Importance of Metal-Ion Exchange for the Biological Activity of Coordination Complexes of the Biomimetic Ligand N4Py

Structural, Theoretical Investigations, Hirshfeld Surface Analysis, and Cytotoxicity Profile of a Neocuproine-Co(II)-Based Discrete Homodinuclear Complex

In this work, we aimed to synthesize a new cobalt(II) complex, namely [Co₂(μ-HIPA)(NC)₂(H₂O)₃(NO₃)]·(NO₃)(C₂H₅OH)(1) (where H₃IPA = 5-hydroxy isophthalic acid and NC = 2,9-dimethyl-1,10-phenanthroline or neocuproine), as a promising chemotherapeutic agent. The diffraction (single crystal-XRD and powder-XRD), spectroscopic (FTIR and UV-visible), molar conductance, and thermal techniques were used to characterize complex 1. Single-crystal X-ray diffraction analysis reveals that Co(II) exists in an octahedral geometry, with the ligation of four oxygen atoms, and two nitrogen atoms. Topological analysis of complex 1 reveals 2,6C6 topological type as an underlying net. The plausible intermolecular interactions within complex 1 that control the crystal packing were analyzed by Hirshfeld surface analysis. In vitro cytotoxicity of complex 1 was evaluated against acute myeloid leukemia (THP-1), colorectal (SW480), and prostate (PC-3) cancer cell lines by utilizing an MTT assay. The result shows that complex 1 can inhibit the growth of cancer cells (THP-1, SW480, and PC-3) at lower inhibitory concentration (IC₅₀) values of > 100, 43.6, and 95.1 µM respectively. The morphological changes induced by complex 1 on THP-1 and SW480 cancer cell lines were carried out with acridine orange/ethidium bromide staining methods. Additionally, comprehensive molecular docking studies were performed to understand the potential binding interactions of complex 1 with different bio-macromolecules.

Manganese Schiff Base Complexes, Crystallographic Studies, Anticancer Activities, and Molecular Docking

Choice of ligands is significant to successful synthesis of metal complexes (coordination compounds). This study reports the use of Schiff base as the right ligand to control the poor bioavailability and neurodegenerative toxicity challenges of manganese ion. In line with this study, document analysis was used as the methodological approach to evaluate the significance of Schiff base ligands in easing these manganese’s challenges and aligning the resultant coordination compounds (manganese Schiff base complexes) as therapeutic agents in anticancer studies. Report also involves crystallographic studies where single crystal X-ray crystallography was used as a chemical characterization technique. In addition, molecular docking studies, MOE2008, and AutoDock software were used to reveal the mode of interaction between the Schiff base and the manganese(II) and (III) ions, as well as scrutinizing the biological efficacy of the manganese(II) and manganese(III) Schiff bases coordination compounds as anticancer agents against some anticancer cell lines. Conclusion drawn was that manganese(II) and manganese(III) Schiff bases coordination compounds gave more active and potent activities than the corresponding Schiff bases. As a result, challenges of neurodegenerative toxicity and poor bioavailability of manganese ion were overcome, and the chelation therapy was fulfilled. Results from single crystal X-ray crystallography confirmed the successful synthesis of manganese(II) and manganese(III) Schiff bases coordination compounds and revealed the mechanism of reaction, while the molecular docking buttressed the biological activities of the Schiff base ligand and manganese Schiff base coordination compounds by portraying the structure activity relationship (SAR) between either Schiff base or the manganese Schiff base coordination compounds and the virtual cancer cell line (receptor protein), where hits were obtained for lead optimizations.

Copper (II) complexes with N, S donor pyrazole-based ligands as anticancer agents

A group of bidentate nitrogen and sulfur donor pyrazole derivative ligands abbreviated as Na[RNCS(Pz)], Na[RNCS(Pz^Me2)], Na[RNCS(Pz^Me3)], Na[RNCS(Pz^PhMe)], Na[RNCS(Pz^Ph2)], where (R = Et, Ph), and their Cu (II) complexes were synthesized and characterized by spectroscopic and physicochemical methods. The crystal structure of [Cu(PhNCSPz^Me3)₂] was determined by X-ray crystallography analysis and the results described a distorted square planar coordination geometry for this complex. Also, the cyclic voltammetry investigations indicated that the synthesized copper complex is an electrochemically active species. Moreover, the cytotoxic activity of all of the twenty synthesized compounds was evaluated using MTT assay against the MCF-7 (human breast carcinoma) cell lines, in vitro. Cu (II) complexes indicate significant cytotoxicity against the MCF-7 cell lines as compared with the free ligands. The docking studies showed that the copper complexes have better interactions with EGFR and CDK2 proteins, compared to the free ligands, and most of the studied compounds have a higher value of binding energy relative to the studied controls. The results of QSAR analysis suggest that dipole moment is in direct correlation with the obtained IC₅₀ values, and it strongly impact the anticancer effects generated by the compounds. Our findings suggest that the developed copper complexes can be good candidates for further evaluations as chemotherapeutic agents in the treatment of cancer.

Spectroscopy, Structure, Biomacromolecular Interactions, and Antiproliferation Activity of a Fe(II) Complex With DPA-Bpy as Pentadentate Ligand

An Fe(II) complex with DPA-Bpy (DPA-Bpy = N,N-bis(2-pyridinylmethyl)-2,20-bipyridine-6 -methanamine) as the ligand was synthesized and characterized to mimic bleomycin. The binding constants (K_b) of the complex with calf thymus DNA and human serum albumin (HSA) were quantitatively evaluated using fluorescence spectroscopy, with K_b as 5.53×10⁵ and 2.40×10⁴ M⁻¹, respectively; the number of the average binding site (n) is close to 1. The thermodynamic analyses suggested that the electrostatic interactions exist between the complex and DNA, and the hydrogen bonding and Van der Waals force exist for the complex and HSA. The Fe complex exhibits cleavage ability toward pBR322 DNA, and the crystal structure of the HSA Fe complex adduct at 2.4 Å resolution clearly shows that His288 serves as the axial ligand of the Fe center complexed with a pentadentate DPA-Bpy ligand. Furthermore, the cytotoxicity of the complex was evaluated against HeLa cells. Both the Fe complex and HSA Fe complex adduct show obvious effect on cell proliferation with an IC₅₀ of 1.18 and 0.82 μM, respectively; they induced cell apoptosis and arrested cell cycles at S phase. This study provides insight into the plausible mechanism underlying their metabolism and pharmacological activity.

Complexes of Zn(II) with a mixed tryptanthrin derivative and curcumin chelating ligands as new promising anticancer agents

In this study, two novel curcumin (H-Cur)-tryptanthrin metal compounds-[Zn(TA)Cl₂], i.e., Zn(TA), and [Zn(TA)(Cur)]Cl, i.e., Zn(TAC)-were synthesized and investigated using 5-(bis-pyridin-2-ylmethyl-amino)-pentanoic acid (6,12-dioxo-6,12-dihydro-indolo[2,1-b]quinazolin-8-yl)-amide (TA) and H-Cur as the targeting and high-activity anticancer chemotherapeutic moieties, respectively. They were then compared with the di-(2-picolyl)amine (PA) Zn(II) complex [Zn(PA)Cl₂], i.e., Zn(PA). When compared with Zn(PA) and cisplatin, the IC₅₀ values of Zn(TA) and Zn(TAC) indicated that the compounds had high cytotoxicity against A549/DDP cancer cells, implying that the H-Cur-tryptanthrin Zn(II) compounds have the potential for use as anticancer drugs. We propose the use of synthesized theragnostic H-Cur-tryptanthrin Zn(II) complexes with nuclear-targeting and DNA-damaging capabilities as a simple therapeutic strategy against tumors. The Zn(TA) and Zn(TAC) complexes could be traced via red fluorescence and were found to accumulate in the cell nuclei and induce DNA damage, cell cycle arrest, mitochondrial dysfunction, and cell apoptosis both in vitro and in vivo. In addition, Zn(TAC) exhibited a higher antiproliferative effect on A549/DDP than Zn(TA) and Zn(PA), which was undoubtedly associated with the key roles of the novel tryptanthrin derivative TA and H-Cur in the Zn(TAC) complex.

Promising Antifungal and Antibacterial Agents Based on 5-Aryl-2,2'-bipyridines and Their Heteroligand Salicylate Metal Complexes: Synthesis, Bioevaluation, Molecular Docking

A series of new 5-aryl-2,2'-bipyridines and their (polyfluoro)salicylate complexes of Cu(II), Co(II) and Mn(II) were synthesized. Their antimicrobial activity was evaluated in vitro against six strains of Trichophytons, E. floccosum, M. canis, C. ablicans and Gram-negative bacteria N. gonorrhoeae. Among azo-ligands, Ph-bipy and Tol-bipy showed promising antifungal activity (minimum inhibitory concentration (MIC)<0.8-27 μM). Their antifungal action was found can be realized via binding Fe(III) ions. Tol-bipy suppressed growth of Gram-positive bacteria S. aureus, S. aureus MRSA and their monospecies biofilms (MIC 6-16 μM). Using molecular docking, the anti-staphylococcal action mechanism based on the inhibition of S. aureus DNA gyrase GyrB was proposed for the lead compounds. Among metal complexes, Cu(II) and Mn(II) complexes based on tetrafluorosalicylic acid and Tol-bipy or Ph-bipy had the high antifungal activity (MIC<0.24-32 μM). Mn(SalF₄ -2H)₂ (Tol-bipy)₂ ] suppressed the growth of seven Candida strains at MIC 12-24 μM. [Cu(Sal-2H)(Ph-bipy)] and [Cu(SalF₃ -2H)(Ph-bipy)₂ ] showed the promising anti-gonorrhoeae activity (MIC 4.2-5.2 μM). (Cu(SalF_n -2H)(Tol-bipy)₂ ], [Cu(SalF₄ -2H)(Ph-bipy)₂ ] and [Cu(SalF₃ -2H)(Ph-bipy)₂ ]) were found active against the bacteria of S. aureus, S. aureus MRSA and their biofilms (MIC 2.4-41.4 μM). The most active compounds were tested for toxicity in vitro against human embryonic kidney (HEK-293) cells and in vivo experiments with CD-1 mice.

Pathway-Dependent Coordination Networks: Crystals versus Films

We demonstrate the formation of both metallo-organic crystals and nanoscale films that have entirely different compositions and structures despite using the same set of starting materials. This difference is the result of an unexpected cation exchange process. The reaction of an iron polypyridyl complex with a copper salt by diffusion of one solution into another resulted in iron-to-copper exchange, concurrent ligand rearrangement, and the formation of metal–organic frameworks (MOFs). This observation shows that polypyridyl complexes can be used as expendable precursors for the growth of MOFs. In contrast, alternative depositions of the iron polypyridyl complex with a copper salt by automated spin coating on conductive metal oxides resulted in the formation of electrochromic coatings, and the structure and redox properties of the iron complex were retained. The possibility to form such different networks from the same set of molecular building blocks by “in solution” versus “on surface” coordination chemistry broadens the synthetic space to design functional materials.

The most reactive iron and manganese complexes with N-pentadentate ligands for dioxygen activation—synthesis, characteristics, applications

The iron and manganese complexes that activate oxygen atom play multiple role in technologically relevant reactions as well as in biological transformations, in which exist in different redox states. Among them, high-valent oxo intermediate seems to be the most important one. Iron, and/or manganese-based processes have found application in many areas, starting from catalysis and sustainable technologies, through DNA oxidative cleavage, to new substances useful in chemotherapeutic drugs. This review is not only the latest detailed list of uses of homogeneous N-pentadentate iron and manganese catalysts for syntheses of valuable molecules with huge applications in green technologies, but also a kind of "a cookbook", collecting "recipes" for the discussed complexes, in which the sources necessary to obtain a full characterization of the compounds are presented. Following the catalytic activity of metalloenzymes, and taking into account the ubiquity of iron and manganese salts, which in combination with properly designed ligands may show similarity to natural systems, the discussed complexes can find application as new anti-cancer drugs. Also, owing to ability of oxygen atom to exchange in reaction with H₂O, they can be successfully applied in photodriven reactions of water oxidation, as well as in chemically regenerated fuel cells as a redox catalyst.

S. Paqui M, Amorim AL, P. de Paula C, Rocha MC, Malavazi I, Cunha A, S. Santana F, Ribeiro RR, Gariani RA, Mendes SR, Xavier FR. Polypyridyl iron(iii) complexes containing long alkyl chains: synthesis, characterization, DFT calculations and biological activity

A bis(picolyl)amine ligand was functionalized with a long alkyl chain, and two iron(iii) complexes were prepared and their biological activity was presented.

Isoxazole-Derived Aroylhydrazones and Their Dinuclear Copper(II) Complexes Show Antiproliferative Activity on Breast Cancer Cells with a Potentially Alternative Mechanism Of Action

This paper reports the design, synthesis and cytotoxicity studies of two new isoxazole-derived aroylhydrazone ligands and their dinuclear copper(II) complexes. Compounds were fully characterized by various spectroscopic and analytical techniques. The molecular structures of four derivatives were confirmed by X-ray crystallography. The stability of the ligands and the complexes in aqueous medium was monitored spectroscopically. Both the ligands and the complexes were shown to interact with calf thymus DNA (ct-DNA). Additionally, structures containing a phenol pendant arm were significantly more cytotoxic than those carrying a pendant pyridine substituent, reaching sub-micromolar IC₅₀ values on the triple-negative human breast cancer cell line MDA-MB-231. The metal chelation and transchelation ability of the compounds towards Fe^II , Fe^III and Zn^II ions was explored as a possible mechanism of action of these compounds.

Development of a synthesis method for odor sesquiterpenoid, (−)-rotundone, using non-heme Fe2+-chelate catalyst and ferric-chelate reductase

(−)-Rotundone, a sesquiterpenoid that has a characteristic woody and peppery odor, is a key aroma component of spicy foodstuffs, such as black pepper and Australian Shiraz wine. (−)-Rotundone shows the lowest level of odor threshold in natural compounds and remarkably improves the quality of various fruit flavors. To develop a method for the synthesis of (−)-rotundone, we focused on non-heme Fe2+-chelates, which are biomimetic catalysts of the active center of oxygenases and enzymatic supply and regeneration of those catalysts. That is, we constructed a unique combination system composed of the oxidative synthesis of (−)-rotundone using the non-heme Fe2+-chelate catalyst, Fe(II)-EDTA, and the enzymatic supply and regeneration of Fe2+-chelate by ferric-chelate reductase, YqjH, from Escherichia coli. In addition, we improved the yield of (−)-rotundone by the application of cyclodextrin and glucose dehydrogenase to this system, and thus established a platform for efficient (−)-rotundone production.

Iron Compounds as Anticancer Agents

Many ferrocene complexes have been prepared for their oncological potential. Some derive from molecules with known biological effects (taxanes, podophyllotoxine, artemisine, SAHA, etc.) while others are synthetic molecules selected for their cytotoxic effects (N-alkylaminoferrocenes and ferrocenyl alkylpyridinium). Although these complexes have received a great deal of attention, the field of iron metallodrugs is not limited to them. A number of inorganic complexes of iron(ii) and iron(iii) with possible anticancer effects have also been published, although research into their biological effects is often only at an early stage. This chapter also includes iron chelators, molecules that are administered in non-metallic form but whose cytotoxic species are their coordination complexes of iron generated in vivo. The most emblematic molecule of this family is bleomycin, used as an anticancer agent in many chemotherapies. To these can be added the iron chelates originally synthesized to treat iron overload, some of which have been shown to possess interesting anticancer properties. They have been, and continue to be, the subject of many clinical trials, whether alone or in combination. Thus, the area of iron metallodrugs includes molecules with very different structures and reactivity, studied from a number of different perspectives, but focused on increasing the number of molecules at our disposal for combatting cancer.

From Pincer to Paddlewheel: C-H and C-S Bond Activation at Bis(2-pyridylthio)methane by Palladium(II)

The bis(2-pyridylthio)methanidopalladium(II) pincer complex (1), containing a Pd-C bond, was obtained from the reaction of bis(2-pyridylthio)methane (H₂L) with palladium(II) acetate in toluene under reflux. When palladium(II) trifluoroacetate was used, H₂L reacted to generate the tetrakis(pyridine-2-thiol)palladium(II) complex (2). Complex 2 was converted to a heterobimetallic palladium(II)-iron(II) paddlewheel complex (3) upon treatment with iron(II) triflate in the presence of a base in acetonitrile at room temperature.