Abstract
Although T(2) -exchange (T(2ex) ) NMR phenomena have been known for decades, there has been a resurgence of interest to develop T(2ex) MRI contrast agents. One indispensable advantage of T(2ex) MR agents is the possibility of using non-toxic and/or bio-compatible diamagnetic compounds with intermediate exchangeable protons. Herein a library of phenol-based compounds is screened and their T(2ex) contrast (exchange relaxivity, r(2ex) ) at 9.4 T determined. The T(2ex) contrast of phenol protons allows direct detection by MRI at a millimolar concentration level. The effect of chemical modification of the phenol on the T(2ex) MRI contrast through modulation of exchange rate and chemical shift was also studied and provides a guideline for use of endogenous and exogenous phenols for T(2ex) MRI contrast. As a proof-of-principle application, phenol T(2ex) contrast can be used to detect enzyme activity in a tyrosinase-catalyzed catechol oxidation reaction.