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1.
Chemosphere ; 238: 124466, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-31425866

RESUMO

Arsenite is a highly toxic compound present in many water sources around the world. The removal of arsenite from water requires its oxidation to arsenate which is much more amenable to treatment using well attested technologies. Prior research has shown that the oxidation of arsenite by hydroxyl radicals is significantly accelerated in the presence of carbonate ions but the intrinsic mechanisms of the acceleration have not yet been established. The main goal of the present work was to examine the oxidation of arsenite in the framework of the density functional theory, to establish a detailed microscopic level mechanism of interactions between arsenite and hydroxyl radicals and to elucidate the nature of the catalytic effect of carbonate ions. Results of this study demonstrate that the [As(OH)2CO3]- complex is the thermodynamically most stable species formed in the system H3AsO3-CO32-/HCO3--H2O. Interactions of the hydroxyl radical with the [As(OH)2CO3]- complex yield the pre-reaction complex [As(OH)3CO3]-∗ in the reaction of subsequent oxidation of arsenite. The structures of the reactants, products and transition states, as well as pre- and post-reaction complexes corresponding to several possible mechanisms of the first stage of As(III) oxidation to As(IV) intermediate using hydroxyl radicals in the absence and in the presence of [As(OH)2CO3]-, were determined in this study. The data demonstrate that the arsenite-carbonate complexes [As(OH)2CO3]- are characterized by a significantly lower activation energy of the first oxidation stage under the action of a hydroxyl radical (2.8 kcal/mol) compared to that for the free arsenite H3AsO3 (13.6 kcal/mol).


Assuntos
Arsenitos/química , Carbonatos/química , Radical Hidroxila/química , Teoria Quântica , Água/química , Catálise , Modelos Moleculares , Conformação Molecular , Oxirredução , Termodinâmica
2.
J Phys Chem A ; 123(25): 5341-5346, 2019 Jun 27.
Artigo em Inglês | MEDLINE | ID: mdl-31199631

RESUMO

An approach for estimating at the DFT level of the standard redox potentials of the inclusion compounds based on Fe(III) and Fe(II) aqua complexes inside the cavities of cucurbit[ n]urils ( n = 6-8) has been proposed. These inclusion compounds were established to have compositions which can be described by the formulas [Fe(H2O)6]3+/2+@CB[6] and [Fe(H2O)6·4H2O]3+/2+@CB[7,8]. Redox potentials E0 relative to the standard hydrogen electrode for the half-reaction Fe(III)/Fe(II) in the CB[ n] cavities calculated at the PBE/TZVP level within the molecular-continuum solvation model are 1.607, 0.949, and 0.847 V for n = 6, 7, and 8, respectively. The obtained values indicate a relative increase of the oxidative ability of Fe(III) aqua-ions in the cavities of the examined CB[ n], especially in CB[6], compared to the calculated value ( E0 = 0.786 V) for the same half-reaction in the bulk of aqueous solution. Possible causes of the detected trend are discussed. The calculations also showed that the Fe(III) aqua complex inside the CB[6] changes its magnetic properties, transforming into a low-spin state with a total spin S = 1/2, whereas for all other systems high-spin states in accord with the classical ligand field theory are realized.

4.
J Environ Radioact ; 120: 19-25, 2013 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-23410594

RESUMO

The paper studies chronic effect of tritiated water, HTO, (0.0002-200 MBq/L) on bioluminescent assay systems: marine bacteria Photobacterium phosphoreum (intact and lyophilized) and coupled enzyme reactions. Bioluminescence intensity serves as a marker of physiological activity. Linear dependencies of bioluminescent intensity on exposure time or radioactivity were not revealed. Three successive stages in bacterial bioluminescence response to HTO were found: (1) absence of the effect, (2) activation, and (3) inhibition. They were interpreted in terms of reaction of organisms to stress-factor i.e. stress recognition, adaptive response/syndrome, and suppression of physiological function. In enzyme system, in contrast, the kinetic stages mentioned above were not revealed, but the dependence of bioluminescence intensity on HTO specific radioactivity was found. Damage of bacteria cells in HTO (100 MBq/L) was visualized by electron microscopy. Time of bioluminescence inhibition is suggested as a parameter to evaluate the bacterial sensitivity to ionizing radiation.


Assuntos
Photobacterium/efeitos dos fármacos , Trítio/farmacologia , Poluentes Radioativos da Água/farmacologia , FMN Redutase/metabolismo , Medições Luminescentes , Microscopia Eletrônica de Transmissão , NAD/metabolismo , Photobacterium/fisiologia , Photobacterium/efeitos da radiação , Photobacterium/ultraestrutura
5.
J Photochem Photobiol B ; 117: 164-70, 2012 Dec 05.
Artigo em Inglês | MEDLINE | ID: mdl-23123596

RESUMO

The paper considers effects of humic substances (HS), as natural attenuators of toxicity, on solutions of model inorganic pollutants, metal salts - Pb(NO(3))(2), СоСl(2), CuSO(4), Eu(NO(3))(3), СrСl(3), and K(3)[Fe(СN)(6)]. Luminous bacteria Photobacterium phosphoreum and bioluminescent system of coupled enzymatic reactions were used as bioassays to monitor toxicity of salt solutions. The ability of HS to decrease or increase toxicity was demonstrated. Detoxifying concentrations of HS were determined; detoxification coefficients were calculated at different times of exposure of salt solutions to HS. To study the combined effects of HS and salts on bioluminescent assay systems, the rates of biochemical reactions and bacterial ultrastructure were analyzed. The detoxifying effects were explained by: (1) decrease of free metal content in water solutions under metal-HS binding; (2) increase of biochemical reaction rates in a bioluminescent assay system under HS effect; (3) enhancement of mucous layers on cell surface as a response to unfavorable impact of toxicants. Detoxifying mechanisms (2) and (3) reveal the active role of bioassay systems in detoxification processes.


Assuntos
Poluentes Ambientais/química , Poluentes Ambientais/toxicidade , Substâncias Húmicas , Medições Luminescentes/métodos , Metais/química , Sais/química , Sais/toxicidade , Bioensaio , Photobacterium/efeitos dos fármacos , Photobacterium/ultraestrutura , Soluções
6.
J Phys Condens Matter ; 20(37): 374103, 2008 Sep 17.
Artigo em Inglês | MEDLINE | ID: mdl-21694411

RESUMO

We develop a simplified, model theory of noise caused by highly damped oscillating conformational fluctuations of a chain molecule mediating a nano-junction. Considering the most 'primitive' approximation of direct tunneling of electrons and barrier coupling with collective coordinates that describe internal conformations of the chain molecule, we derive approximate analytical formulas for the temporary current correlation function, noise power, and Fano factor. We analyze the role of different cumulative parameters of the model that affect the noise, as well as the effect of the temperature and of the number of groups in the chain. We present this analysis in expectation of experiments on this type of noise and in an attempt to trigger such experiments.

7.
J Phys Chem B ; 111(24): 6703-12, 2007 Jun 21.
Artigo em Inglês | MEDLINE | ID: mdl-17497912

RESUMO

Experimental data and theoretical notions are presented for 6-[1'-(6-mercapto-hexyl)-[4,4']bipyridinium]-hexane-1-thiol iodide (6V6) "wired" between a gold electrode surface and tip in an in situ scanning tunneling microscopy configuration. The viologen group can be used to "gate" charge transport across the molecular bridge through control of the electrochemical potential and consequently the redox state of the viologen moiety. This gating is theoretically considered within the framework of superexchange and coherent two-step notions for charge transport. It is shown here that the absence of a maximum in the Itunneling versus electrode potential relationship can be fitted by a "soft" gating concept. This arises from large configurational fluctuations of the molecular bridge linked to the gold contacts by flexible chains. This view is incorporated in a formalism that is well-suited for data analysis and reproduces in all important respects the 6V6 data for physically sound values of the appropriate parameters. This study demonstrates that fluctuations of isolated configurationally "soft" molecules can dominate charge transport patterns and that theoretical frameworks for compact monolayers may not be directly applied under such circumstances.

9.
Chemphyschem ; 6(4): 583-6, 2005 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-15881569

RESUMO

A description of the physical mechanism and operation of a novel nanometric electronic switch [D.I. Gittins et al., Nature 2000 408, 67] is presented. New options for controlling the properties of this device are suggested and analyzed.

10.
Ross Fiziol Zh Im I M Sechenova ; 88(6): 762-73, 2002 Jun.
Artigo em Russo | MEDLINE | ID: mdl-12154573

RESUMO

In chronic experiments, we have studied electrical activity of muscles of the gastro-esophageal sphincter, small curvature, corpus and antrum of the stomach in conditions of hunger, food intake behaviour and satiation of the rabbits. The aim of this study involved particularities of the electrical activity of myogenic pacemaker zone of the stomach. It has been shown that function of myogenic pacemaker of the rabbit stomach is performed by smooth muscles of the small curvature of the stomach. Pacemaker properties of muscles of the small curvature of the stomach are performed in conditions of food intake behaviour and satiation.


Assuntos
Fome/fisiologia , Contração Muscular/fisiologia , Músculo Liso/fisiologia , Saciação/fisiologia , Estômago/fisiologia , Potenciais de Ação/fisiologia , Animais , Ingestão de Alimentos , Eletrodos Implantados , Eletromiografia/instrumentação , Eletrofisiologia , Privação de Alimentos/fisiologia , Masculino , Coelhos
11.
Biochemistry (Mosc) ; 66(7): 715-20, 2001 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-11563949

RESUMO

Extraction of the Mn-cluster from photosystem II (PS II) inhibits the main bands of thermoluminescence and induces a new AT-band at -20 degrees C. This band is attributed to the charge recombination between acceptor QA- and a redox-active histidine residue on the donor side of PS II. The effect of Mn(II) and Fe(II) cations as well as the artificial donors diphenylcarbazide and hydroxylamine on the AT-band of thermoluminescence was studied to elucidate the role of the redox-active His residue in binding to the Mn(II) and Fe(II). At the Mn/PS II reaction center (RC) ratio of 90 : 1 and Fe/PS II RC ratio of 120 : 1, treatment with Mn(II) and Fe(II) causes only 60% inhibition of the AT-band. Preliminary exposure of Mn-depleted PS II preparations to light in the presence of Mn(II) and Fe(II) causes binding of the cations to the high-affinity Mn-binding site, thereby inhibiting oxidation of the His residue involved in the AT-band formation. The efficiency of the AT-band quenching induced by diphenylcarbazide and hydroxylamine is almost an order of magnitude higher than the quenching efficiency of Mn(II) and Fe(II). Our results suggest that the redox-active His is not a ligand of the high-affinity site and does not participate in the electron transport from Mn(II) and Fe(II) to YZ. The concentration dependences of the AT-band inhibition by Mn(II) and Fe(II) coincide with each other, thereby implying specific interaction of Fe(II) with the donor side of PS II.


Assuntos
2,6-Dicloroindofenol/metabolismo , Difenilcarbazida/metabolismo , Ferro/metabolismo , Manganês/metabolismo , Complexo de Proteínas do Centro de Reação Fotossintética/metabolismo , 2,6-Dicloroindofenol/farmacologia , Sítios de Ligação , Difenilcarbazida/farmacologia , Transporte de Elétrons , Ferro/farmacologia , Luz , Manganês/farmacologia , Oxirredução , Complexo de Proteínas do Centro de Reação Fotossintética/efeitos dos fármacos , Complexo de Proteína do Fotossistema II , Spinacia oleracea/metabolismo , Dosimetria Termoluminescente
12.
Izv Akad Nauk Ser Biol ; (4): 435-41, 2001.
Artigo em Russo | MEDLINE | ID: mdl-11525124

RESUMO

We found that extracts from the leaves of medicinal comfrey and cowparsnip strongly inhibit the germination of Erysiphe graminis conidia and uredospores of Puccinia graminis. Spraying wheat seedlings with these extracts, in contrast to the irrigation of soil, markedly diminished infection in plants with powdery mildew. Antifungal activity in vitro and protective activity (when plants were sprayed) correlated with the level of phenolic compounds in these extracts. Experiments with healthy plants have demonstrated that the photosynthetic apparatus of wheat plants is stimulated by extracts. Spraying seedlings with the extracts resulted in an increased rate of O2 evolution calculated per unit of chlorophyll, an increase in the ratio (FM-FT)/FT in the experiments that recorded slow fluorescence induction, an increase in the relative light intensity of band A, and a decrease of relative intensity of band C in experiments with thermoluminescence of wheat leaves. These results provide evidence that the protective activity of comfrey and cowparsnip extracts is associated with their action on the pathogenic fungus and with the activation of natural defense reactions of the host plant.


Assuntos
Antifúngicos/farmacologia , Confrei/química , Heracleum/química , Extratos Vegetais/farmacologia , Antifúngicos/isolamento & purificação , Complexos de Proteínas Captadores de Luz , Complexo de Proteínas do Centro de Reação Fotossintética/efeitos dos fármacos , Triticum/efeitos dos fármacos , Triticum/fisiologia
13.
Biofizika ; 46(2): 381-2, 2001.
Artigo em Russo | MEDLINE | ID: mdl-11357357

RESUMO

The slow fluorescence induction parameter FM/FT was measured for green leaves from maple trees grown in the park, depending on the distance (5-65 m) between the tree and the highway cross. We concluded that the decrease in the value of FM/FT for trees grown in the vicinity of the road cross was caused by exhaust gases.


Assuntos
Exposição Ambiental/efeitos adversos , Monitoramento Ambiental , Veículos Automotores , Árvores/química , Cidades , Fluorescência , Emissões de Veículos/efeitos adversos
14.
Chemosphere ; 42(8): 909-15, 2001 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-11272913

RESUMO

A set of bioluminescent tests was developed to monitor water quality in natural and laboratory ecosystems. It consisted of four bioluminescent systems: luminous bacteria, coupled enzyme system NADH:FMN-oxidoreductase-luciferase and triplet enzyme systems with alcohol dehydrogenase and trypsin. The set of biotests was applied for a small forest pond (Siberia, Russia), laboratory microecosystems polluted with benzoquinone and a batch culture of blue-green algae. Thereby effects of natural water compared to those of models of heavy pollution and "bloom" of blue-greens on the bioluminescent tests were revealed. The set of biotests was not affected by a natural seasonal variability of water quality in the unpolluted pond, but responded to the heavy pollution and the "bloom" of blue-greens. The set of biotests could be recommended as the alarm test to control the acute toxicity of natural water bodies.


Assuntos
Benzoquinonas/efeitos adversos , Monitoramento Ambiental/métodos , Eutrofização , Indicadores e Reagentes/efeitos adversos , NADH NADPH Oxirredutases/metabolismo , Poluentes da Água/análise , Bioensaio/métodos , Cianobactérias , Ecossistema , FMN Redutase , Medições Luminescentes
15.
Luminescence ; 14(5): 263-5, 1999.
Artigo em Inglês | MEDLINE | ID: mdl-10512990

RESUMO

The bacterial bioluminescence has high sensitivity to the action of various inhibitors of biological activity. The lyophilized luminous bacteria Photobacterium phosphoreum (Microbiosensor B17 677F) and luminous strain Escherichia coli (Microbiosensor EC) from the Culture Collection IBSO were used to create bioluminescent biotests. They have been applied in ecological monitoring to determine the overall toxicity of the Yenisei and Angara Rivers and some water sources of Altai Territory. As a rule the heaviest pollution of water in studied rivers was registered near cities and settlements. The luminous bacteria biotests are simple and convenient in work, standardized and quantitative, have rapid response to actions of different substances and high sensitivity to environmental pollutants. It takes less than 30 min to do the biotest (the other biotests take 48--96 h).


Assuntos
Bioensaio/métodos , Água Doce/análise , Poluentes Químicos da Água/análise , Técnicas Biossensoriais , Escherichia coli , Liofilização , Luminescência , Photobacterium , Federação Russa , Sensibilidade e Especificidade
16.
Proc Natl Acad Sci U S A ; 96(4): 1379-84, 1999 Feb 16.
Artigo em Inglês | MEDLINE | ID: mdl-9990032

RESUMO

In situ scanning tunneling microscopy (STM) of redox molecules, in aqueous solution, shows interesting analogies and differences compared with interfacial electrochemical electron transfer (ET) and ET in homogeneous solution. This is because the redox level represents a deep indentation in the tunnel barrier, with possible temporary electronic population. Particular perspectives are that both the bias voltage and the overvoltage relative to a reference electrode can be controlled, reflected in spectroscopic features when the potential variation brings the redox level to cross the Fermi levels of the substrate and tip. The blue copper protein azurin adsorbs on gold(111) via a surface disulfide group. Well resolved in situ STM images show arrays of molecules on the triangular gold(111) terraces. This points to the feasibility of in situ STM of redox metalloproteins directly in their natural aqueous medium. Each structure also shows a central brighter contrast in the constant current mode, indicative of 2- to 4-fold current enhancement compared with the peripheral parts. This supports the notion of tunneling via the redox level of the copper atom and of in situ STM as a new approach to long-range electron tunneling in metalloproteins.


Assuntos
Azurina/metabolismo , Azurina/ultraestrutura , Metaloproteínas/metabolismo , Metaloproteínas/ultraestrutura , Adsorção , Azurina/química , Dissulfetos , Transporte de Elétrons , Ouro/metabolismo , Metaloproteínas/química , Microscopia de Tunelamento/métodos , Modelos Químicos , Modelos Moleculares , Oxirredução , Conformação Proteica , Pseudomonas aeruginosa/metabolismo , Termodinâmica
17.
Proteins ; 28(2): 174-82, 1997 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-9188735

RESUMO

In the semi-continuum treatment of the energetics of charge formation (or transfer) inside a protein, two components of the energy are inevitably present: the energy of interaction of the ion with the pre-existing intraprotein electric field, and the energy due to polarization of the medium by the newly formed charge. The pre-existing field is set up by charges (partial or full) of the protein atoms fixed in a definite structure. The calculation of this field involves only the electronic polarization (the optical dielectric constant epsilon(o)) of the protein because the polarization due to shifts of heavy atoms has already been accounted for by their equilibrium coordinates. At the same time, the aqueous surroundings should be described by the static constant epsilon(sw), as the positions of water molecules are not fixed. The formation of a new charge, absent in the equilibrium X-ray structure, results in shifts of electrons and polar atoms, i.e., it involves all kinds of medium polarization described by the static dielectric constant of protein epsilon(s). Thus, in calculations of the total energy, two different dielectric constants of the protein are operative simultaneously. This differs from a widely used algorithm employing one effective dielectric constant for both components of the ion's energy.


Assuntos
Proteínas/química , Eletricidade Estática
18.
Arch Environ Contam Toxicol ; 22(2): 203-8, 1992 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-1536600

RESUMO

The inhibition of bacterial luminescence has been used in testing industrial enterprises sewage. The toxicity of the sewage is less than the total toxicity of separate components due to neutralization of quinone products of polyphenol oxidation in the reactions with the other phenol components of sewage. Toxicity increase is due to their influence on the cell membrane. Studies of cell ultrastructure confirm this fact. The studied mechanism of the complex effect allowed a more accurate forecast of the ecological situation during the discharge of phenol compounds and metals. It also showed the necessity of taking into account the complex effect of sewage components on contaminant discharge into water reservoirs.


Assuntos
Esgotos , Benzoquinonas/toxicidade , Catequina/toxicidade , Hidroquinonas/toxicidade , Medições Luminescentes , Metais/análise , Fenol , Fenóis/análise , Photobacterium/efeitos dos fármacos , Photobacterium/ultraestrutura , Vibrio/efeitos dos fármacos , Vibrio/ultraestrutura , Poluentes Químicos da Água/toxicidade
20.
FEBS Lett ; 215(2): 219-22, 1987 May 11.
Artigo em Inglês | MEDLINE | ID: mdl-3582649

RESUMO

The influence of temperature, oxygen pressure and inhibitors of laccase on the dioxygen electroreduction reaction has been examined at different solution pH. On the basis of obtained data, a reaction mechanism including electron transfer from the enzyme active site to the oxygen molecule is suggested as the slow step.


Assuntos
Enzimas Imobilizadas/metabolismo , Oxirredutases/metabolismo , Eletroquímica , Eletrodos , Concentração de Íons de Hidrogênio , Lacase , Oxirredução , Oxirredutases/antagonistas & inibidores , Oxigênio
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