Photochemical and photophysical investigations of newly designed supramolecular structures composed of quantum dots and nitric oxide donors

Nitric oxide (NO), a ubiquitous messenger molecule in mammalian physiology, is also known to act as a potent gamma-radiation sensitizer. For this reason, there is considerable interest in the development of thermally stable compounds capable of controllably releasing NO. Such compounds could see broad application for the enhancement of existing cancer treatment strategies. In this context, photochemically activated NO precursors are attractive given the opportunity to control the location and timing of the signal leading to release of NO. With this in mind, the work described here exploits the extraordinary light absorbing capabilities of semiconductor quantum dots (QDs) both in the single photon excitation (SPE) and two photon excitation (TPE) regimes and demonstrates their potential applicability as photosensitizers for NO releasing prodrugs.; In this dissertation, new supramolecular structures will be described that are composed of chromium(III) complexes of cyclam (cyclam = 1,4,8,11-tetraazacyclotetradecane) both covalently bound to and electrostatically assembled on the surface of water soluble CdSe/ZnS QDs. Previous studies on the nitrito (ONO) derivatives of the chromium cyclam complexes indicated that they are photo-labile towards release of NO with quantum yields as high as 50%. However, these complexes lack absorption at long wavelengths (>600 run) where biological tissue penetration is enhanced. Investigations of the electrostatic assemblies in aqueous solution demonstrate that the Cr(III) complexes quench the QD photoluminescence (PL) obtained via either SPE (366-546 nm) or TPE (800 nm) excitation in a concentration dependent manner. Furthermore, in the electrostatic assemblies containing the dinitrito trans-Cr(cyclam)(ONO) 2+ cation and CdSe/ZnS QDs, photolysis of the assembly results in enhanced photochemical NO release (up to 50 fold more) as compared to the Cr(III) complexes alone. The photophysical and photochemical properties of these QD/chromium(III) cyclam structures are the subjects of this dissertation.