Synthetic macrocyclic peptidomimetics as tunable pH probes for the fluorescence imaging of acidic organelles in live cells

Acid test: Macrocyclic compounds that comprise a 9,10-anthracene subunit linked by a C2-symmetric peptidomimetic chain (see formula) are useful as fluorescent probes in a pH range of biomedical interest. Changes in the size of the macrocycle (n=3,4,6,8) produce a shift in the pKa values. Experiments with live mouse macrophage cells show the selective localization of the probe in the acidic organelles (see differential interference contrast image)