Non-associating Components Research Articles

Phase-equilibrium calculations for non-aqueous and aqueous associating systems using continuous thermodynamics

An association model recently introduced by the author [D. Browarzik, Fluid Phase Equilibr. 217 (2004) 125–135] is modified and applied to more systems including aqueous systems. The model is based on chemical theory, on a G E-expression and on continuous thermodynamics and, is focused to the simultaneous description of liquid–liquid equilibrium (LLE) and vapor–liquid equilibrium (VLE). There is an improved calculation of the vapor pressure of the hypothetical pure associates. Furthermore, the calculation of the segment numbers in this version is based on van der Waals volumes. The model permits phase-equilibrium calculations of binary systems consisting of an associating and a non-associating component. The associating component is considered to be a mixture of associates with the composition described by a continuous distribution function that depends on temperature and on one of the mole fractions of the binary system. The equilibrium constant of association is fitted to vapor-pressure data of the associating components. The model needs only one interaction parameter depending on temperature. The accuracy of the simultaneous description of LLE and VLE is reasonably well. The systems considered are: n-pentane + methanol, n-hexane + methanol, n-heptane + methanol, n-octane + methanol, carbon disulfide + methanol, n-hexane + ethanol (VLE only), hexadecane + ethanol, 2-butanone + water, tetrahydrofuran + water.

Nonassociative learning processes determine expression and extinction of conditioned fear in mice

Freezing to a tone following auditory fear conditioning is commonly considered as a measure of the strength of the tone-shock association. The decrease in freezing on repeated nonreinforced tone presentation following conditioning, in turn, is attributed to the formation of an inhibitory association between tone and shock that leads to a suppression of the expression of fear. This study challenges these concepts for auditory fear conditioning in mice. We show that acquisition of conditioned fear by a few tone-shock pairings is accompanied by a nonassociative sensitization process. As a consequence, the freezing response of conditioned mice seems to be determined by both associative and nonassociative memory components. Our data suggest that the intensity of freezing as a function of footshock intensity is primarily determined by the nonassociative component, whereas the associative component is more or less categorical. We next demonstrate that the decrease in freezing on repeated nonreinforced tone presentation following conditioning shows fundamental properties of habituation. Thus, it might be regarded as a habituation-like process, which abolishes the influence of sensitization on the freezing response to the tone without affecting the expression of the associative memory component. Taken together, this study merges the dual-process theory of habituation with the concept of classical fear conditioning and demonstrates that sensitization and habituation as two nonassociative learning processes may critically determine the expression of conditioned fear in mice.

Modeling vapor–liquid interfaces with the gradient theory in combination with the CPA equation of state

With the final purpose of describing the important aqueous + hydrocarbon liquid–liquid interfaces, the gradient theory was combined with the Cubic-Plus-Association equation of state (CPA EOS), taking advantage of the correct representation of interfacial tensions provided by the gradient theory and the correct phase equilibrium of water + hydrocarbon systems already obtained from CPA.In this work, preliminary studies involving the vapor–liquid interfacial tensions of some selected associating and non-associating pure components (water, ethanol, n-butane, n-pentane, n-hexane, n-heptane) are presented and discussed.The good description of equilibrium properties such as vapor pressure and liquid and vapor phase densities is shown in the full range of the vapor–liquid saturation line. For non-associating components, results are compared with those from the Soave–Redlich–Kwong and Peng–Robinson equations of state.A correlation for the influence parameter is presented from which surface tensions can be obtained in a broad temperature range with average errors smaller than 1%.

The endocannabinoid system of the brain: A potential therapeutic target for the treatment of anxiety disorders in traumatised patients?

It is essential for the survival of man and animal to recognise and adequately react to potentially harmful situations. The latter capability is characterised by an initial fear response that wanes in absence of the expected calamity. Following a traumatic event, a subset of humans and animals is no longer able to recover from the incidence. We use fear conditioning in mice in order to characterise cellular correlates of this maladaptation. According to our studies, the fear reaction following conditioning consists of associative and non-associative memory components. Our data indicate that primarily the non-associative component encodes information about the aversive encounter, and is susceptible to extinction. Experiments with mutant mice and pharmacological intervention suggest that this adaptive process critically depends on the endogenous cannabinoid system of the brain, which seems to represent a promising therapeutic target for the treatment of certain anxiety disorders associated with traumatic experiences.

An associated-solution model for hydrogen-bonding molecules and multicomponent liquid–liquid equilibria for methanol, methyl tert-butyl ether, tert-amyl methyl ether, toluene, and 2,2,4-trimethylpentane mixtures

A new UNIQUAC associated-solution model taking into account association of hydrogen-bonding molecules and solvation between unlike molecules with allowance for a non-polar interaction was presented to predict the ternary and quaternary liquid–liquid equilibria (LLE) for the mixtures of associating molecule acetonitrile, aniline, and methanol with non-associating components. The 17 ternary systems were represented successfully using only binary parameters. The model was further used to represent the experimental tie-line data for quaternary mixture of the methanol+2,2,4-trimethylpentane (TMP)+methyl tert-butyl ether (MTBE)+ tert-amyl methyl ether (TAME) system and those of constituent three ternary mixtures of the methanol+TMP+MTBE, methanol+TMP+TAME and methanol+TMP+toluene systems measured at the temperature 298.15 K and ambient pressure. Good agreement between the experimental results and those calculated by the associated-solution model was obtained. Additionally, the results were compared with those calculated by extended and modified UNIQUAC models that assume no chemical equilibria between associating molecules.

Predictive Models for Interfacial Properties of Associating Systems. A Statistical Thermodynamic Approach

The article presents a simple approach for predicting interfacial properties of multicomponent systems exhibiting acid−base interactions. The strategy involves incorporation of association effects arising due to the presence of strong intermolecular interactions, such as hydrogen bonding, into any existing model that accounts for physical interactions. A system under consideration is treated as a mixture of various hydrogen-bonded complexes of associating molecules and monomers of nonassociating components. These molecular entities are assumed to interact with each other through forces as described by a chosen physical model. For the purpose of illustration of the proposed approach, the theory developed by Prigogine and Marechal has been chosen to represent the physical interactions among the molecular entities. The theory requires surface tensions of (only) the monomeric species present in the liquid phase as input parameters. This information can be extracted using the proposed theory from the physical ...

Dissociation of Processes Underlying Spatial S-R Compatibility: Evidence for the Independent Influence of What and Where

The process-dissociation procedure was used to estimate the influence of spatial and form-based processing in the Simon task. Subjects made manual (left/right) responses to the direction of arrows (> or <) presented to the left or right of fixation. Manipulating the proportion of incongruent trails (e.g., a right-pointing arrow presented to the left of fixation) affected both the size and direction of the Simon effect. To account for this pattern of data, we compared process estimates based on three possible relationships between spatial and form-based processing: independence, redundancy, and exclusivity. The independence model provided the best account of the data. Most telling was that independent form-based estimates were superior at predicting observed performance on arrows presented at fixation and did so consistently across conditions (r′s > .80). The results provide evidence that the form ("what") and spatial location ("where") of a single stimulus can have functionally independent effects on performance. They also indicate the existence of two kinds of automaticity—an associative ("implicit learning") component that reflects prior S-R mappings and a nonassociative component that reflects the correspondence between stimulus and response codes.

Tolerance for opiate analgesia: Complex effect of antagonists of receptors for excitatory amino acids

The effect of excitatory amino acid receptor antagonists on the development of the conditioned reflex component of the tolerance for morphine analgesia is studied. It is demonstrated that the antagonists of NMDA and non NMDA receptors reduce the development of associated component of the tolerance, while the magnitude of the nonassociative component changes after co-administration of morphine with NMDA receptor antagonists.

Thermodynamics of liquid mixtures of acids: phase equilibria and excess molar enthalpies of acetic acid mixtures with active non-associating components

Vapour-liquid equilibria and excess molar enthalpies of binary solutions of acetic acid with water, 2-butanone, methyl acetate and ethyl acetate are calculated using the uniquac associated-solution model, which takes into account the autodimerization of acetic acid and the heteroassociation of unlike molecules. Prediction of ternary liquid-liquid equilibria for the acetic acid + water + nonassociating component systems are demonstrated from the same model with only binary parameters. The calculated results agree well with the experimental values.

Thermodynamics of associated solutions: Prediction of ternary excess molar enthalpies of alcohol mixtures containing an active non-associating component

Ternary excess molar enthalpies of 1-propanol+triethylamine + n-heptane, 1-propanol + 1-hexanol + 3-pentanone and 1-propanol + 1-heptanol + 3-pentanone have been predicted using the uniquac associated-solution model with binary parameters alone. For 1-propanol + triethylamine + n-heptane, the uniquac associated-solution model gives better predicted results than those obtained from the eras model of Heintz and the nrtl equation. For the two other ternary systems, the uniquac associated-solution model is superior to the group-contribution model of Nitta-Chao.

Associative learning in a network model of Hermissenda crassicornis. II. Experiments.

A companion paper in a previous issue of this journal presented a resistance-capacitance circuit computer model of the four-neuron visual-vestibular network of the invertebrate marine mollusk Hermissenda crassicornis. In the present paper, we demonstrate that changes in the model's output in response to simulated associative training is quantitatively similar to behavioral and electrophysiological changes in response to associative training of Hermissenda crassicornis. Specifically, the model demonstrates many characteristics of conditioning: sensitivity to stimulus contingency, stimulus specificity, extinction, and savings. The model's learning features also are shown to be devoid of non-associative components. Thus, this computational model is an excellent tool for examining the information flow and dynamics of biological associative learning and for uncovering insights concerning associative learning, memory, and recall that can be applied to the development of artificial neural networks.

Mutual diffusion coefficients for the systems water–enthanol and water–propan-1-ol at 25 °C

Mutual diffusion coefficients have been measured by the Taylor dispersion technique at 25 °C for aqueous solutions of ethanol and propan-1-ol. The results for the ethanol system are in good agreement with the better diaphragm cell results in the literature. Those for the propanol system do not show the large maximum at high propanol concentrations reported by Pratt and Wakeham (Proc. R. Soc. London, Ser. A, 1975, 342, 401), and support the argument of Leaist and Deng (J. Phys. Chem., 1992, 96, 2016) that this maximum is an artifact. The quotient DE/ϕ1ϕ2, the ‘excess’ diffusion coefficient divided by the product of the volume fractions, is found to vary only slightly with composition and to take almost the same values for aqueous methanol, ethanol and propan-1-ol. Similar behaviour is shown by reference systems also having positive excess Gibbs energies but containing non-associating components. However, it has been found that for the aqueous ethanol system the thermodynamically corrected diffusion coefficient, D12/(1 +∂ ln f1/∂ ln x1)T, p, shows a minimum at low ethanol mole fraction, where some thermodynamic properties also show extrema or inflections. This effect is not shown by the reference systems.

Associative learning in honey bees

in spatial orientation and learning during dance communication, but the mechanisms of this kind of learning are little understood. In associative learning, stimuli experienced immediately before the reward (usually sucrose solution) are memorized for the guidance of future behavior. Well-established paradigms have been used to characterize operant and classical conditioning. The classical conditioning of olfactory stimuli is a very effective form of learning in bees and has helped to describe the behavioral and physiological basis of memory formation. It is concluded that memory needs time to be established and is processed in sequential phases. The neuronal compartments of the brain involved in the chemosensory pathway appear to participate differently in the sequential memory phases. A model is developed which assigns the strong non-associative components in olfactory conditioning to the antennal lobes, and the associative components to the mushroom bodies and the lateral output region of the protocerebrum. It is speculated that the amnesia-sensitive memory resides in the mushroom bodies and the amnesia-resistant memory in certain structures (eg the lateral protocerebrum) perhaps together with the mushroom bodies.

Thermodynamics of associated solutions: Prediction of excess molar enthalpies of ternary mixtures containing methanoi, an active non-associating component and n-heptane from binary data

The uniquac associated-solution model is used to predict ternary excess enthalpies of methanol + benzene + n-heptane and methanol + methyl tert-butyl ether + n-heptane from binary information. The model assumes that the excess enthalpy is expressed as the sum of chemical and physical terms. The chemical contribution term is due to the association of alcohol and the solvation between alcohol i-mer and a solvating component and the physical contribution term represents non-specific interactions between unlike molecules in solution.

Thermodynamics of tautomeric solutions: vapour-liquid equilibrium for acetylacetone-non-associating component mixtures

A method is proposed for calculating isothermal vapour-liquid equilibria for binary mixtures of acetylacetone with non-associating components. It uses the thermodynamic equilibrium constant of the tautomerization of acetylacetone and the NRTL equation for expressing the activity coefficients of the keto and enol tautomers of acetylacetone and non-associating components. Calculated values agree satisfactorily with experimental results, showing the utility of the proposed method.

Thermodynamics of Lewis acid‐base mixtures

AbstractThe associated perturbed‐anisotropic‐chain theory (APACT) has been applied to treat multicomponent mixtures, in which components exhibit Lewis acid‐base interactions. Mixtures of amphoteric molecules (such as alcohols), acidic molecules (such as chloroform), and basic molecules (such as ketones) as well as nonassociating components (diluents) are treated. The acid‐base version of the perturbed‐anisotropic‐chain theory (ABPACT) is a closed form equation of state that takes into account explicitly dispersion interactions, polar interactions, and hydrogen bonding interactions between components that self‐associate or solvate. The equation fits binary VLE mixtures quite accurately. Calculated results also are compared with those obtained from the Peng‐Robinson equation of state, UNIFAC and the original APACT. In all cases where there are mixtures of associating components, the ABPACT gives a better fit of experimental data than these other equations.

Thermodynamics of associated solutions of acetonitrile and 2-methyl-2-propanol

Vapour-liquid and liquid-liquid equilibria and excess molar enthalpy data for ternary mixtures formed by 2-methyl-2-propanol, acetonitrile and a non-associating component have been predicted using an association model with binary parameters obtained from constituent binary systems. The model assumes the association of the alcohol and acetonitrile and solvation between unlike molecules, allowing for a non-polar interaction term given by the NRTL equation.

Correlation of the spectroscopic and thermodynamic properties of solutions of propanols or butanols with non-associating components using the UNIQUAC associated-solution model

The UNIQUAC associated-solution model has been applied for representing the spectroscopic and thermodynamic properties of solutions of one of propanols or butanols (A) with non-associating components (B, C) over the entire composition range. The association constants used are those for dimerization, trimerization and higher polymerization of open chain hydrogen-bonded groups and one for cyclic hydrogen-bonded groups (K A 2 for A 1 + A 1 = A 2, K A 3 for A 2 + A 1 = A 3, K A for A i + A 1 = A i + 1, i≥3 and K cy for A i(open) = A i(cyclic), i≥5). The solvation contants for complex formation between the terminal hydroxylic group of open chains and one unassociated component molecule are also taken into account (K AB for A i(open) + B = A iB and K AC for A i(open) + C = A iC). Physical interactions between unlike molecules are represented by the UNIQUAC residual contribution. The model reproduces well the IR spectroscopic data, vapour-liquid equilibria, activity coefficients and excess enthalpies of binary alcohol-unassociated component mixtures and predicts the vapour-liquid equilibria and excess enthalpies of ternary mixtures of an alcohol and two unassociated components.

Thermodynamics of associated solutions containing acetonitrile and 2-butanol

Vapour-liquid and liquid-liquid equilibria and excess molar enthalpy data for ternary mixtures containing 2-butanol, acetonitrile and a non-associating component have been successfully analysed using an association model with binary parameters alone. The model assumes four association constants for the alcohol, two for acetonitrile and solvation constants between unlike molecules, allowing for a non-polar interaction term given by the NRTL equation.

Thermodynamics of solutions of acetonitrile with 2-methyl-1-propanol

The thermodynamic properties of solutions containing 2-methyl-1-propanol and acetonitrile have been analysed using an association model, which assumes the self-association and solvation of 2-methyl-1-propanol and acetonitrile, and includes a non-polar interaction term given by the NRTL equation. Vapour-liquid and liquid-liquid equilibria and excess molar enthalpy data for ternary mixtures including 2-methyl-1-propanol, acetonitrile and a non-associating component have been predicted by the association model using binary parameters only.