Investigation of the magnetic field dependence of CIDNP in multi-nuclear radical pairs.

Abstract

The magnetic field dependence of chemically induced dynamic nuclear polarization (CIDNP) formed in the photoreaction of excited 2,2′-dipyridyl and tyrosine is measured in the field range 0–7 T and compared with numerical simulations. The experiments employ field cycling between a variable field of polarization and a fixed field of detection. The simulations of CIDNP are based on the low-viscosity approximation in the Green function theory of geminate reactions. The effects of adiabatic field change and of duration of the RF excitation pulse are taken into account. Good agreement between theory and experiment in the whole field range is found for both net and multiplet polarization as observed in three coupled spin pairs (CH2 protons in β-position of tyrosine, H2,3 and H5,6 protons of its ring). The wide applicability of the theoretical model and the experimental technique make them useful for the characterization of shortlived reaction intermediates and are suited to CIDNP studies of protein surface structure and folding process of protein.