Metallo-intercalators and metallo-insertors

Since the elucidation of the structure of double helical DNA, the construction of small molecules that recognize and react at specific DNA sites has been an area of considerable interest. In particular, the study of transition metal complexes that bind DNA with specificity has been a burgeoning field. This growth has been due in large part to the useful properties of metal complexes, which possess a wide array of photophysical attributes and allow for the modular assembly of an ensemble of recognition elements. Here we review recent experiments in our laboratory aimed at the design and study of octahedral metal complexes that bind DNA non-covalently and target reactions to specific sites. Emphasis is placed both on the variety of methods employed to confer site-specificity and upon the many applications for these complexes. Particular attention is given to the family of complexes recently designed that target single base mismatches in duplex DNA through metallo-insertion.     

Artificial G-wire switch with 2,2'-bipyridine units responsive to divalent metal ions

Development of a guanine nanowire (G-wire) that is controllable and can be switched by external signals is important for the creation of molecular electronic technologies. Here, we constructed a G-wire in which the thymines of the main chain of d(G4T4G4) were replaced with 2,2'-bipyridine units, which have two aromatic rings that rotate arbitrarily upon coordination with metal ions. Circular dichroism of the DNA oligonucleotides with or without the 2,2'-bipyridine unit showed that divalent metal ions induce the bipyridine-containing oligonucleotide to switch from an antiparallel to a parallel G-quadruplex. Native polyacrylamide gel electrophoresis showed that the parallel-stranded G-quadruplex DNA had a high-order structure. Circular dichroism and native gel electrophoresis analyses suggested that adding Na2EDTA causes a reverse structural transition from a parallel-stranded high-order structure to an antiparallel G-quadruplex. Moreover, atomic force microscopy showed a long nanowire ( approximately 200 nm) in the presence of Ni2+ but no significant image in the absence of Ni2+ or in the presence of both Ni2+ and Na2EDTA. These observations revealed that the parallel-stranded high-order structure is a G-wire containing numerous DNA oligonucleotide strands bound together via divalent metal ion-2,2'-bipyridine complexes. Finally, we found that alternating addition of Ni2+ and Na2EDTA can cycle the G-wire between the high-order and disorganized structures, with an average cycling efficiency of 0.95 (i.e., 5% loss per cycle). These results demonstrate that a DNA oligonucleotide incorporating the 2,2'-bipyridine unit acts as a G-wire switch that can be controlled by chemical input signals, namely, divalent metal ions.     

水杨酸金属配合物与牛血清白蛋白的相互作用

本文采用荧光法研究了水杨酸金属配合物与牛血清白蛋白的相互作用。观察到水杨酸金属配合物对牛血清白蛋白荧光产生猝灭现象,猝灭方式为静态猝灭。计算了结合常数和结合位点数。并且用圆二色谱法研究水杨酸金属配合物对牛血清白蛋白二级结构的影响,发现水杨酸金属配合物的存在明显改变牛血清白蛋白的构象。     

A comparison of the binding of metal complexes to duplex and quadruplex DNA

Electrospray ionisation mass spectrometry (ESI-MS) and circular dichroism (CD) spectroscopy were used to compare the binding of mononuclear nickel, ruthenium and platinum complexes to double stranded DNA (dsDNA) and quadruplex DNA (qDNA). CD studies provided evidence for the binding of intact complexes of all three metal ions to qDNA. ESI mass spectra of solutions containing platinum or ruthenium complexes and qDNA showed evidence for the formation of non-covalent complexes consisting of intact metal molecules bound to DNA. However, the corresponding spectra of solutions containing nickel complexes principally contained ions consisting of fragments of the initial nickel molecule bound to qDNA. In contrast ESI mass spectra of solutions containing nickel, ruthenium or platinum complexes and dsDNA only showed the presence of ions attributable to intact metal molecules bound to DNA. The fragmentation observed in mass spectral studies of solutions containing nickel complexes and qDNA is attributable to the lower thermodynamic stability of the former metal complexes relative to those containing platinum or ruthenium, as well as the slightly harsher instrumental conditions required to obtain spectra of qDNA. This conclusion is supported by the results of tandem mass spectral studies, which showed that ions consisting of intact nickel complexes bound to qDNA readily undergo fragmentation by loss of one of the ligands initially bound to the metal. The ESI-MS results also demonstrate that the binding affinity of each of the platinum and ruthenium complexes towards qDNA is significantly less than that towards dsDNA.     

钌配合物与G-四链体DNA的相互作用研究进展

人体端粒由富含鸟嘌呤(G)的DNA重复序列组成,该序列在一定条件下可以形成G-四链体DNA结构。小分子化合物诱导该结构的形成并使之稳定,可以抑制端粒酶活性而达到抗肿瘤的目的。因此,G-四链体DNA稳定剂的设计和筛选是近年来生物无机化学的重要前沿研究领域之一。在金属配合物中,钌配合物由于具有丰富的光化学、光物理特性以及生物活性,其作为G-四链体DNA稳定剂引起人们的高度关注。本文以近年一些代表性的研究工作为例,对钌配合物与G-四链体DNA相互作用方面的研究进展进行了综述。     

DNA modified with metal complexes: Applications in the construction of higher order metal–DNA nanostructures

DNA has recently emerged as a useful building block for higher order nanostructures, such as extended two-dimensional surfaces and discrete two- and three-dimensional structures. Transition metal complexes can introduce functionality to these otherwise passive nanostructures. This review examines the synthetic strategies used to introduce metals in a site-specific manner to DNA: either by attaching preformed metal complexes to DNA, or by metal coordination to unmodified or modified DNA. The applications of metal–DNA complexes in building higher order nanostructures and the utility of attaching luminescent or electrochemical labels are discussed.     

2-羟基苯乙酮铜(Ⅱ)配合物与ct-DNA的键合作用研究

以小牛胸腺DNA为靶点,通过紫外可见吸收光谱、稳态荧光发射光谱、圆二色谱和DNA粘度滴定实验,从分子水平研究了2-羟基苯乙酮铜(Ⅱ)配合物[ Cu(HAP)2] (1)与ct-DNA的键合方式.结果表明:配合物[ Cu(HAP)2] (1)主要通过插入作用和静电结合方式与ct-DNA形成键合作用,推测插入作用应基于2-...     

Hairpin-shaped heterometallic luminescent lanthanide complexes for DNA intercalative recognition

Luminescent Ln-Pt2 metallohairpin complexes have been developed, and their intercalative recognition with DNA has been demonstrated with linear dichroism spectroscopy. The heterotrimetallic complexes were formed in a one-step reaction, by assembly of an aminopolycarboxylate ligand, a platinum terpyridine unit, and the lanthanide salt. The metallohairpin complexes bear a neutral lanthanide moiety and two positively charged platinum-containing intercalating units. The Nd(III) analogues are luminescent in the near infrared, and this near-IR luminescence is retained upon binding to DNA. The DNA recognition was demonstrated by linear dichroism spectroscopy. The linear dichroism spectra suggested that the complexes bind perpendicular to the DNA helical axis, confirming intercalative recognition accompanied by dramatic stiffening of DNA, which suggests bis-intercalation of the complex.     

Kinetically inert transition metal complexes that reversibly bind to DNA

Transition metal complexes that reversibly bind to DNA have been studied for almost 30 years. In the last few years a variety of new systems have been developed, employing a range of metal ions and ligand architectures. In many cases, high affinity binding and specific selectivities have been observed. These complexes display properties that make them attractive as probes of DNA structure and function, suggesting that they may find a r?le as prototypical tools for a spectrum of applications, from basic molecular biology to medicine. This review presents an overview of some of the structures and properties of such complexes.     

Metal-salen-base-pair complexes inside DNA: complexation overrides sequence information

Two isomeric salicylic aldehyde nucleobases have been prepared and incorporated into various DNA duplexes. Reaction with ethylenediamine leads to formation of the well-known salen ligand inside the DNA double helix. Addition of transition-metal ions such as Cu(2+), Mn(2+), Ni(2+), Fe(2+), or VO(2+) results in the formation of metal-salen-base-pair complexes, which were studied by using UV and circular dichroism (CD) spectroscopy. HPLC and ESI mass spectrometric measurements reveal an unusually high stability of the DNA-metal system. These metal-salen complexes act as interstrand cross-links and thereby lead to a strong stabilization of the DNA duplexes, as studied by thermal de- and renaturing experiments. Complex formation is strong enough to override sequence information even when the preorganization of the ligand precursors is unfavorable and the DNA duplex is distorted by the metal complexation. Furthermore, melting-point studies show that the salen complex derived from ligand 2 fits better into the DNA duplex, in accordance with results obtained from the crystal structure of the corresponding copper-salen complex 8.     

白蛋白结合希夫碱铜配合物及抗氧自由基性能

以水溶性生物高分子牛血清白蛋白(BSA)为载体,与小分子2,4-二羟基水杨醛缩甘氨酸希夫碱金属配合物(SalGlyM,M=Cu、Zn)结合,制得了水溶性生物高分子金属配合物结合体(SalGlyM@BSA)。采用FT-IR、UV-Vis、CD和SDS-PAGE电泳对其结构进行了表征。采用NBT光化学还原法考察了SalGlyM@BSA的抗O2.-活性,探讨了金属配合物结合体清除O2.-的机理。结果表明氨基酸希夫碱具有一定的抗O2.-活性,结合生物高分子载体后,SalGlyM@BSA具有良好的水溶性和O2.-清除能力。     

Synthesis, characterization, DNA binding and cytotoxicity studies of moxifloxacinato complexes

Five metal complexes of the third-generation quinolone antibacterial agent moxifloxacin with Cu(II), Fe(III), Mn(II), Ni(II) and VO(II) have been synthesized and characterized by physicochemical and spectroscopic techniques. In these complexes, moxifloxacin acts as a bidentate deprotonated ligand bound to the metal through ketone and carboxylate oxygens. The interactions between the metal complexes and calf thymus DNA have been studied by UV?CVis, circular dichroism and cyclic voltammetry. Fluorescence competitive binding studies with ethidium bromide (EB) demonstrate the ability of the complexes to displace the EB bound to DNA. The cytotoxicities of the complexes have been evaluated on A549 cells by the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide) method. [Cu(MFL)₂(H₂O)₂] shows the highest anticancer potency. The apoptosis-inducing activity was assessed by acridine orange/ethidium bromide staining assay.     

Interaction of bleomycin with deoxyribonucleic acid oligomer: proton nuclear magnetic resonance titration study using novel bleomycin complexes with Ni2+ and VO3+.

Two metal complexes of bleomycin (BLM), BLM-Ni2+ and BLM-VO3+ are used for studying interactions between BLM and deoxyribonucleic acid (DNA) by nuclear magnetic resonance. Although these BLMs do not mediate DNA strand scission under the usual conditions, they bind to DNA in the same manner as the active metal complexes of bleomycin (BLM-Fe2+ and BLM-Co3+). A self-complementary dodecanucleotide, d(CCCCAGCTGGGG), having a single site for cleavage was synthesized. d(CCCCAATTGGGG), which contains no -GpC- sequence, was also synthesized. The BLM-metal complexes were shown to bind specifically to the GpC site by circular dichroism and fluorescence titration studies. We assigned all the resonances for imino protons and phosphorus, and most of the nonexchangeable proton resonances of d(CCCCAGCTGGGG). No substantial change in the chemical shifts of these signals was observed upon titration with either BLM-Ni2+ or BLM-VO3+. This result is not consistent with a model of the strong intercalation of the BLMs between the base-pairs. The BLMs bind to DNA in a different manner, and DNA does not change its conformation upon binding with BLMs.     

DNA binding and biological activity of some platinum(II) intercalating compounds containing methyl-substituted 1,10-phenanthrolines

This study documents the first detailed investigation into the relationship between molecular structure and biological activity of platinum(II) complexes containing methylated derivatives of 1,10-phenanthroline (phen). A series of square planar platinum(II) compounds incorporating methylated derivatives of phen, 4-methyl-1,10-phenanthroline (4-Mephen), 5-methyl-1,10-phenanthroline (5-Mephen), 4,7-dimethyl-1,10-phenanthroline (4,7-Me2phen), 5,6-dimethyl-1,10-phenanthroline (5,6-Me2phen) and 3,4,7,8-tetramethyl-1,10-phenanthroline (3,4,7,8-Me4phen) were synthesised and the relationship between their structure and biological activity investigated. The biological activity of these compounds was quantified using the in vitro cytotoxicity assay against the L1210 Murine leukaemia cell line. Large variation in cytotoxicities with different methylation was observed. The 5- and 5,6-methylated derivatives of phen displayed a greater biological activity, with IC50 values of 2.8 +/- 0.8 microM and 1.5 +/- 0.3 microM respectively, compared with the phen compound, with an IC50 value of 9.7 +/- 0.3 microM, while all the others were inactive with IC50 values over 50 microM. Binding constants were determined using circular dichroism spectroscopy (CD) and induced circular dichroism (ICD). ICD was used to highlight any differences in the spectra. Viscometry studies and linear dichroism (LD) experiments indicate that the platinum(II) complexes intercalate although for [Pt(en)(4-Mephen)]Cl2 and [Pt(en)(4,7-Me2phen)]Cl2 this mode of binding appears to be concentration dependent. The binding of the platinum(II) complexes to the oligonucleotide d(GTCGAC)2 was studied using two-dimensional 1H NMR spectroscopy. The addition of each metal complex to the hexamer d(GTCGAC)2 produced upfield shifts of the metal complex resonances, characteristic of intercalation. Through the observation of NOE cross-peaks, two-dimensional NMR studies provided insight into the site and groove preferences of these compounds when binding to DNA.     

钌配合物断裂DNA及其机理研究

DNA是遗传信息的携带者和基因表达的物质基础,金属配合物与DNA的相互作用研究受到广泛关注,成为生物无机化学的重要研究内容之一.与其他类型金属配合物相比,钌配合物具有良好的热力学稳定性以及丰富的光化学、光物理和氧化还原特性,其作为DNA断裂试剂也引起人们的极大兴趣.以近年一些代表性的研究工作为例,本文对钌配合物在DNA断裂作用机制方面的研究进展进行了综述.     

Metal complexes of porphyrin–anthraquinone hybrids: DNA binding and photocleavage specificities

A cationic porphyrin–anthraquinone hybrid and its Zn(II), Cu(II), Co(III), and Mn(III) complexes were synthesized and their interactions with duplex DNA were studied using a combination of absorption, fluorescence titration, circular dichroism spectroscopy, thermal DNA denaturation, viscosity measurements, gel electrophoresis, and gas chromatography. Metal coordination induces intermolecular steric hindrance and thus the metal hybrids have smaller DNA binding affinities than the free base hybrid; the steric hindrance could relax the intermolecular aggregation and increase ¹O₂ generation of the metal hybrids. The DNA photocleavage abilities of these hybrids were investigated.     

巯嘌呤金属配合物与小牛胸腺DNA的作用

用溴化乙锭为探针研究了巯嘌呤(mercaptopurine, MP)金属配合物与小牛胸腺 DNA的作用机制，探讨了其作用模式，即巯嘌呤与DNA是非嵌插结合，巯嘌呤金属酴 物与DNA之间的作用为静电方式和一定的嵌入方式。并求得巯嘌呤金属配合物与 DNA的结合常数。     

Comparison of mass spectrometry and other techniques for probing interactions between metal complexes and DNA

Electrospray ionization mass spectrometry (ESI-MS) was used to study the binding interactions of two series of ruthenium complexes, [Ru(phen) 2L] (2+) and [RuL' 2(dpqC)] (2+), to a double stranded DNA hexadecamer, and derive orders of relative binding affinity. These were shown to be in good agreement with orders of relative binding affinity derived from absorption and circular dichroism (CD) spectroscopic examination of the same systems and from DNA melting curves. However, the extent of luminescence enhancement caused by the addition of DNA to solutions of the ruthenium complexes showed little correlation with orders of binding affinity derived from ESI-MS or any of the other techniques. Overall the results provide support for the validity of using ESI-MS to investigate non-covalent interactions between metal complexes and DNA.     

Mass spectrometric studies of alkali metal ion binding on thrombin-binding aptamer DNA

The binding sites and consecutive binding constants of alkali metal ions, (M⁺ = Na⁺, K⁺, Rb⁺, and Cs⁺), to thrombin-binding aptamer (TBA) DNA were studied by Fourier-transform ion cyclotron resonance spectrometry. TBA-metal complexes were produced by electrospray ionization (ESI) and the ions of interest were mass-selected for further characterization. The structural motif of TBA in an ESI solution was checked by circular dichroism. The metal-binding constants and sites were determined by the titration method and infrared multiphoton dissociation (IRMPD), respectively. The binding constant of potassium is 5–8 times greater than those of other alkali metal ions, and the potassium binding site is different from other metal binding sites. In the 1:1 TBA-metal complex, potassium is coordinated between the bottom G-quartet and two adjacent TT loops of TBA. In the 1:2 TBA—metal complex, the second potassium ion binds at the TGT loop of TBA, which is in line with the antiparallel G-quadruplex structure of TBA. On the other hand, other alkali metal ions bind at the lateral TGT loop in both 1:1 and 1:2 complexes, presumably due to the formation of ion-pair adducts. IRMPD studies of the binding sites in combination with measurements of the consecutive binding constants help elucidate the binding modes of alkali metal ions on DNA aptamer at the molecular level.     

应用电子圆二色光谱方法确定手性金属配合物的绝对构型

与电子能级跃迁相关的电子圆二色(ECD)光谱因其研究对象宽泛,与涉及振动能级的振动圆二色(VCD)光谱互补,已成为应用于手性立体化学研究的集成手性光谱的主流表征手段。本文概述了确定手性金属配合物绝对构型的三种主要方法,详细介绍了ECD光谱法在确定手性金属配合物绝对构型中的应用,其中着重强调了激子手性方法,并对集成手性光谱学未来的发展趋势做出了展望。