Mn(III)protoporphyrin IX-6(7)-gly-gly-his methyl ester (MnGGH) has been prepared by condensation of glycyl-glycyl-L-histidine methyl ester with the propionic side chains of Mn(III)protoporphyrin IX. It was characterised by mass spectrometry and UV/VIS spectroscopy. Stopped-flow spectrophotometry was used to study the reaction of the Mn 'microperoxidase' with hydrogen peroxide. The formation of active intermediates analogous to previously described metal-hydroperoxo (compound 0) and metal-oxo (compound I) intermediates of the 'natural' Fe(III) microperoxidase-8 and Mn(III) microperoxidase-8 was observed. The rate of formation of the MnGGH-based compound I analogue was found to increase dramatically with increasing pH. A steady-state kinetic analysis of the catalytic peroxidase activity of MnGGH towards K4[Fe(CN)6], L-tyrosine methyl ester, o-dianisidine, o-methoxyphenol and ascorbic acid showed that the peroxidase reaction proceeds via the formation of a microperoxidase-substrate complex followed by electron transfer from the substrate to the metal. The reactivity of MnGGH depends on the size and hydrophobicity of the substrate, and these properties appear to influence the rate of the electron transfer, which is the rate-limiting step for the whole process. MnGGH showed higher reactivity towards reducing substrates than its Fe(iii) analogue. 相似文献
We report on the successful application of carboxyl-rich plasma polymerized (PP) films as a matrix layer for bioreceptor immobilization in surface plasmon resonance (SPR) immunosensing. Composition and chemical properties of the carboxyl-rich PP films deposited from a mixture of maleic anhydride and acetylene were investigated. Changes in the films stored in air, water, and buffer were studied and the involved chemical changes were described. Performance in SPR immunosensing was evaluated on interactions of human serum albumin (HSA) with a specific monoclonal antibody. The comparison with the mixed self-assembled monolayer of mercaptoundecanoic acid and mercaptohexanol (MUA/MCH) and one of the most widely used surfaces for SPR, the 2D and 3D carboxymethylated dextran (CMD), was presented to show the efficacy of plasma polymerized matrix layers for biosensing. The PP film-based SPR immunosensor provided a similar detection limit of HSA (100 ng/mL) as MUA/MCH- (100 ng/mL) and 3D CMD (50 ng/mL)-based sensors. However, the response levels were about twice higher in case of the PP film-based immunosensor than in case of MUA/MCH-based alternative. The PP film surfaces had similar binding capacity towards antibody as the 3D CMD layers. The response of PP film-based sensor towards HSA was comparable to 3D CMD-based sensor up to 2.5 μg/mL. For the higher concentrations (> 10 μg/mL), the response of PP film-based immunosensor was lower due to inaccessibility of active sites of the immobilized antibody inside the flat PP film surface. We have demonstrated that due to its high stability and cost-effective straightforward preparation, the carboxyl-rich PP films represent an efficient alternative to self-assembled monolayers (SAM) and dextran-based layers in label-free immunosensing.
Following previous surveys of the solid electrolyte ceramics and electrode reaction mechanisms in solid oxide fuel cells,
this review is focused on the comparative analysis of electrochemical performance, thermal expansion, oxygen ionic and electronic
transport, and durability-determining factors in the major groups of electrode materials. The properties of mixed-conducting
oxide phases with perovskite-related and fluorite structures, ceramic–metal and oxide composites, and catalytically active
additives are briefly discussed, with emphasis on the approaches and findings reported during the last 10–15 years. The performance
of conventional and alternative electrode materials in the cells with ZrO2-, CeO2-, LaGaO3-, and La10Si6O27-based electrolytes is appraised in the context of potential optimization strategies. Particular attention is centered on
the cathode and anode compositions providing maximum electrochemical activity and stability and on the critical aspects relevant
for electrode microstructure engineering. 相似文献
The preparation and dynamic behavior of two functionally rigid and degenerate [2]rotaxanes ( 1⋅ 4 PF6 and 2⋅ 4 PF6) in which a π-electron deficient tetracationic cyclophane, cyclobis(paraquat-p-phenylene) (CBPQT4+) ring, shuttles back and forth between two π-electron-rich naphthalene (NP) stations by making the passage along an ethynyl-phenylene-(PH)-ethynyl or butadiyne rod, are described. The [2]rotaxanes were synthesized by using the clipping approach to template-directed synthesis, and were characterized by NMR spectroscopic and mass spectrometric analyses. 1H NMR spectra of both [2]rotaxanes show evidence for the formation of mechanically interlocked structures, resulting in the upfield shifts of the resonances for key protons on the dumbbell-shaped components. In particular, the signals for the peri protons on the NP units in the dumbbell-shaped components experienced significant upfield shifts at low temperatures, just as has been observed in the flexible [2]rotaxanes. Interestingly, the resonances for the same protons did not exhibit a significant upfield shift at 298 K, but rather only a modest shift. This phenomenon arises from the much reduced binding of the ethynyl-NP unit compared to the 1,5-dioxy-NP unit. This effect, in turn, increases the shuttling rate when compared to the 1,5-dioxy-NP-based rotaxane systems investigated previously. The kinetic and thermodynamic data of the shuttling behavior of the CBPQT4+ ring between the NP units were obtained by variable-temperature NMR spectroscopy and using the coalescence method to calculate the free energies of activation (ΔGc≠) of 9.6 and 10.3 kcal mol−1 for 1⋅ 4 PF6 and 2⋅ 4 PF6, respectively, probed by using the rotaxane's α-bipyridinium protons. The solid-state structure of the free dumbbell-shaped compound ( 3 ) shows the fully rigid ethynyl-PH-ethynyl linker with a length (8.1 Å) twice as long as that (3.8 Å) of the butadiyne linker. Full-atomistic simulations were carried out with the DREIDING force field (FF) to probe the degenerate molecular shuttling processes, and afforded shuttling energy barriers (ΔG≠=10.4 kcal mol−1 for 1⋅ 4 PF6 and 2⋅ 4 PF6) that are in good agreement with the experimental values (ΔGc≠=9.6 and 10.3 kcal mol−1 for 1⋅ 4 PF6 and 2⋅ 4 PF6, respectively, probed by using their α-bipyridinium protons). 相似文献