DDAB Film Research Articles

Electrochemical sensing platform for tetrabromobisphenol A at pM level based on the synergetic enhancement effects of graphene and dioctadecyldimethylammonium bromide

Graphene nanosheets (GS) were prepared via solvent exfoliation, and then hybridized with dioctadecyldimethylammonium bromide (DDAB). On the single surface of DDAB and GS film, the direct oxidation activities of tetrabromobisphenol A (TBBPA) are improved effectively, and consequently the oxidation signals enhance obviously. Interestingly, the composite of DDAB and GS exhibits remarkable synergetic effects toward the oxidation of TBBPA, and the peak currents of TBBPA further increase greatly on the DDAB-GS composite film. The signal enhancement mechanism was studied using chronocoulometry. It is found that the greatly-increased accumulation efficiency is the main reason. As a result, a novel electrochemical sensing platform was developed for TBBPA. The linear range is from 0.1 to 400 μg L−1, and the detection limit is as low as 41.8 ng L−1 (76.8 pM). The practical applications in water samples manifest that this new determination system is accurate and feasible.

Direct electrochemistry of CYP109C1, CYP109C2 and CYP109D1 from Sorangium cellulosum So ce56

We report the first direct electrochemistry of CYP109C1, CYP109C2 and CYP109D1 from the myxobacterium Sorangium cellulosum So ce56 immobilized on the screen-printed graphite electrode (SPE) modified by a didodecyldimethylammonium bromide (DDAB) film. Electrochemical response was investigated by cyclic voltammetry. Cyclic voltammograms in a deoxygenated argon saturated 0.1M potassium phosphate buffer, pH 7.4, demonstrated a reversible redox process with E°’ of −0.305±0.005V, −0.313±0.005V, −0.309±0.005V (vs. Ag/AgCl) for CYP109C1, CYP109C2 and СYP109D1, respectively. The apparent surface coverages were (2.5±0.2)×10−11, (2.5±0.2)×10−11, (3.1±0.2)×10−11molcm−2, which corresponded to 5-6% of the total amount of protein that was consumed by the immobilization process. The rate constant ks of heterogeneous electron transfer between the hemoproteins and the SPE modified by DDAB film (SPE/DDAB) were determined as 0.39±0.01s−1, 0.35±0.01s−1, and 0.43±0.02s−1 for CYP109C1, CYP109C2 and СYP109D1, respectively. The investigated CYPs (CYP109C1, CYP109C2 and CYP109D1) demonstrated electrocatalytic activity detected by an increase of the reduction current in the presence of dissolved oxygen. Upon addition of the substrates (myristic acid and the norisoprenoid α-ionone) in the air-saturated solution, the reduction peak current of dissolved oxygen increased, which manifested the catalytic behavior of CYP109C2 and CYP109D1 towards the substrates. CYP109D1-depended electrocatalytic hydroxylation of the myristic acid was analyzed by mass-spectrometry after electrolysis at controlled working electrode potential.

Electrochemistry of mammalian cytochrome P450 2B4 indicates tunable thermodynamic parameters in surfactant films

Electrochemical methods continue to present an attractive means for achieving in vitro biocatalysis with cytochromes P450; however understanding fully the nature of electrode-bound P450 remains elusive. Herein we report thermodynamic parameters using electrochemical analysis of full-length mammalian microsomal cytochrome P450 2B4 (CYP 2B4) in didodecyldimethylammonium bromide (DDAB) surfactant films. Electronic absorption spectra of CYP 2B4–DDAB films on silica slides reveal an absorption maximum at 418nm, characteristic of low-spin, six-coordinate, water-ligated FeIII heme in P450. The FeIII/II and FeII/I redox couples (E1/2) of substrate-free CYP 2B4 measured by cyclic voltammetry are −0.23V and −1.02V (vs. SCE, or 14mV and −776mV vs. NHE) at 21°C. The standard heterogeneous rate constant for electron transfer from the electrode to the heme for the FeIII/II couple was estimated at 170s−1. Experiments indicate that the system is capable of catalytic reduction of dioxygen, however substrate oxidation was not observed. From the variation of E1/2 with temperature (18–40°C), we have measured entropy and enthalpy changes that accompany heme reduction, −151Jmol−1K−1 and −46kJmol−1, respectfully. The corresponding entropy and enthalpy values are less for the six-coordinate low-spin, imidazole-ligated enzyme (−59Jmol−1K−1 and −18kJmol−1), consistent with limited conformational changes upon reduction. These thermodynamic parameters are comparable to those measured for bacterial P450 from Bacillus megaterium (CYP BM3), confirming our prior reports that the surfactant environment exerts a strong influence on the redox properties of the heme.

Temperature-dependent structural changes on DDAB surfactant assemblies evidenced by energy dispersive X-ray diffraction and dynamic light scattering

Cationic amphiphile DDAB (dimethyl-dioctadecyl-ammonium-bromide) can spontaneously form water-dispersed and solid supported mimicking biomembrane structures as well as valuable DNA delivery vehicles whose shape, stability and transfection efficiency can be easily optimized on varying temperature, water content and chemical composition. In this framework, disclosing the thermotropic behavior of DDAB assemblies can be considered as an essential step in conceiving and developing new non-viral vector systems.Our work has been focused primarily on understanding the mesophase structure of silicon supported DDAB thin film on varying temperature at constant relative humidity by energy dispersive X-ray diffraction (EDXD). Diffraction results have then been employed in providing a more comprehensive dynamic light scattering (DLS) analysis of corresponding thermotropic water dispersed vesicles made up of DDAB alone and in combination with helper lecithin DOPC (1,2-dioleoyl-sn-glycero-3-phosphatidylcholine) liposomes.We found that above 55°C silicon-supported DDAB films undergo a significant thinning effect, whilst DDAB–water vesicles exhibit a reduction in size polydispersity. Upon cooling to 25°C a distinct silicon supported DDAB mesophase, exhibiting a relative humidity-dependent spacing, has been pointed out, and modeled in terms of a lyotropic metastable gel–crystalline phase.DDAB/DOPC–water vesicles show a temperature-dependent switching in size distribution, leading to promising biomedical applications.

A Comparison of the Higher Order Harmonic Components Derived from Large-Amplitude Fourier Transformed ac Voltammetry of Myoglobin and Heme in DDAB Films at a Pyrolytic Graphite Electrode

A debate as to whether heme remains bound or is released in myoglobin molecules incorporated into a didodecyldimethylammonium bromide (DDAB) film adhered to a pyrolytic graphite electrode has prompted a comparison of their electrochemistry by the highly sensitive large-amplitude Fourier transformed ac voltammetric method. The accessibility of third, fourth, and higher harmonic components that are devoid of background current and the enhanced resolution relative to that available in dc voltammetry have allowed a detailed comparison of the Fe(III)/Fe(II) and Fe(II)/Fe(I) redox processes of myoglobin and heme molecules to be undertaken as a function of buffer composition and pH and in the presence and absence of NaBr in the buffer and/or film. Under most conditions examined, only very subtle differences, in the Fe(III)/Fe(II) process were found, implying this process cannot be used to indicate the intactness or otherwise of myoglobin in myoglobin-DDAB films. In contrast, higher order ac harmonics obtained from myoglobin-DDAB and heme-DDAB films reveal pH dependent differences with respect to the Fe(II)/Fe(I) couple. Analysis of the ac harmonics, and with the hypothesis that the Fe(II)/Fe(I) process reflects the myoglobin state, suggests that the majority of the iron heme is released from myoglobin-DDAB (pH 5.0, no NaBr) films in contact with pH 5.0 (0.1 M sodium acetate) buffer solution devoid of or containing NaBr. However, myoglobin films prepared with pH 5.0 buffer containing NaBr shows significant difference in the higher harmonic shapes and midpoint potentials in the Fe(II)/Fe(I) process relative to the case when heme molecules are used, although as noted in other studies, a significant fraction of the Mb is rendered electroinactive in the presence of NaBr. The voltammetric responses of myoglobin and heme-DDAB (pH 5.0) films in contact with pH 7.0 (0.1 M) phosphate buffer solution also exhibit significant differences in the Fe(II)/Fe(I) redox couple in the higher harmonics in contrast to a report [de Groot, M.T.; Merkx, M.; Koper, M. T. M. J. Am. Chem. Soc. 2005, 127, 16224] that claimed identical midpoint potentials apply to both films under conditions of dc cyclic voltammetry. The FT-ac voltammetric data therefore suggest that a substantial fraction of myoglobin in myoglobin-DDAB (pH 5.0) films in contact with pH 7.0 phosphate buffer solution remains intact. No evidence of a catalytic effect that enhanced the released of heme from myoglobin was found at the pyrolytic graphite electrode surface. In summary, higher harmonic ac voltammetric data indicate that the Fe(II)/Fe(I) process but not the Fe(III)/Fe(II) reflects the state of myoglobin in DDAB films. On this basis, films prepared at pH 5.0 should include NaBr, or else films should be prepared at neutral pH to achieve films with myoglobin remains in its intact near native state when a myoglobin-DDAB film is confined to a graphite electrode surface. Otherwise, the release of heme in myoglobin molecules incorporated into a DDAB film is likely to be a dominant reaction pathway.

Electrochemical behavior of biocatalytical composite based on heme-proteins, didodecyldimethylammonium bromide and room-temperature ionic liquid

A novel biocompatible composite film based on a water-insoluble surfactant, didodecyldimethylammonium bromide (DDAB), and a hydrophobic room-temperature ionic liquid (RTIL), 1-hexyl-3-methyl-imidazolium hexafluorophosphate (HIMIMPF 6), for the immobilization of biocatalytical proteins was reported. Differential scanning calorimetry (DSC) showed that the DDAB–HIMIMPF 6 composite film has higher thermal stability than the DDAB film alone. SEM images indicated that different microstructures existed between the DDAB film and the composite film, indicating the interaction between DDAB and RTILs. This composite can be used as the immobilization matrix of proteins and other biomacromolecules. Heme-proteins, including hemoglobin (Hb), myoglobin (Mb) and horseradish peroxidase (HRP), were used as model proteins for studying the electrochemical behaviors of the resulting biocatalytical composite films. In the case of Hb, a pair of well-defined quasi-reversible redox peaks was obtained when the composite film containing Hb was modified on a glassy carbon electrode. The formal potential ( E°′), the surface coverage ( Γ *) and the electron transfer rate constant ( k s) were calculated as −0.308 V, 1.32 × 10 −11 mol cm −2 and 11.642 s −1, respectively. While, these parameters for Hb on DDAB films alone were −0.309 V, 7.20 × 10 −12 mol cm −2 and 2.748 s −1, respectively. Therefore, the composite are more suitable for the direct electron transfer between Hb than DDAB alone. The native conformation and bioactivity of Hb adsorbed on the composite film was proved to be maintained, reflected by the unchanged ultraviolet–visible (UV–vis) as well as the catalytic activity toward hydrogen peroxide (H 2O 2) and nitric oxide (NO) compared with the free Hb molecules. Furthermore, Hb on the composite film are more sensitive for the detection of hydrogen peroxide (H 2O 2) and nitric oxide (NO) than that on DDAB film alone. The linear range of H 2O 2 on Hb/DDAB–RTILs/GC electrode is from 0.5 to 57.5 μM with linear regression equations I(μA) = 0.149 + 0.00904 C(μM), while, the linear range of H 2O 2 on Hb/DDAB/GC electrode is from 0.5 to 57.5 μM with linear regression equations I(μA) = 0.0938 + 0.00553 C(μM). For NO, its linear range on Hb/DDAB–RTILs/GC electrode is from 1.8 to 21.6 μM with linear regression equations I(μA) = 0.0937 + 0.0232 C(μM). But its linear range on Hb/DDAB/GC electrode is from 1.8 to 21.6 μM with linear regression equations I(μA) = 0.0285 + 0.0167 C(μM). Similar results were observed for Mb and HRP in the DDAB–HIMIMPF 6 composite film.

Comparison of Kinetics of Hemoglobin Electron Transfer in Solution and Immobilized on Electrode Surface

The electron transfer properties of horse heart hemoglobin are compared using a hydrophilic indium tin oxide electrode and a dilaurydimethylammonium bromide (DDAB) polymer modified PG electrodes. A clear, stable and quasi-reversible redox curve of hemoglobin (Hb) was obtained in the absence of electron transfer mediators or promoters. The formal redox potential of -0.17 vs. Ag/AgCl of Hb was determined. The effects of the sixth axial binding ligands including cyanoand azido binding ligands on the redox properties of Hb were investigated. There are no significant impacts of these ligands on the redox properties of Hb, whereas big effects of the binding ligand on the electrochemical properties of myoglobin were reported. The cyclic voltammetric behavior of hemoglobin was also studied in a DDAB film coated on a pyrolytic graphite electrode. Surface immobilized Hb in DDAB film gave direct, quasi-reversible, nondiffusion-kinetic-controlled electron transfer on the electrode surface. The formal redox potential for Hb in the DDAB film negatively shifted about 140 mV as compared to the diffusion-controlled redox reaction of Hb.

Direct electrochemistry of catalase at multiwalled carbon nanotubes-nafion in presence of needle shaped DDAB for H 2O 2 sensor

The direct electrochemistry of catalase (CAT) at didodecyldimethylammonium bromide (DDAB) present on nafion dispersed multiwalled carbon nanotubes (MWCNTs-NF) modified glassy carbon electrode (GCE) has been reported. The presence of DDAB in MWCNTs-NF-CAT film enhances the surface coverage concentration of CAT (Fe III/II) to 48%. Similarly, in presence of DDAB, there is a 57% enhancement in electron transfer rate ( k s) with 66% increase in CAT stability. (Fe III/II) redox couple exhibits linear dependence with the pH variation (−51 mV pH −1). The UV–vis absorption spectroscopy study reveals the entrapped CAT in DDAB film retains its native structure at MWCNTs-NF modified electrodes. Similarly, electrochemical impedance spectroscopy results confirm the co-existence of CAT and DDAB in the modified film. Further, scanning electron microscopy results reveal the structural morphological difference between various components in MWCNTs-NF-(DDAB/CAT) film. The cyclic voltammetry (CV) and amperometry ( i– t curve) have been used for the measurement of electroanalytical properties of H 2O 2 by means of various film modified GCEs. The sensitivity values of MWCNTs-NF-(DDAB/CAT) film for H 2O 2 using CV (35.62 μA mM −1 cm 2) are higher than the values which are obtained for MWCNTs-NF-CAT film (2.74 μA mM −1 cm 2). Similarly, the sensitivity values using i– t curve are 101.74 μA mM −1 cm 2 for MWCNTs-NF-(DDAB/CAT) and 74.69 μA mM −1 cm 2 for MWCNTs-NF-CAT film. Finally, the diffusion coefficient of H 2O 2 at MWCNTs-NF-(DDAB/CAT) film (3.4 × 10 −10 cm 2 s −1) has been calculated using rotating disc electrode studies.

Electrochemistry of Sc3N@C78 embedded in didodecyldimethylammonium bromide films in aqueous solution

The electrochemical behavior of trimetallic nitride clusterfullerene (Sc3N@C78) embedded in films of the cationic surfactant didodecyldimethylammonium bromide (DDAB) on glassy carbon (GC) electrodes in aqueous solution was investigated. Four pairs of reversible redox peaks were observed in the potential range between +0.6 and −0.9 V vs. SCE. Different to the electrochemistry of pristine Sc3N@C78 in organic solution, the first reduction is a one-electron rather than simultaneous two-electron process because of the strong binding between DDA+ and the monoanion of Sc3N@C78. The generated radial monoanion, dianion and trianion of Sc3N@C78 are stable during continuous potential cycling, while some chemical reactions take place when the third anion is further reduced in the films. The cyclic voltammograms of Sc3N@C78/DDAB films checked at different temperatures pointed to strong temperature dependence. The electrochemical processes were also measured in different electrolytes, which showed pronounced anionic dependence and no cathodic dependence on either the cation or anions present. A possible electron-transfer mechanism of a Sc3N@C78/DDAB film was presented.

Comparative immobilization of antibodies on modified screen-printed graphite electrodes

Immobilization of polyclonal antibodies was studied on native screen-printed graphite electrodes (SPEs) and variously modified electrodes. SPEs coated with didodecylammonium bromide (DDAB, a synthetic membranelike substance) films with gold nanoparticles gave the maximum electrochemical response. DDAB and gold nanoparticle films strongly changed the surface morphology, and the electrochemical signal became more intense and stable. This immobilization method increased the concentration of immobilized antibodies while their activity was retained. The detection limit of the enzymatic label (horseradish peroxidase) was 0.02 ng/L of sample.

Direct Electron Transfer Reactivity of Glucose Oxidase on Electrodes Modified With Zirconium Dioxide Nanoparticles

The direct electron transfer between electrodes and glucose oxidase (GOD) immobilized in a matrix containing zirconium dioxide nanoparticles (ZrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) is described. The protein-nanoparticle assembly is stabilized by charged and uncharged compounds and the direct electron transfer is enhanced. The effects of different compositions on the electrochemical parameters, formal potential, surface loading, and constant heterogeneous electron transfer rate are characterized with cyclic voltammetry. The fastest electron transfer rate with the smallest deviation of the is obtained when GOD is immobilized with ZrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanoparticles, colloidal platinum and poly-Lysine (PLL). Incorporation of charged compounds for immobilization of GOD causes a larger positive shift of the formal potential. Electrochemical and spectroscopic measurements show that the GOD entrapped in ZrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Pt-PLL or ZrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Pt-PVA film retains its bioactivity efficiently and exhibits excellent electrocatalytic behavior towards glucose. No enzymatic activity of the immobilized GOD can be observed on ZrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /DMSO and ZrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /DDAB film.

Direct Electrochemistry of Cytochrome P450 Reductases in Surfactant and Polyion Films

AbstractNADPH‐cytochrome P450 reductase (CPR) serves as electron donor for cytochrome P450 catalyzed monooxygenase reactions utilizing flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD) as electron transfer cofactors. Here, stable films of human and rabbit CPRs with didodecyldimethylammonium bromide (DDAB), dimyristoylphosphatidyl choline (DMPC), and poly(diallyldimethylammonium) (PDDA) were made on pyrolytic graphite (PG) electrodes for comparative structural and electrochemical studies. CD and UV‐VIS absorbance spectra suggested that near native CPR conformation is retained in PDDA films, and some conformational changes occur in DMPC or DDAB films. Cyclic voltammetry of these films gave quasireversible pairs of peaks at average formal potential −0.246±0.008 V vs. NHE. In human CPR‐DDAB (H‐CPR‐DDAB), a second pair of peaks at +0.317 V vs. NHE was found that depended strongly on identity of buffer and salt. Excepting H‐CPR in DDAB, films showed similar voltammetry, formal potentials, and ks values. While CPR‐PDDA films had near native CPR structures, electrochemical parameters did not differ significantly from CPR‐DMPC films. The relative independence of film voltammetry from the influence of film materials for CPRs is in contrast with heme iron proteins that, while retaining near native structures, have formal potentials that depend significantly on identity of the film material.

An electroreflectance approach to study out the puzzling state of myoglobin in a DDAB film on a pyrolytic graphite electrode surface

The state of the heme of myoglobin molecules incorporated in a didodecyldimethylammonium bromide (DDAB) film on a pyrolytic graphite electrode was described using the results of electroreflectance measurements. It was found that the hemes are released from the myoglobin molecules. The ER spectrum of PG electrode|Mb–DDAB film was indistinguishable from the spectrum of PG electrode|hemin–DDAB film, even in the presence of NaBr, but clearly different from PG electrode|imidazole-coordinated hemin–DDAB. These results support the claim of de Groot and coworker [M.T. de Groot, M. Merksx, M.T.M. Koper, J. Am. Chem. Soc. 127 (2005) 16224; M.T. de Groot, M. Merkx, M.T.M. Koper, Electrochem. Commun. 8 (2006) 999]. It is likely that DDAB is not a strong inhibitor of imidazole coordination but acts on the protein, resulting in conformational change and the heme release.

Spectroscopic and Electrochemical Characterization of Cytochrome P450st‐DDAB Films on a Plastic‐Formed Carbon Electrode

AbstractWe have studied the characterization of thermophilic cytochrome P450 (P450st)‐didodecyldimethylammonium bromide (DDAB) films by using UV‐vis absorption, resonance Raman spectroscopy, and electrochemical methods. The observed Raman spectrum indicated near‐native conformation of the heme iron in DDAB film on the surface of a glass slide, while on the surface of a plastic‐formed carbon (PFC) electrode, the conformation of P450st‐DDAB was very similar to that of heme‐DDAB film, suggesting the release of heme from P450st in DDAB films on PFC electrodes. When NaBr was added as salt to the casting solution, the result of Raman spectrum indicated near‐native conformation of P450st in DDAB film even on the PFC electrode, but no redox potential of P450st which has near native structure was observed. This study suggests the essential experimental conditions when working with heme protein‐DDAB films as, in some cases, heme iron from proteins is released on the surface of the electrode.

Effective enhancement of peroxydisulfate electrochemiluminescence on C 60/DDAB films

Effective enhancement of electrochemiluminescence (ECL) of peroxydisulfate on a C 60/didodecyldimethyl ammonium bromide (C 60/DDAB) film coated glassy carbon electrode (GCE) surface is reported in this paper. The C 60/DDAB film gave lower cathodic current in the presence of peroxydisulfate than that from a bare GCE. To our surprise, electrochemiluminescent intensity from peroxydisulfate reduction was effectively enhanced on the C 60/DDAB film, which was 50 times and 250 times higher than those from a DDAB film coated and bare GCE, respectively. Moreover, the ECL onset potential on the C 60/DDAB film was about −0.9 V, which positively shifted 200 mV compared with that from the bare GCE. Dissolved oxygen and the applied potential also affected the electrochemiluminescent intensity. The presence of oxygen decreased the intensity, and the intensity reached maximum at the applied potential of −1.7 V. The unique property will greatly enrich ECL studies and applications based on fullerenes.

Myoglobin retains iron heme and near-native conformation in DDAB films prepared from pH 5 to 7 dispersions

A recent paper [M.T. DeGroot, M. Merkx, M.J.M. Koper, J. Am. Chem. Soc. 127 (2005) 16224] suggests that iron heme is released during casting films of myoglobin (Mb) and didodecyldimethylammonium bromide (DDAB) on pyrolytic graphite (PG) electrodes. Insoluble films of lipids and surfactants have become widely used for protein film electrochemistry, and protein conformation within them is a critical issue. The present communication examines the integrity of myoglobin structure in DDAB films by voltammetry, visible absorption and circular dichroism spectroscopy, and discusses these new data in context with previously reported studies. Voltammetry showed that peak potentials for Mb, horseradish peroxidase and hemin in DDAB films are significantly different, and that Soret band and CD spectra in the films are fully consistent with a near native Mb conformation within the films. The view that pyrolytic graphite surfaces are catalysts for denaturation and heme loss in Mb-DDAB films is discredited by consideration of key results in the literature. On the basis of all results and considerations, this communication confirms that when DDAB films are made from vesicle dispersions at pH 5 to 7 and used in neutral buffers containing NaBr, Mb in the film is in a near-native conformation.

Heme Release in Myoglobin−DDAB Films and Its Role in Electrochemical NO Reduction

Electrochemical nitric oxide (NO) reduction by heme groups incorporated in films of didodecyldimethylammonium bromide (DDAB) on pyrolitic graphite was investigated. It is shown that DDAB most likely induces the release of the heme group from myoglobin and therefore myoglobin-DDAB and heme-DDAB films give the same voltammetric responses. This is confirmed by UV/vis spectroscopy showing a clear shift in the Soret band of myoglobin in a DDAB solution. The electrochemical NO reduction on a heme-DDAB film at different pH values reveals the presence of pH-dependent and pH-independent NO reduction pathways. The selectivity of these pathways is probed by combining the rotating ring-disk electrode technique with online electrochemical mass spectroscopy showing that the product of the pH-independent pathway is N2O and the product of the pH-dependent pathway is NH2OH. The preference for one or the other pathway seems to depend on whether a proton or a NO molecule is transferred to a Fe(II)-NO- reaction intermediate and is influenced by pH, NO concentration, and potential.

Redox Couples of Inducible Nitric Oxide Synthase

We report direct electrochemistry of the iNOS heme domain in a DDAB film on the surface of a basal plane graphite electrode. Cyclic voltammetry reveals FeIII/II and FeII/I couples at -191 and -1049 mV (vs Ag/AgCl). Imidazole and carbon monoxide in solution shift the FeIII/II potential by +20 and +62 mV, while the addition of dioxygen results in large catalytic waves at the onset of FeIII reduction. Voltammetry at higher scan rates (with pH variations) reveals that the FeIII/II cathodic peak can be resolved into two components, which are attributable to FeIII/II couples of five- and six-coordinate hemes. Digital simulation of our experimental data implicates water dissociation from the heme as a gating mechanism for ET in iNOS.

Electroactive endohedral metallofullerene film electrodes in aqueous solutions

The aqueous electrochemistry of Dy@C 82 films and membrane films of didodecyldimethylammonium bromide (DDAB) encapsulated with Dy@C 82 has been studied systematically. The redox responses of the Dy@C 82 films depend strongly on the supporting electrolytes. In the aqueous solution of tetrabutylammonium bromide, we obtained four cathodic waves at 0.040, −0.40, −1.04, and −1.35 V, and one oxidation wave at +0.31 V. For the membrane films of Dy@C 82–DDAB film, however, the well-defined redox responses in water are relatively independent of the supporting electrolytes because of the encapsulation and fine dispersion of Dy@C 82 in the DDAB membrane. Reversible reduction and oxidation waves were obtained even in the pH 7.0 buffer solution containing KCl, which is associated with the charge balance of the DDAB ions with the ions of Dy@C 82. It was found that Dy@C 82 in the DDAB membrane promotes the encapsulation of hemoglobin (Hb) and Hb can catalyze the reduction of Dy@C 82. Significantly enhanced electrocatalytic reduction of O 2 by Hb in the presence of Dy@C 82 has also been demonstrated. Here Dy@C 82 acts an electron-transfer mediator, which points to the potential application of metallofullerenes in biochemical sensing.

535 Phase I study of a new Halichondrin B analog, E7389, administered by 1-hour IV infusion every 21 days

We report the first direct electrochemistry of CYP109C1, CYP109C2 and CYP109D1 from the myxobacterium Sorangium cellulosum So ce56 immobilized on the screen-printed graphite electrode (SPE) modified by a didodecyldimethylammonium bromide (DDAB) film. Electrochemical response was investigated by cyclic voltammetry. Cyclic voltammograms in a deoxygenated argon saturated 0.1 M potassium phosphate buffer, pH 7.4, demonstrated a reversible redox process with E°’ of −0.305 ± 0.005 V, −0.313 ± 0.005 V, −0.309 ± 0.005 V (vs. Ag/AgCl) for CYP109C1, CYP109C2 and СYP109D1, respectively. The apparent surface coverages were (2.5 ± 0.2) × 10−11, (2.5 ± 0.2) × 10−11, (3.1 ± 0.2) × 10−11 mol cm−2, which corresponded to 5-6% of the total amount of protein that was consumed by the immobilization process. The rate constant ks of heterogeneous electron transfer between the hemoproteins and the SPE modified by DDAB film (SPE/DDAB) were determined as 0.39 ± 0.01 s−1, 0.35 ± 0.01 s−1, and 0.43 ± 0.02 s−1 for CYP109C1, CYP109C2 and СYP109D1, respectively. The investigated CYPs (CYP109C1, CYP109C2 and CYP109D1) demonstrated electrocatalytic activity detected by an increase of the reduction current in the presence of dissolved oxygen. Upon addition of the substrates (myristic acid and the norisoprenoid α-ionone) in the air-saturated solution, the reduction peak current of dissolved oxygen increased, which manifested the catalytic behavior of CYP109C2 and CYP109D1 towards the substrates. CYP109D1-depended electrocatalytic hydroxylation of the myristic acid was analyzed by mass-spectrometry after electrolysis at controlled working electrode potential.