Polyethylene green composites modified with post agricultural waste filler: thermo-mechanical and damping properties

The aim of the study was to determine thermo-mechanical properties and applicability of sunflower husk waste as a filler for ultra low density polyethylene composites. The post agricultural waste filler was milled and chemically treated with (3-aminopropyl)triethoxysilane (3-APS). The amount of filler used was 5, 10 and 20 wt%. The mechanical and thermal properties of the composites containing unmodified and modified natural fillers were determined in the course of static tensile test, rebound resilience by Schob method, and dynamic mechanic thermal analysis. The influence of filler loading and chemical modification of the filler on the morphology of natural composites was evaluated by SEM analysis.     

Langmuir evaporation from the (100), (111A), and (111B) faces of GaAs

We have measured the Langmuir evaporation of Ga and As from the (100), (111A), and (111B) faces of GaAs above and below the congruent evaporation temperature T_c. We have found that T_c is lowest for the (111B) face and highest for the (111A) face. These differences can be understood in terms of the different lifetimes of surface Ga on these faces. Furthermore, we have deduced that the evaporation processes are the rate limiting steps in the decomposition of GaAs. Below T_c, decomposition is controlled by the evaporation of Ga; above T_c it is controlled by the evaporation of As.     

Electrostatic Localization of RNA to Protocell Membranes by Cationic Hydrophobic Peptides

Cooperative interactions between RNA and vesicle membranes on the prebiotic earth may have led to the emergence of primitive cells. The membrane surface offers a potential platform for the catalysis of reactions involving RNA, but this scenario relies upon the existence of a simple mechanism by which RNA could become associated with protocell membranes. Here, we show that electrostatic interactions provided by short, basic, amphipathic peptides can be harnessed to drive RNA binding to both zwitterionic phospholipid and anionic fatty acid membranes. We show that the association of cationic molecules with phospholipid vesicles can enhance the local positive charge on a membrane and attract RNA polynucleotides. This phenomenon can be reproduced with amphipathic peptides as short as three amino acids. Finally, we show that peptides can cross bilayer membranes to localize encapsulated RNA. This mechanism of polynucleotide confinement could have been important for primitive cellular evolution.     

System size, energy, pseudorapidity, and centrality dependence of elliptic flow

This Letter presents measurements of the elliptic flow of charged particles as a function of pseudorapidity and centrality from Cu-Cu collisions at 62.4 and 200 GeV using the PHOBOS detector at the Relativistic Heavy Ion Collider. The elliptic flow in Cu-Cu collisions is found to be significant even for the most central events. For comparison with the Au-Au results, it is found that the detailed way in which the collision geometry (eccentricity) is estimated is of critical importance when scaling out system-size effects. A new form of eccentricity, called the participant eccentricity, is introduced which yields a scaled elliptic flow in the Cu-Cu system that has the same relative magnitude and qualitative features as that in the Au-Au system.     

2',3'-Dideoxy-3'-thionucleoside triphosphates: syntheses and polymerase substrate activities

All four 2',3'-dideoxy-3'-thio-nucleosides (ddtNTPs) function as substrates for the Y410F mutant of Deep Vent (exo-) DNA polymerase. Not only are the ddtNTPs incorporated to form the N + 1 product, but further elongations are observed in which the key step is attack of the 3'-thiol on the 5'-triphosphate. Although other polymerases are likely to differ in their use of the ddtNTPs, there does not appear to be a fundamental prohibition against using a thiol nucleophile on a phosphate anhydride electrophile. The syntheses of four ddtNTPs (C, T, A, G) are described. [structure: see text]     

A Fluorescent G‐Quadruplex Sensor for Chemical RNA Copying

Non‐enzymatic RNA replication may have been one of the processes involved in the appearance of life on Earth. Attempts to recreate this process in a laboratory setting have not been successful thus far, highlighting a critical need for finding prebiotic conditions that increase the rate and the yield. Now a highly parallel assay for template directed RNA synthesis is presented that relies on the intrinsic fluorescence of a 2‐aminopurine modified G‐quadruplex. The application of the assay to examine the combined influence of multiple variables including pH, divalent metal concentrations and ribonucleotide concentrations on the copying of RNA sequences is demonstrated. The assay enables a direct survey of physical and chemical conditions, potentially prebiotic, which could enable the chemical replication of RNA.     

The nature of improper, blue-shifting hydrogen bonding verified experimentally.

In the infrared spectra of solutions in liquid argon of dimethyl ether ((CH(3))(2)O) and fluoroform (HCF(3)), bands due to a 1:1 complex between these monomers have been observed. The C-H stretch of the HCF(3) moiety in the complex appears 17.7 cm(-1) above that in the monomer, and its intensity decreases by a factor of 11(2). These characteristics situate the interaction between the monomers in the realm of improper, blue-shifting hydrogen bonding. The complexation shifts the C-F stretches downward by some 9 cm(-1), while the C-H stretches in (CH(3))(2)O are shifted upward by 9-15 cm(-1), and the C-O stretches are shifted downward by 5 cm(-1). These shifts are in very good agreement with those calculated by means of correlated ab initio methods, and this validates a two-step mechanism for improper, blue-shifting hydrogen bonding. In the first step, the electron density is transferred from the oxygen lone electron pairs of the proton acceptor ((CH(3))(2)O) to fluorine lone electron pairs of the proton donor (CHF(3)) which yields elongation of all CF bonds. Elongation of CF bonds is followed (in the second step) by structural reorganization of the CHF(3) moiety, which leads to the contraction of the CH bond. It is thus clearly demonstrated that not only the spectral manifestation of H-bonding and improper H-bonding but also their nature differ.     

Ribosomal synthesis of dehydroalanine-containing peptides

Dehydroalanine is a nonproteinogenic amino acid, but it is a component of a wide variety of natural products with therapeutic activities. Indeed, this alpha,beta-unsaturated residue is a highly versatile building block due to its rigidifying effect on peptide backbones and its electrophilicity which allows site-specific thiol ligations of peptides with small molecules or proteins. To harness such versatility in genetically encoded, combinatorial peptide libraries, we report a simple and robust method for the ribosomal synthesis of dehydroalanine-containing peptides. Selenalysine, a selenium-containing lysine analogue, was recruited as a masked dehydroalanine equivalent. This residue is efficiently incorporated by a reconstituted Escherichia coli translation system at high fidelity and efficiency despite the presence of low levels of lysine. Mild oxidative conditions were used to convert selenalysine into dehydroalanine post-translationally. Using this method, we demonstrate the preparation of polyunsaturated and highly decorated peptides. This report is an important step toward the preparation and selection of large libraries of protein-reactive compounds with potential use as novel drugs or as analytical tools.