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"Impedance Spectroscopy of DNA"
(Garnett and Garnett, Journal of Inorganic Biochemistry, V.74, 1999)
Merrill Garnett , Wade Garnett
Garnett McKeen Lab, 25 East Loop Road,
SUNY Campus, Stony Brook, NY 11790
Impedance spectroscopy is widely used to measure oxidative destruction of metal alloys, but is also used for solvatedsystems.
Currents of diminishing frequency are programmed to traverse the background electrolyte and the solute species
at thevoltage threshold. The frequency perturbations, as fast fourier transforms, provide the conditions for electronic
response whichare calculated from current and resistance at both time average and wave peak. Measurements were
made on Ecochemie andEG&G electro-analytic systems with Hg drop or rotating Pt working electrodes. The supporting
electrolyte 0.1M KCl at 8degrees Celsius at the oxidative potential +0.3 DC volts is necessary for maximum frequency
response and minimum scatter.
Samples measured were DNA (calf thymus), poly de(AT), poly de(GC), and the DNA reducing catalyst: tris (palladium
lipoicacid) -u-thiamine, (e.g. PdLT) (1). In the Nyquist plot (frequency dependent resistance (Z") vs. DC
resistance (Z')), DNA(ct)shows two semi-circle arcs of capacitance, shifting at low frequencies to some scatter.
Electrolyte and stray currents were ruledout. Measurements of DNA(ct) frequency responses in real-time show harmonic
and geometric relations in this series (Hz) :(.073, .146, .285, .57, .68, .8, .92). There are no frequency responses
from poly de(AT), poly de(GC), or their mixture. Harmonicbehavior of DNA has been previously described (2,3), attributing
an energy series to the H bonds of a specific sequence ofduplex DNA. This is an alternating repeat of base pairs
T-A, A-T also called (TATA)2, which has a larger average bond stretchthan stacked base sequence. PdLT uniquely
shares the .285 Hz frequency with calf thymus DNA. The charge on PdLT i sregenerated (cyclic voltammetry) by phospholipid
(egg yolk), suggesting a candidate inward cellular circuit - e.g.:phospholipid membrane to PdLT to DNA.
The electronic analysis model emerging for DNA (ct), is that it behaves as a tunable, variable capacitor. Use of
pulsed currentat resonance, or a redox catalyst with a matching frequency, simulates AC current, minimizing the
resistance to current exchangeof DNA in solution.
References:
1. Garnett,M, U.S.Patent, 1995 Oct. 31; No. 5,463,093
2. Bistolfi,F, Panminerva Medica, 1990 Jan.March; 32 (1): 4-9
3. Beger,R, Feng,Y, Prohofsky,EW, Biophys J, 1990 Aug; 58 (2): 437-445
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