Basic Aqueous Phase Research Articles

Facile Aqueous-Phase Synthesis of an Ultrasmall Bismuth Nanocatalyst for the Reduction of 4-Nitrophenol.

Bismuth metallic nanoparticles have evoked considerable interest in catalysis owing to their small size, high surface area-to-volume ratio, and low toxicity. However, the need for toxic reductants and organic solvents in their synthesis often limits their desirability for application development. Here, we describe a green strategy to synthesize bismuth nanodots via the redox reactions between bismuth nitrate and d-glucose, in the presence of poly(vinylpyrrolidone) in the basic aqueous phase. Both reagents play a crucial role in the formation of monodisperse bismuth nanodots acting as mild reducing and capping agents, respectively. We further demonstrate that the catalytic activity of these dots via the successful reduction of the environmental contaminant 4-nitrophenol to its useful 4-aminophenol analogue requiring only 36 μg/mL nanocatalyst for 20 mM of the substrate. Moreover, they can be recovered and recycled in multiple reactions before the onset of an appreciable loss of catalytic activity. The proposed facile synthetic route and inexpensive matrix materials lead the way to access bismuth nanodots for both the fundamental study of reactions and their industrial catalysis applications.

Interfacial generation of plates assembled with α-Fe2O3 nano-flakes for electrochemical capacitors

In this work, we report facile synthesis of two-dimensional plates formed by the assembly of iron oxide nano-flakes for application in electrochemical capacitors. The α-Fe2O3 nano-flakes plates were synthesized by an interfacial reaction and a subsequent thermal treatment without employing any template or matrix for the self-assembly. The flake size could be easily controlled by varying the duration for which the iron precursor (Fe(CO)5) underwent a reaction with the basic aqueous phase at the oil–water interface. The resulting plates were characterized by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FT-IR). The results indicated that the as-obtained materials were hematite (α-Fe2O3). The thickness and edge size of the nano-flakes were in the range of 30–50nm and 200–800nm, respectively. The electrochemical properties of α-Fe2O3 nano-flakes plates were systematically investigated by means of cyclic voltammetry (CV), galvanostatic charge/discharge cycling, and electrochemical impedance spectroscopy (EIS). The highest specific capacitance of 171Fg−1 was obtained for the NF-1 sample whose average flake size was 250nm and the thickness was 30nm. Capacitance retention of the NF-1 sample after 1000cycles was found to be 85% of the initial capacitance, indicating its good cycle stability.

One-step fabrication of agent-loaded biodegradable microspheroids for drug delivery and imaging applications

Non-spherical particles may offer advantages over conventional spherical systems for drug delivery applications. This work describes the fabrication of agent-loaded poly(lactic-co-glycolic acid) (PLGA) spheroids via the emulsion solvent evaporation (ESE) method. The versatility of this technique for loading a variety of therapeutics is demonstrated via loading of paclitaxel, bovine serum albumin, and cadmium sulfide nanoparticles into PLGA spheroids. The encapsulation efficiency for spheroids fabricated via oil-in-water (O/W) emulsions is highest at low aqueous phase surfactant concentrations while the encapsulation efficiency for spheroids made via water-in-oil-in-water (W/O/W) is highest at high aqueous phase surfactant concentrations and basic aqueous phase pH values. Particle aspect ratio polydispersity can be minimized via the use of high aqueous phase PVA concentration and pH. The ESE technique is an attractive alternative to recently described methods for fabrication of non-spherical particles due to its simplicity in setup, high particle yield and adaptability to a variety of biodegradable polymers and therapeutics.

Benzene Hydroxylation and Simultaneous Extraction of Phenol in Two Membrane Contactors Made with Three-Compartment Cells

Two different three-compartment membrane contactors [called solid membrane contactor (SMC) and liquid membrane contactor (LMC)] were tested in the synthesis and separation of phenol produced by direct hydroxylation of benzene using a Fenton reaction. Phenol produced in the aqueous reacting phase was extracted in the organic phase and simultaneously stripped in the basic aqueous phase. Preliminary tests on phenol recovery evidenced better performances (86.5% of phenol recovered in the strip phase) using the SMC with 0.1 M Na2SO4 in the aqueous feed phase at 35 °C. In the tests of partial oxidation, higher phenol productivity (0.62 gph gcat–1 h–1) was obtained in this last system because the high phenol flux away from the reacting phase permitted one to extract a high amount of phenol in the organic and aqueous (strip) phases. This extraction protected phenol by its subsequent oxidation. It was evidenced that the use of a third compartment containing an alkaline aqueous stripping phase permitted one to reco...

Fabrication of biodegradable spheroidal microparticles for drug delivery applications

Particle shape, in addition to size, is becoming increasingly recognized as important in the design of drug carriers for in vivo use. However, few methods exist for fabricating non-spherical particles from biodegradable polymers. This work describes for the first time the fabrication of biodegradable spheroidal microparticles using the simple oil-in-water emulsion solvent evaporation technique (O/W ESE). Unloaded and paclitaxel-loaded spheroids were fabricated from poly(lactic-co-glycolic acid) (PLGA), and the shape and size of fabricated spheroids were manipulated by controlling fabrication process parameters including stir speed, aqueous and oil phase viscosity, aqueous phase pH, and the polymer molecular weight and end group. The presented data show that high aqueous phase viscosity, basic aqueous phase pH and hydrophilic polymer side chains and end groups are all conditions that favor the formation of spheroidal particles. The described technique is advantageous over methods currently described in the literature in its simplicity in setup, high particle yield and adaptability to a wide range of biodegradable polymers and therapeutics.

A three-phase microfluidic chip for rapid sample clean-up of alkaloids from plant extracts

A three-phase microchip was developed for the rapid and efficient small-scale purification of alkaloids from plant extracts. As part of the development of such a three-phase microchip, first a two-phase microchip with two channels (3.2 cm and 9.3 cm) was used to study the extraction efficiency of strychnine nitrate and strychnine at various flow rates. Strychnine was extracted from a basic aqueous phase to a chloroform phase (extraction) or strychnine was extracted from a chloroform phase into an acidic aqueous phase (back extraction). Subsequently, the "simultaneous extraction and back extraction" of strychnine was carried out in a three-phase microchip. The experimental extraction rate and yield were compared with model data. At a residence time of 25 sec, 79.5% of strychnine was extracted into the acidic aqueous phase using the three-phase microchip. In general, a good correlation was found between experimental results and model data for both two- and three-phase extractions. Finally, the three-phase microchip was employed in the purification of alkaloids (strychnine and brucine) from Strychnos seed extracts.

Cation effect on anion separations by aza-crown ligands in liquid membranes

New carriers have been prepared based on the aza-18-crown-6 structure to facilitate membrane transport of ions. One of these incorporates four aza-18-crown-6 molecules bonded to a resorcinarene ring. The other, aza-18-crown-6 bonded to an undecyl chain, was studied as a monomeric analog. These carriers have been included in dichloromethane bulk liquid membranes (BLMs) to assess cation influence on competitive transport among anions (ReO 4 −, NO 3 −, ClO 4 −). ReO 4 − was investigated as a non-radioactive analog of the pertechnetate anion, which is of interest in nuclear waste separations. The permeability values and selectivity for ReO 4 − and ClO 4 − were the greatest when neutral source and receiving phases were used with K + as the co-transported cation. The carriers also showed selectivity for ReO 4 − and ClO 4 − over NO 3 − with K + and Na + as the co-transported cations using neutral and basic aqueous phase solutions. It was also found that some cations inhibit anion transport.

Cytosine substituted calix[4]pyrroles: neutral receptors for 5'-guanosine monophosphate.

The synthesis and characterization of two cytosine-substituted calix[4]pyrrole conjugates, bearing the appended cytosine attached at either a beta- or meso-pyrrolic position, is described. These systems were tested as nucleotide-selective carriers and as active components of nucleotide-sensing ion-selective electrodes at pH 6.6. Studies of carrier selectivity were made using a Pressman-type model membrane system consisting of an initial pH 6.0 aqueous phase, an intervening dichloromethane barrier containing the calix[4]pyrrole conjugate, and a receiving basic aqueous phase. Good selectivity for the Watson-Crick complementary nucleotide, 5'-guanosine monophosphate (5'-GMP), was seen in the case of the meso-linked conjugate with the relative rates of through-membrane transport being 7.7:4.1:1 for 5'-GMP, 5'-AMP, and 5'-CMP, respectively. By contrast, the beta-substituted conjugate, while showing a selectivity for 5'-GMP that was enhanced relative to unsubstituted calix[4]pyrrole, was found to transport 5'-CMP roughly 4.5 times more quickly than 5'-GMP. Higher selectivities were also found for 5'-CMP when both the beta- and meso-substituted conjugates were incorporated into polyvinyl chloride membranes and tested as ion selective electrodes at pH 6.6, whereas near-equal selectivities were observed for 5'-CMP and 5'-GMP in the case of unsubstituted calix[4]pyrroles. These seemingly disparate results are consistent with a picture wherein the meso-substituted cytosine calix[4]pyrrole conjugate, but not its beta-linked congener, is capable of acting as a ditopic receptor, binding concurrently both the phosphate anion and nucleobase portions of 5'-GMP to the calixpyrrole core and cytosine "tails" of the molecule, respectively, with the effect of this binding being most apparent under the conditions of the transport experiments.

Synthetic noncyclic ionophores with multiple carboxylate groups for alkaline earth metal cations

A series of synthetic ionophores containing two carboxylic acid groups were synthesized as carriers for alkaline earth metal cations. Among them, the lipophilic derivative having a trimenthylene bridge and multiple quinaldate moieties selectively transported barium ion from the basic aqueous phase to the acidic aqueous phase through the bulk dichloromethane liquid membrane. The cation selectivity was explained by considering the fit of the cation diameter with the pseudocyclic cavity.

Determination of phosphatidylcholine and disaturated phosphatidylcholine content in lung surfactant by high performance liquid chromatography.

A rapid isocratic method for determining the total phosphatidylcholine and disaturated phosphatidylcholine levels in lung surfactant preparations by high performance liquid chromatography (HPLC) is described. The analysis was performed on a 3.9 x 300 mm mu-Porasil column with detection by refractive index. The lipids were eluted with a solvent system of chloroform-acetonitrile-methanol-water-85% phosphoric acid 650:650:500:130:2 (v/v/v/v/v). A 4.6 x 30 mm silica guard column was used in place of an injector loop which served as a sample concentrator and purifier. Phosphatidylinositol, phosphatidylserine, phosphatidylethanolamine, and phosphatidylglycerol, all known components of lung surfactants, were eluted from the loop column and were prevented from reaching the analytical column. Sphingomyelin and lysophosphatidylcholine elute later than the phosphatidylcholines on the analytical column. The method was developed so that phosphatidylcholines elute as a single peak regardless of the fatty acid chain length (C12-C20). When the sample was first oxidized with a potassium permanganate-potassium metaperiodate solution, and potentially interfering oxidation products were removed by extraction into a basic aqueous phase, then only the disaturated phosphatidylcholines were analyzed.

Determination of Dimetridazole and Ipronidazole in Feeds at Cross-Contamination Levels

A rapid method for the determination of dimetridazole and ipronidazole in feeds is described. The compounds are extracted from a borate buffer (pH 8.65) with benzene, partitioned into 1N HCl, and then partitioned back into benzene from a basic aqueous phase. The benzene extract is concentrated and injected onto a nonpolar (Apiezon L) gas chromatographic column for determination by 63Ni electron-capture detection. Recoveries from feeds of various composition, spiked at 0.2 ppm with both dimetridazole and ipronidazole, ranged from 70 to 115%; for the same feeds spiked at 1 ppm or more, the recoveries were greater than 80%. Carbadox, furazolidone, levamisole, oxytetracycline, chlortetracycline, sulfamethazine, sulfaquinoxaline, arsanilic acid, piperazine, penicillin, and commonly added vitamins and minerals do not interfere. A 2-dimensional thin layer chromatographic system is presented as a means of additional identification.

Ion Selectivity of 14-Crown-4 Derivative Possessing Two Potential Anionic Sites on Extraction of Alkali and Alkaline-Earth Metal Ions

Abstract A lipophilic 14-crown-4 derivative bearing two dinitrophenol moieties was synthesized and its ion selectivity was elucidated on cation extraction from a basic aqueous phase into an organic phase. The crown ether derivative was found to possess preferences for Ca2+ and Sr2+ as well as Li+.

Brain tryptamine in rats by a new gas chromatography-mass fragmentographic method

A simplified assay for tryptamine (TRYP) by gas chromatographymass fragmentography (GC-MF) is described. TRYP was analyzed as its N-acetyl-1-trifluoroacetyl derivative. Acetylation of TRYP was carried out at basic pH using acetic anhydride dissolved in a diethyl ether vehicle. N-acetyl-TRYP was extracted into the diethyl ether from a basic aqueous phase during the acetylation reaction. TRYP-D 2 was employed as an internal standard. TRYP was quantitatively assayed in human urine and rat brain using multiple ion detection GC-MF. Assay sensitivities of 500 pg could be achieved by single ion and 5 ng by double ion GC-MF. In rats treated with pargyline and pargyline plus tryptophan, brain TRYP was found to be 35.6 ± 4.9 (mean ± SE) and 133 ± 3.8 ng/g, respectively. However, TRYP was not detected in normal rat brain at an assay sensitivity of 500 pg.