While T2-exchange (T2ex) NMR phenomena have been known for decades, only recently there has been a resurgence of interest to develop T2ex MRI contrast agents. One indispensable advantage of T2ex MR agents is the possibility of using non-toxic and/or bio-important diamagnetic compounds with intermediate exchangeable protons. In this study, we screened a library of phenol-based compounds and determined their T2ex contrast (exchange relaxivity, r2ex) at 9.4 T. Our results showed that the T2ex contrast of phenol protons allows them to be detected directly by MRI at a mM concentration level. We also studied the effect of chemical modification of the phenol on the T2ex MRI contrast through modulation of exchange rate and chemical shift. This study provides a guideline for using endogenous and exogenous phenols for T2ex MRI contrast. As a proof-of-principle application, we demonstrated phenol T2ex contrast can be used to detect enzyme activity in a tyrosinase-catalyzed catechol oxidation reaction.
Congrats to Jia for the new publication!