Photoinduced electron transfer between the cationic complexes Ru(NH3)5pz2+ and trans-RuCl([15]aneN4)NO2+ mediated by phosphate ion: visible light generation of nitric oxide for biological targets.
The photochemical behavior of the tetraazamacrocyclic complex trans-RuCl([15]ane)(NO)2+ (RuNO2+) in a 10 mM phosphate buffer solution, pH 7.4, and in the presence of Ru(NH3)5pz2+ (Rupz2+) is reported. Irradiation (436 nm) of an aqueous solution containing both cationic complexes as PF6- salts labilizes NO from RuNO2+ with a quantum yield (phiNO) dependent on the concentration of Rupz2+ with a maximum value of phiNO (1.03(11)x10(-3) einstein mol-1) found for a solution with equimolar concentrations (5x10(-5) M) of the two complexes in phosphate buffer solution. The quantitative behavior of this system suggests that the two cations undergo preassociation such that photoexcitation of the visible absorbing Rupz2+ is followed by electron or energy transfer to RuNO2+, which does not absorb appreciably at the excitation wavelength, and this leads to NO release from the reduced nitrosyl complex. Notably, the NO release was not seen in the absence of phosphate buffer; thus, it appears that phosphate ions mediate NO generation, perhaps by facilitating formation of a supramolecular complex between the two ruthenium cations. Reexamination of the cyclic voltammetry of Rupz2+ showed that the electrochemical behavior of this species is also affected by the presence of the phosphate buffer.
da Silva
Roberto S
RS
Faculdade de Ciências Farmacêuticas de Ribeirão Preto, Universidade de São Paulo, Avenida do Café s/n, CEP 14040-903 Ribeirão Preto (SP), Brazil. silva@usp.Br
Marchesi
Mario S P
MS
Khin
Chosu
C
Lunardi
Claure N
CN
Bendhack
Lusiane M
LM
Ford
Peter C
PC
D001372:Aza Compounds / Q000737:chemistry*; D002412:Cations / Q000737:chemistry; D004579:Electron Transport; D020030:Nitric Oxide Donors / Q000737:chemistry*; D010710:Phosphates / Q000737:chemistry*; D010782:Photolysis; D011719:Pyrazines / Q000737:chemistry*; D017975:Ruthenium Compounds / Q000737:chemistry*; D014466:Ultraviolet Rays
D001372:Aza Compounds; D002412:Cations; D020030:Nitric Oxide Donors; D010710:Phosphates; D011719:Pyrazines; D017975:Ruthenium Compounds