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T. David Westmoreland; Michelle L. Personick; Michael A. Calter




The synthesis and characterization of two distinct sets of Manganese(II) based magnetic resonance imaging (MRI) contrast agents (CAs) are reported. The first set is comprised of a series of cyclen-based derivatives. Included in this series is a new, mixed pendant-arm macrocyclic ligand, 1,4,7,10-tetraazacyclododecane-1,7-bis(acetate)-4,10-bis(acetamide). HXDO2A(X-2)+, HXDO2AMX+, HXDO2A2AM(X-2)+ and their Mn(II) derivatives are characterized by solution state infrared spectroscopy. Full crystallographic details are reported for [Mn(DO2AM)(H2O)](Cl1.34)(Br0.66)·2H2O (triclinic, P1 ; a=7.68140(10), b=8.80980(10), c=16.6027(2) Å; α=103.7880(10)˚, β=97.2190(10)˚, γ=100.9880(10)˚; Z=2) and [Mn(DO2A2AM)](NH4Cl)·3.5H2O (triclinic, P1 ; a=8.4976(5), b=9.5396(2), c=15.6492(8) Å; α=94.139(3)˚, β=103.306(5)˚, γ=90.393(3)˚; Z=2), which are seven- and six-coordinate, respectively. Binding constants for five macrocyclic Mn(II) complexes are reported at 37˚C, along with pH dependent r1 relaxivity measurements. Finally, a temperature dependent study of the 17O transverse relaxivity of the three complexes is used to determine the number of bound waters (q) in each complex: [Mn(HXDO2A)]X+ (q=0), [Mn(DO2AM)]2+ (q=1), and [Mn(HXDO2A2AM)]X+ (q=0).

The second set is comprised of two tris-pyridine amine carboxylic acid derivatives. The synthesis of the two ligands, TPAMA and TPADA, is reported. pKa values for the ligands and binding constants for their Mn(II) complexes are determined by potentiometry at 37˚C. The pH dependent relaxivity profiles are reported and r1 values at physiological pH are compared with other pyridine derived Mn(II) complexes.



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