Systematic review on antibacterial photodynamic therapeutic effects of transition metals ruthenium and iridium complexes

The prevalence of antibiotic-resistant pathogenic bacteria poses a significant threat to public health and ranks among the principal causes of morbidity and mortality worldwide. Antimicrobial photodynamic therapy is an emerging therapeutic technique that has excellent potential to embark upon antibiotic resistance problems. The efficacy of this therapy hinges on the careful selection of suitable photosensitizers (PSs). Transition metal complexes, such as Ruthenium (Ru) and Iridium (Ir), are highly suitable for use as PSs because of their surface plasmonic resonance, crystal structure, optical characteristics, and photonics. These metals belong to the platinum family and exhibit similar chemical behavior due to their partially filled d-shells. Ruthenium and Iridium-based complexes generate reactive oxygen species (ROS), which interact with proteins and DNA to induce cell death. As photodynamic therapeutic agents, these complexes have been widely studied for their efficacy against cancer cells, but their potential for antibacterial activity remains largely unexplored. Our study focuses on exploring the antibacterial photodynamic effect of Ruthenium and Iridium-based complexes against both Gram-positive and Gram-negative bacteria. We aim to provide a comprehensive overview of various types of research in this area, including the structures, synthesis methods, and antibacterial photodynamic applications of these complexes. Our findings will provide valuable insights into the design, development, and modification of PSs to enhance their photodynamic therapeutic effect on bacteria, along with a clear understanding of their mechanism of action.

Lanthanide-grafted hollow bipyridine-based periodic mesoporous organosilicas as chemical sensors

We have synthesized a co-condensed hollow ethane-bipyridine periodic mesoporous organosilica (HEt-bpy-PMO) as a host material to anchor lanthanides for the purpose of developing a multifunctional chemical sensor. The host material was grafted with lanthanide chloride salts or complexes. The luminescence properties of the developed series of hybrid materials were studied in detail in the solid-state and after dispersing in water. The Eu3+ or Tb3+ singly incorporated materials were investigated for their use as ion sensors, showing ions selectivity towards Cu2+, Co2+ and Fe3+. Additionally, the Eu3+ or Tb3+ incorporated materials showed obvious luminescence quenching behavior towards acetone compared to other organic solvents, indicating excellent acetone sensing selectivity.

Ru- and Ir-complex decorated periodic mesoporous organosilicas as sensitizers for artificial photosynthesis

A versatile and facile strategy based on an inverse electron demand Diels-Alder reaction between 5-norbornen-2-yltriethoxysilane and a tetrazine derivative has been established for the synthesis of a new triethoxysilane precursor containing dipyridylpyridazine units. Such a precursor has been incorporated into the mesostructure of an ethylene-bridged periodic mesoporous organosilica (PMO) material through a one-pot synthesis via a co-condensation method. Upon attachment of Ru- and Ir-complexes to the pendant N-chelating heterocyclic ligands, the resulting decorated PMOs have acted as photosensitizers in artificial photosynthetic systems. The deposition of Pt on these PMOs has allowed us to obtain efficient photocatalytic materials for the hydrogen evolution reaction as a result of electron transfer from the light harvesting Ru- and Ir-complexes to the supported Pt nanoparticles through methyl viologen as an electron relay. They have exhibited total turnover number values of 573 and 846, respectively, under visible light irradiation. The role played by each component and the stability of the photocatalytic systems have been discussed. The present approach paves the way to the synthesis of different materials with coordination sites capable of forming surface complexes to be applied as sensitizers and catalysts.

Multi-stimuli Photo and Redox-active Nanostructured Mesoporous Silica Films on Transparent Electrodes

Silica matrices hosting transition metal guest complexes may offer remarkable platforms for the development of advanced functional devices. We report here the elaboration of ordered and vertically oriented mesoporous silica thin films containing covalently attached tris(bipyridine)iron derivatives using a combination of electrochemically assisted self-assembly (EASA) method and Huisgen cycloaddition reaction. Such a versatile approach is primarily used to bind nitrogen-based chelating ligands such as (4-[(2-propyn-1-yloxy)]4'-methyl-2,2'-bypiridine, bpy') inside the nanochannels. Further derivatization of the bpy'-functionalized silica thin films is then achieved via a subsequent in-situ complexation step to generate [Fe(bpy)₂ (bpy')]²⁺ inside the mesopore channels. After giving spectroscopic evidences for the presence of such complexes in the functionalized film, electrochemistry is used to transform the confined diamagnetic (S=0) F e L S b p y 2 b p y ' 2 + species to paramagnetic (S=1/2) oxidized F e L S b p y 2 b p y ' 3 + species in a reversible way, while blue light irradiation (λ=470 nm) enables populating the short-lived paramagnetic (S=2) F e H S b p y 2 b p y ' 2 + excited state. [Fe(bpy)₂ (bpy')]²⁺ -functionalized ordered films are therefore both electro- and photo-active through the manipulation of the oxidation state and spin state of the confined complexes, paving the way for their integration in optoelectronic devices.

Synthesis of novel photofunctional multinuclear complexes using a coupling reaction

Various photofunctional mononuclear complexes could be integrated into hetero-multinuclear complexes using the Mizoroki–Heck reaction.

Study of the redox properties of singlet and triplet Tris(2,2'-bipyridine)ruthenium(II) ([Ru(bpy)3]2+) in aqueous solution by full quantum and mixed quantum/classical molecular dynamics simulations

The oxidation of ground-state (singlet) and triplet [Ru(bpy)3](2+) were studied by full quantum-mechanical (QM) and mixed quantum/classical (QM/MM) molecular dynamics simulations. Both approaches provide reliable results for the redox potentials of the two spin states. The two redox reactions closely obey Marcus theory for electron transfer. The free energy difference between the two [Ru(bpy)3](2+) states amounts to 1.78 eV from both QM and QM/MM simulations. The two methods also provide similar results for the reorganization free energy associated with the transition from singlet to triplet [Ru(bpy)3](2+) (0.06 eV for QM and 0.07 eV for QM/MM). On the basis of single-point calculations, we estimate the entropic contribution to the free energy difference between singlet and triplet [Ru(bpy)3](2+) to be 0.27 eV, which is significantly greater than previously assumed (0.03 eV) and in contradiction with the assumption that the transition between these two states can be accurately described using purely energetic considerations. Employing a thermodynamic cycle involving singlet [Ru(bpy)3](2+), triplet [Ru(bpy)3](2+), and [Ru(bpy)3](3+), we calculated the triplet oxidation potential to be -0.62 V vs the standard hydrogen electrode, which is significantly different from a previous experimental estimate based on energetic considerations only (-0.86 V).

Direct visualization of dye and oligonucleotide diffusion in silica filaments with collinear mesopores

The diffusion dynamics of terrylene diimide (TDI) dye molecules and dye-labeled double-strand DNA were studied in micrometer long silica filaments containing collinear, oriented mesopores using single molecule fluorescence microscopy. TDI was used as a stable and hydrophobic probe molecule for single molecule structural analysis. We used template-free mesoporous silica filaments with 4 nm pore diameter and chemical functionalization with one or two types of trialkoxysilane groups to enhance the affinity between the host system and the guest molecules. Insights about the mesoporous structure as well as the translational and orientational diffusion dynamics of the guest molecules observed along micrometer long trajectories could be obtained. Additionally, the stability of DNA oligomers (15 base pairs, bp, about 5.3 nm long) within the mesopores was examined, showing no degradation of the oligonucleotide upon incorporation into the mesopores. Diffusion of both guest molecules could be controlled by exposure to vapors of water or chloroform; the latter both induced a reversible on-off control of the translational movement of the molecules.