👤 Larráyoz IM

Flavins─one of nature's most ubiquitous organic cofactors─mediate proton and electron transfers in biological systems. Their heterocyclic (iso)alloxazine cores enable such reactivity through pronounced electro- and photochemical properties, as well as hydrogen bonding with surrounding residues. To harness these features in an organometallic context, we developed a redox-active, flavin-derived bidentate ligand (^allLH) that engages both primary and secondary coordination spheres. Coordination with Fe(II) yields an octahedral complex, (^allLH)₂FeX₂ (X = Cl, Br, OTf), stabilized by outer-sphere hydrogen bonds between the ligand and metal-bound (pseudo)halides. Upon deprotonation, ^allLH undergoes tautomerization to the isoalloxazine form (^isoL), generating a hydrogen-bonded aqua complex, (^isoL)₂Fe(OH₂)₂. Furthermore, treatment of (^allLH)₂FeCl₂ with cobaltocene triggers ligand tautomerization, affording [(^allLH)(^isoL)FeCl₂][CoCp₂] and highlighting the redox-responsive nature of the flavin scaffold. This work introduces a novel approach to repurpose flavin as a multifunctional ligand platform for constructing tunable coordination environments around transition metal centers, offering new opportunities in ligand design and bioinspired reactivity. Show less

Title: A new family of luminescent iridium complexes: synthesis, optical, and cytotoxic studies. Abstract: By using N,N-dibutyl-2,2'-bipyridine-4,4'-dicarboxamide as a diimine (dbbpy) and distinctive cyclometalated groups, this work reports a new family of cationic phosphorescent Ir(III) cyclometalated [Ir(C^N)2(N^N)]X compounds [C^N = difluorophenylpyridine (dfppy) a, 2,6-difluoro-3-(pyridin-2-yl)benzaldehyde (CHO-dfppy) b, and 2,6-difluoro-3-pyridin-2-yl-benzoic acid (COOH-dfppy) c; X = Cl-2a,b,c-Cl; X = PF6-2b,c-PF6]. For comparative purposes, the related complex [Ir(dfppy)2(H2dcbpy)]+ (3a-PF6) incorporating 3,3'-dicarboxy-2,2'-bipyridine as an auxiliary ligand (N^N = H2dcbpy) is also presented. All complexes have been fully characterized and their photophysical properties were investigated in detail. The theoretically calculated results obtained by density functional theory (DFT) and time-dependent density functional theory (TD-DFT) studies indicate that luminescence is derived from mixed 3ML'CT (Ir → N^N)/3LL'CT (C^N → N^N) excited states with the predominant metal-to-diimine charge transfer character. Their antineoplastic activity against tumour cell lines A549 (lung carcinoma) and HeLa (cervix carcinoma), as well as the nontumor BEAS-2B (bronchial epithelium) cell line was assessed and fluorescence microscopy studies were performed for their cellular localization. Among them, 2a-Cl exhibited the most potent anticancer activity, being higher than cisplatin. However, 2b-Cl and 2c-Cl,-PF6 were the least toxic, while 2b-PF6 and 3a-PF6 exhibited only moderate activity. Confocal microscopy studies for 2a-Cl suggest that complexes localize preferentially in the lysosomes and to a lesser extent in the cytoplasm, but ultimately causing damage to the mitochondria. Finally, the potential photodynamic behaviour of scarcely toxic complexes 2b-Cl, 2b-PF6, 2c-Cl and 3a-PF6 was also studied. Show less