- Tuning the polarization along linear polyaromatic strands for rationally inducing mesomorphism in lanthanide nitrate complexes
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The opposite orientation of the ester spacers in the rodlike ligands L4C12 (benzimidazole-OOC-phenyl) and L5C12 (benzimidazole-COO-phenyl) drastically changes the electronic structure of the aromatic systems, without affecting their meridional Incoordination to trivalent lanthanides, Ln111, and their thermotropic liquid crystalline (i.e., mesomorphic) behaviors. However, the rich mesomorphism exhibited by the complexes [Ln(L4C12)-(NO3)3] (Ln = La-Lu) vanishes in [Ln-(L5C12)(NO3)3], despite superimposable molecular structures and comparable photophysical properties. Density functional theory (DFT) and time-dependant DFT calculations performed in the gas phase show that the inversion of the ester spacers has considerable effects on the electronic structure and polarization of the aromatic groups along the strands, which control residual intermolecular interactions responsible for the formation of thermotropic liquid-crystalline phases. As a rule of thumb, an alternation of electron-poor and electron-rich aromatic rings favors intermolecular interactions between the rigid cores and consequently mesomorphism, a situation encountered for L4C12, L5C12, [Ln(L4C12)(NO3)3], but not for [Ln(L5 C12)(NO3)3]. The intercalation of an additional electron-rich diphenol ring on going from [Ln(L5C12)-(NO 3)3] to [Ln(L6C12)(NO3)3] restores mesomorphism despite an unfavorable orientation of the ester spacers, in agreement with our simple predictive model.
- Terazzi, Emmanuel,Guenee, Laure,Morgantini, Pierre-Yves,Bernardinelli, Gerald,Donnio, Bertrand,Guillon, Daniel,Piguet, Claude
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p. 1674 - 1691
(2008/02/04)
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- Investigation of the mechanism of action of pyrogallol-phloroglucinol transhydroxylase by using putative intermediates
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Pyrogallol-phloroglucinol transhydroxylase from Pelobacter acidigallici, a molybdopterin-containing enzyme, catalyzes a key reaction in the anaerobic degradation of aromatic compounds. In vitro, the enzymatic reaction requires 1,2,3,5-tetrahydroxy-benzene as a cocatalyst and the trans-hydroxylation occurs without exchange with hydroxy groups from water. To test our previous proposal that the transfer of the hydroxy group occurs via 2,4,6,3′,4′, 5′-hexahydroxydiphenyl ether as an intermediate, we synthesized this compound and investigated its properties. We also describe the synthesis and characterization of 3,4,5,3′,4′,5′-hexahydroxydiphenyl ether. Both compounds could substitute for the cocatalyst in vitro. This indicates that the diphenyl ethers can intrude into the active site and initiate the catalytic cycle. Recently, the X-ray crystal structure of the transhydroxylase (TH) was published[16] and it supports the proposed mechanism of hydroxy-group transfer.
- Paizs, Csaba,Bartlewski-Hof, Ulrike,Rétey, János
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p. 2805 - 2811
(2008/02/05)
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- Oxidative Decarbonylation of Phenolic Acids by Singlet Oxygen
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Phenolic acids containing in addition to p-OH, at least one more activating OH/OCH3 group, on reaction with singlet oxygen generated by the dye-sensitized method, have been foud to undergo replacement of the carboxyl group by a hydroxyl.
- Chibber, S. S.,Dutt, S. K.
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p. 352 - 353
(2007/10/02)
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