Direct electrochemistry of myoglobin based on electrodeposition of Pd nanoparticles with carbon ionic liquid electrode as basic electrode

We report on the direct electrochemistry and electrocatalytic properties of myoglobin (Mb) immobilized on a carbon ionic liquid electrode covered with a matrix composed of an ionic liquid, gellan gum, and Pd nanoparticles. UV-vis and FT-IR spectroscopy confirm that Mb retains its native structure in the composite film on the electrode. Scanning electron microscopy reveals that the nanoparticles are deposited on the surface of the Pd electrode. Cyclic voltametry gives a pair of well-defined and quasireversible redox peaks with a formal potential (E ^0′) of ?332 mV and a peak-to-peak separation of 64 mV at near-neutral pH value. The modified electrode shows good electrocatalytic activity towards the reduction of hydrogen peroxide, with a linear range between 5.0 μM and 0.27 mM and a detection limit of 1.7 μM (S/N = 3). The apparent Michaelis-Menten constant is 88 μM.

Direct Electron Transfer and Electrocatalysis of Myoglobin Based on its Direct Immobilization on Carbon Ionic Liquid Electrode

Direct electron transfer of myoglobin (Mb) was achieved by its direct immobilization on carbon ionic liquid electrode (CILE) with a conductive hydrophobic ionic liquid, 1‐butyl pyridinium hexaflourophosphate ([BuPy][PF₆]) as binder for the first time. A pair of well‐defined, quasi‐reversible redox peaks was observed for Mb/CILE resulting from Mb redox of heme Fe(III)/Fe(II) redox couple in 0.1 M phosphate buffer solution (pH 7.0) with oxidation potential of ?0.277 V, reduction potential of ?0.388 V, the formal potential E°′ (E°′=(E_pa+E_pc)/2) at ?0.332 V and the peak‐to‐peak potential separation of 0.111 V at 0.5 V/s. The average surface coverage of the electroactive Mb immobilized on the electrode surface was calculated as 1.06±0.03×10^?9 mol cm^?2. Mb retained its bioactivity on modified electrode and showed excellent electrocatalytic activity towards the reduction of H₂O₂. The cathodic peak current of Mb was linear to H₂O₂ concentration in the range from 6.0 μM to 160 μM with a detection limit of 2.0 μM (S/N=3). The apparent Michaelis–Menten constant (K and the electron transfer rate constant (k_s) were estimated to be 140±1 μM and 2.8±0.1 s^?1, respectively. The biosensor achieved the direct electrochemistry of Mb on CILE without the help of any supporting film or any electron mediator.     

Syntheses and crystal structures of oxovanadium(V) complexes derived from N′-[1-(2-hydroxynaphthyl)ethylidene]-4-nitrobenzohydrazide and 2-hydroxy-N′-[1-(2-hydroxynaphthyl)ethylidene]benzohydrazide

Reactions of bis(acetylacetonato)oxovanadium(IV) with N??-[1-(2-hydroxynaphthyl)ethylidene]-4-nitrobenzohydrazide (H₂HNB) and 2-hydroxy-N??-[1-(2-hydroxynaphthyl)ethylidene]benzohydrazide (H₂HHB), respectively, product two oxovanadium(V) species with the formulas [VO(OMe)(HNB)]₂ (I) and [VO(OMe)(HHB)] (II). The complexes I and II have been characterized by elemental analysis, IR spectra, and single crystal X-ray diffraction. The crystal of I is monoclinic: space group P2₁/n, a = 8.208(2), b = 14.528(3), c = 16.418(3) ?, ?? = 97.887(3)°, V = 1939.3(7) ?³, Z = 2. The crystal of II is triclinic: space group P $P\bar 1$ a = 8.334(2), b = 10.236(2), c = 11.337(2) ?, ?? = 80.91(3)°, ?? = 75.41(3)°, ?? = 75.63(3)°, V = 902.0(3) ?³, Z = 2. Complex I is a methoxide-bridged dimeric oxovanadium(V) complex, and complex II is a mononuclear oxovanadium(V) complex. The V atom in I is in an octahedral coordination, and that in II is in a square pyramidal coordination.     

Structures and bonding situation of Pb2X2 (X?=?H, F, Cl, Br and I)

Quantum chemical calculations using DFT (BP86) and ab initio methods (MP2, MP4 and CCSD(T)) have been carried out for the title compounds. The nature of the Pb?CPb interactions has been investigated with an energy decomposition analysis. The energy minimum structures of the halogen substituted Pb₂X₂ molecules possess a doubly bridged butterfly geometry A like the parent system Pb₂H₂. The unusual geometry can be explained with the interactions between PbX fragments in the X ²?? ground state which leads to one Pb?CPb electron-sharing ?? bond and two donor?Cacceptor bonds between the Pb?CX bonds as donor and vacant p(??) AOs of Pb. The energy difference between the equilibrium form A and the linear structure XPb??PbX (E) which is a second-order saddle point is much higher when X is a halogen atom than for X?=?H. This is because the a ⁴??^?????X ²?? excitation energies of PbX (X?=?F?CI) are higher than for PbH. The structural isomers B, D1, D2, E, F1, F2 and G of Pb₂X₂ are no minima on the potential energy surface.     

Exploring antibiotic resistant mechanism by microcalorimetry

In an effort to probe the reaction of antibiotic hydrolysis catalyzed by B3 metallo-??-lactamase (M??L), the thermodynamic parameters of penicillin G hydrolysis catalyzed by M??L L1 from Stenotrophomonas maltophilia were determined by microcalorimetric method. The values of activation free energy ??G _?? ^?? are 88.26, 89.44, 90.49, and 91.57?kJ?mol^?1 at 293.15, 298.15, 303.15, and 308.15?K, respectively, activation enthalpy ??H _?? ^?? is 24.02?kJ?mol^?1, activation entropy ??S _?? ^?? is ?219.2511?J?mol^?1?K^?1, apparent activation energy E is 26.5183?kJ?mol^?1, and the reaction order is 1.0. The thermodynamic parameters reveal that the penicillin G hydrolysis catalyzed by M??L L1 is an exothermic and spontaneous reaction.     

Synthesis, crystal structures, DNA binding and cleavage studies of two oxovanadium(IV) complexes of 1,10-phenanthroline and Schiff bases derived from tryptophan

Two new V(IV) complexes, [VO(Naph?Ctrp)(phen)]·CH₃OH (1) and [VO(o-Van?Ctrp)(phen)]·CH₃OH·H₂O (2) (Naph?CTrp?=?Schiff base derived from 2-hydroxy-1-naphthaldehyde and l-tryptophan, o-Van?Ctrp?=?Schiff base derived from o-vanillin and l-tryptophan, phen?=?1,10-phenanthroline), have been synthesized and characterized by physicochemical methods. The V(IV) atoms in both complexes are six-coordinated in a distorted octahedral environment. In the crystals of complex 1, the C?CH···?? and ?ШC?? stacking interactions form a 1D chain structure, whereas for complex 2, hydrogen bonds connect the molecular units into a 2D plane structure. The DNA binding properties and cleavage efficiencies of the complexes have been investigated by spectroscopic methods, viscosity measurements and agarose gel electrophoresis. The results suggest that both complexes can bind to CT-DNA in an intercalative mode and can also cleave pBR322 DNA.     

Mononuclear copper(II) complexes of bis-triazole-based macrocyclic Schiff base hydrazones: direct synthesis,EPR studies,magnetic and thermal properties

Mononuclear copper(II) complexes of 1,2,4-triazole-based Schiff base macrocyclic hydrazones, III and IV, have been reported. The prepared amorphous complexes have been characterized by spectroscopic methods, electron spray ionization mass spectrometry, and elemental analysis data. Electrochemical studies of the complexes in DMSO show only one quasi-reversible reduction wave at +0.43 V (ΔE = 70 mV) and +0.42 V (ΔE = 310 mV) for III and IV, respectively, which is assigned to the Cu(II) → Cu(I) reduction process. Temperature dependence of magnetic susceptibilities of III and IV has been measured within an interval of 2–290 K. The values of χ_M at 290 K are 1.72 × 10^?3 cm³ mol^?1 and 1.71 × 10^?3 for III and IV, respectively, which increases continuously upon cooling to 2 K. EPR spectra of III and IV in frozen DMSO and DMF were also reported. The trend g_|| > g⊥ > g_e suggests the presence of an unpaired electron in the d_x2?y2 orbital of the Cu(II) in both complexes. Furthermore, spectral and antimicrobial properties of the prepared complexes were also investigated.     

Conformational space of tetrakis(2-naphthalenyl)ethene: a naphthologous AIE luminogen

The AIE luminogen tetrakis(2-naphthalenyl)ethene (2-NA ₄ E) was synthesized by Barton’s double extrusion diazo-thione coupling method from 2,2′-dinaphthyl thioketone and 2,2′-(diazomethylene)bisnaphthylene in 77 % yield. The structure of 2-NA ₄ E was confirmed by its ¹H NMR and ¹³C NMR spectra with full assignments. 2-NA ₄ E and its parent tetraphenylethene (Ph ₄ E) have been subjected to a comprehensive computational DFT study, in search of their conformational spaces. Seven conformers and two transition states of 2-NA ₄ E have been located. Four conformers and one transition state of Ph ₄ E have been located. The conformers of 2-NA ₄ E and Ph ₄ E are not overcrowded, as indicated by the contact distances in the fjord and cove regions. The relative free energies (ΔG ₂₉₈) of the six most stable conformers of 2-NA ₄ E are in the narrow range of 2.3 kJ/mol; they make comparable contributions (12–29 %) to the equilibrium mixture. The energy barriers for the diastereomerization D ₂-Z,Z,Z,Z $ \rightleftharpoons $ ? D ₂-E,E,E,E via the transition state C ₁-Z,E,E,Z and for the enantiomerization C ₂-Z,Z,E,E $ \rightleftharpoons $ ? C ₂-E,E,Z,Z via the transition state C _i -Z,E,Z,E are only 29.8 and 29.0 kJ/mol, respectively, indicating very rapid rates of diastereomerization and enantiomerization at room temperature. The values of naphthalenyl torsion angles and ethenic twist angles in 2-NA ₄ E are almost identical to those in the parent Ph ₄ E. The previously proposed “bulkiness” of the naphthalenyl substituents and the validity of the restriction of naphthalenyl rotation are challenged. The analysis of the AIE effect in 2-NA ₄ E should take into account the intermolecular homochiral and heterochiral interactions between the conformers.     

Direct electrochemistry and electrocatalysis of myoglobin using an ionic liquid-modified carbon paste electrode coated with Co3O4 nanorods and gold nanoparticles

A nanohybrid biomaterial was fabricated by mixing Co₃O₄ nanorods, gold nanoparticles (Au-NPs) and myoglobin (Mb), and depositing it on the surface of a carbon paste electrode containing the ionic liquid N-hexylpyridinium hexafluorophosphate as the binder. UV–vis and FT-IR revealed the Mb in the composite film to have remained in its native structure. A pair of well-defined redox peaks appears in cyclic voltammograms and indicates direct electron transfer from the Mb to the underlying electrode. The results are attributed to the favorable orientation of Mb in the composite film, to the synergistic effects of Co₃O₄ nanorods and Au-NPs. The modified electrode shows excellent electrocatalytic ability towards the reduction of substrates such as trichloroacetic acid and nitrite, and displays good stability and reproducibility.

Synthesis, crystal structure and electrochemical properties of [Co(phen)3] · (H3btec) · (H2btec)0.5 · DMF · 6H2O

A new complex [Co(phen)₃] · (H₃btec) · (H₂btec)_0.5 · DMF · 6H₂O (1) (H₄btec = 1,2,4,5-Benzenetetracarboxylic acid, phen = 1,10-phenanthroline, DMF = dimethylformamide) was synthesized by the reaction of pyromellitic dianhydride, phen · H₂O and CoSO₄ · 7H₂O. Complex 1 crystallizes in the triclinic system, space group P-1 with a = 11.8123(14) ?, b = 13.0356(16) ?, c = 17.575(2) ?, ?? = 91.461(2)°, ?? = 101.347(2)°, ?? = 99.830(2)°, FW = 1159.94, Z = 2, V = 2609.5(5) ?³. X-ray crystal structural determination indicates that the Co(II) ion is octahedral coordinated by six nitrogen atoms of three phenanthroline ligands. The [Co(phen)₃]²⁺ cation engages its phen ligands in ??-?? interactions with H₂btec anion. Extensive hydrogen bonding interactions occur between water molecules, DMF, H₃btec and H₂btec anions. The highly-crystalline compounds 1, which are insoluble in water as well as common organic solvents, have been characterized in the solid-state by elemental analysis, thermogravimetric analysis and IR spectra. Moreover, the study of the electrochemistry of complex 1 was carried out by using cyclic voltammetry. It revealed that the Co(II) complex exhibits a quasi-reversible one-electron redox process.     

The reaction of ammonium tetra(isothiocyanato)diamminechromate(III) with ?-caprolactam in aqueous solution. Revised refinement of the structure of (HCpl2)3[Cr(NCS)6]

A reaction of ammonium tetra(isothiocyanato)diamminechromate(III) (ammonium reineckate) with ?-caprolactam in aqueous solution at different pH values gave the novel complexes (NH₄)[Cr(NH₃)₂(NCS)₄] · 7Cpl (I), (NH₄)[Cr(NH₃)₂(NCS)₄] · 2.5Cpl · 0.5(H₂O) (II), and (HCpl₂)[Cr(NH₃)₂(NCS)₄] (III), where Cpl is ?-caprolactam (?-C₆H₁₁NO). The crystals of complexes I?CIII are triclinic, space group $P\bar 1$ ; I: a = 12.7058(4) ?, b = 13.2544(4) ?, c = 19.4487(7) ?, ?? = 105.2360(10)°, ?? = 106.6410(10)°, ?? = 91.5290(10)°, V = 3009.37(17) ?³, ??_calc = 1.245 g/cm³, Z = 2; II: a = 12.3144(5) ?, b = 12.6518(5) ?, c = 23.3300(8) ?, ?? = 75.4580(10)°, ?? = 80.0760(10)°, ?? = 61.0830(10)°, V = 3074.1(2) ?³, ??_calc = 1.358 g/cm³, Z = 4; III: a = 6.4701(4) ?, b = 12.5973(9) ?, c = 16.5556(12) ?, ?? = 108.769(2)°, ?? = 98.543(2)°, ?? = 90.345(2)°, V = 1261.36(15) ?³, ??_calc = 1.437 g/cm³, Z = 2. The structure refinement for (HCpl₂)₃[Cr(NCS)₆] (IV) was revised. Like complex III, complex IV contains the cation (HCpl₂)⁺ stabilized by a strong hydrogen bond between the O atoms of the ?-caprolactam molecules; the cation was structurally characterized for the first time.     

Glassy carbon electrode modified with a film composed of Ni(II), quercetin and graphene for enzyme-less sensing of glucose

We present a modified glassy carbon electrode as a sensing platform for glucose. It is based on a composite film prepared from Ni(II) ion, quercetin and graphene. The sensor was characterized by cyclic voltammetry. The electron transfer coefficient, reaction rate constant and catalytic rate constant were determined and found to be 0.53, 5.4?s^?1 and 2.93?×?10³?M^?1 s^?1, respectively. The catalytic current depends linearly on the concentration of glucose in the range from 3 to 900???M, with a detection limit of 0.5???M (at an S/R of 3). The sensor exhibits good reproducibility, stability, fast response, and high sensitivity.

Two new 2D copper(II) complexes constructed from a flexible bis-pyridyl-bis-amide ligand and two aromatic tricarboxylates: syntheses, crystal structures, fluorescence, and electrochemical properties

Two new 2D metal-organic complexes, namely [Cu(3-dpyb)(1,2,4-HBTC)(H₂O)]·H₂O (1) and [Cu₃(3-dpyb)₃(SIP)₂(H₂O)₈]·6H₂O (2) [3-dpyb?=?N,N??-bis(3-pyridinecarboxamide)-1,4-butane, 1,2,4-H₃BTC?=?1,2,4-benzenetricarboxylic acid, H₃SIP?=?5-sulfoisophthalic acid], have been hydrothermally synthesized and structurally characterized by elemental analyses, IR, TG, and single crystal X-ray diffraction analyses. Single crystal X-ray analyses reveal that the two Cu(II) complexes show different 2D coordination networks, the 4-connected (4⁴·6²) topology for complex 1 and the (4·6²)₂(4²·6²·8²) topology for complex 2. In the 2D layers of complexes 1 and 2, the 3-dpyb ligands adopt a typical ?? ₂-bridging mode (via ligation of two pyridyl nitrogen atoms), while 1,2,4-HBTC and SIP serve as a linear spacer and a ??V??-like linker, respectively, to connect the adjacent Cu(II) centers. The adjacent 2D layers are extended to 3D supramolecular networks via hydrogen-bonding interactions. The fluorescence properties of both complexes and electrochemical properties of complex 2 have also been investigated. The complex 2 bulk-modified carbon paste electrode (2-CPE) displayed a one-electron redox wave in potential range of 600?C200?mV in 1?M H₂SO₄ aqueous solution, and 2-CPE showed good electrocatalytic activity toward the reduction of nitrite.     

Surface Characterization of a Novel D-��-D Type Ligand by IGC at Infinite Dilution

The adsorption properties and acid?Cbase contributions to the surface energy of (E)-N-((E)-3-(4-(dimethylamino)phenyl)allylidene)-4-(4-((E)-((E))-3-(4(dimethylamino)phenyl)allylidene)amino)-3-methylnaphthalen-1-yl)-2-ethylnaphthalen-1-amine which is a new D-??-D Type Schiff base ligand (L) were determined by inverse gas chromatography (IGC) at infinite dilution. The retentions of several organic solvents on L were measured in the temperature range from 40 to 100 °C by IGC. The dispersive component of the surface energy, $ \gamma_{S}^{D} $ of studied adsorbent surface was estimated using retention times of different nonpolar organics in the infinite dilution region. Thermodynamic parameters of adsorption (free energy, $ \Updelta G_{A}^{S} , $ enthalpy, $ \Updelta H_{A}^{S} $ and entrophy, $ \Updelta S_{A}^{S} $ ), dispersive components of the surface energies, $ \gamma_{S}^{D} $ and the acid, K _A and base, K _D constants for the L were calculated. The obtained results proved that IGC is an efficient and successful technique for the characterization of adsorption properties and acid?Cbase quantity of these kinds of materials.     

Crystal structures and thermal decomposition kinetics of lanthanide complexes with 3,4,5-trimethoxybenzoic acid and 1,10-phenanthroline

A series of lanthanide complexes with the 3,4,5-trimethoxybenzoic acid(3,4,5-tmoba) and 1,10-phenanthroline(phen),[Ln(3,4,5-tmoba) 3 phen] 2(Ln = Pr(1),Nd(2) and Ho(3)),have been synthesized and characterized by a series of techniques including elemental analysis,IR spectra,X-ray crystallography and TG/DSC-FTIR technology.The three complexes have two kinds of coordination modes,in which the Pr 3+ and Nd 3+ cations are nine-coordinated and the Ho 3+ cation is eight-coordinated.The three-dimensional IR accumulation spectra of gaseous products for complexes 1-3 were analyzed and the gaseous products were identified by the typical IR spectra obtained from the 3D surface graphs.Meanwhile,we obtained the activation energy E of the first steps of complexes 1-3 by the integral isoconversional non-linear(NL-INT) method and discussed the non-isothermal kinetics of complexes 1-3 using the Malek method.Finally,SB(m,n) was defined as the kinetic method of the first-step thermal decomposition.The thermodynamic parameters △G≠,△H≠ and △S≠ of activation at the peak temperature were also calculated.     

π-Complexes of copper(I) halides with 3-(allylamino)-(C3H5NHC2H4CN, Apn) and 3-(diallylamino)-((C3H5)2NC2H4CN, Dapn)-propanenitrile. syntheses and crystal structures of compounds [CuCl(Apn)], [(H+Apn)Cu2Cl3], [(H+Dapn)CuCl2], and [(H+Dapn)CuBr2]

The ??-complexes [CuCl(C₃H₅NHC₂H₄CN)] (I), [(C₃H₅NH₂C₂H₄CN)Cu₂Cl₃] (II), [((C₃H₅)₂NHC₂H₄CN)CuCl₂] (III), and [((C₃H₅)₂NHC₂H₄CN)CuBr₂] (IV) are obtained as single crystals by the ac electrochemical synthesis on copper wire electrodes from ethanolic solutions of 3-(allylamino)propanenitrile, 3-(diallylamino)propanenitrile, and CuX₂ (X = Cl, Br). Their crystal structures are determined. The crystals of compounds I, III, and IV are monoclinic, space group P2₁/c, Z = 4. The crystals of compound II are triclinic, space group P $\bar 1$ , Z = 2. The unit cell parameters are a = 11.125(4), b = 8.769(4), c = 8.570(4) ?, ?? = 90.94(4)°, V = 835.9(6) ?³ (I); a = 6.2566(4), b = 7.5975(6), c = 11.1251(8) ?, ?? = 90.896(6)°, ?? = 92.827(5)°, ?? = 94.340(5)°, V = 526.57(7) ?³ (II); a = 11.656(4), b = 6.992(4), c = 14.681(5) ?, ?? = 100.89(4)°, V = 1174.9(9) ?³ (III); a =11.845(4), b = 7.282(4), c=14.855(5) ?, ?? = 100.37(4)°, V = 1260.4(9) ?³ (IV). The coordination mode of the Cu(I) atom in complex I includes two halogen atoms, the C=C bond, and the secondary amine N atom. The coordination environment in isostructural crystals of complexes III and IV is formed by the C=C bond and three halogen atoms as in complex II.     

Sensor for lead(II) ion based on a glassy carbon electrode modified with double-stranded DNA and ferric oxide nanoparticles

Shuttle-like Fe₂O₃ nanoparticles (NPs) were prepared by microwave-assisted synthesis and characterized by scanning electron microscopy and X-ray diffraction. The NPs were immobilized on a glassy carbon electrode and then covered with dsDNA. The resulting electrode gives a pair of well-defined redox peaks for Pb(II) at pH 6.0, with anodic and cathodic peak potentials occurring at ?0.50?V and ?0.75?V (vs. Ag/AgCl), respectively. The amperometric response to Pb(II) is linear in the range from 0.12 to 40?nM, and the detection limit is 0.1?nM at a signal-to-noise ratio of 3. The sensor exhibits high selectivity and reproducibility.

Two new manganese(II) complexes bulk-modified carbon paste electrodes: Preparation and electrocatalytic activities

Two new manganese complexes of [(2-py)CNOH]₂Cl₂ (1) and [(2-py)CNOH] ₂(OAc) ₂ (2) were synthesized and their structures were characterized by X-ray crystallography, IR spectroscopy and elemental analysis. Two complexes were used as bulk modifier to fabricate two carbon paste electrodes (Mn-CPE: 1-CPE and 2-CPE). The electrochemical behaviors of two modified electrodes were characterized by cyclic voltammetry. They have similar electrochemical behaviors and good electrocatalytic activities toward the reduction of hydrogen peroxide and nitrite. The results are reproducible with a lower detection limit than earlier reports. There exist a good linear relationship between peak current with the concentration in the range of 0.10?C1.20 ??M and a detection limit of 0.08 ??M for hydrogen peroxide, and in the range of 0.02?C0.10 ??M and a detection limit of 0.01 ??M for nitrite. Also Mn-CPE exhibits remarkable long term stability, simple preparation and inexpensive material, which is important for practical application on electrochemistry sensors.     

Electrochemistry and biosensing activity of cytochrome c immobilized in macroporous materials

An amperometric biosensor for hydrogen peroxide (H₂O₂) has been constructed by immobilizing cytochrome c on an indium/tin oxide (ITO) electrode modified with a macroporous material. Cyclic voltammetry showed that the direct and quasi-reversible electron transfer of cytochrome c proceeds without the need for an electron mediator. A surface-controlled electron transfer process can be observed with an apparent heterogeneous electron-transfer rate constant (k_s) of 29.2?s^?1. The biosensor displays excellent electrocatalytic responses to the reduction of H₂O₂ to give amperometric responses that increase steadily with the concentration of H₂O₂ in the range from 5???M to 2?mM. The detection limit is 0.61???M at pH?7.4. The apparent Michaelis-Menten constant (K_m) of the biosensor is 1.06?mM. This investigation not only provided a method for the direct electron transfer of cytochrome c on macroporous materials, but also established a feasible approach for durable and reliable detection of H₂O₂.

Direct electron transfer and biocatalytic activity of iron storage protein molecules immobilized on electrodeposited cobalt oxide nanoparticles

Ferritin was immobilized on a glassy carbon electrode with electrodeposited cobalt oxide nanoparticles, and its direct electron transfer behavior was studied. It exhibits a pair of redox peaks due to direct electron transfer between ferritin and the nanoparticles. Electrochemical parameters including the formal potential (E^0??), the charge transfer coefficient (??), and the apparent heterogeneous electron transfer rate constant (k_s) were determined. The sensor displays excellent biocatalytic activity in terms of reduction of hydrogen peroxide, and this was applied to electrochemical sensing of hydrogen peroxide.