Artificial Metallonucleases Research Articles

Gene Editing with Artificial DNA Scissors.

Artificial metallo-nucleases (AMNs) are small molecule DNA cleavage agents, also known as DNA molecular scissors, and represent an important class of chemotherapeutic with high clinical potential. This review provides a primary level of exploration on the concepts key to this area including an introduction to DNA structure, function, recognition, along with damage and repair mechanisms. Building on this foundation, we describe hybrid molecules where AMNs are covalently attached to directing groups that provide molecular scissors with enhanced or sequence specific DNA damaging capabilities. As this research field continues to evolve, understanding the applications of AMNs along with synthetic conjugation strategies can provide the basis for future innovations, particularly for designing new artificial gene editing systems.

ÜÇ YENİ BİS(AÇİLHİDRAZON) MONONÜKLEER GEÇIŞ METALI KOMPLEKSİ: SENTEZ, KARAKTERİZASYON VE DNA ETKİLEŞİM ÇALIŞMALARI

In recent years, studies on the design and synthesis of artificial nucleases with biological, structural and coordination properties have been increasing. With this study, mononuclear complex compounds were obtained with Cu(II), Ni(II) and Zn(II) transition metal ion salts of bis(acylhydrazone) ligand, which has the potential to show biological activity and has revolving atoms such as N and O in its structure. The characteristic structures of the obtained complex compounds were elucidated using various techniques such as FTIR, UV-Visible, 1H-NMR, TGA, elemental analysis and magnetic susceptibility. The DNA-binding activities of potential artificial metallonucleases, whose structures were elucidated, were investigated using the UV-visible absorption titration method. Additionally, their DNA-cleavge activities were analyzed using the agarose gel electrophoresis method. The DNA binding mode and cleavage mechanisms were determined as part of this study.. In line with the results obtained, it was determined that the binding mode between DNA and the complexes is a noncovalent interaction. It has been demonstrated that the compounds cleavage DNA both oxidatively and hydrolytically. It has been revealed that the radicals involved in DNA cleavage activity are H2O2, superoxide and hydroxyl radicals. It was revealed that the compound with the highest cleavage and bonding interaction was the Cu(II) complex, followed by Ni(II) and Zn(II) complexes.

A Click Chemistry-Based Artificial Metallo-Nuclease.

Artificial metallo-nucleases (AMNs) are promising DNA damaging drug candidates. Here, we demonstrate how the 1,2,3-triazole linker produced by the Cu-catalysed azide-alkyne cycloaddition (CuAAC) reaction can be directed to build Cu-binding AMN scaffolds. We selected biologically inert reaction partners tris(azidomethyl)mesitylene and ethynyl-thiophene to develop TC-Thio, a bioactive C3 -symmetric ligand in which three thiophene-triazole moieties are positioned around a central mesitylene core. The ligand was characterised by X-ray crystallography and forms multinuclear CuII and CuI complexes identified by mass spectrometry and rationalised by density functional theory (DFT). Upon Cu coordination, CuII -TC-Thio becomes a potent DNA binding and cleaving agent. Mechanistic studies reveal DNA recognition occurs exclusively at the minor groove with subsequent oxidative damage promoted through a superoxide- and peroxide-dependent pathway. Single molecule imaging of DNA isolated from peripheral blood mononuclear cells shows that the complex has comparable activity to the clinical drug temozolomide, causing DNA damage that is recognised by a combination of base excision repair (BER) enzymes.

Polypyridyl-Based Copper Phenanthrene Complexes: Combining Stability with Enhanced DNA Recognition.

We report a series of copper(II) artificial metallo-nucleases (AMNs) and demonstrate their DNA damaging properties and in-vitro cytotoxicity against human-derived pancreatic cancer cells. The compounds combine a tris-chelating polypyridyl ligand, di-(2-pycolyl)amine (DPA), and a DNA intercalating phenanthrene unit. Their general formula is Cu-DPA-N,N' (where N,N'=1,10-phenanthroline (Phen), dipyridoquinoxaline (DPQ) or dipyridophenazine (DPPZ)). Characterisation was achieved by X-ray crystallography and continuous-wave EPR (cw-EPR), hyperfine sublevel correlation (HYSCORE) and Davies electron-nuclear double resonance (ENDOR) spectroscopies. The presence of the DPA ligand enhances solution stability and facilitates enhanced DNA recognition with apparent binding constants (Kapp ) rising from 105 to 107 m-1 with increasing extent of planar phenanthrene. Cu-DPA-DPPZ, the complex with greatest DNA binding and intercalation effects, recognises the minor groove of guanine-cytosine (G-C) rich sequences. Oxidative DNA damage also occurs in the minor groove and can be inhibited by superoxide and hydroxyl radical trapping agents. The complexes, particularly Cu-DPA-DPPZ, display promising anticancer activity against human pancreatic tumour cells with in-vitro results surpassing the clinical platinum(II) drug oxaliplatin.

A Computational Chemistry Approach for the Hydrolysis of DNA Molecule by Hydrated Transition Metal Complexes as Artificial Metallonuclease

인공 핵산분해효소로 작용하는 10종의 수화된 (배위수: 6) 단일 리간드 전이금속 착 화합물([M(H₂O)₆]z⁺ 및 [M(OH)₆]z⁻)과 DNA분자의 해리반응(pKa)전 후 조건에서, 전산화학적인 경계분자궤도(FMO) 이론에 따른 이들 화합물의 반응성을 정량적으로 검토하였다. 그리고 분자 간 FMO에너지 차이(ΔE)로부터, Lewis acid 촉매로서 금속 착 화합물의 친핵성 리간드 활성화(A)에 따른 궤도조절(orbital control) 반응과 금속 착 화합물의 활성화(B)로 인한 전하조절(charge control) 반응이 각각 예측되었다. 모든 경우에 반응성은 물 분자 리간드 금속 착 화합물([M(H₂O)₆]z⁺)보다 hydroxo 리간드 금속 착 화합물([M(OH)₆]z⁻)이 높았으며, 그리고 2가 화합물([M(H₂O)₆]²⁺ 및 [M(OH)₆]⁴⁻)이 3가 화합물([M(H₂O)₆]³⁺ 및 [M(OH)₆]³⁻)보다 빠른 반응성을 나타내었다. 이들의 반응성은 주로 [M(OH)6]z⁻과 해리 후 DNA분자 사이의 음 이온성 반발력이나 착 이온의 입체효과와 전하크기에 의존적이었다. 그러므로 이 같은 리간드 효과로부터 가장 빠른 반응조건에서(6M) HOMO에너지에 의존적인 주 반응(A)에 따른 [M(OH)₆]z⁻에 의한 DNA 분자의 가수분해 전환과정(turnover process)을 제시하였다.The acting as artificial metallonucleases under the condition at before and after dissociation (pKa) of DNA molecule and 10 hydrated (coordination number: 6) homoleptic transition metal complexes ([M(H₂O)₆]z⁺ & [M(OH)₆]z⁻) are reviewed quantitatively based on the frontier molecule orbital (FMO) theory in computational chemistry. In additions, from the FMO energy difference (ΔE) between the complexes and DNA molecule, the orbital control reaction by nucleophilic ligand activation (A) of the metal complexes as Lewis acid catalyst, and the charge control reaction by activation (B) of the metal complexes are predicted, respectively. Hence, the reactivity of [M(OH)₆]z⁻ was higher than that of [M(H₂O)₆]z⁺ in all cases. Moreover, divalent ([M(H₂O)₆]²⁺ and [M(OH)₆]⁴⁻) show rapid responses comparing to the trivalent compounds ([M(H₂O)₆]³⁺ and [M(OH)₆]³⁻). Their reactivity was mainly dependent on the anionic repulsive force between hydroxo ligand metal complex and dissociated DNA molecule, or steric effect and charge size of complexe ions. Therefore, from these results of ligand effect, the turnover process on the hydrolytic decomposition of contaminated DNA molecule by homoleptic hydroxo metal complexes ([M(OH)₆]z⁻) in the fastest reaction condition (6M) was proposed as the major reaction (A) depend upon the HOMO energy.

Fluorescence and absorption studies of DNA-Pd(II) complex interaction: Synthesis, spectroanalytical investigations and biological activities.

Novel palladium(II) complexes (7a-7e) of substituted quinoline derivatives were synthesized. The complexes were characterized using various techniques such as thermogravimetric analysis (TGA), elemental analysis, conductance measurement, mass, absorption, infra-red (IR), 1 H NMR, 13 C NMR and energy-dispersive X-ray spectroscopy (EDX). Complexes for herring sperm DNA (HS DNA) binding were explored and absorption titration and the binding constant (Kb ) as well as Gibb's free energy were evaluated. Complex 7d exhibited the highest binding constant, therefore the thermodynamic parameters of 7d at different temperatures were evaluated. To support the results of the absorption titration, fluorescence titration, viscosity measurement and molecular docking studies were performed. The fluorescence quenching data as evaluated from Stern-Volmer equation were used to calculate KSV , Kf and the number of binding sites. The results of all these studies were in good agreement with the absorption study. DNA electrophoretic mobility was performed to explore the possible application of metal complexes as artificial metallonucleases. The antibacterial activity of the complexes was accessed against different pathogenic bacteria and cytotoxicity was measured using brine shrimp and S. pombe.

A phosphate-targeted dinuclear Cu(II) complex combining major groove binding and oxidative DNA cleavage.

Free radical generation is an inevitable consequence of aerobic existence and is implicated in a wide variety of pathological conditions including cancer, cardiovascular disease, ageing and neurodegenerative disorder. Free radicals can, however, be used to our advantage since their production is catalysed by synthetic inorganic molecules—termed artificial metallonucleases—that cut DNA strands by oxidative cleavage reactions. Here, we report the rational design and DNA binding interactions of a novel di-Cu2+ artificial metallonuclease [Cu2(tetra-(2-pyridyl)-NMe-naphthalene)Cl4] (Cu2TPNap). Cu2TPNap is a high-affinity binder of duplex DNA with an apparent binding constant (Kapp) of 107 M(bp)−1. The agent binds non-intercalatively in the major groove causing condensation and G-C specific destabilization. Artificial metallonuclease activity occurs in the absence of exogenous reductant, is dependent on superoxide and hydrogen peroxide, and gives rise to single strand DNA breaks. Pre-associative molecular docking studies with the 8-mer d(GGGGCCCC)2, a model for poly[d(G-C)2], identified selective major groove incorporation of the complex with ancillary Cu2+-phosphate backbone binding. Molecular mechanics methods then showed the d(GGGGCCCC)2 adduct to relax about the complex and this interaction is supported by UV melting experiments where poly[d(G-C)2] is selectively destabilized.

Cu(II) complexes with hydrazone-functionalized phenanthrolines as self-activating metallonucleases

Cu(II) phenanthroline complexes are able to cleave DNA and show cytotoxic activity against cancer cells. Also, the biological activity of hydrazone-based compounds has been reported in the literature. This motivated us to combine these two systems. Hydrazone-functionalized phenanthroline ligands with acetyl and benzoyl substituents were synthesized and characterized. The DNA cleavage activity of the corresponding Cu(II) complexes 3 and 4 was compared to the one of the well-known [Cu(phen)2]2+ complex (1) and [Cu(phenD)2]2+ complex (2, phenD = 1,10-phenanthroline-5,6-dione, the precursor of hydrazone-functionalized phenanthrolines). In the presence of ascorbate, but also in its absence, oxidative cleavage of DNA was proven by quenching therein involved reactive oxygen species (ROS), specifically hydrogen peroxide and superoxide anion radicals. Only complexes 2–4 were active in the absence of ascorbate, but not [Cu(phen)2]2+ (1). The surprising occurrence of ROS in the absence of any activating agent indicates that 2–4 represent self-activating artificial metallonucleases. Thereby, self-activation was most prominent for the novel hydrazone-based complexes 3 and 4. Cyclic voltammetry and circular dichroism spectroscopy were applied to get an insight in redox behavior and DNA binding characteristics of the Cu(II) complexes and thus to explain their different nuclease activity.

Acetyl pyridine-based palladium(II) compounds as an artificial metallonucleases

Palladium(II) complexes of type [Pd(Ln)Cl2] and [Pd(bdt)(Ln)] have been synthesized using 2-acetyl pyridine derivatives(Ln) and benzene-12-dithiol(bdt). The synthesized complexes have been characterized by various analytical techniques like thermo gravimetric analysis, elemental analysis, conductance measurement, and spectroscopic techniques like elemental analysis, mass spectra, absorption spectra, IR, 1H NMR, energy-dispersive X-ray spectroscopy. The interaction of the complexes with calf-thymus DNA (CT-DNA) has been explored by absorption titration, viscosity measurement methods. Based on the observations, an intercalative binding mode of DNA has been proposed. In order to provide additional evidence for the intercalation mode of binding between the complex and CT-DNA, fluorescence titration experiment was performed. In addition, molecular modeling study has been carried out with the aim of establishing the complex’s binding mode. Antibacterial activity study of the complexes have been screened against pathogenic bacteria such as Staphylococcus aureus, Escherichia coli, Bacillus subtilis, Serratia marcescens, and Pseudomonas aeruginosa. Gel electrophoresis assay demonstrates that all the complexes can cleave the pUC19 plasmid DNA.

Synthesis, spectral investigation and development of tetrahedral copper(II) complexes as artificial metallonucleases and antimalarial agents

Seven new copper(II) complexes of type [Cu(A)(L)]⋅H2O (A = sparfloxacin, ciprofloxacin, levofloxacin, gatifloxacin, pefloxacin, ofloxacin, norfloxacin; L = 5‐[(3‐chlorophenyl)diazenyl]‐4‐hydroxy‐1,3‐thiazole‐2(3H)‐thione) were synthesized and characterized using elemental and thermogravimetric analyses, and electronic, electron paramagnetic resonance (EPR), Fourier transform infrared and liquid chromatography–mass spectroscopies. Tetrahedral geometry around copper is assigned in all complexes using EPR and electronic spectral analyses. All complexes were investigated for their interaction with herring sperm DNA utilizing absorption titration (Kb = 1.27–3.13 × 105 M−1) and hydrodynamic volume measurement studies. The studies suggest the classical intercalative mode of DNA binding. The cleavage reaction on pUC19 DNA was monitored by agarose gel electrophoresis. The results indicate that the Cu(II) complexes can more effectively promote the cleavage of plasmid DNA. The superoxide dismutase mimic activity of the complexes was evaluated by nitroblue tetrazolium assay, and the complexes catalysed the dismutation of superoxide at pH = 7.8 with IC50 values in the range 0.597–0.900 μM. The complexes were screened for their in vitro antibacterial activity against five pathogenic bacteria. All the complexes are good cytotoxic agents and show LC50 values ranging from 5.559 to 11.912 µg ml−1. All newly synthesized Cu(II) complexes were also evaluated for their in vitro antimalarial activity against Plasmodium falciparum strain (IC50 = 0.62–2.0 µg ml−1). Copyright © 2015 John Wiley & Sons, Ltd.

Catalytic Metal Ions and Enzymatic Processing of DNA and RNA

CONSPECTUS: Two-metal-ion-dependent nucleases cleave the phosphodiester bonds of nucleic acids via the two-metal-ion (2M) mechanism. Several high-resolution X-ray structures portraying the two-metal-aided catalytic site, together with mutagenesis and kinetics studies, have demonstrated a functional role of the ions for catalysis in numerous metallonucleases. Overall, the experimental data confirm the general mechanistic hypothesis for 2M-aided phosphoryl transfer originally reported by Steitz and Steitz ( Proc. Natl. Acad. Sci. U.S.A. 1993 , 90 ( 14 ), 6498 - 6502 ). This seminal paper proposed that one metal ion favors the formation of the nucleophile, while the nearby second metal ion facilitates leaving group departure during RNA hydrolysis. Both metals were suggested to stabilize the enzymatic transition state. Nevertheless, static X-ray structures alone cannot exhaustively unravel how the two ions execute their functional role along the enzymatic reaction during processing of DNA or RNA strands when moving from reactants to products, passing through metastable intermediates and high-energy transition states. In this Account, we discuss the role of multiscale molecular simulations in further disclosing mechanistic insights of 2M-aided catalysis for two prototypical enzymatic targets for drug discovery, namely, ribonuclease H (RNase H) and type II topoisomerase (topoII). In both examples, first-principles molecular simulations, integrated with structural data, emphasize a cooperative motion of the bimetal motif during catalysis. The coordinated motion of both ions is crucial for maintaining a flexible metal-centered structural architecture exquisitely tailored to accommodate the DNA or RNA sugar-phosphate backbone during phosphodiester bond cleavage. Furthermore, our analysis of RNase H and the N-terminal domain (PAN) of influenza polymerase shows that classical molecular dynamics simulations coupled with enhanced sampling techniques have contributed to describe the modulatory effect of metal ion concentration and metal uptake on the 2M mechanism and efficiency. These aspects all point to the emerging and intriguing role of additional adjacent ions potentially involved in the modulation of phosphoryl transfer reactions and enzymatic turnover in 2M-catalysis, as recently observed experimentally in polymerase η and homing endonuclease I-DmoI. These computational results, integrated with experimental findings, describe and reinforce the nascent concept of a functional and cooperative dynamics of the catalytic metal ions during the 2M-dependent enzymatic processing of DNA and RNA. Encouraged by the insights provided by computational approaches, we foresee further experiments that will feature the functional and joint dynamics of the catalytic metal ions for nucleic acid processing. This could impact the de novo design of artificial metallonucleases and the rational design of potent metal-chelating inhibitors of pharmaceutically relevant enzymes.

Synthesis, Characterization and Biological Elucidation of Mixed Ligand Cu(II) Complexes as Artificial Metallonucleases

Synthesis, Characterization and Biological Elucidation of Mixed Ligand Cu(II) Complexes as Artificial Metallonucleases Bipyridines (L1–L7) derived from reaction between chalcones and pyridinium salt have been synthesized and characterized by IR, 1H–NMR and 13C–NMR techniques. The synthesized ligands have been screened for their antibacterial and DNA binding activities. Subsequently their complexes have been synthesized with CuCl2•2H2O and ofloxacin and characterized by elemental analysis, magnetic moment measurement, thermal analysis (TG), IR, LC–MS and electronic spectra. Antibacterial activity of complexes has been elucidated in terms of MIC values. Absorption titration, viscosity measurement and gel electrophoresis techniques have been performed to examine the base specific interaction of Cu(II) complexes with DNA. Result shows efficient DNA binding and cleavage ability of synthesized Cu(II) complexes compared to the reference drug and bipyridine derivatives.

Copper Complexes of N‐Donor Ligands as Artificial Nucleases

Invited for the cover of this issue is the group of Nora Kulak at Freie Universitat Berlin. The cover image shows metal complexes capable of cleaving DNA, so-called artificial metallonucleases based on copper as the central atom and comprising N-donor ligands. Heteroaromatic, macrocyclic, and peptidic ligand systems are adumbrated in the background.

Regulating Bioactivity of Cu2+ Bis-1,10-phenanthroline Artificial Metallonucleases with Sterically Functionalized Pendant Carboxylates

The synthetic chemical nuclease, [Cu(1,10-phenanthroline)2](2+), has stimulated research within metallonuclease development and in the area of cytotoxic metallodrug design. Our analysis reveals, however, that this agent is "promiscuous" as it binds both dsDNA and protein biomolecules, without specificity, and induces general toxicity to a diversity of cell lineages. Here, we describe the synthesis and characterization of small-molecule metallonucleases containing the redox-active cation, [Cu(RCOO)(1,10-phen)2](+), where 1,10-phen = 1,10-phenanthroline and R = -H, -CH3, -C2H5, -CH(CH3)2, and -C(CH3)3. The presence of coordinated carboxylate groups in the complex cation functions to enhance dsDNA recognition, reduce serum albumin binding, and offer control of toxicity toward human cancer cells, Gram positive and negative bacteria, and fungal pathogens. The induction of genomic dsDNA breaks (DSBs) were identified in ovarian adenocarcinoma cells using immunodetection of γ-H2AX. Formate, acetate, and pivalate functionalized complexes induced DSBs in a higher percentage of cells compared with [Cu(1,10-phen)2](2+), which supports the importance of inner-sphere modification toward enhancing targeted biological application.

Progress in artificial metallonucleases

The development of synthetic agents able to hydrolytically cleave DNA with high efficiency and selectivity is still a fascinating challenge. Over the years, many examples have been reported reproducing part of the behaviour of the corresponding natural enzymes. Eventually, even the possibility to apply such systems to the manipulation of DNA of higher organisms has been demonstrated. However, efficiency of enzymes is still unrivalled. This feature article discusses the progress reported toward the realization of synthetic nucleases with particular attention to the comprehension of the reaction mechanisms and to the strategies that need to be addressed to obtain more efficient systems.

DNA targeting and cleavage by an engineered metalloprotein dimer

Nature has illustrated through numerous examples that protein dimerization has structural and functional advantages. We previously reported the design and characterization of an engineered "metallohomeodomain" protein (C2) based on a chimera of the EF-hand Ca-binding motif and the helix-turn-helix motif of homeodomains (Lim and Franklin in Protein Sci. 15:2159-2165, 2004). This small metalloprotein binds the hard metal ions Ca(II) and Ln(III) and interacts with DNA with modest sequence preference and affinity, yet exhibits only residual DNA cleavage activity. Here we have achieved substantial improvement in function by constructing a covalent dimer of this C2 module (F2) to create a larger multidomain protein. As assayed via fluorescence spectroscopy, this F2 protein binds Ca(II) more avidly (25-fold) than C2 on a per-domain basis; in gel shift selection experiments, metallated F2 exhibits a specificity toward 5'-TAATTA-3' sequences. Finally, Ca(2)F2 cleaves plasmid DNA and generates a linear product in a Ca(II)-dependent way, unlike the CaC2 monomer. To the best of our knowledge this activation of Ca(II) in the context of an EF-hand binding motif is unique and represents a significant step forward in the design of artificial metallonucleases by utilizing biologically significant metal ions.

Towards Artificial Metallonucleases for Gene Therapy: Recent Advances and New Perspectives

The process of DNA targeting or repair of mutated genes within the cell, induced by specifically positioned double-strand cleavage of DNA near the mutated sequence, can be applied for gene therapy of monogenic diseases. For this purpose, highly specific artificial metallonucleases are developed. They are expected to be important future tools of modern genetics. The present state of art and strategies of research are summarized, including protein engineering and artificial 'chemical' nucleases. From the results, we learn about the basic role of the metal ions and the various ligands, and about the DNA binding and cleavage mechanism. The results collected provide useful guidance for engineering highly controlled enzymes for use in gene therapy.

Investigation and improvement of DNA cleavage models of polyamide + Cu(II) nuclease + OOH- ligands bound to DNA

BackgroundCopper nucleases as a famous class of artificial metallonucleases have attracted considerable interest in relation to their diverse potentials not only as therapeutic agents but also in genomic researches. Copper nucleases present high efficient oxidative cleavage of DNA, in which DNA strand scission occurs generally after hydrogen atom abstracted from a sugar moiety. In order to achieve the selective cleavage of DNA sequences by copper nucleases, the DNA specific recognition agents of the Dervan-type hairpin and cyclic polyamides can be considered as proper carriers of copper nucleases. Investigation of the DNA cleavage selectivity of copper nucleases assisted by the hairpin and cyclic polyamides at the molecular level has not yet been elucidated.ResultsWe carried out a series of molecular dynamics simulations for the nuclease [Cu(BPA)]2+ or [Cu(IDB)]2+ bound to the hairpin/cyclic polyamide and associated with DNA to investigate the selective DNA cleavage properties of Cu(II)-based artificial nucleases. The simulated results demonstrate that the DNA cleavage selectivity of the two nucleases assisted by the hairpin polyamide is improved efficiently. The [Cu(BPA)]2+ or [Cu(IDB)]2+ nuclease with a substrate OOH- bound to the hairpin polyamide can be stably located at the minor groove of DNA, and possibly abstracts H atom from the sugar of DNA. However, the DNA cleavage properties of the two nucleases assisted by the cyclic polyamide are significantly poor due to the rigidity of linking region between the cyclic polyamide and nuclease. With introduction of the flexible linker -CH2CH2CH2NH2, the modified cyclic polyamide can assist the two copper nucleases to improve the selective DNA cleavage properties efficiently.ConclusionA flexible linker and a proper binding site of the polyamide-type recognition agents play an important role in improving the DNA cleavage selectivity of copper nucleases. Current investigations provide an insight into the DNA cleavage specificities of chemical nucleases assisted by an appropriate nucleic acid recognition agent.

Promotive Effect of the Platinum Moiety on the DNA Cleavage Activity of Copper-Based Artificial Nucleases

Copper-based artificial metallonucleases are likely to satisfy more biomedical requirements if their DNA cleavage efficiency and selectivity could be further improved. In this study, two copper(II) complexes, [CuL(1)Cl(2)] (1) and [CuL(2)Cl(2)] (2), and two copper(II)-platinum(II) heteronuclear complexes, [CuPtL(1)(DMSO)Cl(4)] (3) and [CuPtL(2)(DMSO)Cl(4)] (4), were synthesized using two bifunctional ligands, N-[4-(2-pyridylmethoxy)benzyl]-N,N-bis(2-pyridylmethyl)amine (L(1)) and N-[3-(2-pyridylmethoxy)benzyl]-N,N-bis(2-pyridylmethyl)amine (L(2)). These complexes have been characterized by elemental analysis, electrospray ionization mass spectrometry, IR spectroscopy, and UV-vis spectroscopy. The DNA binding ability of these complexes follows an order of 1 < 2 < 3 < 4, as revealed by the results of spectroscopy and agarose gel electrophoresis studies. Their cleavage activity toward supercoiled pUC19 plasmid DNA is prominent at micromolar concentration levels in the presence of ascorbic acid. The introduction of a platinum(II) center to the copper(II) complexes induces a significant enhancement in cleavage activity as compared with copper(II) complexes alone. These results show that the presence of a platinum(II) center in copper(II) complexes strengthens both their DNA binding ability and DNA cleavage efficiency.

Resin-supported catalytic dendrimers as multivalent artificial metallonucleases

Tentagel resin was functionalized with dendrons containing 4 and 8 triazacyclononane ligands able to complex the Zn II metal ion. The supported dendritic metallo-complexes showed enzyme-like behaviour in the cleavage of HPNPP, a model substrate for RNA. The obtained Michaelis–Menten parameters were in excellent agreement with those obtained for the identical catalysts in solution. Diffusion studies have revealed the upper limit for the rate constants that can be assessed under these conditions.