Mineral Surface Chemistry Group
Carrick M. Eggleston
An important
part of geochemistry is the study of how rocks and minerals at the
Earth's surface interact with our chemical environment. Surfaces are
fundamental to understanding how rocks and minerals communicate
chemically with their surroundings, and to predicting the response of
natural systems to environmental problems.
Work in our group focuses on the fundamental chemistry of mineral
surfaces
as it pertains to geo- and environmental chemistry. Recently, our
research has (1) taken a turn toward the mechanics of biological
electron
transfer between bacteria and minerals, and (2) started to concentrate
effort on photocatalysts that might be used in solar hydrogen or
methanol generation (we are working mainly on hematite photocatalysts
whose behavior also has geochemical implications).
Current
projects include:
1)
Redox-linked conformation change: electron transfer from bacterial
proteins to minerals
Dissimilatory
iron-reducing bacteria couple the oxidation of organic matter (food) to
the reduction of ferric iron. Because Fe(III) is generally
insoluble at mid-range pH, this respiratory feat involves electron
transfer from the organism to a solid mineral surface. Because it
has been shown that c-type cytochromes are central to this process, we
have engaged in the study of the interaction of specific proteins with
iron oxide electrode surfaces using electrochemical and
microscopic/spectroscopic techniques. We are studying proteins
from Shewanella oneidensis MR-1, Acidiphilium cryptum, and Geobacter
sulfurreducens. In addition to isolated proteins, we are studying
the electrochemical behavior of living microbial populations in contact
with iron oxide electrodes. This is a collaboration with Prof.
Patricia J.S. Colberg (UW Department of Zoology and Physiology) and
Prof. Tim Magnuson (Idaho State University), and is funded by the NSF
through 2007.
A
project that builds on #1, and that will quantify such things as
protein adsorption density, protein physical density, redox potentials,
surface packing, and optical absorption properties, is funded by the
U.S. Department of Energy through 2009.
Left: Adsorption of the outer-membrane decaheme cytochrome OmcA as a function of time and of pH and ionic strength. The image at right shows not only bacteria on a surface, but also "nanowires" as described by Dr. Yuri Gorby at PNNL.
2) Biogeochemistry Grand Challenge: Metal-Reducing Bacteria
In a project similar to #1, in collaboration with a range of outstanding scientists from Pacific Northwest National Laboratory and elsewhere, we are engaged in a study of proteins isolated and purified from the outer membrane of Shewanella oneidensis MR-1. These are generally multiheme proteins with fascinating electrochemical behavior. This project is funded by the Pacific Northwest National Laboratory through 2007.
The voltammograms at left show a prominent reduction wave at about -300 mV vs. Ag/AgCl for a solution containing the outer-membane cytochrome OmcA (hematite electrode). The plot at right shows currents from an experiment using whole cell suspensions of MR-1 through an anaerobic-aerobic cycle.
3) Waveguide Scanning Photocurrent Microscopy (WaSPM).
This project is funded by the U.S. Department of Energy through 2009, and has the purpose of developing a novel imaging technique capable of molecular-scale resolution and based on optical tunneling coupled to photocurrent detection using a photocatalytic probe tip.
The plot above shows anisotropic photocurrents for hematite (dark currents are given in red and black, photocurrents are given as blue and pink).
NOTE: We are seeking a qualified postdoctoral research scientist to participate in projects 3 and 1!! Please inquire by emailing Carrick M. Eggleston, carrick@uwyo.edu