Lattice model for the surface region of solutions consisting of different-sized molecules with orientation effects

Smirnova, N.A., 1978. Lattice model for the surface region of solutions consisting of different-sized molecules with orientation effects. Fluid Phase Equilibria, 2: 1–25.A multilayer lattice model for the surface region of solutions consisting of different-sized molecules with orientation effects is developed. The system is treated in the grand canonical ensemble on the basis of the quasi-chemical approximation. The results relate to the mixtures of monomers + flexible r-mers, where all r segments of r-mer may be different and the surface of monomer molecules and r-mer segments may be inhomogeneous (thus, the systems with polar components, associated solutions among them, are in the range of applicability of the model). The monomer + r-mer system is described based on the modified model for the multicomponent system formed by monomeric particles with strong directed interactions. Equations for the concentration profile and for the average molecular orientations, with respect to the surface, are derived; the formulae for the adsorption and surface tension are given. The surface properties calculated on the basis of the model for three monomer + dimer systems are in satisfactory agreement with the experimental data. The entropy contribution to the surface tension of pure r-mer composed of identical segments is reported for r = 2, 4, 6, 8, 12 and for different lattice parameters. The model can be generalized to mixtures of r-mers + l-mers.     

Description of cyclopropane with Backone equation of state

This paper aims to accurately describe the thermodynamic properties of Cyclopropane with a molecular based BACKONE equation of state. The parameters of the BACKONE equation of state found by fitting to experimental vapor pressures and liquid densities are the characteristic temperature T ₀, characteristic density ρ₀, anisotropy factor α, and reduced quadrupolar moment Q*². The values of these parameters are 393.9583 K, 6.076139 mol/L, 1.295445, and 0.699483, respectively. The average absolute deviation between experimental values and those derived from BACKONE EOS is 0.29% for vapor pressures, 0.75% for saturated liquid densities. The prediction power of the BACKONE equation of state are investigated. It is shown that the uncertainties of values derived from the BACKONE equation of state are within 0.90% for isobaric densities in the liquid phase and 2.0% for enthalpy of evaporation.     

Corresponding states theory and thermodynamic properties of liquid alkali metals

According to phenomenological scaling and the law of corresponding states, reduced coordinates F ^*-T ^*, where F* represents the reduced thermodynamic properties (enthalpy of vaporization, speed of sound, surface tension, saturated liquid density) and T ^* is the reduced temperature, are introduced for the prediction of the thermodynamic properties of alkali metals. Values of the thermodynamic properties from the melting point up to boiling point are correlated. It has been shown that the correlation between reduced thermodynamic properties, as well as with the reduced temperature, can be expressed as a unique straight-line plot with a linear correlation coefficient of 0.9998. The proposed correlation has a simple form for easy calculation, requires only the melting and boiling point parameters, which are usually easy to acquire, and can predict the thermodynamic properties from the melting temperature up to the boiling temperature accurately.     

Triplet xanthone in n-pentane: multiple emission from a single site

The three phosphorescence components of xanthone in n-pentane originate from three states of one solvated species: From the z sublevel of the second triplet state, of ³nπ^* origin, and from two widely split sublevels of the lowest triplet state, of ³ππ_* origin. Its z sublevel is thermally depleted across the spin-orbit mixing induced zero-field sublevel splitting of 15.1 cm^?1.     

Mechanochemical Synthesis of Nanoparticles by a Dilution Method: Determination of the Particle Mixing Coefficient in a Ball Mill

Experimental study of the kinetics of mechanosynthesis of TlCl nanoparticles in the reaction 2NaCl + Tl₂SO₄ + zNa₂SO₄ = = (z + 1)Na₂SO₄ + 2TlCl with z = z^*₁ = z^* = 11.25 and comparison of kinetic parameters for this reaction with those determined theoretically for the model reaction KBr + TlCl + zKCl = (z + 1)KCl + TlBr with z = z^*₁ = 13.5 made it possible to estimate the mass transfer (mixing of particles) coefficient in a mechanochemical reactor by the mobile milling tools.     

On the origin of some controversial ions (m/z 59, 60, 77, and 119) in the thermospray reagent plasma from ammonium acetate

The origin of ions at m/z 60, 77, and 119 in the thermospray (TSP) reagent plasma is reconsidered. It is demonstrated that these major ions in the TSP spectrum of ammonium acetate are not due to dehydration processes in the gas or liquid phase, as is generally accepted, but to the preexistence of acetamide as an impurity in the commercial salts. Acetamide, characterized by TSP/tandem mass spectrometry, gas chromatography-electron impact ionization mass spectrometry, ¹H-NMR, and ¹³C-NMR, is responsible for the [M +60]⁺ and [M + 77]⁺ adducts observed in some spectra. The buffer ion at m/z 59 is also due to impurities in the ammonium acetate salts. Washing the solid salt with chloroform eliminates most of these impurities. Examples using the pesticides linuron, monuron, and carbaryl show that the ions observed at m/z M_r + 60 and M_r + 59 disappear when a buffer obtained from acetic acid and ammonia is used instead of the commercial salts.     

On the phase equilibrium Stockmayer fluids

The fluid phase equilibrium of the Stockmayer fluid is investigated using a thermodynamic perturbation theory approach. The reference and the perturbation potential are the Lennard–Jones potential and the dipolar–dipolar interactions, respectively. They are assumed to be represented by the modified Benedict–Webb–Rubin equation of state [J.K. Johnson, J.A. Zollweg, K.E. Gubbins, Mol. Phys. 78 (1993) 591–618] and the Padé approximant [G. Stell, J.C. Rasaiah, H. Narang, Mol. Phys. 27 (1974) 1393–1414], respectively. The asymmetry found in an analogous study [M.E. van Leeuwen, B. Smit, E.M. Hendriks, Mol. Phys. 78 (1993) 271–283] based on the BWR equation of state [J.J. Nicolas, K.E. Gubbins, W.B. Streett, D.J. Tildesley, Mol. Phys. 37 (1979) 1429–1454] is now not observed on the vapour–liquid equilibrium coexistence curves of Stockmayer fluids with dipolar strength of μ^*2 = 1, 2, 3, and 4. Results agree with computer simulations for dipolar strength of μ^*2 = 1; however as strength dipole increases, liquid densities are over-estimated.     

Determination of Hyaluronic Acid in a Chitosan-Based Formulation by RP C18 and HILIC LC–ESI-MS: an Evaluation of Matrix Effect

Two simple and fast C18 and HILIC liquid chromatography–electrospray mass spectrometry methods for the determination of hyaluronic acid (HA) in a mucoadhesive chitosan-based formulation were developed and validated. The performances of both methods were compared in terms of validation parameters and matrix effect. A simple sample preparation method based on sulphuric acid-based degradation was optimized for the detection of HA fragments (i.e. m/z 380 2-mer, m/z 759 4-mer, m/z 1,138 8-mer and m/z 1,518 16-mer). By operating under selected ion-monitoring mode, excellent selectivity towards chitosan fragments was obtained. For validation, good linearity, detection limits (<4 μg mL^?1) and precision (RSD % < 16 %) were generally obtained on matrix with both columns. However, HILIC column exhibited improved performances in terms of HA fragment separation and selectivity. By analyzing on the C18 column the chitosan-based formulation and sample extracts from pig mucosa treated with the formulation, matrix effects exhibited a dependence of signal suppression degree (ranging from 37 to 83 %) as a function of the HA fragment dimension. The HILIC column afforded instead a significantly reduced suppression degree (ranging from 1 to 16 %) and a better separation. These findings demonstrated the improved performances of the HILIC column with respect to conventional C18 mechanism for the analysis of HA fragments in complex matrices.     

Composition dependence of the Adam-Gibbs cooperative relaxation parameters in glycerol aqueous solutions

Cooperative relaxation of glycerol and its four aqueous solutions (60%, 70%, 80% and 90% by mass) has been investigated in terms of the nonlinear Adam-Gibbs (AG) enthalpy relaxation theory using differential scanning calorimetry (DSC). The AG parameters were obtained using curve-fitting method. The results indicated that the relaxation time of glycerol/water mixtures is water-sensitive. With the changing of water content, regular trend was found in both the equilibrium and the glassy state. The fitting results were used to estimate the microscopic parameters of the cooperative rearranging region (CRR), in particular the size of the CRR (z*) and the configurational state available to it (W*). The results showed that the W* recommended for polymers led to physically meaningless z* for glycerol and its aqueous solutions. Johari's method, which still based on the AG theory, yielded three to four molecules in the CRR. But the W* is anomalistically higher than those of polymers. With the changing of the water content, the size of CRR estimated using Donth formula seemed to be reasonable according to the analysis of the apparent activation energy (Δh*), the distribution parameter the of relaxation times (β). But it is difficult to reconcile the Adam-Gibbs’ z* with the results obtained using Donth's formula.     

Determination of the carboxylic acid metabolite of clopidogrel in human plasma by liquid chromatography-electrospray ionization mass spectrometry

A rapid and specific liquid chromatographic-mass spectrometric method has been developed and validated for the determination of the carboxylic acid metabolite of clopidogrel in human plasma. Sulphafurazole was used as internal standard. The samples were subjected to a solid phase extraction procedure using Hypercarb cartridges. The chromatographic separation was performed on a reversed phase porous graphitized carbon column using a mobile phase consisting of 70% methanol in water containing 0.1% (v/v) trifluoroacetic acid, pumped at a flow rate of 0.25 ml min⁻¹. The analytes were detected after positive electrospray ionization using the selected ion monitoring mode of the species at m/z 308 for the carboxylic acid metabolite of clopidogrel, m/z 322 for clopidogrel and m/z 268 for sulphafurazole. Calibration graphs were linear (r>0.9994, n=6), in the range 100-1000 ng ml⁻¹ for the carboxylic acid metabolite of clopidogrel. The intra- and inter-day R.S.D. values were <3.1%, while the relative error E_r was less than −9.6% (n=6). The limits of detection (3.3σ) and quantitation (10σ) for the carboxylic acid metabolite of clopidogrel were found to be 28 and 93 ng ml⁻¹, respectively. The efficiency of the solid phase extraction procedure for the carboxylic acid metabolite of clopidogrel averaged 74.6%.     

Theoretical estimation of thermodynamic properties of the system PS/PPO on the basis of modified combining rule of Sanchez-Lacombe lattice fluid model

The three scaling parameters described in Sanchez-Lacombe lattice fluid theory (SLLFT), T^*, P^* and ρ^* of pure polystyrene (PS), pure poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) and their mixtures are obtained by fitting corresponding experimental pressure-volume-temperature data with equation-of-state of SLLFT. A modified combining rule in SLLFT used to match the volume per mer, υ^* of the PS/PPO mixtures was advanced and the enthalpy of mixing and Flory-Huggins (FH) interaction parameter were calculated using the new rule. It is found that the difference between the new rule and the old one presented by Sanchez and Lacombe is quite small in the calculation of the enthalpy of mixing and FH interaction parameter and the effect of volume-combining rule on the calculation of thermodynamic properties is much smaller than that of energy-combining rule. But the relative value of interaction parameter changes much due to the new volume-based combining rule. This effect can affect the position of phase diagram very much, which is reported elsewhere [Macromolecules 34 (2001) 6291]     

LC�CMS Analysis of Sertraline and Its Active Metabolite in Human Serum Using a Silica Column with a Non-Aqueous Polar Mobile Phase

A sensitive liquid chromatography?Cmass spectrometry method for the simultaneous determination of sertraline (SER) and its major metabolite norsertraline (NOR) from serum was developed and validated in the context of a pharmacokinetic study in pregnant women. The separations were achieved on a silica column with a non-aqueous polar mobile phase consisting of acetonitrile, methanol and ammonium acetate at a flow rate of 0.5 mL min^?1. The concentrations were measured using a single quadruple mass spectroscopic detector supplied with atmospheric pressure ionization electrospray. Sample preparation consisted of a simple liquid?Cliquid procedure. The detector was set in selective ion mode for each compound of interest, 306 m/z for SER and 275 m/z for NOR. Calibration curves were generated by least square linear regression for concentration of 5?C160 ng mL^?1 for SER and from 10 to 320 ng mL^?1 for NOR. The curves for both compounds of interest were linear, with correlation coefficients r ² ?? 0.999.     

Sorption and selective properties of binary liquid-crystalline sorbent based on 4-Methoxy-4′-ethoxyazoxybenzene and a cetylated β-Cyclodextrin

The mesomorphous, sorption, and selective properties of a binary sorbent based on achiral liquid crystal 4-methoxy-4′-ethoxyazoxybenzene and macrocyclic heptakis(2,3,6-tri-O-acetyl)-β-cyclodextrin (10.25 wt %) are investigated. Macrocyclic additive was found to induce the formation of a helically twisted nematic phase (N*). The standard and excess thermodynamic functions of sorption by binary sorbent from gaseous phase are determined for 29 organic compounds (n-alkanes, cycloalkanes, arenes, monoatomic alcohols, heterocycles, optical isomers of camphene, limonene, and butanediol-2,3). The investigated sorbent is found to have high structural selectivity over the wide temperature range of the N* mesophase (α _p/m = 1.11–1.06, 95–120°C) and moderately expressed enantioselectivity within the narrow region of transition from the solid crystalline state to the N* mesophase (α_+/? = 1.024–1.088, 91–100°C).     

Zero-point average structures of acetyl chloride and acetyl bromide

The zero-point average structures of acetyl chloride and acetyl bromide have been determined by the combined use of their moments of inertia and average distances, obtained by means of microwave spectroscopy and electron diffraction. The r_z parameters determined are as follows: r_z(CO) = 1.185 ± 0.003 Å, r_z(C-Cl) = 1.796 ± 0.002 Å, r_z(C-C) = 1.505 ± 0.003 Å, r_z(C-H) = 1.092 ± 0.005 Å, φ_z(OCCl) = 121.2 ± 0.6°, φ_z(CCCl) = 111.6 ± 0.6°, φ_z(HCH) = 108.8 ± 0.8° and tilt(CH3) = 1.3 ± 1.0°, for chloride; r_z(CO) = 1.181 ± 0.003 Å, r_z(C-Br) = 1.974 ± 0.003 Å, r_z(C-C) = 1.516 ± 0.003 Å, φ_z(OCBr) = 122.3 ± 1.5°, φ_z(CCBr) = 111.0 ± 1.5°, φ_z(HCH) = 109.9 ± 1.1°, tilt(CH₃) = 1.9 ± 1.0°, for bromide. The barriers V₃ to internal rotation have been revised to 1260 and 1256 cal mol⁻¹ for the chloride and bromide, respectively.     

Excited-state proton transfer kinetics of carbazole

Rate constants for the excited-state proton transfer reaction of carbazole in aqueous alkaline solution have been determined using picosecond single photon counting. Fluorescence decay measurements show that the back reaction is slow compared to the fluorescence decay time and therefore equilibrium is not attained in the excited state. The validity of a pK value for the lowest excited state determined from steady-state fluorescence measurements assuming equilibrium is discussed. It is concluded that the thermodynamic pK^* value for carbazole is 10.98.     

Thermal behavior of selected ferroelectric liquid crystals

Thermal properties of three ferroelectric liquid crystals, namely: 3-octyloxy-6-[2-fluor-4-(fluoroctyloxy)phenyl]-pyridine (FFP), 3-(3-fluor-nonyl)-6[4-heptyloxyphenyl]-pyridine (FNHPh-P), 4-[(S,S)-2,3-epoxyhexyloxy]phenyl 4-(decyloxy)benzoate (EHPhDB) were studied using heat flux differential scanning calorimetry method. All the transitions expected in this compounds, except the SmC^*-SmA^* and SmC^*-S₃ transitions, were detected in the DSC curves. The temperatures of the phase transitions and the enthalpy changes associated with them were determined. The transition from the liquid crystalline to the crystalline state showed significant hysteresis for all three compounds studied. The following transitions: SmA^*-Is, SmG^*-SmC^* for FNHPh-P, N^*-Is for EHPhDB, N^*-Is and SmC^*-N^* for FFP also showed a small hysteresis basing on which first-order character of all the above transitions was implied. All three substances studied in this work are characterized by a complex polymorphism in the solid state.The author is grateful to Dr. Stanislaw Wróbel for his stimulating interest, valuable discussions and supplying the samples. This work has been done in the framework of the KBN grant 2 P302 139 07.     

Equilibrium and relaxation dielectric properties of 1,2-ethanediol

Data on the static relative permittivity (?_s) of 1,2-ethanediol over a temperature range of 243 to 423 K were examined within the framework of the Onsager-Kirkwood-Fröhlich theory. An analysis of the dispersion of the complex relative permittivity ?^*(ω) of ethanol using the Davidson-Cole and Vogel-Fulcher-Tammann was performed empirical equations and the Adam-Gibbs molecular-kinetic theory. The correlation factor g _exp, relaxation time τ _DC, and distribution parameter β were determined. It was established that the parameter β increases from 0.72 to 0.845 as the temperature rises from 243 to 453 K, in contrast to the previous studies, in which it was set temperature-independent. The parameters of the Vogel-Fulcher-Tammann were found to be T ₀₁ = 93.809 K, τ _0VFT1 = 6.96 × 10^?14 s, and U _∞VFT1 ^# = 12.73 kJ/mol. Based on the Adam-Gibbs equation, the number of molecules involved in an elementary event of cooperative structural rearrangement was estimated to be z ^* = 3.1?2.4 within 161–186 K and z ^* = 1.63?1.26 within 243–453 K.     

Molecular dynamics at constant pressure and temperature

Methods are discussed for generating by molecular dynamics isobaric-isoenthalpic, NPH, isochoric-isothermal, NVT, and isobaric-isothermal, NPT, ensembles. Andersen's constant-pressure method is reformulated so that the ensemble rather than the scaled system is directly calculated. Four constant-temperature schemes were considered. Two involve the addition of a stochastic collision term to the molecular trajectories. The Andersen method and a stochastic dynamics approach were examined. The latter employed a velocity damping term in addition to the random force. Two other methods employed uniform velocity scaling applied to all molecules. The NPT algorithm induces a transition to the dilute phase for a Lennard-Jones fluid in the spinodal region (p^* = 0.5, T^* = 1.28) of the phase diagram. The thermodynamic equivalence of the ensembles is demonstrated by long calculations of the chemical potential of Lennard-Jones states by the particle insertion method. The internal energy, pressure, constant volume and pressure specific heats, adiabatic compressibilities, pair radial distribution functions and self-diffusion coefficients are also evaluated. Only for second-order thermodynamic quantities is there evidence of an ensemble dependence.