Search

In this work, we present an electrochemical study of the boron cage monomercaptoundecahydro-closo-dodecaborate [B12H11SH]2− in solution and in a self-assembled monolayer over a polycrystalline gold electrode. Cyclic voltammetry of the anion [B12H11SH]2− in solution showed a shift in the peak potentials related to the redox processes of gold hydroxides, which evidences the interaction between the boron cage and the gold surface. For an Au electrode modified with the anion [B12H11SH]2−, cyclic voltammetry response of the probe Fe(CN)63−/Fe(CN)64− showed a ΔEp value typical for a surface modification. Electrochemical impedance spectroscopy presented Rtc and Cdl values related to the formation of a self-assembled monolayer (SAM). A comparison of electrochemical responses of a modified electrode with thioglycolic acid (TGA) reveals that the boron cage [B12H11SH]2− diminishes the actives sites over the Au surface due to the steric effects. Differential capacitance measurements for bare gold electrode and those modified with [B12H11SH]2− and (TGA), indicate that bulky thiols enhance charge accumulation at the electrode–solution interface. In addition to electrochemical experiments, DFT calculations and surface plasmon resonance measurements (SPR) were carried out to obtain quantum chemical descriptors and to evaluate the molecular length and the dielectric constant of the Boron cage. From SPR experiments, the adsorption kinetics of [B12H11SH]2− were studied. The data fit for a Langmuir kinetic equation, typical for the formation of a monolayer. [ABSTRACT FROM AUTHOR]

In this work the electrochemical behavior, of three Fe(II) polypyridinc complexes [Fe(bipy) 3 ] 2+ , [Fe(phen) 3 ] 2+ , and [Fe(terpy) 2 ] 2+ in acetonitrile solution was explored, to understand the mechanism of the molecular catalysis of carbon dioxide reduction, for metal complexes with no available coordination sites and inert to substitution. Cyclic voltammetry experiments using as working electrodes glassy carbon and platinum in the presence and in the absence of CO 2 were carried out. All the compounds present the oxidation Fe(II)L n + e − ⇄ Fe(III)L n . For the tris chelate systems [Fe(phen) 3 ] 2+ and [Fe(bipy) 3 ] 2+ , three reduction processes over the coordinated ligands are observed. On the other hand, the bis chelate complex [Fe(terpy) 2 ] 2+ shows two reductions processes center in ligands. For experiments with a glassy carbon electrode, a third reduction process that yield the species [Fe 0 (terpy − ) 2 ] is detected. DFT calculations support the idea for the electrochemical reduction in the coordinated ligands. For compound [Fe(bipy) 3 ] 2+ , the catalytic rate constant (k) and the turnover frequency (TOF) relationships were calculated. Spectroelectrochemical experiments in the absence and in the presence of CO 2 were also carried out, demonstrating the regeneration of catalysts. An outer sphere homogenous electron transfer mechanism between the catalyst and CO 2 is proposed, where high negative redox potential values favored the molecular catalysis. [ABSTRACT FROM AUTHOR]

• Full characterization of NiII( tpa ) complexes gives information about its electronic structure which corelates with electrochemical behavior. • NiII( tpa ) complexes presented tunable redox potential for the NiII/NiI reduction. • NiII complex with more negative redox potential presented the high catalytic activity for CO 2 reduction. • Theoretical approach was useful for the analysis and description of electrochemical mechanisms. In this paper, we report the synthesis, characterization, as well as electrochemical, spectroelectrochemical, and density functional theory (DFT) calculations of a series of novel NiII complexes with a flexible tetradentate ligand, tris(2-pyridylmethyl)amine) ( tpa ). The complexes [NiII( tpa )(H 2 O)(MeCN)](BF 4) 2 , [NiII( tpa )(NO 3) 2 ], and [NiII( tpa )Cl 2 ] were studied for their ability to electrochemically reduce CO 2. These complexes were compared with the tris-chelate complex [Ni(bpy) 3 ](BF 4) 2 to understand the role of flexible tetradentate ligands containing a pyridinic ring in the electrochemical reduction of CO 2. Spectroelectrochemical experiments and theoretical studies were performed to rationalize the electrochemical reductions occurring and to predict the redox potential and pathway of CO 2 reduction. The electrochemical behavior of Ni(II) complexes with the ligand tris(2-pyridylmethyl)amine) was studied, in order to explore its ability to reduce electrochemically CO 2. Theoretical studies allowed to rationalize where the electrochemical reductions occur and predict redox potential and the pathway of CO 2 reduction. [Display omitted] [ABSTRACT FROM AUTHOR]

In this work, we report the electrochemical response of a family of Co(II) complexes, [CoII(L)3]2+ and [CoII(L')2]2+ (L = 2,2'-bipyridine, 1,10-phenanthroline, 3,4,7,8-tetramethyl-1,10-phenanthroline, 5,6-dimethyl-1,10-phenanthroline, and 4,7-diphenyl-1,10-phenanthroline; L' = terpyridine and 4-chloro-terpyridine), in the presence and absence of CO2 in order to understand the role of the redox potential and molecular structure on the molecular catalysis of CO2 reduction. The tris chelate complexes exhibited three electron transfer processes [CoII(L)3]2+ ⇄ [CoIII(L)3]3+ + 1e−, [CoΙΙ(L)3]2++1e− ⇄ [CoΙ(L)3]+, and [CoΙ(L)3]+ + 2e- ⇄ [CoΙ(L)(L−)2]−. In the case of complexes with 1,10-phen and 2,2-bipy, the third redox process showed a coupled chemical reaction [CoΙ(L)(L−)2]− → [CoΙ(L−)2]− + L. For bis chelate complexes, three electron transfer processes associated with the redox couples [CoΙΙ(L)2]/[CoIII(L)2]3+, [CoΙΙ(L)2]2+/[CoΙ(L)2]+, and [CoΙ(L)2]+/[CoΙ(L)(L−)] were registered, including a coupled chemical reaction only for the complex containing the ligand 4-chloro-terpyridine. Foot to the wave analysis (FOWA) obtained from cyclic voltammetry experiments allowed us to calculate the catalytic rate constant (k) for the molecular catalysis of CO2 reduction. The complex [Co(3,4,7,8-tm-1,10-phen)3]2+ presented a high k value; moreover, the complex [Co(4-Cl-terpy)3]2+ did not show catalytic activity, indicating that the more negative redox potential and the absence of the coupled chemical reaction increased the molecular catalysis. Density functional theory (DFT) calculations for compounds and CO2 were obtained to rationalize the effect of electronic structure on the catalytic rate constant (k) of CO2 reduction. [ABSTRACT FROM AUTHOR]

• Homogeneous electron transfer rate constant values (ks) between GOD and metal complexes were calculated through (FOWA) from cyclic voltammetry data. • CD spectroscopy reveals no structural changes GOD in the presence of the redox mediators. • Molecular docking studies between GOD and Co(II) complexes and a series of ferrocene derivatives allow to propose a electron transfer model. • Quantitative Structure-Activity Relationship (QSAR) analyses were used to understand electron transfer. In this work, we study the redox mediation of glucose oxidase (GOD) with a series of Co(II) polypyridine complexes [CoIIL 3 ]2+ (L = 5-Nitro-1,10-phenanthroline, 5-Chloro-1,10-phenanthroline, 5-Bromo-1,10-phenanthroline, 1,10-phenanthroline and 5-methyl-1,10-phenanthroline) and Ferrocenecarboxylic acid (Fc-COOH), in order to understand the role of molecular interaction GOD-mediator on homogeneous electron transfer rate constant ( ks ), exploring Marcus cross-relation and tunneling effect model, not reported before. The ks values were calculated through a foot of the wave analysis (FOWA) from cyclic voltammetry data. Circular Dichroism spectroscopy reveals no structural changes in the enzyme in the presence of the redox mediators. The interaction energy between GOD and Co(II) complexes and a series of ferrocene derivatives (FcCOOH, Fc-CH 2 NH(CH 3) 2 , Fc-1,1-CH 3 , Fc-CH CH 2, and Fc) was calculated using DFT and molecular docking. Quantitative Structure-Activity Relationship (QSAR) analyses were explored to rationalize ks values with theoretical calculations. The results allow us to propose that the GOD-mediator interaction, should be considered for a better description of the electron transfer process, useful for potential bioelectronic applications. The redox mediation of (GOD) with a series of Co(II) polypyridine complexes and ferrocene derivatives was studied, to understand the role molecular interaction GOD-mediator on homogeneous electron transfer rate constant ( ks ). Circular Dichroism, DFT and molecular docking studies are reported. Quantitative Structure-Activity Relationship (QSAR) analyses were explored. [Display omitted] [ABSTRACT FROM AUTHOR]

• An EC i mechanism is tuned by the π acceptor descriptor pKa. • Spectroelectrochemistry suggest products in the EC i mechanism. • Linear relationships among E° and k i , with the pKa were observed. • k s GOD-mediator is not controlled by E°. In this work we revisit the role of π-acceptor character of polypyridinc ligands in the electrochemical behavior of bis and tris Fe(II) complexes [FeL 3 ]2+ and [FeL′ 2 ]2+ and in the electron transfer with a representative redox enzyme, glucose oxidase GOD; (L = 1,10-phen, 5-chloro-1,10-phen, 5-nitro-1,10-phen, 5-methyl-1,10-phen, 4-methyl-1,10-phen, 5,6-dimethyl-1,10-phen, 4,7-dimethyl-1,10-phen, 2,2′-bipy, 5,5′-dimethyl-2,2′-bipy, 4,4′-dimethyl-2,2′-bipy, L′ = 2,2′6′,6″-terpy and 4-chloro-2,2′:6′,6″-terpy). The compounds presented a reversible electron transfer [Fe(II)L n ]2+ → [Fe(III)L n ]3+ 1e, (n = 1,2) followed by an unexpected coupled chemical reaction, EC i mechanism. It was established that the redox potential (E°) and the rate constant (k f) of couple reaction are tuned by the pKa of non-coordinated ligand (π acceptor character descriptor). Using UV–vis spectroelectrochemistry different products are proposed for the ECi mechanism. DFT calculations, allow us to state that changes in E°, and pKa are related to HOMO energies. Linear relationships among the electrochemical and kinetic values E°, k f , with the pKa of the ligands were obtained. Using Foot of the Wave Analysis (FOWA) the homogenous electron transfer rate constant ( k s ) for GOD mediation was calculated. From data obtained in this work and choosing similar complexes from literature, it was explored the role of redox potential in this redox mediation. [ABSTRACT FROM AUTHOR]

In this work we report the electrochemical, spectroscopical and spectro-electrochemical studies of a model complex [CuΙΙ(Bztpen)]2+, (Bztpen = (N-benzyl-N,N′,N′-tris(pyridin-2-ylmethyl)ethylenediamine) in order to propose a methodology to evaluate the interaction of potential metal based anticancer agents during electron transfer processes, with transport proteins such as Bovine Serum Albumin (BSA). It was possible to establish a reversible electron transfer [CuΙΙ(Bztpen)]2+ +1e → [CuΙ(Bztpen)]+ and a weak interaction energy between BSA and [CuΙΙ(Bztpen)] and [CuΙ(Bztpen)] species, with no adsorption of protein over the electrode surface. Circular Dichroism (CD) Spectroelectrochemistry, not reported before, reveals no significant changes in BSA structure during the electron transfer [CuΙΙ(Bztpen)]2+ + 1e → [CuΙ(Bztpen)]+. CD experiments at variable temperature for BSA denaturalization in the absence and in the presence of [CuΙΙ(Bztpen)]2+, shown no change in thermodynamic parameters due to low interaction between the transport protein and copper complex. In this work we report the interaction of the complex [Cu(Bztpen)]2+ with Bovine Serum Albumin (BSA) using UV-vis spectroscopy, CD experiments at variable temperature, DFT calculations, electrochemical and CD-spectroelectrochemistry. [Display omitted] • A Cu complex with the ligand Bztepen (N-benzyl-N,N'′,N'′-tris(pyridin-2-ylmethyl)ethylenediamine) is prepared. • It was established the redox process [Cu(Bztpen)]2+ +1e → [Cu(Bztpen)]+. • It was found a weak interaction between BSA and [Cu(Bztpen)]2+/ [Cu(Bztpen)]+. • CD-spectroelectrochemistry reveals no changes during the electron transfer processes. [ABSTRACT FROM AUTHOR]