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| TITLE: | The Influence of Electromagnetic Fields on the Reactions of Biological Transient Species | ||
| Principal Investigator |
Piotr Bilski, Ph.D. | Laboratory of Molecular Biophysics, NIEHS | |
| Health Relevance |
Cancer | ||
| Research Categories |
Cellular Function | Biophysics Cell/Field Interactions | Free Radicals |
| FY95 Funds | DIR-2 $ 30,000 | Start Date 9/93 | End Date 9/95 Rationale and |
| Rationale and Summary |
Prolongation of the life of free radicals has been postulated to be an effect of EMF exposure.
Transient biological species which are involved in regulatory physiological and pathogenic
processes are difficult to investigate directly because in vivo and in vitro their concentration is
usually very low. However, such, or related species may be produced in high yield during laser
pulse irradiation. Many of the biological transients are neutral radicals and radical ions, which,
due to their paramagnetic nature, interact with electromagnetic fields. Such an interaction is a
foundation for EPR spectroscopy which has application for the investigation of the reactions of
biological radicals. Radical ions may be monitored additionally as electrical current or electrical
conductivity, which features a high sensitivity. We are trying to use both EPR and conductivity
techniques to investigate charged radicals that are produced photochemically.
We have already chosen our first chemical model system suitable to observe photoconductivity and EPR signals simultaneously in the same sample. The system consists of trinitrobenzene (TNB) and tetrahydrofuran ether, which has a low background photoconductivity of about 1010 - 1cm-1. Upon UV excitation, the radical anion of TNB is photoproduced accounting for the transient electrical current. The kinetics of this photocurrent relaxation has been investigated in the absence of external magnetic field. It has been found that the photocurrent decay has two exponential components. One is due to pseudo first order recombination, while the second one is caused by ion transport in solution induced by the high voltage applied to the electrodes. We will examine how the magnetic field affects the relaxation kinetics when a suitable electromagnet necessary to complete construction of the apparatus arrives. |
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| Experimental Design and Exposure Conditions |
Direct current (DC) technique is used for the precise measurements of small ohmic conductivities.
The alternative alternating current (AC) methods are very difficult because of the dominating
capacitance of the electric circuit. High voltage that may be applied to well purified ethereal TNB
solutions ranges from a few volts to 5000 volts, which requires a special cell that could be used
for EPR measurements. Presently several designs are being tested. From photoconductivity
measurements the rate constant for bulk relaxation (k2), and the mean ion mobilities (µ) may be
measured using the following equations:
Graphic image with equations to be supplied in this spot at a later date. k, observed PC relaxation rate constant; V, d.c. voltage applied between electrodes; Q, electrical charge that flowed through the circuit; Ro, the electrical resistance of the sample at peak photocurrent; n, number of runs; a, constant. Some of the experimental problems are as follows: a. How does oxygen affect photoconductivity? b. How do polarization effects on the electrodes surface influence the photocurrent? c.To what extend does the space charge separation affect the kinetics measurements? These problem were addressed by: vacuum degassing the samples, by expanding the electrode surface with colloidal platinum, and by investigating how the increasing radical ion concentration contribute to charge separation effect, respectively. While the above experiments were performed in the absence of the magnetic field, the information will ultimately be used to measure the photocurrent and its relaxation in the presence of magnetic fields up to 1 Tesla. |
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| Quality Assurance Measures |
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| Results and Discussion |
Irradiation of TNB in THF efficiently produces radical ions that are observed as electrical current.
Electrochemical reactions on the electrodes are negligible but they may increase in degassed
solutions, and when the electrode surface is covered with colloidal platinum. There is a significant
space charge separation, which depends on the radical ion concentration. It has been proven that
the pulse relaxation of photoconductivity in ethereal solution of s TNB is satisfactorily described
by an exponential decay because ions undergo pseudo first order recombination in solution, and
the ions discharge on the electrodes. Slow bulk neutralization is of the first-kinetic order, which
suggests a rearrangement of the charged forms prior to their neutralization. This component must
involve radical and ion radical pair recombination, and may be affected by the magnetic field.
This area of research will be continued. |
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| Recent Publications |
None to date. | ||