An ultraviolet melting study of the stability of the DNA double helix in the NaDNA-bipyridyl-(ethylenediamine)platintum(II) complex

Complexes of NaDNA with the bipyridyl-(ethylenediamine)platintum(II) (abbreviated [(bipy)Pt(en)]2+) molecular ion have been studied in solution via ultraviolet absorption experiments at 260 nm between 50 and 90 degrees C. These measurements, performed as a function of the molar ratio of the [(bipy)Pt(en)]2+ complex to DNA base pairs, show that the stability of the DNA double helix is increased by the formation of the DNA.[(bipy)Pt(en)]2+ complex: at a molar ratio of 0.33, the temperature at which the DNA double helix separates into two single strands is increased by about 15 degrees C.     

Effects of amine ligand bulk and hydrogen bonding on the rate of reaction of platinum(II) diamine complexes with key nucleotide and amino acid residues

NMR spectroscopy has been used to observe the effects of the amine ligand on the rate of reaction of platinum diamine and triamine complexes with DNA and protein residues. Whereas [Pt(dien)Cl]Cl and [Pt(dien)(D(2)O)](2+) have been known to react faster with thioether residues such as N-AcMet than with 5'-GMP, we found that [Pt(Me(4)en)(D(2)O)(2)](2+) appeared to react faster with 5'-GMP. To quantitatively assess the factors influencing the rates of reaction, rate constants at pH 4 were determined for the reactions of [Pt(en)(D(2)O)(2)](2+) [en = ethylenediamine] and [Pt(Me(4)en)(D(2)O)(2)](2+) with N-AcMet, N-AcHis, 5'-GMP, and Guo (guanosine). In each case the less bulky complex ([Pt(en)(D(2)O)(2)](2+)) reacts more quickly than does the bulkier [Pt(Me(4)en)(D(2)O)(2)](2+), as expected. Both complexes reacted faster with 5'-GMP; however, analysis of the rate constants suggests that the [Pt(en)(D(2)O)(2)](2+) complex favors reaction with 5'-GMP due to hydrogen bonding with the 5'-phosphate, whereas [Pt(Me(4)en)(D(2)O)(2)](2+) disfavors reaction with N-AcMet due to steric clashes. Bulk had relatively little effect on the rate constant with N-AcHis, suggesting that peptides or proteins that coordinate via His residues would not have their reactivity affected by bulky diamine ligands.     

Binding of platinum(II) intercalation reagents to deoxyribnonucleic acid. Dependence on base-pair composition, nature of the intercalator, and ionic strength.

The DNA binding of three platinum(II) intercalation reagents has been studied and found to depend upon base composition, the nature of the intercalator, and the ionic strength of the solvent medium. In 0.2 M NaCl, binding data for calf thymus DNA show the association constants to be approximately 10(4) M-1. The binding constants decrease in the order [(o-phen)Pt(en)]2+ greater than or equal to [(terpy)Pt(HET)]+ greater than [(bipy)Pt(en)]2+. The number of available intercalation sites for the doubly charged intercalators is only 70% of the number expected from the nearest-neighbor exclusion model. Binding of [(o-phen)Pt(en)]2+ and [(terpy)Pt(HET)]+ to various DNAs depends linearly on G.C content. Both reagents exhibit essentially the same degree of G.C specificity. Intercalative binding is a function of ionic strength. Increasing the salt concentration minimizes the importance of metallointercalator charge, and extrapolation to 1 M salt reveals the intercalative abilities, as reflected in binding constants, to be equivalent for [(terpy)Pt(HET)]+ and [o-phen)Pt(en)]2+ and about 1 order of magnitude less than that of ethidium.     

Specific DNA cleavage by an analog of netropsin containing a copper(II) chelating peptide Gly-Gly-His]

Experimental data are reported on DNA-cleaving activity of the synthetic netropsin analogs consisting of the two N-propylpyrrole carboxamide units linked covalently through two or three glycine residues to a copper-chelating tripeptide glycyl-glycyl-L-histidine. Incubation of DNA restriction fragment and netropsin analog in the presence of ascorbate, hydrogen peroxide and Cu2+ ions resulted in selective cleavage of the DNA at or near the preferred sites for binding of netropsin analog. A similar cleavage pattern is observed after X-ray irradiation of DNA complexes with netropsin analogs tethered with Cu2+ ions. The cleavage patterns are found to be dependent on the length of the connecting chain between the histidine-containing tripeptide and netropsin analog. The netropsin analog containing three glycine residues in the connecting chain, but not the analog with a shorter linker chain, can generate an intense cleavage of one of the two polynucleotide chains at a position corresponding to the presumed binding site for the dimeric ligand species. More than 50% of the total DNA can be cleaved at this position after X-ray irradiation. From analysis of the nucleotide sequences surrounding the preferred cleavage site on several DNA fragments we found that the consensus is 5'-TTTTNCA*AAA-3', where N is an arbitrary nucleotide. The Cu(2+)-mediated cleavage of DNA occurs at the second adenine (indicated by an asterisk) from the 5'-end of the sequence. The greatest cleavage activity is observed when the molar ratio of Cu2+ to the netropsin analog is equal to 0.5. Evidently, the Cu(2+)-ligated and unligated oligopeptide species interacts with each other to form a heterodimer bound to DNA at the cleavage site. To test the validity of this model we have studied the binding of unligated netropsin analog and netropsin analog complexed with Cu2+ ion to a self-complementary oligonucleotide 5'-GCGTTTTGCAAAACGC-3'. It is found that binding of Cu(2+)-ligated netropsin analog to the DNA oligomer preincubated with unligated form of the oligopeptide is a cooperative process for which interactions between the two bound ligands are responsible. The cooperativity parameter is estimated to be on the order of factor 6. Finally, a model is proposed in which a heterodimer stabilized by interligand beta-sheet binds in the minor DNA groove.     

Effects of spectator ligands on the specific recognition of intrastrand platinum-DNA cross-links by high mobility group box and TATA-binding proteins

The results presented describe the effects of various spectator ligands, attached to a platinum 1,2-intrastand d(GpG) cross-link in duplex DNA, on the binding of high mobility group box (HMGB) domains and the TATA-binding protein (TBP). In addition to cisplatin-modified DNA, 15-base pair DNA probes modified by [Pt(1R,2R-diaminocyclohexane)](2+), cis-[Pt(NH(3))(cyclohexylamine)](2+), [Pt(ethylenediamine)](2+), cis-[Pt(NH(3))(cyclobutylamine)](2+), and cis-[Pt(NH(3))(2-picoline)](2+) were examined. Electrophoretic mobility shift assays show that both the A and B domains of HMGB1 as well as TBP discriminate between different platinum-DNA adducts. HMGB1 domain A is the most sensitive to the nature of the spectator ligands on platinum. The effect of the spectator ligands on protein binding also depends highly on the base pairs flanking the platinated d(GpG) site. Double-stranded oligonucleotides containing the AG*G*C sequence, where the asterisks denote the sites of platination, with different spectator ligands are only moderately discriminated by the HMGB proteins and TBP, but the recognition of dsTG*G*A is highly dependent on the ligands. The effects of HMGB1 overexpression in a BG-1 ovarian cancer cell line, induced by steroid hormones, on the sensitivity of cells treated with [Pt(1R,2R-diaminocyclohexane)Cl(2)] and cis-[Pt(NH(3))(cyclohexylamine)Cl(2)] were also examined. The results suggest that HMGB1 protein levels influence the cellular processing of cis-[Pt(NH(3))- (cyclohexylamine)](2+), but not [Pt((1R,2R)-diaminocyclohexane)](2+), DNA lesions. This result is consistent with the observed binding of HMGB1a to platinum-modified dsTG*G*A probes but not with the binding affinity of HMGB1a and HMGB1 to platinum-damaged dsAG*G*C oligonucleotides. These experiments reinforce the importance of sequence context in platinum-DNA lesion recognition by cellular proteins.     

DNA binding studies of ruthenium(II) complexes containing asymmetric tridentate ligands

Absorption spectroscopy, fluorescence spectroscopy and viscosity measurements have been used to characterize the DNA binding of [Ru(tpy)(dppt)](2+) (tpy=2,2':6',2"-terpyridine, dppt=3-(1,10-phenanthrolin-2-yl)-5,6-diphenyl-as-triazine), [Ru(tpy)(pta)](2+) (pta=3-(1,10-phenanthrolin-2-yl)-as-triazino[5,6-f]acenaphthylene) and [Ru(tpy)(ptp)](2+) (ptp=3-(1,10-phenanthrolin-2-yl)-as-triazino[5,6-f]-phenanthrene). The results indicate that [Ru(tpy)(pta)](2+) and [Ru(tpy)(ptp)](2+) bind with CT-DNA in an intercalative mode, while [Ru(tpy)(dppt)](2+) binds with DNA by partial intercalation. The ligand planarity of the complex has a significant effect on DNA binding affinity increases in the order [Ru(tpy)(dppt)](2+)<[Ru(tpy)(pta)](2+)<[Ru(tpy)(ptp)](2+).     

Mechanochemical study of NaDNA and NaDNA-netropsin fibers in ethanol-water and trifluoroethanol-water solutions.

Highly oriented calf-thymus NaDNA fibers, prepared by a wet-spinning method, were complexed with netropsin in ethanol-water and trifluoroethanol (TFE)-water solutions. The relative fiber length, L/L0, was measured at room temperature as a function of ethanol or TFE concentration to obtain information on the B-A conformational transition. The B-A transition point and transition cooperativity of the fibers were calculated. The binding of netropsin to NaDNA fibers was found to stabilize B form and to displace the B-A transition to higher ethanol concentration, as indicated by its elongational effect on the fiber bundles. An increased salt concentration was found to reduce netropsin binding. In netropsin-free ethanol solution, the dissociation of bound netropsin from the DNA fibers was observable. Pure B-NaDNA fibers were found to be more stable in TFE solution than in ethanol solution. This was interpreted as being due to a different steric factor and a larger polarity of TFE compared with ethanol, resulting in its smaller capacity to reduce the water activity and dielectric constant of the medium in the immediate vicinity of DNA fibers. Therefore, the effect of netropsin binding on the B-A transition of NaDNA fibers became less obvious in TFE solution. In another series of experiments, L/L0 was measured as a function of temperature to obtain information on the helix-coil transition, or melting, as well as the B-A transition of NaDNA and NaDNA-netropsin fibers. The melting temperature and helix-coil transition width were calculated from the melting curves. A phenomenological approach was used to describe the melting behavior of the fibers in and around the B-A transition region. The effect of netropsin on the melting of DNA fibers was attributed mainly to the stabilization of B-DNA and to a higher melting cooperativity in the B-DNA region.     

Pt(II) complexes with N-(3-pyridyl)-2-(4-(trifluoromethyl)phenyl)diazenecarboxamide and their reactions with glutathione

The reaction between [PtCl(dmso)(en)]Cl (dmso=dimethyl sulfoxide, en=ethylenediamine) and N-(3-pyridyl)-2-(4-(trifluoromethyl)phenyl)diazenecarboxamide (L) was studied using multinuclear NMR spectroscopy. The water-soluble complexes [PtCl(en)(L-N1)](+) (1) and [Pt(en)(L-N1)(2)](2+) (2) were isolated and their reactions with glutathione (GSH) were investigated to assess the oxidation properties of coordinated L. Both species 1 and 2 oxidized GSH to GSSG, while the reduced form of L (semicarbazide, SL) remained coordinated to Pt(2+). In complex 1 the labile chloride ion was substituted by the thiol moiety of GSH, which gave rise to the release of en in excess GSH over a period of 7 days. Complexes [PtCl(dmso)(en)]Cl, 1, 2 and ligand L were tested against T24 bladder carcinoma cells. Ligand L and complexes 1 and 2 showed higher cytotoxicity than [PtCl(dmso)(en)]Cl.     

Interaction of N-acetylmethionine with a non-C2-symmetrical platinum diamine complex

The reaction of N-acetylmethionine (N-AcMet) with the complex [Pt(Et(2)en)(D(2)O)(2)](2+) (Et(2)en=N,N-diethylethylenediamine) was studied by NMR spectroscopy and molecular mechanics calculations. Complexes containing two methionine residues coordinated to the platinum atom were calculated to be relatively high in energy unless the bulk of the methionine residues was directed away from the diethyl group of the Et(2)en ligand. In contrast, sulfur-oxygen chelates were found to be relatively free of steric clashes. Experimentally, two sets of NMR resonances were observed when [Pt(Et(2)en)(D(2)O)(2)](2+) was reacted with N-AcMet; variable temperature experiments indicated intermediate chemical exchange between the two sets of resonances. NMR studies indicated that the resonances corresponded to [Pt(Et(2)en)(N-AcMet-S,O)](+) complexes with the sulfur atom trans to the diethyl group of the Et(2)en ligand. No product with the sulfur atom cis to the diethyl group was observed experimentally even though molecular mechanics calculations suggested that such forms have few steric clashes. The NMR results suggested that the chemical exchange was a result of sulfur chirality inversion. In early stages of the reaction, a [Pt(Et(2)en)(N-AcMet-S)(D(2)O)](+) complex was observed, indicating that coordination of the oxygen to form the chelate is relatively slow.     

Studies on the interaction mechanism between hexakis(imidazole) manganese(II) terephthalate and DNA and preparation of DNA electrochemical sensor

The interaction between hexakis(imidazole) manganese(II) terephthalate ([Mn(Im)(6)](teph).4H(2)O) and salmon sperm DNA in 0.2M pH 2.30 Britton-Robinson buffer solution was studied by fluorescence spectroscopy and cyclic voltammetry. Increasing fluorescence was observed for [Mn(Im)(6)](2+) with DNA addition, while quenching fluorescence phenomenon appeared for EB-DNA system when [Mn(Im)(6)](2+) was added. There were a couple quasi-reversible redox peaks of [Mn(Im)(6)](2+) from the cyclic voltammogram on the glassy carbon electrode. The peak current of [Mn(Im)(6)](2+) decreased with positive shift of the formal potential in the presence of DNA compared with that in the absence of DNA. All the experimental results indicate that [Mn(Im)(6)](2+) can bind to DNA mainly by intercalative binding mode. The binding ratio of the DNA-[Mn(Im)(6)](2+) association complex is calculated to be 1:1 and the binding constant is 4.44x10(3) M(-1). By using [Mn(Im)(6)](teph).4H(2)O as the electrochemical hybridization indicator, the DNA electrochemical sensor was prepared by covalent interaction and the selectivity of ssDNA modified electrode were described. The results demonstrate the use of electrochemical DNA biosensor in the determination of complementary ssDNA.     

Guanine binding of a cytotoxic platinum-acridin-9-ylthiourea conjugate monitored by 1-D 1H and 2-D [1H,15N] NMR spectroscopy: hydrolysis is not the rate-determining step

The reaction of [PtCl(en)(ACRAMTU)](NO(3))(2) (PT-ACRAMTU, 1; ACRAMTU=1-[2-(acridin-9-ylamino)ethyl]-1,3-dimethylthiourea, en=ethane-1,2-diamine) and the [(15)N]-en labeled analogue, 1', with 2'-deoxyguanosine (dG) was studied by (1)H NMR and two-dimensional [(1)H,(15)N] HSQC (heteronuclear single quantum coherence) spectroscopy. Reactions were performed in phosphate buffered solution at 37 degrees C at various ratios and total concentrations of reactants. The (1)H NMR data suggest that the hydrolyzed form of the drug, [Pt(H(2)O)(en)(ACRAMTU)](3+) (1a), forms at a rate (k(1)) similar to that observed in classical platinum chloroam(m)ines but to only a minor extent ( approximately 15%). Attempts to detect and characterize 1'a by two-dimensional NMR spectroscopy, however, were unsuccessful, and 1' and dG( *) were the only species observed in the HSQC spectra. Reaction of the putative aqua intermediate 1a with dG to yield [Pt(en)(dG-N7)(ACRAMTU)](3+) (dG( *)) is slow and is highly dependent on the initial concentrations of the reactants. This unusual observation is consistent with a mechanism in which a second-order term becomes rate-determining (k(2)相似文献   

Encapsulation of platinum(II)-based DNA intercalators within cucurbit[6,7,8]urils

The partial encapsulation of platinum(II)-based DNA intercalators of the type [Pt(5-Cl-phen)(ancillary ligand)](2+), where 5-Cl-phen is 5-chloro-1,10-phenanthroline and the ancillary ligand is ethylenediamine, (1S,2S)-diaminocyclohexane (S,S-dach) or (1R,2R)-diaminocyclohexane, within cucurbit[n]uril (CB[n], where n is 6, 7 or 8) has been examined by (1)H and (195)Pt NMR and mass spectrometry. For CB[7], the molecule encapsulates over the ancillary ligand of all metal complexes, whether this is ethylenediamine or diaminocyclohexane. For CB[8], encapsulation occurs over the sides of the 5-Cl-phen ligand at low [Pt(5-Cl-phen)(S,S-dach)](2+) (5CLSS) to CB[8] ratios (i.e. 0.25:1) but over the ancillary ligand at higher ratios (i.e. 2:1). For CB[6] binding, 5CLSS exhibits both portal and cavity binding, with the ancillary ligand displaying chemical shifts consistent with fast exchange kinetics on the NMR timescale for portal binding and slow exchange kinetics for cavity binding. Binding constants could not be determined using UV-vis, circular dichroism or fluorescence spectrophotometry, but a binding constant for binding of 5CLSS to CB[6] of approximately 10(5) M(-1) was determined using (1)H NMR. Finally, the effect of CB[n] encapsulation on the cytotoxicity of the metal complexes was examined using L1210 murine leukaemia cells in vitro growth inhibition assays. The cytotoxicity is highly dependent on both the metal complex and the CB[n] size, and whilst CB[7] and CB[8] generally decreased cytotoxicity, it was found that CB[6] increased the cyotoxicity of 5CLSS up to 2.5-fold.     

DNA targeted platinum complexes: synthesis, cytotoxicity and DNA interactions of cis-dichloroplatinum(II) complexes tethered to phenazine-1-carboxamides

A series of intercalator-tethered platinum(II) complexes PtLCl2 have been prepared, where L are the diamine ligands N-[2-[(aminoethyl)amino]ethyl]-phenazine-1-carboxamide, N-[3-[(2-aminoethyl)amino]propyl]-phenazine-1-carboxamide, N-[4-[(2-aminoethyl)amino]butyl]-phenazine-1-carboxamide and N-[5-[(aminoethyl)amino]pentyl]-phenazine-1-carboxamide. Measurements of the time-course of unwinding of supercoiled pUC19 plasmid DNA by the phenazine complexes PtLCl2 reveal that the presence of the intercalator leads to enhanced rates of DNA platination when compared with the complex Pt(en)Cl2. The platinum(II) complexes where the polymethylene linker chain contains three, four or five carbon atoms are considerably more cytotoxic against murine P388/W than either cisplatin, Pt(en)Cl2, or the metal-free ligands themselves.     

Counterion dependent variation of DNA secondary structure in (A . T) clusters: evidence by use of netropsin as a structural probe.

The interaction of the oligopeptide antibiotic netropsin (Nt) with (A . T) regions of DNA is characterized by a spectrum of discrete modes. This has been revealed by viscometric analysis, at 20 degrees C and 0.2 M "counterions", for NaDNA in a preceding and for NH4DNA in this paper. The increase of DNA contour length as induced by one Nt molecule was found to depend on the special mode only, while the respective stiffening is generally higher for NH4DNA. The latter property is interpreted in terms of an enhanced flexibility, relative to that of NaDNA, of the (A . T) cluster segments before complex formation. For some of the interaction modes of the DNA-Nt systems a difference in the number of corresponding binding sites has been observed. This phenomenon is understood by assuming an influence of the counterion species upon existing equilibria between different forms of the (A . T) cluster secondary structure. Not less than 5 to 10% of the total DNA are effected in this manner. Upper limits for the local differences in the axial rise per base pair are 0.04 nm and 0.02 nm.     

DNA-binding and cleavage studies of macrocyclic copper(II) complexes

Three hexaaza macrocyclic copper (II) complexes with different functional groups have been synthesized and characterized by elemental analysis and infrared spectra. Absorption and fluorescence spectral, cyclic voltammetric and viscometric studies have been carried out on the interaction of [CuL(1)]Cl(2) (L(1)[double bond]3,10-bis(2-methylpyridine)-1,3,5,8,10,12-hexaazacyclotetradecane), [CuL(2)]Cl(2) (L(2)[double bond]3,10-bis(2-propionitrile)-1,3,5,8,10,12-hexaazacyclotetradecane) and [CuL(3)]Cl(2) (L(3)=3,10-bis(2-hydroxyethyl)-1,3,5,8,10,12-hexaazacyclotetradecane) with calf thymus DNA. The results suggest that three complexes can bind to DNA by different binding modes. The spectroscopic studies together with viscosity experiments and cyclic voltammetry suggest that [CuL(1)](2+) could bind to DNA by partial intercalation via pyridine ring into the base pairs of DNA. [CuL(2)](2+) may bind to DNA by hydrogen bonding and hydrophobic interaction while [CuL(3)](2+) may be by weaker hydrogen bonding. The functional groups on the side chain of macrocycle play a key role in deciding the mode and extent of binding of complexes to DNA. Noticeably, the three complexes have been found to cleave double-strand pUC18 DNA in the presence of 2-mercaptoethanol and H(2)O(2).     

Cytotoxicity studies of chromium(III) complexes on human dermal fibroblasts

The cytotoxicity of certain Cr(III) complexes, such as [Cr(salen)(H(2)O)(2)](+), [Cr(edta)(H(2)O)](-), [Cr(en)(3)](3+), [Cr(ox)(3)](3-), [Cr(pic)(3)], and CrCl(3), which differ in ionic character and ligand environment in human dermal skin fibroblasts, has been studied. After 72 h of exposure to 100 microM doses of chromium(III) complexes, the order in which the complexes had an inhibitory effect on cell viability was [Cr(en)(3)](3+) > [Cr(salen)(H(2)O)(2)](+) > [Cr(ox)(3)](3-) > [Cr(edta)(H(2)O)](-) > [Cr(pic)(3)] > CrCl(3). Based on viability studies it was confirmed that [Cr(en)(3)](3+), a triply charged cation, inhibits cell proliferation, and therefore, it was chosen to carry out further investigations. [Cr(en)(3)](3+), at a dose of 50 microM, was found to bring about surface morphological changes, evidenced by cellular blebbing and spike formation accompanied by nuclear damage. TEM analysis revealed substantial intracellular damage to fibroblasts in terms of the formation of apoptotic bodies and chromatin condensation, thus reflecting cell death. FACS analysis further revealed DNA damage by formation of a sub-G(1) peak with 84.2% DNA as aneuploid DNA and arrest of the G(2) / M phase of the cell cycle. Cellular DNA damage was confirmed by agarose gel electrophoresis with the characteristic appearance of a DNA streak in DNA isolated from [Cr(en)(3)](3+)-treated fibroblasts. The proposed mechanism suggests the plausible role of Cr(V), formed as a result of oxidation of Cr(III) by cellular oxidative enzymes, in the cytotoxic response. Consequently, any Cr(III) complex that is absorbed by cells and can be oxidized to Cr(V) must be considered a potential carcinogen. This has potential implications for the increased use of Cr(III) complexes as dietary supplements and highlights the need to consider the cytotoxicity and genotoxicity of a variety of Cr(III) complexes and to understand the potential hazards of Cr(III) complexes encountered in research laboratories.     

Probing site specificity of DNA binding metallointercalators by NMR spectroscopy and molecular modeling

The molecular recognition of oligonucleotides by chiral ruthenium complexes has been probed by NMR spectroscopy using the template Delta-cis-alpha- and Delta-cis-beta-[Ru(RR-picchxnMe(2)) (bidentate)](2+), where the bidentate ligand is one of phen (1,10-phenanthroline), dpq (dipyrido[3,2-f:2',3'-h]quinoxaline), or phi (9,10-phenanthrenequinone diimine) and picchxnMe(2)() is N,N'-dimethyl-N,N'-di(2-picolyl)-1,2-diaminocyclohexane. By varying only the bidentate ligand in a series of complexes, it was shown that the bidentate alone can alter binding modes. DNA binding studies of the Delta-cis-alpha-[Ru(RR-picchxnMe(2))(phen)](2+) complex indicate fast exchange kinetics on the chemical shift time scale and a "partial intercalation" mode of binding. This complex binds to [d(CGCGATCGCG)](2) and [d(ATATCGATAT)](2) at AT, TA, and GA sites from the minor groove, as well as to the ends of the oligonucleotide at low temperature. Studies of the Delta-cis-beta-[Ru(RR-picchxnMe(2))(phen)](2+) complex with [d(CGCGATCGCG)](2) showed that the complex binds only weakly to the ends of the oligonucleotide. The interaction of Delta-cis-alpha-[Ru(RR-picchxnMe(2))(dpq)](2+) with [d(CGCGATCGCG)](2) showed intermediate exchange kinetics and evidence of minor groove intercalation at the GA base step. In contrast to the phen and dpq complexes, Delta-cis-alpha- and Delta-cis-beta-[Ru(RR-picchxnMe(2))(phi)](2+) showed evidence of major groove binding independent of the metal ion configuration. DNA stabilization induced by complex binding to [d(CGCGATCGCG)](2) (measured as DeltaT(m)) increases in the order phen < dpq and DNA affinity in the order phen < dpq < phi. The groove binding preferences exhibited by the different bidentate ligands is explained with the aid of molecular modeling experiments.     

Synthesis, spectroscopic, cytotoxic, and DNA binding studies of binuclear 2,2'-bipyridine-platinum(II) and -palladium(II) complexes of meso-alpha,alpha'-diaminoadipic and meso-alpha,alpha'-diaminosuberic acids.

Four new binuclear complexes of formula [M2(bipy)2(BAA)]Cl2 (where M is Pt(II) or Pd(II), bipy is 2,2'-bipyridine, and BAA is a dianion of meso-alpha-alpha'-diaminoadipic acid (DAA) or meso-alpha,alpha'-diaminosuberic acid (DSA) have been synthesized. These complexes have been characterized by chemical analysis and ultraviolet-visible, infrared, and 1H NMR spectroscopy. The mode of binding of ligands in these complexes has been ascertained by infrared and detailed 1H NMR spectroscopy. These complexes are 1:2 electrolyte in conductivity water. They have also been tested against P388 lymphocytic leukemia cells and their target is DNA molecules. [Pt2(bipy)2(DSA)]Cl2, [Pd2(bipy)2(DSA)Cl2, and [Pd2(bipy)2(DAA)]Cl2 show I.D.50 values comparable or lower than cis-diamminedichloroplatinum(II) and [Pt(bipy)(Ala)]Cl. In addition, binding studies of [Pt2(bipy)2(DSA)]Cl2 and [Pd2(bipy)2(DAA)]Cl2 to calf thymus DNA have been carried out and the mode of binding seems to be hydrogen bonding, as suggested earlier for analogous mononuclear amino acid-DNA complexes.     

Specific protection of DNA by distamycin A, netropsin and bis-netropsins against the action of DNAse I

Interaction of netropsin, distamycin A and a number of bis-netropsins with DNA fragments of definite nucleotide sequence was studied by footprinting technique. The nuclease protection experiments were made at fixed DNA concentration and varying ligand concentrations. The affinity of ligand for a DNA site was estimated from measurements of ligand concentration that causes 50% protection of the DNA site. Distribution pattern of the protected and unprotected regions along the DNA fragment was compared with the theoretically expected arrangement of the ligand along the same DNA. The comparison led us to the following conclusions: 1. Footprinting experiments show that at high levels of binding the arrangement of netropsin molecules along the DNA corresponds closely to the distribution pattern expected from theoretical calculations based on the known geometry of netropsin--DNA complex. However, the observed differences in the affinity of netropsin for various DNA sequences is markedly greater than that expected from theoretical calculations. 2. Netropsin exhibits a greater selectivity of binding than that expected for a ligand with three specific reaction centers associated with the antibiotic amide groups. It binds preferentially to DNA regions containing four or more successive AT pairs. Among 13 putative binding sites for netropsin with four or more successive AT pairs there are 11 strong binding sites and two weaker sites which are occupied at 2 D/P less than or equal to 1/9 and 2 D/P = 1/4, respectively. 3. The extent of specificity manifested by distamycin A is comparable to that shown by netropsin although the molecule of distamycin A contains four rather than three amide groups. At high levels of binding distamycin A occupies the same binding sites on DNA as netropsin does. 4. The binding specificity of bis-netropsins is greater than that of netropsin. Bis-netropsins can bind to DNA in such a way that the two netropsin-like fragments are implicated in specific interaction with DNA base pairs. However, the apparent affinity of bis-netropsins estimated from footprinting experiments is comparable with that of netropsin for the same DNA region. 5. At high levels of binding bis-netropsins and distamycin A (but not netropsin) can occupy any potential site on DNA irrespectively of the DNA sequence. 6. Complex formation with netropsin increases sensitivity to DNase I at certain DNA sites along with the protection effect observed at neighboring sites.