Mechanisms of Reactions of (*)NO with Complexes with Metal-Carbon sigma-Bonds and with Aliphatic Radicals.
The competition kinetics between metal complexes and (*)NO for aliphatic radicals is a convenient technique for determining the rate constants of the reactions of (*)NO with aliphatic radicals. Thus, the rate constants of (*)CH(3) and (*)CH(2)OH with (*)NO were determined to be (3.4 +/- 1.1) x 10(9) and (5.9 +/- 0.5) x 10(9) M(-)(1) s(-)(1), respectively. The same rate constants can be determined, in several systems, from the decrease in the half-life of transient complexes with metal-carbon sigma-bonds which decompose homolytically. In the presence of (*)NO, the half-life of these transient complexes decreases, and their decomposition turns from second-order to first-order processes. From the dependence of the observed first-order rate constant on (*)NO and on the metal complex concentrations, it is concluded that the mechanism of the decomposition of these transients in the presence of (*)NO involves the reaction of (*)NO with the carbon-centered radicals as well as with the transient with the metal-carbon sigma-bonds to form the same products. The rate constants of the reactions of (*)NO with (cyclam)(H(2)O)Ni(III)CH(3)(2+) and (nta)Co(III)CH(2)OH(H(2)O)(-) were determined to be (1.5 +/- 0.2) x 10(5) and (3.6 +/- 0.4) x 10(8) M(-)(1) s(-)(1), respectively. The reactions of (*)NO with complexes with metal-carbon sigma-bonds are analogous to those of aliphatic radicals and dioxygen with the same complexes. This is not surprising as (*)NO is a radical. The biological implications of these results are discussed.
Goldstein
Sara
S
Department of Physical Chemistry, The Hebrew University of Jerusalem, Jerusalem 91904, Israel, and Chemistry Department, Ben-Gurion University of the Negev, Beer-Sheva, and The College of Judea and Samaria, Kdumim-Ariel, Israel.
Meyerstein
Dan
D
Czapski
Gidon
G