Phenomenology of polymorphism and topological pressure–temperature diagrams

Although polymorphism of drug molecules is often studied with extensive and excellent experimental data, pressure appears to be a forgotten variable. In this article, an analysis is provided of the phase behavior of Atovaquone using available literature data. A pressure–temperature diagram is constructed topologically by way of the Clapeyron equation. The method leads to the conclusion that Atovaquone phase I and III behave enantiotropically, like α- and β-sulfur do in their paradigmatic P–T diagram, and that phase I is stable at room temperature and under “ordinary” pressure.     

The use of composition and high pressure to extend the range of α-quartz isotypes

The use of high pressure and the inclusion of elements such as boron, nitrogen and fluorine increase the number of compounds that adopt the α-quartz-type structure. The α-quartz-type forms of boron phosphate (BPO₄), phosphorus oxynitride (PON) and representatives of the continuous solid solution between silica and phosphorus oxynitride, including the nearly stoichiometric material SiPO₃N, were prepared under high-pressure, high-temperature conditions. The crystal structures of BPO₄ and PON were refined using X-ray and neutron powder diffraction data, respectively. The intertetrahedral A-X-A′ bridging angles of 140.1° and 140.6°, respectively, are slightly lower than in α-quartz as would be expected based on the higher densities of these materials. Preliminary refinements using the X-ray data from the SiO₂-PON solid solutions provide no indication of Si/P order and yield fractional atomic coordinates that are very similar to those observed for the pure end members. These results indicate that one may continuously tune the unit cell and structural parameters by varying the composition of this solid solution. Other compounds, which adopt or may adopt α-quartz-type structures, are also discussed. The present work indicates that the known relationship between the intertetrahedral A-X-A′ bridging angle and the density in α-quartz-type materials also applies to boron compounds, oxynitrides and fluorides. This use of the variables composition and pressure enables structure-property relationships for α-quartz isotypes to be extended and increases the number of potential candidates for piezoelectric materials.     

How does tack depend on time of contact and contact pressure?

The tack of polymer melts on rigid substrates under conditions of short contact times and low pressures is examined. The substrate is modeled as a random rough surface with a distribution of asperities heights. The true contact area between the adhesive and the substrate is calculated for a given total load and elastic modulus of the substrate. The dependence of tack on contact time is accounted for by introducing the relaxation of the adhesive through a time-dependent elastic modulus. For relatively high pressures the tack is predicted to scale with 1/E so that for short contact times, t_c, the tack is predicted to scale with (t_c/τ_e)^1/2, where τ_e is the entanglement time. For lower pressures this simple scaling law is no longer valid and we predict a complex variation of tack with contact time and molecular parameters. © 1996 John Wiley & Sons, Inc.     

Vapour pressure and thermodynamic properties of hexamethyldisilane at 305–387 K

The Swietoslawski's differential ebulliometer has been minimized to be usable for ca. 13 cm³ of liquid. After a performance test with acetone, the vapour pressure of hexamethyldisilane is determined over the temperature range 304.61–386.74 K. The Antoine equation obtained is log₁₀(P/kPa) = 5.97097 − 1319.85/{(T/K) − 52.96} and the normal boiling point is 385.81 K. The present results agree with literature values of Suga and Seki at 287–310 K and Brockway and Davidson at 293–334 K.     

Crystallization behavior of isotactic polypropylene induced by competition action of β nucleating agent and high pressure

Addition of β-form nucleating agent (β-NA) to isotactic polypropylene (iPP) can greatly induce the variation of the crystallization of matrix. Here, we introduce high pressure to the crystallization process of β-NA nucleated iPP. It is observed that there is a competition between the effect of high pressure and the nucleation effect of β-NA on crystallization of iPP. With the increasing of high pressure, both the contents of β-iPP and α-iPP decrease while the content of γ-iPP increases. A novel crystalline morphology of γ-iPP with the fragmentations of γ-spherulites regularly organized in a local region is observed. Namely, γ-spherulites grow on the lateral of β-NA needlelike structure. The dual nucleation effects of the special needlelike structure of β-NA towards β/α-iPP and the effect of high pressure which prevents the growth of β-iPP but promotes the growth of γ-iPP are the main mechanisms for the novel crystalline morphology of γ-iPP. Specifically, the mixed polymorphic β/γ-iPP can be achieved under a certain pressure. This possibly enlarges the application of iPP material.     

Vapour pressure data of ε-caprolactone, δ-hexalactone,and γ-caprolactone

This work reports new vapour pressure data of ε-caprolactone, δ-hexalactone, and γ-caprolactone. Vapour pressure measurements were carried out over the temperature range of (283 to 343) K using the static method with a differential pressure transducer. Degassing was performed inside the equilibrium cell by freezing and thawing the samples under moderate vacuum (about 50 kPa). For ε-caprolactone and δ-hexalactone vapour pressure values varied in the range of (0.045 to 0.769) kPa and (0.005 to 0.354) kPa, respectively, while for γ-caprolactone a maximum value of 1.367 kPa was found. Experimental vapour pressure data were correlated by the Antoine equation with a good agreement between experiment and model.     

Effect of end groups on the raman spectra of lycopene and β-carotene under high pressure

The Raman spectra of all-trans-lycopene in n-hexane were measured under high pressure, and the results compared with those of β-carotene. The different pressure effects on Raman spectra are analyzed taking into account the different structures of lycopene and β-carotene molecules. It is concluded that: (a) the vibronic coupling between the S? and S? states of β-carotene is stronger than that of lycopene, (b) the diabatic frequency increment of the ν? mode is more susceptible to pressure than that of the ν? mode for lycopene, and (c) β-rings rotation can relieve the pressure effect on the C=C bond length in β-carotene. This work provides some insights for elucidating the structural and environmental effects on Raman spectra of carotenoids.     

Dielectric constants of acetonitrile, γ-butyrolactone,propylene carbonate,and 1,2-dimethoxyethane as a function of pressure and temperature

The dielectric constants of 1,2-dimethoxyethane, acetonitrile, -butyrolactone, and propylene carbonate were determined from capacitance measurements extrapolated to infinite frequency; ln are reported as a function of pressure up to 80 MPa at 15, 25, 35, 45°C and as a function of temperature in the range 10 to 50°C at 0.10133 MPa. The variation of ln with temperature or pressure can be expressed by a second order polynomial expression. The isothermal compressibilities of the solvents were determined at 25°C from sound velocities, densities, and heat capacities. A simple correlation can be established between ln /P and for most aprotic solvent.     

p-V-T parameters of propylencarbonate and cis-,trans-decahydronaphthalene in temperature and pressure ranges of 20–50°C and 1–1000 bar

The condensability of propylencarbonate and cis-,trans-decalin (40: 60 wt %) were measured using the liquid weighting method in the temperature and pressure ranges of 20–50°C and 1–1000 bar, respectively. The Tait equation coefficients C and B for this temperature interval were calculated. Taking pro-pylencarbonate as an example, it was demonstrated that equation 1/β _T = 0.9759 × (1000V ₀/ΔV _{1 kbar}) — 4386 proposed earlier for liquids allows us to predict C and B coefficients with good precision.     

Vapor pressure and crystal lattice energy of volatile palladium(II) β-iminoketonates

Volatile palladium(II) β-iminoketonates of the general formula Pd(R–C(NH)–CH–CO–R¹),where R and R¹ are CH₃, CF₃, C(CH₃)₃ in various combinations, were synthesized and identified. Thermal properties of the resulting palladium(II) complexes in the solid phase were studied by thermogravimetric analysis under an argon atmosphere. The temperature dependence of the saturated vapor pressure was measured for the compounds by the flow method and thermodynamic characteristics of vaporization processes, enthalpy ΔH _T and entropy ΔS _T^o, were determined. The atom-atomic potential calculation of the van der Waals energy (E _cryst) of the crystal lattice was performed and the results were compared to the experimental values of the sublimation enthalpy for the complexes under study.     

Experimental and Nitta–Chao model prediction of high pressure density of p-xylene with dialkyl carbonates or n-alkanes

New data of high pressure density have been reported for p-xylene pure component and its binary mixtures with dimethyl carbonate, diethyl carbonate, n-octane and n-decane at (288.15, 298.15 and 308.15) K and (0.1, 5, 10, 20, 30 and 40) MPa and they have been compared with those available in the literature. The high pressure density has been correlated and predicted using a modified Tait equation and Nitta Chao group contribution model respectively. The derived thermophysical properties such as isothermal compressibility (κ_T), isobaric thermal expansivity (α_P) and internal pressure (π) have been also calculated.     

Physical and analytical characteristics of an atmospheric pressure argon–helium radiofrequency capacitively coupled plasma

A very low power radiofrequency capacitively coupled plasma (13.56 MHz, 5–70 W), was generated in our laboratory on a sharp Kanthal tip without any counter electrode, as an intrinsic part of RLC series resonant circuit. Physical characteristics of this plasma obtained in Ar–He mixture, were studied as function of observation height or gas mixture composition. The excitation temperature of Ar (1500–2100 K), He (3000–3500 K) and H (2500–3200 K), the rotational temperature of the OH band (1300–2900 K), the electron temperature (5500–6500 K) and the electron number density (8 · 10¹³–2 · 10¹⁴ cm^− 3) were determined. The evolution of several atomic emission lines or molecular bands was studied in order to investigate the fundamental processes that take place in such plasma. From the point of view of analytical applications it was found that the optimum conditions of excitation (most intense emission lines and lowest detection limits) are met for a 42% He in the gas mixture and an observation height of 1 mm above the electrode. The optimum atomic emission analysis parameters were established for 7 elements (Na, Li, Ca, K, Cd, Zn and Hg) using pneumatically nebulized liquid solutions. It was found that the presence of He in the plasmogenic gas has an enhancing effect on the emission intensities and detection limits.     

The bulk properties of the water-dimethylsulfoxide system at 278–323.15 K and atmospheric pressure

The densities of water-dimethylsulfoxide (DMSO) mixtures were measured over the temperature range 278–323.15 K and over the whole range of compositions at atmospheric pressure. The partial molar volumes of water and dimethylsulfoxide, mixture volumetric thermal expansion coefficients, and partial molar volumetric thermal expansion coefficients of the components were calculated. The composition dependences of the density of the mixture passed a maximum at x ～ 0.6 at all temperatures (x is the mole fraction of dimethylsulfoxide). The composition dependences of the partial molar volumes of water and DMSO also passed extrema.     

High pressure phase behavior and modeling of CO2–propyl acrylate and CO2–propyl methacrylate systems

High pressure phase behavior are obtained for CO₂–propyl acrylate system at 40, 60, 80, 100 and 120 °C and pressure up to 161 bar and for CO₂–propyl methacrylate systems at 40, 60, 80, 100 and 120 °C and pressure up to 166 bar. The solubility of propyl acrylate and propyl methacrylate for the CO₂–propyl acrylate and CO₂–propyl methacrylate systems increases as the temperature increases at constant pressure. The CO₂–propyl acrylate and CO₂–propyl methacrylate systems have continuous critical mixture curves that exhibit maximums in pressure at temperatures between the critical temperatures of CO₂ and propyl acrylate or propyl methacrylate. The CO₂–propyl acrylate and CO₂–propyl methacrylate systems exhibit type-I phase behavior with a continuous mixture critical curve.The experimental results for CO₂–propyl acrylate and CO₂–propyl methacrylate systems are modeled using both the statistical associating fluid theory (SAFT) and Peng–Robinson equations of state. A good fit of the data are obtained with SAFT using two adjustable parameters for CO₂–propyl acrylate and CO₂–propyl methacrylate systems and Peng–Robinson equation using one and two adjustable parameter for CO₂–propyl acrylate and CO₂–propyl methacrylate system.     

Relationship between the internal pressure and cohesive energy density of a liquid nonelectrolyte. Consequences of application of Dack’s concept

Dack’s concept that correlates internal pressure with cohesive energy density of a liquid system is shown to be applicable to identification of energy and structural changes in series of alkanols: MeOH, EtOH, n-PrOH, (i-PrOH), and n-BuOH, (t-BuOH). The side chain of methyl groups that appears in the molecule loosens the structural packing of the alkanol, creating additional steric hindrances for stable hydrogen bonds in alcohol media.     

Optimizing the separation of gaseous enantiomers by simulated moving bed and pressure swing adsorption

The resolution of racemic gas mixtures by simulated moving bed (SMB) and pressure swing adsorption (PSA) is investigated by dynamic simulation and optimization. Enantiomer separation of inhalation anesthetics is important because there is evidence that the purified enantiomers may have different pharmacological properties than the racemate. The model parameters reported in an experimental investigation performed elsewhere are used to study the feasibility of this separation using SMB and PSA configurations. Both processes were modeled in gPROMS^® as systems of differential algebraic equations. Operating conditions are optimized such that the feed throughput and product recovery for each process were maximized subject to equal constraints on the pressures and superficial gas velocities. SMB was found to be capable of resolving racemic feed mixtures with purity and recovery exceeding 99%. On the other hand, PSA was also able to provide a single purified enantiomer with low recovery of about 30% which may limit its application to enantiomer separation. Nevertheless, PSA consumes less desorbent, and achieves higher throughput at the sacrifice of lower recovery.     

Screening and quantification of pesticide residues in fruits and vegetables making use of gas chromatography–quadrupole time-of-flight mass spectrometry with atmospheric pressure chemical ionization

An atmospheric pressure chemical ionization source has been used to enhance the potential of gas chromatography coupled with quadrupole time-of-flight (QTOF) mass spectrometry (MS) for screening and quantification purposes in pesticide residue analysis. A screening method developed in our laboratory for around 130 pesticides has been applied to fruit and vegetable samples, including strawberries, oranges, apples, carrots, lettuces, courgettes, red peppers, and tomatoes. Samples were analyzed together with quality control samples (at 0.05 mg/kg) for each matrix and for matrix-matched calibration standards. The screening strategy consisted in first rapid searching and detection, and then a refined identification step using the QTOF capabilities (MS^E and accurate mass). Identification was based on the presence of one characteristic m/z ion (Q) obtained with the low collision energy function and at least one fragment ion (q) obtained with the high collision energy function, both with mass errors of less than 5 ppm, and an ion intensity ratio (q/Q) within the tolerances permitted. Following this strategy, 15 of 130 pesticides were identified in the samples. Afterwards, the quantitation capabilities were tested by performing a quantitative validation for those pesticides detected in the samples. To this aim, five matrices were selected (orange, apple, tomato, lettuce, and carrot) and spiked at two concentrations (0.01 and 0.1 mg/kg), and quantification was done using matrix-matched calibration standards (relative responses versus triphenyl phosphate used as an internal standard). Acceptable average recoveries and relative standard deviations were obtained for many but not all pesticide–matrix combinations. These figures allowed us to perform a retrospective quantification of positives found in the screening without the need for additional analysis. Taking advantage of the accurate-mass full-spectrum data provided by QTOF MS, we searched for a higher number of compounds (up to 416 pesticides) in a second stage by performing extra data processing without any new sample injection. Several more pesticides were detected, confirmed, and/or tentatively identified when the reference standard was unavailable, illustrating in this way the potential of gas chromatography–QTOF MS to detect pesticides in addition to the ones targeted in quantitative analysis of pesticides in food matrices. Figure

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The compressibility of water-dimethyl sulfoxide mixtures over the temperature and pressure ranges 278–323.15 K and 1–1000 bar

The compressibility coefficients of water-dimethyl sulfoxide (DMSO) binary liquid mixtures were measured over the temperature range 278–323.15 K at pressures from atmospheric to 1000 bar. At these state parameters, the partial molar volumes and partial molar compressibility coefficients $ \bar k_1 $ \bar k_1 and $ \bar k_2 $ \bar k_2 of water and DMSO were calculated. The dependences of the compressibility coefficients of mixtures on mixture composition passed a minimum. The minimum shifted to lower DMSO concentrations as the temperature increased. The dependences contained the inversion region where the k value was independent of pressure. The limiting molar partial compressibility coefficient of DMSO $ \bar k_2 $ \bar k_2 was negative at 278.15 K and increased as the temperature grew.     

The pressure–volume–temperature relationship of cellulose

Pressure–volume–temperature (PVT) measurements of α-cellulose with different water contents, were performed at temperatures from 25 to 180 °C and pressures from 19.6 to 196 MPa. PVT measurements allowed observation of the combined effects of pressure and temperature on the specific volume during cellulose thermo-compression. All isobars showed a decrease in cellulose specific volume with temperature. This densification is associated with a transition process of the cellulose, occurring at a temperature defined by the inflection point T _t of the isobar curve. T _t decreases from 110 to 40 °C with pressure and is lower as moisture content increases. For isobars obtained at high pressures and high moisture contents, after attaining a minimum, an increase in volume is observed with temperature that may be related to free water evaporation. PVT α-cellulose experimental data was compared with predicted values from a regression analysis of the Tait equations of state, usually applied to synthetic polymers. Good correlations were observed at low temperatures and low pressures. The densification observed from the PVT experimental data, at a temperature that decreases with pressure, could result from a sintering phenomenon, but more research is needed to actually understand the cohesion mechanism under these conditions.