Contribution of quinone functional groups to the electron transfer capacity of humic substances

ENVR 107

Nopawan Ratasuk, School of Civil Engineering and Environmental Science, University of Oklahoma, 202 W. Boyd St., Room 334, Norman, OK 73019 and Mark A. Nanny, School of Civil Engineering and Environmental Science, Institute for Energy and Environment, Sarkey Energy Center, University of Oklahoma, 202 West Boyd Street, Rm. 334, Norman, OK 73019.
The role of oxidation-reduction reactions is becoming better characterized with respect to the transformation of organic compounds and the mobility of metals in the natural environment. Recent studies showed that humic substances can facilitate these processes by acting as electron transfer agents. Quinone functional groups are believed to be primarily responsible for the ability of humic substances to act as an electron shuttle due to the correlation observed between organic radicals, presumably quinone radicals, and the electron transfer capacity. In this study, the contribution of quinone functional groups to the ability of humic substances to transfer electrons was directly measured by utilizing the stability of quinone moieties upon catalytic reduction with Pd and H2 at pH 6.5 and 8.0. Evidence from FT-IR and UV-Vis spectroscopy revealed that the catalytic reduction at pH 6.5 irreversibly altered quinone moieties of anthraquinone disulfonate (AQDS), completely eliminating its electron transfer capability. On the other hand, humic samples (Suwannee River humic acid and fulvic acid, soil humic acid and peat humic acid) only lost 20-40% of their electron transferring capacity upon Pd - H2 reduction at pH 6.5. These results indicate that the electron transfer capacity in humic substances is governed by not only quinone, but also other constituent(s) of humic substances. Complexed metals appeared to be irrelevant since their removal with Chelex 100 resin did not cause any significant change in electron transfer capacity of the sample.
 

General Papers
6:00 PM-8:00 PM, Wednesday, March 31, 2004 Anaheim Convention Center -- Hall A, Poster

Division of Environmental Chemistry

The 227th ACS National Meeting, Anaheim, CA, March 28-April 1, 2004