Exploration of the close chemical space of tryptophan and tyrosine reveals importance of hydrophobicity in CW-photo-CIDNP performances

Abstract

Abstract. Sensitivity being one of the main hurdles of nuclear\nmagnetic resonance (NMR) can be gained by polarization techniques including\nchemically induced dynamic nuclear polarization (CIDNP). Kaptein\ndemonstrated that the basic mechanism of the CIDNP arises from\nspin sorting based on coherent electron–electron nuclear spin dynamics\nduring the formation and the recombination of a radical pair in a magnetic\nfield. In photo-CIDNP of interest here the radical pair is between a dye and\nthe molecule to be polarized. Here, we explore continuous-wave (CW)\nphoto-CIDNP (denoted CW-photo-CIDNP) with a set of 10 tryptophan and tyrosine analogues, many of\nthem newly identified to be photo-CIDNP active, and we observe not only signal\nenhancement of 2 orders of magnitude for 1 H at 600\u2009MHz (corresponding\nto 10\u2009000 times in measurement time) but also reveal that polarization\nenhancement correlates with the hydrophobicity of the molecules.\nFurthermore, the small chemical library established indicates the existence\nof many photo-CIDNP-active molecules.