Stereoselective recognition of vicinal diamines with a Zn(II) complex

Zn(II) complex of L (N,N'-bis(2-pyridylmethyl)-N,N'-dimethyl-trans-1,2-diaminocyclohexane) binds chiral vicinal diamines (1,2-diphenylethylenediamine (dpen) and 1,2-diaminocyclohexane (dach)) stereoselectively. Crystallographic studies reveal that the ternary complex has the C2 symmetric cis-alpha topology. 1H NMR shows that the R,R form of the tetradentate zinc complex binds rapidly and reversibly to the R,R form of the diamine over the S,S form with a stereoselectivity of about 5:1. Although the diamine exchange rate is rapid it is slower than the NMR time scale, and distinct signals for the diastereomeric complexes are observed when racemic mixtures of the host and guest molecules are mixed. Origin of stereoselectivity is discussed in terms of steric effects.     

Kinetic analysis of a photosensitive chelator and its complex with Zn(II)

The reversible sequestration and release of metal ions is an important objective in biological and environmental research. Unfortunately, although there have been dramatic examples of metal ion activity control, there are very few quantitative investigations of stoichiometry, equilibria and kinetics. A significant contributor to this lack of quantitative work is the complexity of many photochromic systems. Therefore, we have attempted to create a simple, reversible photochromic metal-ion chelator that can be analyzed quantitatively. The chelator should have certain other attributes as well, namely, that it binds to divalent metal ions (because of their extreme biological importance) and that it binds metal ions in the dark so that light is used to release metal ions rather than sequester them. The photochromic chelator (1) binds to divalent metal ions [Zn(II), Cu(II), Pb(II), Hg(II), Fe(II), Co(II) and Cd(II); other metal ions have not yet been tested] in the dark with a significant binding strength. In both methanol (by spectrophotometry) and methanol-water (by voltammetry), the stoichiometry of the 1-Zn(II) complex is 2:1. The binding constant (K1K2) is on the order of 10(12)-10(14) M(-2) in methanol and 5.0 x 10(8) M(-2) in 50% aqueous methanol. The chelator 1 is photolabile, yielding 2 with a quantum efficiency of 0.91. In a solution containing excess Zn(II), so that over 99% of the ligand exists as the monodentate complex, photolysis produces 2 with a quantum efficiency of 0.15. A kinetic analysis leads to the conclusion that the complex itself is photolabile.     

Crystal structure of a new transition metal-organic Zn(II) complex

A novel Zn(II) coordination polymer [Zn₂(phen)₂]L₄·3H₂O(1) is synthesized by the reaction of Zn(NO₃)₂, Phen(1,10-phenanthroline), and L(2-mercaptonicotinic acid) at room temperature and structurally characterized by X-ray single crystal diffraction along with IR spectra and elemental analysis. Title complex 1 belongs to the triclinic system with the space group (P-1), a = 10.9373(11) Å, b = 11.6201(12) Å, c = 13.1371(14) Å; α = 116.100(1)°, β = 97.717(2)°, γ = 108.652(2)°, V = 1344.4(2) ų; Z = 2, ρ_calc = 1.596 g·cm^?3, F(000) = 664, R ₁ = 0.0708 and wR ₂ = 0.1823 independent reflections for 18523 observed ones (I > 2σ(I)), and the zinc atom is rendered five-coordinated in a distorted tetragonal pyramid coordination geometry by two nitrogen atoms from the phen molecule, two oxygen atoms from two L molecules, and an oxygen atom from the H₂O molecule. Complex 1 forms a 1D chain by O-H…O hydrogen bonds from free-water, while the 2D layer structure is formed by C-H…O hydrogen bonds through the L ligand of adjacent chains. These compounds further result in a 3D network structure by the intermolecular π…π stacking interaction of the neighbouring layers.     

Syntheses and structures of isoindoline complexes of Zn(II) and Cu(II): an unexpected trinuclear Zn(II) complex

Deprotonation of the tridentate isoindoline ligand 1,3-bis[2-(4-methylpyridyl)imino]-isoindoline, 4'-MeLH, and reaction with hydrated zinc(II) perchlorate produces an unexpected trinuclear Zn(II) complex, [Zn(3)(4'-MeL)(4)](ClO(4))(2).5H(2)O (1), whereas reaction with hydrated copper(II) perchlorate in methanol produces the expected mononuclear product, [Cu(4'-MeL)(H(2)O)(2)]ClO(4) (2). X-ray diffraction shows that the trinuclear Zn(II) complex (1) contains a linear zinc backbone, and the arrangement of ligands about the outer chiral zinc(II) atoms is helical. The two terminal zinc ions exhibit approximate C(2) site symmetry, with tetrahedral coordination by two pyrrole and two pyridyl nitrogen atoms of the potentially tridentate isoindoline ligands. The central zinc ion exhibits approximate tetrahedral symmetry, with coordination by four pyridyl nitrogen atoms of four different isoindoline ligands. Pyridyl-pyrrole intramolecular pi-stacking interactions contribute to the stability of the trinuclear cation. The structure of the mononuclear copper(II) complex cation in 2 is best described as a distorted trigonal bipyramid. The isoindoline anion binds Cu(II) in both axial positions and one of the equatorial positions; water molecules occupy the other two equatorial positions.     

Structural investigation of dibromobis(benzimidazole)Zn(II) complex

The molecular structure of the title complex [ZnBr₂(C₇H₆N₂)₂] was investigated by X-ray diffraction and IR spectroscopy methods. Molecules of zinc(II) complex crystallize in the triclinic crystal system with cell constants a=7.526(2) Å, b=7.8971(8) Å, c=13.431(1) Å, Z=2 and V=791.3(2) Å³. In the molecular structure, the Zn atom is coordinated tetrahedrally by two Br⁻ anions and two benzimidazole ligands. Intramolecular steric repulsions between Br⁻ anions and benzimidazole groups have been caused to cis configuration around the central metal atom.     

A novel imidazolate-bridged heterodinuclear Cu(II)Zn(II) complex derived from a unique macrocyclic ligand with two hydroxyethyl pendants

[(CuimZnL-2H)(CuimZnL-H)](ClO4)3, the first imidazolate-bridged Cu(II)-Zn(II) complex of a unique single macrocyclic ligand with two flexible hydroxyethyl pendants, L (L = 3,6,9,16,19,22-hexaaza-6,19-bis(2-hydroxyethyl)tricyclo[22.2.2.2(11,14)]triaconta-1,11,13,24,27,29-hexaene) has been obtained, in which the macrocyclic ligand with two hydroxyethyl arms possesses a markedly different conformation compared to its dicopper analogue.     

Metal-directed self-assembly of a Zn(II)-salpyr complex into a supramolecular vase structure

A new type of supramolecular building block, Zn(II)-salpyr [salpyr = N,N'-3-pyridylenebis(salicylideneimine)], is described that contains both a pyridyl donor and a Lewis acidic Zn(II) acceptor site in the salen framework. As a consequence, this building block self-organizes into a stable tetrameric vase structure via cooperative intermolecular Zn-N(pyr) interactions.     

Recognition of thymine in DNA bulges by a Zn(II) macrocyclic complex

A Zn(II) macrocyclic complex with appended quinoline is a bifunctional recognition agent that uses both the Zn(II) center and the pendent aromatic group to bind to thymine in bulges with good selectivity over DNA containing G, C or A bulges. Spectroscopic studies show that the stem containing the bulge stays largely intact in a DNA hairpin with the Zn(II) complex bound to the thymine bulge.     

Spectroscopic studies and crystal structure of a dimeric Zn(II) complex with diethyl (pyridin-2-ylmethyl)phosphate

The crystal structure of [Zn₂(2-pmOpe)₂Cl₄] (2-pmOpe?=?diethyl (pyridin-2-ylmethyl)phosphate) was determined by X-ray-diffraction method. The compound was also characterized by IR, far-IR, 1H, and ³¹P NMR spectroscopy. In this compound, 2-pmOpe is a bidentate N,O-bridging ligand and Zn(II) are slightly distorted tetrahedral ZnNOCl₂. Zn(II) ions are doubly bridged by the 2-pmOpe ligands, resulting in a dinuclear species. The structure is stabilized by intermolecular C–H?···?O and C–H?···?Cl hydrogen bonds. The spectral properties are in agreement with the structural data.     

A highly reactive mononuclear Zn(II) complex for phosphodiester cleavage

The activity of a Zn(II) complex of a tetradentate, tripodal ligand for catalyzing phosphodiester cleavage is enhanced 750-fold by introducing three hydrogen bond donors to the ligand. Inhibition studies show that the Zn-aqua complex is the kinetically active form and that it binds the transition state with a formal dissociation constant of 3 x 108 M-1. The effect of these ligand modifications on the transition-state affinity is comparable to the rate acceleration provided by the metal ion itself. Overall, this mononuclear complex is more active than the most reactive dinuclear Zn(II) complexes reported to date.     

Turn-on fluorescence sensing of nucleoside polyphosphates using a xanthene-based Zn(II) complex chemosensor

Fluorescence sensing with small molecular chemosensors is a versatile technique for elucidation of function of various biological substances. We now report a new fluorescent chemosensor for nucleoside polyphosphates such as ATP using metal-anion coordination chemistry. The chemosensor 1-2Zn(II) is comprised of the two sites of 2,2'-dipicolylamine (Dpa)-Zn(II) as the binding motifs and xanthene as a fluorescent sensing unit for nucleoside polyphosphates. The chemosensor 1-2Zn(II) selectively senses nucleoside polyphosphates with a large fluorescence enhancement (F/F(o) > 15) and strong binding affinity (K(app) approximately = 1 x 10(6) M(-1)), whereas no detectable fluorescence change was induced by monophosphate species and various other anions. The 'turn-on,' fluorescence of 1-2Zn(II) is based on a new mechanism, which involves the binding-induced recovery of the conjugated form of the xanthene ring from its nonfluorescent deconjugated state which was formed by an unprecedented nucleophilic attack of zinc-bound water. The selective and highly sensitive ability of 1-2Zn(II) to detect nucleoside polyphosphates enables its bioanalytical applications in fluorescence visualization of ATP particulate stores in living cells, demonstrating the potential utility of 1-2Zn(II).     

Complexes of Zn(II) and Mn(II) with biacetyldihydrazone

The complexes [Zn(BdH)₂Cl₂] and [Mn(BdH)₂Cl₂] have been prepared and studied by IR, electronic and ESR spectroscopies and by magnetic measurements. All results agree with a molecular formula for both complexes and a distorted octahedral environment for the metal atoms.     

配合物Zn(II)-BPHA的^1H NMR谱

测定了各pD值下BPHA[BPHA是N,N'-bis(2-aminoethyl)-1,3-propanediaminehexaaceticacid的简称,中文名称为二胺乙基丙二胺六乙酸]和Zn^2^+-BPHA的^1HNMR谱。BPHA两端羧甲基上亚甲基质子的化学位移δ~a和中间羧甲基上亚甲基质子的化学位移δ~b随pD值交替变化。Zn^2^+-BPHA的^1HNMR谱有3种情况:pD<6,对应Zn(II)-H~2BPHA^4^-,有一特征尖峰,显示自由-NH^+(CH~2COO^-)~2残基存在;pD=6-9,对应Zn(II)-HBPHA^5^-,该峰消失,显示4个胺基全部配位;pD>9,对应Zn(II)-BPHA^6^-,该峰再次出现,1个N(CH~2COO^-)~2脱离配位体系。在3种形态的配合物中,Zn-N键都是非活性的,Zn-O键在后两种形态配合物中是非活性的。     

Synthesis,characterization, and biological activity of a Schiff-base Zn(II) complex

Preparation and crystal structure of {4-chloro-2-[(2-morpholinoethylimino)methyl]phenolato} methanolchlorozinc(II) are reported. The X-ray structure reveals highly distorted square pyramidal geometry around zinc, binding to one phenolate O and two imine N atoms of the Schiff base, one methanol and one chloride. The complex and its ligand were tested in vitro for antibacterial and cytotoxic activity with a wide range of bactericidal activity and significant cytotoxic activity.     

Substrate specificity for catalysis of phosphodiester cleavage by a dinuclear Zn(II) complex

The 2.4 kcal mol(-1) greater stabilization of the transition state for cleavage of the minimal substrate HpPNP compared to the nucleoside substrate UpPNP by the efficient dinuclear metal ion catalyst Zn2(L2O) provides evidence that access to the cationic core of Zn2(L2O) is sterically blocked for the bulkier nucleoside substrates, a flaw that will need to be dealt with in later generations of metal ion catalysts of RNA cleavage.     

Synthesis, spectroscopic characterization, insulin-enhancment, and competitive DNA binding activity of a new Zn(II) complex with a vitamin B6 derivative--a new fluorescence probe for Zn(II)

This paper describes the activity of a Schiff base ligand, derived from pyridoxal, as a promising fluorescence probe for biologically important Zn(II) ion sensing. This is the first report of a vitamin based ligand as a fluorescent probe for sensing Zn(II) ions. The Schiff base H(2)pydmedpt, derived from the condensation of pyridoxal (pyd) and N,N-bis[3-aminopropyl]methylamine (medpt), exhibits around a 325-fold increase in fluorescence quantum yield due to zinc triggered fluorescence switching. The response is specific for Zn(II) ions, and remains unaffected by the presence of alkali and alkaline earth metals but is suppressed to varying degrees by transition metal ions. The corresponding Zn(II)-complex, [Zn(pydmedpt], is isolated. The DFT optimized structure of the complex is compatible with elemental analysis, mass spectrometry, FT-IR, electronic and NMR spectra. The isolated complex, having pK(a) values of ～5.3 and ～5, is a moderate intercalator for DNA with an apparent binding constant of 2.3 × 10(6) M(-1). The complex also shows insulin-enhancing activity at par with other reported complexes, with an IC(50) value of 0.65 with respect to ZnSO(4).     

DNA-binding properties studies and spectra of a novel fluorescent Zn(II) complex with a new chromone derivative

A new chromone derivative (6-ethoxy chromone-3-carbaldehyde benzoyl hydrazone) ligand (L) and its two transition metal complexes [Zn(II) complex and Ni(II) complex] have been prepared and characterized on the basis of elemental analysis, molar conductivity, mass spectra, UV–vis spectra and IR spectra. The Zn(II) complex exhibits light blue fluorescence under UV light, and the fluorescent properties of Zn(II) complex and the ligand in solid state and in different solutions (MeOH, DMF, THF and H₂O) were investigated. In addition, the interactions of the Zn(II) complex and the ligand with calf thymus DNA were investigated using UV–vis absorption, fluorescence, circular dichroic spectral methods and viscosity measurement. It was founded that both two compounds, especially the Zn(II) complex, strongly bind with calf thymus DNA, presumably via an intercalation mechanism.     

Thermal,spectral and biological properties of Zn(II) complex compounds with phenazone

The thermal decomposition of the complexes Zn(form)₂⋅2phen (I), Zn(ac)₂⋅2phen (II), Zn(prop)₂⋅2phen (III), Zn(but)₂⋅2phen (IV), where phen=phenazone, form=formiate, ac=acetate, prop=propionate, but=butyrate has been studied in air by TG/DTG and DTA methods. The possible mechanism of the thermal decomposition was proposed. The final product of thermal decomposition was ZnO. IR data show unidentate coordination of carboxylate group to Zn(II) ion. The complexes were tested against various strains of microorganisms and their efficiency decrease in the sequence yeasts >bacteria>filamentous fungi.     

Synthesis and characterization of a Zn(II) complex of a pyrazole-based ligand bearing a chiral l-alaninemethylester

Reaction of ZnCl₂ with a new ligand N,N-bis(3,5-dimethylpyrazolylmethyl)-l-alaninemethylester (bdmpame) in methanol gives [ZnCl₂(bdmpame)]. The structure of [ZnCl₂(bdmpame)]·CH₂Cl₂ has been resolved by X-ray crystallographic analysis. The Zn atom has a distorted tetrahedral geometry involving a nitrogen atom from each pyrazole in bdmpame and two chloro ligands with bond lengths in the range 2.037(4)–2.237(2) Å. The nitrogen atom of the l-alaninemethylester group in the compound was not coordinated to the metal center, giving an eight-membered ring in which the nitrogen atoms of each pyrazole in bdmpame are coordinated to the metal center. The results of the catalytic enantioselective reduction of acetophenone promoted by ligand/Zn(OTf)₂=1:1 mole ratio in the presence of catecholborane for 48 h at 0°C gives (S)-(−)-1-phenylethanol in 21% ee with 68% yield.     

Highly selective colorimetric sensing pyrophosphate in water by a NBD-phenoxo-bridged dinuclear Zn(II) complex

A novel NBD-phenoxo-bridged dinuclear Zn(II) complex is found to be an effective colorimetric sensor for pyrophosphate (PPi) in pure aqueous solution over a wide pH range. This sensor shows high binding affinity (K(a)≈ 3 × 10(8) M(-1)) and high selectivity for PPi, and can be also used to assay the activity of pyrophosphatase in real time.