Molecular dynamics simulation of the equilibrium liquid–vapor interphase with solidification

The equilibrium structure of the finite, interphase interfacial region that exists between a liquid film and a bulk vapor is resolved by molecular dynamics simulation. Argon systems are considered for a temperature range that extends below the melting point. Physically consistent procedures are developed to define the boundaries between the interphase and the liquid and vapor phases. The procedures involve counting of neighboring molecules and comparing the results with boundary criteria that permit the boundaries to be precisely established. Two-dimensional radial distribution functions at the liquid and vapor boundaries and within the interphase region demonstrate the physical consistency of the boundary criteria and the state of transition within the region. The method developed for interphase boundary definitions can be extended to nonequilibrium systems. Spatial profiles of macroscopic properties across the interphase region are presented. A number of interfacial thermodynamic properties and profile curve-fit parameters are tabulated, including evaporation/condensation coefficients determined from molecular flux statistics. The evaporation/condensation coefficients away from the melting point compare more favorably with transition state theory than those of previous simulations. Near the melting point, transition theory approximations are less valid and the present results differ from the theory. The effects of film substrate wetting on evaporation/condensation coefficients are also presented.     

Phase separation in non-ionic surfactant Triton X-100 solutions in the presence of phenol

The influence of concentration conditions and acidity on the phase separation in non-ionic surfactants Triton X-100 solutions in the presence of phenol was investigated. It was shown that the addition of small amounts of phenol results in the decrease of the cloud point temperature of Triton X-100 solutions. On the other hand, the addition of phenol into the investigated system resulted in the decrease of the hydration values of surfactant-rich phases and the increase of their hydrophobicity. The extraction degree and distribution coefficient of phenol between the water and the surfactant-rich phases were studied. On the basis of data obtained the molar parts of water, phenol and Triton X-100 in the non-ionic surfactant-rich phases formed at different concentration conditions were calculated. Possibilities of the application of phenol-induced micellar extraction for microcomponents preconcentration were estimated.     

Application of pyridylazo and thiazolylazo reagents in flow injection preconcentration systems for determination of metals

Pyridylazo and thiazolylazo reagents are synthetic dyes widely used in analytical chemistry. These reagents are also very attractive for use in preconcentration systems. This paper covers the application of pyridylazo and thiazolylazo reagents in flow injection systems for the determination of metals. The article discusses flow injection preconcentration systems with solid-phase extraction, precipitation and cloud point extraction. The use of pyridylazo and thiazolylazo reagents in flow injection detection systems is also presented. The relative advantages and drawbacks of these systems are discussed. The application of pyridylazo and thiazolylazo reagents in new systems is presented in the concluding part of this review article.     

Estimation of Distribution Parameters of Organic Solutes in Cloud Point Extraction

Cloud point extraction of aromatic solutes in the system containing nonionic surfactant polyoxyethylene nonylphenyl ether (PONPE 10) was discussed in terms of their hydrogen-bond donating and accepting abilities and hydrophobicity. It was shown that the Abraham model could be used to estimate the distribution ratio and the effect of aromatic solutes on the cloud point. Copyright 2000 Academic Press.     

Lyophilic properties of surfactant-rich phases of polyethoxylated alkylphenols formed at cloud point temperature

The influence of the concentration conditions, solutions acidity, and electrolyte additions on the lyophilic properties of the surfactant-rich phases of polyethoxylated alkylphenols OP-7 and OP-10 formed at cloud point temperature were studied. The lyophilic properties of surfactant-rich phases were determined by estimating of their effective hydration values and solvation free energy of methylene and carboxyl groups at cloud point extraction of aliphatic monocarboxylic acids. It was shown that the surfactant-rich phases formed from the dilute surfactant solutions have more hydrophobic properties than the phases formed from the high concentrated solutions. The possibility of changing the lyophilic properties of surfactant-rich phases by electrolyte additions was shown: complex formation between electrolyte cation and the polyoxyethylene chain of the surfactant increases the hydrophilic properties of the surfactant-rich phases. Calculations of the solvation free energy of methylene and carboxylic fragments of the aliphatic carboxylic acids at micellar extraction showed the uniqueness of the surfactant-rich phases which are able to energetically advantageously extract both hydrophilic and hydrophobic molecules of substrates.     

Roles of hydrophobicity and volatility of organic substrates on sonolytic kinetics in aqueous solutions

The aquasonolytic rate constants of cyclic C6H(X), aliphatic C6H(X), thioethers, thiophenes, and N-heterocyclic compounds show over a 90-fold variation under identical conditions of ultrasonic irradiations. Henry's Law constant of the substrate has a substantial effect on the aquasonolytic rate; a higher Henry's Law constant leads to a aquasonolytic rate constant, which indicating the transfer process of organic substrate between bulk liquid and cavitational bubbles is essential for aquasonolysis. The aquasonolytic rate constants, however, dramatically show an irregular variation with increasing vapor pressure among various substrates. Although the volatility of substrate has been widely regarded as a basic factor influencing aquasonolysis, it seems that vapor pressure of substrate is not a determining one that accounts for the difference of aquasonolytic rate constants. In contrast, the hydrophobic parameters of volatile substrate such as water solubility and octanol-water partition coefficient have shown obvious correlation with the aquasonolytic rate constant for the model compounds; a higher hydrophobicity of volatile substrate results in a higher aquasonolytic rate constant. It could be concluded that the transfer process from bulk liquid to cavitational bubbles and the aquasonolytic kinetics of organic substrate are jointly controlled by the hydrophobicity and volatility; therein the hydrophobicity dominates the transfer process and the aquasonolysis of volatile substrate.     

Construction of coaxial liquid centrifugal platform for the extraction of active ingredients from natural products

In the classical natural product extraction and separation process, it is tedious and requires large amounts of reagents and time. In this study, an efficient coaxial liquid centrifugal oil-water-oil triple-liquid-phase system with a simple structure and convenient operation was successfully constructed and used to extract flavonoids from Platycladi Cacumen. The results showed that the coaxial liquid centrifugal platform constructed in this study had good stability and 6 ml was the minimum volume of the middle phase for 1000 rpm to stabilize the system. Besides, it was easy to repeat the operation: the relative standard deviations of the extraction yields of flavonoids and sugar in six parallel operations were all less than 10%. Moreover, it was only one-tenth of the time required for this method as traditional liquid-liquid extraction while reducing the use of volatile organic reagents. Finally, the new method was more selective than the traditional method for the extraction of flavonoids. Therefore, this study provides a possibility for the coaxial liquid centrifugal platform to be used in multi-liquid phase systems to achieve the simultaneous extraction of different parts of natural products by different liquid phases. It is expected to provide a reliable reference for further expansion of small-scale experimental operations to industrial production.     

Effect of anionic structure on the phase formation and hydrophobicity of amino acid ionic liquids aqueous two-phase systems

Compared with the conventional ionic liquids, amino acid ionic liquids are more biodegradable and biocompatible, and can enhance stability of biomaterials. In this work, amino acid ionic liquids 1-butyl-3-methylimidazolium L-serine ([C(4)mim][Ser]), 1-butyl-3-methylimidazolium glycine ([C(4)mim][Gly]), 1-butyl-3-methylimidazolium L-alanine ([C(4)mim][Ala]) and 1-butyl-3-methylimidazolium L-leucine ([C(4)mim][Leu]) have been synthesized. These ionic liquids are found to form aqueous two-phase systems (ATPSs) by the salted-out of K(3)PO(4) in aqueous solutions. Phase diagram of the ATPSs and the Gibbs energies of transfer of methylene group from the bottom salt-rich phase to the top ionic liquid-rich phase have been determined at 298.15K and pH 14, and the effect of anionic structure of the ionic liquids on phase formation of the ATPSs and the relative hydrophobicity between the top and the bottom phases are then examined. In order to understand the effect of relative hydrophobicity of the phases in equilibrium in the ATPSs on the extraction/separation capability of biomolecules, the partition coefficients of cytochrome-c (as a model biomolecule) in the ATPSs are measured by spectrophotometry. It is suggested that hydrophobic interactions are mainly responsible for the higher partition coefficients of cytochrome-c in aqueous two-phase systems at pH 14, and the extraction and separation capacity of biomolecules can be improved by the modulation of the relative hydrophobicity of the phases and/or the pH of the system.     

Sorbent extraction in flow injection analysis and its application to enhancement of atomic spectrometry

The extraction of metals as their chelates from aqueous samples can be simplified, miniaturized and automated by flow injection/sorbent extraction techniques. The chelate is formed in the flow stream, sorbed on C-18 bonded silica and then eluted for transfer to the atomic absorption spectrometer. The proposed method is shown to be useful for the preconcentration of copper and lead by means of their chelation with diethyldithiocarbamate or 8-quinolinol; complexation with 1-(2- pyridylazo)-2-naphthol or 4-(2-pyridylazo)resorcinol is also possible. This approach enables organic reagents to be used directly, without immobilization, in “open” flow-injection systems for preconcentration or separation of analytes.     

Sequence‐Based Prediction of Promiscuous Acyltransferase Activity in Hydrolases

Certain hydrolases preferentially catalyze acyl transfer over hydrolysis in an aqueous environment. However, the molecular and structural reasons for this phenomenon are still unclear. Herein, we provide evidence that acyltransferase activity in esterases highly correlates with the hydrophobicity of the substrate‐binding pocket. A hydrophobicity scoring system developed in this work allows accurate prediction of promiscuous acyltransferase activity solely from the amino acid sequence of the cap domain. This concept was experimentally verified by systematic investigation of several homologous esterases, leading to the discovery of five novel promiscuous acyltransferases. We also developed a simple yet versatile colorimetric assay for rapid characterization of novel acyltransferases. This study demonstrates that promiscuous acyltransferase activity is not as rare as previously thought and provides access to a vast number of novel acyltransferases with diverse substrate specificity and potential applications.     

Evaluation of the factors affecting extraction of organic compounds based on the acid-induced phase cloud point approach

On the basis of a better analytical exploitation of acid-induced cloud point approach, a systematic study on the phase behaviour of acid aqueous solutions of anionic surfactants and factors affecting anionic surfactant-mediated extractions was performed. The anionic surfactants investigated were alkylsulphonates (ASS) with alkylchain lengths comprised between 8 and 16 carbon atoms. The critical hydrochloric acid concentration (minimal acid concentration required to separation in two liquid phases) was found to increase as alkylchain length of the anionic surfactant increased from 10 to 14. Non-acid-induced liquid-liquid phase separation was observed for sodium octanesulphonate (SOS) or sodium hexadecyl sulphonate (SHS) in the hydrochloric concentration range 0-10 M. Acid aqueous solutions of sodium decylsulphonate (SDeS) and sodium dodecylsulphonate (SDoS) separated into two liquid phases at temperatures ranging between 10 and 80 °C, while temperatures >35 °C were required for sodium tetradecylsulphonate. The influence on extraction efficiency and concentrating ability of experimental variables such as hydrophobicity and concentration of surfactant, nature and concentration of analyte, hydrochloric acid concentration, time and temperature of extraction and time of equilibration and centrifugation was examined. Advantages provided by anionic surfactant-mediated extractions over the use of non-ionic surfactants (cloud point extractions) are discussed.     

Properties of the material of interphase formations based on lanthanide Di-(2-ethylhexyl)phosphate

The structural, optical, and electrical properties of the material of interphase formations arising spontaneously in the interface region of an extraction system consisting of an aqueous solution of a rare-earth element (REE) salt (a solution of di-(2-ethylhexyl)phosphoric acid (D2EHPA) in an organic solvent) are investigated. The structure of lanthanide di-(2-ethylhexyl)phosphate is determined and its lattice constants are estimated. It is shown that the electric conductivity and optical density of the material of interphase formations transferred onto a glass plate correlate with the accumulation of REEs in the interfacial layer of the extraction system. The difference between the properties of the material of interphase formations based on REEs of the yttrium and cerium subgroups is established.     

Micellar extraction preconcentration of barium with phases of nonionic surfactants at the cloud point

The micellar extraction of barium with phases of nonionic surfactant Triton X-100 was studied in the presence of aliphatic monocarboxylic acids, crown ethers, and Carboxyarsenazo and its mixtures with cetylpyridinium chloride and octylamine. It was shown that the complete extraction of barium into the micellar phase was attained using Carboxyarsenazo and cationic surfactants in the presence of octylamine through the formation of a ternary hydrophobic complex. The conditions for the determination of the atomic absorption of barium in water with preconcentration into the nonionic surfactant phase at the cloud point temperature were developed.     

Clouding behaviour in surfactant systems

A study on the phenomenon of clouding and the applications of cloud point technology has been thoroughly discussed. The phase behaviour of clouding and various methods adopted for the determination of cloud point of various surfactant systems have been elucidated. The systems containing anionic, cationic, nonionic surfactants as well as microemulsions have been reviewed with respect to their clouding phenomena and the effects of structural variation in the surfactant systems have been incorporated. Additives of various natures control the clouding of surfactants. Electrolytes, nonelectrolytes, organic substances as well as ionic surfactants, when present in the surfactant solutions, play a major role in the clouding phenomena. The review includes the morphological study of clouds and their applications in the extraction of trace inorganic, organic materials as well as pesticides and protein substrates from different sources.     

Efficient and Convenient Synthesis of Diethers from Furoin Under Ultrasound and Solid-liquid Phase Transfer Catalysis Conditions

Introduction Compounds having an active hydroxy group, such as, acyloins can be easily alkylated by alkyl halides in the presence of a phase transfer catalyst (PTC). The reaction is usually carried out in the presence of concentrated aqueous sodium or potassium hydroxide and a phase transfer catalyst, such as, quaternary ammonium salts[1-3], which facilitate the interphase transfer of species, making reactions between reagents in two immiscible phases possible. The reaction involves a series of equilibrium and mass-transfer steps.     

Organic Phase PPO Biosensors Prepared by Multilayer Deposition of Enzyme and Alginate Through Avidin‐Biotin Interactions

Films of electrogenerated polypyrrole and hydrophilic alginate, both functionalized with biotin moieties, were used to allow for the transfer of polyphenol oxidase activity in organic media. Enzyme electrodes, based on multilayered structures, were protected at the molecular level by the affinity binding of alginate as a hydrophilic additive, and were then transferred into chlorobenzene, dichloromethane, chloroform, ethyl acetate or acetonitrile. The biosensor performance for the detection of catechol at ?0.2 V was investigated, highlighting the main influence of the hydrophobicity of the solvent and, to a lesser extent, the dielectric constant. The effect of the substrate hydrophobicity on the biosensor response was examined in chlorobenzene.     

The Use of Microemulsions for the Extraction and Simultaneous Preconcentration of Maltenes as Potential Chemical Markers to Identify Hydrocarbon Deposits

The possibility of using microemulsions as extractants during the extraction of chemical markers from oil samples and their subsequent preconcentration by the decomposition of microemulsions and determination of oil components by the gas chromatography-mass-spectrometry method is shown. Due to hydrophobicity, oil components pass into the organic phase after the decomposition of microemulsions and become concentrated due to the reduction of the volume of one of the phases. It is shown that as the preconcentration of the precipitant increases, the preconcentration coefficient of the chemical markers grows to 8–10. The method itself is characterized by low detection limits, good selectivity, and reproducibility.     

Sequence-Based Prediction of Promiscuous Acyltransferase Activity in Hydrolases

Certain hydrolases preferentially catalyze acyl transfer over hydrolysis in an aqueous environment. However, the molecular and structural reasons for this phenomenon are still unclear. Herein, we provide evidence that acyltransferase activity in esterases highly correlates with the hydrophobicity of the substrate-binding pocket. A hydrophobicity scoring system developed in this work allows accurate prediction of promiscuous acyltransferase activity solely from the amino acid sequence of the cap domain. This concept was experimentally verified by systematic investigation of several homologous esterases, leading to the discovery of five novel promiscuous acyltransferases. We also developed a simple yet versatile colorimetric assay for rapid characterization of novel acyltransferases. This study demonstrates that promiscuous acyltransferase activity is not as rare as previously thought and provides access to a vast number of novel acyltransferases with diverse substrate specificity and potential applications.     

Determination of furosemide in urine by HPLC with preconcentration by micellar-extraction

The micellar extraction of furosemide by the nonionic surfactant (NS) Triton X-100 at the cloud point was studied; it was performed in a conventional heating mode and upon induction with phenol. It was shown that the quantitative recovery of the preparation was attained using hydrophobic micellar phases of NS modified with phenol. A procedure was developed for determining furosemide in urine by reversed-phase HPLC with preconcentration by micellar extraction in the presence of phenol. The preconcentration ratio was 80 and the detection limit for furosemide, 3 mg/L. The procedure was used to analyze urine samples by the standard addition method.