AMIDINOQUINOXALINE N-OXIDES: SPIN TRAPPING OF O- AND C-CENTERED RADICALS

NADIA GRUBER; LILIANA R. ORELLI; PIERLUIGI STIPA

Carlos Paz

Conferencia; 13th Latin American Conference on Physical Organic Chemistry; 2015

Universidad Nacional de Córdoba

Electron paramagnetic resonance (EPR)-spin trapping represents one of the most specific and reliable techniques for detecting and identifying short-lived free radicals, such as those produced in chemical and biological processes, whose lifetime is too short in the EPR time scale. This technique, is based upon the fast reaction between a suitable diamagnetic molecule (a spin trap) and a transient free radical with formation of a relatively long-lived radical (spin adduct), whose EPR signal is persistent enough to be recorded and analyzed. Spectral parameters such as hyperfine coupling constants (hfcc) and g-factors are generally characteristic of the type of radical initially trapped [1]. Nitrones (N-oxides) represent the most commonly used spin traps, as they yield nitroxides as spin adducts, and are continuously studied in order to improve their efficiency toward radicals of different nature. Recently we presented a series of 5-aryl pyrimidoquinoxaline N-oxides as novel spin traps [2] and studied their ability in trapping methyl radicals. In the present work, different O- and C-centered radicals have been included, as well as modifications in specific sites of the amidinoquinoxaline moiety. The results obtained show some possible trends concerning hfccs and g-factors of the corresponding adducts. Suitable DFT calculations contributed to rationalize some of these tendencies. Figure 1. Experimental EPR (upper, black trace) and simulated (lower, red trace) spectra of a representative spin adduct. [1] a- E. G. Janzen, B. J. Blackburn, J. Am. Chem. Soc. 1968, 90, 5909. b- M. Iwamura, N. Inamoto, Bull. Chem. Soc. Jpn., 1967, 40, 702. [2] N. Gruber, L. L. Piehl, E. Rubin de Celis, J. E. Díaz, M. B. García, P. Stipa, L. R. Orell, RSC Adv., 2015, 5, 2724.