The Effect of p-Toluidine on the Two-Step Electroreduction of Zn(II) in Water-Methanol and Water-Dimethylformamide

1999 ◽  
Vol 64 (4) ◽  
pp. 585-594 ◽  
Author(s):  
Barbara Marczewska
Keyword(s):  
Electron Transfer ◽  
Binary Mixtures ◽  
Rate Constant ◽  
Rate Constants ◽  
Electrode Surface ◽  
Mercury Electrode ◽  
Forward Rate ◽  
Solvent Molecules ◽  
Activated Complex

The acceleration effect of p-toluidine on the electroreduction of Zn(II) on the mercury electrode surface in binary mixtures water-methanol and water-dimethylformamide is discussed. The obtained apparent and true forward rate constants of Zn(II) reduction indicate that the rate constant of the first electron transfer increases in the presence of p-toluidine. The acceleration effect may probably be accounted for by the concept of the formation on the mercury electrode an activated complex, presumably composed of p-toluidine and solvent molecules.

The Influence of N,N'-Dialkylthioureas on the Two-Step Electroreduction of Zn(II) Ions

1998 ◽  
Vol 63 (6) ◽  
pp. 749-760 ◽  
Author(s):  
Grażyna Dalmata
Keyword(s):  
Electron Transfer ◽  
Double Layer ◽  
Rate Constant ◽  
Electrode Surface ◽  
Mercury Electrode ◽  
Impedance Method ◽  
Dropping Mercury Electrode ◽  
Wide Potential ◽  
Orientation Of Molecules

A two-step reduction of Zn(II) ions at the dropping mercury electrode in 1 M NaClO4/0.001 M HClO4 in the presence of N,N'-dialkylthioureas was examined in wide potential and frequency ranges, using the impedance method. The rate constant of the first electron transfer increases with increasing concentration of N,N'-dialkylthioureas, whereas that of the second electron transfer depends largely on the double layer effects, particularly, on the orientation of molecules on the electrode surface.

scholarly journals Theoretical Study of the Iron Complexes with Lipoic and Dihydrolipoic Acids: Exploring Secondary Antioxidant Activity

Antioxidants ◽  
2020 ◽  
Vol 9 (8) ◽  
pp. 674
Author(s):  
Roger Monreal-Corona ◽  
Jesse Biddlecombe ◽  
Angela Ippolito ◽  
Nelaine Mora-Diez
Keyword(s):  
Antioxidant Activity ◽  
Electron Transfer ◽  
Rate Constant ◽  
Thermodynamic Stability ◽  
Rate Constants ◽  
Theoretical Study ◽  
Oh Radicals ◽  
Single Electron Transfer ◽  
Coordination Numbers ◽  
Ph Conditions

The thermodynamic stability of twenty-nine Fe(III) complexes with various deprotonated forms of lipoic (LA) and dihydrolipoic (DHLA) acids, with coordination numbers 4, 5 and 6, is studied at the M06(SMD)/6-31++G(d,p) level of theory in water under physiological pH conditions at 298.15 K. Even though the complexes with LA- are more stable than those with DHLA−, the most thermodynamically stable Fe(III) complexes involve DHLA2−. The twenty-four exergonic complexes are used to evaluate the secondary antioxidant activity of DHLA and LA relative to the Fe(III)/Fe(II) reduction by O2•− and ascorbate. Rate constants for the single-electron transfer (SET) reactions are calculated. The thermodynamic stability of the Fe(III) complexes does not fully correlate with the rate constant of their SET reactions, but more exergonic complexes usually exhibit smaller SET rate constants. Some Cu(II) complexes and their reduction to Cu(I) are also studied at the same level of theory for comparison. The Fe(III) complexes appear to be more stable than their Cu(II) counterparts. Relative to the Fe(III)/Fe(II) reduction with ascorbate, DHLA can fully inhibit the formation of •OH radicals, but not by reaction with O2•−. Relative to the Cu(II)/Cu(I) reduction with ascorbate, the effects of DHLA are moderate/high, and with O2•− they are minor. LA has minor to negligible inhibition effects in all the cases considered.

Electrode kinetics of Eu3+/Eu2+ reaction by cyclic voltammetry

1982 ◽  
Vol 47 (7) ◽  
pp. 1773-1779 ◽  
Author(s):  
T. P. Radhakrishnan ◽  
A. K. Sundaram
Keyword(s):  
Electron Transfer ◽  
Rate Constants ◽  
Outer Sphere ◽  
Electrode Reaction ◽  
Transfer Reactions ◽  
Cyclic Voltammetric ◽  
Edta Solution ◽  
Kinetics Of ◽  
Activated Complex ◽  
Good Agreement

The paper is a detailed study of the cyclic voltammetric behaviour of Eu3+ at HMDE in molar solutions of KCl, KBr, KI, KSCN and in 0.1M-EDTA solution with an indigenously built equipment. The computed values of the rate constants at various scan rates show good agreement with those reported by other electrochemical methods. In addition, the results indicate participation of a bridged activated complex in the electron-transfer step, the rate constants showing the trend SCN- > I- > Br- > Cl- usually observed for bridging order of these anions in homogeneous electron-transfer reactions. The results for Eu-EDTA system, however, indicate involvement of an outer sphere activated complex in the electrode reaction.

POLAROGRAPHY OF URANIUM: III. URANIUM(VI) IN FLUORIDE MEDIA

1957 ◽  
Vol 35 (10) ◽  
pp. 1225-1236 ◽  
Author(s):  
David J. McEwen ◽  
Thomas De Vries
Keyword(s):  
Electron Transfer ◽  
Transfer Coefficient ◽  
Rate Constant ◽  
Transfer Process ◽  
Rate Constants ◽  
Electrode Reaction ◽  
Electron Transfer Process ◽  
Fold Excess

The uranium(VI) and (V) polarographic waves were studied in chloride and perchlorate supporting electrolytes of 0.1 M to almost neutral acidities and containing 0 to 100 fold excess of fluoride. The concentrations of the uranium(VI)–fluoride species (UO2Fn+2−n, n = 1 − 4) were calculated and it is shown that the first two species, UO2F+ and UO2F2, are either reduced reversibly at the D.M.E., or dissociate rapidly to the uncomplexed ion, UO2++, which is known to reduce reversibly. The UO2F4− species, and possibly also UO2F3− is reduced irreversibly, and the rate constant of the electron transfer process, kf°, and the transfer coefficient, α, were calculated by two methods. The electrode reaction is proposed as UO2Fn+2−n+e− = UO2++nF−. The rate of disproportionation of uranium(V) was found to depend upon the F/U ratio, and the rate constants for the reaction were calculated.

Faradaic Impedance Study of Mn(II) Reduction Mechanism in NaClO4 and NaCl Solutions on Mercury Electrode

2002 ◽  
Vol 67 (11) ◽  
pp. 1589-1595
Author(s):  
Barbara Marczewska ◽  
Andrzej Persona ◽  
Marek Przegaliński
Keyword(s):  
Electron Transfer ◽  
Rate Constants ◽  
Electrochemical Reaction ◽  
Mercury Electrode ◽  
Reduction Mechanism ◽  
True Rate ◽  
Faradaic Impedance ◽  
Impedance Measurements ◽  
Order Of Magnitude ◽  
Adsorptive Properties

The electrochemical reaction of the Mn(II)/Mn(Hg) system on mercury electrode was studied in 1 M NaClO4 and 1 M NaCl as supporting electrolytes of different complexing and adsorptive properties. The impedance measurements confirmed the two-stage electroreduction of the Mn(II) in investigated solutions. Both the apparent and the true rate constants of the second electron transfer in both supporting electrolytes are lower by one order of magnitude than the rate constant of the first electron transfer. Similar values of corrected rate constants in both electrolytes suggest the similarity in mechanism of the Mn(II) electroreduction.

Preferential Control of Forward Reaction Kinetics in Hydrogels Crosslinked with Reversible Conjugate Additions

2020 ◽  
Author(s):  
Thomas FitzSimons ◽  
Felicia Oentoro ◽  
Tej V. Shanbhag ◽  
Eric Anslyn ◽  
Adrianne Rosales
Keyword(s):  
Stress Relaxation ◽  
Rate Constant ◽  
Rate Constants ◽  
Forward Rate ◽  
Self Healing ◽  
Strong Electron ◽  
Kinetic Rate ◽  
Plateau Modulus ◽  
Kinetic Rate Constants ◽  
Reverse Rate Constant

<p>Molecular substitutions were used to demonstrate preferential control over the kinetic rate constants in a poly(ethylene glycol)-based hydrogel with two different reversible thia-conjugate addition reactions. A strong electron withdrawing nitrile group on the conjugate acceptor showed a 20-fold increase in the forward rate constant over a neutral withdrawing group, while the reverse rate constant only increased 6-fold. Rheometry experiments demonstrated that the hydrogel plateau modulus was primarily dictated by reaction equilibrium, while the stress relaxation characteristics of the hydrogel were dominated by the reverse rate constant. Furthermore, the dynamic crosslinking allowed the hydrogel to rapidly and spontaneously self-heal. These results indicate that decoupling the kinetic rate constants of bond exchange allow systematic control over dynamic covalent hydrogel bulk properties, such as their adaptability, stress relaxation ability, and self-healing properties.</p>

Electron-Transfer Reactions in Non-Aqueous Media. IV. A Temperature-Dependence Study of the Reduction of CoCl(NH3)52+ by Iron(II) in N,N-Dimethylformamide

1979 ◽  
Vol 32 (7) ◽  
pp. 1425 ◽  
Author(s):  
KR Beckham ◽  
DW Watts
Keyword(s):  
Electron Transfer ◽  
Temperature Dependence ◽  
Equilibrium Constant ◽  
Rate Constant ◽  
Iron Atom ◽  
Rate Constants ◽  
Aqueous Media ◽  
Transfer Reactions ◽  
Complex Functions ◽  
Temperature Dependences

A detailed study has been made of the temperature dependence of the rate of reduction of CoCl-(NH3)52+ by iron(II) in N,N-dimethylformamide. The observed rate constants (kobs) for this reaction are complex functions of an equilibrium constant (K) for the formation of a bridged intermediate, the rate constant for electron transfer in this bridged intermediate (k), and the iron(II) concentration. From studies of the dependence of kobs on iron(II) concentration at five temperatures the temperature dependences of both K and k have been resolved, yielding respectively ΔH� -20k�12 kJ mol-1, ΔS� -44�40 J K-1 mol-1 and ΔH* 107�4 kJ mol-1, ΔS* 57�16 J K-1 mol-1. The results are interpreted in terms of a bridged intermediate in which the iron atom is tetrahedrally coordinated.

Proton- and ion-transfer reactions

1996 ◽  
Author(s):  
Wolfgang Schmickler
Keyword(s):  
Electron Transfer ◽  
Electrode Surface ◽  
Metal Ion ◽  
Metal Electrode ◽  
Transfer Reactions ◽  
Partial Charge ◽  
Reverse Process ◽  
Proton Transfer Reactions ◽  
Solvent Molecules ◽  
Simultaneous Discharge

We consider the transfer of an ion or proton from the solution to the surface of a metal electrode; often this is accompanied by a simultaneous discharge of the transferring particle, such as by a fast electron transfer. The particle on the surface may be an adsorbate as in the reaction: . . .Cl - (sol) ⇋ Clad + e- (metal) . . . (9.1) In this case the discharge can be partial; that is, the adsorbate can carry a partial charge, as discussed in Chapter 4. Alternatively the particle can be incorporated into the electrode as in the deposition of a metal ion on an electrode of the same composition, or in the formation of an alloy. An example of the latter is the formation of an amalgam such as: . . . Zn2++2e- ⇋ Zn(Hg) . . . (9.2) The reverse process is the transfer of a particle from the electrode surface to the solution; often the particle on the surface is uncharged or partially charged, and is ionized during the transfer. Ion- and proton-transfer reactions are almost always preceded or followed by other reaction steps. We first consider only the chargetransfer step itself. Ions and protons are much heavier than electrons. While electrons can easily tunnel through layers of solution 5 to 10 Å thick, protons can tunnel only over short distances, up to about 0.5 Å, and ions do not tunnel at all at room temperature. The transfer of an ion from the solution to a metal surface can be viewed as the breaking up of the solvation cage and subsequent deposition, the reverse process as the jumping of an ion from the surface into a preformed favorable solvent configuration. In simple cases the transfer of an ion obeys a slightly modified form of the Butler-Volmer equation. Consider the transfer of an ion from the solution to the electrode. As the ion approaches the electrode surface, it loses a part of its solvation sphere, and it displaces solvent molecules from the surface; consequently its Gibbs energy increases at first.

Preferential Control of Forward Reaction Kinetics in Hydrogels Crosslinked with Reversible Conjugate Additions

2020 ◽  
Author(s):  
Thomas FitzSimons ◽  
Felicia Oentoro ◽  
Tej V. Shanbhag ◽  
Eric Anslyn ◽  
Adrianne Rosales
Keyword(s):  
Stress Relaxation ◽  
Rate Constant ◽  
Rate Constants ◽  
Forward Rate ◽  
Self Healing ◽  
Strong Electron ◽  
Kinetic Rate ◽  
Plateau Modulus ◽  
Kinetic Rate Constants ◽  
Reverse Rate Constant

<p>Molecular substitutions were used to demonstrate preferential control over the kinetic rate constants in a poly(ethylene glycol)-based hydrogel with two different reversible thia-conjugate addition reactions. A strong electron withdrawing nitrile group on the conjugate acceptor showed a 20-fold increase in the forward rate constant over a neutral withdrawing group, while the reverse rate constant only increased 6-fold. Rheometry experiments demonstrated that the hydrogel plateau modulus was primarily dictated by reaction equilibrium, while the stress relaxation characteristics of the hydrogel were dominated by the reverse rate constant. Furthermore, the dynamic crosslinking allowed the hydrogel to rapidly and spontaneously self-heal. These results indicate that decoupling the kinetic rate constants of bond exchange allow systematic control over dynamic covalent hydrogel bulk properties, such as their adaptability, stress relaxation ability, and self-healing properties.</p>

Sign in / Sign up

Export Citation Format

Share Document