First solid state alkaline-earth complexes of monensic acid A (MonH): crystal structure of [M(Mon)2(H (2)O)2] (M = Mg, Ca), spectral properties and cytotoxicity against aerobic Gram-positive bacteria

Experimental and DFT Study of Monensinate and Salinomycinate Complexes Containing {Fe3(µ3-O)}7+ Core

Two trinuclear oxo-centred iron(III) coordination compounds of monensic and salinomycinic acids (HL) were synthesized and their spectral properties were studied using physicochemical/thermal methods (FT-IR, TG-DTA, TG-MS, EPR, Mössbauer spectroscopy, powder XRD) and elemental analysis. The data suggested the formation of [Fe3(µ3-O)L3(OH)4] and the probable complex structures were modelled using the DFT method. The computed spectral parameters of the optimized constructs were compared to the experimentally measured ones. In each complex, three metal centres were joined together at the axial position by a μ3-O unit to form a {Fe3O}7+ core. The antibiotics monoanions served as bidentate ligands through the carboxylate and hydroxyl groups located at the termini. The carboxylate moieties played a dual role bridging each two metal centres. Hydroxide anions secured the overall neutral character of the coordination species. Mössbauer spectra displayed asymmetric quadrupole doublets that were consistent with the existence of two types of high-spin iron(III) sites with different environments-two Fe[O5] and one Fe[O6] centres. The solid-state EPR studies confirmed the +3 oxidation state of iron with a total spin St = 5/2 per trinuclear cluster. The studied complexes are the first iron(III) coordination compounds of monensin and salinomycin reported so far.

Novel Cerium(IV) Coordination Compounds of Monensin and Salinomycin

The largely uncharted complexation chemistry of the veterinary polyether ionophores, monensic and salinomycinic acids (HL) with metal ions of type M⁴⁺ and the known antiproliferative potential of antibiotics has provoked our interest in exploring the coordination processes between MonH/SalH and ions of Ce⁴⁺. (1) Methods: Novel monensinate and salinomycinate cerium(IV)-based complexes were synthesized and structurally characterized by elemental analysis, a plethora of physicochemical methods, density functional theory, molecular dynamics, and biological assays. (2) Results: The formation of coordination species of a general composition [CeL₂(OH)₂] and [CeL(NO₃)₂(OH)], depending on reaction conditions, was proven both experimentally and theoretically. The metal(IV) complexes [CeL(NO₃)₂(OH)] possess promising cytotoxic activity against the human tumor uterine cervix (HeLa) cell line, being highly selective (non-tumor embryo Lep-3 vs. HeLa) compared to cisplatin, oxaliplatin, and epirubicin.

Alkaline-earth metal(II) complexes of salinomycin – spectral properties and antibacterial activity

In the present paper the synthesis and structural characterization of alkaline-earth metal(II) complexes of the polyether ionophorous antibiotic salinomycinic acid (SalH.H2O) are discussed. The complexes [M(Sal)2(H2O)2] (M = Mg2+, 1; Ca2+, 2; Sr2+, 3; Ba2+, 4) were obtained reacting salinomycinic acid and Et4NOH with the corresponding metal(II) salts at metal-to-ligand-to-base molar ratio of 1:1:1. The spectral properties of 1–4 were characterized using infrared spectroscopy, fast atom bombardment-mass spectrometry, nuclear magnetic resonance and elemental analysis data. The crystallinity degree and morphology of complex 2 were studied by X-ray powder diffraction and transmission electron microscopy. The biometal(II) salinomycinate complexes 1 and 2 possess an enhanced antimicrobial activity compared to the parent antibiotic against Gram-positive bacteria. The comparison between the effectiveness of the complexes, reported here, and the already known isostructural coordination species of salinomycin and monensin (MonH.H2O), revealed that magnesium(II) and calcium(II) monensinates appear to be promising antibacterial agents against Bacillus subtilis, Bacillus cereus and Micrococcus luteus.

Study on in vitro Toxicity of Biometal(II) Monensinates Against Rat Zajdela Liver Tumour

The ability of Monensic acid A (MonH∙H2O) and its neutral metal complexes [M(Mon)2(H2O)2]with ions of Mg2+, Ca2+, Mn2+, Co2+, Ni2+ and Zn2+ to decrease viability and proliferation of primary cell cultures, originating from a chemically induced transplantable liver tumour of Zajdela in rats, and bone marrow cells from the same tumour-bearers, was evaluated. Experimental data revealed that manganese(II) and nickel(II) complexes of Monensin A are relatively more selective against the tumour as compared to the healthy bone marrow cells.

Comparative study on the effects of salinomycin, monensin and meso-2,3-dimercaptosuccinic acid on the concentrations of lead, calcium, copper, iron and zinc in lungs and heart in lead-exposed mice

BACKGROUND AND AIM

Environmental lead (Pb) exposure damages the lungs and is a risk factor for death from cardiovascular disease. Pb induces toxicity by a mechanism, which involves alteration of the essential elements homeostasis. In this study we compare the effects of salinomycin (Sal), monensin (Mon) and meso-2,3-dimercaptosuccinic acid (DMSA) on the concentrations of lead (Pb), calcium (Ca), copper (Cu), iron (Fe) and zinc (Zn) in the lungs and heart of lead-exposed mice.

METHODS

Sixty days old male ICR mice were divided into five groups: control (Ctrl) - untreated mice obtained distilled water for 28 days; Pb-intoxicated group (Pb) - exposed to 80 mg/kg body weight (BW) Pb(NO₃)₂ during the first 14 days of the experimental protocol; DMSA-treated (Pb + DMSA) - Pb-exposed mice, subjected to treatment with an average daily dose of 20 mg/kg BW DMSA for two weeks; Monensin-treated (Pb + Mon) - Pb-exposed mice, obtained an average daily dose of 20 mg/kg BW tetraethylammonium salt of monensic acid for 14 days; Pb + Sal - Pb-exposed mice, treated with an average daily dose of 20 mg/kg BW tetraethylammonium salt of salinomycinic acid for two weeks. On the 29^th day of the experiment the samples (lungs and heart) were taken for atomic absorption analysis.

RESULTS

The results revealed that exposure of mice to Pb for 14 days significantly increased the concentration of the toxic metal in both organs and elevated the cardiac concentrations of Ca, Cu and Fe compared to untreated mice. Pb exposure diminished the lung concentrations of Ca and Zn compared to that of untreated controls. DMSA, monensin and salinomycin decreased the concentration of Pb in the lungs and heart. Among the tested chelating agents, only salinomycin restored the cardiac Fe concentration to normal control values.

CONCLUSION

The results demonstrated the potential application of polyether ionophorous antibiotic salinomycin as antidote for treatment of Pb-induced toxicity in the lungs and heart. The possible complexation of the polyether ionophorous antibiotics with Ca(II) and Zn(II), which can diminish the endogenous concentrations of both ions in the lungs should be taken into account.

Spectral properties and biological activity of La(III) and Nd(III) Monensinates

The present research is focused on evaluation of complexation ability of Monensic acid (MonH) towards La3+ and Nd3+ ions.

Changes in the SRCD spectrum of Monensinate anion were monitored upon addition of lanthanide(III) ions. The antibiotic undergoes formation of one neutral ([Ln(Mon)3(H2O)3]) and two positively charged complex species of composition [Ln(Mon)2(H2O)2]+ and [Ln(Mon) (H2O)]2+, respectively (Ln = La3+, Nd3+). Neutral complexes were isolated as fine powders and were characterized by IR, FAB-MS and ESI-MS. It is assumed that Monensin acts in bidentate coordination mode via monodentate carboxylate moiety and hydroxyl group, both located at the opposite ends of antibiotic molecule.

Activity of Monensic acid and [Ln(Mon)3(H2O)3] to decrease visible bacteria growth of B. subtilis, S. Lutea and B. mycoides was evaluated by agar hole diffusion method. Results showed that complexation of lanthanide(III) ions to Monensin enhances the activity of non-coordinated ligand.

Antitumor efficacy of compounds was assayed on human triple negative breast cancer and transplantable sarcoma in rat. The cytotoxicity was accessed by MTT test, NR uptake, CV assay and double AO/PI staining. Experimental data revealed that Monensic acid and [Ln(Mon)3(H2O)3] possess concentration- and time-dependent activity, and express promising cytotoxic properties against human and rat permanent cancer cell lines.

Comparative effects of meso-2,3-dimercaptosuccinic acid, monensin and salinomycin on the concentrations of cadmium and some essential elements in skeletal muscles of Cd-exposed mice

Cadmium (Cd) is an environmental pollutant shown to induce multi organ dysfunction. In this study we present novel data about the effects of meso-2,3-dimercaptosuccinic acid (DMSA), monensin and salinomycin on the concentration of Cd in skeletal muscles of mice exposed to Cd (II) acetate treatment for 14 days. The impact of Cd and the chelating agents on the endogenous concentrations of calcium (Ca), copper (Cu), iron (Fe), magnesium (Mg), phosphorous (P), selenium (Se) and zinc (Zn) was also investigated. Subacute exposure of mice to Cd (II) acetate resulted in a significant accumulation of the toxic metal ion in the skeletal muscles compared to the untreated controls. Salinomycin most effectively mobilized Cd from the muscles compared to DMSA and monensin. The Cd exposure and the tested chelating agents did not significantly alter the endogenous concentrations of the selected essential elements in mouse muscles. The presented results confirmed that among the tested chelating agents salinomycin is superior as a potential antidote to Cd poisoning.

Structures and properties of naturally occurring polyether antibiotics

Polyether ionophores represent a large group of natural, biologically active substances produced by Streptomyces spp. They are lipid soluble and able to transport metal cations across cell membranes. Several of polyether ionophores are widely used as growth promoters in veterinary. Polyether antibiotics show a broad spectrum of bioactivity ranging from antibacterial, antifungal, antiparasitic, antiviral, and tumour cell cytotoxicity. Recently, it has been shown that some of these compounds are able to selectively kill cancer stem cells and multidrug-resistant cancer cells. Thus, they are recognized as new potential anticancer drugs. The biological activity of polyether ionophores is strictly connected with their molecular structure; therefore, the purpose of this paper is to present an overview of their formula, molecular structure, and properties.

Structure and antimicrobial properties of monensin A and its derivatives: summary of the achievements

In this paper structural and microbiological studies on the ionophorous antibiotic monensin A and its derivatives have been collected. Monensin A is an ionophore which selectively complexes and transports sodium cation across lipid membranes, and therefore it shows a variety of biological properties. This antibiotic is commonly used as coccidiostat and nonhormonal growth promoter. The paper focuses on both the latest and earlier achievements concerning monensin A antimicrobial activity. The activities of monensin derivatives, including modifications of hydroxyl groups and carboxyl group, are also presented.

Cytostatic and cytotoxic properties of monensic acid and its biometal(II) complexes against human tumor / non-tumor cell lines

The anticancer activity of monensic acid (MonH) and its biometal(II) complexes [M(Mon)2(H2O)2](M = Mg, Ca, Mn, Co, Ni, Zn) was evaluated against cultured human permanent cell lines established from glioblastoma multiforme (8MGBA) and cancers of the lung (A549), breast (MCF-7), uterine cervix (HeLa) and liver (HepG2). The viability and proliferation of the non-tumor human embryonic cell line Lep3 was also tested. The investigations were carried out using a thiazolyl blue tetrazolium bromide test, neutral red uptake cytotoxicity assay, crystal violet staining, colony forming method and double staining with acridin orange and propidium iodide. The results obtained reveal that the compounds applied at concentrations of 0.5–25 µg mL−1 for 24–72 h decrease the viability and proliferation of the treated cells in a time- and concentration-dependent manner. The metal(II) complexes studied (especially those of Co(II), Ni(II) and Zn(II)) have been found to express stronger cytotoxic and cytostatic activities than the non-coordinated monensic acid. The non-tumor human cell line showed strong chemosensitivity towards compounds tested comparable to that of cultured human tumor cell lines.

Cd(II) and Pb(II) complexes of the polyether ionophorous antibiotic salinomycin

Background

The natural polyether ionophorous antibiotics are used for the treatment of coccidiosis in poultry and ruminants. They are effective agents against infections caused by Gram-positive microorganisms. On the other hand, it was found that some of these compounds selectively bind lead(II) ions in in vivo experiments, despite so far no Pb(II)-containing compounds of defined composition have been isolated and characterized. To assess the potential of polyether ionophores as possible antidotes in the agriculture, a detailed study on their in vitro complexation with toxic metal ions is required. In the present paper we report for the first time the preparation and the structure elucidation of salinomycin complexes with ions of cadmium(II) and lead(II).

Results

New metal(II) complexes of the polyether ionophorous antibiotic salinomycin with Cd(II) and Pb(II) ions were prepared and structurally characterized by IR, FAB-MS and NMR techniques. The spectroscopic information and elemental analysis data reveal that sodium salinomycin (SalNa) undergoes a reaction with heavy metal(II) ions to form [Cd(Sal)₂(H₂O)₂] (1) and [Pb(Sal)(NO₃)] (2), respectively. Abstraction of sodium ions from the cavity of the antibiotic is occurring during the complexation reaction. Salinomycin coordinates with cadmium(II) ions as a bidentate monoanionic ligand through the deprotonated carboxylic moiety and one of the hydroxyl groups to yield 1. Two salinomycin anions occupy the equatorial plane of the Cd(II) center, while two water molecules take the axial positions of the inner coordination sphere of the metal(II) cation. Complex 2 consists of monoanionic salinomycin acting in polydentate coordination mode in a molar ratio of 1: 1 to the metal ion with one nitrate ion for charge compensation.

Conclusion

The formation of the salinomycin heavy metal(II) complexes indicates a possible antidote activity of the ligand in case of chronic/acute intoxications likely to occur in the stock farming.

Crystal structures and spectral properties of new Cd(II) and Hg(II) complexes of monensic acid with different coordination modes of the ligand

The single crystal X-ray structures and the spectroscopic properties of complexes of monensic acid (C36H62O11·H2O) with toxic metal ions of Cd(II) and Hg(II) are discussed. The cadmium(II) complex (1) is of composition [Cd(C36H61O11)2(H2O)2] and crystallizes in the monoclinic system (space group P2(1), Z = 2) with a = 12.4090(8), b = 24.7688(16), c = 14.4358(11) Å, β = 91.979(7)°. Two ligand monoanions are bound in a bidentate coordination mode to Cd(II) via the carboxylate and the primary hydroxyl oxygens occupying the equatorial plane of the complex. The axial positions of the inner coordination sphere of Cd(II) are filled by two water molecules additionally engaged in intramolecular hydrogen bonds. The Hg(II) complex (2), [Hg(C36H60O11)(H2O)], crystallizes in the orthorhombic system (space group P2(1)2(1)2(1), Z = 4) with a = 12.7316(2), b = 16.4379(3), c = 18.7184(4) Å. The monensic acid reacts with Hg(II) in a tetradentate coordination manner via both oxygen atoms of the carboxylate function and oxygens of two hydroxyl groups. The twofold negative charge of the ligand is achieved by deprotonation of carboxylic and secondary hydroxyl groups located at the opposite ends of the molecule. Hg(II) is surrounded by five oxygen atoms in a distorted square pyramidal molecular geometry.