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The redox potentials Em(QA/) of the primary quinone electron acceptor QA in oxygen-evolving photosystem II complexes of three species were determined by spectroelectrochemistry. The Em(QA/) values were experimentally found to be −162 ± 3 mV for a higher plant spinach, −171 ± 3 mV for a green alga Chlamydomonas reinhardtii and −104 ± 4 mV vs. SHE for a red alga Cyanidioschyzonmerolae. On the basis of possible deviations for the experimental values, as estimated to differ by 9-29 mV from each true value, plausible causes for such remarkable species-dependence of Em(QA/) are discussed, mainly by invoking the effects of extrinsic subunits on the delicate structural environment around QA. 相似文献
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The reaction of with Co(dmgBF2)2(H2O)2 in 1.0 M HClO4/LiClO4 was found to be first-order in both reactants and the [H+] dependence of the second-order rate constant is given by k2obs = b/[H+], b at 25 °C is 9.23 ± 0.14 × 102 s−1. The [H+] dependence at lower temperatures shows some saturation effect that allowed an estimate of the hydrolysis constant for as Ka = 9.5 × 10−3 M at 10 and 15 °C. Marcus theory and the known self-exchange rate constant for Co(OH2)5OH2+/+ were used to estimate an electron self-exchange rate constant of k22 = 1.7 × 10−4 M−1 s−1 for . 相似文献
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A water-insoluble hyperbranched β-d-glucan (TM3a), extracted from sclerotia of Pleurotus tuber-regium, was treated by microwave exposure to improve its solubility in water. This method led to complete dissolution of the TM3a polysaccharide in 0.02 wt % aqueous NaN3. Various treatment periods were tested, and optimal conditions corresponded to 35 s at 765 W. The solution properties of TM3a in water were studied systematically by using size-exclusion chromatography combined with laser light scattering, viscometry, and dynamic light scattering at 25 °C. The dependences of intrinsic viscosity ([η]), radius of gyration (), and hydrodynamic radius (Rh) on weight average molecular weight (Mw) for TM3a in 0.02 wt % aqueous NaN3 at 25 °C were found to be , , and in the Mw range from 8.20 × 105 to 4.88 × 106. The fractal dimension, ratio of , and the <r2>o/Mw value of TM3a were calculated and discussed. The results indicated that TM3a existed in a sphere-like conformation in 0.02 wt % aqueous NaN3. Furthermore, by using transmission electron microscopy, we observed directly the spherical molecules of TM3a. This work gave valuable information on improvement of solubility and chain conformation characterization of the water-insoluble polysaccharide in water. 相似文献
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Paul T. Maragh 《Inorganica chimica acta》2005,358(13):3610-3616
The aquation of the title complex cation in aqueous perchloric acid proceeded via two steps, both postulated to be the proton attack on the oxygen atom which binds the acetate ligand to the metal centre, followed by Fe-O bond cleavage. This was followed by rapid decomposition to produce aqueous iron(III) and acetate ions. The first-order rate constants for the first and second steps at 25 °C are: k1 = (4.16 ± 0.58) × 10−2 s−1 and k2 = (2.09 ± 0.42) × 10−3 s−1, respectively, and their corresponding activation parameters are . The spontaneous hydrolysis rate constants for the first and second steps were also determined at 25 °C and ionic strength of 1 mol dm−3 and they are k0 = (3.10 ± 0.82) × 10−3 s−1 and , respectively. The corresponding activation parameters are . 相似文献
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Patrick J. Cappillino Gerard T. Rowe Mark Harvey Adonis Stassinopoulos William H. Armstrong 《Inorganica chimica acta》2009,362(7):2136-782
A series of binuclear iron compounds has been synthesized using diamide, bis-phenolate ligands in which the carbon-linker between the amide nitrogen atoms has been varied. Two diferrous compounds in the series, along with their two-electron oxidized, di-μ-methoxy-bridged counterparts, have been crystallographically characterized, as have the di-μ-methoxy compounds (H2Hbab = 1,2-bis(2-hydroxybenzamido) benzene, H2Hbach = trans-1,2-bis(2-hydroxybenzamido) cyclohexane, H2Hbame = 1,2-bis(2-hydroxybenzamido) ethane, H2Hbap = 1,3-bis(2-hydroxybenzamido) propane, H2Hbabn = 1,4-bis(2-hydroxybenzamido) butane, H2Hbapen = 1,5-bis(2-hydroxybenzamido) pentane, N-MeIM = N-methylimidazole and OMe = methoxide). are structurally very similar to previously reported diferrous compounds of this family of ligands that have been shown to be active as oxygen atom transfer catalysts. Flexibility in the carbon-linker allows some variability in the orientation of the phenolate arms of the ligands in the diferric di-μ-methoxy compounds, but the Fe2O2 core remains largely unchanged across the series. Two-electron oxidation of the ferrous compounds in methanol shows a substantial ligand rearrangement that is consistent with other spectroscopic, electrochemical and kinetic investigations. The loss of both phenolate bridges upon oxidation is reminiscent of the “carboxylate shift” observed in binuclear non-heme enzymes and could provide insight into the driving force behind this family of compounds’ function as a catalyst. 相似文献
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Vanessa S.A. Barbosa Antônia C.J. Câmara Daniel P. Oliveira Aldo C. Medeiros 《Experimental parasitology》2009,123(4):309-312
With the aim of investigating the biodistribution of technetium-99 m pertechnetate () in rats infected with Y strain of Tripanosoma Cruzi, at the peak of parasitemia, (14th day of infection), we injected Wistar rats with 0.1 ml of (3.7 MBq). After 60 min, the percentage of radioactivity per gram was counted in several isolated organs and blood, using a gamma counter (1470 Wizard, PerkinElmer Finland). The uptake of increased significantly in blood and decreased in the colon of infected animals (p < 0.05). A significant reduction in serum iron and red blood cells and a significant increase in total proteins, leukocytes and lymphocytes in the infected rats were observed, compared with controls (p < 0.05). A reduction in muscle layer thickness of the colon and mononuclear inflammation were observed. These results conclusively demonstrate that T. cruzi infection would be associated with changes in the biodistribution of and in colon morphology, with potential clinical implications. 相似文献
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The system was studied at 25 °C and at I = 0.1 M NaClO4 using hydrodynamic voltammetry, gold potentiometry, UV-Vis spectrophotometry and Raman spectroscopy. The presence of two mixed-ligand species, Au(S2O3)(SO3)3− and , was detected from the Raman experiments and supported by the gold potentiometric experiments. The stepwise formation constant, log K11r, for the reaction was found to be 1.1 (r = 1) and 4.8 (r = 2) from the hydrodynamic voltammetric experiments. 相似文献
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Rachel Gilbert 《Inorganica chimica acta》2010,363(7):1462-1468
Unlike other chlorometallate complexes that catalyze the photodecomposition of haloalkanes through photodissociation of a chlorine atom, both and catalyze chloroform decomposition through a process that appears to involve C-H bond breakage from an excited state association complex with chloroform. This would account for the greatly retarded rate of decomposition in CDCl3 and for the generation of CCl4 as a side product. In chloroform, and are in slow equilibrium with each other. The rate for the conversion of - in chloroform at 23 °C obeys the expression (0.03 M−1 s−1) [][Cl−]. The equilibrium constant, K = [][Cl−]2/[]2, was estimated to be 3 × 10−3 M in CHCl3. 相似文献
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Linkage relationship between the genes for adenosine deaminase and S-adenosyl-homocysteine hydrolase on human chromosome 20 总被引:2,自引:0,他引:2
Summary The genes for adenosine deaminase (ADA) and Sadenosyl homocysteine hydrolase (AHCY or SAHH) are known to be syntenic and within
measurable distance from each other, on chromosome 20 in man. In the present study an informative family is described in which
the recombination fraction (θ) between the respective genes is estimated to be about 0.18. Together with the published finding
of θ=0.15 (Eiberg and Mohr 1985) in informative Danish families, the recombination fraction for the pooled data is calculated
to be θ=0.14 (in men),
(in women) and
(both sexes taken together). 相似文献
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Daniella Bonaventura Gerson J. Rodrigues Juliana A. Vercesi Roberto S. da Silva Lusiane M. Bendhack 《Journal of inorganic biochemistry》2009,103(10):1366-1374
Nitrosyl ruthenium complexes have been characterized as nitric oxide (NO) donors that induce relaxation in the denuded rat aorta. There are some differences in their vascular relaxation mechanisms compared with sodium nitroprusside. This study investigates whether the endothelium could interfere with the [Ru(terpy)(bdq)NO]3+-TERPY-induced vascular relaxation, by analyzing the maximal relaxation (Emax) and potency (pD2) of TERPY. Vascular reactivity experiments showed that the endothelium negatively modulates (pD2: 6.17 ± 0.07) the TERPY relaxation in intact rat aortic rings compared with the denuded rat aorta (pD2: 6.65 ± 0.07). This effect is abolished by a non-selective NO-synthase (NOS) inhibitor L-NAME (pD2: 6.46 ± 0.10), by the superoxide anion () scavenger TIRON (pD2: 6.49 ± 0.08), and by an NOS cofactor BH4 (pD2: 6.80 ± 0.10). The selective dye for (DHE) shows that TERPY enhances concentration in isolated endothelial cells (intensity of fluorescence (IF):11258.00 ± 317.75) compared with the basal concentration (IF: 7760.67 ± 381.50), and this enhancement is blocked by L-NAME (IF: 8892.33 ± 1074.41). Similar results were observed in vascular smooth muscle cells (concentration of superoxide after TERPY: 2.63 ± 0.17% and after TERPY + L-NAME: −4.63 ± 0.14%). Considering that TERPY could induce uncoupling NOS, thus producing , we have also investigated the involvement of prostanoids in the negative modulation of the endothelium. The non-selective cyclooxygenase (COX) inhibitor indomethacin and the selective tromboxane (TXA2) receptor antagonist SQ29548 reduce the effect of the endothelium on TERPY relaxation (pD2 INDO: 6.80 ± 0.17 and SQ29548: 6.85 ± 0.15, respectively). However, a selective prostaglandin F2α receptor antagonist (AH6809) does not change the endothelium effect. Moreover, TERPY enhances the concentration of TXA2 stable metabolite (TXB2), but this effect is blocked by L-NAME and TIRON. The present findings indicate that TERPY induces uncoupling of eNOS, enhancing concentration. This enhancement in concentration induces COX activation, producing TXA2, which negatively modulates the rat aorta relaxation induced by the NO donor TERPY. 相似文献
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The kinetics of the reduction of by Co(dmgBF2)2(H2O)2 in 0.041 M HNO3/NaNO3 was found to be first-order in both the oxidizing and reducing agents and the second-order rate constant is given by kobs = k1 + k2K[Cl−], with k1=1.59 × 106 M−1 s−1and k2K = 1.83 × 108 M−2 s−1, at 25 °C. The term that is first-order in [Cl−] is attributed to the formation of an ion-pair between and Cl−. For k1, the activation parameters ΔH* and ΔS* are 2.22 ± 0.02 kcal mol−1 and −22.7 ± 0.8 cal mol−1 K−1, respectively. The self-exchange rate constant of k22 ≈ 8.7 × 10−3 M−1 s−1 for was estimated using Marcus theory and the known self-exchange rate constant for . 相似文献
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Didier G. Arqués Jean-Paul Fallot Christian J. Michel 《Bulletin of mathematical biology》1998,60(1):163-194
The self-complementary subset
∪{AAA,TTT} with
= {AAC, AAT, ACC, ATC, ATT, CAG, CTC, CTG, GAA, GAC, GAG, GAT, GCC, GGC, GGT, GTA, GTC, GTT, TAC, TTC} of 22 trinucleotides
has a preferential occurrence in the frame 0 (reading frame established by the ATG start trinucleotide) of protein (coding)
genes of both prokaryotes and eukaryotes. The subsets
∪{CCC} and
∪{GGG} of 21 trinucleotides have a preferential occurrence in the shifted frames 1 and 2 respectively (frame 0 shifted by
one and two nucleotides respectively in the 5′-3′ direction).
and
are complementary to each other. The subset
contains the subset
which has the rarity property (6 × 10−8) to be a complementary maximal circular code with two permutated maximal circular codes
and
in the frames 1 and 2 respectively.
is called a C3 code.
A quantitative study of these three subsets
in the three frames 0, 1, 2 of protein genes, and the 5′ and 3′ regions of eukaryotes, shows that their occurrence frequencies
are constant functions of the trinucleotide positions in the sequences. The frequencies of
in the frame 0 of protein genes are 49, 28.5 and 22.5% respectively. In contrast, the frequencies of
in the 5′ and 3′ regions of eukaryotes, are independent of the frame. Indeed, the frequency of
in the three frames of 5′ (respectively 3′) regions is equal to 35.5% (respectively 38%) and is greater than the frequencies
and
, both equal to 32.25% (respectively 31%) in the three frames.
Several frequency asymmetries unexpectedly observed (e.g. the frequency difference between
and
in the frame 0), are related to a new property of the subset
involving substitutions. An evolutionary analytical model at three parameters (p, q, t) based on an independent mixing of the 22 codons (trinucleotides in frame 0) of
with equiprobability (1/22) followed by t ≈ 4 substitutions per codon according to the proportions p ≈ 0.1; q ≈ 0.1 and r = 1 − p − q ≈ 0.8 in the three codon sites respectively, retrieves the frequencies of
observed in the three frames of protein genes and explains these asymmetries. Furthermore, the same model (0.1, 0.1, t) after t ≈ 22 substitutions per codon, retrieves the statistical properties observed in the three frames of the 5′ and 3′ regions.
The complex behaviour of these analytical curves is totally unexpected and a priori difficult to imagine. 相似文献