Mapping the Stability and Curvature of Emulsions of H2O and Supercritical CO2 with Interfacial Tension Measurements

The stability and curvature of emulsions of H₂O and CO₂ are reported and analyzed in terms of measurements of interfacial tension versus formulation variables, including salinity, CO₂ density, temperature and pH. Among the surfactants studied are, quaternary ammonium cationic ones with perfluoropolyether tails, block copolymer ionomers and a poly (hydroxyethyl methacrylate) with polydimethylsiloxane tails, and a nonionic ethylene oxide surfactant with a fluoroalkane tail. The interfacial tension measurements were made at surfactant concentrations from 0.05 to 1.0 wt% with a variable-volume pendant drop tensiometer up to 345 bar and 363°K. As a formulation variable was varied, the system reached a balanced state characterized by a minimum in interfacial tension, a loss in emulsion stability and in some cases an inversion from a W/C to C/W emulsion. Here the Marangoni-Gibbs stabilization weakens, and also it becomes easy to bend and rupture the surfactant monolayer, causing coalescence. Except in the case of the nonionic fluorinated surfactant C₈F₁₇—SO₂NEt-(CH₂CH₂O)_12–14CH₃, the crossover from the CO₂-continuous (W/C) to the H₂O-continuous (C/W) emulsion occurred abruptly due to clouding of the surfactant out of the CO₂ phase. For PFPE-TMAA, the plot of γ versus surfactant concentration revealed both pre-micellar aggregates and a critical micro emulsion, each of which was dependent on salinity.     

Interfacial Studies of the Formation of Microemulsions of Water in Carbon Dioxide with Fluorinated Surfactants

Measurements of the interfacial tension, γ, for water-CO₂-perfiuoropoly ether (PFPE) ionic surfactant systems are utilized to understand the surfactant affinity for the various phases and adsorption at the interface. A marked decrease in γ with salinity is observed as salt screens electrostatic repulsion and induces microemulsion formation, as confirmed with dynamic light scattering. In several cases, the interfacial tension goes through an unusual maximum with salinity, which is explained in terms of competition between surfactant affinity for the various phases and microemulsion formation. Fundamental studies of interfacial properties provide important insight for designing surfactants and experimental conditions to achieve the desired properties of water/CO² microemulsions and emulsions.     

A sort synthesis of polyhydroxylated pyrrolizidines via sequential 1,3-dipolar cycloaddition and reductive amination

Polyhydroxylated pyrrolizidines bearing a methyl group at C-5 have been synthesized by 1,3-dipolar cycloaddition of five membered cyclic nitrones with methyl vinyl ketone followed by a N–O reductive cleavage and in situ intramolecular reductive amination. The stereochemistry of the obtained compounds is examined in relation to the reactions mechanism.     

Chemical Characterization,Antioxidant and Antimicrobial Properties of Different Types of Tissue of Cedrus brevifolia Henry Extracts

This study aimed to determine the chemical composition of different types of tissue of Cedrus brevifolia Henry (Pinaceae) methanolic extracts, namely needles, twigs, branches, and bark. Cedrus brevifolia is a narrow endemic coniferous tree species of Cyprus, growing in a sole population in the mountainous area of Paphos Forest. Chemical analysis of the extracts was performed using liquid chromatography combined with time-of-flight high-resolution mass spectrometry (LC/Q-TOF/HRMS). The majority of the 36 compounds tentatively identified belonged to the flavonoids family. The extract of needles was the richest extract in terms of secondary metabolites. The extracts were studied for their antioxidant activity using the DPPH free radical scavenging assay. Additionally, the antibacterial activity was evaluated by determining both the minimum inhibitory concentration and the minimum bactericidal concentration against Staphylococcus aureus and Escherichia coli. All extracts demonstrated antioxidant property, while bark gave the highest antioxidant capacity (IC₅₀ value of 0.011 mg/mL) compared to the other tissues. Antibacterial activity was observed against both types of bacteria, with the extract of branches presenting the strongest activity against S. aureus (MIC, 0.097 mg/mL and MBC, 0.195 mg/mL). This is the first time that extracts of needles, twigs, branches, and bark of C. brevifolia are compared regarding their chemical composition as well as their antimicrobial and antioxidant properties.     

Visible-Light-Promoted Reaction of N-Hydroxyphthalimide Esters with Vinyl Boronic Pinacol Ester

A novel and easy-to-execute light-driven protocol for the preparation of alkyl boronic acid pinacol esters from vinyl boronate using N-hydroxyphthalimide esters as the potential precursor is described. In this photochemical protocol, the N-hydroxyphthalimide ester's fragmentation generates C-centered radicals, which undergo a radical Michael addition to vinyl boronic pinacol ester furnishing the desired products. A good substrate scope having various functionalities is presented and good to high yields are obtained.