Substances In Aqueous Solutions Research Articles

Complexation of modified cyclodextrins with hydroxylated substances in aqueous solutions. Calorimetric studies at 298 K

The formation of complexes between hydroxypropyl-β-cyclodextrin or methyl-β-cyclodextrin and 1-alkanols or cycloalkanols has been studied calorimetrically at 298 K in water and in concentrated aqueous solutions of ethanol with the aim of understanding the effects of the solvent medium on the association process. When a complex is formed, calorimetry enables the calculation of both the enthalpy and the association constant, from which the free energy and the entropy of the process can be obtained. The forces involved in the association process are discussed in the light of the signs and values of the thermodynamic parameters obtained. The most important conclusions from this study are: (i) for linear alkanols, hydrophobic interactions are largely the forces acting in the complexation. That is detected by the small enthalpies and by the high and always positive entropies. For cycloalkanols, entropies are positive or negative—an indication that other forces act in the complexation. (ii) In concentrated aqueous solutions of cosolvent, complexation is characterized by enthalpy and entropy changes which depend on the extent of alteration induced by the cosolvent on the structure of water and on the hydration shells of the interacting substances. (iii) A linear correlation exists between enthalpy and entropy of complexation, thus indicating that inclusion is a process dominated by aquation phenomena and ascribed to the modifications experienced by the solvent in the hydration shells of the interacting substances.

Thermodynamic and kinetic aspects of self-association of dyes in aqueous solution

The thermodynamic and kinetic data of monomer–dimer equilibria of dyes and their related substances in aqueous solutions have been reviewed. The enthalpy–entropy compensation relation with the compensation temperature of 273(±5) K was observed. The thermodynamic parameters were found to change with the structure of dye and the species and the concentration of co-existing substances. The kinetic data showed that the compensation relation mainly arose from the forward activation process and there are at least three activation patterns. Redistribution of hydrated water molecules around participating components upon dimerization has been considered to play a central role in these properties. The monomer-dimer equilibria of dyes in aqueous solutions are of great value to be studied as the simplest model systems of many interaction systems.

Crosslinking of dextran with some selective Cl-, P- and N-containing functional substances in aqueous solutions

Crosslinking reactions of Dextran (Dx) ( M n of 5.0×10 5 and 2.0×10 6 g mol −1) with some selective Cl-, P- and N-containing functional monomers such as epichlorohydrin (ECH), phosphorus oxychloride (POC1 3) and N, N′-methylenebisacrylamide (MBAM) as well as with 60Co-γ-irradiation were carried out in the basic aqueous solutions (2.8 N NaOH) at 25–50°C. The optimum conditions of the effective swelling and crosslinking for the each system studied were found. Some swelling parameters such as initial rate of swelling ( R S, %min −1), crosslink density ( ρ, g ml −1), equilibrium swelling ( S eq, %) and average molecular weight of crosslinked fragments ( M c, g mol −1) for the Dx/crosslinker (CL) systems studied were determined by using of kinetic methods and well known Flory-Rehner equation. A substantial difference of these parameters observed for the various Dx/CL systems was explained by the effect of nature and concentration of crosslinking agents on the mechanism of crosslinking and swelling processes. It was shown that R S and ρ values increase while the S eq and M c values decrease depending on the nature of CLs in the following raw: γ-ray-ECH-MBAM-POCl 3. Concentration of MBAM does not influence the initial rate of swelling while effect of CL concentration is strongly advented in the Dx/ECH and Dx/POC1 3 systems. Effectiveness of CLs is also confirmed by TGA analysis of crosslinking polymers. The formation of unsaturated crosslinked fragments, which are easily polymerized or photocyclodimerized as affected of u.v.-irradiation, was confirmed by Fourier transform infrared (FT-IR) spectroscopy. General scheme and proposed mechanism of crosslinking reactions in the Dx/CL systems was also described.

Hydrolysis of some imidazole, benzimidazole, and 1,2,3-benzotriazole derivatives according to HPLC and NMR diffusimetry data

Hydrolysis of 1-mesylimidazole, 1-mesylbenzotriazole, and 1-tosylbenzimidazole was studied by reversed-phase HPLC and pulsed field gradient NMR diffusimetry. The hydrolysis rate constants and half reaction times were determined. The self-diffusion coefficients of the substances in aqueous solutions were measured. The reversed-phase HPLC data agree well with those of NMR diffusimetry.

Nonequilibrium solid-phase microextraction for determination of the freely dissolved concentration of hydrophobic organic compounds: matrix effects and limitations.

Solid-phase microextraction (SPME) has recently been applied to measure the freely dissolved concentration, as opposed to the total concentration, of hydrophobic substances in aqueous solutions. This requires that only the freely dissolved analytes contribute to the concentration in the SPME fiber coating. However, for nonequilibrium SPME the sorbed analytes that diffuse into the unstirred water layer (UWL) adjacent to the SPME fiber can desorb from the matrix and contribute to the flux into the fiber. These processes were described as a model. Experimentally, an equilibrated and disconnected headspace was used as a reference for the freely dissolved concentration. The expected contribution of desorbed analytes to the uptake flux was measured for PCB no. 52 in a protein-rich solution, while it was not measured in a matrix containing artificial soil. The latter was possibly due to slow desorption of the analyte from the artificial soil. On the basis of the present study, a contribution of desorbed analytes to the uptake flux is expected only if(1) the rate-limiting step of the uptake process is diffusion through the UWL, (2) the concentration of the sorbed analyte is high, and (3) desorption from the matrix is fast.

Oxidation of organic substances in aqueous solutions over Ru catalysts by oxygen

The catalytic performance of supported Ru catalysts has been studied in the reactions of wet oxidation of acetonitrile, N, N-dimethyl formamide and carbamide at T=433–533 K and P=2.0–4.6 MPa, and wet oxidation of real sewage from an alcohol plant (so-called Luther water) at T=403–473 K and P=1.5–3.6 MPa. The Luther water contained a mixture of low-boiling (C 1–C 5) aldehydes and alcohols. The experiments were carried out in a perfectly mixed batch autoclave reactor. The conversion of alcohols and aldehydes contained in the Luther water and selectivity of the process towards CO 2 and water as well as the selectivity of the oxidation of acetonitrile, N, N-dimethyl formamide and carbamide towards CO 2, N 2 and water were determined at various temperatures and reaction times. Ru (4.8 wt.%)/graphite-like carbon was effective in the oxidation of Luther water (ΔTOC=97.5% at T=423 K for 1 h), carbamide ( X CO(NH 2) 2 =100%, S CO(NH 2) 2→CO 2 =100%, S CO(NH 2) 2→N 2 =71% at 473 K, 2 h) and acetonitrile ( X CH 3CN =100%, S CH 3CN→CO 2 =100%, S CH 3CN→N 2 =75% at 493 K, 1 h). Ru/active carbon/γ-Al 2O 3 was effective in the oxidation of N, N-dimethyl formamide ( X HCON(CH 3) 2 =100%, S HCON(CH 3) 2→CO 2 =61%, S HCON(CH 3) 2→N 2 =100% at 493 K).

Factors determining the formation of complexes between α-cyclodextrin and alkylated substances in aqueous solutions: a calorimetric study at 25 °C

The formation of complexes of α-cyclodextrin with cycloalkanediols, monoalkylamines and 1-alkanols has been studied calorimetrically at 25 °C in water, in phosphoric acid, pH 1.3, and in phosphate buffer, pH 5.5, respectively. When a complex is formed, calorimetry enables the calculation of both the enthalpy and the association constant, from which the free energy and the entropy of the process can be obtained. A model is proposed to explain the unusual trend of the association parameters for substances having alkyl chains longer than six–seven carbon atoms. The main role played by the different functional groups, and the forces involved in the association process, are discussed in the light of the signs and values of the thermodynamic parameters obtained. The effect of the variation of the aqueous medium on the hydration of the interacting substances and the consequent changes in the association parameters have been investigated. To this end, the thermodynamic parameters for the formation of the complexes between the cyclodextrin and 1-pentanol were determined at increasing concentrations of phosphate buffer. There is an increase in the association constant due to a positive entropy contribution originating from the relaxation of water molecules from the hydrophobic hydration cosphere of the alkanol to an increasingly disordered bulk. Deaquation of the interacting substances is the main factor determining the stability of the inclusion complex.

Effect of Solution Chemistry on the Extent of Binding of Phenanthrene by a Soil Humic Acid: A Comparison of Dissolved and Clay Bound Humic

The effect of pH, ionic strength, and cation in solution on the binding of phenanthrene by a soil humic acid in the aqueous phase was determined using fluorescence quenching. The phenanthrene binding coefficient with the dissolved soil humic, K{sub oc}, decreased with increasing ionic strength and solution cation valence. At low values of ionic strength, K{sub oc} values for this soil humic acid increased with increasing pH. For this humic sample, the experimental results were consistent with a conformational model of the humic substance in aqueous solution where, depending on solution conditions, some parts of the humic structure may be more open to allow increased PAH access to attachment sites. After sorption onto clays, supernatant solutions of the unadsorbed humic fraction yielded lower K{sub oc} values than the original bulk humic acid, suggesting that the humic substance was fractionating during its sorption onto the clays. Additionally, the extent of phenanthrene binding with the adsorbed humic fraction was lower than the results determined for the bulk humic acid prior to adsorption. The conformation of the humic substance when sorbed onto the inorganic surface appears to be affecting the level of phenanthrene binding by the humic acid.

Fluorescence quenching of polycyclic aromatic compounds by humic substances. Part 1. Methodology for the determination of sorption coefficients.

An introduction to the methodology of fluorescence quenching measurements as an experimental tool for investigating the sorption of hydrophobic organic substances by dissolved organic matter (OM) is given. Special attention is paid to the implications of inner-filter effects (IFEs) on the determination of sorption coefficients. The essential aspects of the theoretical description of IFEs are outlined and various procedures for the IFE correction of fluorescence quenching measurements in the presence of dissolved OM are presented. Geometric parameters relevant for the quantitative description of IFE applying a 90 degrees arrangement between fluorescence excitation and detection are determined by different methods, newly developed or adapted from the literature, for the fluorescence spectrometer used in this work. Moreover, an experimental validation of the applicability of different IFE correction procedures is performed. In order to evaluate the variations of sorption coefficients that result from the use of different IFE correction procedures, the quenching of the fluorescence of the well-known polycyclic aromatic compound pyrene by a commercially available humic substance in aqueous solution is investigated. Compared to the apparent sorption coefficient, which is obtained without any IFE correction, the sorption coefficients determined with the correction of primary IFE or with the correction of primary and secondary IFE are on average ca. 40 or 60% lower. The application of different IFE correction procedures allows the determination of sorption coefficients with appropriate precision of +/- 15%.

Effects Of Catalysts During Ozonation Of Salicylic Acid, Peptides And Humic Substances In Aqueous Solution

The oxidation of two model molecules (salicylic acid and a peptide) and humic substances in aqueous solution was studied using ozone in the presence of various catalysts. Experiments were performed in reactors operated either in batch (TOCo = 2.5 mg C.L−1) or in semi-continuous flow mode (TOCo = 42 mg C.L−1).

Generalized approach to chemical thermodynamic description of solutions and homogeneous and heterogeneous processes involving forms

Developing a generalized approach to quantitative thermodynamic description of chemical phenomena within solution phases demanded improving the denotative system of the key notions and the corresponding chemical thermodynamic formalism. This paper gives a concise but full account of the results of these investigations. In particular, the specific features of solution substance partitioning into so-called partial components (and forms assigned to them) are shown, and a system of standardization of their partial characteristics is presented. This system constructively generalizes the tremendous experience accumulated at present in the field of chemical thermodynamic modeling of the state of a substance in aqueous solutions (taking into account the effective principle of locality and partiality of any internal equilibria). The system is applicable to chemical thermodynamic “structuring” of other multicomponent liquid phases, liquid phase-solid solutions, and heterogeneous systems.

COMPARISON OF TWO SIMPLE METHODS FOR THE MEASUREMENT OF DETECTION THRESHOLDS FOR BASIC, UMAMI AND METALLIC TASTES

Two simple methods were followed to determine detection thresholds for the taste of substances in aqueous solution. The methods applied were: a modification of the ascending method of limits and a method based on the use of scales. Detection thresholds were calculated for the four basic tastes (sweet, salty, acid, and bitterness), umami and metallic. Reference substances for each taste were sucrose, sodium chloride, citric acid, caffeine, monosodium glutamate and iron (II) sulfate heptahydrate and the results of the two methods were compared. We found that the threshold values calculated by method ASTM‐679 was within the range of concentrations identified with the scales method.

Increase in Information by Improvement of Measuring Method in a Multichannel Taste Sensor

We have developed a multichannel taste sensor with lipid membranes which can detect and quantify the basic taste substances in aqueous solution. The aim of the present study is to increase selectivity to adsorptive taste substances (bitter, umami and astringent taste substances) for quantification of taste by improving measuring methods. High selectivity to adsorptive taste substances is obtained by CPA measurement algorithm (CPA: Change of membrane Potential caused by Adsorption). High repeatability is also obtained by developing a cleaning technique of taste sensor.

Adsorption Rate of Agricultural Chemicals and Humic Substances in Aqueous Solution on Activated Carbon.

農地やゴルフ場等に散布する農薬によって水道源水が汚染される恐れがある.そこで, これらの農薬を除去するには活性炭吸着による方法が最適である.しかしながら, 水道源水には常時フミン質が含まれているので, このフミン質が農薬の活性炭吸着に影響を与えるであろう.そこで, シマジン, クロロタロニル, イソプロチオラン, 2, 4-D, ダイアジノンの5種類の農薬およびフミン質のそれぞれ単独および共存系について, 回分装置により吸着平衡関係と有効表面拡散係数を算出した.その結果, 単独・共存系の吸着平衡関係はフロイントリッヒ型で示され, 農薬の吸着量は多く, フミン質の吸着量は農薬の1/100程度で少なかった.有効表面拡散係数は他の有機物と同程度であり, 吸着量が増すと大きくなり濃度依存性が示された.農薬・フミン質共存系における農薬の吸着平衡関係は単独の場合よりは低く, 有効表面拡散係数も小さくなり吸着速度が遅くなった.

A RAPID AND SIMPLE FLOUR-DISK BIOASSAY FOR TESTING SUBSTANCES ACTIVE AGAINST STORED-PRODUCT INSECTS

AbstractA rapid and simple flour-disk bioassay was developed to assay biologically active substances on several species of stored-products insects. The speed, simplicity, and parsimony of the bioassay derive from a single-step mixing of the test substance in aqueous solution with flour. Aliquots (100 μL) of the stirred suspension are then pipetted onto a polystyrene Petri dish using an Eppendorf pipettor and allowed to dry at room temperature overnight to produce uniform flour disks containing the test substance. After equilibration at 30 ± 1°C and 70 ± 5% relative humidity for 24 h, the disks are individually weighed and transferred to Petri dishes with weighed stored-products insects. After 3 days, the remainder of the disk and the living insects are weighed again for calculations of food consumption, utilization, growth, and mortality. Based on the flour-disk bioassay, the neem-based insecticide, Margosan-O®, significantly reduced consumption, growth, feeding, and dietary utilization in Cryptolestes ferrugineus (Stephens), Sitophilus oryzae (L.), and Tribolium castaneum (Herbst) in a dose-dependent manner. Margosan-O® also caused mortality, but the species differed widely in sensitivity, C. ferrugineus being the most sensitive and T. castaneum the least. The mortality of C. ferrugineus and S. oryzae was a consequence of both toxic and antifeedant (starvation) effects, but mortality of T. castaneum was caused entirely by its toxic action. Using a whole-kernel bioassay, it was found that Margosan-O® caused a dramatic reduction in the F1 progeny of all three species.

An n-Bottle Lab Exercise With No Hazardous Waste

n-Bottle lab exercises are popular with both students and instructors. They rely on unique patterns of reaction between substances in aqueous solution. Such exercises test observation, measurement, and deductive reasoning skills of students while presenting the puzzle, What's in the bottle? Traditional n-bottle exercises include precipitation reactions of environmentally hazardous substances, thereby creating a waste disposal problem. The lab exercise described here uses substances whose waste can be easily treated and disposed in the trash. Different versions of the lab are presented which pose various levels of difficulty for students.

Complexation equilibria of humic substances in aqueous solution (Review).

腐植物質の溶液内錯平衡研究の現状を整理した.腐植物質は三次元の有機骨格にカルボキシル基やフェノール性水酸基が固定された高分子イオンと見なすことができるので,その錯平衡解析のためには,1)高分子電解質性,及び2)官能基分布の不均一性についての評価が必須である.本総説では相分離を仮定するDonnanモデル等による高分子電解質性の定量化の試み,並びにモデルの検証に関する実験的研究の動向を紹介する.特に,フルボ酸並びにポリアクリル酸を対象とした研究を例にとり,実験手法,溶液内錯平衡のモデルについて詳述する.

A review of industrial catalytic wet air oxidation processes

Wet oxidation is a thermal aqueous phase process in which organic and inorganic substances in aqueous solutions or suspensions are oxidized by oxygen or air at elevated temperatures and pressures. Various catalysts have been developed to reduce the severity of the reaction conditions. The main features of five commercially practised catalytic wet oxidation (CWO) processes for treating industrial waste waters have been analyzed and presented in this paper, along with highlights on several ongoing developments of new CWO technologies.

Experimental determination of partial specific volumes of humic substances in aqueous solutions

Partial specific volume is an important molecular parameter in the measurement of molecular masses by analytical ultracentrifugation and X-ray diffraction studies. Humic substances (aquatic fulvic and humic acids and peat humic acid) were isolated from a natural source (Whitray Fell, UK). The partial specific volumes ( v ̄ 2 ) have been studied by two independent methods, an analytical ultracentrifugation technique based on simultaneous sedimentation equilibrium measurements in water and deuterium oxide and by high precision digital densimetry. Measurements were made in a range of conditions from 0.01 M to 0.5 M salt concentration and in the humic substance concentration range 0.01 to 2 mg ml −1. Partial specific volumes in the range 0.43 to 0.63 cm 3 g −1 were found depending on the samples and conditions. No evidence was found for a dependence of ( v ̄ 2 ) on humic concentration within the ranges studied. Both methods of measurements gave results in reasonable accord. The ultracentrifugation method was more precise for the aquatic fulvic acid than for the more polydisperse humic acids. For the fulvic sample the reproducibility of the ultracentrifugation method was ± 4.31%, comparable to the average reproducibility of the densimetry method which was ± 4.07% over a range of 12 different systems.

The enthalpies of interaction of glycine with some amides and ureas in water at 25°C

Measurement of solution enthalpyiesof glycine in aqueous solutions of formamide (F), N-methylformamide (NMF), N,N-dimethylformamide (DMF), monomethylurea (MMU), 1,3-diethylurea (DEU) and tetramethylurea (TMU) at 25°C have been undertaken. On the basis of the results, enthalpic coefficients of heterotactic interactions between a glycine zwitterion and a molecule of organic substance in aqueous solutions have been calculated. Using the additivity of groups concept by Savage and Wood (SWAG), contributions of each functional group of studied amides and ureas have been estimated. In this model a zwitterion of glycine has been considered as an individual equal to a single functional group.