Aqueous Solution Phase Research Articles

Separation of phenylsuccinic acid enantiomers using biphasic chiral recognition high-speed countercurrent chromatography.

High-speed countercurrent chromatography (HSCCC) combined with biphasic chiral recognition was successfully applied to the resolution of phenylsuccinic acid enantiomers. D-Isobutyl tartrate and hydroxypropyl-β-cyclodextrin were employed as lipophilic and hydrophilic selectors dissolved in the organic stationary phase and aqueous mobile phase, respectively. The two-phase solvent system was made up of n-hexane/methyl tert-butyl ether/water (0.5:1.5:2, v/v/v). Impacts of the type and concentration of chiral selectors, the pH value of the aqueous phase solution as well as the temperature on the separation efficiency were investigated. By means of preparative HSCCC, pure enantiomer was obtained by separating 810 mg of racemate with a purity >99.5% and a recovery rate between 82 and 85%. The experimental results indicate that biphasic recognition HSCCC provide a promising means for efficient separation of racemates.

Role of additives; sodium dodecyl sulphate and manganese chloride on morphology of Zn1−xMnxO nanoparticles and their photoluminescence properties

In the present study Zn1−xMnxO (x = 0, 0.05 and 0.1) nanoparticles (NPs) have been synthesised in aqueous solution phase at mild reaction temperature 100 °C in moderate alkaline medium (pH = 9.5), and the role of external additives; like sodium dodecyl sulphate and manganese chloride on the morphology and size of the products has been explored on the basis of transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectral analyses data. ZnO hexagonal nano-plates, core–shell like spherical/ellipsoidal Zn0.95Mn0.05O structures and thin sheets, thorn/needle mixed shaped Zn0.9Mn0.1O structures have been observed in TEM and SEM images. Zn(OH)2 formed in moderate alkaline medium, converted to Zn(II) hydroxo complex ions on dissolution, which further recrystallizes to produce wurtzite ZnO at 100 °C. From XRD and EDX analysis, successful doping of Mn2+ ions at the Zn2+ sites in ZnO host has been proved. In the photoluminescence spectra, the observed blue shifts in NBE peaks and decrease of emissions intensity on Mn doping have thoroughly been discussed in the present investigation.

Simultaneous determination of 7-O-succinyl macrolactin A and its metabolite macrolactin A in rat plasma using liquid chromatography coupled to tandem mass spectrometry

7-O-Succinyl macrolactin A (SMA) and its major metabolite macrolactin A (MA) are generated from Bacillus polyfermenticus KJS-2. Both substances show inhibitory effects on angiogenesis and cancer cell invasion. SMA in rat plasma is known to be relatively stable at room temperature, but MA was not detected due to its instability. Therefore, a stabilizer is required to accurately measure the substance in biological rat samples. In this study, NaF and eserine were examined to determine whether they could stabilize MA to allow for accurate measurement in rat plasma. We also developed a rapid and simple chromatographic method using tandem mass spectrometry (MS/MS) for the simultaneous determination of these compounds in rat plasma. After simple protein precipitation with acetonitrile including methaqualone (internal standard), the analytes were chromatographed on a Hilic column with a mobile phase of 10mM formic acid aqueous solution, methanol, and acetonitrile (15:15:70, v/v). The accuracy and precision of the assay were in accordance with FDA regulations for the validation of bioanalytical methods. This analytical method was successfully applied to monitor plasma concentrations of both compounds over time following intravenous administration of a salt form of SMA in rats.

Structural and vibrational investigation on species derived from the cyclamic acid in aqueous solution by using HATR and Raman spectroscopies and SCRF calculations

In this study, aqueous solutions at different molar concentrations of sodium cyclamate in water were completely characterized by HATR (Horizontal Attenuated Total Reflectance) and Raman spectroscopies. The theoretical structures of cyclamate ion, the zwitterionic and neutral forms of the cyclamic acid and its dimer were optimized in gas and aqueous solution phases by using the hybrid B3LYP/6-31G* method. The solvent effects for the four species in aqueous solutions were simulated by using self-consistent reaction field (SCRF) calculations employing the integral equation formalism variant (IEFPCM) model. The complete assignments of the vibrational spectra of all the forms of cyclamic acid were performed taking into account the factor group analysis with the Scaled Quantum Mechanics Force Field (SQMFF) methodology. The existence of the zwitterionic and neutral forms of the cyclamic acid and its dimer in a solution of cyclamate in water is evidenced by characteristic bands in the HATR and Raman spectra. The dimerization of cyclamate in aqueous solution was previously reported by conductimetric method. The natural population analysis (NPA) and Merz–Kollman (MK) charges, molecular electrostatic potential (MEP), natural bond orbital (NBO) and atoms in molecules (AIM) calculations predict for all the species the principal donor and acceptor sites for the H bonds formation in aqueous solution. The SQM force fields for the cyclamate ion, the zwitterionic and neutral species of the cyclamic acid were obtained and their corresponding force constants in both phases were reported. Additionally, the solvation energies for those species were reported.

Donnan potentials in aqueous phase-separated polymer mixtures.

A promising approach to texturize water is by the addition of mutually incompatible polymers, leading to phase separation. Here, we demonstrate that the phase stability of aqueous polymer solutions is affected not only by chemical differences between the polymers but also by their electric charge. Direct electrochemical measurements are performed of the electric potential difference between two coexisting phases in aqueous solutions of the charged protein fish gelatin (nongelling) and the uncharged polysaccharide dextran. Charge counteracts demixing because of the entropic cost of confining the counterions to one phase, resulting in a strong shift of the critical point upon an increase of the charge on one of the polymers. Upon phase separation, the charged polymer is spatially confined, and due to the Donnan effect, an interfacial electric potential is developed. A direct proportionality is found between this Donnan potential and the difference in gelatin concentration in the two phases, for which we propose a theoretical explanation. The electrostatics may provide a new handle in the development of stable water-in-water emulsions.

Effect of self-assembly on triiodide diffusion in water based polymer gel electrolytes: An application in dye solar cell

The preparation of ordered polymer gels from the amphiphilic block copolymers, Pluronic® F77, P123 and polyethylene glycol in the presence of ionic liquid, iodine and organic additives is presented. At 35%(w/w) concentration these copolymers (F77 and P123) self-assembled into cubic liquid crystalline phase in aqueous solution and characterized by using SAXS and AFM measurements. The effects of micellar aggregation formed by polymers on the ionic transport and triiodide diffusion have been studied by electrochemistry and SANS experiments. The ionic migration or triiodide diffusion through these polymer gels is found to be affected by the PEO/PPO content in the polymer backbone. These gels were successfully employed as an electrolyte in a dye sensitized solar cell. A remarkable solar to electricity conversion efficiency and good stability was obtained using Pluronic® F77 based gel, which is attributed to its thermoreversible sol to gel transition.

Dynamic encapsulation of hydrophilic nisin in hydrophobic poly (lactic acid) particles with controlled morphology by a single emulsion process

Hydrophilic nisin-loaded hydrophobic poly (lactic acid) (PLA) particles with controlled size and shape were successfully produced utilizing a one-step single emulsification method. Preliminary shear stress and temperature tests showed that there was no significant loss in the nisin inhibition activity during this process. PLA/nisin composite particles were prepared into solid nanocomposite spheres (50–200nm) or hollow microcomposite spheres (1–5μm) under the operative conditions developed in our previous study, in which the hydrophilic nisin in the aqueous phase solution could be entrapped in the hydrophobic polymer in the emulsification process generating either single or multiple emulsions. The incorporation of nisin in PLA had little effect on key processing conditions, which allows the dynamic control of the morphology and property of resulting particles. Microscopic and surface analyses suggested that nisin was dispersed uniformly inside the polymer matrix and adsorbed on the particle surface. The encapsulation amount and efficiency were enhanced with the increase in nisin loading in the aqueous solution. Unique reversible control of particle size and shape by this process was successfully applied in the nisin encapsulation. Alternating temperature in the repeating emulsification steps improved the encapsulation efficiency while generated particles in desired size and shape.

Thermodynamic properties of binary aqueous solutions of orthophosphate salts, sodium, potassium and ammonium at T = 298.15 K

In this investigation, the thermodynamic properties of the aqueous solutions of orthophosphate salts M3−nHnPO4 H2O with n=0, 1, or 2 and M=Na+, K+ or NH4+ at 298.15K are determined. The water activity measurements for NaH2PO4(aq), Na2HPO4(aq), Na3PO4(aq); KH2PO4(aq), K2HPO4(aq), K3PO4(aq), (NH4)H2PO4(aq), (NH4)2HPO4(aq) and (NH4)3PO4(aq) are effectuated from dilution to saturated solution using the hygrometric method. The activity coefficients are evaluated using ionic-interaction model. The mineral solubility of these phosphate salts is investigated at T=298.15K. The prediction of solubility is made for minerals and other solid phases in aqueous solutions of phosphates. Correlating and predicting the phase behavior in such systems is a difficult task, partially caused by chemical reactions in the liquid phase but also due to the possible formation of one or more solid phases. Solid phases, molality of saturated binary solutions ms(exp) and logarithm of solubility product K°sp are also determined at 298.15K. The standard molar Gibbs energies of dissolution ΔG°diss, formation ΔGf Calc° and the literature ΔGf Ref°, of solid phases crystallizing from saturated phosphate salts solutions are evaluated.This investigation allows understanding physicochemical nature and structure of phosphate solutions, in particular, questions of anion or cation hydration, especially at higher concentrations, ion-pairing formation, and the possibility of phosphate complex formation.

Determination of pH Value and Acid-base Property of Ionic Liquid Aqueous Solutions

The ionic liquids (ILs) and their aqueous solutions have been considered as a new generation of absorption working substances for applications in gas separation and absorption refrigeration processes. It is important to understand the physicochemical properties of ionic liquids in aqueous solutions, such as chemical potential and acid-base properties before any industry application. In this study, we focused on the acid-base properties of the IL aqueous solutions by testing the pH values of the aqueous solutions of two ionic liquids, 1-ethyl-3-methylimidazolium acetate ([EMIM]Ac) and 1-hexyl-3-methylimidazolium chloride ([HMIM]Cl). All the tests were carried out at 25 and in a well controlled dry air °C surrounding. There were 16 water mass fractions for each of [EMIM]Ac and [HMIM]Cl aqueous solutions tested in range of 0.04 to 0.95 and 0.01 to 0.96, respectively. There, two methods, the sophisticated pH paper and the pH meter, were applied for the tests and the differences between the two test methods were detected. The test data from the two test methods and their differences were then evaluated with an aggregation film model and the activity theory for the film and aqueous solution phases. The results show that the difference of the pH values tested by the two methods is significant. The pH data from the sophisticated pH paper test present the bulk acid-base property of the IL aqueous solutions, while the pH meter can only reflect the hydrogen ion concentration in the IL aggregation film which was formed on the surface of the electrode of the pH meter. With analysis of acid-base reaction in the IL aqueous solution, a calculation model for the pH value of the bulk solution region was developed, and the data of the sophisticated pH paper test were correlated and the solution acid-base values were obtained. Based on analysis of the water species equilibrium in the IL aggregation film and the bulk aqueous solution phases and its effect on the concentration of hydrogen ions in the aggregation film, a method for calculation of the difference of pH values between the aggregation film and the bulk solution was proposed and the data from the pH meter were then fitted with the proposed calculation method. The results provide experimental data and a quantitative method for analysis of the acid-base property of IL aqueous solution systems.

Characteristics of Dispersed ZnO-Folic Acid Conjugate in Aqueous Medium

The focus of this article is based on the aqueous dispersed state properties of inorganic ZnO nanoparticles (average size ≤ 4 nm), their surface modification and bio-functionalization with folic acid at physiological pH ~ 7.5, suitable for bio-imaging and targeted therapeutic application. While TEM studies of the ZnO nano-crystallites have been performed to estimate their size and morphology in dry state, the band gap properties of the freshly prepared samples, the hydrodynamic size in aqueous solution phase and the wide fluorescence range in visible region have been investigated to establish the fact that the sol is particularly suitable for bio-medical purpose in the aqueous dispersed state.

Graphene oxide for fluorescence-mediated enzymatic activity assays.

Graphene oxide (GO), an oxidized 2-dimensional carbon material, has been studied actively in both academia and industry due to its unique physicochemical properties including high surface area, excellent aqueous dispersibility, quenching capability of contiguous fluorophores and adsorption affinity with diverse biomolecules. Particularly, GO has been widely used in biological applications involving small molecule biosensors, enzymatic reaction monitoring, drug delivery and therapeutic applications. Among these rapidly developing fields, we focused on the current advancements of fluorescence mediated activity assay platforms for enzymes including nucleases, methyltransferases, protein kinases, caspases and helicases by using affinity and fluorescence quenching capability of GO with fluorophore labelled biomolecule substrates in the aqueous solution phase, and its important applications with future perspectives in this article.

A Study on the Adsorption of Heavy Metals by Using Raw Wheat Bran Bioadsorbent in Aqueous Solution Phase

Raw wheat bran (R-WB) was used as a biomass adsorbent. The properties of R-WB were investigated. Moreover, the adsorption of cadmium and lead ions onto R-WB was evaluated. Adsorption equilibrium of cadmium and lead ions onto R-WB was achieved within 10 h, indicating that the adsorption followed a pseudo-second-order model rather than a pseudo-first-order kinetic model. The adsorption amount increased with increasing temperature. Correlation coefficient of the Langmuir equation is 0.999 for cadmium and 0.996 for lead ions, and that of the Freundlich equation is 0.994 for cadmium and 0.993 for lead ions. The negative ΔG value implied that the adsorption of cadmium and lead ions onto R-WB is a spontaneous process. The positive ΔS value indicated an increase in randomness at the solid-liquid interface. The optimal conditions for the adsorption column experiment were investigated (space velocity (SV) 2.2 1/h, linear velocity (LV) 0.1 m/h for cadmium; SV 6.51 1/h, LV 0.23 m/h for lead ions). Further, repeated adsorption-desorption of the cadmium and lead ions could be effected by using 0.01 mol/L HCl or 0.01 mol/L HNO3 solution. Consequently, polluted water could be successfully purified by using a column filled with this bioadsorbent.

Механизм формирования пленок SnS химическим осаждением из водных растворов

The results of investigation of the growth mechanism of SnS thin films prepared by hydrochemical deposition by means of a scanning probe microscopy are presented. According to the results of a comparative analysis of layers morphology at different growth stages and the use of fractal formalism growth model of SnS films by clustercluster aggregation with elements of self-organization is proposed. It is shown that there is a solid layer, which again are deposited particles of the solution. The process has expressed periodic self-organizing nature. The study showed that the proposed model of film growth SnS when hydrochemical deposition agrees well with ex-periments and proves difficult coagulation mechanism of the formation of hard phase of the saturated aqueous solution.

A complete assignment of the vibrational spectra of sucrose in aqueous medium based on the SQM methodology and SCRF calculations

In the present study, a complete assignment of the vibrational spectra of sucrose in aqueous medium was performed combining Pulay’s Scaled Quantum Mechanics Force Field (SQMFF) methodology with self-consistent reaction field (SCRF) calculations. Aqueous saturated solutions of sucrose and solutions at different molar concentrations of sucrose in water were completely characterized by infrared, HATR, and Raman spectroscopies. In accordance with reported data of the literature for sucrose, the theoretical structures of sucrose penta and sucrose dihydrate were also optimized in gas and aqueous solution phases by using the density functional theory (DFT) calculations. The solvent effects for the three studied species were analyzed using the solvation PCM/SMD model and, then, their corresponding solvation energies were predicted. The presence of pure water, sucrose penta-hydrate, and sucrose dihydrate was confirmed by using theoretical calculations based on the hybrid B3LYP/6-31G∗ method and the experimental vibrational spectra. The existence of both sucrose hydrate complexes in aqueous solution is evidenced in the IR and HATR spectra by means of the characteristic bands at 3388, 3337, 3132, 1648, 1375, 1241, 1163, 1141, 1001, 870, 851, 732, and 668cm−1 while in the Raman spectrum, the groups of bands in the regions 3159–3053cm−1, 2980, 2954, and 1749–1496cm−1 characterize the vibration modes of those complexes. The inter and intra-molecular H bond formations in aqueous solution were studied by Natural Bond Orbital (NBO) and Atoms in Molecules theory (AIM) investigation.

Phycocyanin as Potential Natural Dye for its Use in Photovoltaic Cells

Phycocyanin, a blue protein extracted from Spirulina spp, shows promising characteristics that made it suitable for its use as natural dye in photovoltaic devices as the dye sensitized solar cells. In this work, a study of the aqueous solution-phase photochemistry, photophysics, spectroscopy, voltammetry and thermal stability of phycocyanin is presented. Suitable redox potentials (Eox = 1.2 V vs. Ag/AgCl) and a value of 1.96 V for E0,0 (i.e., the energy difference between the vibrationally relaxed levels of the first electronic excited state, S1, and the ground state, S0 of phycocyanin), allows the calculation of energetic profiles that in comparison with the conduction band of the anatase-TiO2 and I-/I3- electrolyte, could predict electron transfer with these components of the cell. The data reported herein should not only help to evaluate the potential use of phycocyanin as sensitizer for solar cells, but should also help in the development of novel solar cells where the photoinduced behavior of this protein can be controlled.

Adsorption–desorption mechanism of a cationic polyelectrolyte based on dimethylaminoethyl polymethacrylates at the water/1,2-dichloroethane interface

The electrochemical behaviour of the cationic polymer Eudragit® E100 at the polarized water/1,2-dichloroethane interface was studied. The voltammetric response was found to be dependent on the pH of the aqueous phase solution, on the nature of the organic electrolyte, and it was also time dependent during multi-cyclic voltammetry experiments. The results suggest that a diffusion process coupled to an adsorption or re-arrangement of E100 molecules at the interface is taking place. From the analysis of the desorption process, it was determined the presence of a strong attractive interaction between the adsorbed species at the interface and the lateral interaction parameter was calculated.

A structural and vibrational investigation on the antiviral deoxyribonucleoside thymidine agent in gas and aqueous solution phases

A structural and vibrational study on the antiviral deoxyribonucleoside thymidine in gas and aqueous solution phases was performed combining the available infrared and Raman spectra with density functional theory (DFT) calculations. Three stable conformers for the title molecule were theoretically determined in both media by using the hybrid B3LYP method together with the 6–31G* basis set. The solvent effects were studied by means of the self-consistent reaction field method employing the polarized continuum model. Complete assignments of the vibrational spectra of thymidine in both phases were performed combining the DFT calculations with Pulay's scaled quantum mechanics force field methodology. The bond orders, atomic charges, solvation energies, dipole moments, molecular electrostatic potentials, and force constants parameters were calculated for the three conformers of thymidine in gas phase and aqueous solution. Selected descriptors, such as chemical potential (µ), electronegativity (χ), global hardness (η), global softness (S), and global electrophilicity index (ω) were used to explain the exact nature of the interactions with electrophiles and/or nucleophiles and to predict the behavior of the three conformers of thymidine in gas and aqueous solution phases. © 2013 Wiley Periodicals, Inc.

Purification of a novel protease enzyme from kesinai plant (Streblus asper) leaves using a surfactant–salt aqueous micellar two-phase system: a potential low cost source of enzyme and purification method

Serine protease from kesinai leaves was purified for the first time by a surfactant–polymer aqueous micellar two-phase system. The effectiveness of different types and concentrations of non-ionic surfactants (Pluronic series and X-114) on the partitioning behaviour of the protease was evaluated. The results showed that the enzyme preferentially partitioned into the bottom surfactant-rich phase, while the hydrophilic amino acid preferred the top aqueous phase. This distribution of the enzyme is due to the hydrophobic interaction of the serine protease with the hydrophobic lid of the micelle core in the bottom phase. The influence of different types of salts (K2SO4, KH2PO4, KCl and KNO3) on the purification and selectivity of the enzyme was determined. The protease partitioning in the bottom phase increased in the presence of KNO3, which confirmed that the salt was able to improve the protein solubility in bottom phase and increase the hydrophobic interaction between the two phases. In addition, the protease from the bottom phase was re-extracted to a new aqueous phase solution to remove and recycle the surfactant. Addition of potassium thiocyanate led to the partitioning of the enzyme in top aqueous phase due to high ionic strength of SCN−, which forced the lighter micellar phase toward the upper position of the system. A high purification factor (10.3) and yield of 92 % of the enzyme were achieved in a solution of 31 % of Pluronic L61 using 0.3 % KNO3 and 50 % crude feedstock at pH 7.0.

Preparation of CTA-based polymer inclusion membrane using calix[4]arene derivative as a carrier for Cr(VI) transport

In this work, the transport of Cr(VI) ions from an aqueous donor phase solution to an acceptor phase that contained an acetic acid/ammonium acetate buffer at pH 5 through a polymer inclusion membrane (PIM) containing p-tert-butylcalix[4]arene amine derivative as carrier was studied. The Cr(VI) passed through a PIM comprised of cellulose triacetate as a support and 2-NPOE as a plasticizer. The transport efficiency of Cr(VI) was studied under various experimental conditions, such as effect of carrier concentration, acceptor phase pH, type of plasticizer in the membrane, stirring rate and membrane thickness. The kinetic parameters were calculated as rate constant (k), permeability coefficient (P), and flux (J). The transport efficiency of Cr(VI) was observed to be 95.07 % after 10 h under optimized conditions. The prepared PIM was characterized with Fourier transform infrared spectroscopy and the atomic force microscopy techniques as well as with contact angle measurements. This is an effective method for the removal of Cr(VI) which is toxic for human body and environment from the waste water.

Structural and vibrational study on zwitterions of l-threonine in aqueous phase using the FT-Raman and SCRF calculations

Quantum mechanical/molecular mechanics (QM/MM) calculations were performed to study the most stable theoretical structure of l-threonine in an aqueous solution phase and to observe the changes occurring in the structural and vibrational properties of l-threonine in the aqueous media. l-threonine was characterized by Raman spectroscopies in the solid state and in aqueous solution. Optimized geometries and relative stabilities for the monomer and two dimers were calculated using the hybrid B3LYP level taking into account the solvent effects by means of the integral equation formalism of the polarizable continuum model (IEF-PCM). The obtained results in the aqueous solution were compared with those calculated for the monomer in the gas phase. The presence of hydrogen bonding in the monomer of l-threonine was studied by means of the Atoms in Molecules theory (AIM) and natural bond orbital (NBO) studies. The complete assignments of the vibrational spectra of l-threonine in the aqueous solution was performed by using the Pulay’s scaled quantum mechanical force field (SQMFF) methodology. Additionaly, hydrated complexes of the monomer considering the interaction with one, two, three and four discrete water molecules were also studied taking into account the solvent effect by using the IEFPCM method. An agreement between theoretical and available experimental results was found.