Reorientational dynamics, hydrogen bonding and hydrophilicity of X-ray contrast agents in solution

In order to probe the hydrophilic and lipophilic properties of iodinated X‐ray contrast agents, a new parameter was introduced, the relative reduced molecular correlation time of reorientational motion. Therefore, the viscosities and 13C spin–lattice relaxation times of the five contrast agents iopromide, iohexol, iopamidol, iotetrol and N‐acetyliotetrol in their solutions with dimethylsulfoxide, water and methanol were measured. From these data the relative reduced molecular correlation times were evaluated, and a relation between these correlation times and measured water/butanol partition coefficients [log(P) values] could be established. The order for the relative reduced molecular correlation times is: iopromide > iopamidol > iohexol > N‐acetyliotetrol > iotetrol. When subdividing the contrast agents into classes of structurally similar compounds, the same order was observed for the log(P) values, namely iopromide > iopamidol > iohexol. Copyright © 2001 John Wiley & Sons, Ltd.