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- 저자 : Dunaway-Mariano, Debra (검색결과 2 건)
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Cho, Dae Won,Latham, John A.,Park, Hea Jung,Yoon, Ung Chan,Langan, Paul,Dunaway-Mariano, Debra,Mariano, Patrick S. American Chemical Society 2011 Journal of organic chemistry Vol.76 No.8
<P>New types of tetrameric lignin model compounds, which contain the common β-O-4 and β-1 structural subunits found in natural lignins, have been prepared and carbon−carbon bond fragmentation reactions of their cation radicals, formed by photochemical (9,10-dicyanoanthracene) and enzymatic (lignin peroxidase) SET-promoted methods, have been explored. The results show that cation radical intermediates generated from the tetrameric model compounds undergo highly regioselective C−C bond cleavage in their β-1 subunits. The outcomes of these processes suggest that, independent of positive charge and odd-electron distributions, cation radicals of lignins formed by SET to excited states of sensitizers or heme-iron centers in enzymes degrade selectively through bond cleavage reactions in β-1 vs β-O-4 moieties. In addition, the findings made in the enzymatic studies demonstrate that the sterically large tetrameric lignin model compounds undergo lignin peroxidase-catalyzed cleavage via a mechanism involving preliminary formation of an enzyme−substrate complex.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/joceah/2011/joceah.2011.76.issue-8/jo200253v/production/images/medium/jo-2011-00253v_0002.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jo200253v'>ACS Electronic Supporting Info</A></P>
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Lim, Suk Hyun,Nahm, Keepyung,Ra, Choon Sup,Cho, Dae Won,Yoon, Ung Chan,Latham, John A.,Dunaway-Mariano, Debra,Mariano, Patrick S. American Chemical Society 2013 Journal of organic chemistry Vol.78 No.18
<P>To gain information about how alkoxy substitution in arene rings of β-O-4 structural units within lignin governs the efficiencies/rates of radical cation C1–C2 bond cleavage reactions, single electron transfer (SET) photochemical and lignin peroxidase-catalyzed oxidation reactions of dimeric/tetrameric model compounds have been explored. The results show that the radical cations derived from less alkoxy-substituted dimeric β-O-4 models undergo more rapid C1–C2 bond cleavage than those of more alkoxy-substituted analogues. These findings gained support from the results of DFT calculations, which demonstrate that C1–C2 bond dissociation energies of β-O-4 radical cations decrease as the degree of alkoxy substitution decreases. In SET reactions of tetrameric compounds consisting of two β-O-4 units, containing different degrees of alkoxy substitution, regioselective radical cation C–C bond cleavage was observed to occur in one case at the C1–C2 bond in the less alkoxy-substituted β-O-4 moiety. However, regioselective C1–C2 cleavage in the more alkoxy-substituted β-O-4 moiety was observed in another case, suggesting that other factors might participate in controlling this process. These observations show that lignins containing greater proportions of less rather than more alkoxylated rings as part of β-O-4 units would be more efficiently cleaved by SET mechanisms.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/joceah/2013/joceah.2013.78.issue-18/jo401680z/production/images/medium/jo-2013-01680z_0014.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jo401680z'>ACS Electronic Supporting Info</A></P>
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