Liquid Chloroform Research Articles

Supramolecular tryptophan-zipper forms a tripeptide as a regular proton transporter

The diverse structure and assembly of two peptide analogues have been investigated. The tripeptide containing tryptophan, α-aminoisobutyric acid and valine self-assembles through various noncovalent interactions to form a tryptophan-zipper-like structure by intermolecular hydrogen bonding and π–π interactions. But the leucine analogue adopts a water-mediated hydrogen-bonded cage-like structure. X-ray crystallography shed some light on the structure of the tryptophan-zipper at the atomic level. Moreover, in U-tube experiments using pH gradient as the driving force across a liquid chloroform phase, the supramolecular tryptophan-zipper acts as a passive regular proton transporter.

Polar stacking of molecules in liquid chloroform.

Using neutron diffraction and the isotopic substitution technique we have investigated the local structure of liquid chloroform. A strong tendency for polar stacking of molecules with collinear alignment of dipole moments is found. We speculate that these polar stacks contribute to the performance of chloroform as a solvent.

Structure of graphene oxide membranes in solvents and solutions.

The change of distance between individual graphene oxide sheets due to swelling is the key parameter to explain and predict permeation of multilayered graphene oxide (GO) membranes by various solvents and solutions. In situ synchrotron X-ray diffraction study shows that swelling properties of GO membranes are distinctly different compared to precursor graphite oxide powder samples. Intercalation of liquid dioxolane, acetonitrile, acetone, and chloroform into the GO membrane structure occurs with maximum one monolayer insertion (Type I), in contrast with insertion of 2-3 layers of these solvents into the graphite oxide structure. However, the structure of GO membranes expands in liquid DMSO and DMF solvents similarly to precursor graphite oxide (Type II). It can be expected that Type II solvents will permeate GO membranes significantly faster compared to Type I solvents. The membranes are found to be stable in aqueous solutions of acidic and neutral salts, but dissolve slowly in some basic solutions of certain concentrations, e.g. in NaOH, NaHCO3 and LiF. Some larger organic molecules, alkylamines and alkylammonium cations are found to intercalate and expand the lattice of GO membranes significantly, e.g. up to ∼35 Å in octadecylamine/methanol solution. Intercalation of solutes into the GO structure is one of the limiting factors for nano-filtration of certain molecules but it also allows modification of the inter-layer distance of GO membranes and tuning of their permeation properties. For example, GO membranes functionalized with alkylammonium cations are hydrophobized and they swell in non-polar solvents.

A Mixed Quantum-Classical Molecular Dynamics Study of anti-Tetrol and syn-Tetrol Dissolved in Liquid Chloroform: Hydrogen-Bond Structure and Its Signature on the Infrared Absorption Spectrum

The intramolecular hydrogen-bond structure of stereoselectively synthesized syn-tetrol and anti-tetrol dissolved in deuterated chloroform is investigated via a mixed quantum-classical molecular dynamics simulation. An extensive conformational analysis is performed in order to determine the dominant conformations, the distributions among them, and their sensitivity to the method for assigning partial charges (RESP vs AM1-BCC). The signature of the conformational distribution and method of assigning partial charges on the infrared absorption spectra is analyzed in detail. The relationship between the spectra and the underlying hydrogen-bond structure is elucidated.

Liquid chloroform structure from computer simulation with a fullab initiointermolecular interaction potential

We have calculated the intermolecular interaction energies of the chloroform dimer in 12 orientations using the second-order Møller-Plesset perturbation theory. Single point energies of important geometries were calibrated by the coupled cluster with single and double and perturbative triple excitation method. Dunning's correlation consistent basis sets up to aug-cc-pVQZ have been employed in extrapolating the interaction energies to the complete basis set limit values. With the ab initio potential data we constructed a 5-site force field model for molecular dynamics simulations. We compared the simulation results with recent experiments and obtained quantitative agreements for the detailed atomwise radial distribution functions. Our results were also consistent with previous results using empirical force fields with polarization effects. Moreover, the calculated diffusion coefficients reproduced the experimental data over a wide range of thermodynamic conditions. To the best of our knowledge, this is the first ab initio force field which is capable of competing with existing empirical force fields for liquid chloroform.

Anharmonic coupling of the CH-stretch and CH-bend vibrations of chloroform as studied by near-infrared electroabsorption spectroscopy

Combination bands that involve CH- or OH-stretch vibrations appear in the near-infrared (NIR) region (4000-10 000 cm(-1)). Because they arise from anharmonic coupling between the component fundamentals, detailed analysis of the frequency and intensity of NIR combination bands allows one to elucidate the mechanisms behind the vibrational coupling in the condensed phase in terms of mechanical and electrical anharmonicities. Nevertheless, little has been studied, in particular experimentally, on the origin of the combination band intensity. Here, we show that NIR electroabsorption (EA) spectroscopy, which directly probes the effects of an externally applied electric field on a combination band, can shed new light on anharmonic vibrational coupling through determination of the direction of the transition moment for the combination band. We studied the combination band of the CH-stretch (ν(1)) and CH-bend (ν(4)) modes of liquid chloroform. The electric-field induced absorbance change of the ν(1) + ν(4) combination band caused by reorientation of the chloroform molecule was measured at various χ angles, where χ is the angle between the direction of the applied electric field and the polarization of the incident IR light. We were able to detect an absorbance change as small as 5 × 10(-8) for the combination band. Using the NIR EA spectra of the combination band together with those of the CH-stretch and bend fundamentals, the angle between the transition moment for the combination band and the permanent dipole moment was determined experimentally for the first time to be (79 ± 14)°. The present investigation indicates that the contribution of the CH-stretch mode to the mechanical anharmonicity is minor and that the CH-bend mode plays a dominant role in the mechanical part of the vibrational coupling between the two fundamentals. Furthermore, density functional theory calculations show that both the mechanical anharmonicity of the CH-bend mode and the electrical anharmonicity may contribute equally to the anharmonic coupling.

HPLC–MS analyses and bioactivities of novel chemicals in Devil’s club (Oplopanax horridus (Sm.) Miq.)

Abstract Devil’s club (Oplopanax horridus (Sm.) Miq.) has traditionally been used as a folk medicine by native North Americans for the treatment of various chronic diseases. A methanolic extract and its sub-fractions by liquid–liquid re-extraction, i.e., chloroform (CHCl3), ethyl acetate (EtOAc), n-butanol (BuOH), and water fractions, were analysed by their anti-cancer activity with in vitro cell proliferative bioassays, and their antioxidant capacities in terms of the determination of total phenolic content (TPC), ORAC value, and DPPH free radical scavenging activity. The whole extract of the dried root contained high TPC and possessed strong ORAC and DPPH radical scavenging activities. In addition, the extract exhibited a strong anti-proliferative ability against HT-29 cancer cells, e.g., with an inhibitive rate of 56.5% with a 0.2-mg/mL extract. Further investigation by HPLC–UV–MS identified significant bioactive phenolic compounds in the chloroform fraction, including gallic acid, caffeic acid, 4-O-feruloylquinic acid, 5-O-feruloylquinic acid, ferulic acid, methyl feruloylquinate, methyl ferulate, and quercetin. These results suggested that the associated bioactivity of the plant might result from the contribution of phenolic compounds.

Non-resonant femtosecond laser control of the molecular dynamics in liquid chloroform

The optical control of the molecular motions in chloroform CHCl3 at room temperature through the non-resonant excitation was enhanced by means of the double-pulse pump-probe technique. When the separation time of the pump pulses and their relative intensity were varied, the amplification or the cancellation of the coherent vibrations of the molecules was achieved. The molecular responses were detected by the time-resolved optically heterodyne-detected optical-Kerr-effect technique.

Refractive-Index Matching Avoids Local Field Corrections and Scattering Bias in Solid-State Na2SO4 Ultraviolet Raman Cross-Section Measurements

We report a refractive-index matching method to measure nonabsorbing solid ultraviolet (UV) Raman cross-sections that avoids the local field correction and interface scattering of incident light. We used refractive-index-matched chloroform as an internal standard to determine the solid-state 995 cm(-1) Na(2)SO(4) 244 nm Raman cross-sections. The pure liquid chloroform 668 cm(-1) 244 nm Raman cross-section was determined by using acetonitrile as an internal standard and by calculating the local field corrections for the observed Raman intensities. Our measured 244 nm UV Raman cross-section of the solid-state 995 cm(-1) SO4(2-) band of 1.97 ± 0.07 × 10(-28) cm(2)/(molc·sr) is about half of its aqueous solution Raman cross-section, indicating interactions between the sulfate species in the solid that decrease the Raman polarizability.

Analysis of thermal expansivity and isothermal compressibility of liquid hexane and chloroform

In the present paper, we have analysed the pressure dependences of thermal expansivity (α p ) and isothermal compressibility (K T ) for the liquid hexane and chloroform. We have used the formulae based on the pseudospinodal model and the Sanchez et al [1,2] equation of state obtained from the Pade approximation. The thermal expansion coefficient and isothermal compressibility follow a power law function of pressures. It is found that the quantities, α p as well as K T decreases with the increasing pressure. The isothermal compressibility decreases more rapidly in comparison to thermal expansivity. The pressure at which the spinodal condition is satisfied, i.e. α p and K T both tend to infinity, has been found to be a characteristic property of the liquid hexane and chloroform.

Silicon Nanocrystals Produced by Nanosecond Laser Ablation in an Organic Liquid

Small (3−5 nm in diameter following HRTEM images) Si nanocrystals were produced in a two-stage process including (1) nanosecond laser ablation of a Si target in an organic liquid (chloroform) that results in formation of big composite polycrystalline particles (about 20−100 nm average diameter) and (2) ultrasonic post-treatment of Si nanoparticles in the presence of HF. The post-treatment is responsible for disintegration of the composite Si particles, release of small individual nanocrystals, and reduction of their size due to HF-induced etching of Si oxide. The downshift and broadening of the ∼520 cm−1 Raman phonon band of the small Si nanocrystals with respect to the bulk Si Raman band is consistent with the presence of ∼4.5 nm Si nanocrystals. The photoluminescence spectra (450−900 nm) and decay kinetics of small Si nanocrystals were detected, and the possible origin of the luminescence is discussed.

Detailed intermolecular structure of molecular liquids containing slightly distorted tetrahedral molecules with C3v symmetry: Chloroform, bromoform, and methyl-iodide

Analyses of the intermolecular structure of molecular liquids containing slightly distorted tetrahedral molecules of the CXY(3)-type are described. The process is composed of the determination of several different distance-dependent orientational correlation functions, including ones that are introduced here. As a result, a complete structure classification could be provided for CXY(3) molecular liquids, namely for liquid chloroform, bromoform, and methyl-iodide. In the present work, the calculations have been conducted on particle configurations resulting from reverse Monte Carlo computer modeling: these particle arrangements have the advantage that they are fully consistent with structure factors from neutron and x-ray diffraction measurements. It has been established that as the separation between neighboring molecules increases, the dominant mutual orientations change from face-to-face to edge-to-edge, via the edge-to-face arrangements. Depending on the actual liquid, these geometrical elements (edges and faces of the distorted tetrahedra) were found to contain different atoms. From the set of liquids studied here, the structure of methyl-iodide was found to be easiest to describe on the basis of pure steric effects (molecular shape, size, and density) and the structure of liquid chloroform seems to be the furthest away from the corresponding "flexible fused hard spheres" like reference system.

Strontium Nitrate Extraction to Ionic Liquids by a Crown Ether: A Molecular Dynamics Study of Aqueous Interfaces with C4mim+- vs C8mim+-Based Ionic Liquids

In order to gain microscopic insights into the extraction mechanism of strontium cations by 18-crown-6 (18C6) to room temperature ionic liquids (ILs), we simulated by molecular dynamics (MD) strontium complexes in neat ionic liquids and at their interfaces with water. We compared two ILs, based on the PF(6)(-) anion and either 1-butyl-3-methylimidazolium (C(4)mim(+)) or 1-octyl-3-methylimidazolium (C(8)mim(+)) cations. Regarding the complexes, two states were considered: charged [Sr⊂18C6](2+) vs neutral [Sr⊂18C6,(NO(3))(2)], where the nitrates are either fully dissociated or coordinated to Sr. In "dry" or "humid" [C(4)mim][PF(6)] and in "dry" [C(8)mim][PF(6)] IL, the neutral complex is found to be the most stable one. In the binary IL/water solutions, the charged complexes mostly partition to the aqueous phase, whereas the neutral [Sr⊂18C6,(NO(3))(2)] complexes are more concentrated in the interfacial domain. The aqueous solutions in contact with the ionic liquids contain C(4)mim(+), but almost no C(8)mim(+) ions, supporting a classical extraction mechanism to [C(8)mim][PF(6)] and an ion exchange mechanism to [C(4)mim][PF(6)]. Furthermore, remarkable events occurred during the dynamics, where complexes were extracted to the IL phases. When compared to the interfacial landscapes obtained with the same solutes at a classical organic liquid (chloroform)/water interface, those with ILs allow us to better understand specific features of liquid-liquid extraction to ILs.

The liquid structure of haloformsCHCl3 andCHBr3

New neutron and x-ray diffraction measurements are reported on liquid chloroform,CHCl3, andbromoform, CHBr3. Experimental total scattering structure factors have been interpreted by the reverseMonte Carlo method of structural modelling. Partial radial distribution functions,intramolecular bond angle distributions and functions characterizing distance-dependentorientational correlations have been calculated directly from the particle coordinates. It hasbeen found that most of these characteristics of the microscopic structure can beapproximated rather well by functions calculated for hard sphere like reference systems.The two liquids show similar features from the point of view of their structure. There arealso some distinctive features in terms of orientational correlations: nearest neighbourmolecules prefer face-to-face arrangement in chloroform whereas in bromoform, edge-to-faceconfigurations dominate, with a significant occurrence of corner-to-face type correlations.

Active Transport of Amino Acids by a Guanidiniocarbonyl–Pyrrole Receptor

Herein we report the synthesis and characterization of a transporter 9 for N-acetylated amino acids. Transporter 9 is a conjugate of a guanidiniocarbonyl pyrrole cation, one of the most efficient carboxylate binding motifs reported so far, and a hydrophobic tris(dodecylbenzyl) group, which ensures solubility in organic solvents. In its protonated form, 9 binds N-acetylated amino acid carboxylates in wet organic solvents with association constants in the range of 10(4) M(-1) as estimated by extraction experiments. Aromatic amino acids are preferred due to additional cation-pi-interactions of the amino acid side chain with the guanidiniocarbonyl pyrrole moiety. U-tube experiments established efficient transport across a bulk liquid chloroform phase with fluxes approaching 10(-6) mol m(-2) s(-1). In experiments with single substrates, the release rate of the amino acid from the receptor-substrate complex at the interface with the receiving phase is rate determining. In contrast to this, in competition experiments with several substrates, the thermodynamic affinity to 9 becomes decisive. As 9 can only transport anions in its protonated form and has a pK(a) value of approximately 7, pH-driven active transport of amino acids is also possible. Transport occurs as a symport of the amino acid carboxylate and a proton.

A one-site polarizable model for liquid chloroform: COS/C

A one-site polarizable liquid chloroform model based on the charge-on-spring method is presented. It consists of five van der Waals sites and point charges, with one polarizable center on the carbon atom. The partial charges were adjusted to fit the gas-phase dipole moment of chloroform, and the Lennard–Jones parameters were varied to reproduce the density and the heat of vapourization of liquid chloroform. In this way, a simple polarizable model for liquid chloroform was obtained that correctly describes a variety of its thermodynamic, dynamic and dielectric properties, while the computational costs are only a factor of 2 higher than for a similar non-polarizable chloroform model. The model is simpler than two previously developed polarizable chloroform models, with four or five polarizable sites. The developed COS/C model is expected to show realistic behaviour of chloroform molecules in response to changes in electric field strength or the dielectric environment and should be applicable in simulations of biomolecules in conjunction with the GROMOS biomolecular force field.

Direct evidence of the dielectric confinement effect in the infrared spectra of organic liquids

In this study, the size (dielectric) confinement effect on the peak position of intra-molecular vibrations in the infrared spectra of liquid benzene, carbon disulphide and chloroform is described theoretically, and observed experimentally, for the first time. It is shown that the shift in the peak position due to the dielectric confinement effect can reach a few tenths of a wavenumber for strong vibrational bands. The results obtained confirm the applicability of the dispersive local-field approach for the description of the dielectric confinement effect for liquid media, as well as for crystalline and amorphous solids.

Microhydration effects on a model SN2 reaction in a nonpolar solvent

Using a recently developed empirical valence bond model for the nucleophilic substitution reaction (S(N)2) in solution, we examine microhydration effects on the benchmark Cl(-) + CH(3)Cl reaction in liquid chloroform. Specifically, the effect of the hydration of the reactive system by one to five water molecules on the reaction-free energy profile and the rate constant is examined. We find that the activation-free energy is highly sensitive to the number of water molecules hydrating the nucleophile, increasing the barrier by about 4 kcal/mol by the first water molecule. With five water molecules, the barrier height is 10 kcal/mol larger than the barrier in bulk chloroform and only 3 kcal/mol below the barrier in bulk water. A number of properties vary monotonically with the number of water molecules, including the rate of change in the system's electronic structure and the solvent stabilization of the transition state. These and other properties are a rapidly varying function of the reaction coordinate. Deviation from transition state theory due to barrier recrossing is not large and falls between the behavior in bulk water and bulk chloroform.

Supercontinuum generation in chloroform-filled photonic crystal fibers

We propose a novel method to achieve highly nonlinear photonic crystal fiber (PCF) by filling highly nonlinear liquid chloroform in the core of hollow-core PCF (HCPCF). The dispersion properties and electric field distribution of the fundamental mode are calculated by using the full-vector finite element method (FVFEM). Simulation results indicate that the zero-dispersion wavelength (ZDWL) of the chloroform-filled PCF is adjustable around 800 nm. Hence the femtosecond laser pulses with central wavelength at 800 nm can propagate in anomalous dispersion regime of the PCF, inducing the spectra broadening.

Polarizable model of chloroform based on classical Drude oscillators

Biophysical studies of membrane proteins through spectroscopic methods often require that the protein be extracted from its lipid environment and solubilized. Liquid chloroform is one of several organic co-solvents that is successfully used for this purpose. However, our understanding of the influence of such environments on the structure and dynamics of proteins is far from complete. Atomically-detailed molecular simulations may provide valuable insights to help interpret the experimental data derived from these complex systems, provided that appropriate developments in the existing force-fields are made. In this communication we present a novel polarizable model for chloroform, based on classical Drude oscillators. This model was calibrated to reproduce the vaporization enthalpy, density, static dielectric constant and self-diffusion constant of the pure liquid at ambient conditions.