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Synthesis, Protonation and CuII Complexes of Two Novel Isomeric Pentaazacyclophane Ligands: Potentiometric, DFT, Kinetic and AMP Recognition Studies

Authors

  • Andrés G. Algarra,

    1. Departamento de Ciencia de Materiales e Ingeniería Metalúrgica y Química Inorgánica, Facultad de Ciencias, Universidad de Cádiz, Apartado 40, Puerto Real, 11510 Cádiz, Spain
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  • Manuel G. Basallote,

    1. Departamento de Ciencia de Materiales e Ingeniería Metalúrgica y Química Inorgánica, Facultad de Ciencias, Universidad de Cádiz, Apartado 40, Puerto Real, 11510 Cádiz, Spain
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  • Raquel Belda,

    1. Departamento de Química Inorgánica, Instituto de Ciencia Molecular, Universidad de Valencia, Apartado Correos 22085, 46071 Valencia, Spain
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  • Salvador Blasco,

    1. Departamento de Química Inorgánica, Instituto de Ciencia Molecular, Universidad de Valencia, Apartado Correos 22085, 46071 Valencia, Spain
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  • C. Esther Castillo,

    1. Departamento de Ciencia de Materiales e Ingeniería Metalúrgica y Química Inorgánica, Facultad de Ciencias, Universidad de Cádiz, Apartado 40, Puerto Real, 11510 Cádiz, Spain
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  • José M. Llinares,

    1. Departamento de Química Orgánica, Facultad de Farmacia, Universidad de Valencia, Avda. Vicente Andrés Estellés s/n, 46100 Burjassot (Valencia), Spain
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  • Enrique García-España,

    1. Departamento de Química Inorgánica, Instituto de Ciencia Molecular, Universidad de Valencia, Apartado Correos 22085, 46071 Valencia, Spain
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  • Laura Gil,

    1. Departamento de Química Inorgánica, Instituto de Ciencia Molecular, Universidad de Valencia, Apartado Correos 22085, 46071 Valencia, Spain
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  • M. Ángeles Máñez,

    1. Departamento de Ciencia de Materiales e Ingeniería Metalúrgica y Química Inorgánica, Facultad de Ciencias, Universidad de Cádiz, Apartado 40, Puerto Real, 11510 Cádiz, Spain
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  • Conxa Soriano,

    1. Departamento de Química Orgánica, Facultad de Farmacia, Universidad de Valencia, Avda. Vicente Andrés Estellés s/n, 46100 Burjassot (Valencia), Spain
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  • Begoña Verdejo

    1. Departamento de Química Inorgánica, Instituto de Ciencia Molecular, Universidad de Valencia, Apartado Correos 22085, 46071 Valencia, Spain
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Abstract

The synthesis and coordination chemistry of two novel ligands, 2,6,9,12,16-pentaaza[17]metacyclophane (L1) and 2,6,9,12,16-pentaaza[17]paracyclophane (L2), is described. Potentiometric studies indicate that L1 and L2 form a variety of mononuclear complexes the stability constants of which reveal a change in the denticity of the ligand when moving from L1 to L2, a behaviour that can be qualitatively explained by the inability of the paracyclophanes to simultaneously use both benzylic nitrogen atoms for coordination to a single metal centre. In contrast, the formation of dinuclear hydroxylated complexes is more favoured for the paraL2 ligand. DFT calculations have been carried out to compare the geometries and relative energies of isomeric forms of the [CuL]2+ complexes of L1 and L2 in which the cyclophane acts either as tri- or tetradentate. The results indicate that the energy cost associated with a change in the coordination mode of the cyclophane from tri- to tetradentate is moderate for both ligands so that the actual coordination mode can be determined not only by the characteristics of the first coordination sphere but also by the specific interactions with additional nearby water molecules. The kinetics of the acid promoted decomposition of the mono- and dinuclear CuII complexes of both cyclophanes have also been studied. For both ligands, dinuclear complexes convert rapidly to mononuclear species upon addition of excess acid, the release of the first metal ion occurring within the mixing time of the stopped-flow instrument. Decomposition of the mononuclear [CuL2]2+ and [CuHL2]3+ species occurs with the same kinetics, thus showing that protonation of [CuL2]2+ occurs at an uncoordinated amine group. In contrast, the [CuL1]2+ and [CuHL1]3+ species show different decomposition kinetics indicating the existence of significant structural reorganisation upon protonation of the [CuL1]2+ species. The interaction of AMP with the protonated forms of the cyclophanes and the formation of mixed complexes in the systems Cu–L1-AMP, Cu–L2-AMP, and Cu–L3-AMP, where L3 is the related pyridinophane containing the same polyamine chain and 2,6-dimethylpyridine as a spacer, is also reported. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

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