Transition metal complexes such as manganese(II) complexes are of interest as potential magnetic resonance imaging (MRI) contrast agents. The solution speciation of Mn(II) complexes has been characterized though a 1H relaxometric approach. A relaxometric technique using the ratios of longitudinal to transverse 1H relaxation times (T1p/T2p ratios) for H2O was previously developed to determine the concentration of [Mn(H2O)6]2+ present in solutions containing Mn(II) complexes.8 A limited number of other metal ions with long electronic relaxation times as well as sufficiently large hyperfine coupling constants are also predicted to behave similarly. Vanadyl, VO (IV), complexes are investigated to determine the general scope and utility of the T1p/T2p ratio approach to solution speciation. Unlike [Mn(H2O)6]2+, the speciation of oxovanadium(IV) aqueous solution as well as the T1p/T2p ratio vary as a function of pH. As the pH is increased above 2.5, the concentration of [VO(H2O)(OH)]+ increases as the T1p/T2p ratio also increases. This characteristic of vanadyl ions makes the speciation more difficult to define from relaxation time measurements. The 1H relaxometric approach that has been developed to understanding the solution speciation of manganese (II) complexes does not apply to vanadyl complexes. In the pH-dependent study, the concentration of the free vanadyl ion cannot be predicted with T1p/T2p ratios since the T1p/T2p ratios continue to increase as the pH value is decreased to where the complex is fully dissociated. In the concentration-dependent study, the inverse of the longitudinal and transverse relaxation times is linear with respect to the concentration of the free vanadyl ion in solution. Once the calibration value for a given complex is determined, the concentration of free vanadyl ion can be determined from a slope of T1p or T2p measurement. This method provides a way to determine the concentration of free vanadyl ion in solution through the observed relaxation times and the relaxation time of the complex.
"},{"label":"Degree","value":["Bachelor of Arts with Departmental Honors"]},{"label":"Administrative Note","value":"Drupal Node ID: 28525