The o-naphthoquinones beta-lapachone (I), CG 8-935 (II), CG 10-248 (II
I) CG 9-442 (IV), mansonone C (VI) mansonone E (VII) and mansonone F (
VIII) catalyze ascorbate, dihydrolipoamide and dithiothreitol oxidatio
n by dioxygen, their catalytic action depending on the quinone structu
re. Mansonone A (V), and the p-naphthoquinone, alpha-lapachone (IX) an
d menadione (X) are much less effective. The oxidative process implies
reduction of quinones, production of the semiquinone, transfer of the
unpaired electron, to oxygen and superoxide anion production. Number
and position of oxygen atoms exert a significant influence on naphthoq
uinones electronic structure. The more electrophylic oxygen atoms (as
compared with carbon atoms) attract pi electrons from the C=O bond, th
us increasing their negative net charge (Q(a)) and decreasing that of
the carbonyl carbon atom. The positive partial net charge of the carbo
nyl dipole carbon atom contrast with the negative charge of the remain
der carbon atoms of the naphthoquinone molecule. The electron density
probability (f(o)(N)) in the molecular atomic centers of quinones vari
es in accordance with the atomic partial net charge. The aromatic stru
cture of the naphthalene ring is essential for the catalytic activity
of naphthoquinones since quinone V, a tetrahydronaphthoquinone was sca
rcely active as catalyst of substrate oxidation. Substitution of a met
hyl group by ethyl or phenyl groups in the o-naphthoquinone molecules
scarcely affect the calculated quantum-chemical parameters. Correlatio
n of catalytic activity and atomic partial net charge values of quinon
es was positive (r greater than or similar to 0,90) for C and O of the
2-carbonyl group. The vicinity of carbonyl groups in o-naphthoquinone
s is essential for their redox activity, as indicated by the different
effects of o-and p-naphthoquinones. Electronic asymetry and polarity
of C=O bond are relevant factors for the oxidizing activity of quinone
s.