First-Principles Simulation of Dielectric Function in Biomolecules

The dielectric spectra of complex biomolecules reflect the molecular heterogeneity of the proteins and are particularly important for the calculations of electrostatic (Coulomb) and electrodynamic (van der Waals) interactions in protein physics. The dielectric response of the proteins can be decomposed into different components depending on the size, structure, composition, locality, and environment of the protein in general. We present a new robust simulation method anchored in rigorous ab initio quantum mechanical calculations of explicit atomistic models, without any indeterminate parameters to compute and gain insight into the dielectric spectra of small proteins under different conditions. We implement this methodology to a polypeptide RGD-4C (1FUV) in different environments, and the SD1 domain in the spike protein of SARS-COV-2. Two peaks at 5.2–5.7 eV and 14.4–15.2 eV in the dielectric absorption spectra are observed for 1FUV and SD1 in vacuum as well as in their solvated and salted models.

Dielectric and piezoelectric properties of modified lead-free NaNbO3–KNbO3/PVDF composite ceramics

This work presents the results of study of the electrophysical properties of composite polymer ceramics (1[Formula: see text][KNN-LTSN]–[Formula: see text]PVDF at [Formula: see text] = 25 vol.% and [Formula: see text]= 50 vol.% in the temperature range of [Formula: see text] = 20–160[Formula: see text]C and frequency range of [Formula: see text] = 2 × 101–2 × 106 Hz. The concentration dependence of piezomodules of the studied materials has been analyzed as a function of temperature. X-ray measurements have also been carried out. A model of description of revealed dielectric parameters dispersion in the material is presented. The nonclassical modified Havriliak–Negami model written for complex electrical conductivity has been used to describe the temperature–frequency properties. It is shown that the dielectric spectra of the studied composites include three relaxation processes in the temperature ranges of 40–80[Formula: see text]C, 80–120[Formula: see text]C and 120–150 [Formula: see text]C, which were confirmed by the dynamics of changes in the dependences of [Formula: see text], tg[Formula: see text], [Formula: see text], [Formula: see text]([Formula: see text]) and [Formula: see text]([Formula: see text]. All three processes are almost exactly described by this model and well correlated with the studies by other researchers of the composites based on PVDF. The results of this work show that the use of such experimental model is suitable for describing the complex dielectric spectra of any nonlinear dielectrics including composite materials.

Effect of Dendritic Side Groups on the Mobility of Modified Poly(epichlorohydrin) Copolymers

The macromolecular dynamics of dendronized copolymer membranes (PECHs), obtained by chemical modification of poly(epichlorohydrin) with the dendron 3,4,5-tris[4-(n-dodecan-1-yloxy)benzyloxy] benzoate, was investigated. In response to a thermal treatment during membrane preparation, these copolymers show an ability to change their shape, achieve orientation, and slightly crystallize, which was also observed by CP-MAS NMR, XRD, and DSC. The phenomenon was deeply analyzed by dielectric thermal analysis. The dielectric spectra show the influence of several factors such as the number of dendritic side groups, the orientation, their self-assembling dendrons, and the molecular mobility. The dielectric spectra present a sub-Tg dielectric relaxation, labelled as γ, associated with the mobility of the benzyloxy substituent of the dendritic group. This mobility is not related to the percentage of these lateral chains but is somewhat hindered by the orientation of the dendritic groups. Unlike other less complex polymers, the crystallization was dismantled before the appearance of the glass transition (αTg). Only after that, clearing transition (αClear) can be observed. The PECHs were flexible and offered a high free volume, despite presenting a high degree of modifications. However, the molecular mobility is not independent in each phase and the self-assembling dendrons can be eventually fine-tuned according to the percentage of grafted groups.

On the temperature and pressure dependence of dielectric relaxation processes in ionic liquids

The temperature and pressure dependence of two dynamic processes in the dielectric spectra of five supercooled ionic liquids equipped with octyl-chains are reported. The microscopic origin of these processes is discussed.

Импедансметрия нанокристаллитов Ag-=SUB=-2-=/SUB=-S, внедренных в нанопористые стекла

The temperature dependences of the dielectric spectra of Ag2S nanocrystallites synthesized inside the channels of nanoporous glasses NPG-17 with an average diameter of filamentous pores of 17 nm are studied. The macroscopic mechanism for the occurrence of the frequency dependence of the electrical response of a nanoporous structure NPG+Ag2S is proposed. Formation of the model of mechanism is based superionic phase transition in Ag2S nanocrystallites fixed inside the channels of nanoporous glass is discussed.