TRANSFER MECHANISM OF QUININE DRUG ACROSS THE OIL/WATER (O/W) INTERFACE

The transfer phenomena of quinine drug at the aqueous 1,2- dichloroethane (DCE)interface have been studied by the current- scanning polarography. The relationships be-tween the wave height and pH of aqueous phase, concentration of quinine as well as therate of water drop are discussed. The effect of supporting electrolyte, buffer solution andthe nature of organic solvent on the polarographic wave is studied. The transfer char-acteristics of quinine in aqueous phase and in organic phase are compared, The mono- pro-tonated and diprotonated quinines can both transfer at the interface so as to produce twopolarographic waves. The transfer process of quinine at the interface is simultaneouslycontrolled by diffusion and reestablishment of the disturbed protonated equilibrium ofquinine. A further investigation is made by chronopotentiometry. On the basis of thetheoretical analysis, the formulae of the limiting current are derived and discussed. Thetheoretical results are in agreement with the experimental ones.     

Electrochemical study of insulin at the polarized liquid-liquid interface

This paper reports on the electrochemical behavior of bovine insulin at the interface between two immiscible electrolyte solutions (ITIES). The voltammetric ion-transfer response obtained in the presence of insulin was dependent on the aqueous phase pH conditions and on the nature of the organic phase electrolyte employed in experiments. Optimal detection was obtained at acidic pH below the isoelectric point of insulin where it was positively charged. A shift in transfer potentials to lower potential values was observed with decreasing hydrophobicity of the anion of the organic phase electrolyte. No ion-transfer response was observed at pH values of the aqueous phase above the isoelectric point, where insulin was negatively charged. These results suggest that the voltammetric response is due to ion-pairing interactions at the ITIES between positively charged insulin and the hydrophobic anion of the organic phase electrolyte, together with adsorption of the ion-pair at the interface. The voltammetric response was obtained for insulin at concentrations down to 1 muM. These results show that electrochemistry is useful in studying the behavior of this important protein molecule at the polarized water-1,2-DCE interface and provides an alternative detection mode for bioanalytical applications.     

Ion Transport Across Liquid|Liquid Interfacial Boundaries Monitored at Generator‐Collector Electrodes

Anion transfer processes at a liquid|liquid interface were studied with an interdigitated gold band array electrode. The organic phase, 4‐(3‐phenylpropyl)‐pyridine containing Co(II)phthalocyanine, was immobilised as random droplets at the electrode surface and then immersed into aqueous electrolyte. Oxidation of Co(II)phthalocyanine at the generator electrode was shown to be associated with anion transfer from the aqueous into the organic phase. The corresponding back reduction at the collector electrode with anion expulsion was delayed by the anion/cation diffusion time across the interelectrode gap. A working curve based on a finite difference numerical simulation model was employed to estimate the apparent diffusion coefficients for anions in the organic phase (PF₆^?4^?3^?). Potential applications in ion analysis are discussed.     

Graphene Oxide Nanosheets at the Water–Organic Solvent Interface: Utilization in One‐Pot Adsorption and Reactive Extraction of Dye Molecules

Graphene oxide (GO) is amphiphilic in nature, due to its structure, which consists of hydrophilic oxygen‐containing functional groups and a hydrophobic basal plane of polyaromatic benzene rings. Due to this amphiphilicity, GO can create stable bubbles at water–organic solvent interfaces. In this study, the formation of bubbles at aqueous–organic interfaces in the presence of GO is investigated with different organic solvents. Bubble formation and transfer of GO from water to the organic phase is more prominent in aromatic solvents compared to aliphatic solvents, due to π–π interactions. Maximum transfer of GO from the aqueous to the organic phase is achieved at pH 2, and decreases with rising pH of the aqueous phase. Based on this property, and the ability of GO to adsorb cationic and anionic dye molecules, its application as a carrier for reactive extraction of cationic and anionic dye molecules is explored in toluene, kerosene, and carbon tetrachloride at pH 2 and 25 °C. The kinetics of the adsorption of the dyes onto GO nanosheets that takes place in the aqueous phase is also evaluated with different models, and a pseudo‐second‐order (linear) model is found to be the best fit. The adsorption isotherm data are also analyzed with different isotherm models. The electrostatic interaction and π–π interaction between the dye molecules and GO nanosheets leads to dye extraction of up to 98.2 % using this technique. The dye extraction is maximum in toluene and at low dye concentration.     

Application of sucrose fatty acid ester to reverse micellar extraction of lysozyme

Reverse micellar extraction of lysozyme has been carried out using an organic solution containing a mixture of monoester and polyester of sucrose fatty acid ester. The forward extraction of lysozyme from the feed aqueous phase to the reverse micellar organic phase of the mixture of monoester and polyester of sucrose fatty acid ester at pH 7.2 was strongly dependent upon the weight fraction of monoester, while any amount of lysozyme was not extracted only by using monoester or polyester. The forward extraction ratio dramatically increased with an increase in the concentration of fatty acid ester, and was high around neutral pH and at low ionic strength. The backward extraction of lysozyme from the reverse micellar organic phase to the recovery aqueous phase exhibited high efficiency at acidic pH value or at high ionic strength. The addition of sucrose into the recovery aqueous phase promoted the backward extraction ratio, and caused the activity of lysozyme recovered from the reverse micellar phase to be retained perfectly.     

Description of the Effects of Non‐ion‐exchange Extraction and Intra‐membrane Interactions on the Ion‐selective Electrodes Response within the Interface Equilibria‐triggered Model

The recently proposed interface equilibria‐triggered dynamic diffusion model of the boundary potential has proven its high predictive efficiency for quantification of the ion exchange and co‐extraction effects at the interface, as well as of the trans‐membrane transfer effect, on the electrode response. It is applicable for both ion exchanger‐based and neutral carrier‐based electrodes. In this communication, the adaptability of this model to more complex cases, when non‐ion‐exchange extraction processes at the interface (partition of organic acids’ and bases’ molecular forms and extraction of ionic associates) are coupled with protolytic equilibria in the aqueous phase and with self‐solvation process in the membrane phase, is demonstrated. By the example of electrodes reversible to ions of highly lipophilic physiologically active bases and acids (amiodarone, verapamil, vinpocetine, salicylic acid), it is shown that the peculiarities of their functioning, such as a very strong pH effect on the potential of cation‐selective electrodes, non‐monotonic pH dependence of the potential and super‐Nernstian response slope in certain pH region for a salicylate‐selective electrode, are well described within the model.     

Diffusion‐Regulated Phase‐Transfer Catalysis for Atom Transfer Radical Polymerization of Methyl Methacrylate in an Aqueous/Organic Biphasic System

A concept based on diffusion‐regulated phase‐transfer catalysis (DRPTC) in an aqueous‐organic biphasic system with copper‐mediated initiators for continuous activator regeneration is successfully developed for atom transfer radical polymerization (ICAR ATRP) (termed DRPTC‐based ICAR ATRP here), using methyl methacrylate (MMA) as a model monomer, ethyl α‐bromophenylacetate (EBrPA) as an initiator, and tris(2‐pyridylmethyl)amine (TPMA) as a ligand. In this system, the monomer and initiating species in toluene (organic phase) and the catalyst complexes in water (aqueous phase) are simply mixed under stirring at room temperature. The trace catalyst complexes transfer into the organic phase via diffusion to trigger ICAR ATRP of MMA with ppm level catalyst content once the system is heated to the polymerization temperature (75 °C). It is found that well‐defined PMMA with controlled molecular weights and narrow molecular weight distributions can be obtained easily. Furthermore, the polymerization can be conducted in the presence of limited amounts of air without using tedious degassed procedures. After cooling to room temperature, the upper organic phase is decanted and the lower aqueous phase is reused for another 10 recycling turnovers with ultra low loss of catalyst and ligand loading. At the same time, all the recycled catalyst complexes retain nearly perfect catalytic activity and controllability, indicating a facile and economical strategy for catalyst removal and recycling.

     

Kinetic study of chitosan‐tripolyphosphate complex reaction and acid‐resistive properties of the chitosan‐tripolyphosphate gel beads prepared by in‐liquid curing method

Chitosan gel beads were prepared using an in‐liquid curing method by the ionotropic crosslinking with sodium tripolyphosphate. Crosslinking characteristics of the chitosan‐TPP beads were improved by the modification of in‐liquid curing mechanism of the beads in TPP solution. Chitosan gel beads cured in pH value lower than 6 were really ionic‐crosslinking controlled, whereas chitosan gel beads cured in pH values higher than 7 were coacervation‐phase inversion controlled accompanied with slightly ionic‐crosslinking dependence. According to the result, significantly increasing the ionic‐crosslinking density of chitosan beads could be achieved by transferring the pH value of the curing agent, TPP, from basic to acidic. The swelling behavior of various chitosan beads in acid appeared to depend on the ionic‐crosslinking density of the chitosan‐TPP beads that were deeply affected by the curing mechanism of the beads. The mechanism of chitosan‐TPP beads swollen in weak acid was chain‐relaxation controlled, while the mechanism of chitosan‐TPP beads swollen in strong acid seem to be not only chain‐relaxation but also chain‐scission controlled. Chitosan‐TPP beads prepared in acidic TPP solution decreased the chain‐scission ability due to the increase of ionic crosslinking density of the beads. By the transition of curing mechanism, the swelling degree of chitosan‐TPP beads was depressed, and the disintegration of chitosan‐TPP beads would not occur in strong acid. The mechanism of ionic‐crosslinking reaction of chitosan beads could be investigated by an unreacted core model, and the curing mechanism of the chitosan beads is mainly diffusion controlled when higher than 5% of chitosan was employed. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1551–1564, 1999     

Synthesis of di‐ and tri‐tertiary amine containing methacrylic monomers and their (co)polymerization via RAFT

The synthesis, reversible addition‐fragmentation chain transfer (RAFT) (co)polymerization, and aqueous phase behavior of three methacrylic monomers containing two or three pendent tertiary amine functional groups are described. Homopolymerizations were conducted with 1‐methyl‐1‐cyanoethyl dithiobenzoate (CPDB) under bulk conditions following standard RAFT procedures. All three monomers, 1,3‐bis(dimethylamino)propan‐2‐yl methacrylate ( M1 ), 1‐(bis(3‐(dimethylamino)propyl) amino)propan‐2‐yl methacrylate ( M2 ), and 2‐((2‐(2‐(dimethylamino)ethoxy)ethyl) methylamino)ethyl acrylate ( M3 ), polymerized in a controlled manner as evidenced by the kinetic and molecular weight profiles. Homopolymerizations conducted at a lower ratio of CPDB:AIBN proceeded faster than those at a higher ratio. Subsequently, the facile copolymerization behavior of M1 and M3 was demonstrated via the synthesis of a range of statistical copolymers with hexyl and lauryl methacrylate comonomers containing 10–90 mol % hydrophobic comonomer. Finally, the aqueous‐solution characteristics of the M1 – M3 homopolymers were briefly examined. All three homopolymers were shown to undergo phase transitions in aqueous media in response to changes in both temperature and pH. Specifically, 1 wt % solutions of poly M1 were shown to possess an LCST of ～22 °C, that of poly M2 at ～33 °C, and for poly M3 the observed cloud point was ～63 °C. Additionally, all homopolymers became hydrophobic and phase separated at high solution pH. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1877–1890, 2009     

The phase transfer mechanism of 18-molybdophosphate anion at the water/nitrobenzene interface

The phase transfer mechanism of 18-molybdophosphate anion at the water/nitrobenzene interface has been investigated by chronopotentiometry with cyclic linear current-scanning (CLC) and cyclic voltammetry (CV). The transfer species is 18-molybdophosphtae anion with a charge number of 4, H₂[P₂Mo₁₈O₆₂]^4-. The transfer process is controlled by diffusion at a slow polarization rate and considerably influenced by pH of the aqueous phase. The stable forms and pH range of the heteropoly anion in the aqueous solution can be directly confirmed through voltammetric behavior. The theoretical analysis of the relationship between the transfer potential and solution pH is identical to the experimental results. The linear concentration relationship with the transfer peak current is suggested to be used in the determination of heteropoly acids (salts).     

Electrochemical Study of s‐Triazine Herbicides Transfer Across the Water/1,2‐Dichloroethane Interface

The transfer of three s‐triazine herbicides, atrazine (ATR), propazine (PRO) and prometrine (PROM), across the water/1,2‐dichloroethane interface was investigated using cyclic voltammetry. A facilitated proton transfer mechanism from the aqueous to organic phase is demonstrated by the analysis of positive peak potential and peak current as a function of pH. It is shown that the determination of 2.5×10^?5 M – 5×10^?4 M concentration of herbicides in aqueous phase may be possible under the experimental conditions employed.     

Multifunctional Core‐Shell‐Corona‐Type Polymeric Micelles for Anticancer Drug‐Delivery and Imaging

We have developed core‐shell‐corona‐type polymeric micelles that can integrate multiple functions in one system, including the capability of accommodating hydrophobic dyes into core and hydrophilic drug into the shell, as well as pH‐triggered drug‐release. The neutral and hydrophilic corona sterically stabilizes the multifunctional polymeric micelles in aqueous solution. The mineralization of calcium phosphate (CaP) on the PAA domain not only enhances the diagnostic efficacy of organic dyes, but also works as a diffusion barrier for the controlled release.     

Structural modifications of dicationic acetylcholinesterase reactivators studied under ion‐pairing mechanism in reversed‐phase liquid chromatography

A study focused on the chromatographic behavior of several acetylcholinesterase reactivators under ion‐pairing mechanism is reported. Among these reactivators, dicationic oximes and carbamoyl‐based pyridinium congeners were studied, which form ion pairs with alkylsulfonate anions. This mechanism was studied for some major experimental parameters, such as the chain length of the ion‐pairing agent added to the aqueous phase, its concentration, temperature, and nature of the organic modifier from mobile phase. Retention data showed one or two possibilities of forming ion pairs and the tautomerism of the studied reactivators, for different pH values of the aqueous component. Double sigmoid shapes were obtained for the studied compounds for the dependence between retention factor and pH, indicating the possibility of one or two tautomeric equilibria: at pH close to 7 these compounds are not stable as dicationic species and they participate in the retention process as nitroso forms, which are not able to form ion pairs with alkylsulfonates. The dependences of the retention factor on the organic modifier content from mobile phase were linear. Two complementary theoretical models were used to explain the functional dependences for the retention data on the experimental parameters.     

Histidine‐modified organic‐silica hybrid monolithic column for mixed‐mode per aqueous and ion‐exchange capillary electrochromatography

A novel organic‐silica hybrid monolith was prepared through the binding of histidine onto the surface of monolithic matrix for mixed‐mode per aqueous and ion‐exchange capillary electrochromatography. The imidazolium and amino groups on the surface of the monolithic stationary phase were used to generate an anodic electro‐osmotic flow as well as to provide electrostatic interaction sites for the charged compounds at low pH. Typical per aqueous chromatographic behavior was observed in water‐rich mobile phases. Various polar and hydrophilic analytes were selected to evaluate the characteristics and chromatographic performance of the obtained monolith. Under per aqueous conditions, the mixed‐mode mechanism of hydrophobic and ion‐exchange interactions was observed and the resultant monolithic column proved to be very versatile for the efficient separations of these polar and hydrophilic compounds (including amides, nucleosides and nucleotide bases, benzoic acid derivatives, and amino acids) in highly aqueous mobile phases. The successful applications suggested that the histidine‐modified organic‐silica hybrid monolithic column could offer a wide range of retention behaviors and flexible selectivities toward polar and hydrophilic compounds.     

Electrocatalytic Determination of Sulfite at Immobilized Microdroplet Liquid|Liquid Interfaces: The EIC′ Mechanism

Liquid|liquid interfaces provide a natural boundary and a reactive interface where an organic phase is in contact with an aqueous analyte. The selectivity of ion transfer processes at liquid|liquid interfaces can help to provide sensitivity, introduce reactive reagents, or allow analyte accumulation at the electrode surface. In this study, microdroplet deposits of the organic liquid 4‐(3‐phenylpropyl)‐pyridine (PPP) with the ferrocenylmethyl‐dodecyldimethylammonium⁺ (FDA⁺) redox system are deposited onto a basal plane pyrolytic graphite electrode and employed to transfer anions from the aqueous into the organic phase. A clear trend of more hydrophobic anions transferring more readily (at more negative potentials) is observed and an ESI‐mass spectrometry method is developed to confirm the transfer. Subsequently, the electrocatalytic oxidation of sulfite, SO₃^2?, within the organic phase and in the presence of different electrolyte anions is investigated. Competition between sulfite transfer and inert anion transfer occurs. The electrocatalytic sulfite oxidation is suppressed in the presence of PF₆^? and occurs most readily in the presence of the hydrophilic nitrate anion. The resulting process can be classified as an electrocatalytic EIC′‐process (E: electron transfer; I: ion transfer; C: chemical reaction step). The effectiveness of the electrocatalytic process is limited by i) competition during anion transfer and ii) the liquid|liquid interface acting as a diffusion barrier. The analytical sensitivity of the method is limited to ca. 100 μM SO₃^2? (or ca. 8 ppm) and potential approaches for improvement of this limit are discussed.     

Star‐shaped polypeptide/glycopolymer biohybrids: Synthesis,self‐assembly,biomolecular recognition,and controlled drug release behavior

Star‐shaped polypeptide/glycopolymer biohybrids composed of poly(γ‐ benzyl L ‐glutamate) and poly(D ‐gluconamidoethyl methacrylate), exhibiting controlled molecular weights and low polydispersities, were synthesized by the combination of ring‐opening polymerization of γ‐benzyl‐L ‐glutamate N‐carboxyanhydride and the direct atom transfer radical polymerization of unprotected D ‐gluconamidoethyl methacrylate glycomonomer. These biohybrids were characterized in detail by means of FTIR, ¹H NMR, gel permeation chromatography, differential scanning calorimetry, and wide angle X‐ray diffraction. Independent of weight fraction of hydrophilic glycopolymer segment, the biohybrids self‐assembled into large spherical micelles in aqueous solution, which had a helical polypeptide core surrounded by a multivalent glycopolymer shell. The deprotected poly(L ‐glutamate)/glycopolymer hybrid exhibited a pH‐sensitive self‐assembly behavior, and the average size of the nanoparticles decreased gradually over the aqueous pH value. Moreover, whatever these biohybrids existed in unimolecular level or glycopolymer‐surfaced nanoparticles, they had specific biomolecular recognition with Concanavalin A compared with bovine serum albumin. Furthermore, star‐shaped biohybrids showed a higher doxorubicin loading efficiency and longer drug‐release time than linear analogues. This potentially provides a platform for fabricating targeted anticancer drug delivery system and studying glycoprotein functions in vitro. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2009–2023, 2009     

Kinetische Betrachtung der Verteilung von elektrisch neutralen Ionophoren zwischen einer Flüssigmembran und einer wässerigen Phase

Kinetic Study of the Distribution of Electrically Neutral Ionophores between a Solvent Polymeric Membrane and an Aqueous Phase The kinetic behaviour of a series of ligands in the transfer from a solvent polymeric membrane into a stirred aqueous phase was investigated and compared with theoretical kinetic models. It was found that the transfer of ligands with low lipophilicity was controlled by the diffusion in the membrane phase, and that of ligands with high lipophilicity was controlled by the exchange reaction at the phase boundary and/or the diffusion through the unstirred Nernst diffusion layer. The diffusion coefficients in the membrane decrease drastically on increase of the content of the polymer in the membrane and are nearly independent of the size and lipophilicity of the ligand, whereas the overall transfer coefficient through the boudary region does not depend on the polymer content but decreases with increasing lipophilicity of the ionophore.     

Dynamic Coupling at the Ångström Scale

While momentum transfer from active particles to their immediate surroundings has been studied for both synthetic and biological micron‐scale systems, a similar phenomenon was presumed unlikely to exist at smaller length scales due to the dominance of viscosity in the ultralow Reynolds number regime. Using diffusion NMR spectroscopy, we studied the motion of two passive tracers—tetramethylsilane and benzene—dissolved in an organic solution of active Grubbs catalyst. Significant enhancements in diffusion were observed for both the tracers and the catalyst as a function of reaction rate. A similar behavior was also observed for the enzyme urease in aqueous solution. Surprisingly, momentum transfer at the molecular scale closely resembles that reported for microscale systems and appears to be independent of swimming mechanism. Our work provides new insight into the role of active particles on advection and mixing at the Ångström scale.     

HPLC of fluoroquinolone antibacterials using chiral stationary phase based on enantiomeric (3,3′‐diphenyl‐1,1′‐binaphthyl)‐20‐crown‐6

A residual silanol group‐protecting chiral stationary phase (CSP) based on optically active (3,3′‐diphenyl‐1,1′‐binaphthyl)‐20‐crown‐6 was successfully applied to the resolution of fluoroquinolone compounds including gemifloxacin mesylate. The chiral recognition ability of the residual silanol group‐protecting CSP was generally greater than that of the residual silanol group‐containing CSP. From these results, it was concluded that the simple protection of the residual silanol groups of the latter CSP with lipophilic n‐octyl groups can improve its chiral recognition ability for the resolution of racemic fluoroquinolone compounds. The chromatographic resolution behaviors were investigated as a function of the content and type of organic and acidic modifiers and the ammonium acetate concentration in aqueous mobile phase and the column temperature. Especially, the addition of ammonium acetate to the mobile phase was found to be a quite effective means of reducing the enantiomer retentions without sacrificing the chiral recognition efficiency of the CSP.     

Uptake of gas-phase nitrous acid by pH-controlled aqueous solution studied by a wetted wall flow tube

Uptake kinetics of gas phase nitrous acid (HONO) by a pH-controlled aqueous solution was investigated by using a wetted wall flow tube. The gas phase concentration of HONO after exposure to the aqueous solution was measured selectively by the chemical ionization mass spectrometer in a high sensitive manner. The uptake rate of the gaseous HONO was found to depend on the pH of the solution. For the uptake by neutral and alkaline solutions, the gas phase concentration was observed to decay exponentially, suggesting that the uptake was fully limited by the gas phase diffusion. On the other hand, the uptake by the acidic solution was found to be determined by both the gas phase diffusion and the liquid phase processes such as physical absorption and reversible acid dissociation reaction. The decay was analyzed by the rate equations using the time dependent uptake coefficient involving the saturation of the liquid surface. While the uptake processes by the solution at pH = 2-3 were well described by those calculated using the physical and chemical parameters reported for the bulk, the uptake rates by the solution at 4 < pH < 7 deviate from the calculated ones. The present result can suggest that the pH at the liquid surface is lower than that in the bulk liquid, which is responsible for the additional resistance of mass transfer from the gas to the liquid phase.