The molecular structure of dimyristoyl phosphatidylserine (DMPS) monolayers on a water substrate in different phase states has been investigated by X-ray reflectometry with a photon energy of ~8 keV. ...According to the experimental data, the transition from a two-dimensional expanded liquid state to a solid gel state (liquid crystal) accompanied by the ordering of the hydrocarbon tails C
14
H
27
of the DMPS molecule occurs in the monolayer as the surface pressure rises. The monolayer thickness is 20 ± 3 and 28 ± 2 Å in the liquid and solid phases, respectively, with the deflection angle of the molecular tail axis from the normal to the surface in the gel phase being 26° ± 8°. At least a twofold decrease in the degree of hydration of the polar lipid groups also occurs under two-dimensional monolayer compression. The reflectometry data have been analyzed using two approaches: under the assumption about the presence of two layers with different electron densities in the monolayer and without any assumptions about the transverse surface structure. Both approaches demonstrate satisfactory agreement between themselves in describing the experimental results.
An operator model of integro-differential equations arising in the theory of viscoelasticity is studied. The spectral analysis of operator functions which are the symbols of Gurtin–Pipkin-type ...integro-differential equations is carried out with the Kelvin–Voigt friction taken into account.
•Different spin orderings found in SinO2n+x clusters.•Spins are located on excessive oxygen atoms on cluster surface.•Magnetism is analyzed via Stoner-like criterion for nanoscale non-metal systems.
...The calculations of spin effects in 20 SinO2n+m nanoclusters with 10⩾m⩾5 and m⩾1 are presented. They include search for the equilibrium atomic structure, the calculations of electron spectra and the energy of different spin orderings. It was found that all SinO2n+m clusters have spin moments, which are located on radical O atoms at the cluster surface. Long radical-to-radical distance weakens their exchange interaction, so energy differences between ferro-, ferri-, and antiferromagnetic states are of 0.01 eV or lower, gaining 0.046 eV only in Si6O13. We analyze this magnetism in terms of electron spectra and individual radical groups. Its similarity to popular molecular magnets based on organic radicals is noticeable. The stability of these SinO2n+m clusters in O2 atmosphere, as well as their relation to silicon technology, is of particular interest for spintronics.
The effect of the adsorption of a polypeptide on the lateral interaction of dimyristoylphosphatidylserine molecules in different phase states on the surface of a 10 mM KCl aqueous solution has been ...studied. Changes in the surface pressure and Volta potential induced by the adsorption of large poly-D-lysine molecules (about 200 links in a chain) have been determined at different areas per lipid molecule in a monolayer. The adsorption of macromolecules noticeably increases the elasticity of the monolayer under lateral compression in the liquid expanded state of lipid and reduces the effective dipole moment from 0.48 to 0.38 D. These properties are in qualitative agreement with X-ray reflectometry data for the lipid monolayer obtained with synchrotron radiation with a photon energy of ≈70 keV. The electron density profiles perpendicular to the surface of the aqueous subphase have been reconstructed from reflectometry data within a model approach to the structure of an interface with two and three layers. These profiles indicate the existence of a wide diffuse polymer layer (150 ± 40) Å in width at the interface of the monolayer in both the liquid expanded and liquid condensed states. A decrease in the area per molecule in the monolayer by a factor of 2 results in the doubling of the surface density of the macromolecule film. The adsorption of the polymer also affects the integral density of the layer of polar phospholipid groups, which decreases by a factor of ≈2 in the liquid expanded phase and by ∼30% in the liquid condensed phase.
This paper considers mechanical systems with linear velocity forces and highly non-linear positional forces containing distributed-delay terms. Asymptotic stability conditions of system equilibria ...are proved using Lyapunov’s direct method and the decomposition method. The developed approaches are applied to the monoaxial stabilization of a solid body. The theoretical outcomes are confirmed by computer simulation results.
Polarized Raman spectra of the epitaxial Ba
0.5
Sr
0.5
TiO
3
film, bi-color BaTiO
3
/Ba
0.5
Sr
0.5
TiO
3
superlattice and tri-color BaTiO
3
/Ba
0.5
Sr
0.5
TiO
3
/SrTiO
3
superlattice were studied in ...a broad temperature range of 80-700 K. Based on the temperature dependence of the polar modes we determined the phase transitions temperatures in the studied heterostructures. In the sub-THz frequency range of the
spectra, we revealed the coexistence of the Debye-type central peak and soft mode in bi-color BaTiO
3
/Ba
0.5
Sr
0.5
TiO
3
superlattice.
The Stoner criterion is known as a useful tool predicting the ferromagnetic state (FM) in metals. This criterion is not applied to nanoobjects, because of their discrete electron spectrum. In our ...paper we consider a generalization of this criterion, which can be applied to magnetism in semiconductor nanoobjects. To derive it, we compare total energies of the FM and non-magnetic states using many-body perturbation theory. The derived criterion has compact form and may be useful for prediction of ferromagnetism in nanoobjects. To check its precision, we performed first-principle calculations of several semiconductor nanoobjects in the FM and non-magnetic states and compared their results with predicted ones.
In this work, we investigated the redox transients of a number of water-soluble spin labels upon their interactions with Photosystem II (PS II) core complexes isolated from spinach leaves. We have ...found that the reactivity of nitroxide radicals, determined by the rate of their reduction upon illumination of PS II, depends on the chemical structure of radicals and the capability of their coming close to low-potential redox centers of photoactive PS II complexes. An enhanced capability of nitroxide radicals to accept electrons from PS II correlates with their chemical structure. Nitroxide radicals NTI (2,2,5,5-tetramethyl-4-nitromethylene-3-imidazolidine-
N
-oxyl) and Tacet (4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl-acetate), containing polar groups, appear to be most efficient acceptors of electrons donated by PS II compared to neutral (TEMPOL, 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl) or positively charged (Tamine, 4-amino-2,2,6,6-tetramethylpiperidine-l-oxyl) spin labels. We assume that enhanced reactivities of polar nitroxide radicals, NTI and Tacet, are determined (1) by their relatively high redox potentials, providing the possibility to accept electrons from PS II, and (2) by their affinities to the closest binding sites on the surface of PS II in the vicinity of the primary plastoquinone acceptor PQ
A
(12–14 Å) or/and in the intraprotein cavity for the secondary plastoquinone PQ
B
(~ 22 Å).
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