Gated electron-transfer behavior in copper(II/I) systems. Comparison of the kinetics for homogeneous cross reactions, NMR self-exchange relaxation, and electrochemical data for a copper macrocyclic tetrathioether complex in aqueous solution

Effect of an Ala81His Mutation on the Met80 Loop Dynamics of Iso-1-cytochromec

“…In our experience, the more favorable heme reduction potential of the native conformer compared to alkaline conformers of iso-1-Cyt c (18, 77) makes path B the dominant path for reduction of the alkaline conformer by a 6 Ru 2+ (25–28, 30, 69). For reduction of the His81-heme alkaline conformer by a 6 Ru 2+ via path B, the rate constant for gated ET, k gET,2 , is given by eq 4 (78–80). $$k_{\text{gET},2}=\frac{k_{\mathrm{normalb},\text{His}81}{k}_{\text{ET}}false[{\mathrm{a}}_6{\text{Ru}}^{2+}false]}{k_{\text{ET}}false[{\mathrm{a}}_6{\text{Ru}}^{2+}false]+k_{\mathrm{normalf},\text{His}81}}$$ When k ET [a 6 Ru 2+ ] ≫ k f,His81 , the rate constant for gated ET, k gET,2 ≈ k b,His81 , allowing direct evaluation of k b,His81 .…”

Electron Transfer by Copper Centers

“…49,50 More extensive kinetic measurements were subsequently conducted on the 13-, 14-, and 15-membered ring tetrathiaethers and two dialcohol derivatives of [14]aneS 4 . 56,133,134 The electron-transfer kinetics for each of these five systems were measured with a total of four reductants and four oxidants, and independent k 11 values were also obtained from NMR line broadening measurements. 56,133,134 In all five systems, the calculated k 11(Red) values were in close agreement with the corresponding values obtained by NMR (Table 7).…”

“…56,133,134 The electron-transfer kinetics for each of these five systems were measured with a total of four reductants and four oxidants, and independent k 11 values were also obtained from NMR line broadening measurements. 56,133,134 In all five systems, the calculated k 11(Red) values were in close agreement with the corresponding values obtained by NMR (Table 7). This observation was in sharp contrast to the original suggestion by Lee and Anson 39 that the k 11 value for Cu(II/I) systems, as determined directly without invoking eq 14, should be the geometric mean of k 11(Red) and k 11(Ox) (see section 4.3).…”

“…Of the five Cu(II/I) complex systems noted above, k RP values of 50, 120, and 50 s -1 were reported for [14]aneS 4 , syn- [14]aneS 4 -diol, and anti- [14]aneS 4 -diol, respectively, with limiting values of g200 and e5 s -1 for the complexes with [13]aneS 4 and [15]aneS 4 , respectively. 56,133,134 If all three terms in eq 20′′ contribute to the reaction kinetics (i.e., second-order kinetics via pathway A, first-order kinetics due to rate-limiting conformational change, and second-order kinetics via pathway B) as the counterreagent concentration is varied, curve fitting can be used to resolve the individual values of k 21(A) , k 21(B) , and k RP . 134 A prime example of such multifold behavior is illustrated in Figure 15 for the oxidation of Cu I (trans-cypt- [14]aneS 4 ) + by Ni III ( [14]aneN 4 ) 3+ for which the three limiting conditions overlap significantly as the oxidant concentration is varied.…”

Outer-sphere electron-transfer between horse heart cytochrome c and anionic Cu(ii/i) complexes. Evidence for precursor formation and coordination sphere reorganization for electron transfer

“…Similar simulations have been performed for other copper complexes in the past. 68, 69 The key parameters which affect the form of the CV wave are the reduction potentials of species (1) and (4) and the rate constants k 41 , k 14 , k 23 and k 32 . ESP can in principle be used to calculate the parameters controlling the electrochemistry and our aim was to use this to resolve the couples which contribute to the overall process.…”