Evaluation of the measurement of biomolecular dipole moment: Dielectric and electrolytic solution parameters by calorimetry

Solutions of biological macromolecules are known to express non-ideality phenomena at physiological conditions. The interaction mechanisms that govern solution characteristics arise out of the electrostatic properties of the macromolecules and attendant solution components. Macromolecule charge and charge asymmetry are thought to be dominant electrostatic properties influencing molecular interactions in solution. The macromolecule charge asymmetry can be approximated as a maacrodipole moment and measured by evaluating a dielectric increment through dielectric spectroscopy methods. In this study, methods of dielectric spectroscopy are evaluated for measurements of macromolecules in physiologically relevant solvents. Novel techniques for dielectric spectroscopy are proposed, including a parallel plate capacitor technique and two methods of dielectric spectroscopy by calorimetry. Prototype designs are constructed, and recommendations are provided to mitigate and correct for electrode polarization difficulties.;A capillary calorimetry technique is developed for measuring the conductivity of a small sample volume, ~20 microl, and is shown to measure a conductivity difference above a 2% limit of detection. However, further refinements are necessary to improve reproducibility of the device. The capillary calorimeter will likely not be able to extend to the high frequency field range necessary to evaluate a dielectric increment and dipole moment of biologic macromolecules. Nevertheless, small volume measurements of low frequency conductivity may prove useful in identifying activity characteristics of macromolecule solutions and should be investigated further as a tool for pharmacological research. Work going forward to identify methods for macrodipole measurement should focus on advancing parallel plate capacitance designs to minimize electrode polarization effects.