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

• Published in: Photochemical & photobiological sciences Vol. 23; no. 1; pp. 153 - 162
• Main Authors: Semionova, Veronica V., Pozdnyakov, Ivan P., Grivin, Vjacheslav P., Eltsov, Ilia V., Vasilchenko, Danila B., Polyakova, Evgeniya V., Melnikov, Alexei A., Chekalin, Sergei V., Wang, Lei, Glebov, Evgeni M.
• Format: Journal Article
• Language: English
• Published: Cham Springer International Publishing 2024
• Subjects: Antineoplastic Agents - chemistry; Antineoplastic Agents - pharmacology; Biochemistry; Biomaterials; Chemistry; Chemistry and Materials Science; Original Papers; Oxygen; Photochemistry; Physical Chemistry; Plant Sciences; Singlet Oxygen; Photo-activated chemotherapy; Ultrafast TA spectroscopy; Photophysics; Dirhodium complexes; Laser flash photolysis; Photochemistry
• ISSN: 1474-905X; 1474-9092
• DOI: 10.1007/s43630-023-00509-y

Photophysics and photochemistry of a potential light-activated cytotoxic dirhodium complex [Rh 2 (µ-O 2 CCH 3 ) 2 (bpy)(dppz)](O 2 CCH 3 ) 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 1 O 2 formation. We proposed that singlet oxygen is produced by photoexcitation of weakly bound van der Waals complexes [Rh2…O 2 ], 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…O 2 ] complexes. Graphical abstract