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1.
Although photooxidation of water and numerous other species which are part of reversible redox couples is poorly efficient at nanocrystalline TiO2, conversely high photocurrent efficiencies are observed for the oxidation of various organic molecules.This is associated with the fact that in most cases photooxidation of organic molecules does not produce species able to act as electron scavengers. The behaviour of nanocrystalline TiO2 photoelectrodes is clearly dominated by the indirect recombination or redox cycling where intermediates or products of the hole transfer act in turn as electron scavengers. These processes occur whatever the applied anodic bias showing that the actual potential in most of the nanocrystalline TiO2 film is disconnected from that imposed to the conducting substrate. 相似文献
2.
Thirty crop species provide 90% of our food, most of which display severe yield losses under moderate salinity. Securing and augmenting agricultural yield in times of global warming and population increase is urgent and should, aside from ameliorating saline soils, include attempts to increase crop plant salt tolerance. This short review provides an overview of the processes that limit growth and yield in saline conditions. Yield is reduced if soil salinity surpasses crop‐specific thresholds, with cotton, barley and sugar beet being highly tolerant, while sweet potato, wheat and maize display high sensitivity. Apart from Na+, also Cl?, Mg2+, SO42‐ or HCO3‐ contribute to salt toxicity. The inhibition of biochemical or physiological processes cause imbalance in metabolism and cell signalling and enhance the production of reactive oxygen species interfering with cell redox and energy state. Plant development and root patterning is disturbed, and this response depends on redox and reactive oxygen species signalling, calcium and plant hormones. The interlink of the physiological understanding of tolerance processes from molecular processes as well as the agronomical techniques for stabilizing growth and yield and their interlinks might help improving our crops for future demand and will provide improvement for cultivating crops in saline environment. 相似文献
3.
The rate constant of the electron self-exchange reaction, which proceeds via the outer sphere mechanism, k11, of a redox couple, reflects the basic tendency of the reaction to participate in redox processes. Often k11 is derived from the rate constant of a redox reaction, k12, by applying the Marcus cross relation: k12 = (k11k22K12f12)1/2W12. This derivation is based on the assumption that the products of the cross reaction are formed in their ground states. However, the k11 values obtained by this method for several redox systems, e.g. for [Co(NH3)6]3+/2+, Cu2+/+(aq) and Eu3+/2+(aq), depend strongly on the redox reaction studied for its derivation. It is proposed that these discrepancies are due to the formation, in some of these reactions, of products in vibrationally excited states and/or as isomers of the final products. Thus, the lowest value of k11 obtained experimentally is either correct or an upper limit for the correct value if correct k22 are used. 相似文献
4.
Lucia Banci Ivano Bertini Simone Ciofi-Baffoni Tatiana Kozyreva Mirko Mori Shenlin Wang 《Journal of biological inorganic chemistry》2011,16(3):391-403
Sco proteins are widespread in eukaryotic and in many prokaryotic organisms. They have a thioredoxin-like fold and bind a
single copper(I) or copper(II) ion through a CXXXC motif and a conserved His ligand, with both tight and weak affinities.
They have been implicated in the assembly of the CuA site of cytochrome c oxidase as copper chaperones and/or thioredoxins. In this work we have structurally characterized a Sco domain which is naturally
fused with a typical electron transfer molecule, i.e., cytochrome c, in Pseudomonas putida. The thioredoxin-like Sco domain does not bind copper(II), binds copper(I) with weak affinity without involving the conserved
His, and has redox properties consisting of a thioredoxin activity and of the ability of reducing copper(II) to copper(I),
and iron(III) to iron(II) of the cytochrome c domain. These findings indicate that the His ligand coordination is the discriminating factor for introducing a metallochaperone
function in a thioredoxin-like fold, typically responsible for electron transfer processes. A comparative structural analysis
of the Sco domain from P. putida versus eukaryotic Sco proteins revealed structural determinants affecting the formation of a tight-affinity versus a weak-affinity
copper binding site in Sco proteins. 相似文献
5.
Redox active metallo-proteins and metallo-peptides attached to self-assembled monolayers (SAM) of thiols on Au electrodes or constituting the SAM on Au electrodes can provide unique opportunities to investigate a range of complicated biological phenomena in controlled abiological constructs. In addition to conventional biochemical tools like site-directed mutagenesis, these constructs allow control over electron transfer (ET) processes, micro solvation (SAM design), folding/misfolding and orientation of these biological entities. This article presents a review of the work done by this group in creating abiological bio-inspired SAM on Au electrodes to probe several important biological processes where redox plays or might play a major role. These include stabilisation of different morphologies of Aβ peptides and which allow investigation of the reactivity of their Cu/Zn/heme-bound forms, determination of both outer-sphere and inner-sphere reorganisation energies of cytochrome c along with deciphering the role of the fluxional methionine and finally creation of bio-chemical constructs of cytochrome c oxidase which not only reduce O2 selectively to H2O efficiently but also provide key insights in O2 reduction mechanism which has aided the development of efficient artificial catalysts. 相似文献
6.
Mor Tsafrir S. Hundal Torill Ohad Itzhak Andersson Bertil 《Photosynthesis research》1997,53(2-3):205-213
The function of the cytochrome b559, a Photosystem II (PS II) reaction center ubiquitous component is not yet known. Cytochrome b559appears in a high (HP) or low (LP) potential form. The HP form is converted into the LP form during aerobic photoinhibition. It has been proposed before that this conversion, assumed to be reversible, ascribes protection against light stress of PS II by redirecting electron flow within PS II thus avoiding charge recombination of the primary radical pair and related oxidative damage. Here, we have used an experimental system allowing to assay the relation between the cytochrome b559redox potential shift, its reversibility and protection against light induced PS II inactivation. Under anaerobic conditions fast reversible photoinactivation of PS II in isolated spinach thylakoids is observed accompanied by monomerisation of PS II. Monomers did not dissociate further into PS II sub-particles and did not migrate out of the grana partitions as observed in aerobic photoinactivation. The anaerobic photoinactivation is accompanied by an increase in the cytochrome b559LP/HP ratio. However, despite recovery of PS II activity and partially of its dimeric form in darkness under aerobic conditions, no reversal of the cytochrome b559redox potential shift accompanied these processes. Re-exposure of reactivated thylakoids having an increased PS II population in the LP form of the cytochrome b559to strong illumination under aerobic conditions, did not result in a measurable protection of PS II as compared to control thylakoids. While it is possible that cytochrome b559may play a protective role against light stress in PS II, the results presented here do not indicate that the increase in the ratio LP/HP form is involved in this process. 相似文献
7.
The reduction of ferricytochrome c in the presence of 6-hydroxydopamine/O2 mixtures was examined under various reaction conditions. As the autoxidation of 6-hydroxy-dopamine progressed to completion, there were fluctuations in the net redox reactivity between reducing and oxidizing steady states. This was reflected in a sequence of damped oscillations in the redox state of cytochrome c. Corresponding to the time when 6-hydroxydopamine was 75–100% exhausted, reoxidation of the ferrocytochrome c occurred (prevented by catalase or catalase plus Superoxide dismutase). After the H2O2, in turn, was mostly consumed, the next phase commenced in which the cytochrome c became reduced for a second time. This reductive phase was 52% inhibited by superoxide dismutase. In the subsequent and final phase of the process, a progressive oxidation of cytochrome c lasting at least 24 h was observed. Of the initial reduction of ferricytochrome c, at most 37% can be attributed to direct reduction by 6-hydroxydopamine or its semiquinone. This initial net reduction of cytochrome c was inhibited 51% by superoxide dismutase and 41% by catalase. However, since either catalase or superoxide dismutase inhibited the autoxidation of 6-hydroxydopamine by at least as much as it slowed the reduction of cytochrome c, their effects in slowing the reduction of cytochrome c resulted largely from the decreased production of those free radicals which reduce ferricytochrome c, and only in part from accelerated removal. Elimination of the actions of transition metal ions (whether by passage of the buffer solutions through Chelex 100 resins or by addition of desferrioxamine to the reaction medium) slowed both the reoxidation and rereduction by up to 96%. Addition of mannitol decreased the rate of the first reoxidation by 25% and increased the rate of the rereduction by 7%. In general, the oscillations are explicable in terms of changes in the steady state levels of O2 and H2O2, with metal ions playing a major role and hydroxyl radicals a minor role in both the reoxidation and rereduction. 相似文献
8.
The processes of speciation and macroevolution of root nodule bacteria (rhizobia), based on deep rearrangements of their genomes and occurring in the N2-fixing symbiotic system, are reconstructed. At the first stage of rhizobial evolution, transformation of free-living diazotrophs (related to Rhodopseudomonas) to symbiotic N2-fixers (Bradyrhizobium) occurred due to the acquisition of the fix gene system, which is responsible for providing nitrogenase with electrons and redox potentials, as well as for oxygen-dependent regulation of nitrogenase synthesis in planta, and then of the nod genes responsible for the synthesis of the lipo-chitooligosaccharide Nod factors, which induce root nodule development. The subsequent rearrangements of bacterial genomes included (1) increased volume of hereditary information supported by species, genera (pangenome), and individual strains; (2) transition from the unitary genome to a multicomponent one; and (3) enhanced levels of bacterial genetic plasticity and horizontal gene transfer, resulting in formation of new genera—of which Mesorhizobium, Rhizobium, and Sinorhizobium are the largest—and of over 100 species. Rhizobial evolution caused by development and diversification of the Nod factor-synthesizing systems may result in either relaxed host specificity range (transition of Bradyrhizobium from autotrophic to symbiotrophic carbon metabolism in interaction with a broad spectrum of legumes) or narrowed host specificity range (transition of Rhizobium and Sinorhizobium to “altruistic” interaction with legumes of the galegoid clade). Reconstruction of the evolutionary pathway from symbiotic N2-fixers to their free-living ancestors makes it possible to initiate the studies based on up-to-date genome screening technologies and aimed at the issues of genetic integration of organisms into supraspecies complexes, ratios of the macro- and microevolutionary mechanisms, and development of cooperative adaptations based on altruistic interaction between the symbiotic partners. 相似文献
9.
《Euro III-Vs Review》1990,3(6):38
There exists an increasing interest in the development of low damage, dry etch processes for III–V materials. For the etching of GaAs, a wide range of gases has been employed, including: Cl2, BCl3, CCl4, SiCl4, CCl2F2 with and without various mixtures of O2, H2, He and Ar. Damage is of particular concern in devices such as MESFETs and HEMTs but it is possible to reduce it by achieving developing etch rate processes (and therefore, shorter etching times) and lower bombardment energies. Oxford Plasma Technology has been involved in the development of CCl2F2/He etching of GaAs by ECR based on the work of Rebecca Cheung1 in which the low damage capabilities of ECR etching over RIE were proved. 相似文献
10.
11.
Oxidation/reduction potential (ORP, redox potential, or Eh) is one of the physicochemical parameters characterizing the state
of microbial cultures. Changes in pH and concentration of the redoxactive gases (O2, H2, and H2S) in the cultivation medium are assumed to be the major factors of redox potential changes in the cultures of aerobic microorganisms.
In the review, results of the studies of redox potential changes in various bacterial cultures under various stress conditions
are summarized. The characteristic feature of these stress factors is the absence of direct correlation between the redox
potential, on one hand, and partial oxygen pressure and pH, on the other. Extracellular low-molecular weight thiols (LWT)
were demonstrated to be the major contributors to such changes in the redox potential. The possible role of the changes in
LWT concentrations inside and outside the cells in the processes of signal transduction and redox regulation of cellular functions
is discussed. 相似文献
12.
Concentrations of 0.5% O2 immediately inhibited CH4 production from methanol by Methanosarcina barkeri. Simultaneously, the redox potential of the medium increased to about +100 mV. However, the rates of CH4 production were not significantly affected, when the redox potential of an anoxic medium was adjusted to values between -420 mV and +100 mV by addition of titanium (III) citrate, sodium dithionite, flavin adenine dinucleotide, or sodium ascorbate. When the redox potential was adjusted to values between -80 mV and +550 mV by means of mixtures of ferrocyanide and ferricyanide, CH4 production was not inhibited until a redox potential of about +420 mV was reached. M. barkeri was able to reduce 0.5 mM ferricyanide solution at +430 mV within <30 min to a value of about +50 mV, and then to start CH4 production. Higher ferricyanide concentrations were only partially reduced. The extent of reduction of ferricyanide was also dependent on the substrate concentration (methanol) and the density of the bacterial suspension. The results show that M. barkeri was able to generate to a certain extent by itself the redox environment which suited the production of CH4. However, the bacteria probably have not enough reducing power to decrease the redox potential below the critical level of +50 mV, if O2 is present at concentrations >0.005%. 相似文献
13.
We explored the behaviour of a series of phenolic acids used as enhancers or inhibitors of luminol chemiluminescence by three different methods to determine if behaviour was associated with phenolic acid structure and redox character. All the phenolic acids inhibited chemiluminescence when hexacyanoferrate(III) was reacted with the phenolic acids before adding luminol. The redox character of these compounds was clearly related to structure. When hexacyanoferrate(III)-luminol-O2 chemiluminescence was initiated by phenolic acid-luminol mixtures some phenolic acids behaved as enhancers of chemiluminescence, and others as inhibitors. We propose a mechanism to explain these findings. We found direct relationships between the redox character of the phenolic acids and the enhancement or inhibition of the chemiluminescence of the luminol–H2O2–peroxidase system and we propose mechanism to explain these phenomena. 相似文献
14.
The source waters of acid‐sulphate‐chloride (ASC) geothermal springs located in Norris Geyser Basin, Yellowstone National Park contain several reduced chemical species, including H2, H2S, As(III), and Fe(II), which may serve as electron donors driving chemolithotrophic metabolism. Microorganisms thriving in these environments must also cope with high temperatures, low pH (~3), and high concentrations of sulphide, As(III), and boron. The goal of the current study was to correlate the temporal and spatial distribution of bacterial and archaeal populations with changes in temperature and geochemical energy gradients occurring throughout a newly formed (redirected) outflow channel of an ASC spring. A suite of complimentary analyses including aqueous geochemistry, microscopy, solid phase identification, and 16S rDNA sequence distribution were used to correlate the appearance of specific microbial populations with biogeochemical processes mediating S, Fe, and As cycling and subsequent biomineralization of As(V)‐rich hydrous ferric oxide (HFO) mats. Rapid As(III) oxidation (maximum first order rate constants ranged from 4 to 5 min?1, t1/2 = 0.17 ? 0.14 min) was correlated with the appearance of Hydrogenobaculum and Thiomonas–like populations, whereas the biogenesis of As(V)‐rich HFO microbial mats (mole ratios of As:Fe ~0.7) was correlated with the appearance of Metallosphaera, Acidimicrobium, and Thiomonas–like populations. Several 16S sequences detected near the source were closely related to sequences of chemolithotrophic hyperthermophilic populations including Stygiolobus and Hydrogenobaculum organisms that are known H2 oxidizers. The use of H2, reduced S(–II,0), Fe(II) and perhaps As(III) by different organisms represented throughout the outflow channel was supported by thermodynamic calculations, confirming highly exergonic redox couples with these electron donors. Results from this work demonstrated that chemical energy gradients play an important role in establishing distinct community structure as a function of distance from geothermal spring discharge. 相似文献
15.
Kerstin Würges Katerina Petrusevska Stephanie Serci Susanne Wilhelm Christian Wandrey Andreas Seidel-Morgenstern Martin P. Elsner Stephan Lütz 《Journal of Molecular Catalysis .B, Enzymatic》2009,58(1-4):10-16
The demand for enantiopure substances, e.g. for pharmaceutical applications or fine chemical production, continues to increase. This has led to the development of numerous stereoselective synthesis methods. Nevertheless a large number of chemical syntheses still result in racemic mixtures making a subsequent enantioseparation step necessary and thus are restricted to a maximum yield of 50%. Our work focuses on strategies to overcome this limitation by combining physicochemical separation processes with enzymatic racemization of the unwanted enantiomer in order to produce enantiopure amino acids. This paper deals with the production and characterization of a suitable amino acid racemase with broad substrate specificity (EC 5.1.1.10) from Pseudomonas putida which we cloned into Escherichia coli. Two enzyme lyophilizates of different purity were obtained from which the crude (CL) was sufficient for the racemization of methionine (Met) and the pure (PL) was used for asparagine (Asn). Racemization reactions of D-/L-Asn in H2O and D-/L-Met in 95 vol.% 100 mM KPi-buffer, 5 vol.% methanol (MeOH) at different pH values and temperatures were characterized. The studied range of reaction parameters was chosen in dependency on planned enantioseparation processes. We found increasing Vmax values when temperature was risen stepwise from 20 to 40 °C for both systems and when pH was shifted from 6 to 8 for the Met system. The presented results provide the basis for engineering enzyme-assisted physicochemical enantioseparation processes. 相似文献
16.
J W Wimpenny 《Biotechnology and bioengineering》1969,11(4):623-629
On increasing aeration rate in chemostat cultures of E. coli the redox potential (Eh) of the culture changes from ?l50 mv to +250 mv. During this period only a slight increase in measured dissolved oxygen concentration is observed. It is suggested that Eh be used as a control variable for aeration in the oxygen limited growth condition, whilst dissolved oxygen concentration be used as control variable in the presence of excess oxygen. Change in cytochrome b1, three tricarboxylic acid cycle enzymes and hydrogenase can be related to culture Eh. These changes are discussed. 相似文献
17.
18.
Gibberellic acid (GA3) is a commercially important plant growth hormone, which is gaining much more attention all over the world due to its effective
use in agriculture and brewing industry. Industrially it is produced by submerged fermentation technique using Ascomycetous
fungusGibberella fujikuroi. Solid state and immobilized cell fermentation techniques had also been developed as an alternative to obtain higher yield
of GA3. This review summarizes the problems of GA3 fermentation such as production of co-secondary metabolites along with GA3, substrate inhibition and degradation of GA3 to biologically inert compound gibberellenic acid, which limits the yield of GA3 in the fermentation medium. These problems can be overcome by various bioprocessing strategiese.g. two-stage and fed batch cultivation processes. Further research on bioreactor operation strategies such as continuous and/or
extractive fermentation with or without cell recycle/retention system need to be investigated for improvement in yield and
productivity. Down stream processing for GA3 isolation is also a challenge and procedures available for the same have been critically evaluated. 相似文献
19.
V. Teplyakov E. Sostina I. Beckman A. Netrusov 《World journal of microbiology & biotechnology》1996,12(5):477-485
Integrated non-porous membrane systems were applied for microbial combustible gas separation processes. Methane/CO2 mixtures of various concentrations from methane fermentation processes (biogas) were separated using a membrane-separation complex of permabsorber type into individual components of technical grade (more than 95% purity). In experiments with three-component mixtures, using a selective membrane valve with various liquid carriers, all the gases of interest (H2, CH4 and CO2) were obtained at greater than 90% purity in one separation step. The perspectives for the further application of non-porous membrane separating devices for various gaseous mixtures from different microbial processes are discussed.V. Teplyakov and E. Sostina are with the A.V. Topchiev institute of Petrochemical Synthesis, Russian Academy of Sciences, Membrane Research Center, Moscow 117912, Russia. E. Sostina is also, and A. Netrusov is with the Microbiology Department, Moscow University, Moscow 119899, Russia. I. Beckman is with the Chemistry Department, Moscow University, Moscow 119899, Russia. 相似文献
20.
Michelle K. Taylor Leonard E.A. Berlouis Alan R. Kennedy 《Inorganica chimica acta》2006,359(8):2455-2464
We report a study which correlates the metrical parameters of the unsubstituted tetradentate copper Schiff base complexes containing N2O2, N2N2 and N2S2 donors with their respective redox potentials. To achieve this aim we were required to structurally characterise many of the seminal species including, [CuAmbpr-H2], [CuH4Amben][ClO4]2, [CuH4Ambpr][ClO4]2, [CuH4Ambbu][ClO4]2, CuH4Salpr and [Cu(SSalen)2][ClO4]2 which were absent from the crystallographic catalogue. The oxidative dehydrogenation of CuH4Salen is revisited through the isolation and structural characterisation of (N-salicyl-N′-salicylidene-1,2-ethylenediamine)copper(II) (CuH3Salen). The redox potentials of the three series of compounds are measured, clearly identifying the operating ranges of each donor set. The modulating effect of coordination geometry on redox potential is evident in the series of N2O2 complexes. This study forms the basis of the rational synthesis of tuneable copper redox sensors by demonstrating the regions in which the various donor sets operate. 相似文献