A Research about Current Techniques of Thermally Stimulated Depolarization Currents (TSDC): Investigating Hydration Structure and Conformational Stability using Thermally Stimulated Depolarization Currents (TSDC)

Abstract

Thermally Stimulated Depolarization Currents (TSDC) technique has been applied to investigate the hydration structure of six proteins with different structural motifs: pepsin, β-lactoglobulin, α-chymotrypsin, bovine serum albumin, human serum albumin and myoglobin, at very low hydration level (water vapor activity aw ≈ 0.80) both in the native state and after treatment in trifluoroethanol/water mixture 80% (v/v). A combined approach based on the use of the TSDC technique, able to distinguish H2O dipoles belonging to the solvation shell in terms of their order degree and mobility, and of FTIR and CD spectroscopies has allowed us to reexamine the problem of conformational stability of macromolecules as a function of their hydration.Two modifications of the Thermally Stimulated Depolarization Current method are proposed to improve resolution and sensitivity of the method by connecting either a real capacitor, or an additional resistor in series with the sample. It is shown experimentally that high sensitivity of the TSDC method with an air gap can be obtained, if the gap is substituted by the capacitor, while all advantages of the method remain in force. It has been found that in one experiment it is possible not only to measure the TSD current, but also to obtain data on the Thermally Stimulated Conductivity, if the properly selected additional resistor is periodically switched on and off.A simplified theory of thermally stimulated depolarization current of a parallel-plate condenser filled with heterogeneous solid consisting of two dielectrics is presented. It is assumed that the particles (with different shapes and dimensions) of one dielectric are sparsely distributed in another dielectric. A second basic assumption is that the average field in the solid is equal to the external electric field.