Investigations on the electronic effects of the peripheral 4′-group on 5-(4′-substituted)phenylazo-8-hydroxyquinoline ligands: zinc and aluminium complexes

Cytotoxic Pt(II) complexes containing alizarin: a selective carrier for DNA metalation

Many efforts have been made in the last few decades to selectively transport antitumor agents to their potential target sites with the aim to improve efficacy and selectivity. Indeed, this aspect could greatly improve the beneficial effects of a specific anticancer agent especially in the case of orphan tumors like the triple negative breast cancer. A possible strategy relies on utilizing a protective leaving group like alizarin as the Pt(II) ligand to reduce the deactivation processes of the pharmacophore enacted by Pt resistant cancer cells. In this study a new series of neutral mixed-ligand Pt(II) complexes bearing alizarin and a variety of diamine ligands were synthesized and spectroscopically characterized by FT-IR, NMR and UV-Vis analyses. Three Pt(II) compounds, i.e., 2b, 6b and 7b, emerging as different both in terms of structural properties and cytotoxic effects (not effective, 10.49 ± 1.21 μM and 24.5 ± 1.5 μM, respectively), were chosen for a deeper investigation of the ability of alizarin to work as a selective carrier. The study comprises the in vitro cytotoxicity evaluation against triple negative breast cancer cell lines and ESI-MS interaction studies relative to the reaction of the selected Pt(II) complexes with model proteins and DNA fragments, mimicking potential biological targets. The results allow us to suggest the use of complex 6b as a prospective anticancer agent worthy of further investigations.

Fluorescence-based method for fast quantification of active aluminums in natural and treated water

Fast quantitative determination of active aluminum (Al_a) in natural and treated water is extremely desirable. The fluorescence method based on complexation by 8-hydroxyquinoline (8-HQ) is highly promising, but the measurement could be severely interfered by hardness ions and natural organic matter (NOM). This study was devoted to refining the 8-HQ complexation-fluorescence method for measurement of Al_a by eliminating the interferences. Results showed that magnesium ions at a typical concentration in natural water could have a substantial positive interference, due to the formation of Mg-8-HQ complexes which have fluorescence regions similar to Al-8-HQ. NOM, represented by fulvic acid (FA), could not interfere the aluminum measurement considerably. It was primarily because 8-HQ has much stronger complexing ability than NOM with aluminum. Theoretical calculations showed that reducing the buffering pH (from 7.5) to 6.5 or using a masking ligand such as edetate (EDTA) could effectively alleviate the interference mainly caused by magnesium. Experimental results confirmed the theoretical predictions. Refined procedures were suggested for more accurate while fast determination of Al_a in natural or treated water. The refined method has a quantification limit of ~4 μg/L, a linear range of measurement up to 700 μg/L, and a relative standard deviation of ~0.8%.

Heteroleptic Zn(II) Complexes: Synthesis, Characterization and Photoluminescence Properties

Heteroleptic Zn (II) complexes containing 8-hydroxy quinoline as preliminary ligand and pyrazolone based derivatives as secondary ligand were synthesized and their structures confirmed by NMR, Mass, FT-IR, UV-vis and Elemental analysis. Theses complexes show good photoluminescence properties in solid and solution state in the range of 505-544 nm with quantum yield 0.38 to 0.50. Whereas these complexes also show good life time in the range of 0.037 to 0.043 ms. These complexes show shift in the range of 25-30 nm. in different polar and nonpolar solvents due to intramolecular charge transfer (ICT). The bandgap of these complexes is around ~2.60 eV. Highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of all complexes are determine by cyclic voltammetry it obtained in the range of and ~ (-5.29 eV) and ~(-2.69 eV). The energy band gap, frontier molecular orbitals (FMO) energy levels and geometrical structures were optimized using density functional theory (DFT) with B3LYP/6-31G* basic set on Spartan'18 software. All complexes displayed high thermal stability. Graphical Abstract Donor-Bridge- Accepter (D-B-A) based Heteroleptic Zn(II) complexes for OLEDs application.

Photoluminescent properties of novel design heteroleptic Zn(II) complexes

Three novel heteroleptic Zn(II) complexes containing 8-hydroxy quinoline and various pyrazolone-based derivatives were synthesized and their structures confirmed by ¹ H-nuclear magnetic resonance, mass spectrometry, Fourier transform infra-red spectroscopy, UV-vis analysis and element analysis. All three complexes showed good photoluminescence properties in the solid state and in solution in the maximum emission range from 475 to 490 nm with a quantum yield of 0.45 to 0.51. Absorption spectra revealed that the complexes possessed a maximum absorption range of 272-281 nm with a band gap of 2.59-2.68 eV. The highest occupied molecular orbital and lowest unoccupied molecular orbital of all the complexes were determine by cyclic voltammetry. All complexes displayed high thermal stability. These characteristics were assessed to find suitability for an alternative cheap light emitter for organic light-emitting diodes.

Distorted octahedral environments in tricarbonylrhenium(I) complexes of 5-[2-(2,4,6-trimethylphenyl)diazen-1-yl]quinolin-8-olate and 5,7-bis[2-(2-methylphenyl)diazen-1-yl]quinolin-8-olate

The Re(I) centres of two Re(I)-tricarbonyl complexes, viz. tricarbonyl(pyridine-κN){5-[2-(2,4,6-trimethylphenyl)diazen-1-yl]quinolin-8-olato-κ(2)N(1),O}rhenium(I), [Re(C23H21N4O)(CO)3], (I), and {5,7-bis[2-(2-methylphenyl)diazen-1-yl]quinolin-8-olato-κ(2)N(1),O}tricarbonyl(pyridine-κN)rhenium(I), [Re(C28H23N6O)(CO)3], (II), are facially surrounded by three carbonyl ligands, a pyridine ligand and either a 5-[2-(2,4,6-trimethylphenyl)diazen-1-yl]quinolin-8-olate [in (I)] or a 5,7-bis[2-(2-methylphenyl)diazen-1-yl]quinolin-8-olate [in (II)] ligand, in a slightly distorted octahedral environment. The crystal structure of (I) is stabilized by two intermolecular C-H···O interactions and that of (II) is stabilized by three intermolecular C-H···O hydrogen-bonding interactions.

Preparation of coordination polymers with 8-hydroxyquinoline azo benzensulfonic acid as a planar multidentate ligand and the study of their photochemical and photo-stability properties

The combination of ditopic ligand 4-(8-hydroxyquinoline-5-azo)-benzensulfonic acid (H2QBS) with metal ions (M = Na(+), Pb(2+), Zn(2+), Mn(2+), Cd(2+)) leads to five different coordination polymers (CPs): [Na2(QBS)(H2O)2]n (1 , 3D framework), {[Pb(QBS)(DMSO)]·2((i)PrOH)}n (2·2(i)PrOH, 2D layer), {[Zn(QBS)(DMSO)]·2DMSO}n (3·2DMSO, 1D chain), [Mn(QBS)((i)PrOH)(DMSO)]n (4, 1D ladder), and [Cd2(QBS)2(DMSO)2(H2O)4]n (5, 1D chain). All compounds were characterized by FT-IR, elemental analysis and TG analysis, and their structures were determined by single crystal X-ray diffraction. As expected, H2QBS acted as a multimode ligand and the azo bond in the trans-form existed in all compounds. Their photo-stability was also studied using irradiation from different light sources (450 nm, 365 nm and 254 nm). Under blue light (450 nm) and lower energy UV light (365 nm), the colors of all compounds were well preserved and the absorption spectra show slight changes. However, when irradiated using higher energy UV light (254 nm), the coordination interaction between the metal ions and the ligand was disassociated and the color faded.

Metal quinolinolate-fullerene(s) donor-acceptor complexes: evidence for organic LED molecules acting as electron donors in photoinduced electron-transfer reactions

Tris(quinolinolate)aluminum(III) (AlQ3) is the most widely used molecule in organic light-emitting devices. There exists a strong demand for understanding the photochemical and photophysical events originating from this class of molecules. This paper provides the first report on the electron donor ability of MQ(n) (M = Al or Zn for n = 3 or 2) complexes covalently connected to a well-known electron acceptor, fullerene. To accomplish this, fullerene was functionalized with 8-hydroxyquinoline at different ligand positions and their corresponding zinc(II) and aluminum(III) complexes were formed in situ. The weakly fluorescent metal quinolinolate-fullerene complexes formed a new class of donor-acceptor conjugates. The stoichiometry and structure of the newly formed metal quinolinolate-fullerene complexes were established from various spectroscopic methods including matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and computational density functional theory studies. Electrochemical studies involving free-energy calculations suggested the possibility of photoinduced electron transfer from excited metal-quinolinolate complex to the appended fullerene entity. Femtosecond transient absorption studies confirmed such a claim and analysis of the kinetic data allowed us to establish the different photophysical events in sufficient detail. The novel features of this class of donor-acceptor conjugates include faster charge recombination compared to charge separation and decay of the charge-separated state to populate the low-lying fullerene triplet state in competition with direct charge recombination to the ground state.

Heterocyclic amines for the construction of peptoid oligomers bearing multi-dentate ligands

Peptoids are oligomers of N-substituted glycine that can be readily assembled using haloacetic acids and primary amines as synthons. Here, we report the synthesis and characterization of three new heterocyclic amines, 2-(2,2':6',2''-terpyridine-4'-yloxy) ethylamine, 2-(1,10-phenanthroline-5-yloxy) ethylamine and 8-hydroxy-2-quinolinemethylamine, and their incorporation into a series of different peptoid oligomer sequences. Since the heterocycles are all known to coordinate metal ions, the peptidomimetic products are designed to bind metal species with the potential for applications in catalysis and materials science.

Experimental and computational evidence of the intermolecular motifs in the crystal packing of luminescent pentacoordinated gallium(iii) complexes

This paper reports the synthesis, characterization, photophysical and structural properties of the homologous series of good emitting pentacoordinated GaQ'2L complexes 1-3, where Q' is 2-methyl-quinolin-8-olate and L is a phenolate substituted in para position with respect to the oxygen donor atom. A combined approach between the experimental structural analysis (i.e. the molecular fragments involved in intermolecular pi-pi interactions) and the computational study (i.e. the nature of the molecular orbitals residing therein) is discussed in order to compare the charge transport aptitude of complexes 1-3, in relation to the facing of their LUMO/LUMO, HOMO/HOMO and HOMO/LUMO arising from the molecular packing. The different phenolate ligands significantly change the packing characteristics of 1-3, with indirect effects on the electron hopping kinetics responsible for conduction in amorphous thin films. The observed preference for pyridyl-pyridyl stacking proves a faster electron conduction in comparison to hole conduction in the three complexes studied.

Blue emitting pentacoordinated Al(iii) complexes based on 2-methylquinolin-8-olate and substituted phenolate ligands. The role of phenolate derivatives on emission and absorption properties

This paper reports the synthesis, characterisation and photophysical investigation of the homologous series of blue-emitting pentacoordinated AlQ'(2)L complexes 1-6, where Q' is 2-methylquinolin-8-olate and L is a phenolate substituted in para to the oxygen donor atom. Both electron attracting and electron releasing substituents have been considered. Also binuclear complexes of formula Q'(2)Al-L'-AlQ'(2), where L' = OC(6)H(4)C(6)H(4)O, OC(6)H(4)(CH(2))(3)C(6)H(4)O and OC(6)H(4)C(CH(3))(2)C(6)H(4)C(CH(3))(2)C(6)H(4)O have been synthesised and characterised. These are interesting blue-emitting materials for OLED (organic light emitting diode) fabrication. A comparison between computational and experimental results allowed the description of the absorption and fluorescence processes. A study of the frontier orbitals involved in the electric conduction and fluorescence emission has been performed. Influences of the phenolate-based ligands on the compounds spectroscopy have been particularly taken into account.