Showing papers by "Jacqueline K. Barton published in 1990"

Molecular light switch for DNA : Ru(bpy)2(dppz)2+

Abstract: Considerable research has focused on the development of nonradioactive probes for nucleic acids. Extensive photophysical studies indicate that Ru(phen){sub 3}{sup 2+} bound to double-helical DNA displays an increase in luminescence owing to intercalation; emission from the metal-to-ligand charge transfer (MLCT) excited state decays as a biexponential with one lifetime of 2 {mu}s attributed to the intercalative form and a second lifetime of 0.6 {mu}s (indistinguishable from the free species) assigned to the surface bound form. Here we report the application of a novel transition-metal complex as a true molecular light switch for DNA. This probe is Ru(bpy){sub 2}(dppz){sup 2+} (bpy = 2,2{prime}-bipyridine, dppz = dipyrido(3,2-a:2{prime},3{prime}-c)phenazine), which shows no photoluminescence in aqueous solution at ambient temperatures, but displays intense photoluminescence in the presence of double-helical DNA, to which the complex binds avidly.

On demonstrating DNA intercalation

Abstract: Considerable attention has focused on new DNA-binding and -modifying agents, from natural products to wholly synthetic designs, as probes of DNA structure and as potential chemotherapeutic agents. The application of these molecules necessitates a precise understanding of the structural details of the agents' mode of interaction with the target molecule, double-helical DNA. DNA binding agents tend to interact noncovalently with the host molecule through two general modes: (i) in a groove-bound fashion stabilized by a mixture of hydrophobic, electrostatic, and hydrogen-bonding interactions and (ii) through an intercalative association in which a planar, heteroaromatic moiety slides between the DNA base pairs. Surprisingly, however, only a fraction of known DNA-interactive agents have been structurally characterized to atomic detail in noncovalent complexes with DNA.

Probing microstructures in double-helical DNA with chiral metal complexes: recognition of changes in base-pair propeller twisting in solution

Abstract: That DNA base pairs are propeller twisted in a sequence-dependent manner has been evident only in viewing crystal structures of oligonucleotides. Here the authors report that shape-selective DNA-binding molecules can recognize and distinguish propeller twisted DNA sites in solution on the basis of shape and symmetry. Enantioselective discrimination is apparent in photocleavage by Rh(phen){sub 2}phi{sup 3+} (phen = 1,10-phenanthroline; phi = 9,10-phenanthrenequinone diimine) at 5{prime}-pyr-pyr-pur-3{prime} steps which are characterized by a high degree of differential propeller twist but not at homopyrimidine-homopurine segments. Neither isomer targets 5{prime}-pur-pyr-3{prime} steps.

1H NMR studies of tris(phenanthroline) metal complexes bound to oligonucleotides: characterization of binding modes.

Abstract: The binding of Ru(phen)_3^(2+), Rh(phen)_3^(3+), and Co(phen)_3^(3+) to the oligonucleotides d(GTGCAC)_2 and 5'-pd(CGCGCG)_i has been examined by ^1H NMR spectroscopy as a function of temperature, concentration, and chirality of the metal complex. The duplex oligonucleotides act as chiral shift reagents for the metal complexes; phenanthroline protons associated with each enantiomer are resolved upon binding to the oligomer. The spectral titrations, consistent with photophysical studies, indicate that the complexes bind to the oligomer through two modes: one assigned as intercalation favoring the A-isomer, and the other assigned as the surface-bound interaction favoring the Λ-isomer. The ligand protons are perturbed in a manner that implies sensitivity of particular protons to binding mode; specifically, the H4,7 protons appear to be altered most for the Λ-enantiomer while the H5,6 protons are perturbed more for the Λ-enantiomer. The NMR chemical shift variations appear particularly sensitive to this surface-bound interaction, which, on the basis of a comparison of binding and photophysical parameters for Ru(phen)_3^(3+), appears more prominant in binding to oligonucleotides than that to polynucleotides. With respect to oligonucleotide proton shifts, the adenine H2 proton, positioned in the minor groove of the helix, shows the largest upfield shifts with metal binding, and more dramatically with Λ-isomers. The major groove thymine methyl protons (TMe) shift downfield to a lesser extent, and more so for Λ-isomers. The different binding modes also differ with respect to their dynamics of association; the longitudinal relaxation rates of Δ- and Λ-4,7 phenanthroline protons of Rh(phen)_3^(3+) are 0.88 and 1.14 s, respectively, in the presence of d(GTGCAC)_2. In contrast to studies with the substitutionally inert metal complexes, addition of racemic Co(phen)_3^(3+) to the oligonucleotide solution yields unequal populations of enantiomers, owing to the rapid racemization of the cobalt complex in the presence of oligomer and reequilibration to that form which favors binding. Duplex melting has also been monitored by ^1H NMR spectroscopy; the complexes increase the duplex melting temperature by ~5 oC. In the case of Co(phen)_3^(3+), with increasing temperature, as the helix melts, a reequlibration of the enantiomers occurs, indicating that the chiral discrimination arises from enantioselective interactions with the helix rather than with the single-stranded oligonucleotides.

Ligand-dependent interaction of ruthenium(II) polypyridyl complexes with DNA probed by emission spectroscopy.

Abstract: The nature of the interaction in buffered aqueous solution of several homo and heteroleptic ruthenium(II) polypyridyl complexes containing 2,2'-bipyridine (bpy), 2,2'-bipyrazine (bpz), 1,10-phenanthroline (phen), 4,7-diphenyl-1,10-phenanthroline (dip), 3,4,7,8-tetramethyl-1,10-phenanthroline (tmp), 1,4,5,8-tetraazaphenanthrene (tap), and 1,4,5,8,9,12-hexaazatriphenylene (hat) with calf thymus DNA and poly(dA-dT).poly(dA-dT) (pdAT) has been investigated by steady-state spectroscopy and emission lifetime measurements. Those complexes containing two or more tap/hat ligands photo-oxidize the guanine base upon binding to DNA with efficiencies that parallel their excited state redox potentials, but display "normal" behavior (increase of both the emission intensity and lifetime) when bound to pdAT. However Ru(tap)(hat)2+2 and Ru(hat)2+3 even photooxidize the adenine base of pdAT, so that their excited states are also quenched in the presence of either polynucleotide. The electron transfer quenching mechanism has been confirmed previously by detection of the monoreduced complex in laser flash photolysis experiments in the presence of mononucleotides. Most of the complexes investigated appear to bind to DNA, at least in part via intercalation, with affinities being dependent on the nature of the largest ligand (hat shows the highest ability in heteroleptic complexes). From lifetime quenching experiments, in the presence of moderate amounts of NaCl, surface binding does not appear to be a general mode for the complexes investigated, and it has been demonstrated unequivocally only for Ru(phen)2+3. In addition, the intercalation of complexes into DNA increases as the ionic strength of the medium decreases, the DNA/Ru ratio increases, or when water is partially replaced by glycerol.

Synthesis and characterization of physical, electronic, and photochemical aspects of 9,10-phenanthrenequinonediimine complexes of ruthenium(II) and rhodium(III)

Abstract: A series of ruthenium(II) and rhodium(III) complexes containing the novel 9,10-phenanthrenequinone diimine (phi) ligand have been prepared and characterized with respect to structure, spectroscopy, and/or photochemical reactivity. Synthetic approaches to mixed-ligand complexes containing the phi ligand include direct addition of the protected N,N'-bis(trimethylsilyl)-phenanthrenequinone diimine ligand to the metal center of chelation first of diaminopohenanthrene followed by oxidation to the coordinated phi ligand

Molecular “Light Switch” for DNA: Ru(bpy)2(dppz)2+.

Abstract: Considerable research has focused on the development of nonradioactive probes for nucleic acids. Extensive photophysical studies indicate that Ru(phen){sub 3}{sup 2+} bound to double-helical DNA displays an increase in luminescence owing to intercalation; emission from the metal-to-ligand charge transfer (MLCT) excited state decays as a biexponential with one lifetime of 2 {mu}s attributed to the intercalative form and a second lifetime of 0.6 {mu}s (indistinguishable from the free species) assigned to the surface bound form. Here we report the application of a novel transition-metal complex as a true molecular light switch for DNA. This probe is Ru(bpy){sub 2}(dppz){sup 2+} (bpy = 2,2{prime}-bipyridine, dppz = dipyrido(3,2-a:2{prime},3{prime}-c)phenazine), which shows no photoluminescence in aqueous solution at ambient temperatures, but displays intense photoluminescence in the presence of double-helical DNA, to which the complex binds avidly.

1H NMR studies of tris(phenanthroline) metal complexes bound to oligonucleotides: structural characterizations via selective paramagnetic relaxation.

Abstract: The selective paramagnetic relaxation of oligonucleotide protons of d(GTGCAC)_2 by Δ- and Λ-Ni(phen)_3^(3+) and Δ- and Λ-Cr(phen)_3^(3+) has been examined to obtain some structural insight into the noncovalent binding of tris(phenanthroline) metal complexes to DNA. The experiments demonstrate that the relative rate of relaxation of different oligonucleotide protons by the paramagnetic metal complex varies with the chirality of the metal complex and, to a lesser extent, the metal charge. The proton most efficiently relaxed in all cases is the adenosine AH2, which is situated in the minor groove of the oligonucleotide helix. For both Λ-Ni(phen)_3^(2+) and Λ-Cr(phen)_3^(3+), the order of relaxation rates varies as AH2 » AH8 > G3H8 = TMe = C4H5. For Δ-Ni(phen)_3^(2+) it varies as AH2 > G3H8 > AH8 > TMe = C4H5 and for Δ-Cr(phen)_3^(3+) as AH2 > TMe = G3H8 = AH8 > C4H5. Distances between the metal center and oligonucleotide protons were calculated on the basis of the relaxation data, and these distances were used to generate a set of models to describe the interactions of the rigid metal complex with the helix. For A-isomers, the data are consistent with a predominant surface-bound association in the minor groove of the DNA helix. The results for A-isomers correlate better with models that incorporate also a major groove intercalative mode. Despite the absence of hydrogen-bonding groups in the metal complex, the surface-bound model of the phenanthroline complex in the minor groove of DNA resembles the noncovalent association seen with other DNA groove binding molecules.

Synthesis, characterization, and solution chemistry of a family of protein-binding inorganic complexes: bis(imidazole)(amino acid-N,N-diacetato)chromium(III)

Abstract: The synthesis and characterization of a family of transition-metal complexes containing amino acid substituents, which has shown an array of recognition characteristics relevant to association with proteins, is described. These molecules are based upon the bis(imidazole)(nitrilotriacetato)chromium(III) core, with the series generated throught substitutions of amino acid side chains onto the methylene position of one of the chelate rings

Mixed ligand complexes and uses thereof as binding agents and probes to DNA

Abstract: This invention concerns a coordination complex or salt thereof which is spectroscopically or photoactively determinable when bound to DNA having the formula ##STR1## wherein M is a suitable transition metal and each of R1, R2 and R3 is ethylenediamine, bipyridine, phenanthroline, diazafluorene-9-one or a substituted derivative thereof, or phenanthrenequinonediimine or a substituted derivative thereof, dypyridophenazine or a substituted derivative thereof; wherein R1, R2 and R3 are bound to M by coordination bonds; provided that at least one of R1, R2 or R3 is dypyridophenazine or a substituted derivative thereof The invention also concerns a labeled DNA probe which comprises the complex covalently bound to the DNA probe Further the invention concerns a method of detecting the presence in a sample a target DNA of interest which comprises contacting the sample containing the target DNA with a complementary labeled DNA probe under hybridizing conditions and measuring the resulting luminescense emitted from the labeled DNA probe, a change in the luminescense as compared with the luminescense in the absence of the sample indicating the presence of the target DNA