RESUMO
Experimental and density functional theory (DFT) studies are described that are focused on outlining the reactivity of the known photochemical nitric oxide precursor trans-Cr(cyclam)(ONO)(2)(+) ("CrONO", cyclam = 1,4,8,11-tetrazacycltetradecane). Studies in both aerated and deaerated aqueous media are described as are the roles of both the oxidant O(2) and a reductant such as glutathione in trapping the apparent Cr(IV) photoreaction intermediate trans-Cr(cyclam)(O)(ONO)(+). Also reported and characterized structurally is the Cr(V) product of long-term photolysis in the absence of reducing agents, the trans-dioxo species [trans-Cr(cyclam)(O)(2)](ClO(4)). Photosensitization experiments indicate that at least a significant fraction of the reaction occurs from the lowest energy doublet excited state(s). Lastly, cell culture experiments demonstrate that CrONO has little or no acute toxicity either before or after photolysis.
Assuntos
Cromo/química , Compostos Heterocíclicos/metabolismo , Monócitos/efeitos dos fármacos , Monócitos/efeitos da radiação , Óxido Nítrico , Fotólise , Fármacos Fotossensibilizantes/metabolismo , Pró-Fármacos/metabolismo , Linhagem Celular Tumoral , Cromo/metabolismo , Cristalografia por Raios X , Espectroscopia de Ressonância de Spin Eletrônica , Glutationa/química , Glutationa/metabolismo , Compostos Heterocíclicos/síntese química , Compostos Heterocíclicos/farmacologia , Humanos , Cinética , L-Lactato Desidrogenase/análise , Luz , Estrutura Molecular , Terapia de Alvo Molecular/métodos , Monócitos/patologia , Óxido Nítrico/química , Óxido Nítrico/metabolismo , Oxirredução/efeitos dos fármacos , Oxirredução/efeitos da radiação , Fotoquímica/métodos , Fotólise/efeitos dos fármacos , Fotólise/efeitos da radiação , Fármacos Fotossensibilizantes/síntese química , Fármacos Fotossensibilizantes/farmacologia , Fototerapia/métodos , Pró-Fármacos/síntese química , Pró-Fármacos/farmacologia , Estereoisomerismo , TermodinâmicaRESUMO
Described is the photoluminescence (PL) of water-soluble CdSe/ZnS core/shell quantum dots (QDs) as perturbed by salts of the chromium(III) complexes trans-Cr(cyclam)Cl2+ (1), trans-Cr(cyclam)(ONO)2+ (2), and trans-Cr(cyclam)(CN)2+ (3) (cyclam = 1,4,8,11-tetraazacyclo-tetradecane). The purpose is to probe the characteristics of such QDs as antennae for photosensitized release of bioactive agents (in the present case, the bioregulatory molecule NO) from transition metal centers. Addition of 1 or 2 to a QD solution results in concentration-dependent quenching of the band edge emission, but 3 has a minimal effect. Added KCl strongly attenuates the quenching by 1, and this suggests that the Cr(III) cations and the QDs form electrostatic assemblies via ion pairing on the negatively charged QD surfaces. Quenching by 2, a known photochemical NO precursor, was accompanied by photosensitized NO release. All three, however, do quench the broad red emission ( approximately 650-850 nm) attributed to radiative decay of surface trapped carriers. The effect of various concentrations of 1 on time-resolved PL and absorbance were explored using ultrafast spectroscopic methods. These observations are interpreted in terms of the Förster resonance energy-transfer mechanism for quenching of the band edge PL by multiple units of 1 or 2 at the QD surface, whereas quenching of the low-energy trap emission occurs via a charge-transfer pathway.