The work describes EPR and 17O NMR measurements followed by theoretical calculation of the rotational correlation time $({ au}_R)$, the water residence time $({ au}_m)$, and the longitudinal electronic spin relaxation time $(T_{le})$(T_1e) for two new gadolinium complexes 1 and 2 of the type [$Gd(L)(H_2O)$] (L = tranexamic esters) in order to investigate their efficiency as a paramagnetic contrast agent (PCA). Of three correlation times, τR plays a major and predominant role to the unusually high relaxivity of 1 and 2 as compared with that of clinically approved MR CAs such as [$Gd(DTPA)(H_2O)]2? (Magnevist${circledR}$), [Gd(DTPA-BMA)(H2O)] (Omniscan${circledR}$), and $[Gd(DOTA)(H_2O)]^-$ (Dotarem${circledR}$). The presence of bulky tranexamic ester in the ligand seems to be responsible for the conformational rigidity, which in turn causes such great an increase in ${ au}_R$.