Homochirality of beta-peptides: a significant biomimetic property of unnatural systems

Homochirality, an interesting phenomenon of life, is mainly an unresolved problem and was thought to be a property of living matter. Herein, we show that artificial beta-peptides have the tendency toward homochiral diastereoselective chain elongation. Chain-length-dependent stereochemical discrimination was investigated in the synthesis of foldamers with various side chains and secondary structures. It was found that there is a strong tendency toward the synthesis of homochiral oligomers. The size of the side chain drastically influenced the selectivity of the stereodiscriminative chain-elongation reaction. It is noteworthy that water as the co-solvent increases the selectivity. Such behavior is a novel fundamental biomimetic property of foldamers with a potential of future industrial application

Rheological and mechanical properties of recycled poly(ethylene terephtalate)/high density polyethylene blends

Triphenylphosphite (TPP) has been used as a chain extender to regenerate polyethylene terephtalate (PET) and high density polyethylene (HDPE) wastes and to improve the properties of PET/HDPE system based on recycled materials. TPP incorporation in PET and HDPE showed a noticeable increase of the torque as a function of the mixing time and proved that the degradation reactions are considerably decreased. In the case of PET/ HDPE blends, the increase of the torque was strongly dependent on the composition of the homopolymers and on the time of mixing. TPP incorporation contributed to significant variations of the rheological and mechanical properties of the regenerated PET and HDPE and their blends

Effect of chemical treatment on thermophysical behavior of Spanish broom flour-reinforced polypropylene biocomposite

This work presents the chemical modification of Spanish broom flour (SBF), and the study of SBF loading and surface treatment on the performances of polypropylene (PP) biocomposites. In order to enhance the interfacial interactions between the PP matrix and the SBF, two types of chemical treatments were used: 2 wt% of sodium hydroxide (NaOH) for different times (8, 24 and 48 h) and 5 wt% of vinyltrimethoxysilane (VTMS), respectively. Different techniques for characterization such as the melting flow index (MFI), X-ray diffraction, transient plane source (TPS) and water absorption were used. The experiment results showed a decrease of the MFI with increasing of modified SBF content, independently of the type of the chemical treatment. Moreover, this decrease became significant in the biocomposites containing SBF-VTMS. The X-ray patterns showed that surface treatment of SBF could improve their crystallinity and crystallite sizes. The TPS measurements illustrates that the thermal conductivity of the biocomposites decreases with 10 wt% of modified SBF loading. Higher content than 20 wt% of SBF, improved the thermal conductivity of the biocomposites. Meanwhile, the lowest values were found when the VTMS is used. Besides, it was accompanied by a decrease in absorptivity due to the better interfacial adhesion SBF-PP

Flow-chemistry enabled efficient synthesis of β-peptides: backbone topology vs. helix formation

Enantiodiscriminative helix formation was observed for beta-peptide H14 helices. This observation is caused by the synperiplanar orientation of H-O atoms which is more unfavorable than those for H-H interaction. The 1,2 H-O interaction leads to the destruction of the helical structure. The introduction of a double C-C bond in the backbone rules out helix formation

Dynamic self-assembly of supramolecular catalysts from precision macromolecules

We show the emergence of strong catalytic activity at low concentrations in dynamic libraries of complementary sequence-defined oligomeric chains comprising pendant functional catalytic groups and terminal recognition units. In solution, the dynamic constitutional library created from pairs of such complementary oligomers comprises free oligomers, self-assembled di(oligomeric) macrocycles, and a virtually infinite collection of linear poly(oligomeric) chains. We demonstrate, on an exemplary catalytic system requiring the cooperation of no less than five chemical groups, that supramolecular di(oligomeric) macrocycles exhibit a catalytic turnover frequency ca. 20 times larger than the whole collection of linear poly(oligomers) and free chains. Molecular dynamics simulations and network analysis indicate that self-assembled supramolecular di(oligomeric) macrocycles are stabilized by different interactions, among which chain end pairing. We mathematically model the catalytic properties of such complex dynamic libraries with a small set of physically relevant parameters, which provides guidelines for the synthesis of oligomers capable to self-assemble into functionally-active supramolecular macrocycles over a larger range of concentrations