Role of backbone-solvent interactions in determining conformational equilibria of intrinsically disordered proteins

Intrinsically disordered proteins (IDPs) are functional proteins that do not fold into well-defined three-dimensional structures under physiological conditions. IDP sequences have low hydrophobicity, and hence, recent experiments have focused on quantitative studies of conformational ensembles of archetypal IDP sequences such as polyglutamine and glycine-serine block copolypeptides. Results from these experiments show that, despite the absence of hydrophobic residues, polar IDPs prefer ensembles of collapsed structures in aqueous milieus. Do these preferences originate in interactions that are unique to polar sidechains? The current study addresses this issue by analyzing conformational equilibria for polyglycine and a glycine-serine block copolypeptide in two environments, namely, water and 8 M urea. Polyglycine, a poly secondary-amide, has no sidechains and is a useful model system for generic polypeptide backbones. Results based on large-scale molecular dynamics simulations show that polyglycine forms compact, albeit disordered, globules in water and swollen, disordered coils in 8 M urea. There is minimal overlap between conformational ensembles in the two environments. Analysis of order parameters derived from theories for flexible polymers show that water at ambient temperatures is a poor solvent for generic polypeptide backbones. Therefore, the experimentally observed preferences for polyglutamine and glycine-serine block copolypeptides must originate, at least partially, in polypeptide backbones. A preliminary analysis of the driving forces that lead to distinct conformational preferences for polyglycine in two different environments is presented. Implications for describing conformational ensembles of generic IDP sequences are also discussed.     

Enhancement of the properties and mesophases stability after the electron beam irradiation on a racemic anti-ferroelectric liquid crystalline mixture

The display parameters and the stability of the various mesophases of a newly synthesised racemic mixture of anti-ferroelectric liquid crystals (AFLCs) have been boosted with the help of the electron beam irradiation. The mixture has phase sequence of isotropic–smectic C–smectic C_A crystal. The effective macroscopic polarisation and transition temperatures of the various mesophases of the irradiated mixture have increased as compared with the pure mixture. The macroscopic polarisation of the mixture has increased from 21 to 27 nC/cm² due to the irradiation. From various studies, we have observed that the temperature range of the smectic C_A phase has increased by 20.6°C with marginal decrease in the temperature range of the smectic C phase.     

Noetherianity of some degree two twisted commutative algebras

The resolutions of determinantal ideals exhibit a remarkable stability property: for fixed rank but growing dimension, the terms of the resolution stabilize (in an appropriate sense). One may wonder if other sequences of ideals or modules over coordinate rings of matrices exhibit similar behavior. We show that this is indeed the case. In fact, our main theorem is more fundamental in nature: It states that certain large algebraic structures (which are examples of twisted commutative algebras) are noetherian. These are important new examples of large noetherian algebraic structures, and ones that are in some ways quite different from previous examples.     

Examining the lateral displacement of HL60 cells rolling on asymmetric P-selectin patterns

The lateral displacement of cells orthogonal to a flow stream by rolling on asymmetrical receptor patterns presents a new opportunity for the label-free separation and analysis of cells. Understanding the nature of cell rolling trajectories on such substrates is necessary to the engineering of substrates and the design of devices for cell separation and analysis. Here, we investigate the statistical nature of cell rolling and the effect of pattern geometry and flow shear stress on cell rolling trajectories using micrometer-scale patterns of biomolecular receptors with well-defined edges. Leukemic myeloid HL60 cells expressing the PSGL-1 ligand were allowed to flow across a field of patterned lines fabricated using microcontact printing and functionalized with the P-selectin receptor, leveraging both the specific adhesion of this ligand-receptor pair and the asymmetry of the receptor pattern inclination angle with respect to the fluid shear flow direction (α = 5, 10, 15, and 20°). The effects of the fluid shear stress magnitude (τ = 0.5, 1, 1.5, and 2.0 dyn/cm(2)), α, and P-selectin incubation concentration were quantified in terms of the rolling velocity and edge tracking length. Rolling cells tracked along the inclined edges of the patterned lines before detaching and reattaching on another line. The detachment of rolling cells after tracking along the edge was consistent with a Poisson process of history-independent interactions. Increasing the edge inclination angle decreased the edge tracking length in an exponential manner, contrary to the shear stress magnitude and P-selectin incubation concentration, which did not have a significant effect. On the basis of these experimental data, we constructed an empirical model that predicted the occurrence of the maximum lateral displacement at an edge angle of 7.5°. We also used these findings to construct a Monte Carlo simulation for the prediction of rolling trajectories of HL60 cells on P-selectin-patterned substrates with a specified edge inclination angle. The prediction of lateral displacement in the range of 200 μm within a 1 cm separation length supports the feasibility of label-free cell separation via asymmetric receptor patterns in microfluidic devices.     

Finite p-groups with non-cyclic center have a non-inner automorphism of order p

Archiv der Mathematik - Let G be a finite non-abelian p-group and let $$W(G)/Z(G)=\Omega _1(Z_2(G)/Z(G))$$ . A longstanding conjecture asserts that G admits a non-inner automorphism of order p. We...     

Studies on the UV-photolytic decomposition of some tensides and complexones inhibiting the inverse-voltammetric determination of metal ions

Summary The UV-photolytic decomposition of some tensides and complexones has been investigated using the DPASV peak of indium as an indicator. The results show that UV-irradiation alone can completely decompose these compounds at lower concentrations within a short time. Higher concentrations need an additional oxidising agent.Dedicated to Professor Dr. Wilhelm Fresenius on the occasion of his 80th birthday     

Removal of Brilliant Green from wastewater using conventional and ultrasonically prepared poly(acrylic acid) hydrogel loaded with kaolin clay: A comparative study

The present work deals with the removal of Brilliant Green dye from wastewater using a poly(acrylic acid) hydrogel composite (PAA-K hydrogel) prepared by incorporation of kaoline clay. The composite has been synthesized using ultrasound assisted polymerization process as well as the conventional process, with an objective of showing the better effectiveness of ultrasound assisted synthesis. It has been observed that the hydrogel prepared by ultrasound assisted polymerization process showed better results. The optimum conditions for the removal of dye are pH of 7, temperature of 35 °C, initial dye concentration of 30 mg/L and hydrogel loading of 1 g. The extent of removal of dye increased with an increase in the contact time and initial dye concentration. A pseudo-second-order kinetic model has been developed to explain the adsorption kinetics of dye on the PAA-K hydrogel. Thermodynamic and kinetic parameters indicate that the adsorption process is spontaneous in nature and the PAA-K hydrogel prepared by ultrasound process is a promising adsorbent compared to conventional process. The obtained adsorption data has also been fitted into commonly used adsorption isotherms and it has been found that Freundlich as well as Langmuir adsorption isotherm models fits well to the experimental results.     

Temperature-dependent magnetic and structural ordering of self-assembled magnetic array of FePt nanoparticles

Silicon nanoparticles (SiNPs) can be synthesized by a variety of methods. In many cases these routines are non-scalable with low product yields or employ toxic reagents. One way to overcome these drawbacks is to use one-pot synthesis based on the chemical reduction of micelles. In the following study trichloroalkylsilanes of differing chain lengths were used as a surfactant, and the level of capping, surface bonding and size of the nanoparticles formed has been investigated. FTIR results show that the degree of alkyl capping for SiNPs with different capping layers was constant, although SiNPs bound with shorter chains display a much higher level of Si–O owing to the reaction of the ethanol used in the method with uncapped sites on the particle. SiNPs with longer chain length capping show a sharp Si–H peak on the FTIR, these were heated at reflux with the corresponding 1-alkene to fully cap these particles, resulting in a reduction/disappearance of this peak with a minimal change in the intensity of the Si–O peak. Other techniques used to analyze the surface bonding and composition, XPS, ¹H-NMR, and TEM/EDX, show that alkyl-capped SiNPs have been produced using this method. The optical properties showed no significant changes between the different capped SiNPs.     

Energy transfers in dynamos with small magnetic Prandtl numbers

We perform numerical simulation of dynamo with magnetic Prandtl number Pm = 0.2 on 1024³ grid, and compute the energy fluxes and the shell-to-shell energy transfers. These computations indicate that the magnetic energy growth takes place mainly due to the energy transfers from large-scale velocity field to large-scale magnetic field and that the magnetic energy flux is forward. The steady-state magnetic energy is much smaller than the kinetic energy, rather than equipartition; this is because the magnetic Reynolds number is near the dynamo transition regime. We also contrast our results with those for dynamo with Pm = 20 and decaying dynamo.