Photoinduced carbon monoxide migration in a synthetic heme-copper complex.
Time-resolved infrared (TRIR) flash photolytic techniques have been employed to initiate and observe the efficient dissociation of CO from a synthetic heme-CO/copper complex, [((6)L)Fe(II)(CO)..Cu(I)](+) (2), in CH(3)CN and acetone at room temperature. In CH(3)CN, a significant fraction of the photodissociated CO molecules transiently bind to copper (nu(CO)(Cu) = 2091 cm(-)(1)) giving [((6)L)Fe(II)..Cu(I)(CO)](+) (4), with an observed rate constant, k(1) = 1.5 x 10(5) s(-)(1). That is followed by a slower direct transfer of CO from the copper moiety back to the heme (nu(CO)(Fe) = 1975 cm(-)(1)) with k(2) = 1600 s(-)(1). Additional transient absorption (TA) UV-vis spectroscopic experiments have been performed monitoring the CO-transfer reaction by following the Soret band. Eyring analysis of the temperature-dependent data yields DeltaH(double dagger) = 43.9 kJ mol(-)(1) for the 4-to-2 transformation, similar to that for CO dissociation from [Cu(I)(tmpa)(CO)](+) in CH(3)CN (DeltaH(double dagger) = 43.6 kJ mol(-)(1)), suggesting CO dissociation from copper regulates the binding of small molecules to the heme within [((6)L)Fe(II)..Cu(I)](+)(3). Our observations are analagous to those observed for the heme(a3)/Cu(B) active site of cytochrome c oxidase, where photodissociated CO from the heme(a3) site immediately (ps) transfers to Cu(B) followed by millisecond transfer back to the heme.
Fry
H Christopher
HC
Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218, USA.
Cohen
Andrew D
AD
Toscano
John P
JP
Meyer
Gerald J
GJ
Karlin
Kenneth D
KD
D002248:Carbon Monoxide / Q000737:chemistry* / Q000528:radiation effects; D003300:Copper / Q000737:chemistry*; D006418:Heme / Q000737:chemistry* / Q000528:radiation effects; D058085:Iron Compounds / Q000737:chemistry; D007700:Kinetics; D008958:Models, Molecular; D010782:Photolysis; D013055:Spectrophotometry, Infrared / Q000379:methods; D013056:Spectrophotometry, Ultraviolet
D058085:Iron Compounds; D006418:Heme; D003300:Copper; D002248:Carbon Monoxide