Partially Solvated Dinuclear Ruthenium Compounds Bridged by Quinoxaline-Functionalized Ligands as Ru(II) Photocage Architectures for Low-Energy Light Absorption

Dinuclear Tridentate Ru(II) Complex with Strong Near-Infrared Light-Triggered Anticancer Activity

The design of the dinuclear Ru(II) complex (Ru2) with strong near-infrared (NIR) absorption properties has been reported for efficient anticancer phototherapy. Under 700 nm LED light excitation, Ru2 exhibited remarkable synergistic type I/II photosensitization ability and photocatalytic activity toward intracellular biomolecules. Ru2 showed impressive 700 nm light-triggered anticancer activity under normoxia and hypoxia compared with the clinically used photosensitizer Chlorin e6. The mechanistic studies showed that Ru2 induced intracellular redox imbalance and perturbed the energy metabolism and biosynthesis in A549 cancer cells. Overall, this work provides a new strategy for developing efficient metal-based complexes for anticancer phototherapy under NIR light.

Study on antitumor activity of three ruthenium arene complexes in vitro

Three ruthenium arene complexes, namely {[(η6-p-cymene)Ru(Cl)]2(dpb)}(PF6)2 (1), [(η6-p-cymene)Ru(dpb)Cl](PF6) (2) and [(η6-p-cymene) Ru(dpb)py](PF6) (3) (dpb = 2,3-bis(2-pyridyl)benzo-quinoxaline, py = pyridine), were synthesized and their antitumor properties were introduced. Complexes 1-3 were characterized by 1H NMR, MS, and elemental analysis. As a binuclear ruthenium structure, the absorption of metal ligand electron transfer (MLCT) of 1 extended to 700 nm. Complex 1 was significantly hydrolyzed under dark conditions. The cytotoxicity in vitro study showed that complexes 1 and 2 are more toxic to human lung cancer cells (A549) and human cervial cancer cells (Hela) than cisplatin. Moreover, there was almost no cross-resistance between complex 1-2 and cisplatin. Under the irradiation at 478 nm, complexes 1-3 all produced singlet oxygen (1O2), and the 1O2 quantum yield of complex 1 in PBS is the highest among complexes 1-3. Complex 1 also produced 1O2 under 600 nm light irradiation. DNA gel electrophoresis showed that 1 caused the photocleavage of plasmid DNA. The hydrolysis rate of complex 1 was accelerated under light (λ > 600 nm). And the phototoxicity of complex 1 to Hela cells under light (λ > 600 nm) was much greater than its dark toxicity, which may be due to its generation of 1O2 and the promotion of its hydrolysis under long-wave light irradiation.

One pot synthesis of two potent Ag(I) complexes with quinoxaline ligand, X-ray structure, Hirshfeld analysis, antimicrobial, and antitumor investigations

In one pot, the self-assembly of AgNO₃ and 2-chloroquinoxaline (2Cl-quinox) in water-ethanol mixture afforded two novel crystalline Ag(I) complexes. The major product is the polymeric complex [Ag(2Cl-quinox)(NO₃)]_n; (1), while the minor product (2) comprises two molecules which are the monomeric [Ag(2Cl-quinox)₂(NO₃)]; (2a) and polymeric [Ag(2Cl-quinox)(NO₃)]_n; (2b) complexes. The single crystal X-ray structure revealed that 1 and 2b are made up of two-dimensional infinite sheets. In contrast, 2a is a monomeric complex which has a highly distorted tetrahedral geometry around Ag(I) center. In all cases, the 2Cl-quinox molecule acts as a terminal monodentate ligand. Complexes 1 and 2b have similar molecular structures and also have almost similar crystal packing. Using Hirshfeld surface analysis, the O…H hydrogen bonds and π-π stacking interactions contributed significantly to the molecular packing. Both complexes have broad-spectrum action towards multi drug-resistance bacteria. The most effective function of 2 is against Proteus morganii, with a MIC value of 8 μg/mL. Complex 2 (IC₅₀ = 5.93 ± 0.52 μg/mL) has remarkably greater cytotoxic effect against lung carcinoma (A-549) than cis-platin (IC₅₀ = 7.5 ± 0.69 μg/mL) and AgNO₃ (IC₅₀ = 14.7 ± 0.53 μg/mL). The higher Ag-content in 2 could be the main reason for its higher cytotoxicity than 1.

Zn Coordination and the Identity of the Halide Ancillary Ligand Dramatically Influence the Excited-State Dynamics and Bimolecular Reactions of 2,3-Di(pyridin-2-yl)benzo[g]quinoxaline

The optical properties of coordination complexes with ligands containing nitrogen heterocycles have been extensively studied for decades. One subclass of these materials, metal complexes utilizing substituted pyrazines and quinoxalines as ligands, has been employed in a variety of photochemical applications ranging from photodynamic therapy to organic light-emitting diodes. A vast majority of this work focuses on characterization of the metal-to-ligand charge-transfer states in these metal complexes; however, literature reports rarely investigate the photophysics of the parent pyrazine or quinoxaline ligand or perform control experiments utilizing metal complexes that lack low-lying charge-transfer (CT) states in order to determine how metal-atom coordination influences the photophysical properties of the ligand. With this in mind, we examined the steady-state and time-resolved photophysics of 2,3-di(pyridin-2-yl)benzo[g]quinoxaline (dpb) and explored how the coordination of ZnX₂ (X = Cl^-, Br^-, I^-) affects the photophysical properties of dpb. In dpb, we find that the dominant mode of deactivation from the singlet excited state is intersystem crossing (ISC). Coordination of ZnX₂ perturbs the relative energies of the ππ* and nπ* excited states of dpb, leading to drastically different rates of ISC as well as radiative and nonradiative decay in the [Zn(dpb)X₂] complexes compared to dpb. These differences in the rates change the dominant singlet-excited-state decay pathway from ISC in dpb to a mixture of ISC and fluorescence in [Zn(dpb)Cl₂] and [Zn(dpb)Br₂] and to nonradiative decay in [Zn(dpb)I₂]. Coordination of ZnX₂ and the choice of the halide ligand also have profound effects on the rate constants for excited-state bimolecular reactions, including triplet-triplet annihilation and oxygen quenching. These results demonstrate that metal coordination, even in complexes lacking low-lying CT states, and the choice of the ancillary ligand can dramatically alter the photophysical properties of chromophores containing nitrogen heterocycles.

The Development of Ru(II)-Based Photoactivated Chemotherapy Agents

Photoactivated chemotherapy (PACT) is a novel cancer treatment method that has drawn increasing attention due to its high selectivity and low side effects by spatio-temporal control of irradiation. Compared with photodynamic therapy (PDT), oxygen-independent PACT is more suitable for treating hypoxic tumors. By finely tuning ligand structures and coordination configurations, many Ru(II) complexes can undergo photoinduced ligand dissociation, and the resulting Ru(II) aqua species and/or free ligands may have anticancer activity, showing their potential as PACT agents. In this mini-review, we summarized the progress in Ru(II)-based PACT agents, as well as challenges that researchers in this field still face.

Acenaphtoquinoxaline as a selective fluorescent sensor for Hg (II) detection: experimental and theoretical studies

A new fluorescent chemosensor based on quinoxaline was successfully synthesized through a facile and green catalytic reaction of ortho-phenylenediamine (O-PDA) and acenaphthylene-1,2-dione in the presence of SBA-Pr-SO3H. Prepared a "switch-off" quinoxaline-based receptor to recognized Hg2+ ion in high selectively and, without any interference from other metal ions, was developed. The photophysical behavior of this fluorophore was studied in acetonitrile by using fluorescence spectra. The fluorescence properties of several cations to acenaphtoquinoxaline were investigated in acetonitrile, and the competition test displayed that the probe fluorescence changes were specific for Hg2+ ion. The obtained results have shown high selectivity and sensitivity only for Hg2+. Also, the detection limit was as low as 42 ppb, and a top linear trend was observed between the concentration of Hg2+ ions and fluorescence intensity. The binding stoichiometry between chemosensor L and Hg2+ was found to be 1:1. Moreover, a computational study was performed to obtain an electronic description of the fluorescence emission and quenching mechanisms. The optimized structures and binding mechanisms were supported with a high correlation and agreement by spectroscopy and DFT calculations.