乳酸-钴(Ⅱ)-1,10-菲啰啉三元配合物与DNA结合的光谱与电化学研究

以1,10-菲啰啉(phen)和乳酸为配体合成了三元钴配合物[Co(phen)(la)_2]。采用紫外光谱、循环伏安法、计时库仑法和微分脉冲伏安法等考察了其与鲱鱼精天然DNA的相互作用。紫外光谱实验显示,在[Co(phen)(la)_2]中加入DNA后,配合物在270 nm处的紫外特征吸收峰出现明显的减色效应,并伴随红移,表明[Co(phen)(la)_2]可通过其phen配体插入DNA中相邻碱基对。循环伏安法和计时库仑法进一步表明,与DNA结合后,复合物在水溶液中扩散系数降低,从而导致电化学信号减弱。微分脉冲伏安实验显示,[Co(phen)(la)_2]氧化峰电流与DNA浓度在2.66×10~(-5)~1.34×10~(-4)mol/L范围内呈现良好的线性关系,表明[Co(phen)(la)_2]可作为一种潜在的DNA检测探针。     

Metal complexes as DNA intercalators

DNA has a strong affinity for many heterocyclic aromatic dyes, such as acridine and its derivatives. Lerman in 1961 first proposed intercalation as the source of this affinity, and this mode of DNA binding has since attracted considerable research scrutiny. Organic intercalators can inhibit nucleic acid synthesis in vivo, and they are now common anticancer drugs in clinical therapy. The covalent attachment of organic intercalators to transition metal coordination complexes, yielding metallointercalators, can lead to novel DNA interactions that influence biological activity. Metal complexes with σ-bonded aromatic side arms can act as dual-function complexes: they bind to DNA both by metal coordination and through intercalation of the attached aromatic ligand. These aromatic side arms introduce new modes of DNA binding, involving mutual interactions of functional groups held in close proximity. The biological activity of both cis- and trans-diamine Pt(II) complexes is dramatically enhanced by the addition of σ-bonded intercalators. We have explored a new class of organometallic "piano-stool" Ru(II) and Os(II) arene anticancer complexes of the type [(η(6)-arene)Ru/Os(XY)Cl](+). Here XY is, for example, ethylenediamine (en), and the arene ligand can take many forms, including tetrahydroanthracene, biphenyl, or p-cymene. Arene-nucleobase stacking interactions can have a significant influence on both the kinetics and thermodynamics of DNA binding. In particular, the cytotoxic activity, conformational distortions, recognition by DNA-binding proteins, and repair mechanisms are dependent on the arene. A major difficulty in developing anticancer drugs is cross-resistance, a phenomenon whereby a cell that is resistant to one drug is also resistant to another drug in the same class. These new complexes are non-cross-resistant with cisplatin towards cancer cells: they constitute a new class of anticancer agents, with a mechanism of action that differs from the anticancer drug cisplatin and its analogs. The Ru-arene complexes with dual functions are more potent towards cancer cells than their nonintercalating analogs. In this Account, we focus on recent studies of dual-function organometallic Ru(II)- and Os(II)-arene complexes and the methods used to detect arene-DNA intercalation. We relate these interactions to the mechanism of anticancer activity and to structure-activity relationships. The interactions between these complexes and DNA show close similarities to those of covalent polycyclic aromatic carcinogens, especially to N7-alkylating intercalation compounds. However, Ru-arene complexes exhibit some new features. Classical intercalation and base extrusion next to the metallated base is observed for {(η(6)-biphenyl)Ru(ethylenediamine)}(2+) adducts of a 14-mer duplex, while penetrating arene intercalation occurs for adducts of the nonaromatic bulky intercalator {(η(6)-tetrahydroanthracene)Ru(ethylenediamine)}(2+) with a 6-mer duplex. The introduction of dual-function Ru-arene complexes introduces new mechanisms of antitumor activity, novel mechanisms for attack on DNA, and new concepts for developing structure- activity relationships. We hope this discussion will stimulate thoughtful and focused research on the design of anticancer chemotherapeutic agents using these unique approaches.     

Synthesis, crystal structure, optical properties, DNA-binding and cell imaging of an organic chromophore

An organic chromophore (4-[N, N- bis(2′-chloroethyl)anilino] ethenyl N-methyl pyridinium-N- methyl iodide) L was synthesized and fully characterized by elemental analysis, IR, ¹HNMR spectra and single crystal X-ray diffraction analysis. One and two-photon fluorescence spectra for it were studied. Interestingly, L exhibited obvious two-photon absorption in the range from 700-850 nm in DMSO solution. The interactions between the chromophore and calf thymus DNA were investigated by absorption, fluorescence spectra and viscosity experiments. The results showed that the chromophore could interact with DNA in the mode of intercalation and be effectively used as fluorescent staining dye for cell imaging applications. Furthermore, the cell viability data for MCF-7 (Human breast carcinoma) cells indicated that the low-micromolar concentrations of the L are essentially non-toxic and can be applied in brighter two-photon fluorescent (TPF) bioimaging.     

Synthesis and biological activity of a platinum(II) 6-phenyl-2,2'-bipyridine complex and its dimeric analogue

We have synthesized (pyridyl)-(6-phenyl-2,2'-bipyridine)platinum(II) hexafluorophosphate (1) and its corresponding dimer, micro-N,N'-bis(isonicotinyl)-1,6-hexanediamino bis-[6-phenyl-2,2'-bipyridine-platinum(II)] dichloride (2). The DNA binding constants of 1 and 2 at 20 degrees C were determined by absorption titration to be 2.25 x 10(4) M(-1) and 3.07 x 10(6) M(-1), respectively. Compound 1 showed an AT preference, while 2 had no base preference. The binding site sizes of 2 for [poly(dA-dT)](2), calf thymus DNA (ctDNA), and [poly(dG-dC)](2), as determined by fluorescence titration, were 6.6, 4.0, and 2.8 bp, respectively. Compound 2 probably bound to [poly(dA-dT)](2) through bisintercalation, and to [poly(dG-dC)](2) by monointercalation. Binding of DNA by both complexes is favorable, since the binding free energies of 1 and 2 were estimated to be -5.8 and -8.7 kcal mol(-1), respectively. The results of viscosity measurements and gel mobility shift assay demonstrated that binding of 1 and 2 caused DNA lengthening. The cytotoxicities of the complexes in various human cancer cell lines were determined by MTT assay. Complex 2 exhibited cytotoxicity comparable to that of cisplatin, and was more toxic than 1 by an order of magnitude.     

The DNA helical biopolymer: A template for the binding, assembly, and reactivity of metal ions and complexes

The helical DNA polymer provides many structural features that facilitate the binding of metal ions or complexes. DNA binding inorganic agents have proven invaluable, with demonstrated applications ranging from chemotherapeutic agents to probes of DNA structure. This broad range of applications attests to the utility of inorganic agents in the design of compounds which interact with the DNA helix and is due, in part, to the ability of inorganic species to define a particular ligand geometry complementary to the DNA structure, bind, or chemically react along the polymer strand. While a diverse array of novel inorganic compounds that interact with DNA have already been studied, many opportunities still exist to exploit inorganic agents in the design of new molecules that will interact uniquely with the DNA polymer. This review examines the structure of the DNA polymer, emphasizing aspects which promote the binding of inorganic agents. Along with a structural overview, the binding modes available to an inorganic element or complex are reviewed, in combination with a discussion of the ability of the DNA to act as a template for the organized binding of inorganic agents. In addition, chemical alteration of the DNA polymer structure by inorganic agents is discussed, along with the potential utility of such modifications.     

Induction of DNA-double-strand breaks by auger electrons from 99mTc complexes with DNA-binding ligands

The potential of certain Auger electron emitting nuclides for systemic radiotherapeutic applications has recently gained much attention. In particular, the ability of several nuclides, including 111In, 125I, and 123I, to induce DNA double-strand breaks (dsb), a good indicator of cytotoxicity, has been extensively studied. However, this ability has never previously been shown experimentally for 99mTc, which, besides the well-known gamma radiation that is used for diagnostic applications, also emits an average of 1.1 conversion electrons and 4 Auger or Coster-Kronig electrons per decay. Owing to the short range of Auger electrons, the radionuclide needs to be located very close to the DNA for dsb to occur. We synthesized two cationic 99mTcI-tricarbonyl complexes with pendant DNA binders, pyrene and anthraquinone. The X-ray crystal structures of the two complexes could be elucidated. Linear dichroism and UV/Vis spectroscopy revealed that the complex with pyrene intercalates DNA with a stability constant, K, of 1.1 x 10(6) M(-1), while the analogous complex with anthraquinone interacts with DNA in a groove-binding mode and has an affinity value of K=8.9 x 10(4) M(-1). We showed with phiX174 double-stranded DNA that the corresponding 99mTc complexes induce a significant amount of dsb, whereas non-DNA-binding [TcO4]- and nonradioactive Re compounds did not. These results indicate that the Auger electron emitter 99mTc can induce dsb in DNA when decaying in its direct vicinity and this implies potential for systemic radiotherapy with 99mTc complexes.     

Understanding the Potential In Vitro Modes of Action of Bis(β-diketonato) Oxovanadium(IV) Complexes

To understand the potential in vitro modes of action of bis(β-diketonato) oxovanadium(IV) complexes, nine compounds of varying functionality have been screened using a range of biological techniques. The antiproliferative activity against a range of cancerous and normal cell lines has been determined, and show these complexes are particularly sensitive against the lung carcinoma cell line, A549. Annexin V (apoptosis) and Caspase-3/7 assays were studied to confirm these complexes induce programmed cell death. While gel electrophoresis was used to determine DNA cleavage activity and production of reactive oxygen species (ROS), the Comet assay was used to determine induced genomic DNA damage. Additionally, Förster resonance energy transfer (FRET)-based DNA melting and fluorescent intercalation displacement assays have been used to determine the interaction of the complexes with double strand (DS) DNA and to establish preferential DNA base-pair binding (AT versus GC).     

A Spectroscopic Study on PtCl(4) Binding to Rabbit Skeletal Muscle G-Actin

It was found that the binding of PtCl(4) (2-) to G-actin and the consequent conformational changes are different with those for hard acids. It is a two-step process depending on molar ratio PtCl(4) (2-)/actin (R). In the first step, R less than 25, the PtCl(4) (2-) ions are bound to sulfur-containing groups preferentially. These high-affinity sites determined by Scatchard approach are characterized by n(1) = 30 with average binding constant K(1)=1.0x10(7)M(-1). The conformational changes are significant as characterized by N-(1-pyrenyl) maleimide(NPM) labeled fluorescence, intrinsic fluorescence and CD spectra. EPR spectroscopy of maleimide spin labeled(MSL) actin demonstrated that even PtCl(4) (2-)binding is limited to a very small fraction of high-affinity sites(R<1), it can bring about a pronounced change of conformation. In the range of R=25-40, high-affinity sites accessible are saturated. In the second step(R>40) , deep-buried binding sites turn out to be accessible as a result of the accumulated conformational changes. These new binding sites are estimated to be n(2)=26 with average binding constant K(2)=2.1x10(6)M(-1). Although in this step the quenching of intrinsic fluorescence goes on and the NPM-labled thiols moves to more hydrophilic environment, no change in alpha-helix content was found. These results suggested that with increasing in PtCl(4) ((2-)) binding, the G-actin turns to an open and loose structure in a discontinuous mode.     

Optimization of Drug Candidates That Inhibit the D-Loop Activity of RAD51

RAD51 is the central protein in homologous recombination (HR) repair, where it first binds ssDNA and then catalyzes strand invasion via a D-loop intermediate. Additionally, RAD51 plays a role in faithful DNA replication by protecting stalled replication forks; this requires RAD51 to bind DNA but may not require the strand invasion activity of RAD51. We previously described a small-molecule inhibitor of RAD51 named RI(dl)-2 (RAD51 inhibitor of D-loop formation #2, hereafter called 2 h ), which inhibits D-loop activity while sparing ssDNA binding. However, 2 h is limited in its ability to inhibit HR in vivo, preventing only about 50 % of total HR events in cells. We sought to improve upon this by performing a structure–activity relationship (SAR) campaign for more potent analogues of 2 h . Most compounds were prepared from 1-(2-aminophenyl)pyrroles by forming the quinoxaline moiety either by condensation with aldehydes, then dehydrogenation of the resulting 4,5-dihydro intermediates, or by condensation with N,N′-carbonyldiimidazole, chlorination, and installation of the 4-substituent through Suzuki–Miyaura coupling. Many analogues exhibited enhanced activity against human RAD51, but in several of these compounds the increased inhibition was due to the introduction of dsDNA intercalation activity. We developed a sensitive assay to measure dsDNA intercalation, and identified two analogues of 2 h that promote complete HR inhibition in cells while exerting minimal intercalation activity.     

Astragalin from Cassia alata Induces DNA Adducts in Vitro and Repairable DNA Damage in the Yeast Saccharomyces cerevisiae

Reverse phase-solid phase extraction from Cassia alata leaves (CaRP) was used to obtain a refined extract. Higher than wild-type sensitivity to CaRP was exhibited by 16 haploid Saccharomyces cerevisiae mutants with defects in DNA repair and membrane transport. CaRP had a strong DPPH free radical scavenging activity with an IC(50) value of 2.27 μg mL(-1) and showed no pro-oxidant activity in yeast. CaRP compounds were separated by HPLC and the three major components were shown to bind to DNA in vitro. The major HPLC peak was identified as kampferol-3-O-β-d-glucoside (astragalin), which showed high affinity to DNA as seen by HPLC-UV measurement after using centrifugal ultrafiltration of astragalin-DNA mixtures. Astragalin-DNA interaction was further studied by spectroscopic methods and its interaction with DNA was evaluated using solid-state FTIR. These and computational (in silico) docking studies revealed that astragalin-DNA binding occurs through interaction with G-C base pairs, possibly by intercalation stabilized by H-bond formation.     

Indolocarbazole glycosides in inactive conformations

Indolocarbazole glycosides related to rebeccamycin represent a promising category of antitumor agents targeting DNA and topoisomerase I. These drugs prefer to adopt a closed conformation with an intramolecular hydrogen bond between the indole NH group and the pyranose oxygen atom. Three pairs of indolocarbazole monoglycosides bearing an NH or an N-methyl indole moiety were synthesized and their biological properties investigated at the molecular and cellular level. Replacing the indole NH proton with a methyl group reduces DNA interaction and abolishes activity against DNA topoisomerase I. Surface plasmon resonance studies performed with a pair of water-soluble indolocarbazole glycosides and two hairpin oligonucleotides containing an [AT]4 or a [CG]4 sequence indicate that both the NH and the N-methyl derivative maintain a relatively high affinity for DNA (Keq = 2 - 6 x 10(5) M(-1)) but the incorporation of the methyl group restricts access to the DNA. The number of ligand binding sites (n) on the oligonucleotides is about twice as high for the NH compound compared to its N-methyl analogue. Modeling and 1H NMR studies demonstrate that addition of the N-methyl group drives a radical change in conformation in which the orientation of the aglycone relative to the beta-glucoside is reversed. The loss of the closed conformation by the N-methyl derivatives perturbs thir ability to access DNA binding sites and prevents the drug from inhibiting topoisomerase I. As a consequence, the NH compounds exhibit potent cytotoxicity against CEM leukemia cells with an IC50 value in the 1 microM range, whereas the N-methyl analogues are 10 to 100 times less cytotoxic. These studies offer circumstantial evidence supporting the importance of the closed conformation in the interaction of indolocarbazole glycosides with their molecular targets, DNA and topoisomerase I.     

Design,Synthesis and DNA Interaction Study of New Potential DNA Bis-Intercalators Based on Glucuronic Acid

A series of novel potential DNA bis-intercalators were designed and synthesized, in which two glucuronic acids were linked by ethylenediamine, and the glucuronic acid was coupled with various chromophores, including quinoline, acridine, indole and purine, at the C-1 position. The preliminary binding properties of these compounds to calf thymus DNA (CT-DNA) have been investigated by UV-absorption and fluorescence spectroscopy. The results indicated that all the target compounds can interact with CT-DNA, and the acridine derivative, 3b, showed the highest key selection vector (KSV) value, which suggested that compound 3b binds most strongly to CT-DNA.     

Synthesis and evaluation of an intercalator-polyamide hairpin designed to target the inverted CCAAT box 2 in the topoisomerase IIalpha promoter

The synthesis and DNA-binding properties of a novel naphthalimide-polyamide hairpin (3) designed to target the inverted CCAAT box 2 (ICB2) site on the topoisomerase IIalpha (topoIIalpha) promoter are described. The polyamide component of 3 was derived from the minor-groove binder, 2, and tailored to bind to the 5'-TTGGT sequence found in and flanking ICB2. The propensity of mitonafide 4 to intercalate between G-C base pairs was exploited by the incorporation of a naphthalimide moiety at the N terminus of 2. Hybrid 3 targeted 5'-CGATTGGT and covered eight contiguous base pairs, which included the underlined ICB2 site. DNase I footprinting analysis with the topoIIalpha promoter sequence demonstrated that 3 bound selectively to the ICB2 and ICB3 sites. Thermal-denaturation studies confirmed these results, and the highest degree of stabilization was found for ICB2 and -3 in preference to ICB1 (4.1, 4.6, and 0.6 degrees C, respectively). CD studies confirmed minor-groove binding and suggested a 1:1 binding stoichiometry. Emission-titration experiments established intercalative binding. Surface plasmon resonance results showed strong binding to ICB2 (2.5x10(7) M(-1)) with no observable binding to ICB1. Furthermore, the binding constant of 3 to ICB2 was larger than that of the parent polyamide 2. The increased binding affinity was primarily due to a reduction in the dissociation-rate constant of the polyamide-DNA complex, which can be attributed to the N-terminal naphthalimide moiety. In addition, the binding site of 3 was larger than that of 2, which innately improved sequence selectivity. We conclude that the polyamide-naphthalimide 3 selectively binds to the ICB2 site by simultaneous intercalation and minor-groove binding, and warrants further investigation as a model compound for the regulation of topoIIalpha gene expression.     

Synthesis,crystal structure,DNA binding properties and antioxidant activities of transition metal complexes with 3-carbaldehyde-chromone semicarbazone

3-Carbaldehyde-chromone semicarbazone (L) and its Cu(II), Zn(II), Ni(II) complexes were synthesized and characterized on the basis of crystal structure and other structural characterization methods. The metal ions and Schiff base ligand can form mononuclear five-coordination complexes with 1:1 metal-to-ligand stoichiometry at the metal ions as centres. The transition metal complexes may be used as potential anticancer drugs, because they bind to calf thymus DNA via an intercalation binding mode with the binding constants at the order of magnitude 10⁵–10⁶ M^? 1, and the metal complexes present stronger DNA binding affinities than the free ligand alone. In addition, the antioxidant activities of the ligand and its metal complexes were investigated through scavenging effects for superoxide anion and hydroxyl radical in vitro, indicating that the compounds show stronger antioxidant activities than some standard antioxidants, such as mannitol and vitamin C.     

Adeno-associated virus Rep78/Rep68 promotes localized melting of the rep binding element in the absence of adenosine triphosphate

We have applied fluorescence anisotropy and molecular beacon fluorescence methods to study the interactions between the Adeno-associated virus Rep78/Rep68 protein and the 23-bp Rep binding element (RBE). Rep78/Rep68 stably interacted with both the single- and double-stranded conformations of the RBE, but the interaction mechanisms of single- and double-stranded DNA appeared to be fundamentally different. The stoichiometry of Rep78 association with both the separate top and bottom strands of the RBE was 1:1, and the relative dissociation constant (K(D)) values of these associations were calculated to be 2.3x10(-8) and 3.2x10(-8) M, respectively. In contrast, the stoichiometry of Rep78 association with the double-stranded RBE was 2:1, and the dissociation constant was determined to be 4.2x10(-15) M(2). Moreover, Rep78/Rep68 interaction with the 23-bp duplex RBE appeared to cause localized melting of the double-stranded DNA substrate in the absence of adenosine triphosphate (ATP). This melting activity showed slower kinetics than binding and may contribute to the initiation of ATP-dependent Rep78 helicase activity.     

Quantification of the Raf-C1 interaction with solid-supported bilayers

By use of the quartz crystal microbalance technique, the interaction of the Raf-Ras binding domain (RafRBD) and the cysteine-rich domain Raf-C1 with lipids was quantified by using solid-supported bilayers immobilized on gold electrodes deposited on 5 MHz quartz plates. Solid-supported lipid bilayers were composed of an initial octanethiol monolayer chemisorbed on gold and a physisorbed phospholipid monolayer varying in its lipid composition as the outermost layer. The integrity of bilayer preparation was monitored by impedance spectroscopy. For binding experiments, a protein construct comprising the RafRBD and Raf-C1 linked to the maltose binding protein and a His tag, termed MBP-Raf-C1, was used. Dissociation constants and rate constants of the association and dissociation were obtained for various 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC)/1,2-dimyristoyl-sn-glycero-3-phosphoserine (DMPS) lipid mixtures. Independently of the phosphatidylserine (PS) content, the dissociation constants were in the order of 5x10(-7) M, while the on-rate constants were in the range of 2x10(3) (M s)(-1) and the off-rate constants in the range of 1x10(-3) s(-1). The maximum frequency shift increased significantly with increasing amounts of DMPS; this indicates that this negatively charged lipid is the primary binding site for MBP-Raf-C1. Exchange of DMPS for 1,2-dimyristoyl-sn-glycero-3-phosphoglycerol (DMPG) did not alter the thermodynamics and kinetics of protein binding, which implies that the protein interaction is mainly electrostatically driven. Scanning force microscopy (SFM) was employed to render protein adsorption visible and to confirm the assumption of a protein monolayer on the lipid layer. SFM images clearly revealed that the protein binds preferentially, but not solely, to negatively charged phosphatidylserine headgroups. We hypothesize that PS-enriched domains are initial binding sites with high affinity for Raf-C1, but that lateral interactions may account for protein domain growth.     

Pyrazolyl-diamine ligands that bear anthracenyl moieties and their rhenium(I) tricarbonyl complexes: synthesis, characterisation and DNA-binding properties

Two novel families of pyrazolyl-diamine ligands that bear an anthracen-9-yl group as a DNA-binding fragment, pz*(CH2)2NH(CH2)2NHCH2-9-anthryl (pz*=pz (L(1)), 3,5-Me2pz (L2)) and pz*(CH2)2NH(CH2)2NH(2 (pz*=4-(9-anthrylmethyl)pz (L3), 3,5-Me2-4-(9-anthrylmethyl)pz (L4)), have been prepared and fully characterised. In the case of L2-L4, the evaluation of their coordination capability towards the fac-[Re(CO)3]+ core led to the synthesis of the organometallic complexes fac-[Re(CO)(3){3,5-Me(2)pz(CH2)2NH(CH2)2NHCH2-9-anthryl}]Br (7) and fac-[Re(CO)3{4-(9-anthrylmethyl)pz*(CH2)2NH(CH2)2NH2}]Br (pz*=pz (8), 3,5-Me2pz 9). The interaction of the novel pyrazole-diamine ligands and the rhenium(I) complexes with calf thymus (CT) DNA has been investigated with a variety of spectroscopic techniques (UV-visible, fluorescence, circular dichroism (CD) and linear dichroism (LD)). All of the evaluated compounds have a moderate affinity to CT DNA (3.46x10(3)相似文献   

The electrochemical formation of graphitebisulphate intercalation compounds

The intercalation of bisulphate ion in graphite has been studied. Oxidation occurs in two stages, at 0.9 V and 1.8 V versus NHE, but the formation of thermally expandable compounds is associated with the second oxidation process. The first oxidation process is associated with the formation of a lower order of intercalation compound. The transport of HSO ₄ ^? between the graphite planes is diffusion controlled and the diffusion coefficient value estimated is in the range of 0.3 to 2.8×10^?6 cm² s^?1 which indicates that the intercalated ions can move quite freely between the graphite planes. The oxidation of the graphite flakes in a fluidized bed electrode was studied by AC and voltammetric techniques. Good interparticle contact was achieved when a slight compressive load was applied and fluidization resulted in a large decrease of the solid phase resistance of the bed electrode.     

Mechanism of the anionic polymerization of lactones,initiated by intercalation graphite compounds

Summary The anionic polymerization of -propiolactone (PL)oxethane-2-one, pivalolactone (PVL) — 3,3-dimethyloxethane-2-one and -caprolactone (CL) — oxepane-2-one, initiated by binary and ternary intercalation compounds (IC) of lithium and potassium in graphite is investigated. The polymerization is carried out in bulk or in xylene. It is established that the lactones penetrate in IC and polymerize in their interlayer spacings. The polymerization causes a delamination of IC. High polymers of the lactones can be obtained by the action of some IC investigated.