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A Pentadentate Member of the Picolinate Family for Mn(II) Complexation and an Amphiphilic Derivative


We report a pentadentate ligand containing a 2,2'-azanediyldiacetic acid moiety functionalized with a picolinate group at the nitrogen atom (H3PAADA), as well as a lipophylic derivative functionalized with a dodecyloxy group at position 4 of the pyridyl ring (H3C12OPAADA). The protonation constants of the PAADA3- ligand and the stability constant of the Mn2+ complex were determined using a combination of potentiometric and spectrophotometric titrations (25 °C, 0.15 M NaCl). A detailed relaxometric characterisation was accomplished by recording 1H Nuclear Magnetic Relaxation Dispersion (NMRD) profiles and 17O chemical shifts and relaxation rates. These studies provide a detailed information on the microscopic parameters that control their efficiency as relaxation agents in vitro. For the sake of completeness and to facilitate comparison, we also characterised the related [Mn(NTA)]- complex (NTA = nitrilotriacetate). Both the [Mn(PAADA)]- and [Mn(NTA)]- complexes turned out to contain two inner-sphere water molecules in aqueous solution. The exchange rate of these coordinated water molecules was slower in [Mn(PAADA)]- (kex298 = 90×107 s -1) than in [Mn(NTA)]- (kex298 = 280×107 s -1). The complexes were also characterised using both DFT (TPSSh/def2 TZVP) and ab initio CAS(5,5) calculations. The lipophylic [Mn(C12OPAADA)]- complex forms micelles in solution characterised by a critical micellar concentration (cmc) of 0.31±0.01 mM. This complex also forms a rather strong adduct with Bovine Serum Albumin (BSA) with an association constant of 5.5×104 M -1 at 25 oC. The enthalpy and entropy changes obtained for the formation of the adduct indicate that the binding event is driven by hydrophobic interactions.

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Publication details

The article was received on 24 Sep 2018, accepted on 03 Dec 2018 and first published on 04 Dec 2018

Article type: Paper
DOI: 10.1039/C8DT03856B
Citation: Dalton Trans., 2018, Accepted Manuscript
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    A Pentadentate Member of the Picolinate Family for Mn(II) Complexation and an Amphiphilic Derivative

    R. Pujales-Paradela, F. Carniato, R. Uzal-Varela, I. Brandariz, E. Iglesias, C. Platas-Iglesias, M. Botta and D. Esteban-Gómez, Dalton Trans., 2018, Accepted Manuscript , DOI: 10.1039/C8DT03856B

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