Search results for "Propylene carbonate"
showing 10 items of 19 documents
Electrochemical reduction of graphene oxide films in aqueous and organic solutions
2013
Abstract Electrochemical reduction of graphene oxide (GO) films cast on tin oxide glass substrates were carried out in aqueous solutions and in propylene carbonate and acetonitrile. Cyclic voltammetric measurements indicate successful reduction of GO films. The reduction process begins in aqueous solutions at less negative potentials than in organic solutions. Additionally the pH value of the aqueous solutions influences the reduction potential. According to spectroscopic analysis the reduction process of the GO film can be controlled by the choice of reduction potential and electrolyte medium. The potential window in this work was made broader by increasing pH or by using organic electroly…
Efficient electroorganic synthesis of 2,3,6,7,10,11-hexahydroxytriphenylene derivatives
2012
2,3,6,7,10,11-Hexahydroxytriphenylene of good quality and purity can be obtained via anodic treatment of catechol ketals and subsequent acidic hydrolysis. The electrolysis is conducted in propylene carbonate circumventing toxic and expensive acetonitrile. The protocol is simple to perform and superior to other chemical or electrochemical methods. The key of the method is based on the low solubility of the anodically trimerized product. The shift of potentials is supported by cyclic voltammetry studies.
Asymmetric Hydrogenation of Nonfunctionalized Olefins in Propylene Carbonate—Kinetic or Thermodynamic Control?
2011
Iridium-catalyzed hydrogenations of nonfunctionalized olefins in propylene carbonate as the solvent allow efficient catalysis with much higher enantioselectivities in comparison with dichloromethane which is usually employed for these reactions. Experimental and computational studies of the hydrogenation of 1-methylene-1,2,3,4-tetrahydronaphthalene have been performed to understand the limitation for this reaction.
Predictability of drug encapsulation and release from propylene carbonate/PLGA microparticles.
2020
Abstract Key parameters for microparticle-based parenteral depot formulation development are entrapment efficiency and sustained drug release, which both depend on the intermolecular affinity of the components. Here, partial solubility parameters were evaluated as descriptors for 21 drug substances and 3 polymers in propylene carbonate (PC). Out of these 21 drug substances, eight BCS class II substances (celecoxib, clotrimazole, erythromycin, ibuprofen, indomethacin, itraconazole, lopinavir and ritonavir) were encapsulated using PLGA (Poly(DL-lactide-co-glycolide)) as polymer matrix and PC as a polar aprotic solvent in order to assign microparticle properties to potential affinity-related i…
Microparticle preparation by a propylene carbonate emulsification-extraction method
2018
Abstract The use of various harmful organic solvents for microparticle formulations is still widespread. Here, an alternative low toxicity solvent (propylene carbonate; PC) is proposed for the preparation of poly(lactic-co-glycolic-acid) (PLGA) microparticles. Based on the classical emulsification-solvent extraction methodology, the use of PC offers the unique advantage of an additional solvent extraction step using hydrolytic solvent cleavage during microparticle preparation. Spherical, rough-surfaced microparticles were obtained with a volume median diameter range from 20 to 60 µm. The residual PC content has been identified to be the major factor for the solidification hindrance, leading…
Slow and fast methyl group rotations in fragile glass-formers studied by NMR
2000
Abstract The spin-lattice relaxation times of the selectively ring deuterated, fragile glass-formers propylene carbonate and toluene were compared with those measured for species which were specifically labeled at the methyl groups. It was found that the dynamics of the CD 3 group is strongly decoupled from that associated with the primary response of toluene, while for propylene carbonate the degree of decoupling is relatively weak. The experimental results could be described successfully using a model which takes into account the ring dynamics as well as those of the methyl group.
Pegylated nanoparticles based on a polyaspartamide. Preparation, physico-chemical characterization and intracellular uptake
2006
Nanoparticles with different surface PEGylation degree were prepared by using as starting material alpha,beta-poly(N-2-hydroxyethyl)-d,l-aspartamide (PHEA). PHEA was functionalized with a PEG amino-derivative for obtaining PHEA-PEG(2000) copolymer. Both PHEA and PHEA-PEG(2000) were derivatized with methacrylic anhydride (MA) for obtaining poly(hydroxyethylaspartamide methacrylated) (PHM) and poly(hydroxyethylaspartamide methacrylated)-PEGylated (PHM-PEG(2000)), respectively. Nanoparticles were obtained by UV irradiation of an inverse microemulsion, using as internal phase an aqueous solution of PHM alone or of the PHM/PHM-PEG(2000) mixture at different weight ratio and as external phase a m…
Ionic conduction through single-pore and multipore polymer membranes in aprotic organic electrolytes
2021
Abstract We experimentally characterize the ionic conduction of single and multipore nanoporous membranes in aprotic organic electrolytes. To this end, soft-etched (SE) membranes with pore diameters in the nanometer range and track-etched (TE) membranes with pore diameters in the tens of nanometers range are investigated. In aqueous conditions, the membrane ionic conduction rates follow the same trend of the bulk solution conductivities. However, the ionic transport through the narrow SE-nanopores dramatically decreases in aprotic electrolytes due to the formation of solvated metal cations and their adsorption on the pore surface. The current-voltage recordings of single conical nanopores i…
Process parameters of microsphere preparation based on propylene carbonate emulsion-precursors.
2020
This study aimed for a detailed understanding of the impact of different process parameters involved during celecoxib-loaded microsphere preparation based on propylene carbonate emulsion-precursors.Microspheres were prepared by a modified emulsification-solvent extraction method. Performed investigations included polymer solubility and viscosity, microsphere size, morphology and stability, propylene carbonate content as well as celecoxib solid state, content and release.Rough-walled round microspheres with sizes between 21 µm and 122 µm and an internal sponge-like structure filled with residual propylene carbonate (content between 1.9 ± 0.1% and 6.7 ± 0.5% w/w) were obtained. Encapsulation …
Nonresonant Spectral Hole Burning in the Slow Dielectric Response of Supercooled Liquids
1996
Large-amplitude, low-frequency electric fields can be used to burn spectral holes in the dielectric response of supercooled propylene carbonate and glycerol. This ability to selectively modify the dielectric response establishes that the non-Debye behavior results from a distribution of relaxation times. Refilling of the spectral hole was consistent with a single recovery time that coincided with the peak in the distribution. Moreover, refilling occurred without significant broadening, which indicates negligible direct exchange between the degrees of freedom that responded to the field. Nonresonant spectral hole burning facilitates direct investigation of the intrinsic response of systems t…