Synthesis and photochemical properties of a novel iron-sulfur-nitrosyl cluster derivatized with the pendant chromophore protoporphyrin IX.
The novel Roussin red-salt ester (PPIX-RSE) with a pendant porphyrin chromophore was prepared and investigated as a precursor for the photochemical generation of nitric oxide. PPIX-RSE has the general formula Fe(2)(NO)(4)[(mu-S,mu-S')P] (where (S,S')P is the bis(2-thiolatoethyl) diester of protoporphyrin IX. The photoexcitation of PPIX-RSE with 436- or 546-nm light in an aerated chloroform solution led to the photodecomposition of the cluster with the respective quantum yields (5.2 +/- 0.7) x 10(-4) and (2.5 +/- 0.5 x 10(-4)) and the concomitant release of NO. PPIX-RSE is a significantly more effective NO generator at longer wavelength excitation than are other Fe(2)(mu-SR)(2)(NO)(4) esters for which R is a simple alkyl group such as CH(3)CH(2)- because of the much higher absorptivity of the pendant PPIX chromophore at these wavelengths and a modestly higher quantum yield. Fluorescence intensity and lifetime data indicate that the photoexcited porphyrin of PPIX-RSE is largely quenched by the energy transfer to the Fe(2)S(2)(NO)(4) cluster's core. However, a small fraction of this emission is not quenched, and it is proposed that PPIX-RSE may exist in solution as two conformers.
Conrado
Christa L
CL
Department of Chemistry & Biochemistry, University of California, Santa Barbara, CA 93106-9510, USA.
Wecksler
Stephen
S
Egler
Christian
C
Magde
Douglas
D
Ford
Peter C
PC
D007501:Iron / Q000737:chemistry*; D009569:Nitric Oxide / Q000737:chemistry; D009603:Nitroso Compounds / Q000737:chemistry*; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry; D010777:Photochemistry; D011524:Protoporphyrins / Q000737:chemistry*; D013455:Sulfur / Q000737:chemistry*
D009603:Nitroso Compounds; D009942:Organometallic Compounds; D011524:Protoporphyrins; D009569:Nitric Oxide; D013455:Sulfur; C028025:protoporphyrin IX; D007501:Iron