Redox sensing by Escherichia coli: effects of copper ions as oxidizers on proton-coupled membrane transport

Escherichia coli is able to grow under anaerobic fermentation conditions upon a decrease in redox potential (E(h)). Indeed, upon a transition of E. coli MC4100 wild-type culture to stationary growth phase a decrease in E(h) from the positive values ( approximately +100 mV) to the negative ones ( approximately -520 mV) was observed, the acidification of the medium and the H(2) production were obtained. An oxidizer, copper ions (Cu(2+)) affected a bacterial growth in a concentration-dependent manner (of 0.1 mM to 10 mM) increasing latent (lag) growth phase duration, delaying logarithmic (log) growth phase and decreasing specific growth rate. Acidification of the medium and the N,N'-dicyclohexylcarbodiimide (DCCD)- and azide-sensitive proton-potassium exchange by bacteria were inhibited, H(2) production upon growth and under assays disappeared with Cu(2+) (0.1 mM). These effects were observed with hycE but not hyfR and hyc(A-H) mutants and under aerobic conditions. Cu(2+) also increased membrane proton conductance. Copper ions are suggested to affect directly the F(0)F(1)-ATPase associated with potassium uptake transport system and/or formate hydrogenlyase composed with hydrogenase 4. A role of the F(0)F(1)-ATPase in redox sensing under fermentation is proposed.     

聚苯胺修饰碳纤维针型复合微pH传感器

由电聚合法用聚苯胺修饰碳纤维电极作为ＰＨ敏感电极。把Ｋ３Ｆｅ（ＣＮ）６／Ｋ４Ｆｅ（ＣＮ）６体系填入医用注射针头内成为参比电极。把经聚苯胺修饰的碳纤维电极安置入该针型参比电极内构成复合针型微ｐＨ传感器。在ＰＨ ２～１２范围内，该传感器呈现超Ｎｅｒｎｓｔ响应，斜率为－７８ ｍＶ／ｐＨ；响应时间<１ｍｉｎ。该传感器成功地应用于在体ｐＨ测定以及水果内微区ｐＨ测定。     

Redox cycling with facing interdigitated array electrodes as a method for selective detection of redox species

A pair of interdigitated ultramicroelectrodes (UMEs) is used to electrochemically detect a weak reductor (dopamine) in the presence of a stronger one (K(4)[Fe(CN)(6)]). In the mixture of both reductors, one of the two interdigitated electrodes (the generator electrode) is used to oxidize both species at 700 mV vs. Ag/AgCl, followed by subsequent (selective) reduction of the oxidized dopamine at 400 mV. A regenerated dopamine molecule can thus be oxidized several times (redox cycling) and enable selective detection even in the presence of the stronger reductor. In order to obtain high redox cycling efficiency, we designed and realized platinum electrodes with widths of 2 and 4 microm and spacing of 2 microm, which gave redox cycling efficiencies of 9 and 4 respectively. Using this electrode design, a dopamine/K(4)[Fe(CN)(6)] selectivity of 2 could be obtained.     

Escherichia coli-catalyzed bioelectrochemical oxidation of acetate in the presence of mediators

Bioelectrocatalytic oxidation of acetate was investigated under anaerobic conditions by using Escherichia coli K-12 (IFO 3301) cells cultured on aerobic media containing poly-peptone, glucose or acetate as the sole carbon source. It was found that all E. coli cells cultured on the three media work as good catalysts of the electrochemical oxidation of acetate as well as glucose with Fe(CN)6(3-), 2,3-dimethoxy-5-methyl-1,4-benzo-quinone (Q0), 2,6-dichloro-indophenol, or 2-methyl-1,4-naphthoquinone as artificial electron acceptors (mediators). Acetate-grown E. coli cells exhibited the highest relative activity of the acetate oxidation against the glucose oxidation. On the other hand, all the artificial electron acceptors used work as inhibitors for the catalytic oxidation of acetate at increased concentrations. The inhibition phenomenon can be interpreted in terms of competitive substrate inhibition as a whole. Apparent values of Michaelis constant, catalytic constant, and inhibition constant were evaluated by amperometric methods. Q0 is an effective artificial mediator as evidenced by a large reaction rate constant between the cell and Q0 at least at low concentrations (<50 microM). However, Fe(CN)6(3-) is a promising mediator in biosensor applications because the inhibition constant is very large and it works as an electron acceptor even under aerobic conditions.     

Stabilization of reduced molybdenum-iron-sulfur single- and double-cubane clusters by cyanide ligation

Recent work has shown that cyanide ligation increases the redox potentials of Fe(4)S(4) clusters, enabling the isolation of [Fe(4)S(4)(CN)4]4-, the first synthetic Fe(4)S(4) cluster obtained in the all-ferrous oxidation state (Scott, T. A.; Berlinguette, C. P.; Holm, R. H.; Zhou, H.-C. Proc. Natl. Acad. Sci. U.S.A. 2005, 102, 9741). The generality of reduced cluster stabilization has been examined with MoFe(3)S(4) clusters. Reaction of single-cubane [(Tp)MoFe(3)S(4)(PEt(3))3]1+ and edge-bridged double-cubane [(Tp)2Mo(2)Fe(6)S(8)(PEt(3))4] with cyanide in acetonitrile affords [(Tp)MoFe(3)S(4)(CN)3]2- (2) and [(Tp)2Mo(2)Fe(6)S(8)(CN)4]4- (5), respectively. Reduction of 2 with KC(14)H(10) yields [(Tp)MoFe(3)S(4)(CN)3]3- (3). Clusters were isolated in approximately 70-90% yields as Et(4)N+ or Bu(4)N+ salts; clusters 3 and 5 contain all-ferrous cores, and 3 is the first [MoFe(3)S(4)]1+ cluster isolated in substance. The structures of 2 and 3 are very similar; the volume of the reduced cluster core is slightly larger (2.5%), a usual effect upon reduction of cubane-type Fe(4)S(4) and MFe(3)S(4) clusters. Redox potentials and 57Fe isomer shifts of [(Tp)MoFe(3)S(4)L3]2-,3- and [(Tp)2Mo(2)Fe(6)S(8)L(4)]4-,3- clusters with L = CN-, PhS-, halide, and PEt3 are compared. Clusters with pi-donor ligands (L = halide, PhS) exhibit larger isomer shifts and lower (more negative) redox potentials, while pi-acceptor ligands (L = CN, PEt3) induce smaller isomer shifts and higher (less-negative) redox potentials. When the potentials of 3/2 and [(Tp)MoFe(3)S(4)(SPh)3]3-/2- are compared, cyanide stabilizes 3 by 270 mV versus the reduced thiolate cluster, commensurate with the 310 mV stabilization of [Fe(4)S(4)(CN)4]4- versus [Fe(4)S(4)(SPh)4]4- where four ligands differ. These results demonstrate the efficacy of cyanide stabilization of lower cluster oxidation states. (Tp = hydrotris(pyrazolyl)borate(1-)).     

Signal enhancement for gene detection based on a redox reaction of [Fe(CN)(6)](4-) mediated by ferrocene at the terminal of a peptide nucleic acid as a probe with hybridization-amenable conformational flexibility

Electrochemically enhanced DNA detection was demonstrated by utilizing the couple of a synthesized ferrocene-terminated peptide nucleic acid (PNA) with a cysteine anchor and a sacrificial electron donor [Fe(CN)(6)](4-). DNA detection sensors were prepared by modifying a gold electrode surface with a mixed monolayer of the probe PNA and 11-hydroxy-1-undecanethiol (11-HUT), protecting [Fe(CN)(6)](4-) from any unexpected redox reaction. Before hybridization, the terminal ferrocene moiety of the probe was subject to a redox reaction due to the flexible probe structure and, in the presence of [Fe(CN)(6)](4-), the observed current was amplified based on regeneration of the ferrocene moiety. Hybridization decreased the redox current of the ferrocene. This occurred because hybridization rigidified the probe structure: the ferrocene moiety was then removed from the electrode surface, and the redox reaction of [Fe(CN)(6)](4-) was again prevented. The change in the anodic current before and after hybridization was enhanced 1.75-fold by using the electron donor [Fe(CN)(6)](4-). Sequence-specific detection of the complementary target DNA was also demonstrated.     

基于环蕃类分子的铁氰化钾电化学存储和释放

通过利用合成的环蕃类化合物1与单壁碳纳米管(SWNTs)间的π-π共轭相互作用,将化合物1固定在SWNTs的表面,制备了1-SWNT修饰电极.利用化合物1氧化态和还原态与铁氰化钾分子之间不同强度的主客体相互作用,实现了铁氰化钾分子在1-SWNT修饰电极表面的电化学可控吸附和解吸.循环伏安和XPS实验结果表明,在本研究采用的实验条件下,铁氰化钾分子在电极表面20s内即可达到吸附平衡;当电极在0.70V下极化1000s后,大多数吸附的铁氰化钾可从电极表面解吸.基于此,制备了铁氰化钾的可控存储和释放的电化学器件,该器件不但可以重复进行铁氰化钾分子的存储和释放,而且多次重复操作表现出较好的稳定性和重现性.本研究在发展具有特殊用途的电化学纳米器件,例如分子搬运器、电化学开关等研究中具有重要意义.     

Electrochemical characteristics of thin nickel hexacyanoferrate films formed on gold and thiol self-assembled monolayers modified gold electrodes.

Nickel hexacyanoferrate (NiHCF) film was prepared and characterized on gold and thiol self-assembled monolayers (SAMs)-modified gold electrodes. It was found that the film exhibited some different electrochemical characteristics compared with that found on a carbon electrode. In the presence of K+, the film exhibited a redox peak at about 0.5 V. The peak potential shifted linearly with the K+ concentration over the range of about 0.1 mM - 0.1 M with slopes of 54 - 60 mV per log[K+]. However, in solutions containing Na+, Li+ or NH4+ ion the film did not generate well-defined peaks, or even a visible redox peak. Therefore, the film showed a selective potential response to K+. The voltammetric behavior of NiHCF film varied with thiols, the preparation procedure and the solution pH. Under certain conditions, the characteristics of the film could be improved to some extent.     

PHOTOCHEMICAL and ENZYMATIC REDOX TRANSFORMATIONS OF REDUCED FORMS OF COENZYME NADP+

The two reduced forms of NADP+, NADPH and its dimer (NADP)2, on irradiation in aqueous medium at 365 nm, are converted to enzymatically active NADP+, with accompanying formation of H2O2. The rate photooxidation of NADPH is strongly dependent on the presence of oxygen, but that of (NADP)2 is similar under aerobic and anaerobic conditions. In the presence of oxygen, but not in its absence, O2-. is an intermediate in the reaction. Generation of H2O2 under anaerobic conditions, confirmed by the fact that presence of peroxidase in irradiated solutions of (NADP)2 enhances photooxidation of the latter, is ascribed to attack on water of the excited dimer. Under anaerobic conditions at pH 9.5, Fe(EDTA)2+ and Fe(CN)4-(6) increase the rate of photooxidation of NADP dimer two-fold. gamma-Irradiation of (NADP)2 at pH 9.5 in the presence of N2O results in 80% conversion to enzymatically active NADP+. A mechanism for photooxidation of (NADP)2 under anaerobic conditions is suggested, and some relevant biological implications are presented.     

Synthesis and electrochemical studies of diiron complexes of 1,8-naphthyridine-based dinucleating ligands to model features of the active sites of non-heme diiron enzymes

A bis(mu-carboxylato)(mu-1,8-naphthyridine)diiron(II) complex, [Fe2(BPMAN)(mu-O2CPhCy)2](OTf)2 (1), was prepared by using the 1,8-naphthyridine-based dinucleating ligand BPMAN, where BPMAN = 2,7-bis[bis(2-pyridylmethyl)aminomethyl]-1,8-naphthyridine. The cyclic voltammogram (CV) of this complex in CH2Cl2 exhibited two reversible one-electron redox waves at +296 mV (DeltaE(p) = 80 mV) and +781 mV (DeltaE(p) = 74 mV) vs Cp2Fe+/Cp2Fe, corresponding to the FeIIIFeII/FeIIFeII and FeIIIFeIII/FeIIIFeII couples, respectively. This result is unprecedented for diiron complexes having no single atom bridge. Dinuclear complexes [Fe2(BPMAN)(mu-OH)(mu-O2CPhCy)](OTf)2 (2) and [Mn2(BPMAN)(mu-O2CPhCy)2](OTf)2 (3) were also synthesized and structurally characterized. The cyclic voltammogram of 2 in CH2Cl2 exhibited one reversible redox wave at -22 mV only when the potential was kept below +400 mV. The CV of 3 showed irreversible oxidation at potentials above +900 mV. Diiron(II) complexes [Fe2(BEAN)(mu-O2CPhCy)3](OTf) (4) and [Fe2(BBBAN)(mu-OAc)2(OTf)](OTf) (6) were also prepared and characterized, where BEAN = 2,7-bis(N,N-diethylaminomethyl)-1,8-naphthyridine and BBBAN = 2,7-bis[2-[2-(1-methyl)benzimidazolylethyl]-N-benzylaminomethyl]-1,8-naphthyridine. The cyclic voltammograms of these complexes were recorded. The M?ssbauer properties of the diiron compounds were studied.     

Theoretical investigation on the electronic structure of pentacyano(L)ferrate(II) complexes with NO(+), NO, and NO(-) ligands. Redox interconversion, protonation, and cyanide-releasing reactions

Reaction pathways for the one- and two-electron reductions of [Fe(CN)(5)NO](2)(-) have been investigated by means of a density functional theory (DFT) approach combined with the polarized continuum model (PCM) of solvation. In addition, UV-vis spectroscopic data were obtained using ZINDO/S calculations including a point-charge model simulation of solvent effects. DFT methodologies have been used to assess the thermodynamical feasibility of protonation and cyanide-release processes for the reduced species. We conclude that [Fe(CN)(5)NO](3)(-) is a stable species in aqueous solution but may release cyanide yielding [Fe(CN)(4)NO](2)(-), consistent with experimental results. On the other hand, the [Fe(CN)(5)NO](4)(-) complex turns out to be unstable in solution, yielding the product of cyanide release, [Fe(CN)(4)NO](3)(-), and/or the protonated HNO complex. All the structural and spectroscopic (IR, UV-vis) predictions for the [Fe(CN)(5)HNO](3)(-) ion are consistent with the scarce but significant experimental evidence of its presence as an intermediate in nitrogen redox interconversion chemistry. Our computed data support an Fe(II)(LS) + NO(+) assignment for [Fe(CN)(5)NO](2)(-), an Fe(II)(LS) + NO assignment for the one-electron reduction product, but an Fe(I)(LS) + NO(+) for the one-electron product after dissociation of an axial cianide, and an Fe(II) + singlet NO(-) for the two-electron reduction species.     

"Abnormal" salt and solvent effects on anion/cation electron-transfer reactions: an interpretation based on Marcus-Hush treatment

Salt and solvent effects on the kinetics of the reactions [Fe(CN)6]3- + [Ru(NH3)5pz](2+) right arrow over left arrow [Fe(CN)6]4- + [Ru(NH3)5pz]3+ (pz = pyrazine) have been studied through T-jump measurements. The forward and reverse reactions show different behaviors: "abnormal" salt and solvent effects in the first case and normal effects in the second one. These facts imply an asymmetric behavior of anion/cation reactions depending on the charge of the oxidant. The results can be rationalized by using the Marcus-Hush treatment for electron-transfer reactions.     

Direct oxidation of L-cysteine by [FeIII(bpy)2(CN)2]+ and [FeIII(bpy)(CN)4]-

The oxidation of L-cysteine by the outer-sphere oxidants [Fe(bpy)2(CN)2]+ and [Fe(bpy)(CN)4]- in anaerobic aqueous solution is highly susceptible to catalysis by trace amounts of copper ions. This copper catalysis is effectively inhibited with the addition of 1.0 mM dipicolinic acid for the reduction of [Fe(bpy)2(CN)2]+ and is completely suppressed with the addition of 5.0 mM EDTA (pH<9.00), 10.0 mM EDTA (9.010.0) for the reduction of [Fe(bpy)(CN)4]-. 1H NMR and UV-vis spectra show that the products of the direct (uncatalyzed) reactions are the corresponding Fe(II) complexes and, when no radical scavengers are present, L-cystine, both being formed quantitatively. The two reactions display mild kinetic inhibition by Fe(II), and the inhibition can be suppressed by the free radical scavenger PBN (N-tert-butyl-alpha-phenylnitrone). At 25 degrees C and micro=0.1 M and under conditions where inhibition by Fe(II) is insignificant, the general rate law is -d[Fe(III)]/dt=k[cysteine]tot[Fe(III)], with k={k2Ka1[H+]2+k3Ka1Ka2[H+]+k4Ka1Ka2Ka3{/}[H+]3+Ka1[H+]2+Ka1Ka2[H+]+Ka1Ka2Ka3}, where Ka1, Ka2, and Ka3 are the successive acid dissociation constants of HSCH2CH(NH3+)CO2H. For [Fe(bpy)2(CN)2]+, the kinetics over the pH range of 3-7.9 yields k2=3.4+/-0.6 M(-1) s(-1) and k3=(1.18+/-0.02)x10(6) M(-1) s(-1) (k4 is insignificant in the fitting). For [Fe(bpy)(CN)4]- over the pH range of 6.1-11.9, the rate constants are k3=(2.13+/-0.08)x10(3) M(-1) s(-1) and k4=(1.01+/-0.06)x10(4) M(-1) s(-1) (k2 is insignificant in the fitting). All three terms in the rate law are assigned to rate-limiting electron-transfer reactions in which various thiolate forms of cysteine are reactive. Applying Marcus theory, the self-exchange rate constant of the *SCH2CH(NH2)CO2-/-SCH2CH(NH2)CO2- redox couple was obtained from the oxidation of L-cysteine by [Fe(bpy)(CN)4]-, with k11=4x10(5) M(-1) s(-1). The self-exchange rate constant of the *SCH2CH(NH3+)CO2-/-SCH2CH(NH3+)CO2- redox couple was similarly obtained from the rates with both Fe(III) oxidants, a value of 6x10(6) M(-1) s(-1) for k11 being derived. Both self-exchange rate constants are quite large as is to be expected from the minimal rearrangement that follows conversion of a thiolate to a thiyl radical, and the somewhat lower self-exchange rate constant for the dianionic form of cysteine is ascribed to electrostatic repulsion.     

Octahedral non-heme non-oxo Fe(IV) species stabilized by a redox-innocent N-methylated cyclam-acetate ligand

The ligand 1,4,8-tri-N-methyl-1,4,8,11-tetraazacyclotetradecane-11-acetic acid (Me3cyclam-acetic acid) has been synthesized by Eschweiler-Clarke methylation of cyclam-acetic acid, and the iron(III) complex [(Me3cyclam-acetate)FeN3]PF6, 1, has been synthesized, which has been found to have significantly different properties than its unmethylated analogue, [(cyclam-acetate)FeN3]PF6, 2. Whereas the iron ion in 2 is low spin with S = 1/2, 1 is found to be high spin at temperatures above 100 K, though low-spin species are observed at lower temperatures, indicating a spin crossover phenomenon. The iron(II) species 1red is electrochemically more accessible than 2red since the Fe2+/3+ redox wave in 1 appears approximately 350 mV more positive than the corresponding wave in 2. Also, 1 displays a reversible Fe3+/4+ redox wave, which is irreversible in 2, denoting that the Fe(IV) species 1ox is kinetically stable. 1red and 1ox have been generated electrochemically in solution and studied spectroscopically. M?ssbauer spectroscopy has confirmed that, in both reduction and oxidation, iron is the redox center, that 1red is high spin (S = 2), and that 1ox is low spin (S = 1), in contrast to 2red which is low spin and 2ox which could not be isolated.     

Electrochemical studies of derivatized thiol self-assembled monolayers on gold electrode in the presence of surfactants.

Electrochemical impendence spectroscopy (EIS), cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were performed to investigate the barrier properties and electron transfer of derivatized thiol self-assembled monolayers (SAMs) on gold in the presence of surfactants. The thiol derivatives used included 2-mercaptoethanesulfonic acid (MES), 2-mercaptoacetic acid (MAA), and N-acetyl-L-cysteine (NAC). A simple equivalent circuit was derived to fit the impedance spectra very well. The negative redox probe [Fe(CN)6](3-/4-) was selected to indicate the electron-transfer efficiency on the interface of the studied electrodes. It was found that by changing the surface structure of SAMs, different surfactants could regulate the barrier properties and electron-transfer efficiency in different ways. A positively charged surfactant lowered the electrostatic repulsion between the negative redox probe and negatively charged surface groups of a monolayer, while enhancing the reversibility of electron transfer by virtue of increasing the redox probe concentration within the electric double-layer region. A neutral surfactant showed no significant effect, while a negative surfactant hindered the access and reaction of redox probe by electrostatic repulsion of same-sign charges.     

Electrochemistry of catechol terminated monolayers with Cu(II), Ni(II) and Fe(III) cations: a model for the marine adhesive interface

The redox electrochemistry of hydroquinone and Cu2+-, Ni2+-, and Fe3+-hydroquinone complexes immobilized at the SAM interface has been studied in aqueous solutions with pH 5 to 12 using cyclic voltammetry. Self-assembled monolayers were constructed with terminal hydroquinone residues designed to model marine adhesive proteins that use the DOPA (3,4-dihydroxyphenylalanine) moiety. Coordination of metal to the hydroquinone group results in a shift to the ligand oxidation potential, with the value for Delta E p,a dependent on the solution pH and identity of the metal. Cu2+ shifts the hydroquinone oxidation by -285 mV (pH 8.8), and Ni2+ by -194 mV (pH 9.16). The hydroquinone oxidation was shifted by -440 mV at pH 5 for Fe3+ solutions examined up to pH 7. By contrast, reduction of the quinone is unperturbed by the presence of Cu2+, Ni2+, and Fe3+ ions. Implications of these results to the mechanism of marine adhesion are discussed.     

Recognition of bile acids at cyclodextrin-modified gold electrodes.

Lipoylamino-beta- and gamma-cyclodextrin (LP-beta-CD and LP-gamma-CD, respectively) were adsorbed at the surface of gold electrodes by sulfur-gold bonding. The resultant electrodes exhibited quasi-reversible voltammograms for the redox reaction of Fe(CN)6(3-/4-) in aqueous solutions, with peak-to-peak separation (deltaEp) being 85 mV at 20 mV s(-1) as a potential sweep rate. When bile acids are added to the solution, deltaEp values increased to 200-300 mV with increasing the concentration of bile acids. A Langmuir-type adsorption analyses satisfactorily afforded the binding constants (Ksurf) of the surface-confined LP-beta-CD and LP-gamma-CD with the bile acids. The obtained Ksurf values of LP-gamma-CD are 5.0-50 times larger than the corresponding binding constants of gamma-CD in homogeneous aqueous solutions. Cyclic voltammetric experiments with positively, negatively, and non-charged adamantane derivatives as well as pH titration experiments revealed that the retardation of the electrode reaction of negatively charged Fe(CN)6(3-/4-) caused by bile acids was attributable (1) to electric potential changes due to the accumulation of the negative charges at the electrode surface, and (2) to an increase in the hydrophobicity of the electrode surface due to the binding of hydrophobic bile acids to the LP-beta-CD and LP-gamma-CD membranes.     

Practical improvements in soil redox potential (Eh) measurement for characterisation of soil properties. Application for comparison of conventional and conservation agriculture cropping systems

The soil redox potential (Eh) can provide essential information to characterise soil conditions. In practice, however, numerous problems may arise regarding: (i) Eh determination in soils, especially aerobic soils, e.g. variations in the instrumentation and methodology for Eh measurement, high spatial and temporal Eh variability in soils, irreversibility of the redox reaction at the surface electrode, chemical disequilibrium; and (ii) measurement interpretation.     

Electrochemical behavior of copper complexes with substituted polypyridinic ligands: an experimental and theoretical study

Experimental redox potentials of the couples [Cu(R-L ( n ))(CH 3CN)] (2+,+), where L (1) is bis-(pyridine-2-ylmethyl)-benzylamine, L (2) is (pyridine-2-ylethyl)(pyridine-2-ylmethyl)-benzylamine, and R is H, Me, or CF 3, were determined in dichloromethane solution. The compounds exhibited one simple quasi-reversible wave over the measured potential range of -500 to +1200 mV, and the E 1/2 values varied from +200 to +850 mV versus SCE. These experimental values were correlated with redox potentials calculated using density functional theory. The optimized geometries and the predicted redox potentials were obtained using the BP86 functional and a combination of the basis sets LACV3P** (for Cu) and cc-pVTZ(-f) (for light atoms). A distortion analysis of all of the optimized geometries for both oxidation states was performed using the generalized interconversion coordinate phi. A linear relation was obtained between this parameter and the redox potentials. However, the [Cu(CF 3-L (1))(CH 3CN)] (+) complex showed the largest deviation, which was explained by the more-rigid structure of the ligand.     

Investigations on the kinetics of electron transfer reactions in magnetic fields

There is a controversial debate if a magnetic field can influence the rate of electron transfer (ET) reactions. In this paper, we report kinetic measurements of the ET rate constants for the redox couples [IrCl6]2-/[IrCl6]3-, [Fe(CN)6]3-/[Fe(CN)6]4-, and [Fe(H2O)6]3+/[Fe(H2O)6]2+ in magnetic fields up to 1 T. To reduce effects arising from magnetically induced mass transport (magnetohydrodynamic effect), disk microelectrodes with a diameter of 50 microm were used in potentiodynamic (cyclic and linear sweep voltammetry) and in electrochemical impedance spectroscopy experiments. None of the investigated redox couples showed a magnetic field effect on the ET rate constant.