Concentrations Of Mixture Components Research Articles

Complex formation in methanol-chloroform solutions: Vibrational spectroscopy and quantum cluster equilibrium study

Methanol-chloroform solutions with different mixing ratios were studied using vibrational (ATR FTIR and Raman) spectroscopy. Obtained spectra were analyzed by different techniques such as excess spectroscopy and multivariate curve resolution. Analysis of vibrational spectra showed that the investigated solutions consist of four kinds of species: ‘pure’ methanol, ‘pure’ chloroform, and two types of ‘effective’ molecular complexes. Molecular complexes were present in the entire concentration range of methanol dilutions in chloroform. Obtained spectral profiles of ‘pure’ methanol and ‘pure’ chloroform were identical to spectra of bulk species which means that their structure in solution is similar to corresponding ones in bulk methanol and chloroform.Minimal sets of possible structures of associates and molecular complexes were calculated using density functional theory. Information about optimized structures was further used for quantum cluster equilibrium (QCE) calculations. These calculations allowed us to explain the concentration dependence of excess enthalpy of methanol-chloroform solution. It was demonstrated that obtained concentrations of mixture components correlate with experimental ones obtained by MCR-ALS.

Induction of the smectic A phase in liquid crystalline mixtures formulated using non-chiral compounds with positive and negative dielectric anisotropy

ABSTRACT The induction of the SmA phase in mixtures of non-chiral nematic compounds with the positive and the negative dielectric anisotropy is presented which is obtained by different substitutions of fluorine atoms. One component is a three-ring tolane with polar group – OCF3 in position 4 and two fluorine atoms in positions 3 and 5 in the terminal phenyl ring. The other component is two ring tolane with two or four fluorine atoms in the lateral position. Based on phase diagrams, the influence of the alkyl chain length of both types of compounds on the induction phenomenon is shown. Results of the X-ray measurements confirm that the induced phase is a monolayer SmA phase. The increase of the alkyl chain length causes the increase in the strength of the induction in mixtures, i.e. the induced SmA phase is observed for a wider range of the temperature and concentration of mixture components.

Thermodynamic Analysis of the Adsorption and Micellization Activity of the Mixtures of Rhamnolipid and Surfactin with Triton X-165.

The surface tension of aqueous solutions of Triton X-165 with rhamnolipid or surfactin mixtures was measured. The obtained results were applied for the determination of the concentration and composition of the Triton X-165 and biosurfactants mixture at the water–air interface as well as the contribution of the particular component of the mixtures to water surface tension reduction and the mutual influence of these components on the critical micelle concentration. The determination of these quantities was based on both the commonly used concepts and a new one proposed by us, which assumes that the composition of the mixed monolayer at the water–air interface depends directly on the pressure of the monolayer of the single mixture component and allows us to determine the surface concentration of each mixture component independently of surface tension isotherms shape. Taking into account the composition of the mixed monolayer at the water–air interface, the standard Gibbs adsorption free energy was considered. The obtained results allow us to state that the concentration of both mixture components corresponding to their saturated monolayer and the surface tension of their aqueous solution can be predicted using the surfactants’ single monolayer pressure and their mole fraction in the mixed monolayer determined in the proposed way.

Nonlinear regimes of binary mixture convection in a two-layer porous medium of different configurations

The results of modeling the convection of a binary mixture of liquid hydrocarbons in a two-layer porous medium are presented. The simulation area is a horizontally elongated rectangular cavity divided into two layers. In one of the considered cases, these sublayers are of equal height, and in the other case, the interface between the layers has the shape of a convex downward circular arc, which imitates a synclinal geological fold. The layers have different permeability. In the cavity, there is a geothermal temperature gradient with an average temperature characteristic of a depth of 2000 m, which corresponds to the average oil depth. The composition of the mixture, the thermal conditions and the geometry used make up the reservoir model of the hydrocarbon deposit. The problem is solved in terms of the Darcy–Boussinesq model with allowance for the effect of thermal diffusion. The emergence and establishment of nonlinear convection regimes, as well as the distribution of the concentration of mixture components for different values of the permeability of the layers and their dependence on which of these layers is more permeable, are considered in simulations. It is found that in the case of a small difference in the permeabilities of the layers, a stationary regime is established in the cavity of any of the considered configurations. With a significant difference in permeability of the layers in the cavity, either quasi-periodic oscillations of a complex shape or irregular oscillations can be observed. A "local" occurrence of convection is shown for a large permeability difference, followed by a weak penetration of the flow into a less permeable layer, as well as a "large-scale" occurrence of convection in the case of an insignificant permeability difference.

Interactions of fungal entomopathogens with synthetic insecticides for the control of Kuschelorhynchusmacadamiae (Coleoptera: Curculionidae)

AbstractThis study investigated the interactions between insecticides (acephate and indoxacarb) and fungal entomopathogens (Beauveria bassiana [Bals.‐Criv.] Vuill. strain B27, Metarhizium anisopliae [Metschn.] Sorokin strain ECS1, and a commercial B. bassiana product, Velifer® Biological Insecticide) for controlling the macadamia seed weevil, Kuschelorhynchus macadamiae Jennings and Oberprieler, in the laboratory and glasshouse. In the laboratory, additive interactions between insecticides at their full field concentrations (776 mg AI/L of acephate and 75 mg AI/L of indoxacarb) and fungal entomopathogens at 107 conidia/ml (ECS1 and B27) or at full field concentration (0.5 ml of Velifer®/L) were seen at 6 days and 12 days post‐application. Under the same experimental conditions, synergistic interactions against K. macadamiae were observed 6 days post‐application when fungal entomopathogens at 2.5 × 106 conidia/ml or at 25% of full field concentration (Velifer®) were co‐applied with insecticides at 25% of their full field concentrations, whilst additive interactions were again observed at 12 days post‐application. In the glasshouse, additive interactions between insecticides (at full field concentrations) and fungal entomopathogens (at 107 conidia/ml, or at full field concentration for Velifer®) were obtained at 6 days and 12 days post‐application. The results from this study suggest that acephate and indoxacarb have both synergistic and additive effects against K. macadamiae when deployed together with fungal entomopathogens, depending on the initial concentrations of mixture components. Combined application of entomopathogens with compatible insecticides promises to provide more effective management of K. macadamiae than individual chemical applications.

Photoreduction of ferricytochrome c in the presence of potassium ferrocyanide.

Ferricytochrome c has been previously shown to photoreduce in the presence of ferrocyanide anions, but the process has been poorly understood. Here, we propose a kinetic model for this phenomenon and support it with resonance Raman measurements that show a clear dependence of photoreduction on the concentration of mixture components and laser power. Our data are consistent with the photoreduction process that is driven by photoexcitation of the heme followed by an electron transfer from the excited state of the heme macrocycle to the heme iron. Concomitantly, the hole in the heme ground state is filled with an electron transferred from a ferrocyanide ion residing in the heme pocket.

Simplified method for calculation of equilibrium plasma composition

In this work, a simplified method for the evaluation of equilibrium composition of plasmas consisted of monoatomic species is proposed. Multicomponent gas systems resulting from thermal ionization of spatially uniform mixtures are assumed enough rarefied to be treated as ideal gases even after multiple ionization steps. The method developed for the calculation of equilibrium composition of these mixtures makes use of the fundamental principles of statistical physics. Equilibrium concentrations of mixture components are determined by integration of distribution functions over the space of momentum and summation over electronic energy levels. These functions correspond to the entropy maximum. To determine unknown parameters, the systems of equations corresponding to the normalization conditions are derived. It is shown that the systems may be reduced to one algebraic equation if the equilibrium temperature is known. Numeral method to solve this equation is proposed. Special attention is given to the ionized mixtures, generated from the atoms of a single chemical species and the situations, when in the gas only the first- or the first- and second-order ionization are possible.

A Novel Calibration-Minimum Method for Prediction of Mole Fraction in Non-Ideal Mixture.

This article proposes a novel concentration prediction model that requires little training data and is useful for rapid process understanding. Process analytical technology is currently popular, especially in the pharmaceutical industry, for enhancement of process understanding and process control. A calibration-free method, iterative optimization technology (IOT), was proposed to predict pure component concentrations, because calibration methods such as partial least squares, require a large number of training samples, leading to high costs. However, IOT cannot be applied to concentration prediction in non-ideal mixtures because its basic equation is derived from the Beer-Lambert law, which cannot be applied to non-ideal mixtures. We proposed a novel method that realizes prediction of pure component concentrations in mixtures from a small number of training samples, assuming that spectral changes arising from molecular interactions can be expressed as a function of concentration. The proposed method is named IOT with virtual molecular interaction spectra (IOT-VIS) because the method takes spectral change as a virtual spectrum x nonlin,i into account. It was confirmed through the two case studies that the predictive accuracy of IOT-VIS was the highest among existing IOT methods.

Testing hypotheses on moments by observations from a mixture with varying concentrations

A mixture with varying concentrations is a modification of a finite mixture model in which the mixing probabilities (concentrations of mixture components) may be different for different observations. In the paper, we assume that the concentrations are known and the distributions of components are completely unknown. Nonparametric technique is proposed for testing hypotheses on functional moments of components.

Modulation of Plasma Antioxidant Activity in Weaned Piglets by Plant Polyphenols

This study was conducted to evaluate the effect of plant polyphenols (PP) on antioxidant activity in weaned piglets. First, a uniform design, one optimising an experimental technique that can rationally arrange the concentrations of mixture components, was used to obtain the best PP mixture of apple, grape seed, green tea and olive leaf polyphenols based on in vitro antioxidant capacity and inhibitory action on bacterial growth. Second, the optimised PP mixture was tested in vivo with an efficacy trial on piglets. The optimal effects of the mix were observed in vitro when apple, grape seed, green tea, olive leaf polyphenols and a carrier (silicon dioxide) accounted for 16.5, 27.5, 30, 2.5 and 23.5%, respectively, of the mixture. Forty-eight weaned piglets were randomly allocated to two dietary treatments (6 replicates of 4 piglets each per treatment) and fed a control diet (CTR) or CTR supplemented with 0.1% of the optimised PP mixture. Dietary PP did not affect growth performance compared to the CTR group. Plasma total protein, urea nitrogen and lysozyme content were not affected by dietary treatment. No differences of E. coli or Clostridia counts in the faeces and caecum content between the CTR and PP groups were observed. A reduced malondialdehyde concentration in the PP group was observed on day 21 compared to the CTR group (P=0.02). In conclusion, the prepared PP mixture has the potential to improve plasma antioxidant activity.

Chemical mixtures in untreated water from public-supply wells in the U.S. — Occurrence, composition, and potential toxicity

Chemical mixtures are prevalent in groundwater used for public water supply, but little is known about their potential health effects. As part of a large-scale ambient groundwater study, we evaluated chemical mixtures across multiple chemical classes, and included more chemical contaminants than in previous studies of mixtures in public-supply wells. We (1) assessed the occurrence of chemical mixtures in untreated source-water samples from public-supply wells, (2) determined the composition of the most frequently occurring mixtures, and (3) characterized the potential toxicity of mixtures using a new screening approach. The U.S. Geological Survey collected one untreated water sample from each of 383 public wells distributed across 35 states, and analyzed the samples for as many as 91 chemical contaminants. Concentrations of mixture components were compared to individual human-health benchmarks; the potential toxicity of mixtures was characterized by addition of benchmark-normalized component concentrations. Most samples (84%) contained mixtures of two or more contaminants, each at concentrations greater than one-tenth of individual benchmarks. The chemical mixtures that most frequently occurred and had the greatest potential toxicity primarily were composed of trace elements (including arsenic, strontium, or uranium), radon, or nitrate. Herbicides, disinfection by-products, and solvents were the most common organic contaminants in mixtures. The sum of benchmark-normalized concentrations was greater than 1 for 58% of samples, suggesting that there could be potential for mixtures toxicity in more than half of the public-well samples. Our findings can be used to help set priorities for groundwater monitoring and suggest future research directions for drinking-water treatment studies and for toxicity assessments of chemical mixtures in water resources.

General statement of the problem of substance analysis by the products of photochemical reactions

The aim of this study was to formulate the problem and develop a formal procedure for structure determination and substance quantification by the products of its photochemical reaction. This problem appears in studies of rapid photochemical processes, when the lifetime of the initial substance is shorter than the time to the moment of its registration (ecology, toxic substances, etc.). Algorithms of solving corresponding inverse problems are considered, and procedure including several steps is proposed. It includes the determination of the composition and concentrations of mixture components by the spectra of a test substance using the theory of molecular spectra; the recovery of the quantitative composition of the initial substance by the structural formulae of the products of a chemical reaction; and the determination of the initial concentrations of substances and the kinetics of the process on the basis of the developed theory of chemical transformations using information on the reactants and their concentrations. The application of the proposed approach is demonstrated on examples.

Evaluation of the combined toxicity of 15 pesticides by uniform design

Environmental pesticides, including insecticides and herbicides, are frequently encountered as mixtures and threaten non-target organisms in water. Evaluation of the combined toxicity of diverse pesticides with various concentration combinations is important, especially using limited experimental effort. Uniform design (UD) is one optimal experimental technique that can rationally arrange the concentrations of mixture components so that, with a minimum number of experimental runs, the combined toxicity of multiple pesticide mixtures can be evaluated. The concentration compositions of 18 pesticide mixture points designed by UD covered almost all possible concentration ranges of the mixture components on account of the two merits of 'space filling' and 'multiple levels'. The combined toxicities of 18 mixture rays extended by using the fixed-ratio ray design (FRRD) from 18 UD mixture points were evaluated by concentration addition (CA) and independent action (IA) models. It was found that the concentration-response curves (CRCs) predicted by CA were, on the whole, located between the 95% confidence intervals of the experimental CRCs, which implied that the combined toxicity of the pesticide mixture rays could be evaluated by CA. The CRCs predicted by IA were very similar to those from CA. The model developed from the UD mixture rays can effectively simulate mixtures with arbitrary concentration compositions of 15 pesticides. The CA model can accurately evaluate and predict the combined toxicity of the pesticides, which provides a useful tool for risk assessment of a mixture of multiple pesticides in the aquatic environment.

De-intercalation of ethidium bromide and propidium iodine from DNA in the presence of caffeine

AbstractCaffeine (CAF) is capable of interacting directly with several genotoxic aromatic ligands by stacking aggregation. Formation of such hetero-complexes may diminish pharmacological activity of these ligands, which is often related to its direct interaction with DNA. To check these interactions we performed three independent series of spectroscopic titrations for each ligand (ethidium bromide, EB, and propidium iodine, PI) according to the following setup: DNA with ligand, ligand with CAF and DNA-ligand mixture with CAF. We analyzed DNA-ligand and ligand-CAF mixtures numerically using well known models: McGhee-von Hippel model for ligand-DNA interactions and thermodynamic-statistical model of mixed association of caffeine with aromatic ligands developed by Zdunek et al. (2000). Based on these models we calculated association constants and concentrations of mixture components using a novel method developed here. Results are in good agreement with parameters calculated in separate experiments and demonstrate de-intercalation of EB and PI molecules from DNA caused by CAF.

Fast and Accurate Determination of Absolute Individual Molecular Weight Distributions from Mixtures of Polymers via Size Exclusion Chromatography−Electrospray Ionization Mass Spectrometry

We present a method to determine accurate and absolute molecular weight distributions (MWDs) as well as absolute concentrations of the individual macromolecular components in mixtures of polymers of the same monomer class yet differing in their end groups. Data gained from size exclusion chromatography coupled online to refractive index (RI) detection and electrospray ionization mass spectrometry (ESI-MS) are processed by a sophisticated computer algorithm based on the maximum entropy principle. The procedure yields, for the first time, absolute molecular weight distributions of each component corrected for chromatographic band broadening. Molecular weights of up to 10 kDa are accessible with a conventional quadrupole ion-trap mass analyzer. The method is applicable to variable polymer systems regardless of the monomer class and without the need for an external calibration or additional model assumptions. It was validated using binary and ternary mixtures of poly(methyl methacrylate) carrying labile funct...

Adiabatic evaporation of binary liquid mixtures on the porous ball surface

Measured data for the temperature of a porous spherical surface to which an evaporating binary liquid mixture was supplied are reported. In the experiments, solutions of ethyl and methyl alcohols in water, and also solutions of acetone in water, were used. The concentration of mixture components was varied throughout the widest possible range of XL = 0−1, and the temperature of dry air flow past the sphere was in the range t 0 = 15−300 °C. In the present study, a strong influence of the composition of the mixtures on their adiabatic evaporation temperature was established. In the heat- and mass-transfer process, the air temperature is also of paramount importance. An experimental correlation is obtained which generalizes data on adiabatic evaporation temperature in a broad range of component concentrations and temperatures for the experimentally examined binary liquid mixtures.

Acoustic instability in combustion of droplets of liquid fuel

This study deals with the excitation of acoustic vibrations under conditions of combustion of droplets of liquid fuel in a direct-flow combustor. In so doing, a distributed model of combustion is employed: it is assumed that the zone of burn-up of fuel droplets is approximately equal to the combustor length. The fuel droplets were taken to be spherical and monodisperse. The coefficients of binary diffusion were taken to be identical and independent of the concentration of mixture components. The Lewis number was taken to be unity. The Soret and Dufour effects were ignored. The flow was assumed to be one-dimensional, with thorough stirring in the transverse direction and with the absence of stirring in the longitudinal direction. In considering acoustic vibrations, the gas mixture was taken to be a perfect gas, and the presence of the dispersed phase in the mixture was ignored. Such assumptions are standard in calculations of the working processes in combustors [2, 3]. Then the equations of continuity, motion, and energy, as well as the equation of continuity for droplets, may be written as

Analysis of mixtures of organic volatile compound in water by MIMS. Semiquantitative evaluation of data

Chemometric analysis of intensities of ion currents measured by MIMS was demonstrated on two mixtures: nonpolar mixture containing benzene–toluene–p-xylene (set I) and polar mixture containing methanol–ethanol–propan-1-ol (set II), both in water solutions. The acquired MIMS data were evaluated off-line using Solver, a tool of Microsoft Excel and then verified by calculation of relative concentrations of components in mixtures. For evaluation we considered the additivity of ion currents coming from fragmentation of components, independent vapor permeation of components through membrane and unimolecular conditions in ion source of MS. By using this evaluation analysis it is possible to determine relative concentrations of organic substances in mixture, which penetrated through the membrane, without any separation. Set I penetrated according to the model analysis and the obtained relative concentrations were in reasonable agreement with the preset values. On the contrary, for set II the agreement of adjusted and calculated relative concentrations was not achieved due to high dielectric permittivity of alcohols.

Analysis of the parameters of a barrier discharge in Kr-I2 and Xe-I2 mixtures

The barrier discharges in Kr-I2 and Xe-I2 mixtures are investigated as possible light sources at wavelengths λ=185 and 253 nm. The spectral and current-voltage characteristics of the barrier discharges are obtained. The concentrations of mixture components are calculated, and the kinetic diagrams of the reactions are constructed. The emission efficiencies are estimated to be approximately 20% for both wavelengths. The optimum conditions for emission at these wavelengths in the mixtures Xe-I2 (400 ± 15 Torr) and Kr-I2 (200 ± 0.1 Torr) are determined.

Mixture toxicity and its modeling by quantitative structure-activity relationships.

Environmental contaminants are frequently encountered as mixtures, and the behavior of chemicals in a mixture may not correspond to that predicted from data on the pure compounds. This paper reviews current quantitative structure-activity relationship (QSAR) methodology for the analysis of mixture toxicity. Interactions of components in a mixture can cause complex and substantial changes in the apparent properties of its constituents, resulting in synergistic or antagonistic effects as opposed to the ideal reference case of additive behavior: concentration addition (CA) and independent action (IA) are two prominent reference models for the evaluation of joint activity, and both have mechanistic support from pharmacology. After discussing graphical tools for analyzing binary mixtures and joint effect indices suitable also for multicomponent mixtures, water solubility and hydrophobicity of mixtures are analyzed with respect to the property contributions of the individual components. With the former, small but significant deviations from ideal behavior are observed even for simple organics, whereas in the case of low concentrations, mixture hydrophobicity was found to agree approximately with the fractional contributions of the components. A variety of studies suggest that mixtures of compounds exerting only one (narcotic or specific) mode of action can be modeled satisfactorily by assuming CA, whereas the interaction of differently acting compounds tends to yield a less than CA joint activity. The QSARs have been used to predict concentrations of components in mixtures from joint effects and defined mixture ratios and have been developed to predict narcotic-type mixture toxicity from molecular descriptors that are calculated as composite properties according to the fractional concentrations of the mixture components. In the case of ionogenic compounds, initial results suggest that CA may serve as a first-order approximation for the joint effect of un-ionized and ionized compound portions.