Anthracene-Containing Metallacycles and Metallacages: Structures, Properties, and Applications

Anthracene-Based Endoperoxides as Self-Sensitized Singlet Oxygen Carriers for Hypoxic-Tumor Photodynamic Therapy

Singlet oxygen is a crucial reactive oxygen species (ROS) in photodynamic therapy (PDT). However, the hypoxic tumor microenvironment limits the production of cytotoxic singlet oxygen through the light irradiation of PDT photosensitizers (PSs). This restriction poses a major challenge in improving the effectiveness of PDT. To overcome this challenge, researchers have explored the development of singlet oxygen carriers that can capture and release singlet oxygen in physiological conditions. Among these developments, anthracene-based endoperoxides, initially discovered almost 100 years ago, have shown the ability to generate singlet oxygen controllably under thermal or photo stimuli. Recent advancements have led to the development of a new class of self-sensitized anthracene-endoperoxides, with potential applications in enhancing PDT effects for hypoxic tumors. This review discusses the current research progress in utilizing self-sensitized anthracene-endoperoxides as singlet oxygen carriers for improved PDT. It covers anthracene-conjugated small organic molecules, metal-organic complexes, polymeric structures, and other self-sensitized nano-structures. The molecular structural designs, mechanisms, and characteristics of these systems will be discussed. This review aims to provide valuable insights for developing high-performance singlet oxygen carriers for hypoxic-tumor PDT.

Chiral SPINOL-Based Pt(II) Metallacycles For Immunogenic Cell Death

The incorporation of chirality endows Pt(II)-based metal-organic complexes (MOCs) with unique potentials in several fields such as nonlinear optics and chiral catalysis. However, the exploration of chiral Pt(II) metallacycles in biological responses remains underdeveloped. Herein, we designed and synthesized two chiral Pt(II) metallacycles 1 and 2 via the coordination-driven self-assembly of chiral 1,1'-spirobiindane-7,7'-diol (SPINOL)-derived ligands and cis-Pt(PEt3)2(OTf)2 (90°Pt). Their structures were well characterized by 1H NMR, 31P{1H} NMR, ESI-TOF-MS, and X-ray crystallography, and their photophysical properties were investigated by UV-vis absorption, fluorescence, and circular dichroism (CD) spectroscopies. Then, the antitumor activity of the two chiral metallacycles in vitro was further tested. Complexes 1 and 2 exhibited strong cytotoxicity, especially toward the A549 cells. The destruction of the mitochondrial function, the inhibition of the glutathione (GSH)/glutathione disulfide (GSSG) level, and the inactivation of superoxide dismutase (SOD) induced by complexes 1 and 2 led to the massive accumulation of reactive oxygen species (ROS). The overloaded ROS then triggered apoptotic cell death, and the release of damage-associated molecular patterns (DAMPs) further induced immunogenic cell death (ICD). To the best of our knowledge, this is the first example of Pt(II)-based metallacycles that can induce immunogenic cell death, providing a new strategy for the future design and construction of immune-modulating platinum agents in cancer therapy.

Aggregation-induced emission enhancement (AIEE) of tetrarhenium(I) metallacycles and their application as luminescent sensors for nitroaromatics and antibiotics

The self-assembly of tetrarhenium metallacycles [{Re(CO)₃}₂(μ-dhaq)(μ-N-N)]₂ (3a, N-N = 1,3-bis(1-butylbenzimidazol-2-yl)benzene; 3b, N-N = 1,3-bis(1-octylbenzimidazol-2-yl)benzene), (H₂-dhaq = 1,4-dihydroxy-9,10-anthraquinone) and [{Re(CO)₃}₂(μ-thaq)(μ-N-N)]₂ (4, N-N = 1,3-bis(1-butylbenzimidazol-2-yl)benzene), (H₂-thaq = 1,2,4-trihydroxy-9,10-anthraquinone) under solvothermal conditions is described. The metallacycles 3a,b and 4 underwent aggregation-induced emission enhancement (AIEE) in THF upon the incremental addition of water. TEM images revealed that metallacycle 3a in a 60% aqueous THF solution formed rectangular aggregates with a wide size distribution, while a 90% aqueous THF solution resulted in the formation of a mixture of nanorods and amorphous aggregates due to rapid and abrupt aggregation. UV-vis and emission spectral profiles supported the formation of nanoaggregates of metallacycles 3a,b and 4 upon the gradual addition of water to a THF solution containing metallacycles. Further studies indicated that these nanoaggregates were excellent probes for the sensitive and selective detection of nitro group containing picric acid (PA) derivatives as well as antibiotics.