Biomolecule surface patterning may enhance membrane association

Under dehydration conditions, amphipathic Late Embryogenesis Abundant (LEA) proteins fold spontaneously from a random conformation into alpha-helical structures and this transition is promoted by the presence of membranes. To gain insight into the thermodynamics of membrane association we model the resulting alpha-helical structures as infinite rigid cylinders patterned with hydrophobic and hydrophilic stripes oriented parallel to their axis. Statistical thermodynamic calculations using Single Chain Mean Field (SCMF) theory show that the relative thickness of the stripes controls the free energy of interaction of the alpha-helices with a phospholipid bilayer, as does the bilayer structure and the depth of the equilibrium penetration of the cylinders into the bilayer. The results may suggest the optimal thickness of the stripes to mimic the association of such protein with membranes.Comment: Published in ACS Nano http://pubs.acs.org/doi/pdf/10.1021/nn204736

Saturation effect for dependence of the electrical conductivity of planar oriented nematic liquid crystal 6CB on the concentration of Cu7PS6 nanoparticles

The influence of Cu7PS6 nanoparticles with the average size 117 nm on the dielectric properties of planar oriented nematic liquid crystal 6CB has been investigated within the frequency range 10(1) ...10(6) Hz and at the temperature 293 K. It has been shown that when changing the concentration of nanoparticles within the range 0 to 1 wt.%, the conductivity of the liquid crystal changes stronger than its dielectric permittivity. It has been shown that the electrical conductivity increases monotonously with increasing the concentration of nanoparticles. However, for this dependence a saturation effect is observed. The mechanism of this effect was proposed.info:eu-repo/semantics/publishedVersio

Accurate magnetic field measurements of Vega-like stars and Herbig Ae/Be stars

We have obtained accurate circular spectropolarimetric observations for a sample of Vega-like and Herbig Ae/Be stars with FORS1 at the VLT in an attempt to detect their magnetic fields. No magnetic field could be diagnosed in any Vega-like star. The most accurate determination of a magnetic field, at 2.6 sigma level, has been performed for the Vega-like star iota Cen for which we have measured = -77+-30 G. In the prototype of Vega-like stars, the star beta Pictoris, which shows conspicuous signs of chromospheric activity, a longitudinal magnetic field is measured only at ~1.5 sigma level. We diagnose for the first time a longitudinal magnetic field at a level larger than 3 sigma for the two Herbig Ae stars HD31648 and HD144432 and we confirm the previous detection of a magnetic field in a third Herbig Ae star, HD139614. Finally, we discuss the discovery of distinctive Zeeman features in the unusual Herbig Ae star HD190073 where the Ca II doublet displays several components in both H and K lines. From the measurement of circular polarization in all Balmer lines from H_beta to H_8 we obtain = +26+-34 G. However, using for the measurement of circular polarization only the Ca II H and K lines, we are able to diagnose a longitudinal magnetic field at 2.8 sigma level, = +84+-30 G.Comment: 7 pages, 3 figures, accepted for publication in A&

Molecular structure and reactions of 1,1'-bi(acenaphthen-1-ylidene)-2,2'-dione

The molecular structure of 1,1'-bi(acenaphthen-1-ylidene)-2,2'-dione 1, a potential building-block for the synthesis of fullerene fragments, has been investigated by X-ray crystallography and semi-empirical (AM1 and PM3) calculations. There is a good agreement between the calculated and crystal structure which is essentially planar and has E-configuration. In the solid state, molecules of 1 pack in an interesting manner as corrugated sheets sustained by a network of C-H···O hydrogen bonds and resulting in the formation of tetrameric loops. While steric factors limit the reactivity of the carbonyl groups in 1, the ene double bond of the ene-dione moiety present in it exhibits propensity toward [4 + 2]-cycloadditions to furnish novel and highly compressed polycycles 8-10

A study of the magnetic field in the photospheric and circumstellar components of Herbig Ae stars

We intend to investigate separately the photospheric and circumstellar (CS) magnetic field components in seven Herbig Ae stars. The study is based on low-resolution (R ~ 2000 and 4000) spectropolarimetric data collected from 2003 to 2005 at the Very Large Telescope (ESO, Chile) with the multi-mode instrument FORS1. We show that the spectropolarimetric results strongly depend on the level of CS contribution to the stellar spectra. We have improved the determination accuracy of magnetic fields up to the 7 sigma level in the two Herbig Ae stars HD139614 and HD144432, observed in 2005 when these objects were at a low level state of their CS activity. We have established that at a higher level state of CS activity the polarisation signatures are related mainly to the CS matter. The presence of CS polarisation signatures formed in the stellar wind supports the assumption that the magnetic centrifuge is a principal mechanism of wind acceleration. We conclude that the most effective way to investigate the magnetism of Herbig Ae stars is to monitor their spectropolarimetric behaviour at different states of CS activity. Obviously, higher resolution spectropolarimetric observations would extend the sample of spectral lines to be used for the measurements of magnetic fields at different levels in the stellar atmosphere and CS envelope. Such observations will give a more complete insight into the magnetic topology in Herbig Ae stars.Comment: 9 pages, 9 figures, 2 tables, accepted for publication in A&

Surface patterning of carbon nanotubes can enhance their penetration through a phospholipid bilayer

Nanotube patterning may occur naturally upon the spontaneous self-assembly of biomolecules onto the surface of single-walled carbon nanotubes (SWNTs). It results in periodically alternating bands of surface properties, ranging from relatively hydrophilic to hydrophobic, along the axis of the nanotube. Single Chain Mean Field (SCMF) theory has been used to estimate the free energy of systems in which a surface patterned nanotube penetrates a phospholipid bilayer. In contrast to un-patterned nanotubes with uniform surface properties, certain patterned nanotubes have been identified that display a relatively low and approximately constant system free energy (10 kT) as the nanotube traverses through the bilayer. These observations support the hypothesis that the spontaneous self-assembly of bio-molecules on the surface of SWNTs may facilitate nanotube transduction through cell membranes.Comment: Published in ACS Nano http://pubs.acs.org/doi/abs/10.1021/nn102763