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

Abstract

Abstract. Sensitivity being one of the main hurdles of Nuclear Magnetic Resonance (NMR) can be gained by polarization techniques including Chemical Induced Dynamic Nuclear Polarization (CIDNP). Kaptein demonstrated that in CIDNP the polarization arises from the formation and the recombination of a radical pair in a magnetic field. In photo-CIDNP of interest here the radical pair is between a dye and the molecule to be polarized. The polarization obtained is thereby dependent on a complex interplay between the two molecules and their physico chemical properties. Here, we explore photo-CIDNP with a set of ten tryptophan and tyrosine analogs and observe not only signal enhancement of two orders of magnitude for 1H at 600 MHz (corresponding to 10'000 times in measurement time), but also reveal that the hydrophobicity of the molecule appears to be an important factor in the polarisation extend. Furthermore, the small chemical library established indicate the existence of many photo-CIDNP active molecules.