Light-triggered and cysteine-mediated nitric oxide release from a biodegradable starch-based film

A new nitric oxide-releasing material produced with cassava starch is described. The ruthenium nitrosyl complex trans-[Ru(NH₃)₄(isn)NO](BF₄)₃ (RuNOisn; isn = isonicotinamide) is able to release NO upon either photolysis or chemical reduction. Impregnating this complex under mild conditions into cassava starch (CS) films produced a NO-delivery platform (CS_x-RuNOisn). Spectroscopic analysis of CS_x-RuNOisn indicates that the coordination sphere of RuNOisn remains intact during film production. Exposure of CS_x-RuNOisn to long wave UV-light (λ_irr = 355 nm) leads to NO release and formation of the paramagnetic photoproduct trans-[Ru^III(NH₃)₄isn(H₂O)]³⁺ in the CS film. Reaction of this aquaruthenium(iii) complex with aqueous nitrite regenerates RuNOisn in the film. Delivery of NO upon photolysis of CS_x-RuNOisn was verified by trapping with oxymyoglobin. Moreover, NO release upon chemical reduction was carried out using l-cysteine as a reductant. Cysteine-mediated NO delivery from CS_x-RuNOisn persisted for more than 7 h, during which physiologically relevant NO concentrations were liberated. These results suggest that CS_x-RuNOisn is a promising candidate for use in biological applications.