Volume Correction Term Research Articles

Ability of biomimetic chromatography and physicochemical systems to predict the skin permeation of neutral compounds. A comparison study

Five in vitro physicochemical systems have been evaluated in terms of its ability to emulate the skin permeation of neutral compounds: the permeation in two different PAMPA membranes, the classical octanol-water partition coefficient, and two biomimetic chromatography systems, one based in cerasome electrokinetic chromatography and another based in reversed-phase liquid chromatography measurements.The coefficients of the solvation parameter model equation of the mentioned systems have been compared to the ones of the skin permeation process through different comparison parameters. Moreover, a method to predict whether a physicochemical system is able to emulate satisfactorily a biological one, just by the analysis of the equation coefficients has been developed. Results reveal that the two PAMPA systems are a good choice to emulate directly the skin permeation of neutral compounds. Instead, the other three systems need a volume correction term to provide a satisfactory emulation. However, after the correction, all the evaluated systems show a similar ability to emulate well skin permeation, as predicted.

Decay of Correlations and Uniqueness of the Infinite-Volume Gibbs Measure of the Canonical Ensemble of 1d-Lattice Systems

We consider a one-dimensional lattice system of unbounded, real-valued spins with arbitrary strong, quadratic, finite-range interaction. We show the equivalence of correlations of the grand canonical (gce) and the canonical ensemble (ce). As a corollary we obtain that the correlations of the ce decay exponentially plus a volume correction term. Then, we use the decay of correlation to verify a conjecture that the infinite-volume Gibbs measure of the ce is unique on a one-dimensional lattice. For the equivalence of correlations, we modify a method that was recently used by the authors to show the equivalence of the ce and the gce on the level of thermodynamic functions. In this article we also show that the equivalence of the ce and the gce holds on the level of observables. One should be able to extend the methods and results to graphs with bounded degree as long as the gce has a sufficient strong decay of correlations.

New experimental density data and derived thermophysical properties of carbon dioxide – Sulphur dioxide binary mixture (CO2 - SO2) in gas, liquid and supercritical phases from 273 K to 353 K and at pressures up to 42 MPa

Due in part to the toxicity of the CO2-SO2 binary system, there are no density data available in the literature. Densities for this system were measured using a vibrating tube densitometer (VTD), Anton Paar DMA 512, and the forced path mechanical calibration (FPMC) method in the gas, liquid and supercritical phases at pressures up to 41.7 MPa. The mole fraction of the mixture was 0.9478 CO2 + 0.0522 SO2 at 298 K and 0.9503 CO2 + 0.0497 SO2 at 273, 283, 323 and 353 K. The compressibility factor, isobaric heat capacity and bubble points were also derived from the measured densities. The classical cubic equations of state, i.e., Soave-Redlich-Kwong (SRK), Peng-Robinson (PR) and Valderrama version of Patel-Teja (VPT) with the CO2 volume correction term and Peneloux shift parameter in addition to a multi parameter EoS based on Helmholtz energy were evaluated using the measured density data. The most accurate EoSs for the investigated system were the multi parameter EoS and the PR-CO2 with overall AAD of 0.6% and 1.0%, respectively.

Measured densities and derived thermodynamic properties of CO2-rich mixtures in gas, liquid and supercritical phases from 273 K to 423 K and pressures up to 126 MPa

The densities of three multi-component mixtures with high CO2 content and common impurities, i.e. hydrocarbons, nitrogen, hydrogen, oxygen, argon and carbon monoxide, were measured using an Anton Paar DMA-HPM densitometer. The mixtures include MIX 1 with 0.9564 mol fraction CO2 and 0.0436 mol fraction impurities of methane and non-condensable gases, MIX 2 with 0.8983 mol fraction CO2 and 0.1017 mol fraction impurity of non-condensable gases and MIX 3 with 0.6999 mol fraction of CO2 and 0.3001 mol fraction of light hydrocarbons. First, the densitometer was calibrated using pure CO2 and then the density measurements of mixtures were carried out in the gas, liquid and supercritical phases at pressures up to 126MPa at various isotherms of T/K=273, 283, 298, 323, 373 and 423. The obtained data then were employed to evaluate the classical cubic equations of state (SRK and PR). In addition, the CO2 volume correction term and the Peneloux shift parameter were introduced to improve density predictions. Comparisons show that applying CO2 volume correction term to SRK EoS with modified kij could improve the density predictions and the AAD was reduced from 4.7% to 1.9%. In addition to the classical cubic equations of state, the new measured data were used to evaluate the GERG EoS. The AAD of the GERG EoS from experimental data measured in this work are 2.8%, 1.0% and 1.2% in the gas, liquid and supercritical phases, respectively. The overall AAD of GERG EoS from the new density data in this work is 1.7%. Thermodynamic properties, i.e. compressibility factor, specific heat capacity, speed of sound and Joule-Thomson coefficient, were then calculated from the experimental density data using thermodynamic equations. Following this the derived properties were compared to the predictions made with the GERG equation of state.

A New Thermodynamic Model for Paraffin Precipitation in Highly Asymmetric Systems at High Pressure Conditions

The predictions of the crystallization temperature and the amount of precipitates of paraffin waxes at high pressure conditions may be inaccurate using existing thermodynamic models. This is mainly due to the lack of experimental data on the molar volume of solid paraffins at high pressures. This inaccuracy is even more pronounced for mixtures of high asymmetry. The present work provides a new accurate modeling approach for solid–fluid equilibrium (SFE) at high pressure conditions, more specifically, for highly asymmetric systems. In contrast to the conventional methods for high pressure SFE modeling which define a Poynting molar volume correction term to calculate the paraffin solid phase nonideality at high pressures, the new method exploits the values of thermophysical properties of importance in SFE modeling (temperatures and enthalpies of fusion and solid–solid transition) evaluated at the high pressure condition using a new insight into the well-known Clausius–Clapeyron equation. These modified para...

VAN DER WAALS EQUATION OF STATE REVISED: GAS MOLECULAR VOLUME CORRECTION

A simple modification has been introduced to the volume correction term in the original van der Waals equation of state based on the intermolecular attractions for real gases, and the new equation of state has been established. While the proposed equation is simpler than other modified equation of state, it produces the best agreement with experiment for density predictions of hydrogen, nitrogen and argon at the pressures up to 100 MPa at a temperature of 298 K. The results show that the proposed equation of state would greatly improve thermodynamic properties studies for real gases, especially at higher pressures.

Calculation of the solid solubilities in supercritical carbon dioxide using a new G ex mixing rule

The aim of this study is to develop a new EOS/G ex-type mixing rule with special attention to calculating the solid solubilities of aromatic hydrocarbons, aliphatic carboxylic acids, aromatic acids, and heavy aliphatic and aromatic alcohols in supercritical carbon dioxide. A volume correction term is applied with a combination of second and third virial coefficients which the equation for the third virial coefficient is quadratic, according to the suggestion by Hall and Iglesias-Silva. In this study, the cubic Peng–Robinson (PR) and Soave–Redlich–Kwong (SRK) equations of state have been used to calculate the solid solubilities of 23 solutes in supercritical CO 2, by using six mixing rules, namely, the Wong–Sandler (WS) rule, the Orbey–Sandler (OS) rule, the van der Waals one fluid rule with one (VDW1) and two (VDW2) adjustable parameters, the covolume dependent (CVD) rule and the new mixing rule. In all cases, the NRTL model was chosen as the excess Gibbs free energy model. The coefficients of the NRTL model and the binary interaction parameters of six mixing rules with two EOSs (PR and SRK EOSs) have been determined for 100 data sets of 23 binary systems over a wide range of temperatures and pressures covering more than 970 experimental data points which are reported in the literature. The results show that the PR EOS with the new mixing rule model is more accurate than the PR and SRK EOSs with the other mixing rules for solid solubility calculations in supercritical carbon dioxide. The regressed interaction parameters of the binary system, without any further modification, were then extended to four ternary mixtures, giving satisfactory results of the solid solubilities in supercritical CO 2.

The temperature dependence of free volume in phenyl salicylate and its relation to structural dynamics: A positron annihilation lifetime and pressure-volume-temperature study

Positron annihilation lifetime spectroscopy (PALS) and pressure-volume-temperature (PVT) experiments were performed to characterize the temperature dependent microstructure of the hole free volume in the low molecular weight glass-former phenyl salicylate (salol). The PALS spectra were analyzed with the new routine LT9.0 and the volume distribution of subnanometer size holes characterized by its mean <v(h)> and standard deviation sigma(h) was calculated. Crystallization of the amorphous sample was observed in the temperature range above 250 K, which leads to a vanishing of the positronium formation. The positronium signal recovered after melting at 303 K. A combination of PALS with PVT data enabled us to calculate the specific density N(h)('), the specific volume V(f), and the fraction of holes f(h) in the amorphous state. From comparison with dielectric measurements in the temperature range above T(B)=265 K, it was found that the primary structural relaxation slows down with temperature, faster than the shrinkage of the hole free volume V(f) would predict, on the basis of the Cohen-Turnbull (CT) free volume theory. CT plots can be linearized by replacing V(f) of the CT theory by (V(f)-DeltaV), where DeltaV is a volume correction term. This was interpreted as indication that the lower wing of the hole size distribution contains holes too small to show a liquidlike behavior in their surroundings. Peculiarities of the relaxation behavior below T(B)=265 K and the possible validity of the Cohen-Grest free volume model are discussed.

Cubic Equations of State Applied to HT/HP and Highly Aromatic Fluids

Summary Pressure/volume/temperature (PVT) data are presented for 38 reservoir fluids including fluids dominated by paraffins, heavy aromatic fluids with a significant content of C81+, and high-temperature/high-pressure (HT/HP) reservoir fluids. By properly taking into account the compositional differences, these fluid types can all be represented using a classical cubic [Soave-RedlichKwong (SRK) or Peng-Robinson (PR)] equation of state (EOS) with volume correction. The plus fraction is split into carbon number fractions and EOS model parameters assigned to each fraction. To keep the number of components at a manageable level, the carbon number fractions are lumped into pseudocomponents, each containing several carbon number fractions. Hydrocarbons as heavy as C200 are considered when splitting up the plus fraction. Neglecting the content of components heavier than C80 will give a false picture of the phase behavior of heavy aromatic fluids. Correlations are presented for Tc, Pc, and w as a function of molecular weight and density. Problems are experienced representing the thermal expansion of stable oils using a cubic EOS in the classical form. It is shown that this deficiency can be cured by introduction of a temperature-dependent volume correction term.

PLASS: Protein-ligand affinity statistical score – a knowledge-based force-field model of interaction derived from the PDB

We have developed PLASS (Protein-Ligand Affinity Statistical Score), a pair-wise potential of mean-force for rapid estimation of the binding affinity of a ligand molecule to a protein active site. This scoring function is derived from the frequency of occurrence of atom-type pairs in crystallographic complexes taken from the Protein Data Bank (PDB). Statistical distributions are converted into distance-dependent contributions to the Gibbs free interaction energy for 10 atomic types using the Boltzmann hypothesis, with only one adjustable parameter. For a representative set of 72 protein-ligand structures, PLASS scores correlate well with the experimentally measured dissociation constants: a correlation coefficient R of 0.82 and RMS error of 2.0 kcal/mol. Such high accuracy results from our novel treatment of the volume correction term, which takes into account the inhomogeneous properties of the protein-ligand complexes. PLASS is able to rank reliably the affinity of complexes which have as much diversity as in the PDB.

Calculation of the solid solubilities in supercritical carbon dioxide using a modified mixing model

The Peng–Robinson equation of state and a modified Huron–Vidal type mixing model with a volume correction term are applied in this study to calculate the solid solubilities of aromatic, fatty acid and heavy alcohol compounds in supercritical carbon dioxide. The UNIFAC activity coefficient model with its optimally fitted binary interaction parameters is used in this study. A volume correction term is employed, and its parameters are correlated as functions of the solid molar volume for both non-polar and polar systems. The effect of the sublimation vapor pressure on the calculation of solid solubilities in supercritical carbon dioxide is examined. The sublimation vapor pressures for heavy compounds are fitted in this study to yield the optimally calculated results of the solid solubility. Reasonable sublimation vapor pressures are obtained and their values are well correlated by the Antoine equation. A generalized calculation model is proposed in this study which gives satisfactory results of the solid solubility in supercritical carbon dioxide for both the binary and ternary systems.

Application of a volume-translated Peng-Robinson equation of state on vapor-liquid equilibrium calculations

A volume-translated Peng-Robinson (VTPR) equation of state (EOS) is developed in this study. Besides the two parameters in the original Peng-Robinson equation of state, a volume correction term is employed in the VTPR EOS. In this equation, the temperature dependence of the EOS energy parameter was regressed by an improved expression which yields better correlation of pure-fluid vapor pressures. The volume correction parameter is also correlated as a function of the reduced temperature. The VTPR EOS includes two optimally fitted parameters for each pure fluid. These parameters are reported for over 100 nonpolar and polar components. The VTPR EOS shows satisfactory results in calculating the vapor pressures and both the saturated vapor and liquid molar volumes. In comparison with other commonly used cubic EOS, the VTPR EOS presents better results, especially for the saturated liquid molar volumes of polar systems. VLE calculations on fluid mixtures were also studied in this work. Traditional van der Waals one-fluid mixing rules and other mixing models using excess free energy equations were employed in the new EOS. The VTPR EOS is comparable to other EOS in VLE calculations with various mixing rules, but yields better predictions on the molar volumes of liquid mixtures.

Correlation of steroid solubilities in supercritical carbon dioxide

A correlation for the solubilities of cholesterol, stigmasterol, ergosterol, pregosterone, and lauric acid is developed. The correlation employs the Patel-Teja cubic equation of state (EOS). The mixture energy parameter of the EOS, am, is determined by a UNIFAC group contribution model at an infinite pressure limit. The excluded volume parameter of the EOS, bm, is evaluated by the van der Waals mixing rule with an excluded volume correction term. New group interaction parameters of the UNIFAC model involving carbon dioxide are reported, and our calculation results are compared with those obtained from other methods. The accuracy of the mixing model with excluded volume correction is shown to be superior to the traditional van der Waals mixing rules with optimally adjusted binary parameters.

Breath-by-breath measurement of true alveolar gas exchange.

A method has been developed for on-line breath-by-breath calculation of alveolar gas exchange by correcting the gas exchange measured at the mouth for changes in lung gas stores. The corrections are applied to the total lung gas exchange, which is found by directly subtracting expired from inspired volume of each gas. Corrections are made for both breath-to-breath changes in lung volumes and changes in alveolar gas concentrations. The lung volume correction term has the effect of reducing the large error sensitivity of O2 exchange that has, in the past, resulted from direct determination by total lung gas exchange. Error each gas. Corrections are made for both breath-to-breath changes in lung volumes and changes in alveolar gas concentrations. The lung volume correction term has the effect of reducing the large error sensitivity of O2 exchange that has, in the past, resulted from direct determination by total lung gas exchange. Error each gas. Corrections are made for both breath-to-breath changes in lung volumes and changes in alveolar gas concentrations. The lung volume correction term has the effect of reducing the large error sensitivity of O2 exchange that has, in the past, resulted from direct determination by total lung gas exchange. Error sensitivity analysis shows that the effect of inaccuracies due to errors in measuring gas flow or gas concentrations are similar in magnitude to those in the open-circuit method that has traditionally been used. The algorithm for alveolar gas exchange has been implemented in a computer program for on-line respiratory analysis alongside the open-circuit calculation of gas exchange at the mouth that has been used in out laboratory. By use of several experimental studies, it is shown that there are very apparent breath-to-breath differences between the gas exchange measured by the two methods. During metabolic and respiratory transients, these differences often have significant influence on interpretation of the underlying physiology.

Functional derivative relations for a finite non-uniform molecular fluid in the canonical ensemble

Functional derivative relations are developed for a finite non-uniform molecular fluid in the canonical ensemble. The total correlation function h(12) satisfies a normalization condition that renders the corresponding response kernel singular. Thus the inverse response kernel does not exist, and the direct correlation function cannot be defined in terms of h(12) by the Ornstein-Zernike equation. This difficulty is circumvented by subtracting the finite volume correction term from h(12) to obtain a modified total correlation function ĥ(12). A simple derivation of the form of this correction term is given; the result confirms and generalizes an earlier result of Lebowitz and Percus. The Ornstein-Zernike equation defines the direct correlation function in terms of ĥ(12). The functional derivative relations then assume the familiar forms appropriate to an infinite system or in the grand canonical ensemble, but with h(12) replaced by ĥ(12) and with the external potential φ(1) replaced by φ(1) - μ, where μ is t...

Polymer-polymer interactions: An extension of maron's theory of nonelectrolytes

Abstract The Maron theory of nonelectrolytes has been extended to include ternary (polymer-polymer-solvent) systems. The effective volume correction term, e/e0, prominent in the original theory, is eliminated. The equations obtained, with this exception, are identical in form to those found in Maron's original theory.