NDLI: Mn(II) complexes of novel hexadentate AAZTA-like chelators : a solution thermodynamics and relaxometric study

Content Provider	World Health Organization (WHO)-Global Index Medicus
Author	Gugliotta, Giuseppe Fekete, Marianna Kálmán, Ferenc K. Tei, Lorenzo Botta, Mauro
Description	Author Affiliation: Tei L ( Dipartimento di Scienze dell'Ambiente e della Vita, Università degli Studi del Piemonte Orientale Amedeo Avogadro, Viale T. Michel 11, 15121, Alessandria, Italy.)
Abstract	Three novel chelators based on the 6-amino-6-methylperhydro-1,4-diazepine scaffold and possessing three pendant N-acetic or N-α-methylacetic acid have been synthesised. The ligands contain six donor atoms for complexation of $Mn^{II}$ ions and thus potentially leave an additional site for coordination of a water molecule. The protonation constants of the ligands and the stability constants of their complexes formed with $Mn^{II}$ ion were determined by pH-potentiometric titrations in 0.15 M NaCl solution at 25 °C and compared to those of the parent AAZTA ligand (AAZTA = 6-amino-6-methylperhydro-1,4-diazepine tetraacetic acid). In spite of the similar value of the total basicity (Σlog K), the values of the stability constants of the $Mn^{II}AAZTA-like$ complexes are more than three orders of magnitude lower than that of MnAAZTA (log $K_{MnL}$ = 14.19). A detailed $^{1}H$ and $^{17}O$ NMR relaxometric study was carried out on the $Mn^{II}$ complexes in aqueous solution as a function of pH, temperature and magnetic field strength. The $^{1}H$ NMRD profiles of all the complexes show a similar shape, typical of low-molecular weight systems, but amplitudes that markedly differ to indicate a different degree of hydration. A similar behaviour is shown by the $^{17}O$ NMR transverse relaxation rates and chemical shift data as a function of temperature. The experimental data can be rationalised by considering the presence in solution of a mixture of two isomeric species differing in coordination number (7 and 6) and in the number (1 and 0) of bound water molecules. Whereas this type of coordination equilibrium has been previously reported for lanthanide(III) complexes, it is observed for the first time on $Mn^{II}$ chelates.
ISSN	14779226
Issue Number	9
Journal	Dalton Trans.
Volume Number	40
e-ISSN	13645447
Language	English
Publisher	Royal Society of Chemistry
Publisher Date	2011-03-07
Publisher Place	Great Britain (UK)
Access Restriction	Subscribed
Subject Keyword	Chemistry
Content Type	Text
Resource Type	Article
Subject	Inorganic Chemistry

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