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Jochen Lutz The Vinh Ho Richard H. Fish Andreas Schmid 《Journal of organometallic chemistry》2004,689(25):4783-4790
The biocatalytic, regioselective hydroxylation of 2-hydroxybiphenyl to the corresponding catechol was accomplished utilizing the monooxygenase 2-hydroxybiphenyl 3-monooxygenase (HbpA). The necessary natural 1,4-dihydronicotinamde adenine dinucleotide (NADH) co-factor for this biocatalytic process was replaced by a biomimetic co-factor, N-benzyl-1,4-dihydronicotinamide, 1b. The interaction between the flavin (FAD) containing HbpA enzyme and the corresponding biomimetic NADH compound, N-benzyl-1,4-dihdronicotinamide, 1b, for hydride transfer, was shown to readily occur. The in situ recycling of the reduced NADH biomimic 1b from 1a was accomplished with [Cp*Rh(bpy)H](Cl); however, productive coupling of this regeneration reaction to the enzymatic hydroxylation reaction was not totally successful, due to a deactivation process concerning the HbpA enzyme peripheral groups; i.e., -SH or -NH2 possibly reacting with the precatalyst, [Cp*Rh(bpy)(H2O)](Cl)2, and thus inhibiting the co-factor regeneration process. The deactivation mechanism was studied, and a promising strategy of derivatizing these peripheral -SH or -NH2 groups with a polymer containing epoxide was successful in circumventing the undesired interaction between HbpA and the precatalyst. This latter strategy allowed tandem co-factor regeneration using 1a or 2a, [Cp*Rh(bpy)(H2O)](Cl)2, and formate ion, in conjunction with the polymer bound, FAD containing HbpA enzyme to provide the catechol product. 相似文献
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Mixtures of a calix[4]arene and a naphthyridine derivative dissolved in 1,2-dichlorobenzene form thermoreversible aggregates. The aggregation process was followed by means of time-resolved multiangle light scattering at two different mixing ratios, 1:3 and 1:4, yielding a detailed record of the relative mass, the radius of gyration, and the particle scattering function of the growing aggregates. On the basis of these data, a conclusive model of the structure is presented for the developing aggregates: monomers aggregate to wormlike filaments which form branching points. Formation of branching points proceeds in a frequency and distribution which is similar to the polycondensation of ABC monomers toward non-randomly branched macromolecules (Burchard, W. Macromolecules 1977, 10, 919-927). Thus, aggregation results in hyperbranched-like particles with striking analogies to the polymerization of glucose to amylopectin. 相似文献
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Recent measurements revealed that commercial magnesium standard solutions showed isotopic abundance variations, which cannot clearly be distinguished from each other by calibrating against the only available isotopic reference material, SRM 980, or reference materials made from SRM 980 like IRMM-009. Therefore new SI-traceable magnesium isotopic reference materials are required. 相似文献
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Micro- and nanotubes of an amorphous carbon nitride material were synthesized by metathesis reactions between cyanuric chloride (C3N3Cl3) and different nitrogen sources, such as Li2(CN2) or Li3(BN2). The intermediate formation of needle-shaped crystals of N(C3N3Cl2)3 was always observed in our reactions, and investigated with respect to their role as a template in the formation of tubes. Chemical analyses of the micro- and nanotubes reveal carbon to nitrogen ratios near 3:4, consistent with the suspected material C3N4. Synthesized carbon nitride materials were thermally stable up to 600 °C in inert atmosphere. They were inspected by a number of physical measurements, mainly using TEM, EDX and IR investigations. 相似文献
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