Fluctuations in mixtures of lamellar- and nonlamellar-forming lipids

We consider the role of nonlamellar-forming lipids in biological membranes by examining fluctuations, within the random phase approximation, of a model mixture of two lipids, one of which forms lamellar phases while the other forms inverted hexagonal phases. To determine the extent to which nonlamellar-forming lipids facilitiate the formation of nonlamellar structures in lipid mixtures, we examine the fluctuation modes and various correlation functions in the lamellar phase of the mixture. To highlight the role fluctuations can play, we focus on the lamellar phase near its limit of stability. Our results indicate that in the initial stages of the transition, undulations appear in the lamellae occupied by the tails, and that the nonlamellar-forming lipid dominates these undulations. The lamellae occupied by the head groups pinch off to make the tubes of the hexagonal phase. Examination of different correlations and susceptibilities makes quantitative the dominant role of the nonlamellar-forming lipids.Comment: 7 figures (better but larger in byte figures are available upon resuest), submitte

New mechanism of membrane fusion

We have carried out Monte Carlo simulation of the fusion of bilayers of single chain amphiphiles which show phase behavior similar to that of biological lipids. The fusion mechanism we observe is very different from the ``stalk'' hypothesis. Stalks do form on the first stage of fusion, but they do not grow radially to form a hemifused state. Instead, stalk formation destabilizes the membranes and results in hole formation in the vicinity of the stalks. When holes in each bilayer nucleate spontaneously next to the same stalk, an incomplete fusion pore is formed. The fusion process is completed by propagation of the initial connection, the stalk, along the edges of the aligned holes.Comment: 4 pages, 3 figure

Distribution of lipids in non-lamellar phases of their mixtures

We consider a model of lipids in which a head group, characterized by its volume, is attached to two flexible tails of equal length. The phase diagram of the anhydrous lipid is obtained within self-consistent field theory, and displays, as a function of lipid architecture, a progression of phases: body-centered cubic, hexagonal, gyroid, and lamellar. We then examine mixtures of an inverted hexagonal forming lipid and a lamellar forming lipid. As the volume fractions of the two lipids vary, we find that inverted hexagonal, gyroid, or lamellar phases are formed. We demonstrate that the non-lamellar forming lipid is found preferentially at locations which are difficult for the lipid tails to reach. Variations in the volume fraction of each type of lipid tail are on the order of one to ten per cent within regions dominated by the tails. We also show that the variation in volume fraction is correlated qualitatively with the variation in mean curvature of the head-tail interface.Comment: 10 pages, 12 figures (better figures are available upon request), to appear in J. Chem. Phy

Sewage treatment

The basic function of the wastewater treatment plant is to speed up the natural processes by which water purifies itself. In earlier years, the natural treatment process in streams and lakes was adequate to perform basic wastewater treatment. As our population and industry grew, increased levels of treatment became necessary before discharging domestic wastewater

On the Question of the Imperative or Dispositivity of the Norm of Paragraph 1 of Article 782 of the Civil Code of the Russian Federation, Which Establishes the Right of the Customer to Unmotivated Refusal of the Contract for the Provision of Paid Services

In this article, the author explores the question of the qualification of Paragraph 1 of Article 782 of the Civil Code of the Russian Federation, which gives the right to unmotivated refuse to perform a contract for the provision of paid services. The paper considers various approaches to the issue of dispositivity or imperativeness of this norm. The positions of scientists on the legal nature of 782 of the Civil Code of the Russian Federation are considered. The author analyzes judicial practice for the possibility of blocking the right to unilateral refusal. Based on the presented analysis, conclusions are drawn about the dispositivity of 782 of the Civil Code of the Russian Federation regarding the inadmissibility of blocking the right to unilateral refusal itself, at the same time, the parties are allowed to establish a different procedure for the implementation of this right. A possible option for improving domestic legislation regulating the termination of a contract for the provision of paid services is also proposed

Magnetic and magnetocaloric properties of (MnCo)1-xGe compounds

The crystal structure, magnetic properties, and heat capacity of the (MnCo)1-xGe compounds with x ≤ 0.05 have been studied. It was found that, as the deviation from the MnCoGe stoichiometric composition increases, the temperature of structural transition from the low-temperature phase with the orthorhombic TiNiSi-type structure to the high-temperature phase with the hexagonal Ni2In-type phase decreases rapidly, whereas the magnetic ordering temperature varies slightly. The temperature of structural transition for the composition with x = 0.02 approximately coincides with the Curie temperature of the hexagonal phase, and the transition is accompanied by a significant entropy change, namely, ΔS = 34 J/(kg K). The application of high magnetic field in the transition-temperature range causes an increase in the relative volume of the orthorhombic phase. An analysis of magnetocaloric properties of these compounds, which was performed with the formal application of the Maxwell's relationship near the temperature of first-order structural phase transition, is shown to give overestimated values of the entropy change. © Pleiades Publishing, Ltd., 2013

Standard Thermodynamic Functions of Tripeptides N-Formyl-L-Methionyl-L-Leucyl-L-Phenylalaninol and N-Formyl-L-Methionyl-L-Leucyl-L-Phenylalanine Methyl Ester

The heat capacities of tripeptides N-formyl-l-methionyl-l-leucyl-l-phenylalaninol (N-f-MLF-OH) and N-formyl-l-methionyl-l-leucyl-l-phenylalanine methyl ester (N-f-MLF-OMe) were measured by precision adiabatic vacuum calorimetry over the temperature range from T = (6 to 350) K. The tripeptides were stable over this temperature range, and no phase change, transformation, association, or thermal decomposition was observed. The standard thermodynamic functions: molar heat capacity C[subscript p,m], enthalpy H(T) – H(0), entropy S(T), and Gibbs energy G(T) – H(0) of peptides were calculated over the range from T = (0 to 350) K. The low-temperature (T ≤ 50 K) heat capacities dependencies were analyzed using the Debye’s and the multifractal theories. The standard entropies of formation of peptides at T = 298.15 K were calculated.National Institute for Biomedical Imaging and Bioengineering (U.S.) (Grant EB-003151)National Institute for Biomedical Imaging and Bioengineering (U.S.) (Grant EB-001960)National Institute for Biomedical Imaging and Bioengineering (U.S.) (Grant EB-002026)Ministry of Education and Science of the Russian Federation (Contract 14.B37.21.0799

New materials of RMn2Ge2 type for thermomagnetic devices

The new type of the working media for thermomagnetic devices is proposed: the intermetallic compounds which have large magnetocrystalline anisotropy and exhibit the spontaneous phase transition from the antiferromagnetic (AF) to ferromagnetic (F) state when the temperature increases above the critical value T$\text{}_{t}$. Moreover, the anisotropy in AF state in the fields below the critical AF-F transition field must be much lower than in the F state. In the present paper the Gd$\text{}_{0.6}$Sm$\text{}_{0.4}$Mn$\text{}_{2}$Ge$\text{}_{2}$ compound belonging to the tetragonal RMn$\text{}_{2}$Ge$\text{}_{2}$ system is investigated. This compound has the critical temperature T$\text{}_{t}$ = 280 K. The thermomagnetic cycle can be realized on the AF-F-AF transition near T$\text{}_{t2}$. The interval of the working temperatures can be shifted with the change of the Gd and Sm concentration