Modulation of Phenol Oxidation in Cofacial Dyads

The
presentation of two phenols on a xanthene backbone is akin
to the tyrosine dyad (Y730 and Y731) of ribonucleotide
reductase. X-ray crystallography reveals that the two phenol moieties
are cofacially disposed at 4.35 Å. Cyclic voltammetry reveals
that phenol oxidation is modulated within the dyad, which exhibits
a splitting of one-electron waves with the second oxidation of the
phenol dyad occurring at larger positive potential than that of a
typical phenol. In contrast, a single phenol appended to a xanthene
exhibits a two-electron process, consistent with reported oxidation
pathways of phenols in acetonitrile. The perturbation of the phenol
potential by stacking is reminiscent of a similar effect for guanines
stacked within DNA base pairs.