Detailed study of the dielectric function of a lysozyme solution studied with molecular dynamics simulations

The spread of microwave technology and new microwave applications in medicine have revitalized interest in the dielectric behavior of biological systems. In this work, the Fröhlich-Kirkwood approach and the linear response theory have been applied in conjunction with molecular dynamics simulations to study the dielectric response of a lysozyme solution as a model. The overall experimental dielectric behavior of a 9.88 mM lysozyme solution has been reproduced in a quantitative manner by employing a method based on the decomposition of the hydration shells close to the solute. Detailed analysis of the calculated spectra identified two δ-processes located at 200 MHz (δ1) and about 1 GHz (δ2), respectively. δ1 is associated mainly with the first hydration shell, while δ2 mainly with bulk water and the second hydration shell. Moreover, indications for the existence of an even faster relaxation in the 10(11)-Hz frequency range were found for the first time. Finally, the static dielectric constants of lysozyme and its first and second hydration shells were calculated based on the Fröhlich-Kirkwood and the linear response theory approaches.