Hongsu Wang

Synthesis, Characterization, and Catalytic Performance of Mesoporous Al-SBA-15 for Tert-butylation of Phenol

Abstract Mesoporous Al-SBA-15 was synthesized by the post-synthesis grafting of Al atoms on a parent siliceous SBA-15. Both SBA-15 and Al-SBA-15 with different Si/Al ratios were characterized by powder X-ray diffraction, transmission electron microscopy, and N2 adsorption-desorption. The hexagonal p6mm mesostructure of the parent siliceous SBA-15 was maintained very well in Al-SBA-15. NH3 temperature-programmed desorption indicated that Al-SBA-15 has both medium and strong acid sites. During the alkylation of phenol with tert-butanol, the Al-SBA-15 catalyst showed a higher conversion of phenol and selectivity for 2,4-di-tert-butyl phenol (2,4- DTBP) than the traditional Al-MCM-41 catalyst. At a reaction temperature of 145°C, a higher phenol conversion of 75.2% and a 2,4-DTBP selectivity of 31.3% over Al-SBA-15 were observed as compared to those over Al-MCM-41, which were 61.3% and 13.4%, respectively. Due to the large pore size (about 9 nm), which allows a faster diffusion of reactants and products, catalyst deactivation of Al-SBA-15 was not observed even after reaction for 5 h.

Insight into the dynamic interaction between different flavonoids and bovine serum albumin using molecular dynamics simulations and free energy calculations

In this study, the binding of Bovine serum albumin (BSA) with three flavonoids, kaempferol-3-O-a-L-rhamnopyranosyl-(1–3)-a-L-rhamnopyranosyl-(1–6)-b-D-galacto- pyranoside (drug 1),kaempfol-7-O-rhamnosyl-3-O-rutinoside (drug 2)andkaempferide-7-O-(4”-O-acetylrhamnosyl)-3-O-ruti- noside (drug 3) is investigated by molecular docking, molecular dynamics (MD) simulation, and binding free energy calculation. The free energies are consistent with available experimental results and suggest that the binding site of BSA-drug1 is more stable than those of BSA-drug2 and BSA-drug3. The energy decomposition analysis is performed and reveals that the electrostatic interactions play an important role in the stabilization of the binding site of BSA-drug1 while the van der Waals interactions contribute largely to stabilization of the binding site of BSA-drug2 and BSA-drug3. The key residues stabilizing the binding sites of BSA-drug1, BSA-drug2 and BSA-drug3 are identified based on the residue decomposition analysis.

Insights into the specific binding site of adenosine to the Stx2, the protein toxin from Escherichia coli O157:H7 using molecular dynamics simulations and free energy calculations

To achieve the structural basis to produce a more accurate model of the catalytic active site of Stx2, we carried out molecular docking and molecular dynamics simulations of adenosine–Stx2 complex, and used the molecular mechanics/Poisson–Boltzmann surface area method to determine the associated free energy profiles. The results reveal that the electrostatic interactions play an important role in the stabilisation of the binding site of Stx2–adenosine, and the key residues of Ser113, Arg119, Arg125 and Arg170 in Stx2–adenosine complex are identified based on the residue decomposition analysis. With this approach, we are able to demonstrate that the substrate adenosine is located in the cavity formed by A-subunit, which is similar to the available experimental binding pattern of Stx2–adenine except for adenine being more close to the residues of Arg170, Tyr77 and Val78. The conformational difference that lies in adenosine is stabilised by the residues around the binding site of adenosine–Stx2, which leads to that the adenine base and furan ring of adenosine are dragged by the residues in the opposite direction during the catalytic process. The above results indicate that the residues around the binding site of adenosine in Stx2 should be used as catalytic active site to depurinate a specific adenine base from 28S rRNA.