The effect of gamma-irradiation on the temperature dependence of D.C. electrical conductivity of dry bone

Changes in thermal and electrical properties of bone as a result of 1 MGy-dose γ-irradiation

Determination of temperature dependencies of electric conductivity and thermal properties by differential scanning calorimetry (DSC) allow to analyse the processes of charge and heat transport in the bone being a complex collagen-hydroxyapatite (HAP)-water system. Modification of the bone structure by high doses of gamma-radiation changes the electrical and thermal properties of the bone. Electrical conductivity (sigma) of the bone decreases with consecutive heating runs. The decrease in sigma observed for irradiated samples was explained by the scission of the main chain of collagen macromolecule. Irradiation decreased the hydration level in the bone, its denaturation temperature and increased both enthalpy and entropy of the denaturation process.

Temporary Changes in the dc ElectricalConductivity of MX (3-Chloro-4(Dichloromethyl)-5-Hydroxy-2(5H)-Furanone) Treated Collagen

The influence of MX(3-Chloro-4(Dichloromethyl)-5-Hydroxy-2(5H)- Furanone), a stronglymutagenic compound, on the temperature dependence of the dcelectrical conductivity of collagen as a function of time was studied.Collagen was immersed in MX solution, next dried and pressed intotablets. The MX concentration was measured by HPLC analysis.The reduction of MX concentration to 10% of the initial value wasobserved in the presence of collagen in the solution, whereas in thecontrol solution concentration of MX decreased to 70% of the initialvalue. Measurements of electrical conductivity were performed for thetemperature range 295-453K and activation energies for the chargeconduction process were calculated. Within the temperature range295-340K, the presence of MX decreased electrical conductivity ofcollagen. Calculated activation energies were typical for dry proteins.Within the temperature range 295-320K activation energy decreasedwith time, probably due to the stronger interactions in thecollagen-water-MX system. For temperatures between 320-410 and430-450K the activation energy was not time dependent and theapplication of MX did not change the structure of the collagenmacromolecule. The temporary changes occurring at the lowertemperatures being due solely to changes in the collagen-waterinteractions.

Analysis of the dielectric properties of keratin in the alpha-dispersion electric field region

The dielectric method has been applied to study the relaxation mechanisms of non-irradiated and gamma-irradiated keratin-water systems in the electric field frequency range of 10(1)-10(5) Hz and at temperatures from 22 to 190 degrees C. Measurements were performed for keratin samples containing 3% water by mass at room temperature. The doses of gamma-irradiation were 5, 50 and 200 kGy. The influence of water and gamma-irradiation on the dielectric behaviour of keratin was negligible up to 120 degrees C but significant in the temperature range of 140-190 degrees C. In the first temperature range, the motion of polar side chains was characterised by a low activation energy of 11 kJ mol(-1), while longer relaxation times varied from 418 to 155 ms. In the range 140-190 degrees C, the release of the strongly bound water in keratin samples irradiated with doses of 0-50 kGy was evidenced by the high value of the activation energy of 84 kJ mol(-1) and shorter relaxation times varying from 43 to 3 ms. The value of the activation energy decreased to 55 kJ mol(-1) for keratin samples irradiated with 200 kGy as a result of degradation of the hydrogen bond between the water and polar groups of the main chain of the macromolecule. The results presented may be useful in bio-electrical impedance analysis, for physiological and clinical research. The method applied in vivo should permit detection of changes in the stratum corneum induced by water, ionising radiation, cosmetics and diseases such as fibromyalagia or diabetic foot ulcers.

The influence of storage time on the temperature dependence of the dc electrical conductivity of horn keratin

The direct current electrical conductivity of horn keratin was measured as a function of temperature, in the temperature range 290-480 K, with a constant heating rate, for samples stored for periods of 2-3 weeks and 5 months. The activation energy of charge conducting process was calculated. The longer storage time reduced the water content, and the electrical conductivity, but increased the activation energy at 290-320 K.