Crystal structures, antioxidation and DNA binding properties of Dy(III) complexes with Schiff-base ligands derived from 8-hydroxyquinoline-2-carboxaldehyde and four aroylhydrazines

Tailoring the Use of 8-Hydroxyquinolines for the Facile Separation of Iron, Dysprosium and Neodymium

Permanent magnets (PMs) containing rare earth elements (REEs) can generate energy in a sustainable manner. With an anticipated tenfold increase in REEs demand by 2050, one of the crucial strategies to meet the demand is developing of efficient recycling methods. NdFeB PMs are the most widely employed, however, the similar chemical properties of Nd (20-30 % wt.) and Dy (0-10 % wt.) make their recycling challenging, but possible using appropriate ligands. In this work, we investigated commercially available 8-hydroxyquinolines (HQs) as potential Fe/Nd/Dy complexing agents enabling metal separation by selective precipitation playing on specific structure/property (solubility) relationship. Specifically, test ethanolic solutions of nitrate salts, prepared to mimic the main components of a PM leachate, were treated with functionalized HQs. We demonstrated that Fe3+ can be separated as insoluble [Fe(QCl,I)3] from soluble [REE(QCl,I)4]- complexes (QCl,I -: 5-Cl-7-I-8-hydoxyquinolinate). Following that, QCl - (5-Cl-8-hydroxyquinolinate) formed insoluble [Nd3(QCl)9] and soluble (Bu4N)[Dy(QCl)4]. The process ultimately gave a solution phase containing Dy with only traces of Nd. In a preliminary attempt to assess the potentiality of a low environmental impact process, REEs were recovered as oxalates, while the ligands as well as Bu4N+ ions, were regenerated and internally reused, thus contributing to the sustainability of a possible metal recovery process.

Promising anticancer agents based on 8-hydroxyquinoline hydrazone copper(II) complexes

We report the synthesis and characterization of a group of benzoylhydrazones (Lⁿ) derived from 2-carbaldehyde-8-hydroxyquinoline and benzylhydrazides containing distinct para substituents (R = H, Cl, F, CH₃, OCH₃, OH and NH₂, for L^1-7, respectively; in L⁸ isonicotinohydrazide was used instead of benzylhydrazide). Cu(II) complexes were prepared by reaction of each benzoylhydrazone with Cu(II) acetate. All compounds were characterized by elemental analysis and mass spectrometry as well as by FTIR, UV-visible absorption, NMR or electron paramagnetic resonance spectroscopies. Complexes isolated in the solid state (1-8) are either formulated as [Cu(HL)acetate] (with L¹ and L⁴) or as [Cu(Lⁿ)]₃ (n = 2, 3, 5, 6, 7 and 8). Single crystal X-ray diffraction studies were done for L⁵ and [Cu(L⁵)]₃, confirming the trinuclear formulation of several complexes. Proton dissociation constants, lipophilicity and solubility were determined for all free ligands by UV-Vis spectrophotometry in 30% (v/v) DMSO/H₂O. Formation constants were determined for [Cu(LH)], [Cu(L)] and [Cu(LH_-1)] for L = L¹, L⁵ and L⁶, and also [Cu(LH_-2)] for L = L⁶, and binding modes are proposed, [Cu(L)] predominating at physiological pH. The redox properties of complexes formed with L¹, L⁵ and L⁶ are investigated by cyclic voltammetry; the formal redox potentials fall in the range of +377 to +395 mV vs. NHE. The binding of the Cu(II)-complexes to bovine serum albumin was evaluated by fluorescence spectroscopy, showing moderate-to-strong interaction and suggesting formation of a ground state complex. The interaction of L¹, L³, L⁵ and L⁷, and of the corresponding complexes with calf thymus DNA was evaluated by thermal denaturation. The antiproliferative activity of all compounds was evaluated in malignant melanoma (A-375) and lung (A-549) cancer cells. The complexes show higher activity than the corresponding free ligand, and most complexes are more active than cisplatin. Compounds 1, 3, 5, and 8 were selected for additional studies: while these complexes induce reactive oxygen species and double-strand breaks in both cancer cells, their ability to induce cell-death by apoptosis varies. Within the set of compounds tested, 8 emerges as the most promising one, presenting low IC₅₀ values, and high induction of oxidative stress and DNA damage, which eventually lead to high rates of apoptosis.

Copper(ii) complexes supported by modified azo-based ligands: Nucleic acid binding and molecular docking studies

Two new copper(ii) complexes [CuL1] (1) and [CuL2] (2) derived from azo-based ligands 2-hydroxy-5-p-tolylazo-benzaldehyde (HL1) and 1-(2-hydroxy-5-p-tolylazo-phenyl)-ethan-one (HL2) were synthesized. These two ligands and their metal complexes were characterized by elemental analysis, nuclear magnetic resonance (1H and 13C), infrared, and UV/Vis spectroscopic techniques. Spectroscopy and other theoretical studies reveal the geometry of copper complexes, and their binding affinity towards nucleic acids are major groove binding.

Dysprosium(III) compounds assembled via a versatile ligand incorporating salicylic hydrazide and 8-hydroxyquinolin units: syntheses, structures and magnetic properties

Assembly of dysprosium(iii) salts with a multidentate ligand H3L ((2-hydroxy)-N'-((8-hydroxyquinolin-2-yl)methylene)-benzohydrazide) affords a variety of products with different topological structures, namely [Dy(H2L)(HL)]·CH3OH (1), [Dy2(HL)2(C6H5COO)2(CH3OH)2]·3CH3OH (2), [Dy2(HL)2(NO3)2(DMF)4]·4DMF (3), [Dy4L4(CH3OH)4]·2CH3OH·4H2O (4) and ([Dy4(HL)4(C6H5COO)4(CH3OH)(H2O)]·2CH3OH·CH3CN·H2O)n (5). The versatile and flexible coordination modes of phenoxo groups from salicylic hydrazide prove to be a key factor in the assembly of corresponding structures depending upon the reaction conditions. It is noteworthy that ligands HL2- act as a long-distance link and further connect the Dy2 fragments into an infinite 1D chain due to the conformational flexibility resulting from the rotatable C-C bond in 5. Furthermore, the magnetic measurements were performed on all complexes. The dc magnetic susceptibility data evidence distinct magnetic coupling interactions in the dinuclear complexes 2 (antiferromagnetic) and 3 (ferromagnetic) despite their similar structures, and only complex 3 shows slow relaxation behavior of magnetization. Ab initio calculations and electrostatic potential analysis on complexes 2, 3, and three other complexes (6, 7, 8) incorporating different kinds of ligands reveal the important interrelationship of magnetic anisotropy, magnetic coupling interactions and SMM properties.

In vitro investigation of biophysical interactions between Ag(I) complexes of bis(methyl)(thia/selena)salen and ct-DNA via multi-spectroscopic, physicochemical and molecular docking methods along with cytotoxicity study

Four silver(I) (Ag(I)) complexes: 1.PF₆ , 2.PF₆ , 1.ClO₄ and 2.ClO₄ of bis(methyl)thia salen (1) and bis (methyl)selena salen (2) with two different counter anions (PF₆ ^- and ClO₄ ^- ) have been investigated for DNA binding properties. In vitro interactional association between the Ag(I) complexes and ct-DNA has been examined by performing spectroscopic titrations on absorption spectrophotometer and fluorescence spectrophotometer. A competitive binding study has also been done using a fluorescence spectrophotometer with ethidium bromide as a classical intercalator. The spectroscopic methods revealed a major groove. Viscometry and agarose gel electrophoresis experiments have also been performed as physicochemical methods to confirm the binding of complex molecules with DNA. Molecular docking analysis has been executed to obtain the theoretical insight into the mode of binding. The docking study demonstrated the major groove binding of all four complexes to the DNA with electrostatic metal-phosphate interactions (between the metal and the backbone of DNA) and hydrophobic interactions. Cytotoxicity of the complexes has been studied on the Human Fibroblast foreskin (HFF) cell line. The cytotoxicity results showed positive gesture for moving ahead to the next level of screening; the values were above 10 μM which are appreciated for the normal cell lines.

Potential molecular and graphene oxide chelators to dissolve amyloid-β plaques in Alzheimer's disease: a density functional theory study

The onset of Alzheimer's disease (AD) is caused by amyloid-β (Aβ) aggregation. Elevated levels of metals, specifically copper, zinc, iron, and aluminum, accumulate in senile Aβ; plaque deposits, disrupting normal brain homeostasis and cognitive functions. In this investigation, we studied the potential of several molecular and graphene oxide chelators to be used for future AD research and chelation therapy. To understand the interactions between selected metals (Cu, Zn, Fe, and Al), the Aβ peptide, and various potential metal chelating compounds, we implemented the density functional theory (DFT) method to calculate the binding energies of each metal-molecule complex. The binding energy of each metal-chelator complex was compared with that of the metal-Aβ compound to determine the chelation potential of the selected chelator. The potential chelating agents studied were 8-hydroxyquinoline-2-carboxaldehyde isonicotinoyl hydrazone (INNHQ), 8-hydroxyquinoline-2-carboxaldehyde 2-furoyl hydrazone (HQFUH), quercetin, and graphene oxide (GO). Our calculated binding energies revealed that the HQFUH molecule holds direct ability to chelate copper, zinc, iron, and aluminum. In addition, the GO complex with a 12.5% oxygen concentration demonstrates aluminum chelation ability. Our results demonstrate that HQFUH and GO can be used in future AD drug development research and therapy to target toxic metal-Aβ interactions and reduce Aβ aggregation.

Chemistry of mixed-ligand oxidovanadium(IV) complexes of aroylhydrazones incorporating quinoline derivatives: Study of solution behavior, theoretical evaluation and protein/DNA interaction

A series of eight hexacoordinated mixed-ligand oxidovanadium(IV) complexes [VO(L^x)(L^N-N)] (1-8), where L^x = L¹ - L⁴ are four differently substituted ONO donor aroylhydrazone ligands and L^N-N are N,N-donor bases like 2,2'-bipyridine (bipy) (1, 3, 5 and 7) and 1,10-phenanthroline (phen) (2, 4, 6 and 8), have been reported. All synthesized complexes have been characterized by various physicochemical techniques and molecular structures of 1 and 6 were determined by X-ray crystallography. With a view to evaluate the biological activity of the V^IVO species, the behavior of the systems V^IVO²⁺/L^x, V^IVO²⁺/L^x/bipy and V^IVO²⁺/L^x/phen was studied as a function of pH in a mixture of H₂O/DMSO 50/50 (v/v). DFT calculations allowed finding out the relative stability of the tautomeric forms of the ligands, and predicting the structure of vanadium complexes and their EPR parameters. To study their interaction with proteins, firstly the ternary systems V^IVO²⁺/L^1,2 with 1-methylimidazole, which is a good model for histidine binding, were examined. Subsequently the interaction of the complexes with lysozyme (Lyz), cytochrome c (Cyt) and bovine serum albumin (BSA) was studied. The results indicate that the complexes showed moderate binding affinity towards BSA, while no interaction takes place with lysozyme and cytochrome c. This could be explained with the higher number of accessible coordinating and polar residues for BSA than for Lyz and Cyt. Further, the complexes were also evaluated for their DNA binding propensity through UV-vis absorption titration and fluorescence spectral studies. These results were consistent with BSA binding affinity and showed moderate binding affinity towards CT-DNA.

Synthesis and characterization of Pt(ii)-based potent anticancer agents with minimum normal cell toxicity: their bio-activity and DNA-binding properties

The Cis-Pt(ii)-dichloro complex and its different intercellular derivates show good DNA-binding, comparable anticancer properties and less normal cell toxicity than cisplatin, and initiates cell death through apoptosis.

High local coordination symmetry around the spin center and the alignment between magnetic and symmetric axes together play a crucial role in single-molecule magnet performance

A tetradentate 8-hydroxyquinoline-based acyl hydrazine ligand was used to construct a series of mono/di-nuclear dysprosium single-molecule magnets (SMMs) with nearly ideal pentagonal bipyramid coordination geometry (D_5h).

Single-molecule magnet behaviour in a tetranuclear DyIII complex formed from a novel tetrazine-centered hydrazone Schiff base ligand

A tetranuclear dysprosium complex, bridged by a novel tetrazine-centered Schiff base ligand, exhibits ferromagnetic exchange coupling and a large anisotropic barrier.

Evaluation of some quinoline-based hydrazone derivatives as insecticidal agents

Seven-day mortality rates of compounds 3c, 3e, 4g, 4h and 6f at 1 mg mL⁻¹ against three-day-old larvae of Spodoptera litura were all greater than 93%. They may be considered as promising insecticidal candidates.

Low-dimensional compounds containing bioactive ligands. Part VI: Synthesis, structures, in vitro DNA binding, antimicrobial and anticancer properties of first row transition metal complexes with 5-chloro-quinolin-8-ol

A series of new 3d metal complexes with 5-chloro-quinolin-8-ol (ClQ), [Mn(ClQ)2] (1), [Fe(ClQ)3] (2), [Co(ClQ)2(H2O)2] (3), [Ni(ClQ)2(H2O)2] (4), [Cu(ClQ)2] (5), [Zn(ClQ)2(H2O)2] (6), [Mn(ClQ)3]·DMF (7) and [Co(ClQ)3]·DMF·(EtOH)0.35 (8) (DMF=N,N-dimethylformamide), has been synthesized and characterized by elemental analysis, IR spectroscopy and TG-DTA thermal analysis. X-ray structure analysis of 7 and 8 revealed that these molecular complexes contain three chelate ClQ molecules coordinated to the central atoms in a deformed octahedral geometry and free space between the complex units is filled by solvated DMF and ethanol molecules. Antimicrobial activity of 1-6 was tested by determining the minimum inhibitory concentration and minimum microbicidal concentration against 12 strains of bacteria and 5 strains of fungi. The intensity of antimicrobial action varies depending on the group of microorganism and can be sorted: 1>ClQ>6>3/4>2>5. Complexes 1-6 exhibit high cytotoxic activity against MDA-MB, HCT-116 and A549 cancer cell lines. Among them, complex 2 is significantly more cytotoxic against MDA-MB cells than cisplatin at all tested concentrations and is not cytotoxic against control mesenchymal stem cells indicating that this complex seems to be a good candidate for future pharmacological evaluation. Interaction of 1-6 with DNA was investigated using UV-VIS spectroscopy, fluorescence spectroscopy and agarose gel electrophoresis. The binding studies indicate that 1-6 can interact with CT-DNA through intercalation; complex 2 has the highest binding affinity. Moreover, complexes 1-6 inhibit the catalytic activity of topoisomerase I.

Oxidovanadium(v) complexes of aroylhydrazones incorporating heterocycles: synthesis, characterization and study of DNA binding, photo-induced DNA cleavage and cytotoxic activities

The interaction of four neutral oxidovanadium(v) complexes with DNA and their cytotoxic activities have been reported.

DNA-binding studies and antioxidant activities of two-, three- and four-coordinate silver(i) complexes containing bis(2-benzimidazolyl)aniline derivatives

Three novel structure Ag(i) complexes have been synthesized and characterized. The three ligands and Ag(i) complexes bind to DNA in an intercalation mode. The Ag(i) complexes have stronger ability of antioxidation for hydroxyl radical and superoxide radical.

Structural and vibrational study of 8-hydroxyquinoline-2-carboxaldehyde isonicotinoyl hydrazone--a potential metal-protein attenuating compound (MPAC) for the treatment of Alzheimer's disease

A comprehensive structural and vibrational study of the potential metal-protein attenuating compound 8-hydroxyquinoline-2-carboxaldehyde isonicotinoyl hydrazone is reported. X-ray diffraction data, as well as FT-IR and Raman frequencies, were compared with the respective theoretical values obtained from DFT calculations. Theory agrees well with experiment. In this context, an attempt of total assignment concerning the FT-IR and Raman spectra of the title compound was performed, shedding new light on previous partial assignments published elsewhere.

Antioxidation and DNA-binding properties of binuclear lanthanide(III) complexes with a Schiff base ligand derived from 8-hydroxyquinoline-7-carboxaldehyde and benzoylhydrazine

8-Hydroxyquinoline-7-carboxaldehyde (8-HQ-7-CA), Schiff-base ligand 8-hydroxyquinoline-7-carboxaldehyde benzoylhydrazone, and binuclear complexes [LnL(NO(3))(H(2)O)(2)](2) were prepared from the ligand and equivalent molar amounts of Ln(NO(3))·6H(2)O (Ln=La(3+), Nd(3+), Sm(3+), Eu(3+), Gd(3+), Dy(3+), Ho(3+), Er(3+), Yb(3+), resp.). Ligand acts as dibasic tetradentates, binding to Ln(III) through the phenolate O-atom, N-atom of quinolinato unit, and C=N and -O-C=N- groups of the benzoylhydrazine side chain. Dimerization of this monomeric unit occurs through the phenolate O-atoms leading to a central four-membered (LnO)(2) ring. Ligand and all of the Ln(III) complexes can strongly bind to CT-DNA through intercalation with the binding constants at 10(5)-10(6) M(-1). Moreover, ligand and all of the Ln(III) complexes have strong abilities of scavenging effects for hydroxyl (HO·) radicals. Both the antioxidation and DNA-binding properties of Ln(III) complexes are much better than that of ligand.

{2-[2-(Isopropyl-amino)-ethyl-imino-meth-yl]-5-meth-oxy-phenolato}(thio-cyanato--κN)nickel(II)

In the title mononuclear complex, [Ni(C₁₃H₁₉N₂O₂)(NCS)], the Ni^II ion is coordinated by one phenolate O atom, one imine N atom, and one amine N atom of a 2-[2-(isopropyl­amino)­ethyl­imino­meth­yl]-5-meth­oxy­phenolate Schiff base ligand, and by one N atom of a thio­cyanate ligand, forming a slightly distorted square-planar geometry.

Bis{1-[3-(diethyl-ammonio)-propyl-imino-meth-yl]naphthalen-2-olato}nickel(II) dinitrate

The asymmetric unit of the title compound, [Ni(C(18)H(24)N(2)O)(2)](NO(3))(2), consists of one half of the centrosymmetric nickel(II) complex cation and a nitrate anion. The Ni(II) atom, lying on an inversion center, is four-coordinated by the phenolate O atoms and imine N atoms of two Schiff base ligands, forming a square-planar geometry. The O- and N-donor atoms are mutually trans. In the crystal structure, the nitrate anions are linked to the complex cations by inter-molecular N-H⋯O hydrogen bonds.

Dibromido{2-[1-(cyclopropylimino)ethyl]pyridine}zinc(II)

In the title compound, [ZnBr₂(C₁₀H₁₂N₂)], the Zn²⁺ ion is coordinated by the N,N′-bidentate Schiff base ligand and two bromode ions in a distorted tetra­hedral arrangement. The dihedral angle between the pyridine and the cyclo­propyl rings is 95.4 (8)°.

Bis[2-(cyclopentyliminomethyl)-5-methoxyphenolato]copper(II)

The title compound, [Cu(C₁₃H₁₆NO₂)₂], is a mononuclear copper(II) complex derived from the Schiff base ligand 2-(cyclo­pentyl­imino­meth­yl)-5-meth­oxy­phenol and copper acetate. The Cu^II atom is four-coordinated by the phenolate O atoms and imine N atoms from two Schiff base ligands, in a highly distorted square-planar geometry. The O- and N-donor atoms are mutually trans and the dihedral angle between the two benzene rings is 55.8 (3)°.