Res. Chem. Intermed.
, Vol. 30, No. 6, pp. 579–593 (2004)
Also available online - www.vsppub.com
Pulse radiolytic reduction studies of
(THMND): effect of tertiary structure
M. C. RATH, V. B. GAWANDI
, T. K. GHANTY, H. MOHAN
and T. MUKHERJEE
Radiation Chemistry and Chemical Dynamics Division, Bhabha Atomic Research Centre, Trombay,
Mumbai 400 085, India
Received 10 March 2004; accepted 22 April 2004
Abstract—Radiolytic reduction of a substituted 5,8-naptha dione (THMND), synthesized in our
laboratory, has been investigated by pulse radiolysis and steady-state γ -radiolysis in pure aqueous,
aqueous-formate and in aqueous-2-propanol-acetone mixed solvent systems. The rate constants
of formation of the semi-dione radicals were approx. 10
in aqueous-formate and
aqueous-2-propanol-acetone mixed solvent. The semi-dione radicals decay by second order kinetics
with rate constants (2k) of about 10
in the above two solvents, respectively.
value of the radical was found to be 5.0 in aqueous-formate solution and 5.8 in the aqueous-2-
propanol-acetone mixed solvent. The one-electron reduction potential (E
) value at pH 7, determined
from the pulse-radiolysis experiment, was found to be −420 ± 20 mV vs. NHE at 298 K and was
independent of solvent. Ab initio calculations on its one-electron reduction reaction suggest the
formation of a radical, which is different from a semiquinone where the electron density is delocalised
over the two oxygen atoms. Experimental absorption maxima of the radical in aqueous solution also
agree very well with the ab initio calculated values. Steady-state γ -radiolysis of THMND produces
the corresponding two-electron reduced species.
Keywords: Pulse radiolysis; aqueous solutions; one-electron reduction; substituted naphthadione.
Carbonyl compounds like diones, quinones, etc., are important chemical agents in
many electron transfer reactions in chemistry and biology [1– 6]. They usually act
as very good electron accepting agents due to the presence of carbonyl (CO) groups
Present address: Department of Chemistry, University of Georgia, Athens, GA 30602, USA.
To whom correspondence should be addressed. Fax: (91-22) 2550-5331 or 2550-5151.