Dielectric relaxations in PEEK by combined dynamic dielectric spectroscopy and thermally stimulated current

The molecular dynamics of a quenched poly (ether ether ketone) (PEEK) was studied over a broad frequency range from 10-3 to 106 Hz by combining dynamic dielectric spectroscopy (DDS) and thermo-stimulated current (TSC) analysis. The dielectric relaxation losses e00 KK has been determined from the real part e0 T(x) thanks to Kramers–Kronig transform. In this way, conduction and relaxation processes can be analyzed independently. Two secondary dipolar relaxations, the c and the b modes, corresponding to non-cooperative localized molecular mobility have been pointed out. The main a relaxation appeared close to the glass transition temperature as determined by DSC; it has been attributed to the delocalized cooperative mobility of the free amorphous phase. The relaxation times of dielectric relaxations determined with TSC at low frequency converge with relaxation times extracted from DDS at high frequency. This correlation emphasized continuity of mobility kinetics between vitreous and liquid state. The dielectric spectroscopy exhibits the ac relaxation, near 443 K, which has been associated with the rigid amorphous phase confined by crystallites. This present experiment demonstrates coherence of the dynamics of the PEEK heterogeneous amorphous phase between glassy and liquid state and significantly improve the knowledge of molecular/dynamic structure relationships

Assembly, organization, and function of the COPII coat

A full mechanistic understanding of how secretory cargo proteins are exported from the endoplasmic reticulum for passage through the early secretory pathway is essential for us to comprehend how cells are organized, maintain compartment identity, as well as how they selectively secrete proteins and other macromolecules to the extracellular space. This process depends on the function of a multi-subunit complex, the COPII coat. Here we describe progress towards a full mechanistic understanding of COPII coat function, including the latest findings in this area. Much of our understanding of how COPII functions and is regulated comes from studies of yeast genetics, biochemical reconstitution and single cell microscopy. New developments arising from clinical cases and model organism biology and genetics enable us to gain far greater insight in to the role of membrane traffic in the context of a whole organism as well as during embryogenesis and development. A significant outcome of such a full understanding is to reveal how the machinery and processes of membrane trafficking through the early secretory pathway fail in disease states

Dynamic and structural investigation of interactions at the origin of the plasticization of a polymer matrix: the case of DMP-plasticized Cellulose Acetate

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Interactions underpinning the plasticization of a polymer matrix: a dynamic and structural analysis of DMP-plasticized cellulose acetate

International audienceThis work establishes that the plasticization effect of a classical petrochemical plasticizer, dimethyl phthalate (DMP), on a polymer matrix, cellulose acetate (CA), is due to the development of intermolecular interactions of dipolar type. Plasticized cellulose acetate films are studied with regard to the interactions between the polymer and plasticizer at the macroscopic scale by thermogravimetric analysis and differential scanning calorimetry. At the molecular level, Fourier transform infrared spectroscopy and dielectric relaxation spectroscopy are used to elucidate the nature of interactions that are responsible for the plasticizing effects. These static and dynamic complementary analyses evidenced that DMP does not establish H-bonding interactions with the polymer chains of cellulose acetate but rather weaker interactions of dipolar type. These dipole–dipole interactions that develop between acetyl side groups of CA and the ester phthalate moieties of DMP increase the overall mobility of CA chains and also locally influence the molecular mobility and the water uptake tendency

Solid State Amorphization of β-Trehalose: A Structural Investigation Using Synchrotron Powder Diffraction and PDF Analysis

International audienceWe have investigated the amorphization of β-trehalose by high energy milling using in situ and ex situ synchrotron powder diffraction and PDF analysis. From this analysis we show that amorphization takes place through a two-phase process involving an amorphous and a long-range ordered phase. The proportion and coherent domain size of the latter rapidly decrease with milling time until the whole sample appears amorphized. The PDF describing the local structure of the amorphous phase after two hours of milling is very close to that of a sample quenched from the liquid, and seems to continue to evolve for longer milling times. Their differences with the PDF expected for a rigid THL molecule confirm the existence of a conformational disorder of the torsion angles from the glycosidic linkage between the two cycles forming the molecule