Magnetic resonance imaging (MRI) is an important diagnostic technique used for generating scans of soft tissues and structures in the body. Contrast agents are commonly administered to patients in order to enhance the definition of the MR image. The present study explores the synthesis and characterization of two ligands: 6,6'-(((pyridin-2-ylmethyl) azanediyl) bis(methylene))dipicolinic acid (TPADA) and 6-[[bis(2-pyridinylmethyl)amino]methyl]-2- pyrazinecarboxylate (brenda). Both ligands are compared to 6-((bis(pyridin-2- ylmethyl)amino)methyl)picolinic acid (TPAMA), which is a tripodal ligand consisting of one pyridine substituted with a carboxylate group and two unsubstituted pyridines. The electronic environments of each ligand differ as follows: TPADA has an additional carboxylate substituent, and brenda has a substituted pyrazine instead of a substituted pyridine. The Mn(II) complexes of each ligand were synthesized and characterized. Potentiometric titrations were conducted to determine protonation states of each compound. The fits of the data were used to generate the stability constants and pKa values of the species present in solution. The hydration states of the complexes were explored using temperature-dependent 17O nuclear magnetic resonance studies. It is proposed that [Mn(HTPADA)]+ exists in two forms, one with one inner sphere water and one with two inner sphere waters, and that [Mn(Hbrenda)]2+ has two inner sphere waters. The pH-dependent proton relaxivities (r1) of the complexes were evaluated to further explore their potential as MRI contrast agents. At physiological pH and temperature, the r1 value for [Mn(HTPADA)]+ is 2.6 mM-1 s-1, and the r1 value for [Mn(Hbrenda)]2+ is 3.4 mM-1 s-1.
"},{"label":"Degree","value":["Bachelor of Arts with Departmental Honors"]},{"label":"Author-supplied Keywords","value":["Manganese","MRI","Brenda"]},{"label":"Administrative Note","value":"Drupal Node ID: 24329