Conxa Soriano

Multifunctional molecular recognition of ATP, ADP and AMP nucleotides by the novel receptor 2,6,10,13,17,21-hexaaza[22]metacyclophane

The novel cyclophane receptor 2,6,10,13,17,21-hexaaza[22]metacyclophane L presents a molecular architecture which enables recognition in aqueous solution of ATP, ADP and AMP through electrostatic, hydrogen bonding and π-stacking interactions; electrostatic interactions occur between the polyammonium sites of L and the phosphate chain of the nucleosides, and π-stacking interactions occur between the m-phenylene subunit incorporated in the receptor as a non-pendant integral part of the macrocyclic framework and the adenine ring of the nucleotides.

Anion detection by fluorescent Zn(II) complexes of functionalized polyamine ligands.

The Zn(2+) coordination chemistry and luminescent behavior of two ligands constituted by an open 1,4,7-triazaheptane chain functionalized at both ends with 2-picolyl units and either a methylnaphthyl (L1) or a dansyl (L2) fluorescent unit attached to the central amino nitrogen are reported. The fluorescent properties of the ZnL1(2+) and ZnL2(2+) complexes are then exploited toward detection of anions. L1 in the pH range of study has four protonation constants. The fluorescence emission from the naphthalene fluorophore is quenched either at low or at high pH values leading to an emissive pH window centered around pH = 5. In contrast, in L2 the fluorescence emission from the dansyl unit occurs only at basic pH values. In the case of L1, a red-shifted band appearing in the visible region was assigned to an exciplex emission involving the naphthalene and the tertiary amine of the polyamine chain. L1 forms Zn(2+) mononuclear complexes of ZnH(p)L1((p+2)+) stoichiometry with p = 1, 0, -1. Formation of the ZnL1(2+)species produces a strong enhancement of the L1 luminescence leading to an extended emissive pH window from pH = 5 to pH = 9. Addition of several anions to this last complex leads to a partial quenching effect. On the contrary, the fluorescence emission of L2 is partially quenched upon complexation with Zn(2+) in the same pH window (5 < pH < 9). The lower stability of ZnL2(2+) with respect to ZnL1(2+) suggests a lack of involvement of the sulfonamide group in the first coordination sphere. However, there is spectral evidence for an interesting photoinduced binding of the sulfonamide nitrogen to Zn(2+). While addition of diphosphate, triphosphate, citrate, and D,L-isocitrate to a solution of ZnL2(2+) restores the fluorescence emission of the system (lambda max ca. 600 nm), addition of phosphate, chloride, iodide, and cyanurate do not produce any significant change in fluorescence. Moreover, this system would permit one to differentiate diphosphate and triphosphate over citrate and d, l-isocitrate because the fluorescence enhancement observed upon addition of the first anions is much sharper. The ZnL2(2+) complex and its mixed complexes with diphosphate, triphosphate, citrate, and D,L-isocitrate have been characterized by (1)H, (31)P NMR, and Electrospray Mass Spectrometry.

Synthesis and protonation behaviour of the macrocycle 2,6,10,13,17,21-hexaaza[22]metacyclophane. Thermodynamic and NMR studies on the interaction of 2,6,10,13,17,21-hexaaza[22]metacyclophane and on the open-chain polyamine 4,8,11,15-tetraazaoctadecane-1,18-diamine with ATP, ADP and AMP

Abstract The novel cyclophane receptor 2,6,10,13,17,21-hexaaza[22]metacyclophane (L) has been synthesised and characterised. The acid-base behaviour and interaction with ATP, ADP and AMP have been studied by potentiometry in 0.15 mol dm−3 at 298.1 K and multinuclear NMR. L presents in its protonated forms a molecular organization which enables its multipoint binding with nucleotides. Salt-bridge formation occur between the polyammonium sites of L and the phosphate chain of the nucleotides while π-stacking between the meta-phenylene subunit incorporated in the receptor and the adenine ring of the nucleotides.

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.

Polyazacyclophanes. 2,6,9,13-Tetraaza[14] paracyclophane as a cationic and anionic receptor

The synthesis and characterization of the new azacyclophane, 2,6,9,13-tetraaza[14]paracyclophane, is described. The acid–base behaviour and the metal and anion coordination capabilities of this compound have been studied by potentiometry at 298.15 K in 0.15 mol dm–3 NaClO4, as well as, by 1H and 13C NMR spectroscopy. The protonation patterns show stabilization effects produced by the presence of the aromatic ring. The aromatic spacer prevents simultaneous involvement of all four nitrogens in the coordination to the metal ions Cu2+ and Zn2+. Stable mono-hydroxylated species have been detected for both metal ions. The triprotonated species is the main one over a wide pH range around neutrality making this ligand a good coordinating agent for such anionic species as ATP4–and p2O74–. Formation of complexed anionic species with degrees of protonation varying from three to six has been detected.

New sensing devices part 1: indole-containing polyamines supported in nanosized boehmite particles

The synthesis, characterisation and optical properties of new sensing systems made by attaching different polyamine chains functionalised with an indole fluorophore to a boehmite matrix is reported for the first time. Firstly, a family of tri(alkoxy)alkylpolyaminosilanes have been reacted with indole-3-carboxaldehyde to form the corresponding Schiff bases which were reduced with sodium borohydride. The anchoring to the surface of the boehmite nanoparticles was carried out by reacting the precursors with the hydroxyl groups available in the surface of the support. The characterisation of the materials by elemental microanalysis, X-ray powder diffraction, CP-MAS 29Si NMR and electron microscopy unambiguously proved that covalent anchorage had occurred. Steady-state fluorescence emission studies showed that these materials present a very efficient sensing behaviour for hydrogen ions, metal ions such as Cu2+ and Zn2+ and for the anionic nucleotides ATP, ADP and AMP.

Thermodynamics and fluorescence emission studies on potential molecular chemosensors for ATP recognition in aqueous solution

The interaction of the open-chain polyamine N-(3-aminopropyl)-N′-[3-(anthrylmethyl)aminopropyl]ethane-1,2-diamine (L) with the relevant anionic forms of adenosine 5′-triphosphate (ATP), adenosine 5′-diphosphate (ADP) and adenosine 5′-monophosphate (AMP) is described. Unambiguous criteria for defining thermodynamic selectivity based on the use of effective stability constants are presented. The interaction of L and several other topologically similar polyammonium receptors with ATP has been shown to occur through electrostatic and π-stacking intermolecular forces. The π-stacking binding mode is modulated by the protonation degree of ATP as indicated by fluorescence emission titrations. Evidence for the use of these receptors as ATP luminescent chemosensors is advanced.

Polyaza[n]paracyclophanes as synthetic models of Zn containing enzymes. The role of a non coordinated nitrogen atom in the proximity of the metal

Abstract 2,6,9,13-Tetraaza[14]paracyclophane ( 3, B323 ) represents a simple model for Zn containing enzymes like HCAII which possess additional reactive groups in the proximity of the metal center. The Zn 2+ . 3 complex shows notable catalytic activity for the hydrolysis of p -nitrophenyl acetate. Structural modifications of 3 which affect to the non coordinated nitrogen atom greatly modify the catalytic activity of the receptor.

Hydrogen and copper ion induced molecular reorganizations in two new scorpiand-like ligands appended with pyridine rings.

The synthesis of two new ligands constituted of a tris(2-aminoethyl)amine moiety linked to the 2,6 positions of a pyridine spacer through methylene groups in which the hanging arm is further functionalized with a 2-pycolyl (L1) or 3-pycolyl (L2) group is presented. The protonation of L1 and L2 and formation of Cu(2+) complexes have been studied using potentiometric, NMR, X-ray, and kinetic experiments. The results provide new information about the relevance of molecular movements in the chemistry of this kind of so-called scorpiand ligand. The comparison between these two ligands that only differ in the position of the substituent at the arm reveals important differences in both thermodynamic and kinetic properties. The Cu(2+) complex with L1 is several orders of magnitude more stable than that with L2, surely because in the latter case the pyridine nitrogen at the pendant arm is unable to coordinate to the metal ion with the ligand acting as hexadentate, a possibility that occurs in the case of [CuL1](2+), as demonstrated by its crystal structure. Significant differences are also found between both ligands in the kinetic studies of complex formation and decomposition. For L1, those processes occur in a single kinetic step, whereas for L2 they occur with the formation of a detectable reaction intermediate whose structure corresponds to that resulting from the movement typical of scorpiands. Another interesting conclusion derived from kinetic studies on complex formation is that the reactive form of the ligand is H(3)L(3+) for L1 and H(2)L(2+) for L2. DFT calculations are also reported, and they allow a rationalization of the kinetic results relative to the reactive forms of the ligands in the process of complex formation. In addition, they provide a full picture of the mechanistic pathway leading to the formation of the first Cu-N bond, including outer-sphere complexation, water dissociation, and reorganization of the outer-sphere complex.