Jamming transition in solutions containing organogelator molecules of amino-acid type: rheological and calorimetry experiments

International audienceThe liquid to organogel transition of solutions containing new organogelator molecules of the amino-acid type is studied using rheological and differential scanning calorimetry (DSC) techniques. This paper describes the formation of the organogel as a function of the temperature for various concentrations of the organogelator molecules, and the mechanical properties of the organogel as a function of concentration, frequency, thermal history and aging. We show that the organogel is not a physical gel, but a jammed suspension. The viscoelastic behavior at different extents of the jamming can be scaled onto a single master curve describing the growth of a solid network in a background fluid. The formation of the solid network exhibits a critical-like behavior that is reminiscent of elasticity percolation. Four characteristic temperatures have been identified: the temperature at which the clusters begin to form, the transition temperature between the liquid and the organogel, the onset temperature of the percolation-like behavior of the solid component of the system and the temperature at which the solid component has a pure elastic response. The comparison between the rheological measurements and the DSC measurements shows that the rheological measurements detect the fluid-to-organogel transition, whereas DSC detects the molecular associations in the material, which are at the origin of the formation of the clusters. The two temperatures differ significantly from each other and their difference gives the temperature range where the clusters are crowding. This study demonstrates for the first time that an organogel is not a physical gel, as it is currently believed, but a jammed suspension

Monitoring the architecture of anionic kappa-carrageenan/cationic glycine betaine amide surfactant assemblies by dilution: A multiscale approach

International audienceThe interaction between glycine betaine-based cationic surfactant and algal polysaccharide kappa-carrageenan was studied by investigating the dilution effect of the surfactant/polymer assemblies driven by electrostatic interactions. Two aqueous solutions of cationic surfactant and kappa-carrageenan at two molar ratios (3.5 and 0.8) diluted with factors of 5 and 10 times, were tested by various analytical methods including a multiscale observation by Transmission Electron Microscopy (TEM) and Laser Scanning Confocal Microscopy (LSCM) to understand the solution behavior of surfactant and oppositely charged polymer at both nano- and micrometer scale. Raman spectroscopy as well as confocal Raman imaging were applied to give Supplementary information about the surfactant/polysaccharide interactions and the distribution of assemblies. These analyses confirmed the formation of singular hybrid surfactant/polymer nano-, microobjects and they revealed the influence of dilution on the nanostructures. These results give an insight of the mechanism of the dilution effect on surfactant/polymer assemblies that could be valuable in pharmaceutical formulations, food and cosmetics fields. (C) 2016 Elsevier Ltd. All rights reserved

Phase I Study Assessing the Pharmacokinetic Profile, Safety, and Tolerability of a Single Dose of Ceftazidime-Avibactam in Hospitalized Pediatric Patients

This study aimed to investigate the pharmacokinetics (PK), safety, and tolerability of a single dose of ceftazidime-avibactam in pediatric patients. A phase I, multicenter, open-label PK study was conducted in pediatric patients hospitalized with an infection and receiving systemic antibiotic therapy. Patients were enrolled into four age cohorts (cohort 1, ≥12 to <18 years; cohort 2, ≥6 to <12 years; cohort 3, ≥2 to <6 years; cohort 4, ≥3 months to <2 years). Patients received a single 2-h intravenous infusion of ceftazidime-avibactam (cohort 1, 2,000 to 500 mg; cohort 2, 2,000 to 500 mg [≥40 kg] or 50 to 12.5 mg/kg [<40 kg]; cohorts 3 and 4, 50 to 12.5 mg/kg). Blood samples were collected to describe individual PK characteristics for ceftazidime and avibactam. Population PK modeling was used to describe characteristics of ceftazidime and avibactam PK across all age groups. Safety and tolerability were assessed. Thirty-two patients received study drug. Mean plasma concentration-time curves, geometric mean maximum concentration (C(max)), and area under the concentration-time curve from time zero to infinity (AUC(0–∞)) were similar across all cohorts for both drugs. Six patients (18.8%) reported an adverse event, all mild or moderate in intensity. No deaths or serious adverse events occurred. The single-dose PK of ceftazidime and avibactam were comparable between each of the 4 age cohorts investigated and were broadly similar to those previously observed in adults. No new safety concerns were identified. (This study has been registered at ClinicalTrials.gov under registration no. NCT01893346.