Ruthenium complexes pulse radiolysis

The systems that we investigated in collaboration with others involved intermolecular and intramolecular electron-transfer reactions between ruthenium complexes and cytochrome c. We also studied a series of intermolecular reactions between chelated cobalt complexes and cytochrome c. A variety of high-pressure experimental techniques, including stopped-flow, flash-photolysis, pulse-radiolysis, and voltammetry, were employed in these investigations. As the following presentation shows, a remarkably good agreement was found between the volume data obtained with the aid of these different techniques, which clearly demonstrates the complementarity of these methods for the study of electron-transfer processes. 

Intramolecular electron transfer from Ru(II) to Fe(III) in (NH3)3Ru(II) (His-33)cyt(Fe(III)) induced by pulse-radiolysis reduction of Ru(III) in the (NH3)5Ru(III) (His-33)cyt(Fe(III)) complex were investigated [84]. The results obtained differ from those of refs. 77-80 where flash photolysis was used to study the similar electron transfer reaction. It was found [84] that, over the temperature range 276-317 K the rate of electron transfer from Ru(II) to Fe(III) is weakly temperature dependent with EA 3.3 kcal mol 1. At 298 K the value of kt = 53 2 s"1. The small differences in the temperature dependence of the electron tunneling rate in ruthenium-modified cytochrome c reported in refs. 77-80 and 84 was explained [84] by the different experimental conditions used in these two studies. 

The contribution of pulse radiolysis to general chemistry is very significant, and this is exemplified by the following studies of transition metal complexes. The reduction of tris(2,2 -bipyridine)ruthenium(III) ion by the hydrated electron was the first example of this type of reaction to show clearly the formation of a product in an electronically excited state [80] ... 

Other Studies.— The kinetics and mechanisms of reactions of tptz (5) complexes of cobalt(ii), copper(ii), and nickel(u) with water and with hydroxide have been established and compared. Covalent hydrates are believed to be important intermediates in aquation of the [M(tptz)(OH2)3] + complexes. Kinetics of aquation of the anions [M(acac)a] (M = Co, Cr, or Ru) have been studied in pulse radiolysis experiments. All three steps were monitored for the cobalt(n) complex, but the first step for the chromium(ii) complex was too fast to follow and, predictably, all steps for the ruthenium(ir) complex were too slow to follow by this technique. The mechanism of acac loss is thought to involve equilibrium... 

It is not clear, at present, whether the spectrum (Figure 2) may be attributed to the penta-ammino-complex or to the ruthenium atoms formed by the rapid dissociation of the complex. There is no evidence, however, for the reduction of the ligand nitrogen under these conditions. Hydrated electrons generated in the pulse radiolysis of aqueous solutions containing cobalt(m) cyanide complexes react very rapidly (jk 10 —10 1 mol s ) with the cobalt solutes. Reactions of the type... 

The reactions of cobalt(m) and ruthenium(m) ammine complexes with Yb , Eu, and Sm have been investigated using a pulse radiolysis technique. Whereas the reaction rates for Eu are similar to those of previous workers, the data for Yb + are in marked contrast to those described above. A previous... 

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