Measuring long-lived 13C2 state lifetimes at natural abundance.

Long-lived disconnected eigenstates (for example, the singlet state in a system with two nearly equivalent carbons, or the singlet-singlet state in a system with two chemically equivalent carbons and two chemically equivalent hydrogens) hold the potential to drastically extend the lifetime of hyperpolarization in molecular tracers for in vivo magnetic resonance imaging (MRI). However, a first-principles calculation of the expected lifetime (and thus selection of potential imaging agents) is made very difficult because of the large variety of relevant intra- and intermolecular relaxation mechanisms. As a result, all previous measurements relied on costly and time consuming syntheses of (13)C labeled compounds. Here we show that it is possible to determine (13)C singlet state lifetimes by detecting the naturally abundant doubly-labeled species. This approach allows for rapid and low cost screening of potential molecular biomarkers bearing long-lived states.