title: Developing the family of picolinate ligands for Mn2+complexation.
abstract: We have reported here a series of ligands containing pentadentate 6,6'-(azanediylbis(methylene))dipicolinic acid units that differ in the substituent present at the amine nitrogen atom (acetate: H3DPAAA; phenyl: H2DPAPhA; dodecyl: H2DPAC12A; 4-hexylphenyl: H2DPAC6PhA). The protonation constants of the hexadentate DPAAA3-and pentadentate DPAPhA2-ligands and the stability constants of their Mn2+complexes were determined using pH-potentiometry (25 °C, 0.15 M NaCl). The mono-hydrated [Mn(DPAAA)]-complex (log KMnL= 13.19(5)) was found to be considerably more stable than the bis-hydrated [Mn(DPAPhA)] analogue (log KMnL= 9.55(1)). A detailed1H and17O NMR relaxometric study was carried out to determine the parameters that govern the proton relaxivities of these complexes. The [Mn(DPAC12A)] complex, which contains a dodecyl lipophilic chain, forms micelles in solution characterized by a critical micellar concentration (cmc) of 96(9) μM. The lipophilic [Mn(DPAC6PhA)] and [Mn(DPAC12A)] derivatives form rather strong adducts with Human Serum Albumin (HSA) with association constants of 7.1 ± 0.1 × 103and 1.3 ± 0.4 × 105M-1, respectively. The X-ray structure of the complex {K(H2O)4}{[Mn(DPAAA)(H2O)]}2shows that the Mn2+ion in [Mn(DPAAA)]-is coordinated to the six donor atoms of the ligand, a coordinated water molecule completing the pentagonal bipyramidal coordination environment.
authors.affiliation: Dipartimento di Scienze e Innovazione Tecnologica, Università del Piemonte Orientale "A. Avogadro", Viale T. Michel 11, 15121 Alessandria, Italy. mauro.botta@uniupo.it.
authors.forename: Attila
authors.initials: A
authors.lastname: Forgács
authors.affiliation: Universidade da Coruña, Centro de Investigacións Científicas Avanzadas (CICA) and Departamento de Química Fundamental, Facultade de Ciencias, 15071, A Coruña, Galicia, Spain. carlos.platas.iglesias@udc.es.
authors.forename: Rosa
authors.initials: R
authors.lastname: Pujales-Paradela
authors.affiliation: Universidade da Coruña, Centro de Investigacións Científicas Avanzadas (CICA) and Departamento de Química Fundamental, Facultade de Ciencias, 15071, A Coruña, Galicia, Spain. carlos.platas.iglesias@udc.es.
authors.forename: Martín
authors.initials: M
authors.lastname: Regueiro-Figueroa
authors.affiliation: Departamento de Química Inorgánica, Facultad de Ciencias, Universidade de Vigo, As Lagoas, Marcosende, 36310 Pontevedra, Spain.
authors.forename: Laura
authors.initials: L
authors.lastname: Valencia
authors.affiliation: Universidade da Coruña, Centro de Investigacións Científicas Avanzadas (CICA) and Departamento de Química Fundamental, Facultade de Ciencias, 15071, A Coruña, Galicia, Spain. carlos.platas.iglesias@udc.es.
authors.forename: David
authors.initials: D
authors.lastname: Esteban-Gómez
authors.affiliation: Dipartimento di Scienze e Innovazione Tecnologica, Università del Piemonte Orientale "A. Avogadro", Viale T. Michel 11, 15121 Alessandria, Italy. mauro.botta@uniupo.it.
authors.forename: Mauro
authors.initials: M
authors.lastname: Botta
authors.affiliation: Universidade da Coruña, Centro de Investigacións Científicas Avanzadas (CICA) and Departamento de Química Fundamental, Facultade de Ciencias, 15071, A Coruña, Galicia, Spain. carlos.platas.iglesias@udc.es.
authors.forename: Carlos
authors.identifier: http://orcid.org/0000-0002-6989-9654
authors.initials: C
authors.lastname: Platas-Iglesias