedron 61 (2005) 5,
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