Nuclear magnetic relaxation dispersion profiles of aqueous solutions of a series of gd(nota) analogs

Nuclear magnetic relaxation dispersion (NMRD) profiles and ESR linewidths have been measured for a series of neutral Gd³⁺ ‐triazamacrocyclic complexes and compared with previous data for the simplest member of the macrocyclic triaza series, Gd(NOTA), and for the widely studied linear triaza complex, Gd(DTPA)^2‐. Water proton relaxivities and their temperature dependence were found to vary widely with the size of the triaza macrocycle and the identity of the side‐chain chelating groups. The number of rapidly exchanging water molecules directly coordinated to the Gd³⁺ ion (q) was found to vary from 2 to 4 for eight of the ten complexes examined and a linear relationship between the 50‐MHz relaxivity value and integral values of q is presented for this series of complexes. τ_s values derived from ESR linewidths for some of the complexes are in reasonable agreement with those derived from their NMRD profiles; however, those complexes which either tended to form aggregates in solution or gave evidence for multiple averaged solution structures showed broad, near Lorentzian linewidths which were clearly not dominated by the electron spin relaxation time (τ_s).