Oligomerization of peripheral membrane proteins provides tunable control of cell surface polarity

Asymmetric distributions of peripheral membrane proteins define cell polarity across all kingdoms of life. These asymmetries are shaped by membrane binding, diffusion and transport. Theoretical studies have revealed a general requirement for non-linear positive feedback to spontaneously amplify and/or stabilize asymmetries against dispersion by diffusion and dissociation. But how specific molecular sources of non-linearity shape polarization dynamics remains poorly understood. Here we study how oligomerization of peripheral membrane proteins shapes polarization dynamics in simple feedback circuits. We show that size dependent binding avidity and mobility of membrane bound oligomers endow polarity circuits generically with several key properties. Size-dependent binding avidity confers a form of positive feedback in which the effective rate constant for subunit dissociation decreases with increasing subunit density. This combined with additional weak linear positive feedback is sufficient for spontaneous emergence of stably polarized states. Size-dependent oligomer mobility makes symmetry-breaking and stable polarity more robust with respect to variation in subunit diffusivities and cell sizes, and slows the approach to a final stable spatial distribution, allowing cells to "remember" polarity boundaries imposed by transient external cues. Together, these findings reveal how oligomerization of peripheral membrane proteins can provide powerful and highly tunable sources of non-linear feedback in biochemical circuits that govern cell-surface polarity. Given its prevalence and widespread involvement in cell polarity, we speculate that self-oligomerization may have provided an accessible path to evolving simple polarity circuits.

Application of Surfactant Material as Anti-hygroscopicity agent for Ammonium Nitrate (NH4NO3)

Ammonium nitrate is a promising rocket propellant oxidizer. It is present as the major component in most industrial explosives. Due to the surface polarity of ammonium nitrate, the particles can easy absorb moisture. In this study, ammonium nitrate particles were coated by cetylalcohol surfactant in order to reduce the hygroscopicity. The optimized physical coating process using cetylalcohol was achieved by (L9 (34 )) Taguchi orthogonal array (TOA).The analysis of TOA revealed that the highest decline of absorption rate was 35.45% with the mass ratio of coating layer was 0.95%. Scanning electron microscopy (SEM) was used to characterize the surface of coated and uncoated ammonium nitrate. The idea and approach presented in this study can help the researchers to improving anti-hygroscopicity of ammonium nitrate.

Correlation between Contact Angle and Surface Roughness of Silicon Carbide Wafers

Two-inch diameter 6H-SiC wafers were sliced from a SiC ingot and the wafers were ground and polished using different diamond slurries (1 m and 0.1 m in particles size) to investigate their dependence on wetting on surface roughness (Ra) and polarity using precisely dispensed de-ionized (DI) water drops. The Ra of the Si-face (0001) SiC wafer, after grinding and polishing, was 5.6 and 1.6 nm, respectively, as measured by atomic force microscopy (AFM). For C-face (000-1) SiC wafers, the Ra was 7.2 nm after grinding and 3.3 nm after polishing. The average contact angle measurement of the SiC wafers after final polishing showed clear differences between surface polarity; the contact angle for the Si-face (0001) was ~7o greater than that for the C-face (000-1). The difference in contact angles between the Si-face (0001) and the C-face (000-1) tends to increase as the reduction of surface roughness approaches the final stage of polishing. The uniformity of Raman peak intensity in the folded transverse optical phonon band at ~780 cm-1 in scanned areas correlated well with the surface roughness measured by AFM. The contact angle measurement can be used as a convenient surface polarity and surface roughness testing technique for SiC wafers.

Significance of Adhesion Theories in Area of Flexible Bonded Structural Joints in Construction Sector

The issue of bonding has been a part of humanity throughout its history. The greatest development in this area occurred in the second half of the 20th century and the issue of bonding has gained a lot of interest from the scientific community. Over the past 80 years, there has been a significant increase in scientific research and grants aimed at defining adhesion. We now know that examining the adhesion of materials, determining the adhesive properties or simply evaluating the test results and assessing the failure of the test specimens is not possible without understanding the basic principles and theories of bonding, i.e. adhesive joining. The presented paper is focused on the description of fundamental adhesion theories and their usage in the field of structural bonding in construction industry. The importance of understanding to adhesive properties of used products is demonstrated on an example of four different surfaces in combination with representatives of high strength flexible adhesive systems intended for façade applications. Representatives with high surface polarity, medium-high polarity and low polarity were deliberately selected. The one-way ANOVA was performed to analyse the impact of surface adhesive properties on adhesion of bonded joints. It was confirmed that the riskiest is bonding of polymer-based materials. For all selected materials it was concluded that the hypotheses of the adsorption theory, which, to some extent, also includes the assumptions of other adhesive theories, seem to be the most fundamental for the presented researched area.

Influence of Nonequilibrium Low-Temperature Plasma on the Properties of Nonwoven Fabric Based on Polypropylene

Investigation of the effect of low-pressure NLTP in nitrogen, argon, propane-butane and air on the properties of a multilayer medical-purpose material based on polypropylene used for the manufacture of sanitary-hygienic and medical products. It is shown that after plasma treatment of argon, nitrogen, propane-butane, the surface polarity of the CMC material changes significantly, as evidenced by a decrease in the wettability angle and an increase in capillarity. The most significant changes in indicators are observed in the case of plasma treatment in argon and nitrogen. However, in the case of argon, less processing time is required to achieve the effect. Plasma treatment leads to a slight decrease in tensile strength, no more than 10-15%. It is also shown that when plasma is treated in an argon atmosphere, such characteristics of a nonwoven material as air permeability, hygroscopicity increase, and a decrease in rigidity is observed. The study of the structure of the material (pore size) showed that the treatment with NLTP leads to a significant decrease in the size of large pores and an increase in the size of medium and small pores

Carbon nitride materials: impact of synthetic method on photocatalysis and immobilization for photocatalytic pollutant degradation

Different synthesis routes for carbon nitride materials (CN) and the resulting products were compared to study the photocatalytic activity (pollutant degradation) in dependence on structure and properties. The CN materials were synthesized by thermal decomposition of dicyandiamide in air and under argon as well as in sealed ampoules with or without the use of a salt melt. The as-prepared materials were characterized by IR spectroscopy, nitrogen adsorption measurement, solid-state NMR spectroscopy, diffuse reflectance UV–Vis spectroscopy, elemental analysis and powder X-ray diffraction (PXRD). The surface polarity of the CN materials was estimated by adsorption of the dicyano-bis(1,10-phenanthroline)-iron(II) complex, which allows an evaluation of the degree of condensation. The CN materials were tested with regard to the photocatalytic degradation of rhodamine B (RhB). It is shown that the photocatalytic activity increases with higher surface polarity. Promising CN materials with high RhB degradation of 85% within 25 min and high surface polarity of 0.89 were selected for an immobilization approach to obtain coatings on a silicone substrate using a high-volume low-pressure (HVLP) spray coating technique. To study the photocatalytic activity of the catalyst coatings, the degradation rates of an aqueous RhB solution and solutions of organic pollutants such as triclosan and ethinyl estradiol were examined. Pollutants are decomposed with up to 63% of the initial concentration. Xenon lamps and different LEDs were used as light sources for comparison. Particularly high degradation efficiencies were obtained using LEDs, and the degradation rates are increased by adjusting the emission spectrum of the lamp to the pollutant and absorption edge of the catalyst, which results in a 40 times higher degradation efficiencies of LEDs compared to a Xe lamp. Graphical abstract