Click
below for more information on research interests
|
|
|
Materials
Chemistry and Nanotechnology |
We
are developing oxidation catalysts such as transition metal-substituted polyoxometalates, metallodendrimers,
and metal oxides. These studies include fundamental characterization of reaction
pathways, applications to sensing and detecting selected biological and
environmental analytes, and, in conjunction with
research on new materials, extensions to energy production and storage. A
typical analytical project is to combine new electrocatalytical
systems to the detection of phospholipids after separation by micro-HPLC and/or
capillary electrophoresis. For an example of our approach, see: S. D. Holmstrom and J. A. Cox, Electrocatalysis
at a Conducting Composite Electrode Doped with a Ruthenium(II)
Metallodendrimer, Anal. Chem., 72, 3191-3195, 2000
and L. Cheng and J. A. Cox, Nanocomposite Multilayer
Film of a Ruthenium Metallodendrimer and a Dawson
-Type Polyoxometalate as a Bifunctional
Catalyst, Chemistry of Materials, 14, 6-8, 2002.
Spin coater
Electrochemical Station
These studies are combinations of electrocatalysis and materials chemistry. For example, we have
shown that a newly synthesized compound, dirhodium phosphomolybdic acid (RhPMA),
catalyzes the electrochemical oxidation of various phospholipids (PLs). It is the first report of such an oxidation of these
compounds. However, the surface properties of almost immediately passivates the electrode. By incorporating RhPMA in a sol-gel with controlled hydrophobic properties,
a stable catalyst was achieved. Several of our recent publications from studies
supported by NSF and NIH relate to this general approach.
Micro
HPLC
Materials
Chemistry and Nanotechnology:
Sol-gels,
which are porous, glasslike solids prepared by room temperature processing, are
promising materials for several areas related to analytical chemistry. Included
are platforms for optical sensors, solid electrolytes for gas phase
electrochemical sensors, and stationary phases for separation science. In
addition, they serve as novel hosts for reactions in that the pore structure is
proposed to alter the reaction pathway and the product distribution. We are
investigating the synthesis of sol-gels, alone and as hybrid materials, for
these applications. Of particular interest is the use of dendrimers
to physically strength and to control the pore structure of these materials. We
are using mass spectrometry, electrochemistry, scanning probe microscopy,
electron microscopy, and various spectroscopic methods in these studies.
Examples of our progress in this area are: J. Widera,
G. E. Pacey, W. H. Steinecker,
and J. A. Cox, Voltammetry in Electrolyte-Free
Liquids Using a Three-Electrode Probe with a Sol-Gel Matrix, Journal of Applied
Electrochemistry, 33, 121-124, 2003; A.M. Kijak, J.C.
Moller, and J.A. Cox, Strengthening Silica Prepared
by Sol-Gel Chemistry with a Polyamindoamine Dendrimer Dopant, J. Sol-Gel. Sci. Technol., 21, 213-219, 2001;
and Mark E. Tess and James A. Cox, Chemical and
Biochemical Sensors Based on Advances in Materials Chemistry, J. Pharm. Biomed. Anal.,
19, 55-68, 1999.
Nanocomposites are being prepared by the systematic
deposition of single layers and multiple bilayers of
reagents on surfaces. For example, an organized layer comprising a selective
chemical reagent tethered to gold via a thiol group
can trap an analyte of interest from a complex
sample. By oxidizing the thiol, the layer plus analyte is released into the microchannels
of a lab-on-a-chip system and flowed to a downstream detector. Other studies
involve organized layering of supramolecular
oxidation catalysts. In studies supported by NIH, these approaches are being
used to detect biological compounds that are initially trapped by pi-donor complexation. A variation on the work is to use magnetic nanoclusters with immobilized reagents to capture analytes from liquids and then recover these clusters using
their chemical and magnetic properties. For an example, see: James A. Cox, Janaki Seneviratne, Gilbert E. Pacey, James R. Gord, Michael S.
Brown, Terrence S. Meyer, and Long Cheng, Evaluation of Electrochemical Release
of Self-Assembled Reagents as a Component of a Preconcentrator
for Flow-Injection Analysis, Electroanalysis, 14,
1339-1343, 2002.