28
views
0
recommends
+1 Recommend
1 collections
    0
    shares
      • Record: found
      • Abstract: found
      • Article: found
      Is Open Access

      Theoretical studies of the insertion of carbenes in the zeolite framework: modification of the acidity and creation of chiral sites

      research-article

      Read this article at

      Bookmark
          There is no author summary for this article yet. Authors can add summaries to their articles on ScienceOpen to make them more accessible to a non-specialist audience.

          Abstract

          A theoretical study of the insertion of carbenes (CH2, CHCHO) in the framework structure of zeolite Y was carried out. The "our own n-layered integrated molecular orbital and molecular mechanics" (ONIOM) scheme M062x/6-31G(d,p):PM6 was used to describe the insertion of methylene (CH2) in the T-O bonds (T = Si, Al) of the framework yielding four isomeric structures. In all cases, calculations indicated a high exothermic process for the insertion of methylene in the framework, regardless of the spin multiplicity of the carbene (singlet or triplet). Insertion into the acidic O-H bond to afford an adsorbed methoxy group was the most favourable process, but this pathway does not occur if insertion is carried out on the deprotonated zeolite. Insertion of formylcarbene (CHCHO) creates chiral sites in the framework. The acidity of the zeolite structures after carbene insertion was calculated by means of the deprotonation energy. The calculations predicted the possibility of designing acidic zeolites with chiral sites that could mimic enzymes, especially for uses in fine chemical processes and biomass transformations.

          Translated abstract

          Foi realizado um estudo teórico da inserção de carbenos (CH2 e CHCHO) na estrutura cristalina da zeólita Y. O método our own n-layered integrated molecular orbital and molecular mechanics (ONIOM) M062x/6-31G(d,p):PM6 foi utilizado para descrever a inserção do metileno (CH2) nas ligações T-O (T = Si ou Al) da rede resultando em quatro estruturas isômeras. Em todos os casos os cálculos indicaram uma alta exotermicidade para a inserção do metileno na rede cristalina, independentemente da multiplicidade do carbeno (singlete ou triplete). A inserção na ligação O-H ácida para formar um grupo metóxi adsorvido foi o processo mais favorável, mas este caminho não ocorre se a inserção é feita na zeólita desprotonada. A inserção do formil-carbeno (CHCHO) cria centros quirais na estrutura cristalina. A acidez da zeólita após a inserção dos carbenos foi calculada usando a energia de desprotonação. Os cálculos predizem a possibilidade de desenvolver zeólitas ácidas com centros quirais, que poderiam imitar enzimas, especialmente para uso em processos de química fina e transformação de biomassa.

          Related collections

          Most cited references46

          • Record: found
          • Abstract: not found
          • Article: not found

          Recent advances in solid sorbents for CO2capture and new development trends

            Bookmark
            • Record: found
            • Abstract: found
            • Article: not found

            Efficient and limiting reactions in aqueous light-induced hydrogen evolution systems using molecular catalysts and quantum dots.

            Hydrogen produced from water and solar energy holds much promise for decreasing the fossil fuel dependence. It has recently been proven that the use of quantum dots as light harvesters in combination with catalysts is a valuable strategy to obtain photogenerated hydrogen. However, the light to hydrogen conversion efficiency of these systems is reported to be lower than 40%. The low conversion efficiency is mainly due to losses occurring at the different interfacial charge-transfer reactions taking place in the multicomponent system during illumination. In this work we have analyzed all the involved reactions in the hydrogen evolution catalysis of a model system composed of CdTe quantum dots, a molecular cobalt catalyst and vitamin C as sacrificial electron donor. The results demonstrate that the electron transfer from the quantum dots to the catalyst occurs fast enough and efficiently (nanosecond time scale), while the back electron transfer and catalysis are much slower (millisecond and microsecond time scales). Further improvements of the photodriven proton reduction should focus on the catalytic rate enhancement, which should be at least in the hundreds of nanoseconds time scale.
              Bookmark
              • Record: found
              • Abstract: not found
              • Article: not found

              Structural biology: the ins and outs of drug transport.

                Bookmark

                Author and article information

                Contributors
                Role: ND
                Role: ND
                Role: ND
                Journal
                jbchs
                Journal of the Brazilian Chemical Society
                J. Braz. Chem. Soc.
                Sociedade Brasileira de Química (São Paulo )
                1678-4790
                June 2014
                : 25
                : 6
                : 1021-1028
                Affiliations
                [1 ] Universidade Federal do Rio de Janeiro Brazil
                [2 ] Fundação Centro Universitário Estadual da Zona Oeste Brazil
                [3 ] Universidade Federal do Rio de Janeiro Brazil
                Article
                S0103-50532014000600005
                10.5935/0103-5053.20140074
                d49682df-42a4-4946-a039-1281ef2eb6c8

                http://creativecommons.org/licenses/by/4.0/

                History
                Product

                SciELO Brazil

                Self URI (journal page): http://www.scielo.br/scielo.php?script=sci_serial&pid=0103-5053&lng=en
                Categories
                CHEMISTRY, MULTIDISCIPLINARY

                General chemistry
                zeolites,acidity,carbene,theoretical calculations,chirality
                General chemistry
                zeolites, acidity, carbene, theoretical calculations, chirality

                Comments

                Comment on this article