Photodissociation of nitric oxide from designed ruthenium nitrosyl complex: Studies on wound healing and antibacterial activity

A photoactivable NO releasing complex [Ru(L^1-2)(PPh₃)(NO)Cl₂](PF₆)(1a) have been synthesized by complex [RuL^1-2(PPh₃)₂Cl₂](1). Newly designed bidentate ligands, i.e., 4-methoxy-N'-phenyl-N'-(pyridin-2-ylmethyl)benzohydrazide(L¹) and 4-nitro-N'-phenyl-N'-(pyridin-2-ylmethyl)benzohydrazide (L²) were utilized to synthesize complex (1). Complex (1) was characterized by ESI-MS, and the solid structure of the complex [1a](PF₆) was acquired by X-ray crystallography. Different spectroscopic techniques were employed for the identification of ligands (L¹ and L²) and complexes (1 and [1a](PF₆)). Calculations employing DFT and TD-DFT were made better to understand the electronic properties of the complex [1a](PF₆). The photo liberation experiments were screened in the presence of visible light lamp. Griess assay experiment was used to quantify the photo released amount to NO. The photo liberated NO was successfully transferred to reduced myoglobin (Mb). The complex [1a](PF₆) at 50 μg/mL concentration was used for wound healing and antimicrobial activity on B16F1 mouse skin cells and Escherichia coli bacteria, respectively. In results, we observed a considerable wound healing activity of [1a](PF₆) complex after 36 h of incubation in the light-treated cells compared to the control medium, and also it shows more than 99% inhibition of bacterial cells after 1.5 h of treatment in the presence of light. These study suggested that this complex 1a](PF₆) could be utilized for topical delivery of NO for combating several dermatological infections.

Dissociation of Bipyridine and Coordination with Nitrosyl: Cyclometalated Ruthenium Nitrosyl Complex

A novel family of ruthenium nitrosyl complexes [Ru(bpy)(C^∧N)(MeCN)NO](PF₆)₂ (2a-2e, bpy = 2,2'-bipyridine, HC^∧N = 2-phenylpyridine and its derivatives) has been prepared by reacting cyclometalated ruthenium complexes [Ru(bpy)₂(C^∧N)][PF₆] (1a-1e) with NO⁺, which were comprehensively characterized by mass, IR, NMR, and UV-vis spectra as well as the single-crystal X-ray structure determinations. Herein, the coordination geometry of Ru atoms in 2a-2e is a distorted octahedron and {Ru^II-NO⁺}⁶ is present in these complexes. Theoretical calculations suggest that the reactions involving dissociation of one bipyridine and coordination with NO⁺ proceed spontaneously (ΔG < 0) and the transformation from 1a-1e to the intermediates is dominated by substituents (ΔG_RI varies from -1.19 to -1.53 eV), which influence the binding energy between Ru(II) and NO⁺ in complexes 2a-2e (-89.42 to -101.17 kcal/mol) and thus control the photorelease of NO on a certain scale. The weak absorption bands in the visible region could be attributed to the contribution of dπ(Ru^II) → π*(NO⁺), which were enhanced greatly under light, indicating the possible release of NO. The photoinduced NO, as well as singlet oxygen (¹O₂), was then confirmed by EPR spectra, and the amount of NO released from 2a-2e was estimated via Griess reagent assay. The cytotoxicity of these complexes with or without visible light irradiation was also investigated using an MTT assay.

Near-IR light-induced photorelease of nitric oxide (NO) on ruthenium nitrosyl complexes: formation, reactivity, and biological effects

Polypyridyl backbone nitrosyl complexes of ruthenium with the molecular framework [RuII(antpy)(bpy)NO+/˙]n+ [4](PF6)3 (n = 3), [4](PF6)2 (n = 2), where antpy = 4'-(anthracene-9-yl)-2,2':6',2''-terpyridine and bpy = 2,2'-bipyridine, were synthesized via a stepwise synthetic route from the chloro precursor [RuII(antpy)(bpy)(Cl)](PF6) [1](PF6) and [RuII(antpy)(bpy)(CH3CN)](PF6)2 [2](PF6)2 and [RuII(antpy)(bpy)(NO2)](PF6) [3](PF6). After column chromatographic purification, all the synthesized complexes were fully characterized using different spectroscopic and analytical techniques including mass spectroscopy, 1H NMR, FT-IR and UV-vis spectrophotometry. The Ru-NO stretching frequency of [4](PF6)3 was observed at 1941 cm-1, which suggests moderately strong Ru-NO bonding. A massive shift in the νNO frequency occurred at Δν = 329 cm-1 (solid) upon reducing [4](PF6)3 to [4](PF6)2. To understand the molecular integrity of the complexes, the structure of [3](PF6) was successfully determined by X-ray crystallography. The redox properties of [4](PF6)3 were thoroughly investigated together with the other precursor complexes. The rate constants for the first-order photo-release of NO from [4](PF6)3 and [4](PF6)2 were determined to be 8.01 × 10-3 min-1 (t1/2 ∼ 86 min) and 3.27 × 10-2 min-1 (t1/2 ∼ 21 min), respectively, when exposed to a 200 W Xenon light. Additionally, the photo-cleavage of Ru-NO occurred within ∼2 h when [4](PF6)3 was irradiated with an IR light source (>700 nm) at room temperature. The first-order rate constant of 9.4 × 10-3 min-1 (t1/2 ∼ 73 min) shows the efficacy of the system and its capability to release NO in the photo-therapeutic window. The released NO triggered by light was trapped by reduced myoglobin, a biologically relevant target protein. The one-electron reduction of [4](PF6)3 to [4](PF6)2 was systematically carried out chemically (hydrazine hydrate), electrochemically and biologically. In the biological reduction, it was found that the reduction is much slower with double-stranded DNA compared to a single-stranded oligonucleotide (CAAGGCCAACCGCGAGAAGATGAC). Moreover, [4](PF6)3 exhibited significant photo-toxicity to the VCaP prostate cancer cell line upon irradiation with a visible light source (IC50 ∼ 8.97 μM).

Ruthenium nitrosyl complexes with the molecular framework [RuII(dmdptz)(bpy)(NO)]n+ (dmdptz: N,N-dimethyl-4,6-di(pyridin-2-yl)-1,3,5-triazin-2-amine and bpy: 2,2′-bipyridine). Electronic structure, reactivity aspects, photorelease, and scavenging of NO

Two ruthenium nitrosyl complexes have been stabilized both in {Ru–NO}⁶ and {Ru–NO}⁷ configurations which show facile photocleavage of Ru–NO bond on exposure to visible light. The photo liberated NO is captured by reduced myoglobin.

The influence of L ligands on the {RuNO}6/7 bonding situation in cis-[Ru(NO)(NO2)L1–4]q complexes: a theoretical insight

The nature of the Ru–NO interaction before and after reduction of cis-[Ru(NO)(NO₂)L_1–4]^q complexes is modulated by the coordination environment of the metallic center, resulting in more labile on complexes with weak π-acceptor ligands.

Bidirectional non-innocence of the β-diketonato ligand 9-oxidophenalenone (L-) in [Ru([9]aneS3)(L)(dmso)]n, [9]aneS3 = 1,4,7-trithiacyclononane

The new compound [Ru(II)([9]aneS3)(L)(dmso)]ClO4 ([]ClO4) ([9]aneS3 = 1,4,7-trithiacyclononane, HL = 9-hydroxyphenalenone, dmso = dimethylsulfoxide) has been structurally characterised to reveal almost equal C-O bond distances of coordinated L(-), suggesting a delocalised bonding situation of the β-diketonato ligand. The dmso ligand is coordinated via the sulfur atom in the native (1+) and reduced states (1 and 1-) as has been revealed by X-ray crystallography and by DFT calculations. Cyclic voltammetry of 1+ exhibits two close-lying one-electron oxidation waves at 0.77 V and 0.94 V, and two similarly close one-electron reduction processes at -1.43 V and -1.56 V versus SCE in CH2Cl2. The electronic structures of 1n in the accessible redox states have been analysed via experiments (EPR and UV-vis-NIR spectroelectrochemistry) and by DFT/TD-DFT calculations, revealing the potential for bidirectional non-innocent behaviour of coordinated L(˙/-/˙2-). Specifically, the studies establish significant involvement of L based frontier orbitals in both the oxidation and reduction processes: [([9]aneS3)(dmso)Ru(III)-L˙](3+) (1(3+)) ⇌ [([9]aneS3)(dmso)Ru(III)-L(-)](2+)/[([9]aneS3)(dmso)Ru(II)-L˙](2+) (1(2+)) ⇌ [([9]aneS3)(dmso)Ru(II)-L(-)](+) (1(+)) ⇌ [([9]aneS3)(dmso)Ru(II)-L(˙2-)] (1) ⇌ [([9]aneS3)(dmso)Ru(II)-L(3-)](-)/[([9]aneS3)(dmso)Ru(I)-L(˙2-)](-) (1-).

Ru–NO and Ru–NO2bonding linkage isomerism in cis-[Ru(NO)(NO)(bpy)2]2+/+complexes – a theoretical insight

Calculated energy profile (kcal mol⁻¹) for linkage isomers relative to the ground state structure (GS)1aprior the monoelectronic reduction.