Direct electrochemistry of hemoglobin based on chitosan–ionic liquid–ferrocene/graphene composite film

This paper described an ingenious approach for the fabrication of a promising biosensor, hemoglobin (Hb)/chitosan (Chit)–ionic liquid (IL)–ferrocene (Fc)/graphene (Gr)/glassy carbon electrode (GCE), that exploited the synergistic beneficial characteristics of Fc, Gr and IL for Hb. The proposed biosensor showed a strong electrocatalytic activity toward the reduction of H₂O₂, which could be attributed to the favored orientation of Hb in the well-confined surface as well as the high electrical conductivity of the resulting Chit–IL–Fc/Gr inorganic hybrid composite. The developed biosensor exhibited a fast amperometric response (2 s), a good linear response toward H₂O₂ over a wide range of concentration from 50 μM to 1200 μM, and a low detection limit of 3.8 μM. The apparent Michaelis–Menten constant (K_m) of Hb on the composite medium was 0.16 mM, showing high bioelectrocatalytic activity of immobilized protein toward H₂O₂ reduction. High sensitivity and stability, technically simple and possibility of preparation at short period of time are of great advantages of the developed biosensors.     

The BK channel accessory β1 subunit determines alcohol-induced cerebrovascular constriction

Ethanol-induced inhibition of myocyte large conductance, calcium- and voltage-gated potassium (BK) current causes cerebrovascular constriction, yet the molecular targets mediating EtOH action remain unknown. Using BK channel-forming (cbv1) subunits from cerebral artery myocytes, we demonstrate that EtOH potentiates and inhibits current at lower and higher than ∼15 μM, respectively. By increasing cbv1’s apparent -sensitivity, accessory BK β₁ subunits shift the activation-to-inhibition crossover of EtOH action to <3 μM , with consequent inhibition of current under conditions found during myocyte contraction. Knocking-down KCNMB1 suppresses EtOH-reduction of arterial myocyte BK current and vessel diameter. Therefore, BK β₁ is the molecular effector of alcohol-induced BK current inhibition and cerebrovascular constriction.     

An amperometric biosensor fabricated from electro-co-deposition of sodium alginate and horseradish peroxidase

A convenient and effective strategy for fabrication of hydrogen peroxide biosensor based on sodium alginate (SA) and polyvinyl butyral (PVB) as matrices was reported in this paper. The horseradish peroxidase (HRP) and SA were electro-co-deposited onto the surface of gold electrode, and the HRP–SA/Au electrode was further coated with PVB. The interaction between HRP and SA was characterized by UV–vis absorption spectroscopy, and the fabricating process of biosensor was characterized by electrochemical impedance spectroscopy (EIS). The electrochemical characteristics of the biosensor were studied by cyclic voltammetry and chronoamperometry. Experimental conditions were investigated which influence the performance of the biosensor, such as pH, and applied potential. The biosensor showed a linear response to H₂O₂ over a concentration range from 7.0 × 10⁻⁶ to 4.1 × 10⁻³ M with a detection limit of 1.8 × 10⁻⁶ M based on a signal-to-noise ratio of 3 under optimum conditions. The value of HRP in the composite was evaluated to be 1.38 mM. The biosensor obtained from this study possesses high sensitivity, good reproducibility, and long-term stability.     

Synthesis and characterization of a family of binuclear non-heme iron monooxygenase model compounds: Evidence for a “phenolate/amide carbonyl (PAC) shift” upon oxidation

A series of binuclear iron compounds has been synthesized using diamide, bis-phenolate ligands in which the carbon-linker between the amide nitrogen atoms has been varied. Two diferrous compounds in the series, along with their two-electron oxidized, di-μ-methoxy-bridged counterparts, have been crystallographically characterized, as have the di-μ-methoxy compounds (H₂Hbab = 1,2-bis(2-hydroxybenzamido) benzene, H₂Hbach = trans-1,2-bis(2-hydroxybenzamido) cyclohexane, H₂Hbame = 1,2-bis(2-hydroxybenzamido) ethane, H₂Hbap = 1,3-bis(2-hydroxybenzamido) propane, H₂Hbabn = 1,4-bis(2-hydroxybenzamido) butane, H₂Hbapen = 1,5-bis(2-hydroxybenzamido) pentane, N-MeIM = N-methylimidazole and OMe = methoxide). are structurally very similar to previously reported diferrous compounds of this family of ligands that have been shown to be active as oxygen atom transfer catalysts. Flexibility in the carbon-linker allows some variability in the orientation of the phenolate arms of the ligands in the diferric di-μ-methoxy compounds, but the Fe₂O₂ core remains largely unchanged across the series. Two-electron oxidation of the ferrous compounds in methanol shows a substantial ligand rearrangement that is consistent with other spectroscopic, electrochemical and kinetic investigations. The loss of both phenolate bridges upon oxidation is reminiscent of the “carboxylate shift” observed in binuclear non-heme enzymes and could provide insight into the driving force behind this family of compounds’ function as a catalyst.     

Anation kinetics of pentacyanoaquachromate(III) by thiocyanate and azide

The kinetics of the reaction of Cr(CN)₅(H₂O)²⁻ with NCS⁻ and were studied at pH 5.0 and at pH 6.3-7.0, respectively, as a function of the temperature between 25.0 and 55.0 °C, and at various ionic strengths. Anation occurs in competition with aquation of CN⁻, with rate constants that exhibit less-than-first-order dependence on the concentration of the entering anions. The results are interpreted in terms of ligand interchange in a context of association of the two reacting anions mediated by the Na⁺ or Ca²⁺ counterions. The degree of aggregation depends mainly on the total cationic charge rather than on the ionic strength, and is ca. 2-fold larger for than for NCS⁻. Within the associated species, is a better entering ligand than NCS⁻ by a factor of 4.5. The Cr(CN)₅(NCS)³⁻ and Cr(CN)₅(N₃)³⁻ complexes were also synthesized, and the rates of aquation of NCS⁻ and were measured at pH 5.0 and between 55.0 and 80.0 °C, over the same range of ionic strengths. The ionic strength enhances the anation rates but has little effect on the aquation rates. The average activation enthalpies of the interchange step are 80 ± 3 and 76 ± 3 kJ mol⁻¹ for entry of NCS⁻ and , respectively. Those of the corresponding aquation reactions are 94 ± 4 and 107 ± 4 kJ mol⁻¹. Within error limits, all ΔH^‡ values are independent of the ionic strength. The results are consistent with an I_d mechanism for substitution in Cr(CN)₅X^z− complexes.     

Large catalase based bioelectrode for biosensor application

A large catalase (CAT) (Mr ~ 90 kDa), immobilized on multiwalled carbon nanotubes—Nafion^® (MWCNT-NF) matrix and encapsulated with polyethylenimine (PEI) on glassy carbon electrode (GCE), showed a pair of nearly reversible cyclic voltammetric peaks for Fe^(III)/Fe^(II) couple with formal potential of about −0.45 V (vs. Ag/AgCl electrode at pH 7.5). PEI significantly reduced the charge transfer resistance and stabilized the bioelectrode through electrostatic interaction. The electron transfer rate constant and surface coverage of the immobilized CAT were 1.05 ± 0.2 s⁻¹ and 2.1 × 10⁻¹⁰ mol cm⁻², respectively. Studies on electrocatalytic activity and kinetics of GCE/MWCNT-NF/CAT/PEI for hydrogen peroxide (H₂O₂) showed the apparent Michaelis-Menten constant of 3 mM, linear response in the range of 10 μM to 5 mM, response time of ~ 2 s for steady state current, and detection limit of ~ 1 μM. A high operational and storage stability was also demonstrated for the bioelectrode. Hence, the direct electrochemistry of the large catalase and its potential biosensor application have been established through this investigation.     

Determination of glycated hemoglobin with special emphasis on biosensing methods

The glycated hemoglobin (HbA1c) level in blood is a measure of long-term glycemic status in patients with diabetes mellitus. Current clinical methods for determination of the HbA1c level include electrophoresis/electroendosmosis, ion exchange chromatography, high-performance liquid chromatography, boronate affinity chromatography, immunoassay, and liquid chromatography–tandem mass spectroscopy in addition to fluorometry and colorimetry. These methods have certain drawbacks such as being complex, time-consuming, and requiring expensive apparatus and trained persons to operate. These drawbacks were overcome by biosensing methods. We review these biosensors, which are based on (i) measurement of electrons, that is, current generated from splitting of hydrogen peroxide released during oxidation of fructosyl valine by immobilized fructosyl amino acid oxidase, which is directly proportional to HbA1c concentration, and (ii) direct measurement of HbA1c by some specific reaction. HbA1c biosensors work optimally within 4 to 1800 s, between pH 7.0 and 9.0 and between 25 and 45 °C, and in the range of 1 to 10,000 μM, with a detection limit between 20 and 500 μM and sensitivity between 4.6 nA and 21.5 μA mM⁻¹ cm⁻² and stable over a period of 5 to 90 days. We suggest the ways to modify existing HbA1c biosensors, leading to simple, reliable, and economical sensors ideally suited for point-of-care treatment.     

A criterion for proper cosolvents used for ionic liquids: The Lewis acidic and basic dual nature of propylene carbonate

Probe of the Lewis acidic property of propylene carbonate (PC) has been initiated by temperature-dependent ¹⁹F chemical shifts recorded for 1-butyl-3-methylimidazolium hexafluorophosphate/PC (BMIPF₆/PC) mixtures. Investigation of hyperconjugative interactions by natural bond orbital method reveals the trend of electron-accepting capabilities from anion, PC > dimethyl sulfoxide (DMSO) > N,N-dimethyl formamide (DMF) > acetonitrile (AN). Comparison of solvent-induced ionic association of BMIPF₆ in the four basic aprotic organic solvents, made by monitoring concentration- and temperature-dependent-ratios of solvent diffusion coefficients to BMI⁺-containing components, D_sol/D_BMI, shows that the extent of original ionic association can be reduced by solvent dilution in the same decreasing order, PC ∼ DMSO > DMF > AN. In DMF and AN, two basic solvents having similar dielectric constants, the greater Lewis acid of DMF accounts for its better ability to dissociate aggregates of BMIPF₆. By replacing ethanol with 2,2,2-trifluoroethanol (TFE), the poor miscibility of BMIPF₆ with ethanol can be greatly enhanced due to the CF₃ group, capable of adapting electron density from anions via hyperconjugative interactions. In BMIPF₆/TFE mixtures, values of measured on ¹⁹F resonances show larger aggregates than measured on ¹H resonances, indicating charged clusters prefer anionic to cationic states. This observation can be explained by varying ionic states concerning with unbalanced charged aggregates between positive and negative ones.     

Heterodimetallic Pd-based carboxylate-bridged complexes: Synthesis and structure of single-crystalline Pd-M (M = Mn, Co, Ni, Cu, Zn, Nd, Eu, Ce) acetates

A series of crystalline Pd^II-based heterodimetallic acetate-bridged complexes containing the transition (Mn^II, Co^II, Ni^II, Cu^II), post-transition (Zn^II) and rare-earth (Ce^IV, Nd^III, Eu^III) metals were synthesized starting from Pd₃(OOCMe)₆ and the complementary metal(II, III) acetates. The crystal and molecular structures of the binuclear Pd^IIM^II(μ-OOCMe)₄L (M = Mn, Co, Ni, Zn; L = H₂O, MeCN), trinuclear and tetranuclear (M = Nd, Eu) and complexes were established by X-ray diffraction.     

Interaction of gold(I) with thiosulfate-sulfite mixed ligand systems

The system was studied at 25 °C and at I = 0.1 M NaClO₄ using hydrodynamic voltammetry, gold potentiometry, UV-Vis spectrophotometry and Raman spectroscopy. The presence of two mixed-ligand species, Au(S₂O₃)(SO₃)³⁻ and , was detected from the Raman experiments and supported by the gold potentiometric experiments. The stepwise formation constant, log K_11r, for the reaction was found to be 1.1 (r = 1) and 4.8 (r = 2) from the hydrodynamic voltammetric experiments.     

Synthesis of bimetallic fulvalene and bis(cyclopentadienyl)methane derivatives of niobium and tantalum tetracarbonyl

Ring coupled bimetallic derivatives (μ-η^5:5-C₅H₄C₅H₄)[Nb(CO)₄]₂ and [μ-CH₂(η⁵-C₅H₄)₂][M(CO)₄]₂, where M = Nb and Ta have been prepared. The molecular structures of the latter two compounds have been determined: , triclinic, , a = 8.028(2) Å, b = 11.414(1) Å, c = 12.711(2) Å, α = 75.020(8)°, β = 80.34(2)°, γ = 79.46(2)°, V = 1097.3(4) ų, Z = 2, R(F) = 2.79%; [μ-CH₂(η⁵-C₅H₄)₂][Ta(CO)₄]₂, triclinic, , a = 7.815(3) Å, b = 10.275(4) Å, c = 13.135(4) Å, α = 104.25(3)°, β = 100.26(4)°, γ = 96.86(3)°, V = 991.2(6) ų, Z = 2, R(F) = 3.00%.     

Photocatalysis of chloroform degradation by μ-dichlorotetrachlorodipalladate(II)

Unlike other chlorometallate complexes that catalyze the photodecomposition of haloalkanes through photodissociation of a chlorine atom, both and catalyze chloroform decomposition through a process that appears to involve C-H bond breakage from an excited state association complex with chloroform. This would account for the greatly retarded rate of decomposition in CDCl₃ and for the generation of CCl₄ as a side product. In chloroform, and are in slow equilibrium with each other. The rate for the conversion of - in chloroform at 23 °C obeys the expression (0.03 M⁻¹ s⁻¹) [][Cl⁻]. The equilibrium constant, K = [][Cl⁻]²/[]², was estimated to be 3 × 10⁻³ M in CHCl₃.     

Ruthenium(II) complexes possessing the η-p-cymene ligand

Complexes possessing a soft donor η⁶-arene and hard donor acetylacetonate ligand, [(η⁶-p-cymene)Ru(κ²-O,O-acac-μ-CH)]₂[OTf]₂ (1) (OTf = trifluoromethanesulfonate; acac = acetylacetonate) and {Ar′ = 3,5-(CF₃)-C₆H₃}, were prepared and fully characterized. The lability of the μ-CH linkage for complex 1 and the THF ligand of 2 allow access to the unsaturated cation [(η⁶-p-cymene)Ru(κ²-O,O-acac)]⁺. The reaction of with KTp {Tp = hydridotris(pyrazolyl)borate} produces . The azide complex forms upon reaction of with N₃Ar (Ar = p-tolyl), and reaction of with CHCl₃ at 100 °C yields the chloride-bridged binuclear complex . The details of solid-state structures of [(η⁶-p-cymene)Ru(κ²-O,O-acac-μ-CH)]₂[OTf]₂ (1), and are disclosed.     

Kinetic studies of the reduction of hexaaquacobalt(III) perchlorate by a cobaloxime, [Co(dmgBF2)2(H2O)2]

The reaction of with Co(dmgBF₂)₂(H₂O)₂ in 1.0 M HClO₄/LiClO₄ was found to be first-order in both reactants and the [H⁺] dependence of the second-order rate constant is given by k_2obs = b/[H⁺], b at 25 °C is 9.23 ± 0.14 × 10² s⁻¹. The [H⁺] dependence at lower temperatures shows some saturation effect that allowed an estimate of the hydrolysis constant for as K_a = 9.5 × 10⁻³ M at 10 and 15 °C. Marcus theory and the known self-exchange rate constant for Co(OH₂)₅OH^2+/+ were used to estimate an electron self-exchange rate constant of k₂₂ = 1.7 × 10⁻⁴ M⁻¹ s⁻¹ for .     

A new Cu(4,5-diazafluoren-9-one)-capped Keggin derivative: Hydrothermal synthesis and crystal characterization

A new α-Keggin POM derivative (1) (DF = 4,5-diazafluoren-9-one) has been prepared under hydrothermal conditions and characterized by single-crystal X-ray diffraction, elemental analysis, IR, XPS spectra, thermogravimetric analysis and cyclic voltammetry. In compound 1, the polyoxoanion cluster is decorated by a single capping {Cu(DF)}²⁺ subunit via four bridging oxygen atoms on a {Mo₄O₄} pit. The isolated copper dimer unit acts as counter cation, in which the organic ligand DF exhibits a rare coordination mode. Furthermore, the capped Keggin polyoxoanions are fused together via the copper dimers through the weak Cu ? O interactions to form chains. Hybrid 1 was used as a solid bulk modifier to fabricate a carbon paste electrode (1-CPE) by direct mixing. The electrochemical and electrocatalytic behaviors of the 1-CPE have been studied in detail.     

Kinetics and mechanism of the aquation of the trinuclear cation, [μ3-oxo-triaqua-hexakis(acetato)tris(iron(III))]in perchloric acid media

The aquation of the title complex cation in aqueous perchloric acid proceeded via two steps, both postulated to be the proton attack on the oxygen atom which binds the acetate ligand to the metal centre, followed by Fe-O bond cleavage. This was followed by rapid decomposition to produce aqueous iron(III) and acetate ions. The first-order rate constants for the first and second steps at 25 °C are: k₁ = (4.16 ± 0.58) × 10⁻² s⁻¹ and k₂ = (2.09 ± 0.42) × 10⁻³ s⁻¹, respectively, and their corresponding activation parameters are . The spontaneous hydrolysis rate constants for the first and second steps were also determined at 25 °C and ionic strength of 1 mol dm⁻³ and they are k₀ = (3.10 ± 0.82) × 10⁻³ s⁻¹ and , respectively. The corresponding activation parameters are .     

Polynuclear complex formation of trivalent lanthanides by 5-sulfosalicylate in an aqueous system—potentiometric, H NMR, and TRLIFS studies

The complex formation between several trivalent lanthanides (Ln) and 5-sulfosalicylate, (SSA)³⁻, was investigated by potentiometry, ¹H NMR, and time resolved laser-induced fluorescence spectroscopy (TRLIFS). The potentiometric data were used to deduce the stoichiometry and equilibrium constants for the reactions pLn³⁺ + rL ? Ln_pH_−qL_r + qH⁺ at 298 K in an ionic medium with a constant concentration of Na⁺ equal to 1.00 M. Note that “L” denotes the SSA ligand where all protons are dissociated. Two mononuclear chelating complexes, LnL(aq) and , were identified. Their stability constants obtained by least-squares refinement of the potentiometric data agree well with previously published information. In addition, two additional dinuclear complexes, and , which have very different ¹H NMR and fluorescence characteristics, were identified by least-squares refinement in the −log[H⁺] range of 6.0-10.0. ¹H NMR spectra from the ligand in the complex showed separate peaks having two different rates of exchange with free ligand in the bulk solution besides a signal from the free and carboxylate-coordinated ligands. This indicates that the dinuclear complex, , consists of two different types of chelating ligands: μ-{OR}-type chelating ligands between metals to form the {Ln₂L₂}-type core structure and the bidentate ligands outside the {Ln₂L₂}-type core. This core structure is different from the An(IV)-SSA case (An(IV): tetravalent actinide), in which hydroxides play the role of forming the {An₂(OH)₂}-type core structure. TRLIFS measurement gave further information about the dynamics and molecular structures of the complexes.