The first dinuclear copper(ii) and zinc(ii) complexes containing novel Bis-TACN: syntheses, structures, and DNA cleavage activities

Distinct chemical factors in hydrolytic reactions catalyzed by metalloenzymes and metal complexes

The selective hydrolysis of the extremely stable phosphoester, peptide and ester bonds of molecules by bio-inspired metal-based catalysts (metallohydrolases) is required in a wide range of biological, biotechnological and industrial applications. Despite the impressive advances made in the field, the ultimate goal of designing efficient enzyme mimics for these reactions is still elusive. Its realization will require a deeper understanding of the diverse chemical factors that influence the activities of both natural and synthetic catalysts. They include catalyst-substrate complexation, non-covalent interactions and the electronic nature of the metal ion, ligand environment and nucleophile. Based on our computational studies, their roles are discussed for several mono- and binuclear metallohydrolases and their synthetic analogues. Hydrolysis by natural metallohydrolases is found to be promoted by a ligand environment with low basicity, a metal bound water and a heterobinuclear metal center (in binuclear enzymes). Additionally, peptide and phosphoester hydrolysis is dominated by two competing effects, i.e. nucleophilicity and Lewis acid activation, respectively. In synthetic analogues, hydrolysis is facilitated by the inclusion of a second metal center, hydrophobic effects, a biological metal (Zn, Cu and Co) and a terminal hydroxyl nucleophile. Due to the absence of the protein environment, hydrolysis by these small molecules is exclusively influenced by nucleophile activation. The results gleaned from these studies will enhance the understanding of fundamental principles of multiple hydrolytic reactions. They will also advance the development of computational methods as a predictive tool to design more efficient catalysts for hydrolysis, Diels-Alder reaction, Michael addition, epoxide opening and aldol condensation.

Novel silver glycinate conjugate with 3D polymeric intermolecular self-assembly architecture; an antiproliferative agent which induces apoptosis on human breast cancer cells

The new water soluble silver(I) complex of glycine (GlyH) with formula [Ag₃(Gly)₂NO₃]_n (AGGLY) was synthesized. The compound was characterized by melting point (m.p.), Fourier-transform infrared (FT-IR), Ultraviolet-visible (UV-vis) and Nuclear Magnetic Resonance (¹H-,¹³C NMR) spectroscopic techniques and X-ray crystallography. The in vitro cytotoxic activity of AGGLY against human breast adenocarcinoma cell lines: MCF-7 (hormone depended (HD)) and MDA-MB-231 (hormone independent (HI)) was determined. For comparison other adenocarcinoma cells such as human cervical adenocarcinoma (HeLa) cells and lung adenocarcinoma cells (A549) were also screened. AGGLY inhibits both breast cancer cell lines stronger than cisplatin. On the contrary, AGGLY, exhibits lower toxicity against fetal lung fibroblast (MRC-5) cells than cisplatin. Its genotoxicity against MRC-5 cells was detected from the presence or absence of micronucleus using fluorescence microscopy, while the in vivo genotoxicity was evaluated using Allium cepa model. The MCF-7 cells morphology suggests apoptotic pathway for their death. The apoptotic pathway was confirmed by cell cycle arrest, Acridine Orange/Ethidium Bromide (AO/EB) Staining, and permeabilization of the mitochondrial membrane tests. The molecular mechanism of action was further studied by the binding affinity of AGGLY towards the calf thymus (CT) DNA.

Cu(ii)-TACN complexes selectively induce antitumor activity in HepG-2 cells via DNA damage and mitochondrial-ROS-mediated apoptosis

A novel 1,4,7-triazacyclononane derivative (btacn), and its related copper complexes, Cu(btacn)Cl₂ and [Cu(btacn)₂]·(ClO₄)₂, exhibit potent anti-proliferation activity towards HepG-2 and HeLa cells, but low cytotoxicity towards normal cell lines.

Zinc complex of tryptophan appended 1,4,7,10-tetraazacyclododecane as potential anticancer agent: Synthesis and evaluation

With the rising incidences of cancer cases, the quest for new metal based anticancer drugs has led to extensive research in cancer biology. Zinc complexes of amino acid residue side chains are well recognized for hydrolysis of phosphodiester bond in DNA at faster rate. In the presented work, a Zn(II) complex of cyclen substituted with two l-tryptophan units, Zn(II)-Cyclen-(Trp)₂ has been synthesized and evaluated for antiproliferative activity. Zn(II)-Cyclen-(Trp)₂ was synthesized in ∼70% yield and its DNA binding potential was evaluated through QM/MM study which suggested good binding (G=-9.426) with B-DNA. The decrease in intensity of the positive and negative bands of CT-DNA at 278nm and 240nm, respectively demonstrated an effective unwinding of the DNA helix with loss of helicity. The complex was identified as an antiproliferative agent against U-87MG cells with 5 fold increase in apoptosis with respect to control (2h post incubation, IC₅₀ 25µM). Electrophoresis and comet assay studies exhibited an increase in DNA breakage after treatment with complex while caspase-3/β-actin cleavage established a caspase-3 dependent apoptosis pathway in U-87 MG cells after triggering DNA damage. In vivo tumor specificity of the developed ligand was validated after radiocomplexation with ^99mTc (>98% radiochemical yield and specific activity of 2.56GBq/µmol). Avid tumor/muscle ratio of >6 was depicted in biodistribution and SPECT imaging studies in U-87 MG xenograft model nude mice.

Binding affinities of Schiff base Fe(II) complex with BSA and calf-thymus DNA: Spectroscopic investigations and molecular docking analysis

The binding interaction of a synthesized Schiff base Fe(II) complex with biological macromolecules viz., bovine serum albumin (BSA) and calf thymus(ct)-DNA have been investigated using different spectroscopic techniques coupled with viscosity measurements at physiological pH and 298K. Regular amendments in emission intensities of BSA upon the action of the complex indicate significant interaction between them, and the binding interaction have been characterized by Stern Volmer plots and thermodynamic binding parameters. On the basis of this quenching technique one binding site with binding constant (Kb=(7.6±0.21)×10(5)) between complex and protein have been obtained at 298K. Time-resolved fluorescence studies have also been encountered to understand the mechanism of quenching induced by the complex. Binding affinities of the complex to the fluorophores of BSA namely tryptophan (Trp) and tyrosine (Tyr) have been judged by synchronous fluorescence studies. Secondary structural changes of BSA rooted by the complex has been revealed by CD spectra. On the other hand, hypochromicity of absorption spectra of the complex with the addition of ct-DNA and the gradual reduction in emission intensities of ethidium bromide bound ct-DNA in presence of the complex indicate noticeable interaction between ct-DNA and the complex with the binding constant (4.2±0.11)×10(6)M(-1). Life-time measurements have been studied to determine the relative amplitude of binding of the complex to ct-DNA base pairs. Mode of binding interaction of the complex with ct-DNA has been deciphered by viscosity measurements. CD spectra have also been used to understand the changes in ct-DNA structure upon binding with the metal complex. Density functional theory (DFT) and molecular docking analysis have been employed in highlighting the interactive phenomenon and binding location of the complex with the macromolecules.

Two dpa-based zinc(ii) complexes as potential anticancer agents: nuclease activity, cytotoxicity and apoptosis studies

Two new mononuclear Zn(ii)-PhMe-dpa complexes have been synthesized and the apoptosis-inducing activity of1was assessed by Hoechst 33342 staining, Annexin V binding and cell cycle experiments.

Synthesis, characterization, and DNA interaction of novel Pt(ii) complexes and their cytotoxicity, apoptosis and molecular docking

The complexes [Pt{Ar(COOH)₂}(OH)₂] (1), [Pt{Ar(COOH)₂}(OH)₂]·H₂O (2) have been synthesized and characterized by IR, ¹H NMR, element analysis and single-crystal X-ray diffractometry.

Syntheses, characterization, interaction with DNA, cytotoxic and apoptosis of two novel complexes of Zn(II) and Mn(II) with 2-methyl-1H-4,5-imidazoledicarboxylic acid

Two new complexes, Zn(L)2(H2O)2 (1) and Mn(L)2(H2O)2 (2) [L = 2-Methyl-1H-4,5-imidazoledicarboxylic acid] were synthesized and characterized by elemental analysis, infrared spectroscopy, and single crystal X-ray diffraction. Intramolecular weak interactions, such as hydrogen-bond and intermolecular interactions were presented in the complexes. The activities of the complexes binding with DNA, and cytotoxic activities were studied. The binding of complexes with fish sperm DNA (FS-DNA) was investigated by fluorescence spectra. Gel electrophoresis assay demonstrated the ability of the complexes to cleave the pBR322 plasmid DNA. The cytotoxic activities of the complexes were tested against the KB cell line. Cytotoxic activity studies showed the two complexes exhibited significant cancer cell inhibitory rate. The most active compound was complex 1 with IC50 and CC50value of 36.5, 429, with the selectivity index (SI = 11.75) among the tested compounds.

Chelating ability and biological activity of hesperetin Schiff base

Hydrazone hesperetin Schiff base (HHSB) - N-[(±)-[5,7-dihydroxy-2-(3-hydroxy-4-methoxy-phenyl)chroman-4-ylidene]amino]benzamide has been synthesized and its crystal structure was determined. This compound was used for the formation of Cu(II) complexes in solid state and in solution which were characterized using different spectroscopic methods. The analyses of potentiometric titration curves revealed that monomeric and dimeric complexes of Cu(II) are formed above pH7. The ESI-MS (electrospray ionization-mass spectrometry) spectra confirmed their formation. The EPR and UV-visible spectra evidenced the involvement of oxygen and nitrogen atoms in Cu(II) coordination. Hydrazone hesperetin Schiff base can show keto-enol tautomerism and coordinate Cu(II) in the keto (O(-), N, Oket) and in the enolate form (O(-), N, O(-)enol). The semi-empirical molecular orbital method PM6 and DFT (density functional theory) calculations have revealed that the more stable form of the dimeric complex is that one in which the ligand is present in the enol form. The CuHHSB complex has shown high efficiency in the cleavage of plasmid DNA in aqueous solution, indicating its potential as chemical nuclease. Studies on DNA interactions, antimicrobial and cytotoxic activities have been undertaken to gain more information on the biological significance of HHSB and copper(II)-HHSB chelate species.

Synthesis, characterization, and biological activities of two Cu(II) and Zn(II) complexes with one polyquinoline ligand

Two new complexes, [CuLCl]ClO4 (1) and [Zn2L2SO4(H2O)2](ClO4)2 (2) [L=N,N-bis(quinolin-2-ylmethyl)quinolin-8-amine], have been synthesized and structurally characterized. The interactions of two complexes with CT-DNA have been investigated by UV absorption, fluorescence spectroscopy, viscosity measurements and gel electrophoresis under physiological conditions. Results show that the complexes bind to CT-DNA with a moderate intercalative mode and exhibit efficient DNA cleavage activity on UV-A light of 365 nm. Furthermore, two complexes could quench the intrinsic fluorescence of BSA in a static quenching process based on BSA binding experiments. Notably, in vitro cytotoxicity study of two complexes on four human tumor cells lines (7404, HeLa, MCF-7, and HepG-2) indicate that both of them have the potential to act as effective anticancer drugs with low IC50 values.

Ligand effect and cooperative role of metal ions on the DNA cleavage efficiency of mono and binuclear Cu(II) macrocyclic ligands complexes

Two binuclear Cu(II) complexes of N-functionalized macrocycle ligands, namely 1,3-bis(1,4,7-triaza-1-cyclonomyl)propane and 1-(3-(1,4,7-triazonan-1-yl)propyl)-1,4,7,10-tetraazacyclo-dodecane, were synthesized and their ability to hydrolyze the cleavage of supercoiled plasmid DNA (pBR322) was compared with that of structurally related non-functionalized mononuclear Cu(II) complexes. The former, binuclear Cu(II) complex with the symmetrical ligand exhibited enhanced double-strand cleavage activity compared to the other three complexes at the same [Cu(2+)] concentration. In contrast, the latter binuclear complex with unsymmetrical macrocylic ligand did not give rise to double-strand DNA cleavage. The linear DNA formation induced by the mononuclear Cu(II) 1,4,7,10-tetraazacyclo-dodecane complex was realized via a non-random double-stranded scission process. The differential cleavage activity is discussed in relation to dimer formation, effective cooperation and coordination environment of the metal center. The hydrolytic cleavage by the copper complexes without H2O2 is supported by evidence from an anaerobic reaction, free radical quenching, and nitro blue tetrazolium assay. In contrast, both the binuclear complexes cleaved supercoiled DNA efficiently to Form III (linearized DNA) in the presence of H2O2, indicating that nuclearity is a crucial parameter in oxidative cleavage. The radical scavenger inhibition study and nitro blue tetrazolium assay suggested the involvement of H2O2 and superoxide ions in the oxidative cleavage of DNA by the binuclear complexes.