598-75-4Relevant articles and documents
Synthesis and characterization of Mn/Co/Ti LDH and its utilization as a photocatalyst in visible light assisted degradation of aqueous Rhodamine B
Chowdhury, Priyadarshi Roy,Bhattacharyya, Krishna G.
, p. 112016 - 112034 (2016)
Luminescent Mn/Co/Ti LDH, synthesized by a single step hydrothermal route, has been found to be optically responsive for utilization as a highly efficient photocatalyst in destruction of the cationic dye Rhodamine B, in aqueous solution under visible light irradiation. The material has been found to be better than the commercial catalysts like MnO, CoO, TiO2 and Degussa P25. Multiple techniques like XRD, XPS, FT-IR, EIS, TG, UV-visible DRS, PL, TRES, N2-sorption-desorption, dynamic light scattering, TEM-EDS and AFM analyses were used to characterize the LDH. The results indicated Mn/Co/Ti LDH to have a multilayered crystalline structure with hexagonal morphology that carries metal ions in mixed valences, oxygen vacancies, defect states, thermal stability, narrow band gap, high surface area, and electrostatic surface charge variation with pH. The photocatalytic activity of the LDH could be co-related with the structural aspects such as oxidation states, narrow band gap, high surface area and existence of defects. The active species responsible for photocatalysis have been evaluated with EPR, terephthalic acid fluorescence probe and indirect radical-hole trapping experiments. The photodegradation mechanism involves electron and hole hopping across the material and also photosensitization of the dye. Ex situ1H-NMR and GC-MS analyses of the colorless end products of Rhodamine B destruction provide further insight into the reaction mechanism. The complete mineralization of the decolorized end product of degradation was evaluated with TOC analysis. The results indicate the potential for using multi metal incorporated LDH in destroying dyes and their degradation products in industrial wastewater.
Discovery and Redesign of a Family VIII Carboxylesterase with High (S)-Selectivity toward Chiral sec-Alcohols
Park, Areum,Park, Seongsoon
, p. 2397 - 2402 (2022/02/17)
Highly enantioselective lipase has been widely utilized in the preparation of versatile enantiopure chiral sec-alcohols through kinetic or dynamic kinetic resolution. Lipase is intrinsically (R)-selective, and it is difficult to obtain (S)-selective lipase. Recent crystal structures of a family VIII carboxylesterase have revealed that the spatial array of its catalytic triad is the mirror image of that of lipase but with a catalytic triad that is distinct from lipase. We, therefore, hypothesized that the family VIII carboxylesterase may exhibit (S)-enantioselectivity toward sec-alcohols similar to (S)-selective serine protease, whose catalytic triad is also spatially arrayed as its mirror image. In this study, a homologous enzyme (carboxylesterase from Proteobacteria bacterium SG_bin9, PBE) of a known family VIII carboxylesterase (pdb code: 4IVK) was prepared, which showed not only moderate (S)-selectivity toward sec-alcohols such as 3-butyn-2-ol and 1-phenylethyl alcohol but also (R)-selectivity toward particular sec-alcohols among the substrates explored. Furthermore, the (S)-selectivity of PBE has been significantly improved by rational redesign based on molecular modeling. Molecular modeling identified a binding pocket composed of Ser381, Ala383, and Arg408 for the methyl substituent of (R)-1-phenylethyl acetate and suggested that larger residues may increase the enantioselectivity by interfering with the binding of the slow-reacting enantiomer. As predicted, substituting Ser381with larger residues (Phe, Tyr, and Trp) significantly improved the (S)-selectivity of PBE toward all sec-alcohols explored, even the substrates toward which the wild-type PBE exhibits (R)-selectivity. For instance, the enantioselectivity toward 3-butyn-2-ol and 1-phenylethyl alcohol was improved from E = 5.5 and 36.1 to E = 2001 and 882, respectively, by single mutagenesis (S381F).
Conformationally Controlled Linear and Helical Hydrocarbons Bearing Extended Side Chains
Aggarwal, Varinder K.,Butts, Craig P.,Davy, Matthew,Dutton, Oliver J.,Guo, Lin,Kucukdisli, Murat,Myers, Eddie L.,Wagnières, Olivier
supporting information, p. 16682 - 16692 (2021/10/21)
Conformationally controlled flexible molecules are ideal for applications in medicine and materials, where shape matters but an ability to adapt to multiple and changing environments is often required. The conformation of flexible hydrocarbon chains bearing contiguous methyl substituents is controlled through the avoidance of syn-pentane interactions: alternating syn-anti isomers adopt a linear conformation while all-syn isomers adopt a helical conformation. From a simple diamond lattice analysis, larger substituents, which would be required for most potential applications, result in significant and unavoidable syn-pentane interactions, suggesting substantially reduced conformational control. Through a combination of computation, synthesis, and NMR analysis, we have identified a selection of substitution patterns that allow large groups to be incorporated on conformationally controlled linear and helical hydrocarbon chains. Surprisingly, when the methyl substituents of alternating syn-anti hydrocarbons are replaced with acetoxyethyl groups, the main chain of almost 95% of the population of molecules adopt a linear conformation. Here, the side chains adopt nonideal eclipsed conformations with the main chain, thus minimizing syn-pentane interactions. In the case of all-syn hydrocarbons, concurrent removal of some methyl groups on the main chain adjacent to the large substituents is required to maintain a high population of molecules adopting a helical conformation. This information can now be used to design flexible hydrocarbon chains displaying functional groups in a defined relative orientation for multivalent binding or cooperative reactivity, for example, in targeting the interfaces defined by disease-relevant protein-protein interactions.
London Dispersion Interactions Rather than Steric Hindrance Determine the Enantioselectivity of the Corey–Bakshi–Shibata Reduction
Eschmann, Christian,Song, Lijuan,Schreiner, Peter R.
, p. 4823 - 4832 (2021/02/01)
The well-known Corey–Bakshi–Shibata (CBS) reduction is a powerful method for the asymmetric synthesis of alcohols from prochiral ketones, often featuring high yields and excellent selectivities. While steric repulsion has been regarded as the key director of the observed high enantioselectivity for many years, we show that London dispersion (LD) interactions are at least as important for enantiodiscrimination. We exemplify this through a combination of detailed computational and experimental studies for a series of modified CBS catalysts equipped with dispersion energy donors (DEDs) in the catalysts and the substrates. Our results demonstrate that attractive LD interactions between the catalyst and the substrate, rather than steric repulsion, determine the selectivity. As a key outcome of our study, we were able to improve the catalyst design for some challenging CBS reductions.