CIDNP in tyrosyl protons of luliberin

WE report here on the possibility of extending CIDNP (chemically induced nuclear magnetic polarisation)-assisted NMR studies of the tyrosyl unit to medium sized peptides. Our previous studies indicate that, strong ¹H nuclear polarisation may usually be obtained in phenols in the presence of dyes such as fluorescein or any of its halogenated derivatives, such as rose bengal, erythrosin B or eosin Y, and others excited to their triplet state^1-4 The polarisation is due to the H atom transfer from the hydroxyl of the phenol ArOH to the triplet excited dye ³D, (a) ArOH+³D → ArO^.+DH^.and back, (b) ArO^.+DH^. → ArOH+D Steps (a) and (b) were shown to be chemically reversible, the nuclear polarisation resulting from the magnetic interactions in spin-correlated radical pairs ArO^.+DH^..