Time domain reflectrometry: the difference method applied to conductive aqueous solutions

Dielectric studies of native, unfolded and intermediate forms of beta -lactamase

Time-domain dielectric spectroscopy has been applied to native, intermediate and unfolded beta -lactamase structures both in the hydrated solid state and in solution. Gravimetric and dielectric measurements indicate that nearly three times as many water molecules are multiply hydrogen bonded to the unfolded compared with the native protein. By contrast, the primary hydration population of the state A intermediate is only 20% larger than that of the folded enzyme. Analysis of the beta -dispersions in terms of rotational relaxation of the protein's permanent dipole has indicated that there is no significant difference in the dimensions of the three structures. This is not consistent with the findings of previous studies employing different experimental techniques.

Dielectric studies of chain melting and denaturation in native DNA

Dielectric methods, based on time domain reflectometry (TDR), have been employed to characterise DNA chain melting and denaturation. A dielectric dispersion has been identified, centred in the low megahertz region, which has been attributed to the fluctuation of counterions along short segments of the DNA chain. Chain melting studies have shown that the magnitude of this dispersion is dependent not only on the relative proportions of single to double stranded DNA but also on the intermolecular interactions between the DNA chains.

Dielectric measurements of lysozyme and tri-N-acetyl-D-glucosamine association at radio and microwave frequencies

Time domain dielectric measurements were applied to the monitoring of molecular recognition by proteins. Lysozyme and tri-N-acetyl-D-glucosamine((NAG)3) were selected as a typical lock and key type recognition system. After association of (NAG)3, relaxation related to lysozyme itself was increased and depended on the pH of the solution. No change was detected in hydration of the enzyme before and after association.

Dielectric studies of intermolecular interactions in native DNA

The concentration dependence of the high frequency dielectric dispersion exhibited by solutions of DNA and the sensitivity of this to the ionic strength of the solution are described. Dielectric data obtained are consistent with a model involving the fluctuation of counterions along short segments of the DNA chain. The concentration and ion strength dependencies are discussed in terms of intermolecular interactions which are considered responsible for the existence of structure in DNA solutions.

Time domain dielectric spectroscopy study of human cells. I. Erythrocytes and ghosts

A method, allowing correction of electrode polarization effect in case of cell suspensions of small volume fraction is proposed. The dielectric behavior of human erythrocytes and erythrocyte ghosts suspensions was studied by time domain dielectric spectroscopy (TDDS) and the estimation of the dielectric constants of cell's structural parts (membrane, cytoplasm) on the basis of suitable models are presented. It was shown that in the case of small volume fraction of cells in suspension, the electrode polarization effect can be taken into account by the additional measurement of the corresponding supernatant. The optimal volume fraction of cells in suspensions in the TDDS measurements was found to be 3%-10%. The erythrocyte and erythrocyte ghost suspensions were found to demonstrate a single dispersion which can be described by the Debye equation. The membrane dielectric constant of different erythrocytes and ghosts was distributed near 5.

Time-domain reflectometry studies on Halobacterium halobium and Halobacterium marismortui

The dielectric properties of Halobacterium halobium and Halobacterium marismortui measured over the frequency range 1 MHz to 1 GHz are compared with a single-shell model for interfacial polarization. In the case of Halobacterium halobium, the model shows excellent agreement with the experimental data for reasonable values of membrane and cytoplasmic conductivity and permittivity. For Halobacterium marismortui however, an acceptable fit to the data can only be achieved by invoking a plasma membrane conductivity some three orders of magnitude larger than that of Halobacterium halobium and adding a second high-frequency dielectric dispersion. These observations confirm the findings of a previous study and are consistent with a scheme for Halobacterium marismortui involving thermodynamic compartmentalization of Na and K ions and the existence of a conductive plasma membrane.

Dielectric studies of ion fluctuation and chain bending in native DNA

The high-frequency dielectric dispersion exhibited by solutions of native DNA is characterised as a function of electrolyte concentration, counterion type, temperature and pH. The data are interpreted in terms of counterion fluctuation along short segments (subunits) of the DNA chain. From calculation of the subunit length from dielectric relaxation time and increment, information is derived regarding the static and dynamic bending of the DNA chain. Activation enthalpies for the ion fluctuation process are obtained from temperature-dependent dielectric data.

Time-domain dielectric spectroscopy applied to cell suspensions

A precision difference time-domain reflectometry (TDR) technique is described for the investigation of the dielectric properties of cell suspensions. The dielectric spectra obtained for erythrocytes using TDR are comparable with those reported in previous dielectric studies employing frequency-domain technique.