A Modular Approach for the Synthesis of Nanometer-Sized Polynitroxide Multi-Spin Systems

The
synthesis of rigid symmetric polyradical model systems with
inter-spin distances between 1.4 and 4 nm and their room temperature
continuous wave (CW) EPR spectra are reported. Conditions for attachment
of the spin-label via esterification have been optimized on the direct
synthesis of polyradicals from commercially available polyphenols
and the carboxylic acid functionalized nitroxide TPC. A common synthetic
protocol utilizing 4-hydroxy-4′-iodobiphenyl as a key building
block has been used to synthesize an equilateral biradical and a triradical
in only two steps from commercially available starting materials.
The first synthesis of a tetraradical based upon an adamantane core
bearing six equivalent nitroxide–nitroxide distances is also
reported. These systems are very promising candidates for studying
multi-spin effects in pulsed EPR distance measurements.