The coordination chemistry of LnDOTA chelates exhibits an abrupt change at Ho3+ at which point lanthanide contraction induces a sudden reversal in the energy of the twsited square antiprismatic (TSAP) geometry.1  This change in solution state coordiation chemistry was initially ascribed to a change in the hydration number (from 1 to 0) of the TSAP geometry.  We recently published the crystal structure of HoDOTMA which reveals that the TSAP geometry of HoDOTA-type chelates  is in fact partially hydrated in the solid state,2 casting doubt on the hypothesis that a descrete dehydrated TSAP  isomer can exist in solution.   A more complex picture of hydration in HoDOTA-type chelates is also indicated by variable temperature 1H NMR studies into coordination isomer distribution of HoDOTA and DOTMA.  The energy of each coordination geometry changes with temperature (and water exchange rate).  In order to gain a more profound understanding of these systems and the the possible interplay between water exchange, chelate hydration, and coordination chemistry variable temperature 1H NMRD profiles and 17O relaxation studies were undertaken on HoDOTA and HoDOTMA.  The relaxivity of each chelate exhibits a different and yet highly unusual field dependence.  Fitting these data to theory provides new understanding of the coordination chemistry of late Ln3+ chelates of DOTA and a useful assessment of how the hydration state (a key parameter in contrast agent design) of these chelates changes with coordination chemistry.

Effects of coordination geometry on hydration state

247th National Meeting (2014)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.