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Modulation of Impedance in DNA Solutions by Ions and Molecules:
1. Effect of Alkali Metal Ions
(Krishnan and Garnett, 204th Meeting of Electrochemical Society, Abstract 1378,
Orlando 2003)
C.V.Krishnan, and Merrill Garnett
Garnett McKeen Lab, Inc.
150 Islip Ave, Suite 6, Islip, NY 11751 USA
This is the first part of a series of impedance measurements of DNA solutions in the presence of different solutes
such as alkali and alkaline earth metal ions, mono, di-, and tri- alkyl substituted ammonium ions, tetraalkylammonium
ions, tetraphenyl phosphonium, arsonium and boride ions, alkyl sulfonates, aliphatic alcohols, and biological molecules
such as hyaluronic acid, prothrombin, and biotin in order to elucidate the process of electron transfer mechanisms
in biological systems in terms of electronic equivalent circuitry. The comprehensive list of ions and molecules
is intended to provide information on solute-solute, solute solvent, and solvent-solvent interactions near the
electrode surface. These include effect of hydration, water structure breaking, multiple hydrogen bonding, hydrophobic
and πbonding (in both positive and negative ions) interactions, and specific interactions.
The electrochemical analysis of nucleic acids at very low concentrations and at negative potentials of the mercury
electrode is elegantly summarized recently(1). Our measurements are at fairly large concentrations of DNA in order
to achieve packing of DNA and at slightly positive potentials of the mercury electrode in order to produce a dopant
mercury ion. Our recent impedance measurements of palladium lipoic acid complex using a mercury electrode at slightly
positive potentials reveal a complex electronic equivalent circuitry indicative of the complex packing of the molecule
serving as a semiconductor and the dopant coming from the mercury electrode(2,3). This had a catalytic effect on
our long term interest of developing electronic pathways in biological systems and implications for energy based
restorative medicine.
The impedance measurements of 0.01M solutions of Li+to Cs+chlorides at pH 6.0-7.0 and of NaCl in alkaline pH exhibited
unique Mott-Schottky plots indicative of both p-type and n-type semiconducting behavior of mercury electrode at
slightly positive potentials(4). Using these concentrations as background electrolytes, impedance measurements
of calf thymus DNA, 5 mg/mL at near neutral pH were carried out using a static dropping mercury electrode. To understand
the influence of chloride, measurement of DNA solution was also done without any alkali halide.
Figure 1 shows the Mott-Schottky plots and Figure 2 shows the complex plane plots of DNA terminating at 5 mHz.,
in the presence of 0.01M Li+, Na+, and K+chlorides. The observed zonal behavior can be explained in terms of contributions
from ion-solvent interactions and the interaction of the ions with the phosphate in DNA.
References:
1. E. Palecek, M. Fojta, F. Jelen, and V. Vetterl in Bioelectrochemistry, Vol 9, Chapter 12, 365, Edited by George
S. Wilson, Wiley-VCH,Weinheim, 2002
2. C.V.Krishnan and Merrill Garnett, 1stSpring Meeting of the International Society of Electrochemistry, Alicante,
Spain, 2003, Abstract P06
3. C.V.Krishnan, M. Garnett, and J. L.Remo, 203rdMeeting of ECS, Paris 2003, Abstract 2703
4. C.V.Krishnan and M.Garnett, 226thMeeting of American Chemical Society, New York 2003, Abstract 670792
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