A series of organometallic Ru(II)-arene complexes of the type [(η⁶-p-cymene)Ru(L)Cl](BF₄) 1–6, where L is 3-phenyl-1-pyridin-2-yl-imidazo[1,5-a]pyridine (L1), dimethyl-[4-(1-pyridin-2-yl-imidazo[1,5-a]pyridin-3-yl)phenyl]-amine (L2), diphenyl-[4-(1-pyridin-2-yl-imidazo[1,5-a]pyridin-3-yl)phenyl]amine (L3), 9-[4-(1-pyridin-2-yl-imidazo-[1,5-a]pyridin-3-yl)-phenyl]-9H-carbazole (L4), 9-ethyl-3-(1-pyridin-2-yl-imidazo-[1,5-a]pyridin-3-yl)-9H-carbazole (L5), and 10-ethyl-3-(1-pyridin-2-yl-imidazo[1,5-a]pyridin-3-yl)-10H-phenothiazine (L6), has been isolated and characterised by elemental analysis, ESI-MS, NMR and cyclic voltammetry. The photophysical properties of the complexes have been studied by electronic absorption and emission spectral techniques. All the ligands exhibit tuneable photoluminescence behaviour with the emission maximum spanning through the visible region (475–670 nm) in dichloromethane while all the complexes are emissive in acetonitrile. The single crystal X-ray structures of 2, 3 and 4 reveal that the complexes have a “piano stool” coordination geometry, comprising one π-bonded arene centroid, two σ-bonded nitrogen atoms from the chelating ligand and one Cl⁻ ion. From DNA induced EthBr emission quenching experiments the apparent DNA binding constants of the complexes (K_app) have been evaluated, which follows the order, 2 (1.3) < 1 (1.5) < 6 (1.7) < 4 (1.8) < 5 (2.4) < 3 (2.8 × 10⁵ M⁻¹). This trend reveals the role of ligand hydrophobicity on the DNA binding ability of complexes, the non-planar phenothiazine ring (6) and the specific interactions the planar carbazole chromophore (4, 5) make with DNA. The value of K_sv obtained as the slope of the linear plot of F₀/F vs. [complex] follows the order 1 (3.1) < 6 (8.2) < 2 (13.1) < 3 (15.7) < 5 (17.1) ≈ 4 (17.2 L M⁻¹), which supports the inferences from DNA binding experiments. All the complexes, except, 1 and 2 (>100 μM), exhibit in vitro cytotoxicity against A549 small lung cancer cell lines higher than cisplatin (∼69 μM), as revealed by both MTT (11.8–18.1 μM) and crystal violet staining (12.7–23.5 μM) assays, which is in agreement with their DNA and BSA binding affinity. Also, the complexes 3–6 cause higher cell death mainly through the apoptotic mode, as revealed by the observation of a higher percentage of apoptotic cells in AO/EB (36–43%) and Annexin V-Cy3 (36–45%) stained cancer cells.

Esculetin, a bioactive 6,7-dihydroxy derivative of coumarin, possesses pharmacological activities against obesity, diabetes, renal failure, and cardiovascular disorders (CVDs). Platelet activation plays a major role in CVDs. Thus, disrupting platelet activation represents an attractive therapeutic target. We examined the effect of esculetin in human platelet activation and experimental mouse models. At 10–80 μM, esculetin inhibited collagen- and arachidonic acid-induced platelet aggregation in washed human platelets. However, it had no effects on other agonists such as thrombin and U46619. Esculetin inhibited adenosine triphosphate release, P-selectin expression, hydroxyl radical (OH·) formation, Akt activation, and phospholipase C (PLC)γ2/protein kinase C (PKC) phosphorylation, but did not diminish mitogen-activated protein kinase phosphorylation in collagen-activated human platelets. Platelet function analysis indicated that esculetin substantially prolonged the closure time of whole blood. In experimental mice, esculetin significantly increased the occlusion time in thrombotic platelet plug formation and reduced mortality associated with acute pulmonary thromboembolism. However, it did not prolong the bleeding time. This study demonstrates that esculetin inhibits human platelet activation via hindering the PLCγ2–PKC cascade, hydroxyl radical formation, Akt activation, and ultimately suppressing platelet activation. Therefore, esculetin may act as an essential therapeutic agent for preventing thromboembolic diseases.

The bpy (IC₅₀, 7 nM) and 5,6-dmp (IC₅₀,13.57 nM) Cu(ii) complexes exhibit phenomenal cytotoxicity.

The Ni(ii) complexes of diazepane-based N₃-ligands with a cis-β configuration showed the conversion of atmospheric or pure CO₂ into cyclic carbonates under 1 atm pressure via a CO₂-bound nickel(ii) intermediate.