Chemically Induced Dynamic Nuclear Polarization

Abstract

Chemical reactions induced thermally or by light irradiation in an NMR spectrometer may result in strongly enhanced NMR spectra in emission or absorption, known as chemically induced dynamic nuclear polarization (CIDNP). The effects are induced in radical or radical ion pairs by the interplay of pair diffusion, magnetic interactions, and reactivity. The signal directions and intensities of CIDNP effects are governed by the magnetic properties of the radicals or radical ions, the initial spin multiplicity of the pair, and by the mechanism of product formation. The observed effects may be used to probe the spin multiplicity of intermediates involved in a reaction, the spin density distribution and structure of radical or radical ion intermediates, or provide insights into biochemical problems, such as protein structure and folding, photosynthetic reaction centers, and the mechanisms of DNA photorepair. Keywords: nuclear spin polarization; radical (ion) pairs; electron transfer; photochemistry; photosynthetic reaction center; photorepair of DNA; carbene reactivity; spin density distribution in radical cations; radical cation structure; triplet recombination of radical ions