The study of redox reactions of bisarenechromium complexes by the rotating disk and the rotating ring disk electrode techniques: III. Cathodic reduction of chromium(0) π-complexes and the corresponding arenes in dimethyl sulfoxide solutions

The rotating disk (RDE) and the rotating ring-disk (RRDE) electrode techniques have been employed to study the cathodic behavior of eight bisarenechromium complexes and seven corresponding arenes in DMSO solutions. In the first electrochemical step of the process reversible addition of one electron results in anion-radicals, whose formation has been demonstrated for certain arenes and chromium π-complexes by oxidation of these particles on the ring electrode.Substituents on different ligands of bisarenechromium complexes were found to exert pronounced mutual influences. The role of the chromium atom in transfer of electronic effects from one ligand to another is discussed.It was found that a linear correlation exists between the variations in the free energy of the equilibrium “initial compound

anion-radical” (due to coordination of free arene with chromium which is displayed as a shift of the cathodic process half-wave potential ΔE_{$\text{1}\text{2}$}^CL) and the half-wave potential of the oxidation of the corresponding Cr⁰ π-complex to a cation E_{$\text{1}\text{2}$}^X ΔE_{$\text{1}\text{2}$}^CL = a + αE_{$\text{1}\text{2}$}^X At E_{$\text{1}\text{2}$}^X < ?0.3 V, complex formation slows down the cathodic process and at E_{$\text{1}\text{2}$}^X > ?0.3 V the process is facilitated.     

Biodegradation of soluble redox polymers. Part 2: (0.017ferrocene)amylose at a rotating disk electrode

The behavior of (ferrocene)amylose (FA), in the presence of amylolytic depolymerases (α-amylase from Aspergillus oryzae and human saliva), has been investigated by cyclic voltammetry at a rotating disk electrode (CVA/RDE). Growth of the limiting current with time in the presence of the enzymes is proportional to the amount of enzyme introduced. The quantitative data treatment to assay the endoamylolytic activity of enzymes at CVA/RDE involves plotting (i_dt/i_d0)^4.5 against time; the slope of the linear plot being equal to (rate) M_n0C⁻¹, where i_dt and i_d0 are the limiting currents at time t and 0, respectively, (rate) is the enzymatic activity, M_n0 is the number averaged molecular weight of FA at t = 0, and c is its concentration. The comparison of CVA/RDE with the 3,5-dinitrosalicylic acid and the Somogyi–Nelson reducing saccharides procedures shows advantages of the former, especially in assaying small quantities of enzymes. Also the CVA/RDE approach is simpler and takes place under much milder conditions. The main disadvantage of CVA/RDE is the inhibiting effect of Triton X-100 in the reaction between FA and the amylases which is not observed in the case of native, ferrocene-free amylose. In general, CVA/RDE appears to be an attractive analytical method for monitoring diverse enzymatic depolymerization reactions.     

Electroreduction kinetics and mechanism of palladium(II) glycinate chloride complexes on rotating palladium disk electrode

The electroreduction kinetics of Pd(Hgly)₂Cl₂ on rotating palladium disk electrode was studied by means of cyclic voltammetry. The double layer range of the palladium charging curve showed a single wave with the diffusion limited current I _d, which yielded the diffusion coefficient of Pd(Hgly)₂Cl₂ complex D = 6 × 10⁻⁶ cm²/s. The plotted direct and reverse voltammetric curves were linearized in coordinates E, log[I/(I _d − I)]. The slope of this line gave b _k factor evidencing the slow electrochemical step. When [Cl⁻] decreased from 1 to 0.2 M, E _1/2 potential shifted to positive values. This was accounted for by reversible cleavage of Cl⁻ ion from Pd(Hgly)₂Cl₂ complexes before the irreversible electrochemical step. The pulse galvanostatic experiment resulted in the double electrical layer capacity and roughness factors f of electrolytic palladium deposits. The calculated values of f from 60 to 310 were attributed to adsorption of glycine particles on the electrodeposited palladium surface, which promotes to increasing number of palladium microcrystal growing centers.     

Development of rotating liquid membrane disk electrode and rotating liquid membrane ring-liquid membrane disk electrode and evaluation of characteristics of ion transfer reactions at the rotating aqueous/organic solution interface.

A liquid membrane disk electrode, LMDE, and a liquid membrane ring-liquid membrane disk electrode, LMRE-LMDE, were developed by placing a gelled polyvinyl chloride thin membrane impregnated with 2-nitrophenyl octyl ether, NPOE-LM, on the surface of a glassy carbon, GC, disk or ring electrode. The voltammogram for the ion transfer at the interface between an aqueous solution, W, and NPOE-LM was recorded by setting the developed electrode in W and rotating at a rate, omega, between 0 and 4000 rpm. The sensitivity of the ion-transfer current at the WINPOE-LM interface, I, was enhanced to be more than 100 times better than that at the WINPOE (solution) interface when LMDE was rotated at omega higher than 200 rpm. The reversibility of the ion transfer reaction could be evaluated based on the dependence of I on omega of LMDE, and the reaction product at LMDE could be identified at LMRE when the rotating LMRE-LMDE system was adopted.     

A rotating disk electrode study on catalytic activity of iron(II) phthalocyanine-modified electrodes for oxygen reduction in acidic media

Journal of Solid State Electrochemistry - Catalytic activity of monometric metal macrocycles for oxygen reduction reaction (ORR) was investigated using rotating disk electrode voltammetry in acidic...     

Theory of electrode reactions of redox couples confined to electrode surfaces at monolayer levels: Part I. Expression of the current-potential relationship for simple redox reactions

A statistical mechanical treatment of redox couples and an activated complex confined to electrode surfaces at monolayer levels is presented in which not only interaction energies but also molecular arrangements are taken into consideration. Expressions for the activity coefficients of the relevant species are derived using a two-dimensional quasi-crystalline lattice model and the quasi-chemical approximation introduced by Guggenheim. An expression of the current-potential relationship is derived for simple one-step surface redox-electrode reactions of the species confined to electrode surfaces at monolayer levels based on the transition-state rate theory. It is shown that the equation derived for the current-potential relationship includes, as a limiting case, the one that has been derived on the assumption of a random distribution of the adsorbed species.     

Theory of a.c. voltammetry at a rotating disk electrode: Part III. Redox-electrode reactions coupled with first-order chemical reactions

A theory of a.c. voltammetry at a rotating disk electrode is developed for systems with coupled first-order chemical reactions. A general expression for a.c. waves, together with that for d.c. waves, is derived. It is shown that the effect of hydrodynamics on the phase angle is negligible under the condition of p≤0.35, where p is a parameter defined by the frequency of of a.c. wave, the rotation speed of the electrode and Schmidt number.     

Theory of a.c. voltammetry at a rotating disk electrode: Part II. Quasi-reversible and irreversible redox-electrode reactions

Alternating current response at a rotating disk electrode to a small a.c. potential wave superimposed on the slowly changing d.c. potential is theoretically treated for an quasireversible and an irreversible redox-electrode process. Expressions for alternating current-d.c. potential curves are given for three types of a.c. signals, i.e., sinusoidal, rectangular and triangular waves. It is shown that the effect of the coupling of the diffusion layers due to hydrodynamics and a.c. polarization can be expressed in terms of a parameter which is defined by the ratio of the frequency of a.c. wave to that of the rotation of the electrode and Schmidt number.     

Rotating disk electrode study of the kinetics of formation of palladium(II) ethylenediaminechloride complexes from palladium(II) bis-ethylenediamine complexes

The kinetics of substitution of chloride ions for ethylendiamine in a bis-ethylenediamine complex of palladium(II) is studied in solutions with pH 0.3–2.0 and the ionic strength of 0.11–1.0 M by measuring the transients of limiting diffusion currents of the electroreduction of palladium(II) ethylenediamine complexes on a rotating disk electrode. The first reaction orders in hydrogen and chloride ions are found at the ionic strength of 1 M (NaClO₄). The activation energy of the homogeneous reaction under study is determined from the temperature dependence of its rate constant. The mechanism of substitution of chloride ions for ethylenediamine is discussed.     

气体电极反应动力学的薄膜旋转圆盘电极方法研究

薄膜旋转圆盘电极方法是一种常用的评价气体物质在纳米电催化剂上的反应活性的方法,但是在数据分析过程中经常忽视了气体反应物在催化剂层中到活性位点的传质可能对估算的反应动力学参数的影响.本文以氧电极反应为例,使用薄膜旋转圆盘电极研究了不同担载量Pt/C电极的氧还原活性.实验结果表明,根据Koutecky-Levich方程求算相同电位下的"表观动力学电流密度"(对Pt活性面积归一化的mA/cm2Pt)或比质量电流(mA/μg Pt)随Pt担载量的减小而增大,说明在估算动力学电流时不能忽略O2在催化剂层中的扩散传质,而气体在催化剂层中的传质与催化剂层的结构、厚度、纳米催化剂的分散度等密切相关.建议在使用薄膜旋转圆盘电极方法来研究纳米催化剂气体电极反应活性时,首先系统考察担载量、分散度与催化剂层厚的影响,然后根据不同担载量催化剂归一化后的动力学电流密度(或比质量电流)-电势曲线是否重合来验证得到的是否是真实的动力学电流,从而得到更为准确的评价结果.     

Photogeneration and reactions of cobalt(I) complexes

Cobalt(I) polypyridine complexes (which are capable of reducing H⁺ to H₂ and CO₂ to CO) may be generated from polypyridineruthenium(II) excited-state reactions by a variety of routes. The relation between the energetics and the rate constants for these routes are considered. In addition, factors leading to loss of cobalt(I) and the mechanisms of substrate reduction are discussed.     

Modeling of mass and charge transfer in an inverted rotating disk electrode (IRDE) reactor

In this work, the validation of a newly constructed inverted rotating disk electrode (IRDE) reactor is reported. Compared to the rotating disk electrode (RDE) reactor, the working electrode is changed in position from the top to the bottom of the electrochemical cell. The IRDE reactor is designed to facilitate the actual study of gas evolution reactions. It is studied whether the first-order analytical expression for the velocity field in an RDE reactor is also acceptable for an IRDE configuration. To that purpose, the kinetic parameters of the well-known ferri/ferro cyanide redox system are determined in both configurations and compared. This is done qualitatively by comparing the polarization curves obtained in the inverted and the conventional RDE configuration. Additionally, a statistically founded fitting algorithm is used to quantitatively determine the model parameters of the oxidation and reduction reaction. Not only the diffusion coefficients of Fe²⁺ and Fe³⁺ are calculated, but also the rate constants (k_ox and k_red) and the transfer coefficients (α_ox and α_red) are quantified and compared together with their respective standard deviation. It is found that the parameters of mass and charge transfer in both configurations agree well. So it is concluded that the same analytical equations of mass and charge transfer can be used in both the RDE and the IRDE reactor.     

An easy to build rotating disk electrode: Application to β-diketonates of Co(II) and Co(III)

An easy to build and dependable rotating disk electrode is described, rotating up to 25×10³ rev min^?1. Application is made to the study of the oxidation-reduction of β-diketonates of Co^II and Co^III.     

The hydrodynamics of the amperometric detector flow cell with a rotating disk electrode

Series of photographs of the sample flow pattern in the flow cell with a stationary as well as a rotating disk electrode (RDE) were taken with a motor-driven camera. With the stationary electrode, the flow pattern in the cell was mushroom-like. Rotating the electrode generated a secondary fluid motion in the flow cell which manifested itself as vertical circulation of the solution present in the flow cell. A qualitative hydrodynamic explanation of the observed flow patterns is given. Peak broadening effects induced by the RDE in the flow cell were observed only at very fast rotation speeds and high nozzle heights. The response surface of the amperometric detector flow cell with the RDE as a function of the rotation speed and the nozzle height was measured by applying the detector in combination with high-performance liquid chromatography, flow injection analysis and continuous flow analysis. Model curve-fitting calculations indicate that the flow pattern in the flow cell can be laminar or turbulent, depending on the exact cell geometry, rotation speed and nozzle height.     

Cu(I)-amido complexes in the Ullmann reaction: reactions of Cu(I)-amido complexes with iodoarenes with and without autocatalysis by CuI

A series of Cu(I)-amido complexes both lacking ancillary ligands and containing 1,10-phenanthroline (phen) as ancillary ligand have been prepared. These complexes react with iodoarenes to form arylamine products, and this reactivity is consistent with the intermediacy of such complexes in catalytic Ullmann amination reactions. The stoichiometric reactions of the Cu(I)-amido complexes with iodoarenes are autocatalytic, with the free CuI generated during the reaction serving as the catalyst. Such autocatalytic behavior was not observed for reactions of iodoarenes with copper(I) amidates, imidates, or phenoxides. The selectivity of these complexes for two sterically distinct aryl halides under various conditions imply that the autocatalytic reaction proceeds by forming highly reactive [CuNPh(2)](n) lacking phen. Reactions with radical probes imply that the reactions of phen-ligated Cu(I)-amido complexes with iodoarenes occur without the intermediacy of aryl radicals. Density functional theory calculations on the oxidative addition of iodoarenes to Cu(I) species are consistent with faster reactions of iodoarenes with CuNPh(2) species lacking phen in DMSO than reactions of iodoarenes with LCuNPh(2) in which L = phen. The free-energy barrier computed for the reaction of PhI with (DMSO)CuNPh(2) was 21.8 kcal/mol, while that for the reaction of PhI with (phen)CuNPh(2) was 33.4 kcal/mol.     

Therapeutic applications of gold complexes: lipophilic gold(III) cations and gold(I) complexes for anti-cancer treatment

Gold and its complexes have long been known to display unique biological and medicinal properties. Extensive cell-based (in vitro) and animal (in vivo) studies have revealed the potent anti-cancer activities of diverse classes of gold(I) and gold(III) complexes. Most of the reported anti-cancer active gold complexes are highly cytotoxic and unstable under physiological conditions, which hamper their development to be launched clinically. Several clinical reports showed that lipophilic organic cations are promising anti-cancer drug candidates targeting to mitochondria. Through metal-ligand coordination, gold(I) and gold(III) ions can form stable lipophilic cations containing organic ligands having tunable lipophilicity and diverse functionalities. The present highlight summarizes the recent development of lipophilic gold(III) cations and gold(I) complexes with promising anti-cancer activities.