Titration Calorimetric Investigation of Interactions of Zinc(II), Nickel(II), and Copper(II) Tetraphenylporphine Complexes with Pyridine in Three Solvents

Titration calorimetry was used in a thermodynamic study on the interactions of pyridine (Py) with zinc(II)-tetraphenylporphine (ZnTPP), nickel(II)-tetraphenyl-porphine (NiTPP), and copper(II)-tetraphenylporphine (CuTPP) in benzene, chloroform, and carbon tetrachloride solutions. The coordinating properties of the metalloporphyrins in relation to pyridine were found to diminish in the order ZnTPP > CuTPP > NiTPP. Solvation effects were estimated from the interactions between metalloporphyrins (MP) and Py. The more negative values of the enthalpy and entropy of reaction of ZnTPP with Py, following the order of solvents CCl₄ > C₆H₆ > CHCl₃, was found to be related to the different types of (MP–solvent) and (Py–solvent) interactions. The NiTPP and CuTPP complexes showed the opposite trend.     

Thermodynamics of aqueous potassium carbonate,piperazine, and carbon dioxide

CO₂ solubility was measured in a wetted-wall column in 0.6–3.6 molal (m) piperazine (PZ) and 2.5–6.2 m potassium ion (K⁺) at 40–110 °C. Piperazine speciation was determined using ¹H NMR for 0.6–3.6 m piperazine (PZ) and 3.6–6.2 m potassium ion (K⁺) at 25–70 °C. The capacity of CO₂ in solution increases as total solute concentration increases and compares favorably with estimates for 7 m (30 wt.%) monoethanolamine (MEA). The presence of potassium in solution increases the concentration of CO₃²⁻/HCO₃⁻ in solution, buffering the solution. The buffer reduces protonation of the free amine, but increases the amount of carbamate species. These competing effects yield a maximum fraction of reactive species at a potassium to piperazine ratio of 2:1.A rigorous thermodynamic model was developed, based on the electrolyte nonrandom two-liquid (ENRTL) theory, to describe the equilibrium behavior of the solvent. Modeling work established that the carbamate stability of piperazine and piperazine carbamate resembles primary amines and gives approximately equal values for the heats of reaction, ΔH_rxn (18.3 and 16.5 kJ/mol). The pK_a of piperazine carbamate is twice that of piperazine, but the ΔH_rxn values are equivalent (∼−45 kJ/mol). Overall, the heat of CO₂ absorption is lowered by the formation of significant quantities of HCO₃⁻ in the mixed solvent and strongly depends on the relative concentrations of K⁺ and PZ, ranging from −40 to −75 kJ/mol.     

Structure,chemical bonding,and 45Sc solid state NMR of Sc2RuSi2

The silicide Sc₂RuSi₂ was synthesized from the elements by arc-melting. The structure was refined on the basis of single crystal X-ray diffractometer data: Zr₂CoSi₂ type, C2/m, a = 1004.7 (2), b = 406.8 (1), c = 946.6 (2) pm, β = 117.95 (2), wR2 = 0.0230, 743 F² values, and 32 variables. The structure consists of a rigid three-dimensional [RuSi₂] network in which the two crystallographically independent scandium atoms fill larger cages of coordination numbers 16 and 15, respectively. The [RuSi₂] network shows short Ru–Si distances (234–247 pm) and two different Si₂ pairs: Si1–Si1 at 247 and Si2–Si2 at 243 pm. Each silicon atom has trigonal prismatic Sc₆ (for Si2) or Sc₄Ru₂ (for Si1) coordination. These building units are condensed via common edges and faces. The various Sc–Sc distances between the prisms range from 327 to 361 pm. From electronic structure investigation within DFT, chemical bonding shows a major role of Ru–Si bonding and the presence of strong electron localization around Si–Si pairs pointing to a polyanionic silicide network [RuSi₂]^δ?. The ⁴⁵Sc MAS-NMR spectra recorded at 11.7 and 9.4 T clearly resolve the two distinct scandium sites. The large electric field gradients present at both scandium sites result in typical line shapes arising from second-order quadrupole perturbation effects.     

DFT study of group 8 catalysts for the hydrophenylation of ethylene: Influence of ancillary ligands and metal identity

Computational methods are used to investigate catalytic hydrophenylation of ethylene using complexes of the type [(Y)M(L)(CH₃)(NCMe)]ⁿ⁺ [Y = Mp, n = 1; Y = Tp, n = 0; M = Ru or Os; L = PMe₃, PF₃, or CO; Mp = tris(pyrazolyl)methane; Tp = hydrido-tris(pyrazolyl)borate]. The conversion of ethylene and benzene to ethylbenzene with [(Y)M(L)(Ph)]ⁿ⁺ as catalyst involves four steps: (1) ethylene coordination, (2) ethylene insertion into the M–Ph bond, (3) benzene coordination, and (4) benzene C–H activation. DFT calculations form the basis to compare stoichiometric benzene C–H activation by [(Y)M(L)(CH₃)(NCMe)]ⁿ⁺ complexes to yield methane and [(Y)M(L)(Ph)(NCMe)]ⁿ⁺. In addition, starting from the 16-electron species [(Y)M(L)(Ph)]ⁿ⁺, potential energy surfaces for the formation of ethylbenzene are calculated to reveal the impact of modifications to the scorpionate ligand (Mp or Tp), co-ligand (L) and metal center (M).     

Molecular interaction of organic dyes in bulk and confined media

Molecular interactions of five thiazine dyes with increasing alkyl substitution have been studied in aqueous and microemulsion media at 303 K within a concentration range of (1.35–7.00) × 10^?4 M. The dimerization constant (K_d) values for the five dyes are ranged between 1.761 and 6.258 × 10³ l mol^?1 in bulk water media, where as in microemulsion media, K_d's are ranged between 1.760 and 4.110 × 10³ l mol^?1. Thionine (with no methyl substitution) and azure A (with two methyl substitution) displayed slightly larger K_d values in microemulsion water pools compared to bulk water while other dyes recorded significant drop in K_d values. The influence of microemulsion media on the molecular interaction of dyes has been explained in terms of electrostatic and hydrophobic factors. The monomer and the dimer spectra are explained in terms of molecular exciton model and the optical absorption parameters of both the species are reported in bulk and confined media.     

High-throughput investigation and characterization of strontium-phosphonatoethanesulfonates

Using the polyfunctional ligand 2-phosphonethanesulfonic acid (H₃L) a high-throughput (HT) study was started for the systematic investigation of the system SrCl₂/H₃L/NaOH/H₂O. The HT experiment comprising 48 individual reactions were performed to systematically investigate the influence of pH of the starting mixture as well as the molar ratio Sr²⁺:H₃L. Two new compounds SrH(O₃P–C₂H₄–SO₃) (1) and Sr₃(O₃P–C₂H₄–SO₃)₂(H₂O)₂ (2) were obtained and structurally characterized by single-crystal X-ray diffraction. The reaction products synthesized under hydrothermal conditions always contain traces of SrSO₄, which are due to the decomposition of small amounts of the ligand. While compound 2 could only be obtained under hydrothermal conditions, the synthesis of 1 could be accomplished under milder reaction conditions and a reaction scale-up could be performed. Compound 1 crystallizes in a monoclinic system with space group C2/c (no. 15), a = 534.73(11) pm, b = 1648.7(3) pm, c = 825.43(17) pm, β = 105.34(3)°, V = 701.8(2)–10⁶ pm³, Z = 4, R1 = 0.0268, and wR₂ = 0.0642 for I > 2σ(I). Compound 2 crystallizes in a triclinic system with space group P-1 (no. 2), a = 700.97(14) pm, b = 1008.5(2) pm, c = 1274.8(3) pm, α = 97.63(3)°, β = 92.03(3)°, γ = 92.03(3)°, V = 843.7(3)–10⁶ pm³, Z = 2, R1 = 0.0360, and wR₂ = 0.0896 for I > 2σ(I). In the structure of compound 1 the phosphorous and sulfur atoms cannot be distinguished due to identical crystallographic positions. Thus, an averaged structure was obtained which is built up by edge-sharing SrO₈ polyhedra that form infinite M–O–M chains. Compound 2 contains corner-, edge-, and face-sharing SrO₈ polyhedra which form inorganic M–O–M layers. These M–O–M chains (1) and layers (2) are connected to a three-dimensional network by the –CH₂CH₂– group of the ligand, respectively. Additional characterization by thermogravimetric analysis and IR-spectroscopy for compound 1 is also presented.     

Kinetic spectrophotometric method for trace determination of thiocyanate based on its inhibitory effect

A kinetic spectrophotometric method for the determination of thiocyanate, based on its inhibitory effect on silver(I) catalyzed substitution of cyanide ion, by phenylhydrazine in hexacyanoferrate(II) is described. Thiocyanate ions form strong complexes with silver(I) catalyst which is used as the basis for its determination at trace level. The progress of reaction was monitored, spectrophotometrically, at 488 nm (λ_max of [Fe(CN)₅PhNHNH₂]^3?, complex) under the optimum reaction conditions at: 2.5 × 10^?3 M [Fe(CN)₆]^4?, 1.0 × 10^?3 M [PhNHNH₂], 8.0 × 10^?7 M [Ag⁺], pH 2.8 ± 0.02, ionic strength (μ) 0.02 M (KNO₃) and temperature 30 ± 0.1 °C. A linear relationship obtained between absorbance (measured at 488 nm at different times) and inhibitor concentration, under specified conditions, has been used for the determination of [thiocyanate] in the range of 0.8–8.0 × 10^?8 M with a detection limit of 2 × 10^?9 M. The standard deviation and percentage error have been calculated and reported with each datum. A most plausible mechanistic scheme has been proposed for the reaction. The values of equilibrium constants for complex formation between catalyst–inhibitor (K_CI), catalyst–substrate (K_s) and Michaelis–Menten constant (K_m) have been computed from the kinetic data. The influence of possible interference by major cations and anions on the determination of thiocyanate and their limits has been investigated.     

Electrochemical characterization on cobalt sulfide for electrochemical supercapacitors

High capacitance at a high charge–discharge current density of 50 mA/cm² for a new type of electrochemical supercapacitor cobalt sulfide (CoS_x) have been studied for the first time. The CoS_x was prepared by a very simply chemical precipitation method. The electrochemical capacitance performance of this compound was investigated by cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge–discharge tests with a three-electrode system. The results show that CoS_x has excellent electrochemical capacitive characteristic with potential range −0.3 ∼ 0.35 V (versus SCE) in 6 M KOH solution. Charge–discharge behaviors have been observed with the highest specific capacitance values of 475 F/g at the current density of 5 mA/cm², even at the high current density of 50 mA/cm², CoS_x also shows the high specific capacitance values of 369 F/g.     

Potential energy surface and rate constant of the inversion substitution reactions CH3X + O2 → CH3O2• + X• (X = SH,NO2)

The temperature dependence of the rate constant of the inversion substitution reactions CH₃X + O₂ → CH₃O₂^? + X^? (X = SH, NO₂), can be expressed as k = 6.8 × 10^–12(T/1000)^1.49exp(–62816 cal mol^–1/RT) cm³ s^–1 (X = SH) and k = 6.8 × 10^–12(T/1000)^1.26 × × exp(–61319 cal mol^–1/RT) cm³ s^–1 (X = NO₂), as found with the use of high-level quantum chemical methods and the transition state theory.     

(Vapour + liquid) equilibria,volumetric and compressibility behaviour of binary and ternary aqueous solutions of 1-hexyl-3-methylimidazolium chloride,methyl potassium malonate,and ethyl potassium malonate

(Vapour + liquid) equilibrium data (water activity, vapour pressure, osmotic coefficient, and activity coefficient) of binary aqueous solutions of 1-hexyl-3-methylimidazolium chloride ([C₆mim][Cl]), methyl potassium malonate, and ethyl potassium malonate and ternary {[C₆mim][Cl] + methyl potassium malonate} and {[C₆mim][Cl] + ethyl potassium malonate} aqueous solutions were obtained through the isopiestic method at T = 298.15 K. These results reveal that the ionic liquid behaves as surfactant-like and aggregates in aqueous solutions at molality about 0.4 mol · kg⁻¹. The constant water activity lines of all the ternary systems investigated show small negative deviations from the linear isopiestic relation (Zdanovskii–Stokes–Robinson rule) derived using the semi-ideal hydration model. The density and speed of sound measurements were carried out on solutions of methyl potassium malonate and ethyl potassium malonate in water and of [C₆mim][Cl] in aqueous solutions of 0.25 mol · kg⁻¹ methyl potassium malonate and ethyl potassium malonate at T = (288.15 to 308.15) K at atmospheric pressure. From the experimental density and speed of sound data, the values of the apparent molar volume, apparent molar isentropic compressibility and excess molar volume were evaluated and from which the infinite dilution apparent molar volume and infinite dilution apparent molar isentropic compressibility were calculated at each temperature. Although, there are no clear differences between the values of the apparent molar volume of [C₆mim][Cl] in pure water and in methyl potassium malonate or ethyl potassium malonate aqueous solutions, however, the results show a positive transfer isentropic compressibility of [C₆mim][Cl] from pure water to the methyl potassium malonate or ethyl potassium malonate aqueous solutions. The results have been interpreted in terms of the solute–water and solute–solute interactions.     

Crystal structures and magnetic properties of complexes of M(NO3)2; M = MnII,CoII, NiII,and CuII,with pyridine ligands carrying an aminoxyl radical

Four complexes of M(NO₃)₂(4NOPy-OMe)₂, (4NOPy-OMe = 4-(N-tert-butyloxylamino)-2-(methoxymethylenyl)pyridine, and M = Mn^II, 1; Co^II, 2; Ni^II, 3; Cu^II, 4), were prepared and fully characterized. X-ray single crystal analysis reveals that four complexes are isostructural. The molecular structures are distorted octahedral in which the methoxy oxygen atoms coordinate to the metal ion by trans-configuration while the pyridyl nitrogen atoms and the nitrate oxygen atoms coordinate by cis-configuration. The magnetic properties of all complexes were investigated by SQUID magneto/susceptometry. Temperature dependence of the molar magnetic susceptibilities in the temperature range of 2–300 K indicated that the magnetic coupling between aminoxyl radicals and metal ion was antiferromagnetic in the complex 1 and were ferromagnetic in the complexes 2–4. The quantitative analysis based on the spin Hamiltonian, H = −2J(S₁S_M + S_MS₂) yielded the best fit as J/k_B = −13.4 ± 0.1 K, g = 1.94 ± 0.002, and θ = −0.78 ± 0.02 K for the complex 1, J/k_B = 48.7 ± 2.1 K, g = 2.07 ± 0.02, and θ = −2.83 ± 0.41 K for the complex 3 (the data in the temperature range 300–50 K were used), and J/k_B = 57.0 ± 1.2 K, g = 2.002 ± 0.004, and θ = −9.8 ± 0.1 K for the complex 4.     

Excess molar enthalpies of binary systems containing 2-octanone,hexanoic acid,or octanoic acid at T = 298.15 K

An isothermal titration calorimeter was used to measure the excess molar enthalpies (H^E) of six binary systems at T = 298.15 K under atmospheric pressure. The systems investigated include (1-hexanol + 2-octanone), (1-octanol + 2-octanone), (1-hexanol + octanoic acid), (1-hexanol + hexanoic acid), {N,N-dimethylformamide (DMF) + hexanoic acid}, and {dimethyl sulfoxide (DMSO) + hexanoic acid}. The values of excess molar enthalpies are all positive except for the DMSO- and the DMF-containing systems. In the 1-hexanol with hexanoic acid or octanoic acid systems, the maximum values of H^E are located around the mole fraction of 0.4 of 1-hexanol, but the H^E vary nearly symmetrically with composition for other four systems. In addition to the modified Redlich–Kister and the NRTL models, the Peng–Robinson (PR) and the Patel–Teja (PT) equations of state were used to correlate the excess molar enthalpy data. The modified Redlich–Kister equation correlates the H^E data to within about experimental uncertainty. The calculated results from the PR and the PT are comparable. It is indicated that the overall average absolute relative deviations (AARD) of the excess enthalpy calculations are reduced from 18.8% and 18.8% to 6.6% and 7.0%, respectively, as the second adjustable binary interaction parameter, k_bij, is added in the PR and the PT equations. Also, the NRTL model correlates the H^E data to an overall AARD of 10.8% by using two adjustable model parameters.     

Buffer standards for the physiological pH of N-[2-hydroxy-1,1-bis(hydroxymethyl)ethyl]glycine (TRICINE) from T = (278.15 to 328.15) K

The pH values of two buffer solutions without NaCl and seven buffer solutions with added NaCl, having ionic strengths (I = 0.16 mol · kg⁻¹) similar to those of physiological fluids, have been evaluated at 12 temperatures from T = (278.15 to 328.15) K by way of the extended form of the Debye–Hückel equation of the Bates–Guggenheim convention. The residual liquid junction potentials (δE_j) between the buffer solutions of TRICINE and saturated KCl solution of the calomel electrode at T = (298.15 and 310.15) K have been estimated by measurement with a flowing junction cell. For the buffer solutions with the molality of TRICINE(m₁) = 0.06 mol · kg⁻¹, NaTRICINE(m₂) = 0.02 mol · kg⁻¹, and NaCl(m₃) = 0.14 mol · kg⁻¹, the pH values at T = 310.15 K obtained from the extended Debye–Hückel equation and the inclusion of the liquid junction correction are 7.342 and 7.342, respectively. These are in excellent agreement. The zwitterionic buffer TRICINE is recommended as a secondary pH standard in the region for clinical application.     

Effect of sodium acetate on the rheological behaviour of some mono-, di-, and tri-saccharides in aqueous solutions over the temperature range (288.15 to 318.15) K

The Jones–Dole viscosity B-coefficients for various mono-, di-, and tri-saccharides in water and in (0.5, 1.0, 2.0, and 3.0) mol · kg^?1 aqueous solutions of sodium acetate have been determined at different temperatures, T = (288.15, 298.15, 308.15, and 318.15) K from viscosity data. Densities used to determine viscosities have been reported earlier. The viscosity B-coefficients of transfer, Δ_tB, has been estimated for the transfer of saccharides from water to aqueous sodium acetate solutions. The positive Δ_tB values were obtained in all cases and their magnitudes increase with the increase in concentration of sodium acetate. Pair, η_AB and higher order, η_ABB viscometric interaction coefficients (using McMillan–Mayer theory), and dB/dT coefficients have also been determined. Activation Gibbs free energies and other related thermodynamic activation parameters of viscous flow have been determined using Feakin’s transition-state theory. These parameters have been discussed in terms of solute–solute and solute–solvent interactions occurring in these solutions.     

A ruthenium(II) complex with the propionate ion: Synthesis,characterization and cytotoxic activity

The complex [Ru(η²-O₂CCH₂CH₃)(dppe)₂]PF₆ (dppe = 1,2-bis(diphenylphosphino)ethane) was prepared and characterized by elemental analysis, spectroscopic techniques, X-ray crystallography, HRESIMS and HRESIMS/MS. The characterization data are consistent with a cis arrangement for the dppe ligands and a bidentate coordination of the propionate ligand through carboxylate oxygens. Cytotoxicity assays were carried out on human and murine cancer and normal cell lines. In general, the [Ru(η²-O₂CCH₂CH₃)(dppe)₂]PF₆ complex was more cytotoxic than both its precursor cis–[RuCl₂(dppe)₂] and the reference metallodrug cisplatin. The best results against the HepG2 human tumour cell line and S180 murine tumour cell line were found with IC₅₀ values of 6.5 ± 0.2 and 0.18 ± 0.03 μM, respectively.     

The solubility measurements of sodium dicarboxylate salts; sodium oxalate,malonate, succinate,glutarate, and adipate in water from T = (279.15 to 358.15) K

The solubility measurements of sodium dicarboxylate salts; sodium oxalate, malonate, succinate, glutarate, and adipate in water at temperatures from (278.15 to 358.15 K) were determined. The molar enthalpies of solution at T = 298.15 K were derived: Δ_solH_m (m = 2.11 mol · kg^?1) = 13.86 kJ · mol^?1 for sodium oxalate; Δ_solH_m (m = 3.99 mol · kg^?1) = 14.83 kJ · mol^?1 for sodium malonate; Δ_solH_m (m = 2.45 mol · kg^?1) = 14.83 kJ · mol^?1 for sodium succinate; Δ_solH_m (m = 4.53 mol · kg^?1) = 16.55 kJ · mol^?1 for sodium glutarate, and Δ_solH_m (m = 3.52 mol · kg^?1) = 15.70 kJ · mol^?1 for sodium adipate. The solubility value exhibits a prominent odd–even effect with respect to terms with odd number of sodium dicarboxylate carbon numbers showing much higher solubility. This odd–even effect may have implications for the relative abundance of these compounds in industrial applications and also in the atmospheric aerosols.     

Excited state structural dynamics and Herzberg–Teller coupling of tetraphenylporphine explored via resonance Raman spectroscopy and density functional theory calculation

Resonance Raman spectra of free-base tetraphenylporphine (TPP) were obtained with 397.9, 416, and 435.7 nm excitation wavelengths and density functional calculations were done to elucidate the electronic transitions and the resonance Raman spectra (RRs) of TPP. The RRs indicate that the Franck–Condon region photodynamics for S₀ → S₄ electronic state is predominantly along the C_m–ph stretch while that for S₀ → S₃ electronic state is predominantly along the porphin ring C_βC_β stretch. Non-totally symmetric vibrational modes were regularly presented in resonance Raman spectra: the shorter the excitation wavelengths were, the stronger intensity the modes had, which can be interpreted in terms of electric dipole transition moments caused by Franck–Condon and Herzberg–Teller coupling.Four non-total symmetry vibrational mode υ_52, υ₆₄, υ₉₇ and υ₁₃₀ in A₂ irreducible representative of TPP were observed in 397.9, 416 and 435.7 nm resonance Raman spectrum. With the shorter wavelength laser excitations at 416 or 397.9 nm, the A₂ vibrational modes show more enhanced Raman intensity by comparison with those in the TPP spectrum excited at 435.7 nm.     

Synthesis and asymmetric catalytic application of chiral imidazolium–phosphines derived from (1R,2R)-trans-diaminocyclohexane

Reaction between a chiral imidazole–amine precursor derived from (1R,2R)-trans-diaminocyclohexane and P¹Cl (where P¹ = PPh₂, P(1,3,5-Me₃C₆H₃)₂, P(2,2′-O,O′-(1,1′-biphenyl), P((R)-(2,2′-O,O′-(1,1′-binaphthyl))) and P((S)-(2,2′-O,O′-(1,1′-binaphthyl)))) followed by RX (where R = ⁿPr, ⁱPr, CHPh₂, X = Br; R = ⁱPr, X = I), respectively, gives a selection of chiral imidazolium–phosphine compounds. Deprotonation of the imidazolium salt gives the corresponding NHC–P ligands that can be used in metal-mediated asymmetric catalytic applications. Catalytic reactions show that NHC–P ligands give a significantly greater rate of reaction for a palladium catalysed allylic substitution reaction in comparison to analogous di-NHC or NHC–imine ligands and that NHC–P hybrids are also effective for iridium catalysed transfer hydrogenation.     

ATP- and redox-induced conformational changes in the activator of the radical enzyme 2-hydroxyisocaproyl-CoA dehydratase

A [4Fe–4S]¹⁺ cluster-containing protein activates 2-hydroxyisocaproyl-CoA dehydratase by an ATP-driven electron transfer. The activator has been proposed to change its conformation by MgATP similarly to nitrogenase Fe-protein. Iron chelation by bathophenanthroline removed the reduced [4Fe–4S]¹⁺ cluster from the activator in an ATP-dependent manner (rate, v = 0.128 ± 0.004 min⁻¹; K_m = 21 ± 1 μM); with ADP no chelation was observed (v < 0.001 min⁻¹). Chelation of the oxidised [4Fe–4S]²⁺ cluster occurred faster with ADP (v = 0.34 ± 0.05 min⁻¹) than with ATP (v = 0.132 ± 0.005 min⁻¹). The data indicate that reduction of the activator and binding of ATP induce conformational changes necessary to transfer the electron to the dehydratase. Interaction of both proteins promotes ATP hydrolysis (K_m = 0.5 ± 0.1 μM).     

Synthesis,characterizations of silica-coated gold nanorods and its applications in electroanalysis of hemoglobin

Gold nanorods (GNRs) were synthesized by a seed–mediated growth approach followed by TEOS polymerization leading to the formation of silica layer surrounding the gold nanorod core. TEM images showed that the silica-coated gold nanorods (GNRs@SiO₂) were dispersed with an average aspect ratio of 3.1 for the GNRs cores and a uniform thickness of the silica shell. The core/shell nanocomposites were further used as efficient supports for the immobilization of hemoglobin (Hb) to fabricate a novel biosensor. The immobilized Hb showed an enhanced electron transfer for its heme Fe(III) to Fe(II) redox couple. This biosensor showed an excellent bioelectrocatalytic activity towards H₂O₂ with a linear range from 8.0 × 10⁻⁷ to 6.1 × 10⁻⁵ M, and the detection limit was 6.0 × 10⁻⁸ M at 3σ. The apparent Michaelis–Menten constant of the immobilized hemoglobin was calculated to be 0.13 mM.