Why does nature use zinc--a personal view

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.

Benchmarking biomolecular force field-based Zn2+ for mono- and bimetallic ligand binding sites

Zn²⁺ is one of the most versatile biologically available metal ions, but accurate modeling of Zn²⁺ -containing metalloproteins at the biomolecular force field level can be challenging. Since most Zn²⁺ models are parameterized in bulk solvent, in-depth knowledge about their performance in a protein environment is limited. Thus, we systematically investigate here the behavior of non-polarizable Zn²⁺ models for their ability to reproduce experimentally determined metal coordination and ligand binding in metalloproteins. The benchmarking is performed in challenging environments, including mono- (carbonic anhydrase II) and bimetallic (metallo-β-lactamase VIM-2) ligand binding sites. We identify key differences in the performance between the Zn²⁺ models with regard to the preferred ligating atoms (charged/non-charged), attraction of water molecules, and the preferred coordination geometry. Based on these results, we suggest suitable simulation conditions for varying Zn²⁺ site geometries that could guide the further development of biomolecular Zn²⁺ models.

Comparison of Empirical Zn2+ Models in Protein–DNA Complexes

Zinc ions are the second most abundant ions found in humans. Their role in proteins can be merely structural but also catalytic, owing to their transition metal character. Modelling their geometric–coordination versatility by empirical force fields is, thus, a challenging task. In this work, we evaluated three popular models, specifically designed to represent zinc ions with regard to their capability of preserving structural integrity. To this end, we performed molecular dynamics simulations of two zinc-containing protein–DNA complexes, which differed in their zinc coordination, i.e., four cysteines or two cysteines and two histidines. The most flexible non-bonded 12-6-4 Lennard–Jones-type model shows a preference for six-fold coordination of the Zn2+-ions in contradiction to the crystal structure. The cationic dummy atom model favours tetrahedral geometry, whereas the bonded extended zinc AMBER force field model, by construction, best preserves the initial geometry of a regular or slightly distorted tetrahedron. Our data renders the extended zinc AMBER force field the best model for structural zinc ions in a given geometry. In more complicated cases, though, more flexible models may be advantageous.

Structural and biochemical insights into Zn2+-bound EF-hand proteins, EFhd1 and EFhd2

EF-hand proteins, which contain a Ca²⁺-binding EF-hand motif, are involved in regulating diverse cellular functions. Ca²⁺ binding induces conformational changes that modulate the activities of EF-hand proteins. Moreover, these proteins occasionally modify their activities by coordinating metals other than Ca²⁺, including Mg²⁺, Pb²⁺ and Zn²⁺, within their EF-hands. EFhd1 and EFhd2 are homologous EF-hand proteins with similar structures. Although separately localized within cells, both are actin-binding proteins that modulate F-actin rearrangement through Ca²⁺-independent actin-binding and Ca²⁺-dependent actin-bundling activity. Although Ca²⁺ is known to affect the activities of EFhd1 and EFhd2, it is not known whether their actin-related activities are affected by other metals. Here, the crystal structures of the EFhd1 and EFhd2 core domains coordinating Zn²⁺ ions within their EF-hands are reported. The presence of Zn²⁺ within EFhd1 and EFhd2 was confirmed by analyzing anomalous signals and the difference between anomalous signals using data collected at the peak positions as well as low-energy remote positions at the Zn K-edge. EFhd1 and EFhd2 were also found to exhibit Zn²⁺-independent actin-binding and Zn²⁺-dependent actin-bundling activity. This suggests the actin-related activities of EFhd1 and EFhd2 could be regulated by Zn²⁺ as well as Ca²⁺.

Synthesis, crystal structure, potential drug properties for Coronavirus of Co(II) and Zn(II) 2-chlorobenzoate with 3-cyanopyridine complexes

Two new complexes of Co(II) and Zn(II) 2-chlorobenzoate (2-ClBA) with 3-cyanopyridine (CNP) of the general formula [Co(2-ClBA)₂(CNP)₂(H₂O)₂] and [Zn(2-ClBA)₂(CNP)₂(H₂O)₂] were synthesized. The structures of the complexes were characterized by single crystal XRD and FT-IR and NMR spectroscopy and Mass Spectrometry (MALDI-TOF MS) methods. Mononuclear complexes exhibit octahedral coordination. In addition, Hirshfeld surface analysis was performed to determine non-covalent interactions in crystal packing. The geometry optimization of the molecules was carried out using the LANL2DZ level of theory of the DFT method and the obtained findings were confirmed by comparing with the data obtained from the single crystal X-ray diffraction method. The theoretical and experimental bond angles and lengths are very close to each other. The effectiveness of the complexes against SARS-CoV-2 enzymes was investigated in silico using the molecular docking method, and a binding score of -8.0 kcal/mol on NSP16 of complex 1 as an inhibitor was obtained. To investigate the drug potential of the complexes, their pharmacokinetic and toxicokinetic properties were estimated by ADMET calculations.

Hybrid QM/MM Simulations Confirm Zn(II) Coordination Sphere That Includes Four Cysteines from the P2 × 4R Head Domain

To ascertain the role of Zn(II) as an allosteric modulator on P2X4R, QM/MM molecular dynamic simulations were performed on the WT and two P2X4R mutants suggested by previous electrophysiological data to affect Zn(II) binding. The Gibbs free energy for the reduction of the putative P2X4R Zn(II) binding site by glutathione was estimated at −22 kcal/mol. Simulations of the WT P2X4R head domain revealed a flexible coordination sphere dominated by an octahedral geometry encompassing C126, N127, C132, C149, C159 and a water molecule. The C132A mutation disrupted the metal binding site, leading to a coordination sphere with a majority of water ligands, and a displacement of the metal ion towards the solvent. The C132A/C159A mutant exhibited a tendency towards WT-like stability by incorporating the R148 backbone to the coordination sphere. Thus, the computational findings agree with previous experimental data showing Zn(II) modulation for the WT and C132A/C159A variants, but not for the C132A mutant. The results provide molecular insights into the nature of the Zn(II) modulation in P2X4R, and the effect of the C132A and C132A/C159A mutations, accounting for an elusive modulation mechanism possibly occurring in other extracellular or membrane protein.

Rapid atmospheric carbon dioxide fixation by nickel(II) complexes: meridionally coordinated diazepane-based 3N ligands facilitate fixation

Octahedral complexes of the type [Ni(L)(H2O)3](ClO4)2 (1 and 2), where L is the tridentate 3N ligand 4-methyl-1-(pyrid-2-ylmethyl)-1,4-diazacycloheptane (L1, 1), or 4-methyl-1-(N-methylimidazolyl)-1,4-diazacycloheptane (L2, 2), have been isolated and characterized using elemental analysis, ESI-MS and electronic absorption spectroscopy. The DFT optimized structures of 1 and 2 reveal that the tridentate 3N ligands are coordinated meridionally constituting a distorted octahedral coordination geometry around nickel(ii). In methanol solution, the complexes, upon treatment with triethylamine, generate the reactive red colored low-spin square planar Ni-OH intermediate [Ni(L1/L2)(OH)]+ (1a and 2a), as characterized by ESI-MS and electronic absorption spectroscopy, and energy minimized structures. The latter when exposed to the atmosphere rapidly absorbs atmospheric CO2 to produce the carbonate bridged dinickel(ii) complexes [Ni2(L1/L2)2(μ-CO3)(H2O)2](ClO4)2 (3 and 4), as characterized by elemental analysis and the IR spectral feature (∼1608 cm-1) characteristic of bridging carbonate. The single crystal X-ray structure of 3 reveals the presence of a dinickel(ii) core bridged by a carbonate anion in a symmetric mode. Both the Ni(ii) centers are identical to each other with each Ni(ii) possessing a distorted octahedral coordination geometry constituted by a meridionally coordinated 3N ligand, a carbonate ion and a water molecule. The decay kinetics of the red intermediates generated by 1 (kobs, 7.7 ± 0.1 × 10-5 s-1) and 2 (kobs, 5.8 ± 0.3 × 10-4 s-1) in basic methanol solution with atmospheric CO2 has been determined by absorption spectroscopy. DFT studies illustrate that meridional coordination of the 3N ligand and the electron-releasing imidazole ring as in 2 facilitate fixation of CO2. The carbonate complex 3 efficiently catalyzes the conversion of styrene oxide into cyclic carbonate by absorbing atmospheric and pure CO2 with excellent selectivity.

Broadening the scope of high structural dimensionality nanomaterials using pyridine-based curcuminoids

We present a new heteroditopic ligand (3pyCCMoid) that contains the typical skeleton of a curcuminoid (CCMoid) decorated with two 3-pyridyl groups. The coordination of 3pyCCMoid with ZnII centres results in a set of novel coordination polymers (CPs) that display different architectures and dimensionalities (from 1D to 3D). Our work analyses how synthetic methods and slight changes in the reaction conditions affect the formation of the final materials. Great efforts have been devoted toward understanding the coordination entities that provide high dimensional systems, with emphasis on the characterization of 2D materials, including analyses of different types of substrates, stability and exfoliation in water. Here, we foresee the great use of CCMoids in the field of CPs and emphasize 3pyCCMoid as a new-born linker.

Zinc transporters and their functional integration in mammalian cells

Zinc is a ubiquitous biological metal in all living organisms. The spatiotemporal zinc dynamics in cells provide crucial cellular signaling opportunities, but also challenges for intracellular zinc homeostasis with broad disease implications. Zinc transporters play a central role in regulating cellular zinc balance and subcellular zinc distributions. The discoveries of two complementary families of mammalian zinc transporters (ZnTs and ZIPs) in the mid-1990s spurred much speculation on their metal selectivity and cellular functions. After two decades of research, we have arrived at a biochemical description of zinc transport. However, in vitro functions are fundamentally different from those in living cells, where mammalian zinc transporters are directed to specific subcellular locations, engaged in dedicated macromolecular machineries, and connected with diverse cellular processes. Hence, the molecular functions of individual zinc transporters are reshaped and deeply integrated in cells to promote the utilization of zinc chemistry to perform enzymatic reactions, tune cellular responsiveness to pathophysiologic signals, and safeguard cellular homeostasis. At present, the underlying mechanisms driving the functional integration of mammalian zinc transporters are largely unknown. This knowledge gap has motivated a shift of the research focus from in vitro studies of purified zinc transporters to in cell studies of mammalian zinc transporters in the context of their subcellular locations and protein interactions. In this review, we will outline how knowledge of zinc transporters has been accumulated from in-test-tube to in-cell studies, highlighting new insights and paradigm shifts in our understanding of the molecular and cellular basis of mammalian zinc transporter functions.

A trinuclear Zn(ii) Schiff base azido compound: synthesis, structure and exploration of antimicrobial activity

The synthesis, characterization, X-ray crystal structure and antimicrobial activity of a trinuclear zinc(ii) complex have been explored.

An air-stable, Zn2+-based catalyst for hydrosilylation of alkenes and alkynes

Hydrosilylation of C[double bond, length as m-dash]C double and C[triple bond, length as m-dash]C triple bonds is one of the most widely used processes in organosilicon chemistry, mostly catalyzed by Pt-based complexes. We report here the synthesis of an air-stable dicationic Zn2+-based complex in a hemilabile tris(2-methyl-6-pyridylmethyl) phosphine (TmPPh) ligand, 12+[B(C6F5)4]2. When heated, 12+[B(C6F5)4]2 activates Si-H bonds reversibly via ligand/metal cooperation between Lewis acidic Zn2+ and Lewis basic N centers in a frustrated Lewis pair (FLP) type fashion. Consequently, 12+[B(C6F5)4]2 was found to be an effective catalyst for hydrosilylation reactions of C[double bond, length as m-dash]C double and C[triple bond, length as m-dash]C triple bonds. Remarkably, these hydrosilylation reactions can be loaded under aerobic conditions, as well as, in some cases, work under neat conditions. The mechanism of the activation of the Si-H bond and the hydrosilylation reaction is proposed based on experiments and density functional theory (DFT) calculations.

One-carbon metabolism, folate, zinc and translation

The translation process, central to life, is tightly connected to the one-carbon (1-C) metabolism via a plethora of macromolecule modifications and specific effectors. Using manual genome annotations and putting together a variety of experimental studies, we explore here the possible reasons of this critical interaction, likely to have originated during the earliest steps of the birth of the first cells. Methionine, S-adenosylmethionine and tetrahydrofolate dominate this interaction. Yet, 1-C metabolism is unlikely to be a simple frozen accident of primaeval conditions. Reactive 1-C species (ROCS) are buffered by the translation machinery in a way tightly associated with the metabolism of iron-sulfur clusters, zinc and potassium availability, possibly coupling carbon metabolism to nitrogen metabolism. In this process, the highly modified position 34 of tRNA molecules plays a critical role. Overall, this metabolic integration may serve both as a protection against the deleterious formation of excess carbon under various growth transitions or environmental unbalanced conditions and as a regulator of zinc homeostasis, while regulating input of prosthetic groups into nascent proteins. This knowledge should be taken into account in metabolic engineering.

Zinc(II) complexes with aromatic nitrogen-containing heterocycles as antifungal agents: Synergistic activity with clinically used drug nystatin

Three novel Zn(II) complexes, [ZnCl₂(qz)₂] (1), [ZnCl₂(1,5-naph)]_n (2) and [ZnCl₂(4,7-phen)₂] (3), where qz is quinazoline, 1,5-naph is 1,5-naphthyridine and 4,7-phen is 4,7-phenanthroline, were synthesized by the reactions of ZnCl₂ and the corresponding N-heterocyclic ligand in 1:2 molar ratio in ethanol at ambient temperature. The characterization of these complexes was done by NMR, IR and UV-Vis spectroscopy, and their crystal structures were determined by single-crystal X-ray diffraction analysis. Complexes 1 and 3 are mononuclear species, in which Zn(II) ion is tetrahedrally coordinated by two nitrogen atoms belonging to two qz or 4,7-phen ligands, respectively, and by two chloride anions, while complex 2 is a 1D coordination polymer that contains 1,5-naph as bridging ligand between two metal ions. In agar disc-diffusion assay, complexes 1-3 manifested good inhibitory activity against two investigated Candida strains (C. albicans and C. parapsilosis), while not inducing toxic effects on the healthy human fibroblast cell line (MRC-5). This activity was not fungicidal, as revealed by the broth microdilution assay, however complex 3 showed the ability to modulate Candida hyphae formation, which is an important process during infection and showed significant synergistic effect with clinically used antifungal polyene nystatin.

Why Diorganyl Zinc Lewis Acidity Dramatically Increases with Narrowing C-Zn-C Bond Angle

The Lewis acidity of a metal center is influenced not only by the electronic properties of the bonded ligands but also by the bond angles, which we suggest to be important for zinc diorganyls. Molecular orbital correlation predicts that a narrower C-Zn-C bond angle of the R₂Zn fragment lowers its lowest unoccupied molecular orbital (LUMO) and increases its Lewis acidity, such that it binds added ligands more strongly. Computations on Me₂Zn(bipy) (bipy = 2,2'-bipyridine) yield that, for every 10° of C-Zn-C narrowing close to tetrahedral geometry, the Zn-N distance shortens by 0.027 Å (0.048 Å per 10° for the range 180-90°) and that the LUMO of the Me₂Zn fragment drops by 0.24 eV. A total of 10 dialkyl zinc complexes of bipy or 4,4'-di-tert-butyl-2,2'-bipyridine are crystallographically characterized here. Structure correlations (published and new data) confirm the link between the C-Zn-C angle and Zn-N distance. Principal component analysis provides a detailed picture of the correlated distortions. Relevance for zinc fingers/zinc enzymes is discussed.

3-Amino-1-propanol and N-methylaminoethanol: coordination to zinc(ii) vs. decomposition to ammonia

The coordination of amino alcohols 3-amino-1-propanol and N-methylaminoethanol to zinc(ii) and their decomposition to ammonia were investigated.

A comparison of computational methodologies for the structural modelling of biologically relevant zinc complexes

The impact of a variety of modern computational methods on the structure of biologically relevant zinc complexes is studied. Different density functionals and a Hartree-Fock-based method, scalar-relativistic effects, and basis set integration grid choices, among others, are assessed for set of high-resolution crystallographic structures. While a previous study recommends incorporating relativistic effects into density functional theory calculations in order to improve the accuracy of obtained geometries for small Zn(II) coordination compounds, we show that, for the set in study, relativistic effects do not affect the geometries to a significant extent. The PBEh-3c composite method emerges as good alternative for the treatment of Zn(II) complexes, while the HF-3c method can be employed when computational efficiency is important. Graphical Abstract Which methods are best suited for the computation of Zn(II) bioligand complexes?

The copper(II) binding centres of carbonic anhydrase are differently affected by reductants that ensure the redox intracellular environment

Copper is involved in several biological processes. The static and labile copper pools are controlled by means of a network of influx and efflux transporters, storage proteins, chaperones, transcription factors and small molecules as glutathione (GSH), which contributes to the cell reducing environment. To follow the fate of intracellular copper labile pool, a variant of human apocarbonic anhydrase has been proposed as fluorescent probe to monitor cytoplasmic Cu²⁺. Aware that in this cellular compartment copper ion is present as Cu⁺, electron spin resonance technique (ESR) was used to ascertain whether (bovine or human) carbonic anhydrase (CA) was able to accommodate Cu⁺ in the same sites occupied by Cu²⁺, in the presence of naturally occurring reducing agents such as ascorbate and GSH. Our ESR results on Cu²⁺ complexes with CA allow for a complete characterization of the two metal binding sites of the protein in solution. The use of the reported affinity constants of zinc in the catalytic site and of Cu²⁺ in the peripheral and catalytic site, allow us to obtain the speciation of copper species mimicking the spectroscopic study conditions. The different Cu²⁺ coordination features in the catalytic and the peripheral (the N-terminus cleft mouth) binding sites influence the chemical reduction effect of the two main naturally occurring reductants. Ascorbate reversibly reduces the Cu²⁺ complex with CA, while glutathione irreversibly induces the formation of Cu²⁺ complex with its oxidized form (GSSG). Our results questioned the use of CA as intracellular Cu²⁺ sensor. Furthermore, translating these findings to intracellular environment, the conversion of GSH in GSSG can significantly alter the metallostasis.

A new probe for detecting zinc-bound carbonic anhydrase in cell lysates and cells

We report the synthesis and application of a small molecule probe for carbonic anhydrase (CA) to track holo-CA in cell lysates and live-cell models of zinc dyshomeostasis. The probe displays a 12-fold increase in fluorescence upon binding to bovine CA and also responds to human CA isoforms.

Precise control of pore hydrophilicity enabled by post-synthetic cation exchange in metal-organic frameworks

The ability to control the relative humidity at which water uptake occurs in a given adsorbent is advantageous, making that material applicable to a variety of different applications.

The ability to control the relative humidity at which water uptake occurs in a given adsorbent is advantageous, making that material applicable to a variety of different applications. Here, we show that cation exchange in a metal–organic framework allows precise control over the humidity onset of the water uptake step. Controlled incorporation of cobalt in place of zinc produces open metal sites into the cubic triazolate framework MFU-4l, and thereby provides access to materials with uptake steps over a 30% relative humidity range. Notably, the MFU-4l framework has an extremely high water adsorption capacity of 1.05 g g^–1, amongst the highest known for porous materials. The total water capacity is independent of the cobalt loading, showing that cation exchange is a viable route to increase the hydrophilicity of metal–organic frameworks without sacrificing capacity.

Experimental and Computational Investigation of Salophen-Zn Gas Phase Complexes with Cations: A Source of Possible Interference in Anionic Recognition

We explore the possibility that protonated molecular ions might be an unexpected source of interference in the recognition process of anions and neutral species by Zn-salophen receptors. Zn-salophen complexes are known to bind anions and neutral molecules in solution. We present here evidence (from computational work and IRMPD spectroscopy) that these complexes can also be the binding site for protonated pyridine or quinuclidine. The resulting binding pattern does not involve the Zn ion, but one of the oxygen atoms directly attached to it. The resulting complex therefore turns out to have a positive charge adjacent to the Zn-salophen binding site. This finding seems to point to the existence of an interfering factor in the quantification of the experimental data about the association constant.

Tris(2-mercaptoimidazolyl)hydroborato Cadmium Thiolate Complexes, [TmBut]CdSAr: Thiolate Exchange at Cadmium in a Sulfur-Rich Coordination Environment

A series of cadmium thiolate compounds that feature a sulfur-rich coordination environment, namely [TmBut]CdSAr, have been synthesized by the reactions of [TmBut]CdMe with ArSH (Ar = C6H4-4-F, C6H4-4-But, C6H4-4-OMe, and C6H4-3-OMe). In addition, the pyridine-2-thiolate and pyridine-2-selenolate derivatives, [TmBut]CdSPy and [TmBut]CdSePy have been obtained via the respective reactions of [TmBut]CdMe with pyridine-2-thione and pyridine-2-selone. The molecular structures of [TmBut]CdSAr and [TmBut]CdEPy (E = S or Se) have been determined by X-ray diffraction and demonstrate that, in each case, the [CdS4] motif is distorted tetrahedral and approaches a trigonal monopyramidal geometry in which the thiolate ligand adopts an equatorial position; [TmBut]CdSPy and [TmBut]CdSePy, however, exhibit an additional long-range interaction with the pyridyl nitrogen atoms. The ability of the thiolate ligands to participate in exchange was probed by 1H and 19F nuclear magnetic resonance (NMR) spectroscopic studies of the reactions of [TmBut]CdSC6H4-4-F with ArSH (Ar = C6H4-4-But or C6H4-4-OMe), which demonstrate that (i) exchange is facile and (ii) coordination of thiolate to cadmium is most favored for the p-fluorophenyl derivative. Furthermore, a two-dimensional EXSY experiment involving [TmBut]CdSC6H4-4-F and 4-fluorothiophenol demonstrates that degenerate thiolate ligand exchange is also facile on the NMR time scale.

Synthesis, characterization, DNA binding, cleavage activity, cytotoxicity and molecular docking of new nano water-soluble [M(5-CH₂PPh₃-3,4-salpyr)](ClO₄)₂ (M = Ni, Zn) complexes

Some new water soluble complexes [N,N'-bis{5-[(triphenyl phosphonium chloride)-methyl]salicylidine}-3,4-diaminopyridine] M(ii), which are formulated as nano-[Zn(5-CH2PPh3-3,4-salpyr)](ClO4)2 (), [Zn(5-CH2PPh3-3,4-salpyr)](ClO4)2 (), nano-[Ni(5-CH2PPh3-3,4-salpyr)](ClO4)2 (), [Ni(5-CH2PPh3-3,4-salpyr)](ClO4)2 (), and [N,N'-bis{5-[(triphenyl phosphonium chloride)-methyl]salicylidine}-2,3-diaminopyridine]Ni(ii) [Ni(5-CH2PPh3-2,3-salpyr)](ClO4)2 () have been isolated and characterized by elemental analysis, FT-IR, (1)H NMR, (13)C NMR, (31)P NMR, and UV-vis spectroscopy. The morphology and size of the nano complexes were determined using FE-SEM and TEM. In vitro DNA binding studies were investigated by UV-vis absorption spectroscopy, viscosity measurements, CD spectroscopy, cyclic voltammetry, emission spectra and gel electrophoresis, which suggest that the metal complexes act as efficient DNA binders. The absorption spectroscopy of the compounds with DNA reveals that the DNA binding affinity (Kb) has this order: > > > > > Ligand. The metal complexes show DNA binding stronger than the ligand, which is expected due to the nature of the metal. The nano complexes display DNA binding stronger than the other complexes which is related to the effect of size on binding affinity and the Ni(ii) complexes reveal DNA binding stronger than the corresponding Zn(ii) analogues, which is expected due to their z* effect and geometry. The prominent double strand DNA cleavage abilities of compound are observed in the absence of H2O2 with efficiencies of more than 50% even at 70 μM complex concentration. Surprisingly, Zn(ii) complexes (compounds & ) exhibit a higher cytotoxicity (IC50: 7.3 & 10.9 μM at 24 h; IC50: 4.6 & 8.7 μM at 48 h) against human hepatoma (HepG2) and HeLa cell lines than the Ni(ii) complexes (compounds , & ) and 5-fluorouracil as control in spite of their inability to cleave DNA. Finally, DNA binding interactions were performed by docking studies. Density functional theory (DFT) studies were performed using the GAUSSIAN 03 program. The DFT method with B3LYP functional, LANL2DZ basis set for metal centers and 6-311g* for other atoms was used. The synthesized compounds and DNA were simulated by molecular docking to explore more details of the ligands conformation and their orientations in the active site of the receptor.

Dinuclear ZnII and mixed CuII-ZnII complexes of artificial patellamides as phosphatase models

The patellamides (cyclic pseudo-octapeptides) are produced by Prochloron, a symbiont of the ascidians, marine invertebrate filter feeders. These pseudo-octapeptides are present in the cytoplasm and a possible natural function of putative metal complexes of these compounds is hydrolase activity, however the true biological role is still unknown. The dinuclear Cu^II complexes of synthetic patellamide derivatives have been shown in in vitro experiments to be efficient hydrolase model catalysts. Many hydrolase enzymes, specifically phosphatases and carboanhydrases, are Zn^II-based enzymes and therefore, we have studied the Zn^II and mixed Zn^II/Cu^II solution chemistry of a series of synthetic patellamide derivatives, including solution structural and computational work, with the special focus on model phosphatase chemistry with bis-(2,4-dinitrophenyl)phosphate (BDNPP) as the substrate. The Zn^II complexes of a series of ligands are shown to form complexes of similar structure and stability compared to the well-studied Cu^II analogues and the phosphatase reactivities are also similar. Since the complex stabilities and phosphatase activities are generally a little lower compared to those of Cu^II and since the concentration of Zn^II in Prochloron cells is slightly smaller, we conclude that the Cu^II complexes of the patellamides are more likely to be of biological importance.