A new, bioactive structural motif: Visible light induced DNA photobinding and oxygen independent photocleavage by RuII, RhIII bimetallics

Primary processes in photophysics and photochemistry of a potential light-activated anti-cancer dirhodium complex

Photophysics and photochemistry of a potential light-activated cytotoxic dirhodium complex [Rh2(µ-O2CCH3)2(bpy)(dppz)](O2CCH3)2, where bpy = 2,2'-bipyridine, dppz = dipyrido[3,2-a:2',3'-c]phenazine (Complex 1 or Rh2) in aqueous solutions was studied by means of stationary photolysis and time-resolved methods in time range from hundreds of femtoseconds to microseconds. According to the literature, Complex 1 demonstrates both oxygen-dependent (due to singlet oxygen formation) and oxygen-independent cytotoxicity. Photoexchange of an acetate ligand to a water molecule was the only observed photochemical reaction, which rate was increased by oxygen removal from solutions. Photoexcitation of Complex 1 results in the formation of the lowest triplet electronic excited state, which lifetime is less than 10 ns. This time is too short for diffusion-controlled quenching of the triplet state by dissolved oxygen resulting in 1O2 formation. We proposed that singlet oxygen is produced by photoexcitation of weakly bound van der Waals complexes [Rh2…O2], which are formed in solutions. If this is true, no oxygen-independent light-induced cytotoxicity of Complex 1 exists. Residual cytotoxicity deaerated solutions are caused by the remaining [Rh2…O2] complexes.

Co(II) coordination polymer: Treatment activity on the chronic obstructive pulmonary disease by reducing the inflammatory cytokines releasing

In the current study, using a semi-flexible quadritopic N-donor ligand, 5,5′-bipyrimidine (bpym), a new azide-based coordination polymer, [Co(bpym)(N3)2]n (1), was synthesized and structurally characterized via the single crystal X-ray diffraction along with the elemental analysis. Its treatment activity on the chronic obstructive pulmonary disease (COPD) would be evaluated and the related mechanism was explored. Firstly, the ELISA (enzyme linked immunosorbent assay) detection assay was performed and the levels of the inflammatory cytokines were measured. In addition to this, the NF-κB signaling pathway activation in the lung epithelial cells was measured with the real time RT-PCR (reverse transcription-polymerase chain reaction). Both six-membered rings containing nitrogen and the azide group on the designed drug molecule were confirmed by molecular docking simulation to have activities to the NF-kappaB.

Synthesis, DNA binding and antimicrobial studies on rhodium(II) complexes of dicyandiamide

The synthesis and characterization on four rhodium(II) complexes with the formula [Rh₂(CH₃COO)₂(AMUH)₂(dcda)₂](CH₃COO)₂(1),[Rh₂(CH₃COO)₂(AEUH)₂(dcda)₂](CH₃COO)₂(2),[Rh₂(CH₃COO)₂(APrⁿUH)₂(dcda)₂](CH₃COO)₂(3),[Rh₂(CH₃COO)₂(ABⁿUH)₂(dcda)₂](CH₃COO)₂(4), where AMUH = 1-amidino-O-methylurea, AEUH = 1-amidino-O-ethylurea, APrⁿUH = 1-amidino-O-n-propylurea, ABⁿUH = 1-amidino-O-n-butylurea, dcda = dicyandiamide are reported. The complexes were prepared by the reaction of dicyandiamide with rhodium(II) acetate in methanol (1), ethanol (2), n-propanol (3) and n-butanol (4) respectively and characterized by various techniques such as C, H, N analysis, FTIR, UV-Visible, EPR, conductance, SEM, EDX, powder XRD pattern and mass spectral studies. The interaction studies of the complexes with CT-DNA suggested the non-intercalative mode of binding for these complexes. The antimicrobial activity of the complexes against the tested microorganisms viz. Bacillus subtilis, Enterococcus faecium, Staphylococcus aureus and Escherichia coli, using the standard antibiotics streptomycin as positive control is also reported.

Mechanistic Investigation into DNA Modification by a RuII ,RhIII Bimetallic Complex

Despite significant progress in the treatment of cancer, there remains an urgent need for more effective therapies that also have less impact on patient wellbeing. Photodynamic therapy employs targeted light activation of a photosensitizer in selected tissues, thereby reducing off-target toxicity. Our group previously reported a Ru^II ,Rh^III bimetallic architecture that displays multifunctional covalent photomodification of DNA in the therapeutic window in an oxygen-independent manner, features that are essential for treating deep and hypoxic tumors. Herein, we explore the mechanism by which a new analogue, [(phen)₂ Ru(dpp)Rh(phen)Cl₂ ]³⁺ , or Ru^II -Rh^III , interacts with DNA. We established that Ru^II -Rh^III exhibits "light switch" behavior in the presence of DNA, undergoing strong electrostatic interactions that might involve groove binding. Furthermore, these noncovalent interactions play a major role in the covalent photobinding and photocleavage of DNA, which occur according to an oxygen-independent mechanism. Polymerase chain reaction (PCR) revealed that covalent modification of DNA by Ru^II -Rh^III , especially photobinding, is critical to inhibiting amplification, thus suggesting that the complex could exert its toxic activity by interfering with DNA replication in cells. This new structural motif, with phenanthroline at all three terminal ligand positions, has a number of properties that are promising for the continued refinement of photodynamic-therapy strategies.

Dual Photoreactivity of a New Rh2(II,II) Complex for Biological Applications

A new Rh₂(II,II) complex containing one dppn (benzo[i]dipyrido[3,2-a:2,3-c]phenazine) ligand with an extended π-system, cis-H,H-[Rh₂(OCCH₃NH)₂(dppn)(CH₃CN)₂]²⁺ (2), was synthesized and characterized. The dppn ligand, which serves as a DNA base pair intercalator, chelates to a single Rh center and is positioned trans to the amidato N atoms of the bridging acetamide ligand. This ligand also possesses a low-lying dppn-centered ³ππ* state that is advantageous for the sensitization of singlet oxygen (¹O₂), which complex 2 produced with a quantum yield, Φ _¹O2⁴⁶⁰, of 0.22(7) with 460 nm excitation. In addition, one equivalent of CH₃CN is released from 2 upon irradiation with visible light, generating cis-H,H-[Rh₂(OCCH₃NH)₂(dppn)(H₂O)(CH₃CN)]²⁺ in aqueous media with photoinduced ligand exchange quantum yield, Φ_LE⁴⁵⁰, of 0.0033(1). Thermal denaturation and relative viscosity studies are consistent with a π-stacking interaction of 2 with double-stranded DNA together with covalent binding to the duplex upon irradiation with visible light. Therefore, 2 exhibits dual photoreactivity towards DNA, making it potentially useful for photochemotherapy with enhanced activity relative to compounds able to achieve only one mode of cell death upon irradiation.

Control and utilization of ruthenium and rhodium metal complex excited states for photoactivated cancer therapy

The use of visible light to produce highly selective and potent drugs through photodynamic therapy (PDT) holds much potential in the treatment of cancer. PDT agents can be designed to follow an O2-dependent mechanism by producing highly reactive species such as 1O2 and/or an O2 independent mechanism through processes such as excited state electron transfer, covalent binding to DNA or photoinduced drug delivery. Ru(II)-polypyridyl and Rh2(II,II) complexes represent an important class of compounds that can be tailored to exhibit desired photophysical properties and photochemical reactivity by judicious selection of the ligand set. Complexes with relatively long-lived excited states and planar, intercalating ligands localize on the DNA strand and photocleave DNA through 1O2 production or guanine oxidation by the excited state of the chromophore. Photoinduced ligand substitution occurs through the population of triplet metal centered (3MC) excited states and facilitates covalent binding of the metal complex to DNA in a mode similar to cisplatin. Ligand photodissociation also provides a route to selective drug delivery. The ability to construct metal complexes with desired light absorbing and excited state properties by ligand variation enables the design of PDT agents that can potentially provide combination therapy from a single metal complex.

DNA photocleavage in anaerobic conditions by a Ru(ii) complex: a new mechanism

Photoinduced homolytic cleavage of the Ru–O bond of a novel Ru(ii) complex leads to formation of ligand-based reactive radicals capable of breaking DNA in an oxygen-dependent manner and Ru fragments capable of binding DNA covalently.