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 state1–4 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˙.