Bentonite-Based Organoclays as Innovative Flame Retardants Agents for SBS Copolymer

Two organophilic bentonites, based on nitrogen-containing compounds, have been synthesised via ion exchange starting from pristine bentonite with octadecyltrimethylammonium bromide (OTAB) and with synthetic melamine-derived N2,N4-dihexadecyl-1,3,5-triazine-2,4,6-triamine (DEDMEL). The chemical and morphological characterization of the organoclays was based on XRD, TEM, Laser Granulometry, X-Ray Fluorescence and CEC capacity. Copoly(styrene-butadiene-styrene)-nanocomposites (SBS-nanocomposites) were obtained by intercalation of the SBS-copolymer into these new organoclays by melt intercalation method. XRD and TEM analysis of the organoclays and of the micro/nano-composites obtained are presented. The effect of the organoclays on the SBS-nanocomposite's flammability properties was investigated using cone calorimeter. An encouraging decrease of 20% in the peak heat released rate (PHRR) has been obtained confirming the important role of melamine's based skeleton and its derived organoclays to act as effective fire retardants and for the improvement of this important functional property in SBS copolymers.

Structural determinants and significance of regulation of electrogenic Na+-HCO 3 − cotransporter stoichiometry

Na+-HCO[Formula: see text]cotransporters play an important role in intracellular pH regulation and transepithelial HCO[Formula: see text] transport in various tissues. Of the characterized members of the HCO[Formula: see text]transporter superfamily, NBC1 and NBC4 proteins are known to be electrogenic. An important functional property of electrogenic Na+-HCO[Formula: see text] cotransporters is their HCO[Formula: see text]:Na+ coupling ratio, which sets the transporter reversal potential and determines the direction of Na+-HCO[Formula: see text] flux. Recent studies have shown that the HCO[Formula: see text]:Na+ transport stoichiometry of NBC1 proteins is either 2:1 or 3:1 depending on the cell type in which the transporters are expressed, indicating that the HCO[Formula: see text]:Na+ coupling ratio can be regulated. Mutational analysis has been very helpful in revealing the molecular mechanisms and signaling pathways that modulate the coupling ratio. These studies have demonstrated that PKA-dependent phosphorylation of the COOH terminus of NBC1 proteins alters the transport stoichiometry. This cAMP-dependent signaling pathway provides HCO[Formula: see text]-transporting epithelia with an efficient mechanism for modulating the direction of Na+-HCO[Formula: see text] flux through the cotransporter.

Thermal gelation and denaturation of bovine β-lactoglobulins A and B

SummaryHeat-induced gelation, an important functional property of β-lactoglobulin, was studied by measuring the rheological properties of both the A and B variants of the protein during and after heat treatment within a range of pH, temperature and concentration. Gel electrophoresis was used to determine the extent of denaturation and disulphide bond crosslinking of some samples. Both variants formed gel networks on heating at temperatures > 75 °C, and under most conditions the storage modulus (G′) of βlactoglobulin A gels was higher than the G′ of β-lactoglobulin B gels, in particular after cooling to 25 °C. A minimum protein concentration of 50 g/1 was required for gel formation at pH 7·0 in 0·1 M-NaCl by both variants at 80 °C. Increasing the protein concentration above 50 g/1 increased G′, the extent of increase being much greater for the A variant than the B variant. G′ of variant A gels was not much influenced by pH whereas G′ of variant B gels decreased slightly from pH 3 to pH 6 and increased between pH 6 and pH 9. When mixtures of the two variants were gelled G′ increased at the temperature of heating (80 °C) and after cooling (25 °C) as the relative quantity of variant A was increased. Comparisons of the loss of discrete protein bands from electrophoretic gels (native-PAGE, SDS-PAGE and SDS-PAGE of reduced samples) showed that heating β-lactoglobulin solutions of 100 g/1 at pH 7 in 0·1 M-NaCl and at 75, 80 and 85 °C caused a faster loss of both native and SDS-soluble β-lactoglobulin A than of β-lactoglobulin B. It was concluded that the loss of native β-lactoglobulin structure from these solutions during heating was faster than the formation of disulphidelinked aggregates, which was faster than gel formation for both β-lactoglobulin A and β-lactoglobulin B, and that each of these reactions was faster for β-lactoglobulin A than for β-lactoglobulin B. This contrasts with conclusions drawn from some previous studies and may arise from the differences in protein concentration between the present study (∼ 100 g/1) and the previous ones (< ∼ 10 g/1).

Increased sulphation improves the anticoagulant activities of heparan sulphate and dermatan sulphate

Heparan sulphate and dermatan sulphate have both antithrombotic and anticoagulant properties. These are, however, significantly weaker than those of a comparable amount of standard pig mucosal heparin. Antithrombotic and anticoagulant effects of glycosaminoglycans depend on their ability to catalyse the inhibition of thrombin and/or to inhibit the activation of prothrombin. Since heparan sulphate and dermatan sulphate are less sulphated than unfractionated heparin, we investigated whether the decreased sulphation contributes to the lower antithrombotic and anticoagulant activities compared with standard heparin. To do this, we compared the anticoagulant activities of heparan sulphate and dermatan sulphate with those of their derivatives resulphated in vitro. The ratio of sulphate to carboxylate in these resulphated heparan sulphate and dermatan sulphate derivatives was approximately twice that of the parent compounds and similar to that of standard heparin. Anticoagulant effects were assessed by determining (a) the catalytic effects of each glycosaminoglycan on the inhibition of thrombin added to plasma, and (b) the ability of each glycosaminoglycan to inhibit the activation of 125I-prothrombin in plasma. The least sulphated glycosaminoglycans were least able to catalyse the inhibition of thrombin added to plasma and to inhibit the activation of prothrombin. Furthermore, increasing the degree of sulphation improved the catalytic effects of glycosaminoglycans on the inhibition of thrombin by heparin cofactor II in plasma. The degree of sulphation therefore appears to be an important functional property that contributes significantly to the anticoagulant effects of the two glycosaminoglycans.