Electrochemical Preparation and Characterization of Chemically Modified Electrodes
Research within the Brown group is focused on two areas of Analytical Chemistryelectroanalytical chemistry and separation science. In the area of electroanalytical chemistry, the
Brown group studies The Electrochemical Preparation and Characterization of Chemically
Modified Electrodes. A variety of compounds have been investigated as monomers for
oxidative electropolymerization feasibility and these include: 3,4 ethylenedioxythiophene
(EDOT),
Fe(II) and Ru(II)-tris(5-amino-1,10 phenanthroline), and metal(II)-tetraaminophthalocyanine. A joint collaboration with Professor Elizabeth Sanford and
research students is devoted towards preparing organic conducting polymer films
using monomers of EDOT. The polymer films are formed via oxidative
electropolymerization using cyclic voltammetry (CV) and are being used on
different electrode surfaces for sensing applications of metals, and biologically and
environmentally important molecules. The CV shown below is the
3,4-ethylenedioxythiophene
electropolymerization an EDOT-based compound which is
fluorinated.
EDOT with fluorinated substituent
Electropolymerization of EDOT-fluorinated compound
The electropolymerization of Ru(II)-tris(5-amino-1,10 phenanthroline) shows cathodic and
anodic peaks that represent a reversible electron transfer process corresponding to Ru3+ + e- ⇌
Ru2+.
Another major aspect of the research program is devoted to understanding the mechanisms of
charge transfer within the polymeric films by various electrochemical characterization
techniques. This involves calculating the apparent diffusion coefficients using electrochemical
techniques, and thin film thickness using ion beam techniques or atomic force microscopy. The
students involved in this research will gain a fundamental understanding in a variety of
electrochemical (CV and chronocoulometry) hyphenated techniques (spectroelectrochemistry).
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The CV on the left is the characterization of the fluorinated EDOT compound. When the
polymer film is exposed to aqueous solutions, the electrochemical activity diminishes, but is
restored with return to an organic-based supporting electrolyte solution.
The CV
characterization on the right depicts the reversible charge transfer occurring within the Ru-based
film.
CV characterization of Ru-based film
CV characterization of EDOTcompound
A more thorough examination and characterization of
the films is accomplished using electrochemical
impedance spectroscopy. The figure shown on the
right is a nyquist plot of Ru(II)-tris(5-amino-1,10
phenanthroline). Mixed kinetic and mass transfer
impedances are present in the polymer film as
evidenced by the semicircle and a 45o warburg
diagonal at high and low frequencies, respectively.
Those interested in working in the Brown or Sanford
research groups should email either researcher at
brownk@hope.edu or sanford@hope.edu.
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Impedance spectrum of Ru(II)-tris(5amino-1,10 phenanthroline)
Chemical Aspects of Ethnobotany and Plant Physiology
Most medicinal compounds currently used in industrialized nations are chemically synthesized,
but a large number of medicines can trace their origin to specific compounds isolated from
plants. In many cases, these biologically active compounds were first discovered because of
their use by native peoples. Ethnobotanical studies aim to examine how the people of a
particular region utilize the plants around them. Plant physiology is the study of how plants
function. Plants are such amazing biochemical factories that are continuously adapting to new
selection pressures. As a result, they are evolving continuously at the chemical level. The fields
of ethnobotany and pharmacology rely upon the evolution of these chemical novelties to treat
new medicinal problems in our modern society. Very little is known about how plants can be
manipulated under certain environmental and biotic cues to produce effective quantities of these
medicinal chemicals. The central plant physiological theme is to gain knowledge about how
plants allocate resources to various chemical pools of interest in response to environmental and
biotic cues during plant growth, development, and survival.
Analytical Chemistry
The methods used to study the chemical properties of compounds involved in certain plants at
the cellular level will be drawn primarily from Analytical Chemistry and Organic Chemistry.
Various instrumental techniques in the area of Separation Science and Spectroscopy are used to
understand the dynamic and synergistic impact of environmental and biotic manipulative
implants of chemicals on animal growth, animal development, and animal survival. Each of
these areas are monitored using modern methods in High Performance Liquid Chromatography
(HPLC) with UV and Electrochemical Detection, and Gas Chromatography-Mass Spectrometry.
Students working on this research will utilize chemical information from literature resources to
acquire background information about the utilization of Analytical Chemistry techniques applied
to medicinal chemistry.
Genistein Project
Several different groundnut Apios species obtained from various locations in China and North
America were evaluated for genistein and total protein content. This preliminary research was
conducted to determine the viability of these species as potential food sources. HPLC
instrumentation was used for the determination of genistein in Apios (Fabaceae) species
including A. carnea and A. fortunei from China and A. americana from North America. The
extracts of 80% ethanol were analyzed under HPLC isocratic
conditions at a wavelength of 270 nm and the Lowry Protein
Assay at 650 nm was utilized to determine the amount of protein
in the samples. A linear calibration range of 0 ppm-340 ppm for
genistein was obtained and presence of genistein in the samples
Figure of genistein
were confirmed using LC-MS (M+, m/z 271). Genistein was
present from 15-393 µg genistein/g plant, with the most genistein found within the groundnut
tuber system. Of the samples analyzed, the A. americana plant contained the largest amount of
genistein. The protein content ranged from 14-30 mg/g plant.
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This research is focused on:
• establishing a living repository of Apios species from North America and Asia,
• testing the adaptive capacity of diploid and polyploid populations,
• obtaining genomic DNA of all species, examine their genetic structures, and
elucidating the origin and relationships among species of Apios,
• analyzing chemical compositions of different organs of each species, and
• breeding new varieties of food and medicine of high quality via hybridization
among species.
The figure below on the left shows the groundnut tuber as found in its natural habitat. The figure
on the right is the inside of the groundnut tuber with the outside skin removed.
Figures of Apios species in its natural habitat and the inside of the groundnut tuber.
HLPC with UV-Vis detection is the primary method used in the Brown lab to investigate the
chemical composition of the plant species. Shown below is a chromatogram of an extract of the
groundnut tuber, which was tested for the presence of genistein. The peak near 23 minutes
occurs with pure standards of genistein as
was confirmed using LC-MS.
Current
research is exploring the use of
electrochemical detection of genistein and
several other compounds of medicinal
importance in this plant species.
Students interested in this project or similar
projects should contact Professor Brown at
brownk@hope.edu
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