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A simple and reliable colorimetric probe N,N′-bis-(4-diethylamino-2-hydroxybenzylidene)-1,10-phenanthroline-2,9-carbohydrazide (L) has been synthesised by reacting 4-(diethylamino)salicylaldehyde with 1,10-phenanthroline-2,9-dicarbohydrazide. The sensing ability of L was studied by its interactions with various f-block metal ions and other selected metal ions from s- and d-block by colorimetry, UV-visible spectrophotometry, and smartphone integrated red-green-blue (RGB) model in DMSO : H2O (7 : 3, v/v). The pale-yellow colour of L turns to wine-red upon interaction with uranyl ions (UO22+) and yellow-orange in the presence of Th4+, Zr4+, Fe3+, and Lu3+ ions. Other tested metal ions did not show any colour change of L. This color change offered a simple, quick, and consistent method for the selective and sensitive visual detection of trace levels of UO22+ ions without any need for sophisticated instruments. Sensor L exhibits two absorption bands at 358 and 389 nm due to ligand-to-ligand charge transfer (LLCT). Upon interaction of L with UO22+ and Th4+ ions, absorption bands are exhibited at 480 nm and 422 nm, respectively, due to ligand-to-metal charge transfer (LMCT). The UV-vis spectral studies indicated the formation of a 1 : 2 ligand-to-metal complex between L and UO22+ with an estimated association constant of 1.0 × 104 M−2. Using L, the concentration of UO22+ can be detected as low as 73 nM and 150 nM by spectrophotometry and RGB methods, respectively, without any interference from other tested ions with an RSD < 5% (n = 3). The binding mechanism was studied by 1H NMR titration, ESI mass, and FT-IR spectral analysis and was well supported by theoretical results. Overall, sensor L demonstrates promising analytical applicability for the detection of UO22+ ions in a semi-aqueous medium. [ABSTRACT FROM AUTHOR]

In this article, Ru(ii)–arene-2-pyridinylbenzoxazole complexes [(η6-p-cymene)RuCl(κ2-N,N-5-bromo-2-(pyridine-2-yl)benzo[d]oxazole)] (4) and [(η6-benzene)RuCl(κ2-N,N-5-bromo-2-(pyridine-2-yl)benzo[d]oxazole)] (5) and Ru(ii)–arene-2-quinolylbenzoxazole complexes [(η6-p-cymene)RuCl(κ2-N,N-5-bromo-2-(quinoline-2-yl)benzo[d]oxazole)] (4′) and [(η6-benzene)RuCl(κ2-N,N-5-bromo-2-(quinoline-2-yl)benzo[d]oxazole)] (5′) were synthesized and characterized using various spectroscopic techniques. Structural analysis indicates that the Ru(ii) centres are in a distinct mononuclear, one-sided octahedral [RuN6] coordination geometry with two neutral bidentate nitrogen donors in the bromobenzoxazole ligands. All four complexes exhibit three different electronic bands: a sharp band at 300–330 nm due to ligand-to-ligand charge transfer (LLCT); a band around 400 nm due to metal-to-ligand charge transfer; and a small broad peak at around 600 nm due to ligand-to-metal charge transfer. The fluorescence abilities of the four complexes were studied using the LLCT absorption peak as the excitation energy in dimethylsulfoxide: water (1 : 1, v/v), and the quantum yield was found to decrease in the order of 5′ ＞ 4′ ＞ 4 ＞ 5. Density functional theory calculations reveal that the highest-occupied molecular orbital is primarily located on the benzoxazole ring system, while the lowest-unoccupied molecular orbital is mainly located on the Ru atom, which implies possible charge transfer from ligand to metal. The binding strengths of the Ru(ii) complexes with DNA (5′ ＞ 4′ ＞ 4 ＞ 5) and bovine serum albumin (4′ ＞ 5′ ＞ 5 ＞ 4) were on the order of 105–106 and 103–105 M−1, respectively. The conductometric data reveal that all four complexes are non-electrolytic in nature, and viscosity decreases in the order of 5′ ＞ 4′ ＞ 4 ＞ 5. This might be due to the effective intercalation of 5′ compared to the other complexes. DNA and protein docking studies suggest that all the complexes interact with DNA through the minor groove and favourably occupy the active sites of proteins based on dipole–dipole interactions. Gel electrophoresis studies show that all complexes degrade plasmid DNA (1 kb) completely within 1 h of exposure time. MTT assay results indicate that all complexes exhibit highly selective cytotoxicity for two cancer cell lines (Caco-2 and HeLa) with respect to normal HEK-293 cells. Among the complexes, 4′ and 5 show the highest cytoselectivities for the Caco-2 and HeLa cell lines, respectively. [ABSTRACT FROM AUTHOR]