共查询到20条相似文献,搜索用时 32 毫秒
1.
Joshua Telser Kun-Yuan Chen Dmitry Smirnov J. Krzystek 《Journal of inorganic biochemistry》2009,103(4):487-495
Aminocarboxylate complexes of vanadium(III) are of interest as models for biologically and medicinally relevant forms of this interesting and somewhat neglected ion. The V(III) ion is paramagnetic, but not readily suited to conventional EPR, due to its integer-spin ground state (S = 1) and associated large zero-field splitting (zfs). High-frequency and -field EPR (HFEPR), however, has the ability to study such systems effectively. Three complexes, all previously structurally characterized: Na[V(trdta)] · 3H2O, Na[V(edta)(H2O)] · 3H2O, and [V(nta)(H2O)3] · 4H2O (where trdta stands for trimethylenediamine-N,N,N′,N′-tetraacetate and nta stands for nitrilotriacetate) were studied by HFEPR. All the investigated complexes produced HFEPR responses both in the solid state, and in aqueous solution, but those of [V(nta)(H2O)3] · 4H2O were poorly interpretable. Analysis of multi-frequency HFEPR spectra yielded a set of spin Hamiltonian parameters (including axial and rhombic zfs parameters: D and E, respectively) for these first two complexes as solids: Na[V(trdta)] · 3H2O: D = 5.60 cm−1, E = 0.85 cm−1, g = 1.95; Na[V(edta)(H2O)] · 3H2O: D = 1.4 cm−1, E = 0.14 cm−1, g = 1.97. Spectra in frozen solution yielded similar parameters and showed multiple species in the case of the trdta complex, which are the consequence of the flexibility of this ligand. The EPR spectra obtained in frozen aqueous solution are the first, to our knowledge, of V(III) in solution in general and show the applicability of HFEPR to these systems. In combination with very insightful previous studies of the electronic absorption of these complexes which provided ligand-field parameters, it has been possible to describe the electronic structure of V(III) in [V(trdta)]− and [V(edta)(H2O)]−; the quality of data for [V(nta)(H2O)3] does not permit analysis. Qualitatively, six-coordinate V(III) complexes with O,N donor atoms show no electronic absorption band in the NIR region, and exhibit relatively large magnitude zfs (D ? 5 cm−1), while analogous seven-coordinate complexes do have a NIR absorption band and show relatively small magnitude zfs (D < 2 cm−1). 相似文献
2.
Electron paramagnetic resonance (EPR) signals at g′ = 4.3 are commonly encountered in biological samples owing to mononuclear high-spin (S = 5/2) Fe3+ ions in sites of low symmetry. The present study was undertaken to develop the experimental method and a suitable g′ = 4.3 intensity standard and for accurately quantifying the amount of Fe3+ responsible for such signals. By following the work of Aasa and Vänngård (J. Magn. Reson. 19:308–315, 1975), we present equations relating the EPR intensity of S = 5/2 ions to the intensities of S = 1/2 standards more commonly employed in EPR spectrometry. Of the chelates tested, Fe3+–EDTA (1:3 ratio) in 1:3 glycerol/water (v/v), pH 2, was found to be an excellent standard for frozen-solution S = 5/2 samples at 77 K. The spin concentrations of Cu2+–EDTA and aqua VO2+, both S = 1/2 ions, and of Fe3+–transferrin, an S = 5/2 ion, were measured against this standard and found to agree within 2.2% of their known metal ion concentrations. Relative standard deviations of ±3.6, ±5.3 and ±2.9% in spin concentration were obtained for the three samples, respectively. The spin concentration determined for Fe3+–desferrioxamine of known Fe3+ concentration was anomalously low suggesting the presence of EPR-silent multimeric iron species in solution. 相似文献
3.
Brandon N. Hudder Jessica Garber Morales Audria Stubna Eckard Münck Michael P. Hendrich Paul A. Lindahl 《Journal of biological inorganic chemistry》2007,12(7):1029-1053
Mitochondria from respiring cells were isolated under anaerobic conditions. Microscopic images were largely devoid of contaminants, and samples consumed O2 in an NADH-dependent manner. Protein and metal concentrations of packed mitochondria were determined, as was the percentage of external void volume. Samples were similarly packed into electron paramagnetic resonance tubes, either in the as-isolated state or after exposure to various reagents. Analyses revealed two signals originating from species that could be removed by chelation, including rhombic Fe3+ (g = 4.3) and aqueous Mn2+ ions (g = 2.00 with Mn-based hyperfine). Three S = 5/2 signals from Fe3+ hemes were observed, probably arising from cytochrome c peroxidase and the a3:Cub site of cytochrome c oxidase. Three Fe/S-based signals were observed, with averaged g values of 1.94, 1.90 and 2.01. These probably arise, respectively, from the [Fe2S2]+ cluster of succinate dehydrogenase, the [Fe2S2]+ cluster of the Rieske protein of cytochrome bc 1, and the [Fe3S4]+ cluster of aconitase, homoaconitase or succinate dehydrogenase. Also observed was a low-intensity isotropic g = 2.00 signal arising from organic-based radicals, and a broad signal with g ave = 2.02. Mössbauer spectra of intact mitochondria were dominated by signals from Fe4S4 clusters (60–85% of Fe). The major feature in as-isolated samples, and in samples treated with ethylenebis(oxyethylenenitrilo)tetraacetic acid, dithionite or O2, was a quadrupole doublet with ΔE Q = 1.15 mm/s and δ = 0.45 mm/s, assigned to [Fe4S4]2+ clusters. Substantial high-spin non-heme Fe2+ (up to 20%) and Fe3+ (up to 15%) species were observed. The distribution of Fe was qualitatively similar to that suggested by the mitochondrial proteome. 相似文献
4.
The oxygen evolving complex of Photosystem II undergoes four light-induced oxidation transitions, S0-S1,…,S3-(S4)S0 during its catalytic cycle. The oxidizing equivalents are stored at a (Mn)4Ca cluster, the site of water oxidation. EPR spectroscopy has yielded valuable information on the S states. S2 shows a notable heterogeneity with two spectral forms; a g = 2 (S = 1/2) multiline, and a g = 4.1 (S = 5/2) signal. These oscillate in parallel during the period-four cycle. Cyanobacteria show only the multiline signal, but upon advancement to S3 they exhibit the same characteristic g = 10 (S = 3) absorption with plant preparations, implying that this latter signal results from the multiline configuration. The fate of the g = 4.1 conformation during advancement to S3 is accordingly unknown. We searched for light-induced transient changes in the EPR spectra at temperatures below and above the half-inhibition temperature for the S2 to S3 transition (ca 230 K). We observed that, above about 220 K the g = 4.1 signal converts to a multiline form prior to advancement to S3. We cannot exclude that the conversion results from visible-light excitation of the Mn cluster itself. The fact however, that the conversion coincides with the onset of the S2 to S3 transition, suggests that it is triggered by the charge-separation process, possibly the oxidation of tyr Z and the accompanying proton relocations. It therefore appears that a configuration of (Mn)4Ca with a low-spin ground state advances to S3. 相似文献
5.
Patrick L. Feng Christopher C. Beedle Changhyun Koo Jon Lawrence Stephen Hill David N. Hendrickson 《Inorganica chimica acta》2008,361(12-13):3465-3480
We review an extensive body of single-crystal high-frequency electron paramagnetic resonance (HFEPR) data in order to determine the transverse spin Hamiltonian parameters that control the tunneling of the direction of magnetization in a variety of integer and half-integer-spin single-molecule magnets (SMMs). The SMMs studied are members of the following families: S = 9/2 [Mn4O3Cl]6+; S = 5 [Mn3NiO4]6+; S = 6 [Mn3ZnO4]6+; and S = 4 [Ni4(OR)4]4+. HFEPR spectra for the half-integer S = 9/2 Mn4 complexes that have C3 symmetry do not provide measurable evidence for transverse spin Hamiltonian terms. This finding is consistent with the relatively large coercive field seen in the magnetization hysteresis loops for these complexes. On the other hand, a low symmetry S = 9/2 complex exhibits a much faster rate of ground-state magnetization tunneling, in agreement with HFEPR spectra for a powder sample that gives a rhombic zero-field splitting (ZFS) parameter of E = 0.140 cm?1. The S = 5 Mn3Ni systems exhibit magnetization tunneling that is much faster than seen for the high-symmetry S = 9/2 Mn4 complexes. This can be attributed to their integer-spin ground states. Like the C3 symmetry Mn4 SMMs, the HFEPR spectra for high-symmetry Mn3Ni complexes do not provide measurable evidence for transverse ZFS terms. However, the spectra exhibit broad peaks, suggesting distributions in the local molecular environments brought about by disordered solvate molecules. This disorder likely explains the fast tunneling in the high-symmetry S = 5 Mn3Ni systems, though one cannot rule out fourth- (and higher-) order interactions that cannot be detected by HFEPR due to the broad resonances. The one S = 6 Mn3Zn complex shows an even faster rate of tunneling compared to the isostructural S = 5 Mn3Ni complex. Finally, the S = 4 [Ni(hmp)(dmb)Cl]4 complex provides unique insights into the origin of fourth- (and higher-) order interactions found for many SMMs on the basis of analysis using a giant spin Hamiltonian (GSH) approximation. We conclude that the fourth-order anisotropy found for the S = 4 ground state of [Ni(hmp)(dmb)Cl]4 originates from the second-order ZFS interactions associated with the individual NiII ions, but only as a result of higher-order processes that occur via S-mixing between the ground state and higher-lying (S < 4) spin-multiplets. The S-mixing is relatively strong in this system because of comparable exchange and anisotropy energy scales. The relatively fast tunneling is a direct consequence of this S-mixing, as opposed to any intrinsic fourth-order (spin–orbit) anisotropy associated with NiII. 相似文献
6.
Jinyou Shen Xin Zhang Dan Chen Xiaodong Liu Libin Zhang Xiuyun Sun Jiansheng Li Huiping Bi Lianjun Wang 《Bioprocess and biosystems engineering》2014,37(6):1185-1192
Biodegradation of pyridine by a novel bacterial strain, Rhizobium sp. NJUST18, was studied in batch experiments over a wide concentration range (from 100 to 1,000 mg l?1). Pyridine inhibited both growth of Rhizobium sp. NJUST18 and biodegradation of pyridine. The Haldane model could be fitted to the growth kinetics data well with the kinetic constants μ* = 0.1473 h?1, K s = 793.97 mg l?1, K i = 268.60 mg l?1 and S m = 461.80 mg l?1. The true μ max, calculated from μ*, was found to be 0.0332 h?1. Yield coefficient Y X/S depended on S i and reached a maximum of 0.51 g g?1 at S i of 600 mg l?1. V max was calculated by fitting the pyridine consumption data with the Gompertz model. V max increased with initial pyridine concentration up to 14.809 mg l?1 h?1. The q S values, calculated from $V_{ \hbox{max} }$ , were fitted with the Haldane equation, yielding q Smax = 0.1212 g g?1 h?1 and q* = 0.3874 g g?1 h?1 at S m′ = 507.83 mg l?1, K s′ = 558.03 mg l?1, and K i′ = 462.15 mg l?1. Inhibition constants for growth and degradation rate value were in the same range. Compared with other pyridine degraders, μ max and S m obtained for Rhizobium sp. NJUST18 were relatively high. High K i and K i′ values and extremely high K s and K s′ values indicated that NJUST18 was able to grow on pyridine within a wide concentration range, especially at relatively high concentrations. 相似文献
7.
Marcus Hans Wolfgang Buckel Eckhard Bill 《Journal of biological inorganic chemistry》2008,13(4):563-574
The key enzyme of the fermentation of glutamate by Acidaminococcus fermentans, 2-hydroxyglutarylcoenzyme A dehydratase, catalyzes the reversible syn-elimination of water from (R)-2-hydroxyglutaryl-coenzyme A, resulting in (E)-glutaconylcoenzyme A. The dehydratase system consists of two oxygen-sensitive protein components, the activator (HgdC) and the actual dehydratase (HgdAB). Previous biochemical and spectroscopic studies revealed that the reduced [4Fe–4S]+ cluster containing activator transfers one electron to the dehydratase driven by ATP hydrolysis, which activates the enzyme. With a tenfold excess of titanium(III) citrate at pH 8.0 the activator can be further reduced, yielding about 50% of a superreduced [4Fe–4S]0 cluster in the all-ferrous state. This is inferred from the appearance of a new Mössbauer spectrum with parameters δ = 0.65 mm/s and ΔE Q = 1.51–2.19 mm/s at 140 K, which are typical of Fe(II)S4 sites. Parallel-mode electron paramagnetic resonance (EPR) spectroscopy performed at temperatures between 3 and 20 K showed two sharp signals at g = 16 and 12, indicating an integer-spin system. The X-band EPR spectra and magnetic Mössbauer spectra could be consistently simulated by adopting a total spin S t = 4 for the all-ferrous cluster with weak zero-field splitting parameters D = ?0.66 cm?1 and E/D = 0.17. The superreduced cluster has apparent spectroscopic similarities with the corresponding [4Fe–4S]0 cluster described for the nitrogenase Fe-protein, but in detail their properties differ. While the all-ferrous Fe-protein is capable of transferring electrons to the MoFe-protein for dinitrogen reduction, a similar physiological role is elusive for the superreduced activator. This finding supports our model that only one-electron transfer steps are involved in dehydratase catalysis. Nevertheless we discuss a common basic mechanism of the two diverse systems, which are so far the only described examples of the all-ferrous [4Fe–4S]0 cluster found in biology. 相似文献
8.
Richard D. Harcourt 《Journal of biological inorganic chemistry》2014,19(1):113-123
For the Fe–O2(S = 0) linkages of oxyhemes, valence bond (VB) structures are re-presented for the McClure [FeII(S = 1) + O2(S = 1)], Pauling–Coryell [FeII(S = 0) + O2*(S = 0)], and Weiss [FeIII(S = ½) + O2 ?(S = ½)] models of bonding. The VB structures for the McClure and Weiss models are of the increased-valence type, with more electrons participating in bonding than occur in their component Lewis structures. The Fe–O bond number and O–O bond order for the McClure structure are correlated with measured Fe–O and O–O bond lengths for oxymyoglobin. Back-bonding from O 2 ? to FeIII of the Weiss structure gives a restricted form of the McClure structure. The McClure and Weiss increased-valence structures are used to provide VB formulations of mechanisms for the oxyhemoglobin + NO reaction. The products of these two formulations are Hb+ and NO3 ? (where Hb is hemoglobin) and Hb+ and OONO?, respectively. Because Hb+ and NO3 ? are the observed products, they provide an experimental procedure for distinguishing the McClure and Weiss models. It is also shown that the same type of agreement between McClure-type theory and experiment occurs for oxycoboglobin + NO, cytochrome P450 monooxygenases, and related hydrogen atom transfer reactions. In the appendices, the results of density functional theory and multireference molecular orbital calculations for oxyhemes are related to one formulation of the increased-valence wavefunction for the McClure model, and theory is presented for the calculation of approximate weights for the Lewis structures that are components of the McClure increased-valence structure. 相似文献
9.
Xin Li Jinhong Pan Qigui Liu Enqing Xiong Zhiwen Chen Zhansong Zhou Yongping Su Gensheng Lu 《Molecular biology reports》2013,40(3):2431-2438
The Glutathione S-transferases (GSTs) polymorphisms have been implicated in susceptibility to male idiopathic infertility, but study results are still controversial. To investigate the genetic associations between GSTs polymorphisms and risk of male idiopathic infertility, a systematic review and meta-analysis were performed. Meta-analysis was performed by pooling odds ratio (OR) with its corresponding 95 % confidence interval (95 % CI) form studies in electronic databases up to March 16, 2012. Glutathione S-transferase M 1 (GSTM1) null genotype, Glutathione S-transferase T 1 (GSTT1) null genotype, and dual null genotype of GSTM1/GSTT1 were analyzed independently. 14 eligible studies with a total of 1,845 idiopathic infertility males and 1,729 controls were included. There were 13 studies on GSTM1 polymorphism, 10 ones on GSTT1 polymorphism and 5 ones on GSTM1-GSTT1 interaction analysis. Meta-analyses of total relevant studies showed GSTM1 null genotype was significantly associated with an increased risk of male idiopathic infertility (OR = 1.40, 95 % CI 1.07–1.84, P OR = 0.015). The GSTM1-GSTT1 interaction analysis showed dual null genotype of GSTM1/GSTT1 was also significantly associated with increased risk of male idiopathic infertility (OR = 1.85, 95 % CI 1.07–3.21, P OR = 0.028). Subgroup analyses by ethnicity showed the associations above were still statistically significant in Caucasians (For GSTM1, OR = 1.51, 95 % CI 1.11–2.05, P OR = 0.009; For GSTM1/GSTT1, OR = 2.10, 95 % CI 1.51–2.91, P OR < 0.001). This meta-analysis suggests GSTM1 null genotype contributes to increased risk of male idiopathic infertility in Caucasians, and males with dual null genotype of GSTM1/GSTT1 are particularly susceptible to developing idiopathic infertility. 相似文献
10.
Nils Hamann Eckhard Bill Jacob E. Shokes Robert A. Scott Marina Bennati Reiner Hedderich 《Journal of biological inorganic chemistry》2009,14(3):457-470
In type E succinate:quinone reductase (SQR), subunit SdhE (formerly SdhC) is thought to function as monotopic membrane anchor of the enzyme. SdhE contains two copies of a cysteine-rich sequence motif (CX n CCGX m CXXC), designated as the CCG domain in the Pfam database and conserved in many proteins. On the basis of the spectroscopic characterization of heterologously produced SdhE from Sulfolobus tokodaii, the protein was proposed in a previous study to contain a labile [2Fe–2S] cluster ligated by cysteine residues of the CCG domains. Using UV/vis, electron paramagnetic resonance (EPR), 57Fe electron–nuclear double resonance (ENDOR) and Mössbauer spectroscopies, we show that after an in vitro cluster reconstitution, SdhE from S. solfataricus P2 contains a [4Fe–4S] cluster in reduced (2+) and oxidized (3+) states. The reduced form of the [4Fe–4S]2+ cluster is diamagnetic. The individual iron sites of the reduced cluster are noticeably heterogeneous and show partial valence localization, which is particularly strong for one unique ferrous site. In contrast, the paramagnetic form of the cluster exhibits a characteristic rhombic EPR signal with g zyx = 2.015, 2.008, and 1.947. This EPR signal is reminiscent of a signal observed previously in intact SQR from S. tokodaii with g zyx = 2.016, 2.00, and 1.957. In addition, zinc K-edge X-ray absorption spectroscopy indicated the presence of an isolated zinc site with an S3(O/N)1 coordination in reconstituted SdhE. Since cysteine residues in SdhE are restricted to the two CCG domains, we conclude that these domains provide the ligands to both the iron–sulfur cluster and the zinc site. 相似文献
11.
Jennifer Morton Maria Chrysina Vincent S.J. Craig Fusamichi Akita Yoshiki Nakajima Wolfgang Lubitz Nicholas Cox Jian-Ren Shen Elmars Krausz 《BBA》2018,1859(2):88-98
Photosystem II passes through four metastable S-states in catalysing light-driven water oxidation. Variable temperature variable field (VTVH) Magnetic Circular Dichroism (MCD) spectra in PSII of Thermosynochococcus (T.) vulcanus for each S-state are reported. These spectra, along with assignments, provide a new window into the electronic and magnetic structure of Mn4CaO5. VTVH MCD spectra taken in the S2 state provide a clear g = 2, S = 1/2 paramagnetic characteristic, which is entirely consistent with that known by EPR. The three features, seen as positive (+) at 749 nm, negative (?) at 773 nm and (+) at 808 nm are assigned as 4A → 2E spin-flips within the d3 configuration of the Mn(IV) centres present. This assignment is supported by comparison(s) to spin-flips seen in a range of Mn(IV) materials. S3 exhibits a more intense (?) MCD peak at 764 nm and has a stronger MCD saturation characteristic. This S3 MCD saturation behaviour can be accurately modelled using parameters taken directly from analyses of EPR spectra. We see no evidence for Mn(III) d-d absorption in the near-IR of any S-state. We suggest that Mn(IV)-based absorption may be responsible for the well-known near-IR induced changes induced in S2 EPR spectra of T. vulcanus and not Mn(III)-based, as has been commonly assumed. Through an analysis of the nephelauxetic effect, the excitation energy of S-state dependent spin-flips seen may help identify coordination characteristics and changes at each Mn(IV). A prospectus as to what more detailed S-state dependent MCD studies promise to achieve is outlined. 相似文献
12.
Hsiou-Ting Kuo Po-An Yang Wei-Ren Wang Hao-Chun Hsu Cheng-Hsun Wu Yu-Te Ting Ming-Huei Weng Li-Hung Kuo Richard P. Cheng 《Amino acids》2014,46(8):1867-1883
The charge-containing hydrophilic functionalities of encoded charged amino acids are linked to the backbone via different numbers of hydrophobic methylenes, despite the apparent electrostatic nature of protein ion pairing interactions. To investigate the effect of side chain length of guanidinium- and carboxylate-containing residues on ion pairing interactions, α-helical peptides containing Zbb–Xaa (i, i + 3), (i, i + 4) and (i, i + 5) (Zbb = carboxylate-containing residues Aad, Glu, Asp in decreasing length; Xaa = guanidinium residues Agh, Arg, Agb, Agp in decreasing length) sequence patterns were studied by circular dichroism spectroscopy (CD). The helicity of Aad- and Glu-containing peptides was similar and mostly pH independent, whereas the helicity of Asp-containing peptides was mostly pH dependent. Furthermore, the Arg-containing peptides consistently exhibited higher helicity compared to the corresponding Agp-, Agb-, and Agh-containing peptides. Side chain conformational analysis by molecular mechanics calculations showed that the Zbb–Xaa (i, i + 3) and (i, i + 4) interactions mainly involved the χ 1 dihedral combinations (g+, g+) and (g?, g+), respectively. These low energy conformations were also observed in intrahelical Asp–Arg and Glu–Arg salt bridges of natural proteins. Accordingly, Asp and Glu provides variation in helix characteristics associated with Arg, but Aad does not provide features beyond those already delivered by Glu. Importantly, nature may have chosen the side chain length of Arg to support helical conformations through inherent high helix propensity coupled with stabilizing intrahelical ion pairing interactions with the carboxylate-containing residues. 相似文献
13.
Cristina Nardi Cristian Escudero Natalia Villarreal Gustavo Martínez Pedro Marcos Civello 《Journal of plant research》2013,126(1):151-159
A putative carbohydrate binding module (CBM) from strawberry (Fragaria × ananassa Duch.) expansin 2 (CBM-FaExp2) was cloned and the encoding protein was over-expressed in Escherichia coli and purified in order to evaluate its capacity to bind different cell wall polysaccharides “in vitro”. The protein CBM-FaExp2 bound to microcrystalline cellulose, xylan and pectin with different affinities (Kad = 33.6 ± 0.44 mL g?1, Kad = 11.37 ± 0.87 mL g?1, Kad = 10.4 ± 0.19 mL g?1, respectively). According to “in vitro” enzyme assays, this CBM is able to decrease the activity of cell wall degrading enzymes such as polygalacturonase, endo-glucanase, pectinase and xylanase, probably because the binding of CBM-FaExp2 to the different substrates interferes with enzyme activity. The results suggest that expansins would bind not only cellulose but also a wide range of cell wall polymers. 相似文献
14.
Daniele Kasper Elisabete Fernandes Albuquerque Palermo Christina Wyss Castelo Branco Olaf Malm 《Hydrobiologia》2012,694(1):87-98
Hydroelectric reservoirs can stratify, producing favorable conditions for mercury methylation in the hypolimnion. The methylmercury (MeHg) can be exported downstream, increasing its bioavailability below the dam. Our objective was to assess the mercury levels in plankton, suspended particulate matter (SPM) and fish collected upstream (UP) and downstream (DW) from the Reservatório de Samuel dam, an Amazonian reservoir that stratifies during half of the year. Mercury concentrations in both SPM and plankton were similar between the two sites, which could indicate there are no conditions favoring methylation at the moment of sampling (absence of stratification). Almost all mercury found in the muscle of fishes was in organic form, and differences of mercury levels between sites were dependent on the fishes trophic level. Herbivores showed similar mean organic mercury levels (UP = 117 μg g?1; DW = 120 μg g?1; n = 12), whereas omnivores (UP = 142 μg g?1; DW = 534 μg g?1; n = 27) and carnivores (UP = 545 μg g?1; DW = 1,366 μg g?1; n = 69) showed significantly higher values below the dam. The absence of a reservoir effect in herbivores is expected, since they feed on grassy vegetation, near the riverbanks, which is not much influenced by mercury in aquatic systems. On the other hand, the higher mercury levels below the dam observed for omnivores and carnivores suggest a possible influence of the reservoir since they feed on items that could be contaminated by MeHg exported from upstream. The results highlight the necessity of assessing areas downstream of reservoirs. 相似文献
15.
Effects of hyper-enriched reactive Fe on sulfidisation in a tidally inundated acid sulfate soil wetland 总被引:1,自引:0,他引:1
Annabelle F. Keene Scott G. Johnston Richard T. Bush Leigh A. Sullivan Edward D. Burton Angus E. McElnea Colin R. Ahern Bernard Powell 《Biogeochemistry》2011,103(1-3):263-279
Solid phase Fe and S fractions were examined in an acid sulfate soil (ASS) wetland undergoing remediation via tidal inundation. Considerable diagenetic enrichment of reactive Fe(III) oxides (HCl- and dithionite-extractable) occurred near the soil surface (0?C0.05 m depth), where extremely large concentrations up to 3534 ??mol/g accounted for ~90% of the total Fe pool. This major source of reactive Fe exerts a substantial influence on S cycling and the formation, speciation and transformation of reduced inorganic S (RIS) in tidally inundated ASS. Under these geochemical conditions, acid volatile sulfide (AVS; up to 57 ??mol/g) and elemental sulfur (S0; up to 41 ??mol/g) were the dominant fractions of RIS in near surface soils. AVS?CS to pyrite?CS ratios exceeded 2.9 near the surface, indicating that abundant reactive Fe favoured the accumulation of AVS minerals and S0 over pyrite. This is supported by the significant correlation of poorly crystalline Fe with AVS?CS and S0?CS contents (r = 0.83 and r = 0.85, respectively, P < 0.01). XANES spectroscopy provided direct evidence for the presence of a greigite-like phase in AVS?CS measured by chemical extraction. While the abundant reactive Fe may limit the transformation of AVS minerals and S0 to pyrite during early diagenesis (~5 years), continued sulfidisation over longer time scales is likely to eventually lead to enhanced sequestration of S within pyrite (with a predicted 8% pyrite by mass). These findings provide an important understanding of sulfidisation processes occurring in reactive Fe-enriched, tidally inundated ASS landscapes. 相似文献
16.
Robert L. Hopkins II Bradley M. Altier Derek Haselman Andrea D. Merry Jacob J. White 《Hydrobiologia》2013,713(1):87-95
Surface coal mining results in dramatic alterations of the landscape in central Appalachia, leading to a myriad of environmental problems. In this study, we explore the long-term effects of surface coal mining on stream chemistry and endeavor to gain a better understanding of the efficacy of reclamation. We examined 30 sites in the Raccoon Creek watershed in southeastern Ohio, where the majority of surface mine sites are in various stages of reclamation. Our results show that conductivity (r = 0.862; P = 0.000), sulfate (r = 0.619; P = 0.000), and aluminum (r = 0.469; P = 0.009) levels increase linearly as a function of the areal extent of reclaimed mines in each subwatershed, suggesting limited success of reclamation to restore natural stream chemistry. In contrast, pH was not significantly linearly correlated with the areal extent of surface mines. This suggests that local acid mine drainage remediation projects are able to regulate acidity levels in the watershed but not conductivity and certain heavy metal concentrations. Many sites had conductivity levels high enough to impair aquatic biota via ionic and osmoregulatory stress. In sum, surface coal mining appears to have a strong legacy effect on stream chemistry in the Raccoon Creek watershed. 相似文献
17.
Ismael Nieto Andrew Ozarowski J. Krzystek Jeremy M. Smith 《Inorganica chimica acta》2009,362(12):4449-9517
Two four-coordinate nickel complexes, HB(tBuIm)3NiBr and HB(tBuIm)3NiNO, were prepared by reaction of a bulky tris(carbene)borate ligand with NiBr2(PPh3)2 and NiBr(NO)(PPh3)2, respectively, and structurally and spectroscopically characterized. In addition to standard techniques, high-frequency and -field electron paramagnetic resonance (HFEPR) was employed to understand the spin triplet (S = 1) ground state of the bromo complex. HFEPR, combined with electronic absorption spectroscopy allows comparison of this novel complex with other paramagnetic four-coordinate Ni(II) species. The tris(carbene)borate ligand is a stronger σ-donor than corresponding tris(pyrazolyl)borates (traditional “scorpionate” ligands). The tris(carbene)borate ligand may also act as a π-acceptor, in contrast to tris(pyrazolyl)borates, which show relatively little π-bonding interactions. The influence of tris(carbene)borate substituents on the donor strength of the ligand have been elucidated from IR spectroscopic investigations of {NiNO}10 derivatives. HFEPR spectra of HB(tBuIm)3NiBr exhibit hyperfine coupling from Br, which indicates the strong electronic interaction between Ni(II) and this halide ligand, consistent with studies on tris(pyrazolyl)borate Ni(II) complexes. 相似文献
18.
Zhong-Yu You Zhi-Qiang Liu Yu-Guo Zheng 《Applied microbiology and biotechnology》2014,98(4):1671-1680
A carbonyl reductase (SCR2) gene was synthesized and expressed in Escherichia coli after codon optimization to investigate its biochemical properties and application in biosynthesis of ethyl (S)-4-chloro-3-hydroxybutanoate ((S)-CHBE), which is an important chiral synthon for the side chain of cholesterol-lowering drug. The recombinant SCR2 was purified and characterized using ethyl 4-chloro-3-oxobutanoate (COBE) as substrate. The specific activity of purified enzyme was 11.9 U mg?1. The optimum temperature and pH for enzyme activity were 45 °C and pH 6.0, respectively. The half-lives of recombinant SCR2 were 16.5, 7.7, 2.2, 0.41, and 0.05 h at 30 °C, 35 °C, 40 °C, 45 °C, and 50 °C, respectively, and it was highly stable in acidic environment. This SCR2 displayed a relatively narrow substrate specificity. The apparent K m and V max values of purified enzyme for COBE are 6.4 mM and 63.3 μmol min?1 mg?1, respectively. The biocatalytic process for the synthesis of (S)-CHBE was constructed by this SCR2 in an aqueous–organic solvent system with a substrate fed-batch strategy. At the final COBE concentration of 1 M, (S)-CHBE with yield of 95.3 % and e.e. of 99 % was obtained after 6-h reaction. In this process, the space-time yield per gram of biomass (dry cell weight, DCW) and turnover number of NADP+ to (S)-CHBE were 26.5 mmol L?1 h?1 g?1 DCW and 40,000 mol/mol, respectively, which were the highest values as compared with other works. 相似文献
19.
Sónia P. M. Ventura Valéria C. Santos-Ebinuma Jorge F. B. Pereira Maria F. S. Teixeira Adalberto Pessoa João A. P. Coutinho 《Journal of industrial microbiology & biotechnology》2013,40(5):507-516
There is a growing demand for natural colorants. This is prompting the search for new alternative and “benign” separation systems allowing higher recoveries, extraction yields, and selectivities. This work investigates the use of aqueous two-phase systems (ATPS) based on ionic liquids as extraction processes for the recovery of red colorants from the fermented broth of Penicillium purpurogenum DPUA 1275. Several ATPS based on quaternary ammonium and imidazolium were studied in this work aiming at separating the red colorants produced from the remaining colorants and contaminant proteins present in the fermented broth. The results suggest that the red colorants can be isolated by an appropriate manipulation of some of the process conditions, such as the use of quaternary ammonium with short alkyl chains, alkaline media, and short tie-line lengths (extraction point systems with lower concentrations of ionic liquid). These conditions allow large partition coefficients for the red colorants (K red = 24.4 ± 2.3), high protein removal (60.7 ± 2.8 %) and selectivity parameters (S red/prot = 10.05). 相似文献
20.
Ufuk Paksu Canan Aydaş Ülkü Rabia Yüce Talat Aydın Mustafa Polat Birol Engin 《Radiation and environmental biophysics》2013,52(2):255-267
Electron spin resonance (ESR) and thermoluminescence (TL) signals induced by gamma irradiation in linden (Tilia vulgaris) were studied for detection and dosimetric purposes. Before irradiation, linden leaf samples exhibit one singlet ESR signal centred at g = 2.0088. Besides this central signal, in spectra of irradiated linden samples, two weak satellite signals situated about 3 mT left (g = 2.0267) and right (g = 1.9883) were observed. Dose–response curves for the left satellite signal and the central single signal were constructed, and it was found that both of these curves can be described best by the combination of two exponential saturation functions. Variable temperature and fading studies at room temperature showed that the radiation-induced radicals in linden leaf samples are very sensitive to temperature. The stabilities of the left satellite (g = 2.0267) and the central single (g = 2.0088) signal at room temperature over a storage period of 126 days turned out to be best described by a sum of two first-order decay functions. The kinetic features of the left satellite signal were studied over the temperature range of 313–373 K. The results indicate that the isothermal decay curves of the left satellite ESR signal also proved to be best fitted by the combination of two first-order decay functions. Fading and annealing studies suggested the existence of two different radiation-induced free radical species. At the same time, Arrhenius plots evidenced two different kinetic regimes with two different activation energies. TL investigation of polyminerals from the linden samples allowed to discriminate clearly between irradiated and unirradiated samples even 75 days after irradiation. 相似文献