Liquid Chloroform Research Articles

Termodinâmica estatística de líquidos com o método de Monte Carlo. II. O líquido clorofórmio

Thermodynamic properties and radial distribution functions for liquid chloroform were calculated using the Monte Carlo method implemented with Metropolis algorithm in the NpT ensemble at 298 K and 1 atm. A five site model was developed to represent the chloroform molecules. A force field composed by Lennard-Jones and Coulomb potential functions was used to calculate the intermolecular energy. The partial charges needed to represent the Coulombic interactions were obtained from quantum chemical ab initio calculations. The Lennard-Jones parameters were adjusted to reproduce experimental values for density and enthalpy of vaporization for pure liquid. All thermodynamic results are in excelent agreement with experimental data. The correlation functions calculated are in good accordance with theoretical results avaliable in the literature. The free energy for solvating one chloroform molecule into its own liquid at 298 K and 1 atm was computed as an additional test of the potential model. The result obtained compares well with the experimental value. The medium effects on cis/trans convertion of a hypotetical solute in water TIP4P and chloroform solvents were also accomplished. The results obtained from this investigation are in agreement with estimates of the continuous theory of solvation.

Detailed Study of Potassium Solvation Using Molecular Dynamics Techniques

Molecular dynamics simulations are carried out to examine the solvation properties and the ion-solvation shell exchange process of the K+ ion in liquid water, chloroform, and carbon tetrachloride. The solvent molecules are found to form well-defined solvation shells around the K+ ion and show a preferred orientational order toward the ion. The induced dipole moment distribution of K+ becomes broader and shifts to a larger average value from chloroform to carbon tetrachloride to water. It is observed that the K+ ion diffuses more rapidly in the aqueous phase than in liquid chloroform and carbon tetrachloride. We have also evaluated both ion and first solvent shell velocity autocorrelation functions and the residence time autocorrelation functions for the ion in water, chloroform, and carbon tetrachloride. The residence time is found to be 9.4 ps for water and about 30 ps for both chloroform and carbon tetrachloride. By use of a constrained molecular dynamics technique, the first solvation shell exchange pr...

LIQUID CHROMATOGRAPHY OF MACROMOLECULES UNDER LIMITING CONDITIONS OF ADSORPTION. I. PRINCIPLES OF THE METHOD

A novel separation method for macromolecules, viz. liquid chromatography under limiting conditions of adsorption (LC LCA), is presented. LC LCA is designed for discrimination of complex polymers. It combines exclusion and adsorption mechanisms so that they mutually compensate. This results in the absence of separation of macromolecules according to their size or molar mass. In LC LCA, the eluent is a liquid moderately promoting adsorption of polymer species. The column packing attracts macromolecules and, if the sample were dissolved and injected in eluent, it would be retained within column. Therefore, the polymer is injected in a solvent that effectively suppresses adsorption. Experimental conditions can be identified with regard to the eluent, column packing, temperature as well as sample solvent, and injected sample volume under which macromolecules of various molar masses are eluted together with their initial solvent. in this way, binary polymer blends, with components exhibiting different adsorptive properties can be separated. The LCA behavior of poly(methyl methacrylate) is presented using bare silica gel or “active” polystyrene/divinyl benzene column packings, tetrahydrofuran as desorption promoting liquid and toluene or chloroform as adsorption promoting liquids.

Volumetric data from light scattering and perturbation theory for carbon tetrachloride, chloroform and dichloromethane

The ratio of isothermal compressibility to the square of isobaric expansivity (κT/αp2) was determined via Rayleigh light scattering experiments for liquid carbon tetrachloride, chloroform and dichloromethane as a function of temperature. This ratio was also calculated by means of renormalized perturbation theory (in the case of polar molecules) and by the use of Johnson–Zollweg–Gubbins equation of state (in the case of carbon tetrachloride), respectively. The data coming from light scattering show reasonable agreement with those from theoretical calculations and from volumetric experiments given in the literature.

Structure of Liquid Chloroform as Investigated by Energy-Dispersive X-Ray Diffraction

Abstract The structure of liquid chloroform has been investigated by energy-dispersive X-ray diffraction. For the stability of the sample thickness, even for a volatile liquid, a glass capillary tube has been used as a sample container. The intensity function has been accounted for by a bcc (body-centered cubic)-like local lattice structure model with a lattice constant of 6.24 Å. However, it has been necessary to replace a fraction (34%) of the nearest neighbors by super-near configurations in which molecules are rather tightly correlated. The correlation is, however, rapidly lost as the distance between molecules increases, and the long range structure is characterized by a large Prins parameter. The structure of liquid chloroform is much less ordered than that of carbon tetrachloride.

Brillouin spectra and vibrational–translational energy exchange in liquid acetonitrile

Polarized light scattering experiments in the GHz frequency range (Rayleigh–Brillouin spectra) are reported for liquid acetonitrile. Hypersonic velocities and absorption coefficients have been measured as a function of temperature and of transferred wave vector. The plots of these quantities versus frequency show characteristic dispersion which is indicative of relaxation phenomena. The occurring relaxation has been interpreted as due to a thermal process in which the translational energy of molecules is transferred, during the collisions or through dipolar interactions, into internal degrees of freedom of low quanta vibrational motions. The quite strange behavior of the relaxation time with the temperature has been interpreted and compared with the behavior of the relaxation time in liquid chloroform.

Liquid acetone and chloroform: a comparison between Monte Carlo simulation, molecular Ornstein-Zernike theory, and site-site Ornstein-Zernike theory

Liquid acetone and chloroform: a comparison between Monte Carlo simulation, molecular Ornstein-Zernike theory, and site-site Ornstein-Zernike theory

Liquid acetone and chloroform: a comparison between Monte Carlo simulation, molecular Ornstein-Zernike theory, and site-site Ornstein-Zernike theory

Site-site distribution functions, internal energies, compressibilities, and dielectric constants of liquid acetone and chloroform are computed and compared. The hypernetted chain approximation is used for the molecular Ornstein-Zernike (MOZ) and site-site Ornstein-Zernike (SSOZ) theories. Both solvent molecules are described as sets of interaction sites, which are the centres of Lennard-Jones potentials and which carry partial electric charges. How the approximations inherent in both OZ theories affect the calculated liquid properties is discussed. In contrast to SSOZ theory, MOZ theory yields a correct description of the liquid structure as defined by the site-site distribution functions of simulations. The MOZ results for the dielectric constants are in good agreement with simulation, but both OZ theories slightly underestimate the internal excess energies. In contrast to the SSOZ formalism and to the simulations, the molecular pair distribution of MOZ theory can be computed readily for all two-molecule configurations, allowing a detailed study of the complex relief of this distribution. A search was performed for configurations that are highly probable in the liquid. They can be assigned to a small number of peaks of the molecular distribution function. These peaks have major contributions to the Kirkwood factors, which measure the orientational order in the liquid, and to the electrostatic part of the excess energies. The partitioning of the whole two-molecule configuration space makes it possible to study the details of the site-site distribution functions. For instance, a sharp peak in the oxygen-oxygen distribution in acetone results from many superimposed contributions of acetone-acetone arrangements of low and medium statistical weights, and not from the highly probable arrangements.

ChemInform Abstract: Efficient and Highly Selective Copper(II) Transport Across a Bulk Liquid Chloroform Membrane Mediated by Lipophilic Dipeptides.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Picosecond IR spectroscopy using internal reflection

The internal reflection technique is introduced in picosecond time-resolved infrared spectroscopy. First results on liquid chloroform are presented and compared to results obtained in transmission geometry. The requirements for a good performance of corresponding experiments are discussed as well as the procedures for determining the changes in the optical constants from measured reflection changes.

Ion Solvation in Polarizable Chloroform: A Molecular Dynamics Study

The structural, thermodynamic, and dynamical properties of the alkali-metal cations and the halide anions in liquid chloroform are investigated using molecular dynamics simulation techniques. From the atomic radial distribution analysis, the chloroform molecules are found to form well-defined solvation shells around the alkali-metal cations and the halide anions. The size of the solvation cage and the coordination number both increase with increasing ion size. In liquid chloroform, all these ions are shown to induce a strong orientational order in the surrounding chloroform molecules as evidenced by the angular distribution functions. We found that the mean electric potentials induced by the chloroform molecules shifted to smaller magnitudes with increasing ion size. Because of the greater electric polarizabilities of the larger ions, the average induced dipole moments were enhanced with increasing ion size. The diffusion coefficients of the alkali-metal cations and the halide anions in liquid chloroform are estimated from the mean-square displacements and the velocity autocorrelation functions. Generally, the diffusion constants of the cations are larger than those of the anions. For the cations, the diffusion constants are of similar magnitudes and do not depend on the ion size. However, the diffusion coefficients of the halide anions show a strong dependence on the ion size. The motion of the first coordination shell chloroform molecules is examined via their velocity autocorrelation functions. These correlation functions behave very similarly, suggesting that the motion of the first solvation shell is not governed by the sizes or the charges of these ions. In addition, the residence time autocorrelation functions of the first solvation shell are evaluated. As expected, the residence time decreases as the ion size increases.

Efficient and Highly Selective Copper(II) Transport across a Bulk Liquid Chloroform Membrane Mediated by Lipophilic Dipeptides

Several structurally simple N-monoalkylated and -dialkylated dipeptides made of α-amino acids Gly, Phe, and Leu, 1−11, were synthesized and investigated as carriers for the transport of Cu(II), Zn(II), and Ni(II) from an aqueous pH = 5.6 buffer source to a 0.1 M HCl receiving phase across a bulk chloroform membrane. The proton-driven translocation was followed during the process by analyzing the metal ion concentrations in the three phases. The transport efficiency depends on the ease of formation of a neutral complex with Cu(II) (the peptide group and carboxylic acid being deprotonated) at the source−chloroform interface and on that of its disruption by protonation at the receiving phase: the carrier's lipophilicity favors the metal ion uptake and not the release. By modulating the length of the N-alkyl chains and the hydrophobicity of the dipeptide moiety, a quite remarkable transport efficiency was observed for Cu(II), in most cases superior to that of the industrial extractant Kelex 100. Moreover, using l,l- and l,d-N-octyl-PheLeu as carriers, remarkable diastereomeric effects were observed in the rate of uptake and release of Cu(II) ion although the differences mutually compensate in the overall transport rate. Under the conditions used the carriers are much less effective in the translocation of Zn(II) and Ni(II) and their transport efficiency drops dramatically in the presence of Cu(II), the latter being favored by factors of 1.2 × 103 and >104, respectively. Such very high selectivities depend on the fact that only Cu(II) among other transition metal ions can form neutral complexes at the pH value of the source phase.

Preparation of Decachlorocorannulene and Other Perchlorinated Fragments of Fullerenes by Electrical Discharge in Liquid Chloroform

地址: 1. XIAMEN UNIV, DEPT CHEM, STATE KEY LAB PHYS CHEM SOLID SURFACE, XIAMEN 361005, FUJIAN PEOPLES R CHINA

Dielectric and structural results for liquid acetonitrile, acetone and chloroform from the hypernetted chain molecular integral equation

This paper reports an attempt to model pure liquids of polar polarizable molecules of arbitrary symmetry and to compute their structural properties in a simple, rapid but fairly accurate way. The models consist of approximating each molecule as a superposition of Lennard-Jones sites with a centred point polarizable electric dipole and a point electric quadrupole. The calculation of the liquid structure is performed using the hypernetted-chain approximation, in which the solvent polarizability is treated at the self-consistent mean-field level. The quadrupole moments are measured or obtained by ab-initio molecular orbital calculations. The orientational correlations between the molecules, as measured by the Kirkwood g factor, and the dielectric constants are mainly determined by the molecular shapes, sizes and electrostatic interactions but are nearly independent of the Lennard-Jones attraction. The theoretical values of the dielectric constants are in satisfactory agreement with the experimental data, pro...

Dielectric and structural results for liquid acetonitrile, acetone and chloroform from the hypernetted chain molecular integral equation

This paper reports an attempt to model pure liquids of polar polarizable molecules of arbitrary symmetry and to compute their structural properties in a simple, rapid but fairly accurate way. The models consist of approximating each molecule as a superposition of Lennard-Jones sites with a centred point polarizable electric dipole and a point electric quadrupole. The calculation of the liquid structure is performed using the hypernetted-chain approximation, in which the solvent polarizability is treated at the self-consistent mean-field level. The quadrupole moments are measured or obtained by ab-initio molecular orbital calculations. The orientational correlations between the molecules, as measured by the Kirkwood g factor, and the dielectric constants are mainly determined by the molecular shapes, sizes and electrostatic interactions but are nearly independent of the Lennard-Jones attraction. The theoretical values of the dielectric constants are in satisfactory agreement with the experimental data, provided that both the effects of the quadrupole moment and of the polarizability are incorporated in the electrostatic intermolecular potential. The liquid structure is presented by the dominant configurations found between two molecules. The Kirkwood g factor is correlated to these configurations.

Supercritical fluid extraction and bioassay identification of prodrug substances from natural resources

For arbitrarily chosen thirty types of natural resources which have been widely used in oriental traditional herb medicine, supercritical CO2 extraction (SFE) and organic liquid solvent extraction (LSE) withn-hexane, chloroform and methanol were carried out to extract pharmaceutical substances. To evaluate relative advantages and shortcomings between the SFE and LSE, five types of bioactivity assays as well as gas- and thin layer-chromatographic analysis were performed for all the extracts obtained by the two extraction methods. Types of bioassays performed included cytotoxicity, bleb forming, DNA binding, oxygen free radical scavenger and Xanthine oxidase inhibitor tests. To evaluate economic viability of the SFE over the traditional LSE, extractability of prodrug substances was evaluated as the functions of extraction temperature and pressure. SFE was proven to be a feasible alternative over LSE. Also, the optimum SFE conditions which provided maximum extraction and cytotoxicity for each selected sample were presented.

Monte Carlo Study of Structural and Thermodynamic Properties of Liquid Chloroform Using a Five Site Model

A five site potential model combining Lennard–Jones plus Coulomb potential functions has been developed for chloroform molecule. The partial charges needed for Coulombic interactions were derived using the chelpg procedure implemented in the gaussian 92 program. These calculations were performed at the MP2 level with MC-311G* basis set for Cl and 6-311G** for C and H atoms. The parameters for the Lennard–Jones potentials were optimized to reproduce experimental values for the density and enthalpy of vaporization of the pure liquid at 298 K and 1 atm. The statistical mechanics calculations were performed with the Monte Carlo method in the isothermic and isobaric (NpT) ensemble. Besides the values obtained for density, ρ, and molar enthalpy of vaporization at constant pressure, Δ HV, for liquid chloroform, results for molar volume, Vm, molar heat capacity, Cp, isobaric thermal expansivity, αp, and isothermal compressibility, κT, for this pure liquid are also in very good agreement with experimental observations. Size effects on the values of thermodynamic properties were investigated. The potential model was also tested by computing the free energy for solvating one chloroform molecule into its own liquid at 298 K using a statistical perturbation approach. The result obtained compares well with the experimental value. Site–site pair correlation functions were calculated and are in good accordance with theoretical results available in the literature. Dipole–dipole correlation functions for the present five site model were also calculated at different carbon–carbon distances. These correlations were compared to those obtained using the four site model reported in the literature. An investigation of the solvent dependence of the relative free energy for cis/trans conversion of a hypothetical solute in TIP4P water and chloroform was accomplished. The results show strong interaction of water and chloroform molecules with the gauche conformer. The value obtained for the free energy barrier for cis/trans rotation in TIP4P water is higher than that for chloroform. This result is in agreement with the continuous theory for solvation as the conformer with higher dipole moment is more favoured by the solvent with higher dieletric constant. The results also show an increase in entropy as the solute goes from the cis to the trans geometry and this result is more appreciable in the aqueous solution.

Structure Investigations of Liquid Chloroform by Statistical‐Mechanical Calculations and Reverse Monte Carlo Simulation

AbstractThe structure of liquid Chloroform at 298 K is determined with Reverse Monte Carlo simulations. Three independent neutron and one X‐ray scattering experiments are fitted simultaneously to obtain higher evidence in the structural results. The structure is described in form of atom pair correlation and angular distribution functions. Furthermore, the atom pair correlation functions are used to calculate a probability that gives the spatial correlation of atoms of neighbouring molecules around a center molecule. The results are compared with Molecular Dynamics simulations of chloroform from literature and a very good agreement between both methods is found. The aim to reproduce experimental results with statistical mechanical calculations based on site‐site Ornstein Zernike (SSOZ or R1SM) theory in combination with the HNC closure fails. The comparison between statistical mechanical calculations and simulations reveals the unability of the SSOZ theory to describe the short range order of liquid chloroform. SSOZ theory predicts correlations of the hydrogen atom at short distances which clearly are not possible in the real liquid.

Photodissociation of ICN in liquid chloroform: Molecular dynamics of ground and excited state recombination, cage escape, and hydrogen abstraction reaction

The photodissociation of ICN in liquid chloroform on different electronic states of the à band is studied using molecular dynamics simulations. By taking into account nonadiabatic transitions to the ICN ground state and by using a simple statistical model for the reaction between the CN radical and a chloroform molecule, the competition between recombination, cage escape and hydrogen abstraction reaction with the solvent is examined. Good agreement with the cage escape results of a recent experiment by Raftery et al. [J. Chem. Phys. 101, 8572 (1994)] is found. Simulations which did not include the nonadiabatic transitions to the ground state overestimated the probability for cage escape by about a factor of two. Very fast translational relaxation of the CN fragment and very low probability for achieving a transition state configuration for the abstraction reaction are calculated. This supports the suggestion that the abstraction reaction proceeds thermally and is controlled by a structural (entropic) barrier.

Surfactant abnormalities in ALTE and SIDS.

Abnormalities in the relative concentrations of the components of surfactant have been implicated in prolonged expiratory apnoea (PEA) and sudden infant death syndrome (SIDS). Controversy has, however, surrounded these findings, as they may be secondary to terminal life events. In this study the physical properties of surfactant were measured in children with recurrent apparent life threatening events (ALTEs), PEA, and SIDS. Bronchial lavage samples were obtained from 21 children with recurrent ALTEs, two SIDS victims, and 26 control patients. Lipid components were immediately elutriated from these samples with liquid chloroform. The physical properties of the extracted surfactant were studied on a Langmuir trough in which the area (A) of the monolayer was cycled continuously as the surface tension (gamma) was measured by the Wilhelmy method using a platinum 'flag'. The investigators performing these tests were unaware of the clinical diagnosis. Twenty one of 23 patients displayed abnormal physical properties while seven of 26 controls displayed similar abnormalities. These abnormalities were partially inverted hysteresis (figure of eight) loops and inverted (anticlockwise) loops that also generally exhibited less hysteresis. Of the 26 controls 20 exhibited a wide hysteresis pattern that cycled in a normal (clockwise) direction. These differences were significantly different. It is concluded that children with recurrent ALTEs have definable abnormalities in the physical properties of surfactant and that these findings may provide a sensitive means of identifying those at risk of recurrent ALTEs and SIDS.