Ruthenium nitrosyl (RuNO) complexes are promising photoactivated NO donors (photoNORMs), although their poor emissive properties and limited absorption within the phototherapeutic window limit their theragnostic potential. This paper explores a molecular design strategy directed towards overcoming these limitations on a set of RuNO complexes. A comparison is made between previous systems, reported by our group, and novel bridged analogues where the ligand framework contains phenyl or thienyl π-bridges. This structural modification aimed at extending the conjugation of the ligand scaffold, sensitize them toward visible-light excitation, and promote intraligand (IL) excitations to enhance the emissive properties of the complexes. In line with these expectations, spectroscopic and TD-DFT studies revealed pronounced bathochromic shifts for the thienyl derivatives (Δλ = 65–67 nm, λmax ≈ 471–487 nm) and a reduced energy barrier for IL excitations. All complexes displayed efficient NO photorelease under UV irradiation (365 nm), while thienyl-bridged systems additionally enabled NO release under visible-light irradiation (490 nm). Although luminescence and two-photon absorption measurements revealed only modest enhancements introduced by the π-bridges, this work identifies thienyl π-bridge incorporation as an effective strategy for promoting IL excitations and increase the potential theragnostic applications of RuNO photoNORMs.
The current year marks the fortieth anniversary of Albert Szent-Györgyi's death. He is generally remembered for the discovery of vitamin C, for the characterization of the role of dicarboxylic acids in the respiratory cycle, and for his work on muscle contraction. But the current article focuses on a different aspect of his scientific legacy: the “protein semiconductor” concept. The initial form of this proposal, first presented 85 years ago, hypothesized that proteins, being large assemblies of atoms packed with considerable regularity, may possess common energy bands, analogous to those of crystalline solids, along which an electron could carry energy from the site of its absorption to a distant site where that energy can perform useful work. This proposal, in its original form, encountered serious energetic objections, which Szent-Györgyi acknowledged by 1960; the revised version that he subsequently developed, in which the protein is “doped” by covalently incorporated electron acceptors, likewise failed to become established as a general mechanism of biological charge transport. Nevertheless, the larger underlying questions that he raised (are proteins in the business of electron transfer? is the movement of electrons an essential component of the living state? are quantum-mechanical events relevant to biology?) were monumental ones, raised far ahead of mainstream biochemical thinking. This article reviews his hypothesis and the modern experimental answers to the questions it raised, including biological electron tunnelling, proton-coupled electron transfer, hole hopping along tyrosine and tryptophan chains, and the calmodulin-gated electron conduit that is nitric oxide synthase.
The current year marks the fortieth anniversary of Albert Szent-Györgyi's death. He is generally remembered for the discovery of vitamin C, for the characterization of the role of dicarboxylic acids in the respiratory cycle, and for his work on muscle contraction. But the current article focuses on a different aspect of his scientific legacy: the "protein semiconductor" concept. The initial form of this proposal, first presented 85 years ago, hypothesized that proteins, being large assemblies of atoms packed with considerable regularity, may possess common energy bands, analogous to those of crystalline solids, along which an electron could carry energy from the site of its absorption to a distant site where that energy can perform useful work. This proposal, in its original form, encountered serious energetic objections, which Szent-Györgyi acknowledged by 1960; the revised version that he subsequently developed, in which the protein is "doped" by covalently incorporated electron acceptors, likewise failed to become established as a general mechanism of biological charge transport. Nevertheless, the larger underlying questions that he raised (are proteins in the business of electron transfer? is the movement of electrons an essential component of the living state? are quantum-mechanical events relevant to biology?) were monumental ones, raised far ahead of mainstream biochemical thinking. This article reviews his hypothesis and the modern experimental answers to the questions it raised, including biological electron tunnelling, proton-coupled electron transfer, hole hopping along tyrosine and tryptophan chains, and the calmodulin-gated electron conduit that is nitric oxide synthase.
