Artificial Control of Cell Signaling Using a Photocleavable Cobalt(III)–Nitrosyl Complex

Recent advances on the development of NO-releasing molecules (NORMs) for biomedical applications

Nitric oxide (NO) is an important biological messenger as well as a signaling molecule that participates in a broad range of physiological events and therapeutic applications in biological systems. However, due to its very short half-life in physiological conditions, its therapeutic applications are restricted. Efforts have been made to develop an enormous number of NO-releasing molecules (NORMs) and motifs for NO delivery to the target tissues. These NORMs involve organic nitrate, nitrite, nitro compounds, transition metal nitrosyls, and several nanomaterials. The controlled release of NO from these NORMs to the specific site requires several external stimuli like light, sound, pH, heat, enzyme, etc. Herein, we have provided a comprehensive review of the biochemistry of nitric oxide, recent advancements in NO-releasing materials with the appropriate stimuli of NO release, and their biomedical applications in cancer and other disease control.

A new photoactivable NO-releasing {Ru-NO}6 ruthenium nitrosyl complex with a tetradentate ligand containing aniline and pyridine moieties

A new type of photoactivable NO-releasing ruthenium nitrosyl complex, [Ru(EPBP)Cl(NO)], with a tetradentate ligand, N,N'-(ethane-1,2-diyldi-o-phenylene)-bis(pyridine-2-carboxamide) (= H₂ EPBP) was synthesized. Single crystal X-ray crystallography revealed that the complex has a distorted octahedral coordination geometry and NO is positioned at cis to Cl^- ion. NO-photolysis was observed under a white room light. The photodissociation of Ru-NO bond was identified by various techniques including X-ray crystallography, IR, UV/Vis absorption, electron paramagnetic resonance (EPR), and NMR spectroscopies. Quantum yields for the NO-photolysis of the complex in CH₃ OH, CHCl₃ , DMSO, CH₃ CN, and CH₃ NO₂ were measured to be 0.19-0.36 with 400 (±5) nm excitation. Density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations were performed to understand the details of the photodissociation of the complex. The calculations suggest that the NO photolysis is most likely initiated by the electronic transition from the aniline moiety π MOs (π (aniline)) of the EPBP^2- chelating ligand to the π-antibonding MO of Ru-NO (π*(Ru-NO)). Experimental and theoretical investigations indicate that the EPBP^2- ligand provides an effective platform forming ruthenium nitrosyl complexes useful for NO-photoreleasing.