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1.
Holding potential affects the apparent voltage-sensitivity of sodium channel activation in crayfish giant axons. 总被引:5,自引:4,他引:1
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Sodium channel activations, measured as the fraction of channels open to peak conductance for different test potentials (F[V]), shows two statistically different slopes from holding potential more positive than -90 mV. A high valence of 4-6e is indicated a test potentials within 35 mV of the apparent threshold potential (circa -65 mV at -85 mV holding potential). However, for test potentials positive to -30 mV, the F(V) curve shows a 2e valence. The F(V) curve for crayfish axon sodium channels at these "depolarized" holding potentials thus closely resembles classic data obtained from other preparations at holding potentials between -80 and -60 mV. In contrast, at holding potentials more negative than -100 mV, the high slope essentially disappears and the F(V) curve follows a single Boltzmann distribution with a valence of approximately 2e at all potentials. Neither the slope of this simple distribution nor its midpoint (-20 mV) was significantly affected by removal of fast inactivation with pronase. The change in F(V) slope, when holding potential is increased from -85 to -120 mV, does not appear to be caused by the contribution of a second channel type. The simple voltage dependence of sodium current found at Vh -120 mV be used by to discriminate between models of sodium channel activation, and rules out models with three particles of equal valence. 相似文献
2.
Selective Cytotoxicity of 1,3,4-Thiadiazolium Mesoionic Derivatives on Hepatocarcinoma Cells (HepG2)
Gustavo Jabor Gozzi Amanda do Rocio Andrade Pires Glaucio Valdameri Maria Eliane Merlin Rocha Glaucia Regina Martinez Guilhermina Rodrigues Noleto Alexandra Acco Carlos Eduardo Alves de Souza Aurea Echevarria Camilla Moretto dos Reis Attilio Di Pietro Sílvia Maria Suter Correia Cadena 《PloS one》2015,10(6)
In this work, we evaluated the cytotoxicity of mesoionic 4-phenyl-5-(2-Y, 4-X or 4-X-cinnamoyl)-1,3,4-thiadiazolium-2-phenylamine chloride derivatives (MI-J: X=OH, Y=H; MI-D: X=NO2, Y=H; MI-4F: X=F, Y=H; MI-2,4diF: X=Y=F) on human hepatocellular carcinoma (HepG2), and non-tumor cells (rat hepatocytes) for comparison. MI-J, M-4F and MI-2,4diF reduced HepG2 viability by ~ 50% at 25 μM after 24-h treatment, whereas MI-D required a 50 μM concentration, as shown by 3-(4,5-dimethythiazol-2-yl)-2,5-diphenyltetrazolium bromide assays. The cytotoxicity was confirmed with lactate dehydrogenase assay, of which activity was increased by 55, 24 and 16% for MI-J, MI-4F and MI-2,4diF respectively (at 25 μM after 24 h). To identify the death pathway related to cytotoxicity, the HepG2 cells treated by mesoionic compounds were labeled with both annexin V and PI, and analyzed by flow cytometry. All compounds increased the number of doubly-stained cells at 25 μM after 24 h: by 76% for MI-J, 25% for MI-4F and MI-2,4diF, and 11% for MI-D. It was also verified that increased DNA fragmentation occurred upon MI-J, MI-4F and MI-2,4diF treatments (by 12%, 9% and 8%, respectively, at 25 μM after 24 h). These compounds were only weakly, or not at all, transported by the main multidrug transporters, P-glycoprotein, ABCG2 and MRP1, and were able to slightly inhibit their drug-transport activity. It may be concluded that 1,3,4-thiadiazolium compounds, especially the hydroxy derivative MI-J, constitute promising candidates for future investigations on in-vivo treatment of hepatocellular carcinoma. 相似文献
3.
4.
Rhein (4,5-dihydroxyanthraquinone-2-carboxylic acid) which has been previously employed as an inhibitor for electron transport particles, NADH dehydrogenase, and other flavoproteins is reducible under physiological conditions. Soluble hydrogenase from Alcaligenes eutrophus H 16, several flavoproteins, and electron transport particles from baker's yeast and from beef heart were found to catalyse NADH oxidation with 9 micrometers to 2mM rhein as the electron acceptor. Dithionite or enzymatically reduced rhein (lambda max = 408 nm) is immediately reoxidized to rhein lambda max = 437 nm) by oxygen. Cyclovoltagrams reveal the midpoint redox potentials --0.240 V, -0.270 V, -0.280 V, -0.335 V at pH 6.0, 7.0, 7.7, 9.2, respectively. Due to its redox behaviour, caution should be exercised using rhein as a flavin-site-directed inhibitor for biological electron transfer systems. 相似文献
5.
The ba3 cytochrome c oxidase from Thermus thermophilus has been studied with a combined electrochemical, UV/VIS, and FTIR spectroscopic approach. Oxidative electrochemical redox titrations yielded midpoint potentials of Em1= -0.02 +/- 0.01 V and Em2 = 0.16 +/- 0.04 V for heme b and Em1 = 0.13 +/- 0.04 V and Em2 = 0.22 +/- 0.03 V for heme a(3) (vs Ag/AgCl/3 M KCl). Fully reversible electrochemically induced UV/VIS and FTIR difference spectra were obtained for the full potential step from -0. 5 to 0.5 V as well as for the critical potential steps from -0.5 to 0.1 V (heme b is fully oxidized and heme a3 remains essentially reduced) and from 0.1 to 0.5 V (heme b remains oxidized and heme a3 becomes oxidized). The difference spectra thus allow to us distinguish modes coupled to heme b and heme a3. Analogous difference spectra were obtained for the enzyme in D2O buffer for additional assignments. The FTIR difference spectra reveal the reorganization of the polypeptide backbone, perturbations of single amino acids and of hemes b and a3 upon electron transfer to/from the four redox-active centers heme b and a3, as well as CuB and CuA. Proton transfer coupled to redox transitions can be expected to manifest in the spectra. Tentative assignments of heme vibrational modes, of individual amino acids, and of secondary structure elements are presented. Aspects of the uncommon electrochemical and spectroscopic properties of the ba3 oxidase from T. thermophilus are discussed. 相似文献
6.
Markevich NI Korystova AF Grichenko AS Lankina DA Kokoz YM 《Membrane & cell biology》2000,14(1):109-127
The regulation of L-type Ca2+ current in isolated rat cardiac cells was studied using the perforated patch-clamp technique. A dual effect of the cAMP-dependent phosphorylation activator, isoproterenol, at different holding potentials (V(h)) was shown. The currents increased at V(h) = -50 mV and decreased at V(h) = -30 mV. A dihydropyridine agonist, BAY K 8644, and isoproterenol had an additive effect on the activation of Ca2+ channels at holding potentials close to the resting potential. The additivity was disturbed at more positive V(h). The activating effect of BAY K 8644 did not virtually change in the presence of a protein kinase blocker, H8, and a phosphatase activator, acetylcholine. The results were interpreted within the framework of a two-site phosphorylation model with two independent pathways of Ca2+ current regulation. 相似文献
7.
Rodrigues RF Castro-Pinto D Echevarria A dos Reis CM Del Cistia CN Sant'Anna CM Teixeira F Castro H Canto-Cavalheiro M Leon LL Tomás A 《Bioorganic & medicinal chemistry》2012,20(5):1760-1766
The biological activities of a series of mesoionic 1,3,4-thiadiazolium-2-aminide derivatives have been studied. The most active compounds (MI-HH; MI-3-OCH(3); MI-4-OCH(3) and MI-4-NO(2)) were evaluated to determine their effect on trypanothione reductase (TryR) activity in Leishmania sp. and Trypanosoma cruzi. Among the assayed compounds, only MI-4-NO(2) showed enzyme inhibition effect on extracts from different cultures of parasites, which was confirmed using the recombinant enzyme from T. cruzi (TcTryR) and Leishmania infantum (LiTryR). The enzyme kinetics determined with LiTryR demonstrated a non-competitive inhibition profile of MI-4-NO(2). A molecular docking study showed that the mesoionic compounds could effectively dock into the substrate binding site together with the substrate molecule. The mesoionic compounds were also effective ligands of the NADPH and FAD binding sites and the NADPH binding site was predicted as the best of all three binding sites. Based on the theoretical results, an explanation at the molecular level is proposed for the MI-4-NO(2) enzyme inhibition effect. Given TryR as a molecular target, it is important to continue the study of mesoionic compounds as part of a drug discovery campaign against Leishmaniasis or Chagas' disease. 相似文献
8.
Synergistic effect of cadmium chloride and acetaldehyde on cytotoxicity and its prevention by quercetin and glycyrrhizin 总被引:3,自引:0,他引:3
Cadmium chloride at concentrations of 10-50mM and acetaldehyde (AA) at 1-5mM showed synergistic toxic effects on V79 cells in vitro. Furthermore, synergistic effects of these chemicals were also observed in mutagenicities of the Hprt gene within certain dose ranges (cadmium chloride 5-10mM, and AA 1-2.5mM). Moreover, lipid peroxide formation, malondialdehyde (MDA) formation, detected by 2-thiobarbituric acid (TBA) reaction and the mitochondrial membrane potentials detected by rhodamine 123 uptake were significantly increased with the combined effect of cadmium and AA in V79. Thus, the cytotoxicity and genotoxicity displayed by combination of these chemicals can be considered to be associated with oxidative stress. Further, these effects were efficiently reduced by quercetin and less efficiently with glycyrrhizin. 相似文献
9.
Interactions of surface-confined DNA with electroreduced mitomycin C comparison with acid-activated mitomycin C 总被引:1,自引:0,他引:1
The anticancer activity of the antineoplastic drug mitomycin C (MC) was investigated using transfer stripping cyclic voltammetry (TSCV) with single-stranded DNA-modified hanging mercury drop electrode (HMDE). Reductive activation of MC is necessary for drug covalent binding to DNA, and we have found that some potential-controlled interactions of MC with DNA occur at the electrode, i.e. MC can be activated by electroreduction. Acid and electroreductive MC activations were compared and different adducts were subsequently generated, suggesting that the drug can bind to DNA in more than one way. Under conditions of acid activated MC, a monofunctional adduct between C-1 of MC and N-7 of guanine was formed on the electrode surface, reduced at - 0.44 V (vs. SCE). However, when the DNA-modified electrode was immersed in a MC solution and potentials corresponding to the quinone moiety reduction (- 0.3 V or more negative vs. SCE) were applied, an intrastrand bifunctional adduct between C-1 and C-10 of MC and two N-7 of a pair of adjacent guanines in ssDNA were formed at the electrode, reduced at - 0.49 V, i.e. 50 mV more negative than the monoadduct. The results presented in this paper show for the first time electrochemical detection of DNA-MC adducts at the hanging mercury drop electrode. 相似文献
10.
The oxidation-reduction potential values for the two electron transfers to glucose oxidase were obtained at pH 5.3, where the neutral radical is the stable form, and at pH 9.3, where the anion radical is the stable form. The midpoint potentials at 25 degrees were: pH 5.3 EFl1ox + e- H+ equilibrium EFlH. Em1 = -0.063 +/- 0.011 V EFlH. + e- + H+ equilibrium EFlredH2 Em2 = -0.065 +/- 0.007 V pH 9.3 EFlox + e- EFi- Em1 = -0.200 +/- 0.010 V EFi- + e- + H+ equilibrium EFlredH- Em2 = -0.240 +/- 0.005 V All potentials were measured versus the standard hydrogen electrode (SHE). The potentials indicated that glucose oxidase radicals are stabilized by kinetic factors and not by thermodynamic energy barriers. The pK for the glucose oxidase radical was 7.28 from dead time stopped flow measurements and the extinction coefficient of the neutral semiquinone was 4140 M-1 cm-1 at 570 nm. Both radical forms reacted with oxygen in a second order fashion. The rate at 25 degrees for the neutral semiquinone was 1.4 X 10(4) M-1 s-1; that for the anion radical was 3.5 X 10(4) M-1 s-1. The rate of oxidation of the neutral radical changed by a factor of 9 for a temperature difference of 22 degrees. For the anion radical, the oxidation rate changed by a factor of 6 for a 22 degrees change in temperature. We studied the oxygen reactivity of the 2-electron reduced form of the enzyme over a wide wavelength range and failed to detect either oxygenated flavin derivatives or semiquinoid forms as intermediates. The rate of reoxidation of fully reduced glucose oxidase at pH 9.3 was dependent on ionic strength. 相似文献
11.
Proenza C Wilkens C Lorenzon NM Beam KG 《The Journal of biological chemistry》2000,275(30):23169-23174
We have used the yeast two-hybrid technique and expression of truncated/mutated dihydropyridine receptors (DHPRs) to investigate whether the carboxyl tail of the DHPR is involved in targeting to junctions between the sarcolemma and sarcoplasmic reticulum in skeletal muscle. The carboxyl tail was extremely reactive in yeast two-hybrid library screens, with the reactivity residing in amino acids 1621-1647 and abolished by a point mutation (V1642D). Dysgenic myotubes were injected with cDNA encoding green fluorescent protein fused to the amino terminus of DHPRs truncated after either residue 1620 (Delta1621-1873) or residue 1542 (Delta1543-1873) or of full-length DHPRs with the V1642D mutation (V1642D). For either Delta1621-1873 or V1642D, the restoration of excitation-contraction coupling was reduced approximately 40%, and the number of functional DHPRs in the sarcolemma was reduced approximately 30%, compared with the wild-type DHPR. The restoration of excitation-contraction coupling and surface expression was more drastically reduced (by approximately 90 and approximately 55%, respectively) for Delta1543-1873. Fluorescence microscopy revealed that Delta1621-1873 and V1642D were concentrated in a longitudinally restricted region near the injected nucleus, whereas wild-type DHPRs were present relatively uniformly along the length of a myotube. The intensity of fluorescence was greatly reduced for Delta1543-1873, indicating a low level of protein expression. Thus, residues 1543-1647 appear to play a role in the biosynthetic processing, transport, and/or anchoring of DHPRs, with residues 1543-1620 being particularly important for expression. 相似文献
12.
We compared the effects exerted by two classes of Cl(-) transport inhibitors on a Cl(-)-selective, passive anion transport route across the skin of Bufo viridis, the conductance (G(Cl)) of which can be activated by transepithelial voltage perturbation or high cAMP at short circuit. Inhibitors of antiporters (erythrosine, eosin) or cotransporters (furosemide) reduced voltage-activated G(Cl) with IC(50) of 6 +/- 1, 54 +/- 12, and 607 +/- 125 microM, respectively; they had no effect on the cAMP-induced G(Cl). The voltage for half-maximal activation of G(Cl) (V(50)) increased compared with controls, but effects on the maximal G(Cl) at more positive clamp potentials were small. Cl(-) channel blockers from the diphenylamino-2-carboxylic acid (DPC) family [dichloro-DPC, niflumic acid, flufenamic acid, and 5-nitro-2-(3-phenylpropylamino)benzoic acid] reduced the voltage-activated G(Cl) with IC(50) of 8.3 +/- 1.2, 10.5 +/- 0.6, 16.5 +/- 3.4, and 36.5 +/- 11.4 microM, respectively, and also inhibited the cAMP-induced G(Cl), albeit with slightly larger IC(50). V(50) was not significantly changed compared with controls; the maximal G(Cl) was strongly reduced. We conclude that the pathway for Cl(-) is composed of the conductive pore proper, which is blocked by the derivatives of DPC, and a separate, voltage-sensitive regulator, which is influenced by blockers of cotransporters or antiporters. This influence is partly overcome by increasing the clamp potential and removed by high concentrations of cAMP, which renders the pathway insensitive to voltage. 相似文献
13.
1. The mid-point reduction potentials of the various groups in xanthine oxidase from bovine milk were determined by potentiometric titration with dithionite in the presence of dye mediators, removing samples for quantification of the reduced species by e.p.r. (electron-paramagnetic-resonance) spectroscopy. The values obtained for the functional enzyme in pyrophosphate buffer, pH8.2, are: Fe/S centre I, -343 +/- 15mV; Fe/S II, -303 +/- 15mV; FAD/FADH-; -351 +/- 20mV; FADH/FADH2, -236 +/-mV; Mo(VI)/Mo(V) (Rapid), -355 +/- 20mV; Mo(V) (Rapid)/Mo(IV), -355 +/- 20mV. 2. Behaviour of the functional enzyme is essentially ideal in Tris but less so in pyrophosphate. In Tris, the potential for Mo(VI)/Mo(V) (Rapid) is lowered relative to that in pyrophosphate, but the potential for Fe/S II is raised. The influence of buffer on the potentials was investigated by partial-reduction experiments with six other buffers. 3. Conversion of the enzyme with cyanide into the non-functional form, which gives the Slow molybdenum signal, or alkylation of FAD, has little effect on the mid-point potentials of the other centres. The potentials associated with the Slow signal are: Mo(VI)/Mo(V) (Slow), -440 +/- 25mV; Mo(V) (Slow)/Mo(IV), -480 +/- 25 mV. This signal exhibits very sluggish equilibration with the mediator system. 4. The deviations from ideal behaviour are discussed in terms of possible binding of buffer ions or anti-co-operative interactions amongst the redox centres. 相似文献
14.
N Iwata K Fukuhara K Suzuki N Miyata A Takahashi 《Chemico-biological interactions》1992,85(2-3):187-197
The nitroreductase activities of rat liver microsomes and cytosol towards various nitrated naphthalenes (1-, 2-mononitro-, 1,3-, 1,5-, 1,7-, 1,8-dinitro-1,3,5- and 1,3,8-trinitronaphthalenes) were characterized as follows. (1) The rates of reduction of nitrated naphthalenes in either microsomal or cytosolic incubation were found to increase in the order of trinitro- > dinitro- > mono-nitronaphthalene, although, in the case of microsomal nitroreduction, trinitronaphthalenes were reduced more rapidly than in cytosol. (2) The effective cofactors, electron donors, in the nitroreduction of nitrated naphthalenes in cytosol were NADH and hypoxanthine, but not NADPH. (3) The nitrated naphthalenes with a nitro group at a beta-position appear to be more easily reduced among the various isomers. The cytosolic nitroreductase activities towards the nitrated naphthalenes were closely related to the single-electron reduction potentials measured by cyclic voltammetry and hence, there was a good relationship between the logarithm of nitroreductase activities and the electrochemical reduction potentials. In microsomes, nitroreductase activities were rather less well related to electrochemical reduction potentials. 相似文献
15.
《Electronic Notes in Theoretical Computer Science》1987,68(3):202-208
We studied auditory and visual evoked potentials in D.W., a patient with congenital stenosis of the cerebral aqueduct. Head CT scans revealed marked hydrocephalus with expanded ventricles filling more than 80% of the cranium and compressing brain tissue to less than 1 cm in thickness. Despite the striking neuroanatomical abnormalities, however, the patient functioned well in daily life and was attending a local community college at the time of testing.Evoked potentials provided evidence of preserved sensory processing at cortical levels. Pattern reversal visual evoked potentials had normal latencies and amplitudes. Brain-stem auditory evoked potentials (BAEPs) showed normal wave V latencies. Na and Pa components of middle-latency AEP had normal amplitudes and latencies at the vertex, although amplitudes at lateral electrodes were larger than at the midline.In contrast to the normal sensory responses, long-latency auditory evoked potentials to standard and target tones showed abnormal P3 components. Standard tones (probability 85%), evoked NN1 components with normal amplitudes (−3.7 μV) and latencies (103 msec), but also elicited large P3 components (17 μV, latency 305 msec) that were never observed following frequent stimuli in control subjects. Target stimuli (probability 15%) elicited P3s in D.W. and controls, but P3 amplitudes were enhanced in D.W. (to more than 40 μV) and the P3 showed an unusual, frontal distribution. The results are consistent with a subcortical sources of the P300. Moreover, they suggest that the substitution of controlled for automatic processes may help high-functioning hydrocephalics compensate for abnormalities in cerebral structure. 相似文献
16.
Lipid dependence of surface conformations of protein kinase C 总被引:1,自引:0,他引:1
The change of conformation of protein kinase C interacting with the surface of a mercury electrode directly from a solution or through a lipid monolayer was inferred from the number of cystine residues exposed and reduced on the electrode and from their reduction potentials. Soluble protein kinase C was estimated to have 5-6 disulfide bonds which could potentially react with the mercury electrode. Two major reduction peaks of cystine at different microenvironments within the protein molecule adsorbed to a mercury surface. They were observed in a.c. polarograms and cyclic voltamograms at two distinct potentials. The potential of these peaks became more negative as the pH of the solution increased, which was consistent with relaxation or decrease in alpha-helicity (ordered structure) of the protein as determined by circular dichroism (CD) estimations of secondary structure. The peak at the more positive potentials (-0.46 V relative to NAg/AgCl electrode at pH 7.4) tended to vanish upon cyclic reduction and reoxidation of the cystine, while the more negative peak (-0.62 V at pH 7.4) was enhanced. Addition of Mg2+ or Ca2+ had no significant effect on the potential but there was a reduction in their amplitude which appeared to affect the disappearance of these peaks upon pH adjustment. This suggests that the tertiary structure of the molecule is stabilized by Ca2+ and Mg2+, as substantiated by CD spectral analysis of secondary structures. Protein kinase C penetrated lipid monolayers to some extent. Addition of diacylglycerol or phorbol ester to the lipid monolayers facilitated this penetration. These compounds stabilized the protein surface conformation by destabilizing the monolayer at more positive potentials, resulting in an enhanced reduction peak at -0.42 V. This phenomenon was not significantly affected by Mg2+ or by Ca2+. The region of the protein kinase C (PKC) sequence which penetrated the monolayer contains cysteines and a primary amine(s), and may have homology to a region of phospholipase A2 which has been proposed as a phospholipid binding site for the two enzymes. Additionally, these polarographic studies suggest that PKC associates with and penetrates monolayers in a divalent cation-independent manner in agreement with our previous physical analyses of PKC interactions with lipid bilayers. 相似文献
17.
S G Mayhew 《European journal of biochemistry》1999,265(2):698-702
Calculation shows that there is poor agreement between frequently cited values for the midpoint redox potentials of the two one-electron steps in the reduction of flavin mononucleotide and equations for the lines that relate these potentials to pH and that use the published pKa values for the three redox states of the flavin [Draper, R. & Ingraham, L.L. (1969) Arch. Biochem. Biophys. 125, 802-808]. Equilibrium data for the first step in the reduction obtained by pulse radiolysis [Anderson, R.F. (1983) Biochim. Biophys. Acta 722, 158-162] show much closer agreement with theory and lead to values for the semiquinone formation constant of flavin mononucleotide that are close to those derived from measurements of the radical concentration using ESR spectroscopy. It is concluded that the data from the second method are more reliable. The redox potentials for flavin mononucleotide at pH 7.0 and 20 degrees C are calculated to be -0.207 V for the overall two-electron reduction (Em), -0.313 V for reduction of the oxidized flavin to the semiquinone (E2) and -0.101 V for the reduction of the semiquinone to the hydroquinone (E1). Information is provided to allow calculation of the three redox potentials at other pH values in the physiological range. 相似文献
18.
Zorn-Pauly K Schaffer P Pelzmann B Bernhart E Lang P Koidl B 《Physiological research / Academia Scientiarum Bohemoslovaca》2004,53(4):369-377
The aim of this investigation was to study L-type and T-type Ca(2+) current (I(CaL) and I(CaT)) in short-term cultured adult guinea pig ventricular myocytes. The isolated myocytes were suspended in serum-supplemented medium up to 5 days. Using whole-cell patch clamp techniques ICaL and ICaT were studied by applying voltage protocols from different holding potentials (-40 and -90 mV). After 5 days in culture the myocytes still showed their typical rod shaped morphology but a decline in cell membrane capacitance (26 %). The peak density of ICaT was reduced significantly between day 0 (-1.6+/-0.37 pA/pF, n=9) and day 5 (-0.4+/-0.13 pA/pF, n=11), whereas peak ICaL density revealed no significant differences during culturing. The I(CaT)/I(CaL) ratio dropped from 0.13 at day 0 to 0.05 at day 5. Compared with day 0 I(CaL) the steady state inactivation curve of day 1, day 3 and day 5 myocytes was slightly shifted to more negative potentials. Our data indicate that guinea pig ventricular L-type and T-type Ca(2+) channels are differently regulated in culture. 相似文献
19.
Two-electron electrochemical oxidation of quercetin and kaempferol changes only the flavonoid C-ring
Lars Viborg J rgensen Claus Cornett Ulla Justesen Leif H. Skibsted Lars O. Dragsted 《Free radical research》1998,29(4):339-350
Bulk electrolysis of the antioxidant flavonoids quercetin and kaempferol in acetonitrile both yield a single oxidation product in two-electron processes. The oxidation products are more polar than their parent compounds, with an increased molecular weight of 16 g/mol, and were identified as 2-(3,4-dihydroxybenzoyl)-2,4,6-trihydroxy-3(2H)-benzofuranone and 2-(4-hydroxybenzoyl)-2,4,6-trihydroxy-3(2H)-benzofuranone for quercetin and kaempferol, respectively. Two-electron oxidation of the parent flavonoid is suggested to yield a 3,4-flavandione with unchanged substitution pattern in the A- and B-ring, which may rearrange to form the substituted 3(2H)-benzofuranone through the chalcan-trione ring-chain tautomer. The acidity of the 3-OH group is suggested to determine the fate of the flavonoid phenoxyl radical, originally formed by one-electron oxidation, as no well-defined oxidation product of luteolin (lacking the 3-OH group) could be isolated despite rather similar half-peak potentials: EP/2 = 0.97 V, 0.98 V and 1.17 V vs. NHE for quercetin, kaempferol and luteolin, respectively, as measured by cyclic voltammetry in acetonitrile. 相似文献
20.
Gold nanotubular electrode ensembles were prepared by using electroless deposition of the metal within the pores of polycarbonate track-etched membranes. Mono-enzyme (GOx) and monolayer/bilayer bienzyme (GOx/HRP) bioelectrodes were prepared by immobilizing the enzymes onto gold nanotubes surfaces modified with mercaptoethylamine. Batch amperometric responses to glucose for the different bioelectrodes were determined and compared. The response of the two geometries (monolayer and bilayer) of the bienzyme electrodes was shown to vary with regard to sensitivity at detection potentials above 0V. On the contrary, at detection potentials below 0V, no noticeable influence of the configuration of the bienzyme on the response intensity was observed. The mono-enzyme (650 microAmM-1 in benzoquinone (BQ) at -0.8 V versus Ag/AgCl) and the two bienzyme bioelectrodes (+/-400 microAmM-1 in hydroquinone (H2Q) at -0.2V versus Ag/AgCl) display remarkable sensitivities compared to a classical GOx-modified gold macroelectrode (13 microAmM-1 in BQ at -0.8 V versus Ag/AgCl). A remarkable feature of the bienzyme electrodes is the possibility to detect glucose at very low applied potentials where the noise level and interferences from other electro-oxidizable compounds are minimal. Another important characteristic of the monolayer bienzyme electrode is the possible existence of a direct electronic communication between HRP and the transducer surface. 相似文献