Home About us Contact
|
Home About us Contact | ||
|
|
||
Zn2+ Complexes (zn2+ + complex)
Selected AbstractsZn2+ Complexes of Di- and Tri-nucleating Azacrown Ligands as Base-Moiety-Selective Cleaving Agents of RNA 3,,5,-Phosphodiester Bonds: Binding to Guanine BaseCHEMBIOCHEM, Issue 11 2008Qi Wang Dr. Abstract The ability of the dinuclear Zn2+ complex of 1,4-bis[(1,5,9-triazacyclododecan-3-yloxy)methyl]benzene (L1) to promote the cleavage of the phosphodiester bond of dinucleoside-3,,5,-monophosphates that contain a guanine base has been studied over a narrow pH range from pH 5.8 to 7.2 at 90,°C. Comparative measurements have been carried out by using the trinuclear Zn2+ complex of 1,3,5-tris[(1,5,9-triazacyclododecan-3-yloxy)methyl]benzene (L2) as a cleaving agent and guanylyl-3,,5,-guanosine (5,-GpG-3,) as a substrate. The strength of the interaction between the cleaving agent and the starting material has been elucidated by UV spectrophotometric titrations. The speciation and binding mode have been clarified by potentiometric titrations with hydrolytically stable 2,- O -methylguanylyl-3,,5,-guanosine and 1H NMR spectroscopic measurements with guanylyl-3,,5,-guanosine. The results show that the guanine base is able to serve as a site for anchoring for the Zn2+,azacrown moieties of the cleaving agents L1 and L2, analogously to uracil base. The interaction is, however, weaker than with the uracil base and, hence, only the 5,-GpG-3, site (in addition to 5,-GpU-3, and 5,-UpG-3, sites) is able to markedly modulate the phosphodiester cleavage by the Zn2+ complexes of di- and trinucleating azacrown ligands containing an ether oxygen as a potential H-bond-acceptor site. [source] Toward an Allosteric Metallated ContainerEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 2 2009Helga Szelke Abstract Polytopic ligands L1 and L2 in which three 2,2,-bipyridine units are linked to a central tris(pyrid-2-yl)amine (L1) or tris(pyrid-2-yl)methanol (L2) moiety by alkyl spacers were prepared by multistep organic syntheses. The parent tris(pyrid-2-yl)-type ligands were shown to be modest-to-good chelators for Zn2+ and Cu2+ ions in solution, and bi- and tridentate N-coordination was confirmed by crystal structures of CuII and RuII complexes, respectively. FeII and RuII smoothly form stable, cage-like 1:1 complexes with L1 and L2, in which the metal ion is coordinated to the tris(bpy) site of the ligands. The vacant tris(pyrid-2-yl) site of these complexes is, however, a poor donor site for Zn2+ and Cu2+ ions. In addition, FeII modulates the coordination behaviour of the tris(pyrid-2-yl) site toward Zn2+: Whereas tris(5-methylpyrid-2-yl)amine forms a 2:1 complex with Zn2+ in CH2Cl2, [Fe(L1)]2+ forms a 1:1 Zn complex. Spectrophotometric titrations suggest that [Fe(L2)]2+ forms a polynuclear Zn2+ complex in CH2Cl2, possibly involving bridging coordination of the alcohol OH group, which contrasts the smooth formation of a 2:1 complex of the parent tris(pyrid-2-yl)-type ligand with Zn. FeII might therefore be considered as an allosteric effector, which modulates the metal binding properties of the second tris(pyrid-2-yl) site of L1 and L2. Contrary to expectation, Zn2+ and Cu2+ appear to associate weakly with donor atoms directed toward the exterior of the cage-like complexes [Fe(Ln)]2+ and [Ru(L1)]2+, rather than locating in the interior of the container by tripodal coordination to the tris(pyrid-2-yl) site.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Zn2+ Complexes of Di- and Tri-nucleating Azacrown Ligands as Base-Moiety-Selective Cleaving Agents of RNA 3,,5,-Phosphodiester Bonds: Binding to Guanine BaseCHEMBIOCHEM, Issue 11 2008Qi Wang Dr. Abstract The ability of the dinuclear Zn2+ complex of 1,4-bis[(1,5,9-triazacyclododecan-3-yloxy)methyl]benzene (L1) to promote the cleavage of the phosphodiester bond of dinucleoside-3,,5,-monophosphates that contain a guanine base has been studied over a narrow pH range from pH 5.8 to 7.2 at 90,°C. Comparative measurements have been carried out by using the trinuclear Zn2+ complex of 1,3,5-tris[(1,5,9-triazacyclododecan-3-yloxy)methyl]benzene (L2) as a cleaving agent and guanylyl-3,,5,-guanosine (5,-GpG-3,) as a substrate. The strength of the interaction between the cleaving agent and the starting material has been elucidated by UV spectrophotometric titrations. The speciation and binding mode have been clarified by potentiometric titrations with hydrolytically stable 2,- O -methylguanylyl-3,,5,-guanosine and 1H NMR spectroscopic measurements with guanylyl-3,,5,-guanosine. The results show that the guanine base is able to serve as a site for anchoring for the Zn2+,azacrown moieties of the cleaving agents L1 and L2, analogously to uracil base. The interaction is, however, weaker than with the uracil base and, hence, only the 5,-GpG-3, site (in addition to 5,-GpU-3, and 5,-UpG-3, sites) is able to markedly modulate the phosphodiester cleavage by the Zn2+ complexes of di- and trinucleating azacrown ligands containing an ether oxygen as a potential H-bond-acceptor site. [source] Radioiodinated clioquinol as a biomarker for ,-amyloid: Zn2+ complexes in Alzheimer's diseaseAGING CELL, Issue 1 2006Carlos Opazo Summary Neocortical ,-amyloid (A,) aggregates in Alzheimer's disease (AD) are enriched in transition metals that mediate assembly. Clioquinol (CQ) targets metal interaction with A, and inhibits amyloid pathology in transgenic mice. Here, we investigated the binding properties of radioiodinated CQ ([125I]CQ) to different in vitro and in vivo Alzheimer models. We observed saturable binding of [125I]CQ to synthetic A, precipitated by Zn2+ (Kd = 0.45 and 1.40 nm for A,1-42 and A,1-40, respectively), which was fully displaced by free Zn2+, Cu2+, the chelator DTPA (diethylene triamine pentaacetic acid) and partially by Congo red. Sucrose density gradient of post-mortem AD brain indicated that [125I]CQ concentrated in a fraction enriched for both A, and Zn, which was modulated by exogenous addition of Zn2+ or DTPA. APP transgenic (Tg2576) mice injected with [125I]CQ exhibited higher brain retention of tracer compared to non-Tg mice. Autoradiography of brain sections of these animals confirmed selective [125I]CQ enrichment in the neocortex. Histologically, both thioflavine-S (ThS)-positive and negative structures were labeled by [125I]CQ. A pilot SPECT study of [123I]CQ showed limited uptake of the tracer into the brain, which did however, appear to be more rapid in AD patients compared to age-matched controls. These data support metallated A, species as the neuropharmacological target of CQ and indicate that this drug class may have potential as in vivo imaging agents for Alzheimer neuropathology. [source] A theoretical density functional study of association of Zn2+ with oxazolidine and its thio derivatives in the gas phaseJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 8 2010Zaki S. Safi Abstract We have performed density functional theory (DFT) calculations in order to study the gas-phase interaction of oxo- and thio-oxazolidine derivatives with Zn2+. The calculations were performed at B3LYP/6-311+(2df,2p) level of theory. It has been found, in all cases, that the direct association of Zn2+ with the carbonyl and thiocarbonyl groups takes place at the heteroatom attached to position 2 irrespective of its nature. This preference has been attributed to the resonance effects caused by the nearest heteroatoms (oxygen and nitrogen). The most stable complexes correspond to structures with Zn2+ bridging between the heteroatom at position 2 or 4 of the 4- or 2-enol (or the 4- or 2-enethiol) tautomer and the dehydrogenated ring nitrogen atom, N3. Zn2+ association has a clear catalytic effect on the tautomerization processes which connect the oxo,thione forms with the enol,enethiol tautomers. Hence, although the enol,enethiol tautomers of oxazolidine and its thio derivatives should not be observed in the gas phase, the corresponding Zn2+ complexes are the most stable species and should be accessible, because the tautomerization barriers are smaller than the Zn2+ binding energies. Copyright © 2010 John Wiley & Sons, Ltd. [source] Metallosupramolecular approach toward functional coordination polymersJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 21 2005Rainer Dobrawa Abstract An appropriate definition of metallosupramolecular coordination polymer is offered, and the relationship between the polymer length, binding constant, and concentration is clarified. The possibility of influencing the binding constant with chelating ligands is discussed on the basis of examples of different Zn2+ complexes and their respective binding constants. In the main part, coordination polymers constructed by a supramolecular approach from different metal ions and pyridine,ligand systems are highlighted, and their applications as functional materials for artificial membrane and enzyme models, responsive gels, light-harvesting systems, and organic light-emitting diodes are discussed on the basis of individual examples. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4981,4995, 2005 [source] Zn2+ Complexes of Di- and Tri-nucleating Azacrown Ligands as Base-Moiety-Selective Cleaving Agents of RNA 3,,5,-Phosphodiester Bonds: Binding to Guanine BaseCHEMBIOCHEM, Issue 11 2008Qi Wang Dr. Abstract The ability of the dinuclear Zn2+ complex of 1,4-bis[(1,5,9-triazacyclododecan-3-yloxy)methyl]benzene (L1) to promote the cleavage of the phosphodiester bond of dinucleoside-3,,5,-monophosphates that contain a guanine base has been studied over a narrow pH range from pH 5.8 to 7.2 at 90,°C. Comparative measurements have been carried out by using the trinuclear Zn2+ complex of 1,3,5-tris[(1,5,9-triazacyclododecan-3-yloxy)methyl]benzene (L2) as a cleaving agent and guanylyl-3,,5,-guanosine (5,-GpG-3,) as a substrate. The strength of the interaction between the cleaving agent and the starting material has been elucidated by UV spectrophotometric titrations. The speciation and binding mode have been clarified by potentiometric titrations with hydrolytically stable 2,- O -methylguanylyl-3,,5,-guanosine and 1H NMR spectroscopic measurements with guanylyl-3,,5,-guanosine. The results show that the guanine base is able to serve as a site for anchoring for the Zn2+,azacrown moieties of the cleaving agents L1 and L2, analogously to uracil base. The interaction is, however, weaker than with the uracil base and, hence, only the 5,-GpG-3, site (in addition to 5,-GpU-3, and 5,-UpG-3, sites) is able to markedly modulate the phosphodiester cleavage by the Zn2+ complexes of di- and trinucleating azacrown ligands containing an ether oxygen as a potential H-bond-acceptor site. [source] A New Fluorescent Probe for Zinc(II): An 8-Hydroxy-5- N,N -dimethylaminosulfonylquinoline-Pendant 1,4,7,10-TetraazacyclododecaneCHEMISTRY - A EUROPEAN JOURNAL, Issue 35 2006Shin Aoki Prof. Abstract A new fluorescent probe for Zn2+, namely, 8-hydroxy-5- N,N -dimethylaminosulfonylquinolin-2-ylmethyl-pendant cyclen (L8), was designed and synthesized (cyclen=1,4,7,10-tetraazacyclododecane). By potentiometric pH, 1H NMR, and UV spectroscopic titrations, the deprotonation constants pKa1,pKa6 of L8,4,HCl were determined to be <2, <2, <2 (for amino groups of the cyclen and quinoline moieties), 7.19±0.05 (for 8-OH of the quinoline moiety), 10.10±0.05, and 11.49±0.05, respectively, at 25,°C with I=0.1 (NaNO3). The results of 1H NMR, potentiometric pH, and UV titrations, as well as single-crystal X-ray diffraction analysis, showed that L8 and Zn2+ form a 1:1 complex [Zn(H,1L8)], in which the 8-OH group of the quinoline ring of L8 is deprotonated and coordinates to Zn2+, in aqueous solution at neutral pH. On addition of one equivalent of Zn2+ and Cd2+, the fluorescence emission of L8 (5 ,M) at 512 nm in aqueous solution at pH 7.4 [10 mM HEPES with I=0.1 (NaNO3)] and 25,°C increased by factors of 17 and 43, respectively. We found that the cyclen moiety has the unique property of quenching the fluorescence emission of the quinolinol moiety when not complexed with metal cations, but enhancing emission when complexed with Zn2+ or Cd2+. In addition, the Zn2+,L8 complex [Zn(H,1L8)] is much more thermodynamically and kinetically stable (Kd{Zn(H,1L8)}=[Zn2+]free[L8]free/[Zn(H,1L8)]=8 fM at pH 7.4) than the Zn2+ complexes of our previous Zn2+ fluorophores ([Zn(H,1L2)] and [Zn(L3)]). Furthermore, formation of [Zn(H,1L8)] is much faster than those of [Zn(H,1L2)] and [Zn(L3)]. The staining of early-stage apoptotic cells with L8 is also described. [source] | ||||||||||