Project Abstract

Probing the Redox Properties of Environmental Systems: Natural Phenolic Materials

Principal Investigator

Robin Helburn
Northern Arizona University
E-mail: Robin.Helburn@nau.edu

Goal

The long term goals of this research are to:

Use cyclic voltammetry to study the redox properties of tannins, and other natural organic materials that contain quinone and phenol components;
Study the quinone and phenol constituents in natural organic material using chronoamperometry;
Investigate the properties and potential environmental applications of a colored water soluble organic free radical. We propose that the latter "dye" may be used to probe the free radical scavenging behavior of natural polyphenols in environmental and biological systems.

Rationale

The success of environmental remediation depends on our ability to obtain a scientific understanding of the natural chemical processes occurring at a given site. It is known that redox processes play an important role in the overall chemistry of environmental systems. We are examining the redox properties of some natural organic components which may occur in these systems.

Approach

Standard voltammetry and chronoamperometric techniques are being used to study the redox properties of model tannins and phenols under controlled anaerobic conditions. The "probe-like" properties of the water soluble organic free radical are being evaluated using uv-visible absorbance measurements at 750 nm. The uv-visible measurements allow us to monitor the disappearance of the colored free radical in the presence and absence of natural polyphenols. The uv-visible studies are being followed up with electron spin resonance measurements. We are using 1H NMR to probe the mechanism of interaction between the free radical scavenging polyphenol and the colored water soluble free radical.

Status

Beginning in the summer of 1995, voltammetry studies began by identifying some optimal conditions (i.e. solvent, supporting electrolyte and electrode materials) for studying the electrochemical properties of natural tannins. Glassy carbon was found to be a suitable working electode. Dimethylsulfoxide (DMSO) with tetrabutylammonium perchlorate (TBAP) is being used as the supporting solvent and electrolyte, respectively. For some of the more "reversible" tannins, DMSO can be used to separate the individual one- and two-electron-transfer oxidation and reduction waves. Currently, some of the fundamental aspects of the electrochemical behavior of natural tannins are being addressed in protic vs. aprotic solvents. In applying the above electrode-cell system to a reference humic acid, an unexpected result was obtained. The low concentrations of iron in the humic acid produced a highly reversible set of oxidation and reduction waves. Based on this observation, cyclic voltammetry may be used to compare the properties of redox-active metal humate complexes to those of the uncomplexed metal, or to the properties of other environmentally significant metal-organic complexes. Studies of the colored water soluble organic free radical have progressed to the point where a calibration curve has been obtained showing a linear decrease in absorbance (at 750 nm) with increasing concentration of a free radical scavenging polyphenol.