A two-photon antenna for photochemical delivery of nitric oxide from a water-soluble, dye-derivatized iron nitrosyl complex using NIR light.
The experiments described here demonstrate the use of two-photon excitation (TPE) to sensitize nitric oxide (NO) release from a dye-derivatized iron/sulfur/nitrosyl cluster Fe2(mu-RS)2(NO)4 (Fluor-RSE, RS = 2-thioethyl ester of fluorescein) with near-infrared (NIR) light in the form of femtosecond pulses from a Ti:sapphire laser. TPE at 800 nm leads both to weak fluorescence from the organic chromophore at lambda(max) = 532 nm and to NO labilization from the cluster. Since the emission from the reference compound Fluor-Et (the ethyl ester of fluorescein) under identical conditions (50/50 CH3CN/phosphate buffer (1 mM) at pH 7.4) is considerably more intense, the weaker emission from Fluor-RSE and the NO generation indicate that the fluorescein excited states initially formed by TPE are largely quenched by energy transfer to the cluster core. The two-photon absorption (TPA) cross section of Fluor-RSE at 800 nm was determined to be delta = 63 +/- 7 GM via the TPA photoluminescence technique. This can be compared to the TPA cross section of 36 GM reported for fluorescein dye in pH 11 aqueous solution and of 32 +/- 3 GM for Fluor-Et measured under conditions comparable to those used for Fluor-RSE. Pulse intensity dependence studies showed that the quantity of NO released from the latter as the result of NIR photoexcitation follows a quadratic relationship to excitation intensity, consistent with the expectation for a TPE process. These studies demonstrate the potential utility of a two-photon antenna for sensitization of the photochemical release of an active agent (in this case, NO) from a photoactive pro-drug.
Department of Chemistry and Biochemistry, University of California, Santa Barbara, Santa Barbara, California 93106-9510, USA.
Stephen R
SR
Wecksler
Alexander
A
Mikhailovsky
Dmitry
D
Korystov
Peter C
PC
Ford
D005452:Fluoresceins / Q000737:chemistry; D007259:Infrared Rays; D007501:Iron / Q000737:chemistry*; D009569:Nitric Oxide / Q000737:chemistry*; D020030:Nitric Oxide Donors / Q000737:chemistry*; D009589:Nitrogen Oxides / Q000737:chemistry*; D010777:Photochemistry; D017785:Photons; D011355:Prodrugs / Q000737:chemistry; D012995:Solubility; D014867:Water / Q000737:chemistry
D005452:Fluoresceins; D020030:Nitric Oxide Donors; D009589:Nitrogen Oxides; D011355:Prodrugs; D014867:Water; D009569:Nitric Oxide; C073661:dinitrosyl iron complex; D007501:Iron