Liquid Acetonitrile Research Articles

Photophysical properties of cyclometalated Pt(II) complexes attached with pyrene by C [sbnd]C single bond

Luminescent complexes, [(C^N^N)Pt(C≡CR)](HC^N^N = 4-(1-phenyl)-6-phenyl-2,2′-bipyridine, R = Ph ( 1, PPPt); HC^N^N = 4-(1-pyrene)-6-phenyl-2, 2′-bipyridine; R = Ph ( 2, PyPPt), p-Et-Ph ( 3, PyEPPt)), were synthesized and their photophysical properties were investigated in acetonitrile liquid solution and butyronitrile glasses at 77 K. These complexes display steady state dual emissions at room temperature and 77 K. The emission lifetime and transient absorption of these complexes illustrated that the 3IL triplet state of the molecules could be acquired through the intersystem crossing directly from 1MLCT state and the triplet–triplet internal conversion from the 3MLCT state to the 3IL state was negligible in the molecules.

Can Marcus Theory Be Applied to Redox Processes in Ionic Liquids? A Comparative Simulation Study of Dimethylimidazolium Liquids and Acetonitrile

Simulations of a model system of charged spherical ions in the ionic liquids dimethylimidazolium chloride, [dmim][Cl], dimethylimidazolium hexafluorophosphate, [dmim][PF6], and the polar liquid acetonitrile, MeCN, are used to investigate the applicability of Marcus theory to electrochemical half-cell redox processes in these liquids. The free energy curves for solvent fluctuations are found to be approximately parabolic and the Marcus solvent reorganization free energies and activation free energies are determined for six possible redox processes in each solvent. The similarities between the different types of solvent are striking and are attributed to the essentially long-range nature of the relevant interactions and the effectiveness of the screening of the ion potential. Nevertheless, molecular effects are seen in the variation of solvent screening potential with distances up to 2 nm.

Analysis of Liquid Structure without Construction of Any Structure Models by the X-Ray Scattering Method

A simple approach for determining a liquid structure using X-ray scattering data, in which a liquid structure is uniquely evaluated without construction of any plausible structure models, has been applied to liquid acetonitrile, acetone and cyclohexane. For a pair of molecules, a given point within a molecule is located at the origin with a given molecular orientation. The site of the given point of another molecule is defined by the polar coordinates and the molecular orientation is treated by three Eulerian angles. These parameters are optimized by a non-linear least-squares calculation applied to X-ray scattering data. The reliability of the method was examined by determining the liquid structure of polar acetonitrile and the obtained intermolecular interatomic distances are in good agreement with the previously reported values. The method was then successfully applied to the determination of the liquid structure of acetone and cyclohexane. Especially for nonpolar cyclohexane, the construction of a variety of plausible structural models is very difficult. It was revealed that acetone has an ordered liquid arrangement similar to that found in its crystal, although the intermolecular distances in liquid acetone are different from those in the crystal. On the other hand, the liquid structure of cyclohexane is disordered.

N-Methyl- N-propylpiperidinium bis(trifluoromethanesulphonyl)imide as an electrolyte for carbon-based double-layer capacitors

N-Methyl- N-propylpiperidinium bis(trifluoromethanesulphonyl)imide (MePrPipNTf 2), as well as its mixture with a molecular liquid acetonitrile (MeCN) were tested as electrolytes for carbon-double-layer capacitors. The conductivity of the MePrPipNTf 2 neat ionic liquid is at the level of 1.5 mS cm −1, while the corresponding value for the mixture (48 wt.% MePrPipNTf 2 + 52 wt.% of MeCN) is ca. 40 mS cm −1 (both recorded at 25 °C). The electrochemical stability of the electrolyte (both neat ionic liquid, as well as its mixture with acetonitrile), detected at the glassy carbon electrode, was as broad as 5.7 V. However, the tested capacitors with activated carbon as the active electrode material show considerable lower stability, reduced to ca. 3.7 V. The specific capacity estimated from both cyclic voltammetry and charging/discharging experiments was ca. 140 F g −1, and after ca. 700 cycles, decreased to ca. 100 F g −1. The effect of the loss of the part of initial specific capacity is probably due to the loss of Faradaic pseudo-capacity. The specific energy of the activated carbon in the tested devices was at the level of 240 kJ kg −1 while the specific power density was ca. 25 kW kg −1.

Paracrine stimulation of vascular smooth muscle proliferation by diadenosine polyphosphates released from proximal tubule epithelial cells

The purinergic receptor system plays an important role in the regulation of both vascular and tubular functions within the kidney; however, the release of purinergic agonists other than ATP by renal tissue is not known. In this investigation, we determine if kidney tissue is a source of diadenosine polyphosphates, which have high affinity for the P(2X) and P(2Y) receptors. Both diadenosine pentaphosphate and hexaphosphate were identified by matrix-assisted laser desorption ionization-mass spectrometry in extracts purified from both whole porcine kidney and from cloned cells of the LLC-PK1 cell line. Both polyphosphates in nanomolar concentrations were found to significantly stimulate the proliferation of vascular smooth muscle cells derived from rat thoracic aortas. The purinergic-receptor antagonist, suramin, did not significantly affect the growth-stimulatory properties of the polyphosphates. The growth stimulation of vascular smooth muscle cells by platelet-derived growth factor was potentiated by both diadenosine polyphosphates. We conclude that diadenosine polyphosphates are endogenous purinergic agonists of the kidney that have physiologic and pathophysiologic relevance. These epithelial cell metabolic products have vasoregulatory properties while linking the energy supply and tubular function.

New six‐site acetonitrile model for simulations of liquid acetonitrile and its aqueous mixtures

A new six site flexible acetonitrile molecular model is developed. The AMBER force field was used for description of intramolecular parameters, the atomic charges were calculated from a high level ab initio theory and finally the Lennard-Jones parameters were tuned to fit the experimental density and evaporation heat. The obtained in this way model reproduces correctly densities of water-acetonitrile mixtures as well as provides qualitative description of the dielectric permittivity and self-diffusion coefficients.

Calculation of the Microscopic and Macroscopic Linear and Nonlinear Optical Properties of Liquid Acetonitrile. II. Local Fields and Linear and Nonlinear Susceptibilities in Quadrupolar Approximation

A discrete model based on the multipolar expansion including terms up to hexadecapoles was employed to describe the electrostatic interactions in liquid acetonitrile. Liquid structures obtained form molecular dynamics simulations with different classical, nonpolarizable potentials were used to analyze the electrostatic interactions. The computed average local field was employed for the determination of the environmental effects on the linear and nonlinear electrical molecular properties. Dipole-dipole interactions yield the dominant contribution to the local field, whereas higher multipolar contributions are small but not negligible. Using the effective in-phase properties, macroscopic linear and nonlinear susceptibilities of the liquid were computed. Depending on the partial charges describing the Coulomb interactions of the force field employed, either the linear properties (refractive index and dielectric constant) were reproduced in good agreement with experiment or the nonlinear properties [third-harmonic generation (THG) and electric field induced second-harmonic (EFISH) generation] and the bulk density but never both sets of properties together. It is concluded that the partial charges of the force fields investigated are not suitable for reliable dielectric properties. New methods are probably necessary for the determination of partial charges, which should take into account the collective and long-range nature of electrostatic interactions more precisely.

Affinity of xenon(II) and carbon in the (heptafluorocyclohexa-1,4-dien-1-yl)xenonium ion for fluoride ion and acetonitrile

The results of B3LYP&PCM quantum-chemical calculations confirmed the possibility for formation of fluoro(heptafluorocyclohexa-1,3-dien-1-yl)xenon and (octafluorocyclohex-3-en-1-ylidene)xenon from (heptafluorocyclohexa-1,4-dien-1-yl)xenonium in liquid acetonitrile. The Xe(II) and C2 atoms in the cation are characterized by a strong affinity for fluoride ion, but the Xe(II) atom binds acetonitrile molecule. The addition of F− to C2 in [XeC6F7]+ is more favorable (by 6 kcal/mol) than replacement of the fluorine atom on Xe(II) by MeCN molecule. The charge on the xenon atom in (octafluorocyclohex-3-en-1-ylidene)xenon is small, the Xe-C bond is weakened, and its cleavage leads to ring contraction to perfluoro(3-methylidenecyclopent-1-ene).

Calculating fifth-order Raman signals for various molecular liquids by equilibrium and nonequilibrium hybrid molecular dynamics simulation algorithms

The fifth-order two-dimensional (2D) Raman signals have been calculated from the equilibrium and nonequilibrium (finite field) molecular dynamics simulations. The equilibrium method evaluates response functions with equilibrium trajectories, while the nonequilibrium method calculates a molecular polarizability from nonequilibrium trajectories for different pulse configurations and sequences. In this paper, we introduce an efficient algorithm which hybridizes the existing two methods to avoid the time-consuming calculations of the stability matrices which are inherent in the equilibrium method. Using nonequilibrium trajectories for a single laser excitation, we are able to dramatically simplify the sampling process. With this approach, the 2D Raman signals for liquid xenon, carbon disulfide, water, acetonitrile, and formamide are calculated and discussed. Intensities of 2D Raman signals are also estimated and the peak strength of formamide is found to be only five times smaller than that of carbon disulfide.

Endogenous Lipid Hydroperoxide-mediated DNA-adduct Formation in Min Mice

Despite intensive research over the last two decades, there are still no specific markers of endogenous lipid hydroperoxide-mediated DNA damage. We recently demonstrated that heptanone-etheno-2'-deoxyguanosine adducts are formed in the DNA of rat intestinal epithelial cells that stably express cyclooxygenase-2. Heptanone-etheno adducts can only arise from the reaction of lipid hydroperoxide-derived 4-oxo-2(E)-nonenal with DNA. This raised the possibility that similar adducts would be formed in vivo in settings where cyclooxygenase-2 expression is increased. Therefore, DNA-adduct formation was studied in C57BL/6JAPC(min) mice, a colorectal cancer mouse model in which cyclooxygenase-2 is up-regulated. 15(S)-Hydroperoxy-5Z,8Z,11Z,13E-eicosatetraenoic acid is the major lipid hydroperoxide produced endogenously by cyclooxygenase-2. It undergoes homolytic decomposition to the DNA-reactive bifunctional electrophile 4-oxo-2(E)-nonenal, which forms heptanone-etheno adducts with DNA. A quantitative comparison was made of the heptanone-etheno-DNA adducts present in C57BL/6J and C57BL/6JAPC(min) mice. Using highly specific and sensitive methodology based on stable isotope dilution liquid chromatography/tandem mass spectrometry, we have detected the endogenous formation of heptanone-etheno adducts in mammalian tissue DNA for the first time. In addition, we found that there were statistically significant increased levels of the heptanone-etheno-2'-deoxyguanosine and heptanone-etheno-2'-deoxycytidine adducts in the C57BL/6JAPC(min) mice when compared with the control C57BL/6J mice.

New integrated measurement protocol using capillary electrophoresis instrumentation for the determination of viscosity, conductivity and absorbance of ionic liquid–molecular solvent mixtures

The low vapor pressure and the versatility of the physico-chemical properties of ionic liquids make them really attractive as an alternative for conventional molecular solvents. The knowledge of their physico-chemical properties (viscosity, conductivity, miscibility with organic solvents and anion–cation interactions) has appeared mandatory for better targeting their applications, although it is generally still lacking or incomplete. This work promotes capillary electrophoresis instrumentation as an integrated apparatus for measurement of viscosity, conductivity and absorbance of pure ionic liquids and ionic liquid–molecular solvent mixtures. Compared to current conventional techniques, the assets of this instrumentation for this purpose are the combined availability of a pressure delivery system, power supply, diode array absorbance detector and thermoregulation device, allowing unattended, automatic and easy operation, involving minimum sample handling. Most importantly, the required sample volume can be reduced to about 50 μL, making this protocol very cost-effective. A protocol was optimized with respect to time, sample consumption and data reliability for the determination of these physico-chemical parameters. Ionic liquids selected for method development and validation differed in the nature of their cation (butyl- and ethyl-methylimidazolium) and anion (trifluoromethanesulfonate and bis(trifluoromethanesulfonyl)imide). Various molecular solvents were mixed with these ionic liquids (acetonitrile, methanol, dimethylformamide and trifluoroethanol) and the same physico-chemical properties were determined by optimized methods. The knowledge of these data should be of great support in various application areas, including the development of new separation media for capillary electrophoresis and chromatographic techniques.

Acetonitrile revisited: a molecular dynamics study of the liquid phase

The subject of this report is the calibration of a model of the liquid state of acetonitrile (methyl cyanide). The model describes the liquid in terms of molecular mechanics with each molecule of the liquid treated as a rigid body that is composed of three interaction sites, between which Coulomb and dispersion interactions are computed. A brief overview of the literature on such models is given and a set of parameters for the model is presented. The representation of liquid acetonitrile produced by the parameters is compared to that produced by several other parameter sets available in the literature. It is concluded that, of the parameter sets for the three-site molecular mechanics model that currently are available, under the simulation conditions used, the one presented produces the most rounded representation of the properties of liquid acetonitrile.

Unusual Solvent Effect on a SN2 Reaction. A Quantum-Mechanical and Kinetic Study of the Menshutkin Reaction between 2-Amino-1-methylbenzimidazole and Iodomethane in the Gas Phase and in Acetonitrile

The quaternization reaction between 2-amino-1-methylbenzimidazole and iodomethane was investigated in the gas phase and in liquid acetonitrile. Both experimental and theoretical techniques were used in this study. In the experimental part of this work, accurate second-order rate constants were obtained for this reaction in acetonitrile from conductivity data in the 293-323 K temperature range and at ambient pressure. From two different empirical equations describing the effect of temperature on reaction rates, thermodynamic functions of activation were calculated. In the theoretical part of this work, the mechanism of this reaction was investigated in the gas phase and in acetonitrile. Two different quantum levels (B3LYP/[6-311++G(3df,3pd)/LanL2DZ]//B3LYP/[6-31G(d)/LanL2DZ] and B3LYP/[6-311++G(3df,3pd)/LanL2DZ]//B3LYP/[6-31+G(d)/LanL2DZ]) were used in the calculations, and the acetonitrile environment was modeled using the polarized continuum model (PCM). In addition, an atoms in molecules (AIM) analysis was made aiming to characterize possible hydrogen bonding. The results obtained by both techniques are in excellent agreement and lead to new insight into the mechanism of the reaction under examination. These include the identification and thermodynamic characterization of the relevant stationary species, the rationalization of the mechanistic role played by the solvent and the amine group adjacent to the nucleophile nitrogen atom, the proposal of alternative paths on the modeled potential energy surfaces, and the origin of the marked non-Arrhenius behavior of the kinetic data in solvent acetonitrile. In particular, the AIM analysis confirmed the operation of intermolecular hydrogen bonds between reactants and between products, both in the gas phase and in solution. It is also concluded that the unusual solvent effect on this Menshutkin reaction stems from the conjunction of a nucleophile possessing a relatively complex chemical structure with a dipolar aprotic solvent that is protophobic.

Quantum-Chemical Investigation of Structure and Vibration Spectrum of [C(NPCl3)3]+ Cation

Structural parameters of the cation [C(NPCl3)3]+ in vacuum and in acetonitrile are calculated by the methods RHF/6-311G(3d6), RHF/6-31(3d5) and B3LYP/6-311(3d5f7). Formation energy of the free adduct (MeCN) 2[C(NPCl3)3]+ is calculated and nonspecific character of interaction of the cation with liquid acetonitrile is established. Vibration spectrum of the cation is calculated and theoretical interpretation of IR and Raman spectra of the salt [C(NPCl3)3]+[SbCl6]− is refined.

Polarizability response in polar solvents: Molecular-dynamics simulations of acetonitrile and chloroform

The relaxation of the many-body polarizability in liquid acetonitrile and chloroform at room temperature was studied by molecular-dynamics simulations. The collective polarizability induced by intermolecular interactions was included using first- and all-orders dipole-induced-dipole models and calculated considering both molecule-centered and distributed site polarizabilities. The anisotropic response was analyzed using a separation scheme that allows a decomposition of the total response in terms of orientational and collision-induced effects. We found the method effective in approximately separating the contributions of these relaxation mechanisms, although the orientational-collision-induced interference makes a non-negligible contribution to the total response. In both liquids the main contribution to the anisotropic response is due to orientational dynamics, but intermolecular collision-induced (or translational) effects are important, especially at short times. We found that higher-order interaction-induced effects were essentially negligible for both liquids. Larger differences were found between the center-center and site-site models, with the latter showing faster polarizability relaxation and better agreement with experiment. Isotropic and anisotropic spectra were computed from the corresponding time correlation functions. The lowest-frequency contributions are largely suppressed in the isotropic spectra and their overall shape is similar to the purely collision-induced contribution to the anisotropic spectra, but with an amplitude which is smaller by a factor of approximately 5 in acetonitrile and approximately 3 in chloroform.

Electronic polarization in liquid acetonitrile: A sequential Monte Carlo/quantum mechanics investigation

The electronic polarization of liquid acetonitrile is investigated using the sequential Monte Carlo/quantum mechanics methodology. Second-order Møller–Plesset and density-functional theory calculations of the dipole moment are performed on statistically uncorrelated structures of liquid acetonitrile generated by the MC simulation. Our best result, obtained at the MP2/aug-cc-pVTZ level, gives an average dipole moment of 4.65 ± 0.19 D, in agreement with an experimental prediction of 4.5 ± 0.1 D. This result corresponds to an increase of 0.71 ± 0.19 D in going from the gas to the liquid state.

Raman spectra of CN vibrations of acetonitrile in aqueous and other solutions. Experimental results andab initio calculations

Quantum-chemical calculations showed a possibility of formation of dimers in pure acetonitrile, as well as molecular aggregates in its solutions with water and formic acid. Accordingly, a low-wavenumber asymmetry of the CN band in Raman spectra of liquid acetonitrile can be related to presence of dimers. In neutral solvents within the range of concentrations 1–0.1 mole fraction, the asymmetry of the CN band is preserved. However, in aqueous solutions and solutions with formic acid, an asymmetry of another type is observed. First of all, with dilution of acetonitrile, a high-wavenumber asymmetry is observed, and the band broadens. At concentrations that are lower than 0.5 mole fraction, the low-wavenumber asymmetry is observed again. In the present work such peculiarities of the CN band's behavior are related to the presence of aggregates, which consist of molecules of acetonitrile and the proton-donor solvent. A difference of the wavenumber of the CN band's maxima in parallel and perpendicular polarizations of the scattered light also indicates the presence of aggregates in acetonitrile–water solution. This difference changes with changing concentration of acetonitrile. The wavenumber difference is connected with the complexity of the band, since within the band there is an overlap of the CN bands of acetonitrile molecules, which either form H-bonds with molecules of water or are free from H-bonds. The overlapping bands are different with respect to wavenumber and depolarization ratio. Copyright © 2005 John Wiley & Sons, Ltd.

Microscopic and macroscopic polarization within a combined quantum mechanics and molecular mechanics model

A polarizable quantum mechanics and molecular mechanics model has been extended to account for the difference between the macroscopic electric field and the actual electric field felt by the solute molecule. This enables the calculation of effective microscopic properties which can be related to macroscopic susceptibilities directly comparable with experimental results. By separating the discrete local field into two distinct contribution we define two different microscopic properties, the so-called solute and effective properties. The solute properties account for the pure solvent effects, i.e., effects even when the macroscopic electric field is zero, and the effective properties account for both the pure solvent effects and the effect from the induced dipoles in the solvent due to the macroscopic electric field. We present results for the linear and nonlinear polarizabilities of water and acetonitrile both in the gas phase and in the liquid phase. For all the properties we find that the pure solvent effect increases the properties whereas the induced electric field decreases the properties. Furthermore, we present results for the refractive index, third-harmonic generation (THG), and electric field induced second-harmonic generation (EFISH) for liquid water and acetonitrile. We find in general good agreement between the calculated and experimental results for the refractive index and the THG susceptibility. For the EFISH susceptibility, however, the difference between experiment and theory is larger since the orientational effect arising from the static electric field is not accurately described.

Bond lengths of [formula omitted] and [formula omitted] states of [formula omitted] hexahalides

Ligand and solvent effects on the bond length shift experienced by complexes of lanthanide ions upon 4 f → 5 d excitation, addressed by means of ab initio embedded cluster calculations, are presented on the clusters ( CeF 6 ) 3 - , ( CeCl 6 ) 3 - , and ( CeBr 6 ) 3 - in solid elpasolites, in liquid acetonitrile and in vacuo. Previous predictions of bond length shortening upon 4 f → 5 d ( t 2 g ) excitation seem to be general and, in particular, chloride and bromide compounds in liquid solution are predicted to be good candidates for excited-state EXAFS measurements of the distortion signs. A quantitative analysis of contributions to the bond length shifts is presented, which shows the importance of ligand field effects and points out insufficiencies in the Judd–Morrison model proposed to account for 4 f → 5 d transitions in crystals.

Can larger dipoles solvate less? solute–solvent hydrogen bond and the differential solvation of phenol and phenoxy

Quantum mechanical calculations of the dipole moments and binding energies of phenol and phenoxy radical in liquid acetonitrile and water are made using hydrogen-bonded configurations extracted from Monte Carlo simulations. We contend that the preferential solvation of phenol (the lower dipole moment solute) over phenoxy derives from the hydrogen-bond shell. The reconciliation with the usual understanding, that larger dipole solvates better, is obtained if we consider not the dipole moment of the isolated solute but, instead, the average dipole moment in solution of the solute–solvent hydrogen-bonded solvation shell.