Liquid Dichloromethane Research Articles

Synthesis and Photophysical Evaluation of Isoleptic Pt(II) and Pd(II) Complexes Utilizing N^N^N Ligands as Luminophoric Chelators with Different Ancillary Ligands

We herein report on the synthesis and structural characterization, as well as on the photophysical properties, of a series of isoleptic Pt(II) and Pd(II) complexes featuring tridentate N^N^N chelators as luminophores while bearing diverse ancillary co-ligands. Six new palladium complexes were synthesized using 2,6-bis(3-(tert-butyl/trifluoromethyl)-1H-1,2,4-triazol-5-yl)pyridine (tbu or CF3, respectively) in combination with four distinct ancillary ligands, namely: 4-amylpyridine (AmPy), 2,6-dimethylphenyl isonitrile (CNR), triphenylphosphane (PPh3), and 1,3,5-triaza-7-phosphaadamantane (PTA). Thus, two novel Pt(II) complexes incorporating the co-ligands CNR and PTA were explored. The remaining platinum-based complexes, namely CF3-Pt-AmPy, tbu-Pt-AmPy, CF3-Pt-PPh3, and tbu-Pt-PPh3, were re-synthesized according to our previous work for a systematic comparison with their Pd(II) homologues. Thus, photophysical studies were performed in different solvents and conditions. The Pt(II) complexes demonstrated comparable or superior photophysical characteristics in toluene when compared with their solutions in liquid dichloromethane at room temperature. In contrast, the Pd(II) complexes exhibited no significant photoluminescence in dichloromethane, but a surprisingly clear emission was observed for tbu-Pd-AmPy, tbu-Pd-CNR, and tbu-Pd-PPh3 in liquid toluene at room temperature. The significant differences regarding excited state lifetimes and photoluminescence quantum yields underscore the impact of solvent selection on photophysical characteristics, emphasizing the need to consider metal-ligand interactions, as well as the surrounding microenvironment, for a comprehensive interpretation of their photophysical properties. In addition, it is clear that AmPy and CNR render better luminescence efficiencies, whereas PTA is only suitable in toluene.

Kinetics and Energetics of Electron Transfer to Dimer Radical Cations.

Spectra of the dimer cations naphthalene (Nap2•+) and ethene (Ethene2•+) were measured in liquid dichloromethane (DCM). The spectra peak at very different energies, 1.2 and 3.3 eV. In DCM dimerization stabilizes Nap2•+ by ΔGd°(Nap2•+) = -218 meV relative to the monomer Nap•+ as determined from the dimerization equilibrium constant. Both dimers can transfer a positive charge to hole acceptor molecules, but for both the rate constants rise more gradually with reaction energetics than do many charge transfer reactions previously studied. A striking observation finds that the rate constant for hole transfer from the Nap2•+ dimer to phenanthrene is smaller by two decades than that from biphenyl•+ monomer to Nap, although both reactions have the same -ΔG° = 0.05 eV. A plausible interpretation for these observations is the presence of an energy of reorganization, λ(M2), for the dimer that involves movement apart of the two partners in the dimer. While the dimerization equilibrium cannot be measured for Ethene2•+, the charge transfer data imply that both ΔGd°(Ethene2•+) and λ(Ethene2•+) are considerably larger, perhaps by factors of 2-4 than for Nap2•+.

Photochemical Kinetics of a Phosphine Oxide Free Radical Initiator from Femtosecond UV-Pump/Mid-IR-Probe Spectroscopy.

Femtosecond UV-pump/mid-infrared-probe spectroscopy was used to explore in detail the primary photochemical events of the free radical initiator, (2,4,6-trimethylbenzoyl)diphenylphosphine oxide, in liquid dichloromethane solution at room temperature. Following electronic excitation of its lowest excited singlet state, S1, the radical initiator undergoes an intersystem crossing to the triplet ground state, T1, with a time constant of 135 ps. A subsequent α-cleavage occurs from the triplet state with a time constant of 15 ps and yields a trimethylbenzoyl radical together with a diphenylphosphinoyl radical. Transient absorptions from the S1 and T1 states are observed that can be assigned to the P═O stretching mode and the symmetric in-plane deformation mode of the trimethylphenyl moiety of the radical initiator.

A quantum chemical study of [1.1.1.1]pagodane and its related compounds

The PBE0/6-31G** quantum chemical method is used to determine the symmetry and equilibrium structural parameters of the molecules of [1.1.1.1]pagodane (C20H20, D2h), two dienes (C20H20, D2h), two diradicals (C20H20, C2ν), and two dications (C20H202+, D2h and C2ν). The energy of a highly symmetric dication with a rectangular cycle is lower by 36 kcal/mole than that of a low symmetric dication with a trapezoidal cycle. The polarization interaction with liquid methylene chloride causes its decrease by 147 kcal/mole.

Characterization of Brazilian oil shale byproducts planned for use as soil conditioners for food and agro-energy production

The Brazilian oil shale byproducts resulting from the Petrosix pyrolysis (retortage) process were submitted to a set of analytical techniques to evaluate their possible use as agricultural soil conditioners. Liquid dichloromethane extracts from the solid samples were analyzed using capillary column gas chromatography–mass spectrometry. The results showed that of the 16 PAHs designated by the U.S. EPA as priority pollutants, only phenanthrene, fluorene and naphthalene, present in the retorted oil shale sample taken from inside storage piles; benzo[k]fluoranthene, present in the dolomite limestone layer between the two layers of oil shale in the mine structure; and naphthalene, present in powdered raw oil shale, were above the limits established by the EPA. The solid Brazilian oil shale byproduct samples were also analyzed by X-ray diffractometry (XRD), diffuse reflectance ultraviolet–visible spectroscopy (DRUV–VIS), X-ray fluorescence spectroscopy (XRF) and electron paramagnetic resonance (EPR) spectroscopy. The XRD analysis showed that the pyrolysis process produces a “weathering” transformation, for example with the appearance of kaolinite diffraction lines in the retorted samples. The DRUV–VIS and XRF spectroscopy results indicated iron oxide goethite interactions with the PAHs present in the solid samples studied. The EPR spectroscopy showed that the samples row oil shale (g=2.0044) and the powder oil shale (g=2.0035), before the dichloromethane extraction, presented organic free radical signals associated with oxygen atoms. The other Brazilian oil shale byproduct samples, before and after the dichloromethane extraction, showed organic free radical signals associated with carbon atoms (g=2.0022–2.0031).

Dichloromethane: Revision and extension of pρT relationships for the liquid

In spite of the great importance of the PVT data of dichloromethane, only limited information on these data seems to be available in the literature. In this work, we present experimental densities of the liquid dichloromethane over the ranges T = (270 to 330) K and p = (0.1 to 30) MPa using a vibrating tube densimeter, model DMA 512P from Anton Paar with an estimated uncertainty lower than ±0.5 kg · m −3. The high consistency of our data compared with those measured by other authors allows that all the experimental results have been combined and correlated together with the Tait equation in the temperature and pressure ranges T = (244 to 430) K and p = (0.1 to 101) MPa. From the Tait equation, thermomechanical coefficients as the isothermal compressibility, isobaric expansivity, thermal pressure, and internal pressure were calculated. Some of the measurements of density were made at pressures lower than the critical pressure which enabled us to obtain very reliable values for the density of the saturated liquid within the range T = (270.0 to 330.0) K. These data were combined with other values existing in the literature, which made it possible to extend the information on the saturated liquid density to the range T = (208 to 399) K. From these data, a new equation describing the saturated liquid density of dichloromethane was found covering the entire temperature range between the triple and the critical temperatures. A new equation for the vapour pressure was found by using selected values from the literature covering the entire temperature range between the triple and the critical temperatures.

Molecular level properties of the free water surface and different organic liquid/waterinterfaces, as seen from ITIM analysis of computer simulation results

Molecular dynamics simulations of the interface of water with four different apolar phases,namely water vapour, liquid carbon tetrachloride, liquid dichloromethane (DCM) andliquid dichloroethane (DCE) are performed on the canonical ensemble at 298 K. Theresulting configurations are analysed using the novel method of identification of the trulyinterfacial molecules (ITIM). Properties of the first three molecular layers of the liquidphases (e.g. width, spacing, roughness, extent of the in-layer hydrogen bonding network) aswell as of the molecules constituting these layers (e.g., dynamics, orientation) areinvestigated in detail. In the analyses, particular attention is paid to the effect of thepolarity of the non-aqueous phase and to the length scale of the effect of the vicinity ofthe interface on the various properties of the molecules. The obtained resultsshow that increasing polarity of the non-aqueous phase leads to the narrowing ofthe interface, in spite of the fact that, at the same time, the truly interfaciallayer of water gets somewhat broader. The influence of the nearby interface isfound to extend only to the first molecular layer in many respects. This resultis attributed to the larger space available for the truly interfacial than for thenon-interfacial molecules (as the shapes of the two liquid surfaces are largelyindependent of each other, resulting in the presence of voids between the two phases),and to the fact that the hydrogen bonding interaction of the truly interfacialwater molecules with other waters is hindered in the direction of the interface.

Partial radial distribution functions of methylene halide molecular liquids

The total scattering structure factors of liquid methylene chloride (CH 2Cl 2), methylene bromide (CH 2Br 2) and methylene iodide (CH 2I 2) have been determined at room temperature and atmospheric pressure by neutron and X-ray diffraction. Experimental data were interpreted by means of the Reverse Monte Carlo structural modelling technique, which provided large particle configurations that were consistent with the measured structure factors. From the models, partial radial distribution functions were calculated directly. Comparison with hard sphere like reference systems showed that a surprisingly large part of the pair correlations can be captured via the simple concept of steric effects (packing fraction and molecular shape).

Proton transfer in a polar solvent from ring polymer reaction rate theory

We have used the ring polymer molecular dynamics method to study the Azzouz-Borgis model for proton transfer between phenol (AH) and trimethylamine (B) in liquid methyl chloride. When the A-H distance is used as the reaction coordinate, the ring polymer trajectories are found to exhibit multiple recrossings of the transition state dividing surface and to give a rate coefficient that is smaller than the quantum transition state theory value by an order of magnitude. This is to be expected on kinematic grounds for a heavy-light-heavy reaction when the light atom transfer coordinate is used as the reaction coordinate, and it clearly precludes the use of transition state theory with this reaction coordinate. As has been shown previously for this problem, a solvent polarization coordinate defined in terms of the expectation value of the proton transfer distance in the ground adiabatic quantum state provides a better reaction coordinate with less recrossing. These results are discussed in light of the wide body of earlier theoretical work on the Azzouz-Borgis model and the considerable range of previously reported values for its proton and deuteron transfer rate coefficients.

Ethylene oxide-bridged bipyridine oligomers that function as selective host molecules for the encapsulation of small alkali cation guests

Two novel ethylene oxide-bridged bipyridine oligomers were synthesized that contain host pockets with four (1) or six (2) oxygen donor atoms and a pyridyl nitrogen donor. The alkali picrate extracting ability and selectivity of these free ligands was investigated using a liquid–liquid dichloromethane–water extraction study. Both open-chain oligomer frameworks display unexpectedly high extraction efficiency (EE) values for specific guest ions (EE = 57% Na+ extracted by 1, and EE = 39% Cs+ extracted by 2). These extraction values are comparable to macrocyclic analogues and their ion selectivities follow the ‘same-fit’ concept that has been extensively reported for fixed pocket systems. The shorter chain oligomer (1) binds ions in the series (Na+ > K+ > Cs+), while the larger oligomer (2) binds ions in the reverse order (Cs+ > K+ > Na+). Formation of the host–guest ligand–ion complexes were verified by 1H NMR spectroscopy and MALDI-TOF mass spectrometry experiments. A Job’s plot analysis based on UV spectral data also supported the 1:1 (oligomer to ion) complexation observed in the MALDI mass spectra.

Structure of liquid methylene chloride: Molecular dynamics simulation compared to diffraction experiments

Molecular dynamics simulation and diffraction (X-ray and neutron) studies are compared on methylene chloride with aiming at the determination of the liquid structure. Beyond that, the capabilities of the methods to describe liquid structure are discussed. For the studied liquid, the diffraction methods are performing very well in determination of intramolecular structure, but they do not give detailed structural information on the intermolecular structure. The good agreement between the diffraction experiments and the results of molecular dynamics simulations justify the use of simulations for the more detailed description of the liquid structure using partial radial distribution functions and orientational correlation functions. Liquid dichloromethane is described as a molecular liquid without strong intermolecular interactions like hydrogen bonding or halogen-halogen contacts, but with detectable orientational correlations resulting in antiparallel, tail-to-tail orientation of the first nearest neighbours, which is lost very quickly and slight preference of parallel head-to-tail and L-shaped orientation can be detected. On the other hand some orientational correlations between rather distant molecules can also be observed.

A Simple, Sensitive, and Rapid Method for the Determination of Cotinine in Urine by High-Performance Liquid Chromatography with UV Detection

Cotinine levels in biological fluids are a reliable indicator of the presence of nicotine. In this paper, a simple and sensitive high-performance liquid chromatography (HPLC) procedure for the determination of cotinine in urine following liquid-liquid extraction with dichloromethane in an alkaline medium is described. Calibration curves show linearity over the 50 to 3000 ng/mL range with low intra- and interday variability as well as good selectivity and specificity. No solid-phase extraction is performed because the liquid dichloromethane extraction step yields excellent results. This method is a good alternative for routine analysis of urinary cotinine in laboratories where gas chromatography or HPLC-mass spectrometry is not available.

Cross-orientational motion in liquid dichloromethane and trichloromethane (chloroform) by molecular dynamics simulation

Using molecular dynamics the l = 1 orientational auto- and cross-correlation functions of one of the C–H bond directions of neat dichloromethane at 273 K and that of chloroform between 301 and 438 K in its neat state and in solution with tetrachloromethane and liquefied methane (at 183 K) have been simulated. The simulations are confined to a model of singly rotating, individual molecules in the absence of induced absorption and translation-rotation coupling. It is found throughout that the orientational cross-correlation functions are equivalent to the auto-correlation functions, therefore bearing the same information content. On the basis of a simple thermodynamic argument, this phenomenon is extended to be generally valid to orientational correlation functions from vibration–rotation spectra of mobile liquids. Consequences of the equivalence are, first, that dilution does not break the symmetry between orientational auto- and cross-correlation functions of the solute species and, second, that the simulated auto-correlation functions of total and individual dipole moments of undressed dipoles in the system are indistinguishable.

Path integral evaluation of the quantum instanton rate constant for proton transfer in a polar solvent

The quantum instanton approximation for thermal rate constants, a type of quantum transition state theory (QTST), is applied to a model proton transfer reaction in liquid methyl chloride developed by Azzouz and Borgis. Monte Carlo path integral methods are used to carry out the calculations, and two other closely related QTST's, namely, the centroid-density and Hansen-Andersen QTST, are also evaluated for comparison using the present path integral approach. A technique is then introduced that calculates the kinetic isotope effect directly via thermodynamic integration of the rate with respect to hydrogen mass, which has the practical advantage of avoiding costly evaluation of the activation free energy. The present application to the Azzouz-Borgis problem shows that the above three types of QTST provide very similar results for the rate, within 30% of each other, which is nontrivial considering the totally different derivations of these QTSTs; the latter rates are also in reasonable agreement with some other previous results (e.g., obtained via molecular dynamics with quantum transitions), within a factor of approximately 2(7) for the H(D) transfer, thus significantly diminishing the possible range of the exact rates. In addition, it is revealed that a small but nonnegligible inconsistency exists in the parametrization of the Azzouz-Borgis model employed in previous studies, which resulted in the large apparent discrepancy in the calculated rates.

The Role of the trans‐Planar Mesophase in the Polymorphic Behavior of Syndiotactic Polypropylene

AbstractThe transformations of the trans‐planar mesophase of syndiotactic polypropylene (sPP) subjected to thermal, mechanical and solvent treatments, were investigated. The unoriented trans‐planar mesophase, obtained by quenching the melt at 0°C, was annealed at 80°C and the thermal transformation was investigated by X‐rays, infrared and dynamic‐mechanical analysis. The presence of the helical form II was recognized in the annealed sample. The oriented trans‐planar mesophase, obtained by drawing at room temperature and releasing the tension, was immersed in liquid dichloromethane for 24 hours. After drying the sample showed the presence of the oriented form II, although it was not possible to exclude a partial transition into form IV. On the basis of the present and literature results we suggested a scheme of the polymorphic transitions of sPP, in which the central role of the trans‐planar mesophase is enlightened.

Molecular dynamics with quantum transitions for proton transfer: Quantum treatment of hydrogen and donor–acceptor motions

The mixed quantum/classical molecular dynamics with quantum transitions (MDQT) method is extended to treat the donor–acceptor vibrational motion as well as the hydrogen motion quantum mechanically for proton transfer reactions. The quantum treatment of both the hydrogen and the donor–acceptor motions requires the calculation of two-dimensional vibrational wave functions. The MDQT surface hopping method incorporates nonadiabatic transitions among these adiabatic vibrational states. This approach is applied to a model representing intramolecular proton transfer within a phenol-amine complex in liquid methyl chloride. For this model, the rates and kinetic isotope effects are the same within statistical uncertainty for simulations in which only the hydrogen motion is treated quantum mechanically and simulations in which both the hydrogen and the donor–acceptor vibrational motions are treated quantum mechanically. The analysis of these simulations elucidates the fundamental issues arising from a quantum mechanical treatment of the donor–acceptor vibrational motion as well as the hydrogen motion. This insight is relevant to future mixed quantum/classical molecular dynamics simulations of proton and hydride transfer reactions in solution and in enzymes.

Variational transition state theory evaluation of the rate constant for proton transfer in a polar solvent

Variational transition state theory (VTST) is used to calculate rate constants for a model proton transfer reaction in a polar solvent. We start from an explicit description of the reacting solute in a solvent, and we model the effects of solvation on the reaction dynamics by a generalized Langevin equation (GLE) for the solute. In this description, the effects of solvation on the reaction energetics are included in the potential of mean force, and dynamical, or nonequilibrium, solvation is included by solvent friction. The GLE solvation dynamics are approximated by a collection of harmonic oscillators that are linearly coupled to the coordinates of the reacting system. This approach is applied to a model developed by Azzouz and Borgis [J. Chem. Phys. 98, 7361 (1993)] to represent proton transfer in a phenol-amine complex in liquid methyl chloride. In particular, semiclassical VTST, including multidimensional tunneling contributions, is applied to this model with three explicit solute coordinates and a multioscillator GLE description of solvation to calculate rate constants. We compare our computed rate constants and H/D kinetic isotope effects to previous calculations using other approximate dynamical theories, including approaches based on one-dimensional models, molecular dynamics with quantum transitions, and path integrals. By examining a systematic sequence of 18 different sets of approximations, we clarify some of the factors (such as classical vibrations, harmonic approximations, quantum character of reaction-coordinate motion, and nonequilibrium solvation) that contribute to the different predictions of various approximation schemes in the literature.

Intermolecular interactions of liquid dichloromethane and equilibrium properties of liquid–vapor and liquid–liquid interfaces: A molecular dynamics study

Extensive molecular dynamics simulations are carried out to study the molecular interactions, liquid states, and liquid/vapor properties of dichloromethane. The study is also extended to the equilibrium properties of the liquid/liquid interface of water-dichloromethane. The intermolecular interactions among water, dichloromethane, and water-dichloromethane are described using our polarizable potential models. The equilibrium properties of liquid dichloromethane, including the radial distribution functions, the intermolecular structural factor, the self-diffusion coefficient, and the dielectric constant, are evaluated. The dielectric constant is computed using Ewald summation techniques and the computed result compared reasonably well with the available experimental data. Properties such as surface tensions and density profiles of liquid/vapor dichloromethane are evaluated. We found that the computed surface tensions for several temperatures are in excellent agreement with experimental data. The computed density profile of the liquid/liquid interface of water-dichloromethane is averaged over 1 ns and we found the computed profile to be quite smooth and stable. The effect of polarization on the liquid/liquid interfacial equilibrium properties is evaluated by computing the dipole moments of water and dichloromethane molecules as a function of the distance normal to the interface. We found that these values deviated significantly from the simulations that are based on nonpolarizable potential models. We attribute these observations to the changes in the electric fields around the water and dichloromethane molecules near the interface.

Quantum proton transfer with spatially dependent friction: Phenol-amine in methyl chloride

In a recent paper [D. Antoniou and S. D. Schwartz, J. Chem. Phys. 110, 465 (1999)] we calculated the reaction rate for a proton transfer reaction in liquid methyl chloride. In that work, we used a spectral density obtained from a molecular dynamics simulation as input to a quantum Zwanzig Hamiltonian which we solved using our exponential resummation method. In the present paper we perform a similar calculation, allowing for a position dependent friction using the method of G. Haynes, G. Voth, and E. Pollak [J. Chem. Phys. 101, 7811 (1994)]. Compared with the results of our previous work, we found that including spatial dependence to the friction led to enhancement of the reaction rate and to reduction of the H/D kinetic isotope effect.

The hypervolume Monte Carlo method at constant pressure applied to liquid methyl chloride

The hypervolume Monte Carlo (HVMC) in the isoenthalpic–isobaric ensemble (NpH), recently proposed by Fernandes and Freitas [1] has been applied to a molecular system. Thermal and structural properties as well as speed distribution functions of the liquid methyl chloride, obtained in a series of thermodynamics states, have been compared with NpT molecular dynamics (MD) [2,3] and some experimental results [4]. The agreement between the calculated and experimental densities is fairly good and the comparison with molecular dynamics results is excellent.