Aqueous Solution Phase Research Articles

Synthesis of Ag-liposome nano composites

Silver nanoparticles were synthesized and stabilized by a simple, environment-friendly method in a liposomes structure. Liposomes were prepared by facing lecithin to the aqueous-phase solutions while stirring vigorously. The ratio of lecithin concentration to silver nitrate (KLec/Ag = [Lecithin]/[AgNO3]) is the influencing factor in the synthesis of silver nanoparticles. The stability, size distribution, and antibacterial properties of synthesized silver nanoparticles were studied by ultraviolet (UV)-visible, dynamic light scattering, and antibacterial assay. The UV spectra indicated a single symmetric extinction peak at 400 nm, confirming the spherical shape of the synthesized silver nanoparticles. A high KLec/Ag value leads to a reduction in the intensity of extinction spectra and increases the size of Ag-liposomes nanocomposites. The large Ag-liposomes nanocomposites are transformed to the smaller Ag-liposomes nanocomposites (from 342 to 190 nm) due to sonication treatment. The stabilized silver nanoparticles with various lecithin concentrations showed a good antibacterial activity against Staphylococcus aureus, a Gram-positive bacterium, and Escherichia coli, a Gram-negative bacterium.

Voltammetric Ion-Selective Electrodes for the Selective Determination of Cations and Anions

A general theory has been developed for voltammetric ion sensing of cations and anions based on the use of an electrode coated with a membrane containing an electroactive species, an ionophore, and a supporting electrolyte dissolved in a plasticizer. In experimental studies, a membrane coated electrode is fabricated by the drop coating method. In one configuration, a glassy carbon electrode is coated with a poly(vinyl chloride) based membrane, which contains the electroactive species, ionophore, plasticizer and supporting electrolyte. In the case of a cation sensor, ionophore facilitated transfer of the target cation from the aqueous solution to the membrane phase occurs during the course of the reduction of the electroactive species present in the membrane in order to maintain charge neutrality. The formal potential is calculated from the cyclic voltammogram as the average of the reduction and oxidation peak potentials and depends on the identity and concentration of the ion present in the aqueous solution phase. A plot of the formal potential versus the logarithm of the concentration exhibits a close to Nernstian slope of RT/F millivolts per decade change in concentration when the concentration of K(+) and Na(+) is varied over the concentration range of 0.1 mM to 1 M when K(+) or Na(+) ionophores are used in the membrane. The slope is close to RT/2F millivolts for a Ca(2+) voltammetric ion-selective electrode fabricated using a Ca(2+) ionophore. The sensor measurement time is only a few seconds. Voltammetric sensors for K(+), Na(+), and Ca(2+) constructed in this manner exhibit the sensitivity and selectivity required for determination of these ions in environmentally and biologically important matrixes. Analogous principles apply to the fabrication of anion voltammetric sensors.

Physicochemical study on microencapsulation of hydroxypropyl-β-cyclodextrin in dermal preparations

Objective: To investigate the effect of hydroxypropyl-β-cyclodextrin (HP-β-CD) concentration on the physicochemical properties of the sunscreen agents, namely oxybenzone (Oxy), octocrylene (Oct), and ethylhexyl-methoxy-cinnamate (Cin), in aqueous solution and cream formulations. Methods: The inclusion complexes of sunscreen agents with hydroxypropyl-β-cyclodextrin (HP-β-CD) in aqueous solution and solid phase were studied by UV-vis spectrophotmetery, differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and 13C-NMR techniques. The photodegradation reaction of the sunscreen agents' molecules in lotion was explored using UV-vis spectrophotometry and high-performance liquid chromatography (HPLC). Results: The formation of the inclusion complexes was confirmed experimentally using DSC, SEM, and 13C-NMR. The results of spectrophotometric and HPLC studies have shown that the inclusion complexation with HP-β-CD has the potential to enhance the photostability of the selected sunscreen agents in lotion. HPLC results indicated that HP-β-CD has approximately increases the photostability of Oct by six- to eightfold. Moreover, the presence of HP-β-CD in lotion controlled the isomerization process of Cin to a certain degree, which was found to be a function of the amount of HP-β-CD added. Conclusions: It has been demonstrated that the photostability of the tested sunscreen agents has been enhanced upon forming inclusion complexes with HP-β-CD in lotion. The results of this study demonstrate that HP-β-CD can be utilized as photostabilizer additive for enhancing the photostability of the sunscreen agents' molecules.

UV Resonance Raman Elucidation of the Terminal and Internal Peptide Bond Conformations of Crystalline and Solution Oligoglycines

Spectroscopic investigations of macromolecules generally attempt to interpret the measured spectra in terms of the summed contributions of the different molecular fragments. This is the basis of the local mode approximation in vibrational spectroscopy. In the case of resonance Raman spectroscopy independent contributions of molecular fragments require both a local mode-like behavior and the uncoupled electronic transitions. Here we show that the deep UV resonance Raman spectra of aqueous solution phase oligoglycines show independent peptide bond molecular fragment contributions indicating that peptide bonds electronic transitions and vibrational modes are uncoupled. We utilize this result to separately determine the conformational distributions of the internal and penultimate peptide bonds of oligoglycines. Our data indicate that in aqueous solution the oligoglycine terminal residues populate conformations similar to those found in crystals (3(1)-helices and β-strands), but with a broader distribution, while the internal peptide bond conformations are centered around the 3(1)-helix Ramachandran angles.

The Role of Interfacial Molecular Structure in the Adsorption of Ions at the Liquid−Liquid Interface

One of the most common and important interfaces is the boundary layer between an aqueous phase solution of ions and a hydrophobic medium. Whether the hydrophobic medium is a membrane, a macromolecular assembly, or a simple organic liquid, our molecular-level understanding of how ions in an adjacent aqueous phase approach, alter, and transport across the boundary is still quite deficient, largely due to experimental challenges in making the appropriate measurements. This paper reports some of the first measurements of the behavior of common inorganic ions at the interface between different aqueous phase salt solutions (NaCl, NaBr, NaNO3, and Na2SO4) and a hydrophobic organic liquid (CCl4). The results show that the ions reside within the interfacial region where they affect the water hydrogen bonding in a manner specific to the ion under study. Distinct differences in the behavior of ions at this interface relative to the air−water interface are found and discussed.

Phase formation in sodium dodecylsulfate solutions in the presence of salicylic acid for preconcentration purposes

AbstractThe occurrence of surfactant-rich phases in aqueous sodium dodecylsulfate solutions in the presence of salicylic acid was investigated. The effect of acidity, electrolyte and salicylic acid concentrations on the parameters of phase formation were studied. Optimal conditions for microcomponent preconcentration were found. The features of solubilization efficiency changes of organic substances depending on their charge and hydrophobicity were established. High efficacy of preconcentration of strongly hydrophobic, positively charged substrates by low-temperature surfactant-rich phases obtained in the sodium dodecylsulfate-salicylic acid-sodium chloride ternary system is shown.

Development and validation of a stability-indicating RP-HPLC method for assay of betamethasone and estimation of its related compounds

Betamethasone (9α-fluoro-16β-methylprednisolone) is one of the members of the corticosteriod family of active pharmaceutical ingredient (API), which is widely used as an anti-inflammatory agent and also as a starting material to manufacture various esters of betamethasone. A stability-indicating reverse-phase high performance liquid chromatography (RP-HPLC) method has been developed and validated which can separate and accurately quantitate low levels of 26 betamethasone related compounds. The stability-indicating capability of the method was demonstrated through adequate separation of all potential betamethasone related compounds from betamethasone and also from each other that are present in aged and stress degraded betamethasone stability samples. Chromatographic separation of betamethasone and its related compounds was achieved by using a gradient elution at a flow rate of 1.0 mL/min on a ACE 3 C18 column (150 mm × 4.6 mm, 3 μm particle size, 100 Å pore size) at 40 °C. Mobile phase A of the gradient was 0.1% methanesulfonic acid in aqueous solution and mobile phase B was a mixture of tert-butanol and 1,4-dioxane (7:93, v/v). UV detection at 254 nm was employed to monitor the analytes. For betamethasone 21-aldehyde, the QL and DL were 0.02% and 0.01% respectively. For betamethasone and the rest of the betamethasone related compounds, the QL and DL were 0.05% and 0.02%. The precision of betamethasone assay is 0.6% and the accuracy of betamethasone assay ranged from 98.1% to 99.9%.

Use of piezosensors for determining the composition of the equilibrium gas phase of aqueous protein solutions

Possibility of using modified piezosensors to determine the composition of multicomponent gas mixtures was studied. The sorption conditions of readily volatile components of aqueous protein solutions on modifier films of varied nature for piezoquartz resonators were examined and optimized. A set of methods for determining aroma-forming components of complex mixtures was developed. The possibility of using the methods developed for determining the nature of aroma-forming additives to milk drinks was demonstrated.

Catalyzing Racemizations in the Absence of a Cofactor: The Reaction Mechanism in Proline Racemase

The origin of the catalytic proficiency of the cofactor-independent enzyme proline racemase (ProR) has been investigated by a combined classical and quantum simulation approach with a hybrid quantum mechanics/molecular mechanics potential energy surface. The present study shows that the ProR reaction mechanism is asynchronous concerted with no distinct intermediate. Various mechanisms are investigated, and it is concluded that active site residues other than the Cys dyad are not involved in chemical catalysis. When compared to an analogous aqueous solution-phase reaction, we find that the free-energy barrier is reduced by 14 kcal/mol in ProR, although the reaction mechanisms in the enzyme and in water are similar. The computed catalytic effect is comparable to that in the isofunctional enzyme alanine racemase (AlaR). However, in AlaR the catalytic burden is divided between the cofactor pyridoxal 5'-phosphate and the enzyme environment, whereas in ProR it is borne entirely by the enzyme environment. This is ascribed to a highly preorganized active site facilitating transition state stabilization via a tight network of hydrogen bonds donated by nearby active site residues.

One- and Two-Photon Excitation of β-Carbolines in Aqueous Solution: pH-Dependent Spectroscopy, Photochemistry, and Photophysics

Beta-carboline (betaC) alkaloids are present in a wide range of biological systems and play a variety of significant photodependent roles. In this work, a study of the aqueous solution-phase photochemistry, photophysics, and spectroscopy of three important betaCs [norharmane (nHo), harmane (Ho), and harmine (Ha)] and two betaC derivatives [N-methylnorharmane (N-Me-nHo) and N-methylharmane (N-Me-Ho)] upon one- and two-photon excitation is presented. The results obtained depend significantly on pH, the ambient oxygen concentration, and the betaC substituent and provide unique insight into a variety of fundamental photophysical phenomena. The data reported herein should not only help to understand the roles played by betaC alkaloids in biological systems but should also help in the development of methods by which the photoinduced behavior of these important compounds can be controlled.

A DFT study on the carbamates formation through the absorption of CO 2 by AMP

DFT calculations in gas and aqueous solution phases have been performed to study the mechanism of carbamate formation by the absorption of CO 2 in 2-amino-2-methyl-1-propanol (AMP). The results reveal the importance of considering the effect of water as solvent for the reaction to proceed. Furthermore water molecules play an important role as a basic reactant leading to stable intermediates formation. These results point at a single-step, third order reaction as the most probable mechanism for the formation of carbamate by the absorption process.

Multiscale dynamics of pretransitional fluctuations in the isotropic phase of a lyotropic liquid crystal

Using an improved static and dynamic light-scattering technique, we have observed multiscale relaxation of the pretransitional fluctuations in the isotropic phase of a cromolyn aqueous solution, a lyotropic liquid crystal where rods are formed by aggregates of disklike molecules. We have detected the onset of cromolyn aggregation about 12 degrees C above the transition temperature. The onset is manifested by the emergence of strong scattering due to the fluctuations of local anisotropy and by the split of the diffusion dynamics into two distinctly different modes, one associated with the relatively fast diffusion of monomer-size particles and the other one with the much slower diffusion of the cromolyn aggregates. A third observed dynamic mode is associated with the pretransitional slowing down of fluctuations of the local anisotropy. This mode behaves differently in polarized and depolarized light scattering, due to a coupling between fluctuations of the local-anisotropy and velocity fluctuations.

Mineral Precipitation Kinetics

Precipitation of solid phases in aqueous solutions which deviate from thermodynamic equilibrium is an ubiquitous kinetic phenomena. It may occur in soft chemistry experiments where the concentration of a solute in the aqueous solution, is prepared in excess with respect to the solubility of a desired compound (Adamson 1960; Markov 1995). As first recognized by Gibbs, the solid phase first appears as small nuclei which subsequently grow. The understanding and control of these nucleation and growth processes is of prime importance in modern technology which aims at producing artificial nano-size objects, such as ultra-thin films, nano-dots, nano-clusters, whether by molecular beam epitaxy methods (Pimpinelli and Villain 1998), chemistry in aqueous solution (Jolivet et al. 2004), electro-deposition (Schmickler 1996), etc. For example, it has recently been possible (Jolivet et al. 2006) to synthesize oxide nano-particles with a high surface to volume ratio displaying interesting properties: catalytic activity, optical, electronic and magnetic properties, liquid crystal properties, etc. The control of many of their size and shape dependent characteristics can be obtained by playing with external parameters, such as the acidity of the solution, the presence of specific anions, the temperature, etc. In the geochemical context, nucleation and growth processes are also particularly relevant for complex oxides, such as alumino-silicates or clays, which are ubiquitous in our environment, being often produced as secondary nano- to micro-phases in all alteration processes of rock forming minerals: weathering processes near the Earth’s surface, diagenetic or hydrothermal processes in the Earth’s crust, etc. The geochemical modeling of water-rock interactions has been intensively developed since the pioneering work of Helgeson and co-workers (1970). The aim of geochemists was to be able to better understand the evolution of the aqueous solution (AS) composition in the different water cycles as summarized by Drever (1997): in weathering systems …

Electrochemical behaviour of hen-egg-white lysozyme at the polarised water/1, 2-dichloroethane interface

The electrochemical behaviour of hen-egg-white lysozyme (HEWL) was studied at the polarized water/1,2-dichloroethane interface. The voltammetric ion-transfer response was found to be dependent on the pH and ionic strength of the aqueous phase solution and also on the nature of the organic phase electrolyte anion. The current-pH behaviour of HEWL was dominated by the charge of the biomolecule at each pH, as indicated by the close relationship between the experimental peak currents and the theoretical curve for HEWL based on its known acid-base chemistry. Three organic electrolyte anions of differing hydrophobicities were investigated (TFPB-, TPBCl- and TPB-) and it was found that the ion transfer voltammetric peaks occurred at successively higher potentials in the order of increasing hydrophobicity, Deltaphi(TPB) < Deltaphi(TPBCl) < Deltaphi(TPBF). The voltammetric response was time dependent during multi-cyclic voltammetry experiments, with the formation of a white film of precipitate at the interface. A pre-peak consistent with adsorption of the HEWL ion transfer product at the liquid/liquid interface was also observed. The results suggest that an adsorption or re-arrangement of HEWL molecules with time at the interface is taking place. A mechanism for the response on application of a triangular potential waveform with cyclic voltammetry is proposed based on an i-C-i mechanism. Our results indicate that HEWL is electroactive at the polarized liquid/liquid interface and that such electrochemical methods may provide an approach to the label-free detection and characterization of protein molecules.

Enhanced thermoelectric properties in PbTe Nanocomposites

AbstractDimensional nanocomposites of PbTe with varying carrier concentrations were prepared from undoped and Ag doped PbTe nanocrystals synthesized utilizing an alkaline aqueous solution-phase reaction. The nanocrystals were densified by Spark Plasma Sintering (SPS) for room temperature resistivity, Hall, Seebeck coefficient, and temperature dependent thermal conductivity measurements. The nanocomposites show an enhancement in the thermoelectric properties compared to bulk PbTe with similar carrier concentrations, thus demonstrating a promising approach for enhanced thermoelectric performance.

Ageing of a phosphate ceramic used to immobilize chloride contaminated actinide waste

A process for the immobilization of intermediate level waste containing a significant quantity of chloride using Ca3(PO4)2 as the host material has been developed. Waste ions are incorporated into two phosphate-based phases, chlorapatite [Ca5(PO4)3Cl] and spodiosite [Ca2(PO4)Cl]. Non-active trials performed using Sm as the actinide surrogate demonstrated the durability of these phases in aqueous solution. Trials of the process, in which actinide-doped materials were used, were performed at PNNL which confirmed the wasteform resistant to aqueous leaching. Initial leach trials conducted on 239Pu/241Am loaded ceramic at 313K/28 days gave normalized mass losses of 1.2×10−5gm−2 and 2.7×10−3gm−2 for Pu and Cl, respectively. In order to assess the response of the phases to radiation-induced damage, accelerated ageing trials were performed on samples in which the 239Pu was replaced with 238Pu. No changes to the crystalline structure of the waste were detected in the XRD spectra after the samples had experienced an α radiation fluence of 4×1018g−1. Leach trials showed that there was an increase in the P and Ca release rates but no change in the Pu release rate.

Effect of Tannic Acid on the Dyeing Process of Nylon 6 Fabric with Cationic Dye

Nylon 6 fabric is pretreated with tannic acid and subsequently dyed with a cationic dye, Rhodamine B, from an aqueous dye solution and emulsion phase. The emulsion phase of n-hexadecane is emulsified by isopropyl alcohol and stabilized by Rhodamine B/tannic acid complex. Different factors affecting pretreatment and dyeing process have been studied. Changes of moisture regain, tensile strength, elongation and binding stiffness of the pretreated fabric are investigated. The FTIR spectra of tannic acid pretreatment of nylon are also examined. The pretreated fabric with 10% owf tannic acid shows a slight increase in the tensile strength and elongation percentage. A higher moisture regain and binding stiffness are observed with increases in the amount of tannic acid. The results also indicate that the pretreatment for cationic dyed nylon 6 fabrics with tannic acid promote a higher dye uptake and cationic dye-based emulsion system with better fastness properties relative to those of the dye solution based system. A further improvement in wet fastness is secured by an aftertreatment of all dyed fabrics with a commercial anionic fluorescent whitening agent, Uvitex® RSB 150%.

PNP-16-crown-6 derivatives as ion carriers for Zn(II), Cd(II) and Pb(II) transport across polymer inclusion membranes

Transport rate of metal cations can be explained by the size of substituents, namely larger substituents such as 7 and 8 prefer Pb(II) cations. The bis-PNP-lariat ethers remove Zn(II), Cd(II) and Pb(II) more efficiently than simple PNP-lariat ethers. The increase of linker length in the bis-PNP-lariat ether molecules lowers the metal cations’ transport rate. In addition, the synergetic effect for lead(II) transport across polymer inclusion membrane (PIM) with PNP-lariat ether 9 and DNNS was using PNP-lariat ethers—carriers 1 and 2 in a PIM system, Zn(II) and Cd(II) were transported with low selectivity from acidic aqueous source phase solutions. The ether 3 used to transport Zn(II) and Cd(II) cations from aqueous phase at pH 5.0 into hydrochloric aqueous solution shows high selectivity of Cd/Zn, but small efficiency of process. The competitive transport of equimolar mixtures of Zn(II), Cd(II), and Pb(II) ions from aqueous source phase ( c Me = 0.0001 M) across polymer inclusion membranes with mono- and bis-PNP-lariat ethers as ion carriers has been studied. In these experiments the influence of substituents attached to the simple PNP-lariat ether molecules on the selectivity and efficiency of Zn(II), Cd(II), and Pb(II) transport through PIMs containing cellulose triacetate as the support and o-nitrophenyl pentyl ether as the plasticizer was investigated. The PIM contained 0.3 M lariat ether and 4.0 ml ONPPE per 1.0 g CTA. The transport selectivity order for the PIM with 7 and 8 was: Pb(II) > Cd(II) > Zn(II), whereas for 1 and 4 the order: Zn(II) > Cd(II) ≥ Pb(II) was found. We also found out that the transport of metal cations across PIM with bis-lariat ether 9 occurs at the same level when sodium nitrate in source phase is in the range of 10 −3 to 0.10 M.

Physical Polymerization and Liquid Crystallization of RNA Oligomers

Ultrashort complementary RNA oligomers, as short as six base pairs in length, are found to exhibit chiral nematic and columnar liquid crystal phases in aqueous solution, through end-to-end adhesion into physically bound, but chemically segmented, polymers. Geometrical constraints indicate that the phosphate helix is continuous along the aggregated chain. The end-to-end adhesion is due to a base-staking type interaction, whose energy and temperature dependence are determined.

Heavy metal separation with polymer inclusion membranes

Using functionalized calix[4]arene carrier 1 in a PIM system, Hg(II) is transported with high selectivity from acidic aqueous source phase solutions of Cd(II), Hg(II) and Pb(II) with high NaNO 3 concentration into aqueous receiving solutions containing EDTA. To gain insight into this transport selectivity, complexation studies of the three heavy metal perchlorate species by ligand 1 were conducted in acetonitrile. Although 1:1 complexation of the divalent heavy metal cation by 1 was observed for Cd(II), the stoichiometries were more complicated for Hg(II) and Pb(II). Selective Hg(II) transport across the PIM is attributed to both the strength and stoichiometry of the metal ion-carrier species forming at the source phase-membrane interphase and its stripping from the membrane into the receiving phase by EDTA.