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The dielectric properties of polyelectrolyte solutions are studied in terms of counterion condensation by measurements of the dielectric response of pH buffered Na polyacrylate solutions. pH values are selected to allow variation of the charge density parameter ξ in the range between 0.5–2.8, that is, across ξ=1, the theoretical critical level for counterion condensation. The dielectric increment of the high frequency dispersion, Δε2, is found to have nonzero values only above the counterion condensation threshold and is therefore linked to the occurrence of counterion condensation. Above the condensation threshold Δε2 (≊6) and its corresponding polarizability α||2 (≊6×10-16 cm3) are found to be approximately constant with increasing ξ. This result is predicted by Manning’s polarizability model for condensed counterions which results in a good fit to the experimental data when the average length of the polyion segments parallel to the external field, Ls, is set to 284 Å. This value of Ls is also shown to be in relatively close agreement with the value calculated for the length of a rigid subunit in Mandel’s polyion model, obtained using the relaxation time of the high frequency dispersion. The length Ls, which is larger than the persistence length, is estimated to be of the order of magnitude of the correlation length between segments. [ABSTRACT FROM AUTHOR]

The occurrence of counterion condensation is demonstrated through measurements of the incremental ionic conductivity of pH buffered Na polyacrylate solutions. pH values were selected to allow variation of the charge density parameter ξ in the range between 0.4 and 2.8, that is, across ξ=1, the theoretical critical level for counterion condensation. The results show two regions where the incremental conductivity, ΔσP, varies differently with ξ. For ξ<1.3, ΔσP remains relatively constant. A sharp drop in ΔσP is observed between ξ=1.3 and ξ=1.7 corresponding to the onset of counterion condensation. It is suggested that this discontinuity reflects a drastic change in the polyion mobility caused by a structural rearrangement of the macromolecule. For ξ>=1.7, ΔσP decreases with approximately constant slope. This latter behavior agrees qualitatively but not quantitatively with the prediction of the counterion condensation model. [ABSTRACT FROM AUTHOR]

Purpose: To investigate the ability of electromagnetic (EM) field pre-exposures to induce protection in chick embryos against subsequent ultraviolet (UV) light exposure., Materials and Method: Chick embryos in the 4th day of gestation were exposed for 20 minutes (short term) or 96 hours (long term) to 60 Hz, 8 microT magnetic or sham fields (controls) followed by 30 minutes rest. They were then exposed to UV radiation of either low (30J/m2) or high (45J/m2) intensity (long term was exposed only to 30J/m2) for 75 minutes. Mortality measurements were made every 30 minutes following UV exposure., Results: At both UV intensities, short-term, EM field-exposed embryos showed significantly higher post-UV survival (p<0.05) at each time point as compared to controls. Long-term EM field exposures, however, offered no protection against low intensity UV light, in fact, 96 hour-EM field-exposed embryos were significantly less protected than non-EM field-exposed controls (p<0.05)., Conclusions: Results of the present study demonstrate that EM field exposures of appropriate duration induce protection against damage from UV light exposure. Because EM field exposures have been reported to activate stress protein response pathways and protect against anoxia/re-oxygenation damage, stress proteins are thought to play a role in the observed UV protection.

Alteration of ODC activity in animals or cultured cells exposed to extremely low frequency electromagnetic fields, or to modulated microwave fields, has been documented by several laboratories. However, an evaluation of the dose-response relationship in these experiments has not been done. We examined ODC activity in L929 fibroblasts exposed for 4 h to 60 Hz magnetic fields of different amplitudes. Our results show a clear threshold response which could be fitted to a sigmoidal function, with the 50% point occurring at approximately 5 microT. This sigmoidal response is characteristic of biological responses which are governed by ligand-receptor binding, and has been previously observed in the incidence of magnetic-field induced morphological abnormalities in chick embryos. The implications of this study are discussed in terms of environmental exposures to EM fields.

We have previously demonstrated that microwave fields, amplitude modulated (AM) by an extremely low-frequency (ELF) sine wave, can induce a nearly twofold enhancement in the activity of ornithine decarboxylase (ODC) in L929 cells at SAR levels of the order of 2.5 W/kg. Similar, although less pronounced, effects were also observed from exposure to a typical digital cellular phone test signal of the same power level, burst modulated at 50 Hz. We have also shown that ODC enhancement in L929 cells produced by exposure to ELF fields can be inhibited by superposition of ELF noise. In the present study, we explore the possibility that similar inhibition techniques can be used to suppress the microwave response. We concurrently exposed L929 cells to 60 Hz AM microwave fields or a 50 Hz burst-modulated DAMPS (Digital Advanced Mobile Phone System) digital cellular phone field at levels known to produce ODC enhancement, together with band-limited 30-100 Hz ELF noise with root mean square amplitude of up to 10 microT. All exposures were carried out for 8 h, which was previously found to yield the peak microwave response. In both cases, the ODC enhancement was found to decrease exponentially as a function of the noise root mean square amplitude. With 60 Hz AM microwaves, complete inhibition was obtained with noise levels at or above 2 microT. With the DAMPS digital cellular phone signal, complete inhibition occurred with noise levels at or above 5 microT. These results suggest a possible practical means to inhibit biological effects from exposure to both ELF and microwave fields.