Abstract
Free radicals with extended lifetimes at room temperature, formed by pyrolysis (from 473 to 773 K) of the non-dialysable melanoidins, were studied by electron spin resonance (ESR) and electron nuclear double resonance (ENDOR) spectroscopy. The ESR spectra showed an identical symmetrical absorption line with g = 2.0035 ± 0.0009 and with line-shape changing depending on the carbonisation temperatures. The ENDOR spectra of the free radicals possessed similar characteristics in all the cases and did not show significant couplings of the unpaired electron on a C atom to α-protons ( A iso=14.35 MHz). This comparison of ESR and ENDOR results provides insight into paramagnetic electron Heisenberg spin exchange interaction existing in melanoidin molecules.
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