Syntheses, characterization, biological activities and photophysical properties of lanthanides complexes with a tetradentate Schiff base ligand

Erbium(III) complexes with fluoroquinolones: Structure and biological properties

Four erbium(III) complexes with the fluoroquinolones enrofloxacin, levofloxacin, flumequine and sparfloxacin as ligands were synthesized and characterized by a wide range of physicochemical and spectroscopic techniques as well as single-crystal X-ray crystallography. The compounds were evaluated for their activity against the bacterial strains Staphylococcus aureus, Bacillus subtilis, Escherichia coli and Xanthomonas campestris, which was higher than that of the corresponding free quinolones. The interaction mode of the complexes with calf-thymus DNA is via intercalation, as suggested by diverse studies such as UV-vis spectroscopy, DNA-viscosity measurements and competitive studies with ethidium bromide. Fluorescence emission spectroscopy revealed the high affinity of the complexes for bovine and human serum albumin and the determined binding constants suggested a tight and reversible binding of the compounds with both albumins.

Erbium(III) coordination compounds with substituted salicylaldehydes: Characterization and biological profile

Five erbium(III) complexes with salicylaldehyde (saloH for 1), and mono- (5-X-saloH; X = NO₂ and Me for 2 and 3, respectively) or di-substituted salicylaldehydes (3,5-diX-saloH; X = Cl and Br for 4 and 5, respectively) were synthesized and characterized by physicochemical and spectroscopic techniques and single-crystal X-ray crystallography. All five complexes have the general formula [Er(deprotonated salicylaldehyde)₃(MeOH)(H₂O)]. The structure of complexes [Er(3,5-diCl-salo)₃(MeOH)(H₂O)]·1.5MeOH (complex 4) and [Er(3,5-diBr-salo)₃(MeOH)(H₂O)]·1.75MeOH (complex 5) were verified by single-crystal X-ray crystallography. The evaluation of antioxidant activity of the complexes was focused on their ability to scavenge 1,1-diphenyl-picrylhydrazyl and 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) free radicals and to reduce H₂O₂. The interaction of the complexes with calf-thymus DNA was investigated by UV-vis spectroscopy, viscosity measurements and via competitive studies with ethidium bromide in order to evaluate the possible DNA-binding mode and to determine the corresponding DNA-binding constants. The affinity of the complexes for bovine and human serum albumins was explored by fluorescence emission spectroscopy and the corresponding binding constants were determined.

Bovine serum albumin interaction, molecular docking, anticancer and antimicrobial activities of Co(II) Schiff base complex derived from Nophen ligand

In this report, synthesis, characterization, biological and molecular modeling studies of Nophen Schiff base [N,N-bis(2-hydroxy-1-naphthaldehyde)-o-phenylenediamine] and Co(II)-Nophen complex have been furnished. BSA binding affinities of the ligand and Co(II)-Nophen complex have been appraised by UV-visible, fluorescence and cyclic voltammetric techniques. Spectroscopic measurements indicate strong binding of the complex with BSA protein through static quenching mechanism with binding constant in the order of 10⁴ M^-1. The negative shift of the peak potential in cyclic voltammetry suggested an electrostatic interaction. Molecular docking analysis reveals significant binding affinity (-6.3 kcal/mol) of the complex towards BSA protein. It is amazing that the in vitro cytotoxicity of Co(II)-Nophen complex against A549 cell lines (Human lung carcinoma cells) has remarkable potentials with 29 ± 1.2 µM as IC₅₀ value. Comparing the biological activity towards microorganisms, Co(II)-Nophen complex show substantial response than the Nophen ligand.Communicated by Ramaswamy H. Sarma.

Synthesis and Characterization of Lanthanide Metal Ion Complexes of New Polydentate Hydrazone Schiff Base Ligand

The new homodinuclear complexes of the general formula [Ln₂L₃(NO₃)₃] (where HL is newly synthesized 2-((2-(benzoxazol-2-yl)-2-methylhydrazono)methyl)phenol and Ln = Sm³⁺ (1), Eu³⁺ (2), Tb³⁺ (3a, 3b), Dy³⁺ (4), Ho³⁺ (5), Er³⁺ (6), Tm³⁺ (7), Yb³⁺ (8)), have been synthesized from the lanthanide(III) nitrates with the polydentate hydrazone Schiff base ligand. The flexibility of this unsymmetrical Schiff base ligand containing N₂O binding moiety, attractive for lanthanide metal ions, allowed for a self-assembly of these complexes. The compounds were characterized by spectroscopic data (ESI-MS, IR, UV/Vis, luminescence) and by the X-ray structure determination of the single crystals, all of which appeared to be different solvents. The analytical data suggested 2:3 metal:ligand stoichiometry in these complexes, and this was further confirmed by the structural results. The metal cations are nine-coordinated, by nitrogen and oxygen donor atoms. The complexes are two-centered, with three oxygen atoms in bridging positions. There are two types of structures, differing by the sources of terminal (non-bridging) coordination centers (group A: two ligands, one nitro anion/one ligand, two nitro anions, group B: three ligands, three anions).

Recent Progress of Rare Earth Doped Hydroxyapatite Nanoparticles: Luminescence Properties, Synthesis and Biomedical Applications

Hydroxyapatite nanoparticles (HAP NPs) are host materials and can be modified with various substrates and dopants. Among them, rare earth (RE) ions doped HAP NPs have gathered attention due to their unique physicochemical and imaging properties. Compared to other fluorescence probes, RE-doped HAP NPs display advantages in high brightness, high contrast, photostability, nonblinking, and narrow emission bands. Meanwhile, their intrinsic features (composition, morphology, size, crystallinity, and luminescence intensity) can be adjusted by changing the dopant ratio, synthesizing temperature, reaction time, and techniques. And they have been used in various biomedical applications, including imaging probe, drug delivery, bone tissue engineering, and antibacterial studies. This review surveys the luminescent properties, fluorescence enhancement, synthetic methods, and biocompatibility of various RE-doped HAP NPs consolidated from different research works, for their employments in biomedical applications. For this literature review, an electronic search was conducted in the Pubmed, Web of Science, Google Scholar, Scopus and SciFinder databases, using the keywords: hydroxyapatite, rare earth, lanthanide, fluorescence, and imaging. Literature searches of English-language publications from 1979 with updates through April, 2022, and a total of 472 potential papers were identified. In addition, a few references were located by noting their citation in other studies reviewed. STATEMENT OF SIGNIFICANCE: Hydroxyapatite nanoparticles (HAP NPs) have a broad range of promising biological applications. Although prospective biomedical applications are not limited to rare earth-doped hydroxyapatite nanoparticles (RE-doped HAP NPs), some cases do make use of the distinctive features of RE-elements to achieve the expected functions for HAP families. This review surveys the luminescent properties, synthetic methods, and biocompatibility of various RE-doped HAP NPs consolidated from different research works, for their employments in biomedical applications, including imaging probe, drug delivery, bone tissue repair and tracking, and anti-bacteria. Overall, we expect to shed some light on broadening the research and application of RE-doped HAP NPs in biomedical field.

Experimental and molecular topology-based biological implications of Schiff base complexes: a concise review

This review is a gentle introduction toward Schiff bases with special attention to bioinorganic aspects. Depending on the nature of condensation moieties (ketonic or aldehydic) with primary amine, a large number of novel compounds are reported every year with applicability in various material science aspects. Herein, a burgeoning literature overview is presented to provide a salient discussion of the current status of these molecular systems. Schiff bases are designed depending on the particular desirable properties. For instance, to enlighten a biologically relevant molecule, it is always appreciated when a prepared compound shows biological membrane crossing and nucleic acid linking potential. Under such purview, the Schiff base functional group can serve as an enhancer of biomembrane traversing capability. In addition to various other catalytic aspects, the type of disease to be encountered also matters. Nowadays, theoretical chemistry is applied before synthesizing a compound of this sort and fruitful results are first depicted and, if found feasible, a suitable synthetic route is followed to synthesize Schiff base compounds. Molecular charge topology analysis under theoretical expression is analyzed generally to predict the biological relevance of a molecule.

Anti-cancer study and whey protein complexation of new lanthanum(III) complex with the aim of achieving bioactive anticancer metal-based drugs

In this study, a new lanthanum (III)-amino acid complex utilizing cysteine has been synthesized and characterized. The anticancer activities of the prepared La(III) complex against MCF-7 cell lines were studied. Results of MTT assay showed that at all three incubation times, the cytotoxic effect of prepared La(III) complex on MCF-7 breast cancer cell lines displays a time- and dose-dependent inhibitory effects. The interactions of the La(III) complex with two whey proteins (bovine serum albumin, BSA, and Bovine β-lactoglobulin, βLG) have been explored by using spectroscopic and molecular dicking methods. The obtained results indicated that La(III) complex strongly quenched the fluorescence of two carrier proteins in static quenching mode and also, BSA hah stronger binding affinity toward studied complex than βLG whit binding constant values of K_{BSA-La Complex} ∼ 0.11 × 10⁴ M^-1 and K_{βLG-La Complex} ∼ 0.63 × 10³ M^-1 at 300 K. The thermodynamic parameters revealed the contribution of hydrogen bond and Vander Waals interactions in both systems. The distances of the La(III) complex whit whey proteins were calculated using Förster energy transfer theory and proved existence of the energy transfer between two proteins and prepared La(III) complex with a high probability. FT-IR and UV-Vis absorption measurements indicated that the binding of the La(III) to BSA and βLG may induce conformational and micro-environmental changes of the proteins. The docking results indicate that the La(III) complex bind to residues located in the site II of BSA and second site of βLG. Communicated by Ramaswamy H. Sarma.

Coordination properties of N,N'-bis(5-methylsalicylidene)-2-hydroxy-1,3-propanediamine with d- and f-electron ions: crystal structure, stability in solution, spectroscopic and spectroelectrochemical studies

Template reaction between 5-methylsalicylaldehyde and 2-hydroxy-1,3-propanediamine in the presence of copper ion led to dinuclear and mononuclear copper(ii) complexes [Cu2L(CH3COO)(CH3OH)](CH3OH) (1) and [CuHL](CH3OH) (2), where H3L is N,N'-bis(5-methylsalicylidene)-2-hydroxy-1,3-propanediamine. The result of the reactions between 5-methylsalicylaldehyde and 2-hydroxy-1,3-propanediamine in the presence of lanthanide ions and/or copper(ii) ion was N,N'-bis(5-methylsalicylidene)-2-hydroxy-1,3-propanediamine (H3L B) or [CuHL](CH3OH) (2), respectively. Structures of the compounds were determined by single-crystal X-ray diffraction and physicochemical methods. The microstructures and phase compositions of crystals were studied by scanning electron microscopy (SEM). In dinuclear complex [Cu2L(CH3COO)(CH3OH)](CH3OH) (1), two copper(ii) ions are bond to one H3L ligand and one acetate ion. Coordination modes of the two copper centers are different: the geometry of copper 1 is almost ideal square-planar, while that for copper 2 can be described as tetragonal pyramidal. In complex [CuHL](CH3OH) (2), the copper(ii) ion is four coordinated and the coordination, rather than square-planar, can be described as flattened tetrahedral. Formation of complexes between copper(ii) or lanthanide ions with N,N'-bis(5-methylsalicylidene)-2-hydroxy-1,3-propanediamine (H3L) was also studied in solution by pH potentiometry. It should be mentioned that the complexes of lanthanide ions exist only in solution. Additionally, the salen-type ligand H3L and its dinuclear and mononuclear copper(ii) complexes were studied by cyclic voltammetry, and their spectroelectrochemical properties were examined.

Tunable ligand emission of napthylsalophen triple-decker dinuclear lanthanide(iii) sandwich complexes

The ligand 1,1′-((1E,1′E)-(1,2-phenylenebis(azanylylidene))bis(methanylylidene)) bis(naphthalen-2-ol) (H₂L) was used to prepare lanthanide(iii) metal complexes found to self-assemble as triple decker sandwich complexes of the type (Ln₂L₃).

From Synthesis to Biological Impact of Pd (II) Complexes: Synthesis, Characterization, and Antimicrobial and Scavenging Activity

The Pd (II) complexes with a series of halosubstituted benzylamine ligands (BLs) have been synthesized and characterized with different spectroscopic technique such as FTIR, UV/Vis, LCMS, ¹H, and ¹³C NMR. Their molecular sustainability in different solvents such as DMSO, DMSO : H₂O, and DMSO : PBS at physiological condition (pH 7.2) was determined by UV/Vis spectrophotometer. The in vitro antibacterial and antifungal activities of the complexes were investigated against Gram-positive and Gram-negative microbes and two different fungi indicated their significant biological potential. Additionally, their antioxidant activity has been analyzed with DPPH^• free radical through spectrophotometric method and the result inferred them as an antioxidant. The stronger antibacterial and antioxidant activities of the synthesized complexes suggested them as a stronger antimicrobial agent. Our study advances the biological importance of palladium (II) amine complexes in the field of antimicrobial and antioxidant activities.

Biological Impact of Pd (II) Complexes: Synthesis, Spectral Characterization, In Vitro Anticancer, CT-DNA Binding, and Antioxidant Activities

A new series of Pd (II) complexes of methyl substituted benzylamine ligands (BLs) has been synthesized and characterized via spectroscopic techniques such as UV/Vis. FTIR, LCMS, ¹H, and ¹³C NMR. The UV/Vis study in DMSO, DMSO + water, and DMSO + PBS buffer (pH = 7.2) confirmed their molecular sustainability in liquids. Their in vitro anticancer activity against breast cancer cell lines such as MCF-7 and MDA-MB-231 makes them interesting for in vivo analysis. Their stronger DNA binding activity (DBA) compared with free ligand suggested them as a good DNA binder. DBA was further confirmed by physicochemical studies such as surface tension and viscosity of complex + DNA which inferred the disruption of DNA and intercalation of complexes, respectively. Their % binding activity, % disruption of DNA base pairs (DNABP), and % intercalating strength are reported in this paper for the first time for better understanding of DNA binding mechanism. Along with this, their scavenging activity (SA) determined through DPPH free radical and the results indicate good antioxidant behaviour of complexes.

Spectral and thermal characterization of salophen type Schiff base and its implementation as solid contact electrode for quantitative monitoring of copper(II) ion

Salophen templated Schiff base 2,3-bis(salicylaldimino)pyridine (H2IF) has been synthesized and fully characterized by a series of different spectroscopic methods and thermogravimetric analysis (TGA). It has been also further probed electrochemically and explored as a cation recognition ionophore in the form of a polymeric membrane as selective sensor for quantitative monitoring of Cu(2+). Dielectric properties of the membrane have been studied by electrochemical impedance spectroscopy (EIS). The potentiometric results have demonstrated that the sensor exhibits very good selectivity and sensitivity towards Cu(2+) over a wide variety of cations. The electrode has a linear response to Cu(2+) with a detection limit of 4.46×10(-8) and displays a Nernstian slope (29.14 mV/decade) between pH 3.0 and 6.0 with a fast response time less than 10s. The solid contact electrodes have been exploited over five mounts period with good reproducibility. The analytical availability of the proposed electrode has been evaluated by applying in the determination of Cu(2+) ions in water samples. The structural features and complexation of ionophore with Cu(2+) have been monitored by UV-Vis spectroscopy and spectral findings have been further supported by DFT and TD-DFT calculations.

A study of in vitro antibacterial activity of lanthanides complexes with a tetradentate Schiff base ligand

OBJECTIVE

To establish the antibacterial activity of lanthanides complexes with a tetradentate Schiff base ligand L.

METHODS

(N, N'-bis (1-naphthaldimine)-o-phenylenediamine) was prepared from the condensation of 2-hydroxy-1-naphthaldehyde with o-phenylenediamine in a molar ratio of 2:1. The antimicrobial activity of the resultant Ln (III) complexes was investigated using agar well diffusion and micro-broth dilution techniques; the latter was used to establish the minimum inhibitory concentrations for each compound investigated.

RESULTS

Most of Ln (III) complexes were found to exhibit antibacterial activities against a number of pathogenic bacteria with MICs ranging between 1.95-250.00 µg/mL. Staphylococcus aureus was the most susceptible bacterial species to [LaL(NO3)2(H2O)](NO3) complex while Shigella dysenteriae and Escherichia coli required a relatively higher MIC (250 µg/mL). The complexes La (III) and Pr (III) were effective inhibitors against Staphylococcus aureus, whereas Sm (III) complex was effective against Serratia marcescens. On the other hand, Gd (III), La (III) and Nd (III) were found to be more potent inhibitors against Pseudomonas aeruginosa than two of commonly used antibiotics. The remaining Ln (III) complexes showed no remarkable activity as compared to the two standard drugs used.

CONCLUSIONS

Tetradentate Schiff base ligand L and its complexes could be a potential antibacterial compounds after further investigation.

Synthesis and characterization of chromium(III) Schiff base complexes: antimicrobial activity and its electrocatalytic sensing ability of catechol

A series of acyclic Schiff base chromium(III) complexes were synthesized with the aid of microwave irradiation method. The complexes were characterized on the basis of elemental analysis, spectral analysis such as UV-Visible, Fourier transform infrared (FT-IR), nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR) spectroscopies and electrospray ionization (ESI) mass spectrometry. Electrochemical analysis of the complexes indicates the presence of chromium ion in +3 oxidation state. Cr (III) ion is stabilized by the tetradentate Schiff base ligand through its nitrogen and phenolic oxygen. From the spectral studies it is understood that the synthesized chromium(III) complexes exhibits octahedral geometry. Antimicrobial activity of chromium complexes was investigated towards the Gram positive and Gram negative bacteria. In the present work, an attempt was made to fabricate a new kind of modified electrode based on chromium Schiff base complexes for the detection of catechol at nanomolar level.