Pilar Díaz

A Ferromagnetic [Cu3(OH)2]4+ Cluster Formed inside a Tritopic Nonaazapyridinophane: Crystal Structure and Solution Studies†

Chemists working in coordination and/or supramolecular chemistry find a continuous source of inspiration in biomolecules and enzyme active sites. In this respect, trinuclear Cu centers have attracted a lot of interest due to their resemblance to multicenter blue copper oxidases like ascorbate oxidase, ceruloplasmin, lacase oxidase, and particulate methane monooxygenase. These enzymes contain at least four copper centers, which are necessary for four-electron reduction of molecular oxygen to water. For instance, the high-resolution structure of ascorbate oxidase shows that the mononuclear electron-transfer copper site of type 1 (T1) is connected to the trinuclear site through a patch formed by a cysteine residue from which two histidine residues diverge to bind the T3 copper ions. In the oxidized form of the enzyme, the T3 Cu atoms, apart from the imidazole moiety of the histidine residues of the patch, are coordinated by another two imidazole units and by an OH group that bridges the two atoms, which are 3.71 far apart from each other. The geometry around each metal ion can be best described as a trigonal bipyramid with a vacant equatorial position oriented towards the T2 copper atom, which completes the trinuclear center. In the T2 site the Cu center is coordinated in a very particular T-shaped geometry by two histidine residues and a monodentate hydroxo group or a water molecule. The mechanism by which these centers catalyze the fourelectron reduction of molecular dioxygen to water and the magnetic properties of these particular arrangements of copper ions have attracted great interest from both the biochemical and magnetochemical points of view. Therefore, small-molecule studies aimed at mimicking their properties are of great relevance in this respect.

Cation and anion recognition characteristics of open-chain polyamines containing ethylenic and propylenic chains

Abstract The interaction of the polyamines 4,7,10,13-tetraazahexadecane-1,16-diamine (L1) and 4,7,10-triazatridecane-1,13-diamine (L2) with H + , Cu 2+ , Zn 2+ , Co 2+ and the nucleotides ATP, ADP and AMP has been followed by NMR and potentiometric studies performed at 298.1 K in 0.15 mol dm −3 NaClO 4 . The influence of the different sequences of hydrocarbon chains and chelate rings present in the ligands on the values of the protonation constants, the stability of the metal ion complexes as well as in the co-ordination to nucleotides is analysed. The formation of mixed complexes has been investigated for the system Cu 2+ –L1–AMP.

Switching from intramolecular energy transfer to intramolecular electron transfer by the action of pH and Zn2+ co-ordination

Abstract Intramolecular electron (eT) and energy transfer (ET) have shown to occur in a covalently linked donor–acceptor (CLDA) system consisting of a naphthalene donor covalently linked through a polyamine chain connector to an anthracene acceptor; the connector has been chosen in order to switch ON or OFF the energy flux as a function of its protonation state as well as by co-ordination to Zn 2+ . The largest energy transfer efficiency ( η =0.61) occurs for the fully protonated form (pH 9 (eT) from the lone pairs of the nitrogens to the excited fluorophore takes place, leading to complete quenching of the emission. On the other hand at neutral and basic pH values, co-ordination of Zn 2+ prevents the eT quenching allowing the ET process to occur.

Naphthalene-containing polyamines supported in nanosized boehmite particles

Boehmite nanoparticles with covalently linked polyamine chains functionalized with naphthalene fluorophores have been prepared and characterized. The characterization of the materials by elemental microanalysis, X-ray powder diffraction, MAS 29Si NMR and electron microscopy unambiguously prove that the covalent anchorage had occurred. Steady-state fluorescence emission studies show that the luminescent properties of the modified nanoparticles are sensitive to changes in concentration of hydrogen ions, metal ions and anionic nucleotides such as ATP. The behaviour of the attached materials in aqueous solution is parallel to the behaviour of the single fluorophoric polyamines. Comparisons are established with analogous systems containing indole as a fluorophore.

Copper(ii) and Zn(ii) coordination chemistry of tetraaza[n]cyclophanes

The acid–base behaviour and Zn2+ and Cu2+ metal coordination chemistry of the novel orthocyclophane ligands 2,5,8,11-tetraaza[12]orthocyclophane (L2) and 2,5,9,12-tetraaza[13]orthocyclophane (L3) and metacyclophane 2,5,8,11-tetraaza[12]metacylophane (L1) are studied. Important differences in the chemistry of these compounds are found depending on the substitution of the aromatic ring. The ortho derivatives are much more basic in their first two protonation steps while the metacyclophane presents much larger constants in the third and fourth protonation stages. The crystal structure of the picrate salt of [H2L3]2+ shows an alternate disposition of the protons in the molecule with formation of N–H+⋯N hydrogen bonds between the protonated and non-protonated amino groups. While formation of mononuclear Cu2+ complexes is observed for L2 and L3, the metaderivative L1 forms also binuclear Cu2+ species which predominate largely for molar ratios M∶L 2∶1. The crystal structure of the complex [CuL3Cl](ClO4) shows a chain-like arrangement with the [CuL3]2+ units interconnected by chlorine atoms. The coordination geometry around the metal ion is a distorted octahedron with the nitrogen atoms of the macrocycle at the vertices of the equatorial plane and chloride anions asymmetrically disposed at the axial positions. The Zn2+ complexes of the ortho derivatives L2 and L3 are also much more stable than the meta counterparts. The crystal structure of [ZnL3Cl]Cl·H2O shows a square pyramidal geometry with the nitrogen atoms of the macrocycle at the vertices of the equatorial plane and one chloride anion occupying the axial position. In this case there are not chain arrangements. The involvement of all the nitrogen atoms in the coordination of Zn2+ by L3 in aqueous solution is proved by 1H and 13C NMR.

Amplitud de distribución eritrocitaria y riesgo de mortalidad en pacientes con insuficiencia cardiaca aguda

BACKGROUND AND OBJECTIVE Red cell distribution width (RDW) is a quantitative measure of the variability in size of erythrocytes, and it is used for the differential diagnosis of anemia. Recent reports have suggested that high RDW could play a role for risk stratification in patients with chronic heart failure. However, the prognostic role of RDW in unselected population with acute heart failure (AHF), after a thoroughly multivariate adjustment, has not been well established. The aim of this study was to establish the association between RDW and long-term mortality in patients admitted for AHF. PATIENTS AND METHOD We analyzed 1,190 consecutive patients admitted for AHF in our center. RDW measurement was performed on admission. RDW values were stratified into quartiles (Q) and the association of RDW with total mortality was assessed using Cox regression. RESULTS After a median follow-up of 15 months (interquartile range 3-33 months) 458 (38%) deaths were identified. There was a progressive increase in mortality rates from Q1 to Q4: 1.34, 1.82, 2.56 and 3.53 per 10 patients-year of follow-up (for Q1, Q2, Q3 and Q4 respectively, P for trend <.001). In the multivariate analysis, this association remained independent for patients in Q3 (15-16%) and Q4 (>16%) versus Q1 (≤14%), hazard ratio (HR): 1.66, 95% confidence interval (95% CI) 1.24-2.22, P<.01, HR: 1.80, 95% CI 1.33-2.43, p<.01, respectively, in a model adjusted for established prognostic markers in AHF. CONCLUSION In patients with AHF, higher RDW values were associated with increased long-term mortality.

Polyamines containing naphthyl groups as pH-regulated molecular machines driven by light

A series of compounds made up by linking methylnaphthalene fragments at both ends of different polyamine chains have shown to behave as pH-regulated molecular machines driven by light and fluorescence emission studies have proved the formation of an excimer between the two naphthalene units whose appearance, fluorescence intensity and decay times depend on the pH value of the media.

New molecular catalysts for ATP cleavage. Criteria of size complementarity

The interaction of the cyclophane receptor 2,5,8,11,14,17-hexaaza[18]metacyclophane (L) with the nucleotides ATP, ADP and AMP is described. L yields one of the largest rate enhancements for hydrolytic ATP cleavage observed in macrocyclic polyamines. The process is specific for the formation of ADP and involves a high degree of geometrical complementarity between host and guest species. The analogue compound 24-hydroxy-2,5,8,11,14,17-hexaaza[18]metacyclophane (L11) shows also a high degree of ATP activation. However, in this case deprotonation of the hydroxy group results in almost complete quenching of the ATPase activity above pH 7.0.

Controlled building of CdSe@ZnS/Au and CdSe@ZnS/Au2S/Au nanohybrids

The addition of Au3+ to spherical amine-capped CdSe@ZnS nanoparticles in toluene at room temperature and under darkness can lead to ternary CdSe@ZnS/Au nanohybrids. We demonstrate that this happens only when the nanoparticles possess a relatively thin ZnS shell, thus showing that thickness plays a key role in gold deposition on the CdSe@ZnS nanoparticle surface. Our hypothesis is that the amine ligand acts as the reductant of Au3+ ions into Au+ ions, whose affinity for sulfur would keep them at the CdSe@ZnS surface. This interaction stabilizes the Au+ ion, making it less prone to reduction than a non-coordinated Au+ ion. In CdSe@ZnS with a thin shell, Au+ ions at the surface of, or most probably within, the ZnS shell cause the transfer of Cd2+ ions into the solution. Subsequently, the core Se2– anion, which is a better reductant than the shell S2–, reduces Au+ ions to Au(0), and large gold nanoparticles (AuNPs) are quickly deposited on the CdSe@ZnS surface in room temperature process, leading to ternary CdSe@ZnS/Au nanohybrids. In solution, these ternary nanohybrids progressively transform into quaternary CdSe@ZnS/Au2S/Au nanohybrids due to the reaction of the shell S2– anion with the remaining Au+ at the CdSe@ZnS surface, thus leading to the growth of Au2S nanoparticles on the CdSe@ZnS surface while Zn concomitantly leaches from the nanohybrid into the solution. Photoirradiation of the heterostructures with visible light enhances their emission efficiency. Comparatively, irradiation of the precursors, i.e., CdSe@ZnS nanoparticles, causes a drastic decrease in their emission accompanied by a blue shift of their emission maximum. The optical properties of these nanohybrids were analyzed by absorption and fluorescence (steady-state and time-resolved) spectroscopy, and the composition of the samples and the chemical states were determined by energy dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS), respectively. Finally, the structural and morphological characterizations of the nanohybrids were performed by bright-field transmission electron microscopy (TEM), dark-field TEM, high-resolution TEM (HRTEM), and selected-area electron diffraction (SAED).

Ground and excited state properties of polyamine chains bearing two terminal naphthalene units

A series of compounds bearing two naphthalene units linked through methylene groups to both ends of different open-chain polyamines has been investigated. The fluorescence emission studies show the presence of an excimer species whose formation depends on the protonation state and length of the polyamine chains and implies the existence of a bending movement in the excited state allowing the two naphthalene units to approach and interact. This interpretation was clearly proven by time-resolved fluorescence with the appearance of double exponential decays with a rise time observed at the excimer emission wavelength. For comparison purposes one bis-chromophoric compound containing a rigid chain, and two mono-chromophoric analogs bearing a single terminal naphthalene unit were studied. Their emission spectra show a unique band and the fluorescence decays, are single exponential at pH values where just one species is present in the ground state, showing that in these cases no excimer or exciplex species is formed. The kinetics of excimer formation was used to evaluate the influence of the length and the pH in the flexibility of the polyamine chain.