Molecular Insights into Dipole Relaxation Processes in Water–Lysine Mixtures

Abstract

Dielectric spectroscopy is a robust method to investigate relaxations of molecular dipoles. It is particularly useful for studies of biological solutions because of the potential of this method to cover a broad range of dynamical time scales typical for such systems. However, this technique does not provide any information about the nature of the molecular motions, which leads to a certain underemployment of dielectric spectroscopy for gaining microscopic understanding of material properties. For such detailed understanding, computer simulations are valuable tools because they can provide information about the nature of molecular motions observed by, for example, dielectric spectroscopy and to further complement them with structural information. In this work, we acquire information about the nature of dipole relaxation, in n-lysine solutions by means of molecular dynamics simulations. Our results indicate that the experimentally observed main relaxation process of n-lysine has different origins for the single monomer and the polypeptide chains. The relaxation of 1-lysine is due to the motions of whole molecules, whereas the experimentally observed relaxation of 3-lysine and 4-lysine is due to the motions of the residues, which, in turn, are promoted by water relaxation. Furthermore, we propose a new structural model of the lysine amino acids, which can quantitatively account for the experimental dielectric relaxation data. Hydrogen bonding and the structure of water are also discussed in terms of their influence on relaxation processes.

Dynamics of aqueous peptide solutions in folded and disordered states examined by dynamic light scattering and dielectric spectroscopy

“…Molecular simulations on smaller 1-and 4-lysine molecules have shown that no aggregation is observed at high pH values. 49,50 These facts strongly suggest that the origin of the A-DLS cannot be due to concentration fluctuations. Additionally, a process observed by dynamic light scattering with the same phenomenological behaviour as observed here for e-PLL, has previously been found for other aqueous solutions (such as water mixtures of xylitol, 43 glucose, 51 or a-cyclodextrin 52 ).…”

Maxwell-Wagner-Sillars interfacial polarization in dielectric spectra of composite materials: Scaling laws and applications

“…The electrical and dielectric properties of matter can be fully described by the complex dielectric permittivity function ε∗=ε′−iε″ (or, since σ∗=iωε0ε∗, by the complex conductivity function σ∗=σ′+iσ″) 1 . The spectral and temperature dependence of ε∗ directly reveal phenomena taking place at the molecular scale such as for instance dipolar relaxation processes 2–4 , phase transitions 5–7 and charge transport processes. 8–13 The direct correlation existing between the spectral dependence of ε∗ and molecular phenomena is drastically impacted by the presence of interfaces and interphases, when the materials under study are heterogeneous (composite materials, multiphase materials, etc.).…”