Equilibrium Mixture Research Articles

α-Ketophosphonates in the Synthesis of α-iminophosphonates

The potentialities of condensation of α-ketophosphonates with primary amines for direct synthesis of α-iminophosphonates have been revealed. Diesters of α-ketophosphonic acids react with the primary amines by two competitive pathways: with a formation of α-iminophosphonates or a C-P bond cleavage resulting in a hydrogen phosphonate and an acylated amine. In many cases, the latter undesirable pathway is dominant, especially for more nucleophilic alkyl amines. Using metallic salts of α-ketophosphonates avoids the C-P bond cleavage, allowing direct preparation of α-phosphorylated imines by the reaction with primary amines. This strategy provides an atom economy single-stage synthesis of iminophosphonates – precursors of bio relevant phosphorus analogs of α-amino acids. Methyl sodium iminophosphonates, bearing aryl or heteryl substituents at the imino carbon atom exist in solutions at room temperature as an equilibrium mixture of Z- and E-isomers. A configuration of the C=N bond can be controlled by the solvent: changing the aprotic dipolar solvent DMSO-d6 by water or alcohols leads to the change from a predominant Z-isomer to almost an exclusive E-form. In contrast, diesters of the respective iminophosphonates exist in non-protic solvents predominantly in Econfiguration. The solvent effect on E-Z stereochemistry is demonstrated by DFT calculations.

Fate and transport of bromide and mononuclear aromatic hydrocarbons in aqueous solutions through Berea Sandstone

A series of miscible displacement tests were performed on a 51 mm wide by 76 mm long well-laminated core of Berea Sandstone to determine the transport parameters of the anion bromide and a homologous series of seventeen mononuclear aromatic hydrocarbons (MAHs). In each test, a continuous input pulse of a single tracer was passed through the cylindrical core housed in a hydrostatic core holder at a confining pressure of 200 bar. The effluent concentration, as measured by in-line UV absorbance, versus time resulted in smooth high-resolution sinusoidal breakthrough curves (BTCs). In comparison to the near Gaussian BTCs of bromide, the transport of the MAHs was differentially retarded with minimal levels of delayed transport along the more rapid flow lines, but with progressively more along the slower flow paths. These results show that despite a lack of significant hydraulic heterogeneity, there is a high degree of heterogeneity among the sorption sites. The BTCs were aptly modeled with a one-dimensional flow model consisting of a mixture of instantaneous equilibrium and rate-limited reversible sorption sites. The relative fraction of instantaneous sites increased proportionately with the rate the subject MAH passed through the core. Potential quantitative structure-retention relationships (QSRR) between common chemical parameters of the MAHs and their overall retardation factors, sorption coefficients and the fraction of instantaneous equilibrium were evaluated. Among the compounds examined, relatively strong correlations were found with molecular weight, aqueous solubility, and octanol-water partitioning coefficient with which relative MAH transport retardation, the linear phase distribution coefficient, and the dimensionless partitioning coefficient between sorption sites.

Physico-chemical study of systems involving ethanol, promising for use as a biofuel

The use of renewable biofuels is a necessity today and entails the improvement and optimization of related processes. The work presents new thermodynamic parameters necessary to optimize the operation of internal combustion engines, improve characteristics and predict the properties of biofuels. Based on the obtained liquid-liquid equilibrium (LLE) data, binodal curves and surfaces are constructed for a system containing ethanol, propionic acid, ethyl propionate and water at 293.15 K and 303.15 K and atmospheric pressure, as well as model calculations of vapor-liquid equilibrium (VLE) data were carried out according to literature results on compositions of chemically equilibrium (CE) mixtures. The results of modeling on liquid-phase and vapor-liquid equilibrium using NRTL and UNIFAC models respectively are presented. A comparative analysis of the results under the temperature conditions of this study is given.

Evolvulin III, a new resin glycoside isolated from Evolvulus alsinoides

Abstract A new resin glycoside named evolvulin III (1) was isolated from the whole plants of Evolvulus alsinoides. Compound 1 was identified as a pentasaccharide macrolactone with a distinctive 3S,11R,14R-trihydroxyhexadecanoic acid acting as the aglycone. Interestingly, evolvulin III (1) is interconvertible with a known resin glycoside, namely, evolvulin II (2), by intramolecular transesterification. The structure of compound 1 was determined by spectroscopic data and the chemical analysis of the equilibrium mixture of 1 and 2.

Jeans instability for an inert binary mixture: a kinetic theory approach in the Euler regime

The Jeans stability criterion for gravitational collapse is examined for the case of an inert binary mixture in local equilibrium, neglecting dissipative effects. The corresponding transport equations are established using kinetic theory within the Euler regime approximation. It is shown that the corresponding dispersion relation is modified; yielding corrections to the Jeans wave number that can be generalized for several interesting cases involving positive entropy production such as matter- antimatter systems and ordinary matter-dark matter dynamics.

Single- and mixed-gas sorption in large-scale molecular models of glassy bulk polymers. Competitive sorption of a binary CH4/N2 and a ternary CH4/N2/CO2 mixture in a polyimide membrane

Three molecular simulation techniques to predict the gas sorption isotherms in a glassy polymer membrane in contact with a single- or a mixed-gas reservoir have been tested on a large-scale ~50000 atom 6FDA-6FpDA polyimide bulk model over a wide range of pressures. Both single- and mixed-gas uptake curves were obtained for CH4, N2 and CO2 over the 0–60 bar range using either a Grand Canonical Monte Carlo (GCMC), an iterative test particle insertion - molecular dynamics (TPI-MD) or an iterative GCMC-MD method. Virtual TPI and actual GCMC insertions of gas molecules into the polymer matrices were performed using the excluded-volume map sampling approach (EVMS), which improved the sampling efficiencies by a factor of ~10–20 over random insertions.The simulation techniques were first used to obtain the single-gas sorption isotherms and the associated ideal gas sorption selectivities. The TPI-MD and GCMC-MD approaches gave consistent results in agreement with experiment. Further tests were made on a binary 2:1 CH4/N2 and a ternary 16:8:1 CH4/N2/CO2 gas mixture in equilibrium with the 6FDA-6FpDA model matrix. For such mixed-gas feeds, the uptake of each gas in the polymer depends on its gas phase concentration and on its solubility in both the gas mixture and the polymer phases. Solubilities of penetrants in the polymer phase correlated well to the total penetrant concentration. In the binary mixture, the sorption of N2 was strongly hindered by that of CH4. In the ternary mixture, the introduction of the highly-soluble CO2 at a relatively low partial pressure significantly reduced the sorption of both CH4 and N2, although its concentration was insufficient to plasticize the polymer. As such, the mixed-gas CH4/N2, CO2/CH4 and CO2/N2 sorption selectivities were found to differ from their ideal values. Interference effects were characterized by a novel technique which estimates the proportions of molecules of each type of penetrant excluded by competitive sorption for the mixtures under study.The main asset of such iterative molecular simulations is their ability to take implicitly into account the interdependence of the different gas concentrations and solubilities as well as the associated changes in the matrices over a large range of pressures and temperatures. In addition, the iterative GCMC-MD method should be applicable to even more complex mixtures, which is obviously pertinent with respect to industrial gas separation applications.

Conformational Solvatomorphism in a [2]Catenane

The combination of a flexible pyridine-appended ligand (L1) with 4,4′-bipyridine (L2) and cis-protected Pd(II) units, Pd(L′)(NO3)2, in water yielded a concentration-dependent equilibrium mixture of the corresponding [2]catenanes [Pd2(L′)2(L1)(L2)]2(NO3)8 and their constituent macrocycles [Pd2(L′)2(L1)(L2)](NO3)4. The cis-protecting units (L′) used were ethylenediamine (en), tetramethylethylenediamine (tmeda), 2,2′-bipyridine (bpy), and 1,10-phenanthroline (phen). Crystallization of the [2]catenanes via slow evaporation of their CH3CN/H2O (1:1) solutions yielded a single crystalline form in the case of [Pd2(2,2′-bpy)2(L1)(L2)]2(NO3)8 and two concomitant crystalline forms (solvates) in the case of [Pd2(phen)2(L1)(L2)]2(NO3)8. The formation of the [2]catenane is facilitated by noncovalent interactions such as N–H···O, C–H···O, and C–H···π contacts and π···π stacking. The solvates of [Pd2(phen)2(L1)(L2)]2(NO3)8 revealed differences in the orientation of the amide carbonyl group and conformational differences in the ligands and phen units in the macrocycles and may thus be termed conformational solvatomorphs. The molecular packing in all the structures was found to be driven by intermolecular π···π stacking interactions between the aromatic rings in their cis-protected Pd(II) units. However, because of the awkward shape of the molecules, the closest 2,2′-bpy and phen units in all the structures overlap differently rather than the commonly observed “head-to-tail” or “head-to-head” modes.

Stereochemistry and tautomerism of silicon-containing 1,2,3-triazole: ab initio and NMR study

In this paper, an approach is proposed for determining the ratio of prototropic annular tautomers of organosilicon 1,2,3-triazoles, which are hardly experimentally determined in solution by NMR technique. The comparison of experimental and calculated (at the CCSD level) NMR chemical shifts allows the predominant tautomer in the equilibrium mixture to be determined.

Synthesis and conformational study of some N-nitroso-t(3)-benzyl-r(2),c(6)-bis(aryl)piperidin-4-one oximes using NMR spectra

A series of heavily substituted N-nitroso-t(3)-benzyl-bis(aryl)piperidin-4-one oximes 9–13 have been synthesized by mixing N-nitroso-t(3)-benzyl-bis(aryl)piperidin-4-ones 5–8 with hydroxylamine hydrochloride and sodium acetate trihydrate in ethanol medium. The synthesized compounds 9–13 were characterized by elemental analysis, IR and NMR spectral studies (1H, 13C, HOMOCOSY and HSQC). At room temperature the N-nitroso-t(3)-benzyl-r(2),c(6)-bis(aryl)piperidin-4-one oximes 9–13 exist in two isomeric forms and the isomers are labeled as syn (nitroso oxygen is same side to N–OH group) and anti (nitroso oxygen is opposite side to N–OH group) isomers. Analysis of the spectral data shows that in 10–13 the NOH group is anti to the benzylic group at C(3). The favoured conformations of both the isomeric forms of N-nitroso oximes were determined by comparison of spectral data with those of the corresponding parent N-nitroso amines 5–8 and with the aid of substituent parameters. The observed coupling constants in 9 predict alternate chair form CA for the syn isomer and a highly distorted boat form B1 (aryl group at C(2) occupies flagpole position) for the anti isomer. Conformational analysis performed through DFT using Gaussian 09 program calculations also supports the conformations for the syn isomer of 9 whereas for the anti isomer of 9 there is a discrepancy between the results derived from theoretical and coupling constant studies. For N-nitroso-t(3)-benzyl oxime derivatives 10–13 the observed coupling constants predict an equilibrium mixture of boat form B1 and alternate chair form CA for the anti isomers and an equilibrium mixture of boat forms B1 and B5 (both the aryl groups occupy axial like orientations) for the syn isomers. The both syn and anti isomers of 9–13 the preferred conformation of benzylic group at C(3) is predicted to be A in which the phenyl group is gauche to C(4) and anti to C(2).

Total Synthesis of the Antitumor Depsipeptide FE399 and Its S‐Benzyl Derivative: A Macrolactamization Approach

An efficient and practical method for the synthesis of (9R,14R,17R)‐FE399, a novel antitumor bicyclic depsipeptide, was developed. A 2‐methyl‐6‐nitrobenzoic anhydride (MNBA)‐mediated dehydration condensation reaction was effectively employed for the formation of the 16‐membered macrocyclic depsipeptide moiety of FE399. FE399 was found to exist as an inseparable equilibrium mixture of conformational isomers; the mixture was quantitatively transformed into the corresponding S‐benzyl product and isolated as a single isomer. Thus, we could confirm that the molecular structure of FE399 obtained by this method is identical to that of the natural product.

Group 6 Oxyfluoro-Anion Salts of [XeF5 ]+ and [Xe2 F11 ]+ : Syntheses and Structures of [XeF5 ][M2 O2 F9 ] (M=Mo, W), [Xe2 F11 ][M'OF5 ] (M'=Cr, Mo, W), [XeF5 ][HF2 ]⋅CrOF4 , and [XeF5 ][WOF5 ]⋅XeOF4.

The reactions of the fluoride-ion donor, XeF6 , with the fluoride-ion acceptors, M'OF4 (M'=Cr, Mo, W), yield [XeF5 ]+ and [Xe2 F11 ]+ salts of [M'OF5 ]- and [M2 O2 F9 ]- (M=Mo, W). Xenon hexafluoride and MOF4 react in anhydrous hydrogen fluoride (aHF) to give equilibrium mixtures of [Xe2 F11 ]+ , [XeF5 ]+ , [(HF)n F]- , [MOF5 ]- , and [M2 O2 F9 ]- from which the title salts were crystallized. The [XeF5 ][CrOF5 ] and [Xe2 F11 ][CrOF5 ] salts could not be formed from mixtures of CrOF4 and XeF6 in aHF at low temperature (LT) owing to the low fluoride-ion affinity of CrOF4 , but yielded [XeF5 ][HF2 ]⋅CrOF4 instead. In contrast, MoOF4 and WOF4 are sufficiently Lewis acidic to abstract F- ion from [(HF)n F]- in aHF to give the [MOF5 ]- and [M2 O2 F9 ]- salts of [XeF5 ]+ and [Xe2 F11 ]+ . To circumvent [(HF)n F]- formation, [Xe2 F11 ][CrOF5 ] was synthesized at LT in CF2 ClCF2 Cl solvent. The salts were characterized by LT Raman spectroscopy and LT single-crystal X-ray diffraction, which provided the first X-ray crystal structure of the [CrOF5 ]- anion and high-precision geometric parameters for [MOF5 ]- and [M2 O2 F9 ]- . Hydrolysis of [Xe2 F11 ][WOF5 ] by water contaminant in HF solvent yielded [XeF5 ][WOF5 ]⋅XeOF4 . Quantum-chemical calculations were carried out for M'OF4 , [M'OF5 ]- , [M'2 O2 F9 ]- , {[Xe2 F11 ][CrOF5 ]}2 , [Xe2 F11 ][MOF5 ], and {[XeF5 ][M2 O2 F9 ]}2 to obtain their gas-phase geometries and vibrational frequencies to aid in their vibrational mode assignments and to assess chemical bonding.

Equilibrium Formation of Stable All‐Silicon Versions of 1,3‐Cyclobutanediyl

Main group analogues of cyclobutane‐1,3‐diyls are fascinating due to their unique reactivity and electronic properties. So far only heteronuclear examples have been isolated. Here we report the isolation and characterization of all‐silicon 1,3‐cyclobutanediyls as stable closed‐shell singlet species from the reversible reactions of cyclotrisilene c‐Si3Tip4 (Tip=2,4,6‐triisopropylphenyl) with the N‐heterocyclic silylenes c‐[(CR2CH2)(NtBu)2]Si: (R=H or methyl) with saturated backbones. At elevated temperatures, tetrasilacyclobutenes are obtained from these equilibrium mixtures. The corresponding reaction with the unsaturated N‐heterocyclic silylene c‐(CH)2(NtBu)2Si: proceeds directly to the corresponding tetrasilacyclobutene without detection of the assumed 1,3‐cyclobutanediyl intermediate.

Exploring Natural Product Artifacts: The Polyketide Enterocin Warms to a Ballet of Isomers.

The polyketide enterocin is responsive to environmental stimuli, where mild heating promotes an equilibrium mixture of the isomeric acetals enterocins B and C, which subsequently undergo pseudo-chair-boat inversion to enterocin D. When exposed to aqueous base, enterocin is converted to the isomeric Michael acceptor enterocin F. These studies demonstrate that knowledge of environmental stimuli and associated artifacts is critical to understanding the chemical and ecological properties of enterocins and other classes of natural products.

Fluorocyclization of N‐Propargyl Carboxamides by λ3‐Iodane Catalysts with Coordinating Substituents

AbstractAiming at the enhanced catalytic activity of fluoro‐λ3‐iodane generated from iodoarene precatalyst with Selectfluor and HF⋅pyridine, this study focused on the λ3‐iodanes bearing coordinating substituents. Compared to 4‐iodoanisole as a precatalyst of our previous method, N‐methyl‐2‐iodobenzamide or 2‐iodobenzamide worked well in the fluorocyclization of N‐propargyl carboxamides to oxazoles. Control experiments suggest the equilibrium mixture of iodane‐amine complexes and cyclic iodane fluorides would be involved in the present catalysis.magnified image

Thermally Activated Delayed Photoluminescence: Deterministic Control of Excited-State Decay.

Thermally activated photophysical processes are ubiquitous in numerous organic and metal-organic molecules, leading to chromophores with excited-state properties that can be considered an equilibrium mixture of the available low-lying states. Relative populations of the equilibrated states are governed by temperature. Such molecules have been devised as high quantum yield emitters in modern organic light-emitting diode technology and for deterministic excited-state lifetime control to enhance chemical reactivity in solar energy conversion and photocatalytic schemes. The recent discovery of thermally activated photophysics at CdSe nanocrystal-molecule interfaces enables a new paradigm wherein molecule-quantum dot constructs are used to systematically generate material with predetermined photophysical response and excited-state properties. Semiconductor nanomaterials feature size-tunable energy level engineering, which considerably expands the purview of thermally activated photophysics beyond what is possible using only molecules. This Perspective is intended to provide a nonexhaustive overview of the advances that led to the integration of semiconductor quantum dots in thermally activated delayed photoluminescence (TADPL) schemes and to identify important challenges moving into the future. The initial establishment of excited-state lifetime extension utilizing triplet-triplet excited-state equilibria is detailed. Next, advances involving the rational design of molecules composed of both metal-containing and organic-based chromophores that produce the desired TADPL are described. Finally, the recent introduction of semiconductor nanomaterials into hybrid TADPL constructs is discussed, paving the way toward the realization of fine-tuned deterministic control of excited-state decay. It is envisioned that libraries of synthetically facile composites will be broadly deployed as photosensitizers and light emitters for numerous synthetic and optoelectronic applications in the near future.

Evaluation of association schemes in the CPA and PC-SAFT equations of state in modeling VLE of organic acids + water systems

The performance of various association schemes was evaluated in modeling isothermal and isobaric vapor–liquid equilibria of mixtures of organic acids and water with the CPA and the PC-SAFT equations of state. The organic acids considered were formic, acetic, propanoic and butanoic acid. Combinations of the 1A and 2B association schemes for the acids and the 2B, 3B, and 4C for water were tested. Polar contributions were also studied in PC-SAFT. The case in which no association contribution is included in the thermodynamic model was also assessed. It is concluded that the chosen association scheme greatly affects the performance of the equation of state. It was not possible to identify a single association scheme combination that would work well for all the systems and conditions studied. On average, PC-SAFT with the organic acid modeled as 1A and water as 4C showed the greatest accuracy. Interestingly, for some of the mixtures the nonassociation case gave considerably better representations than when the association term was used. When a binary interaction parameter is used the performance of the equations studied is comparable to the classic PR.

Wide-ranging prediction of phase behavior in complex systems by CP-PC-SAFT with universal kij values. I. Mixtures of non-associating compounds with [C2mim][EtSO4], [C4mim][MeSO4], and [C2mim][MeSO3] ionic liquids

This study shows that the inter-relations between critical constants can explain various phenomena occurring in the ionic liquids (IL) systems, such as the higher solubility of aromatic compounds and the differences between solubilities in the specific ILs. Indeed, as the critical constants get more remote, the systems become more asymmetric, increasing thus the immiscibility gaps. The Critical Point-based Perturbed-Chain Statistical Association Fluid Theory (CP-PC-SAFT) EoS rigorously obeys the Tc and Pc of ordinary substances. Moreover, its high precision in modelling the liquid phase properties yields realistic estimations of the imaginary critical constants of ILs. Such features attach an enhanced predictive capacity to this model, even while neglecting the complex chemical background of ILs. Although the substantial disagreements between different sources allow examining the general truthfulness of predictions rather their quantitative precision, it is demonstrated that using the universal value of k12 = 0.027 obtained for just one of the VLE datasets, CP-PC-SAFT realistically predicts various phase equilibria in mixtures of non-reacting gases, n-alkanes, aromatic hydrocarbons, ethers, ketones and haloalkanes with the considered ILs. The accuracies of these predictions are comparable with the widely implemented COSMO-RS approach. However, unlike it, CP-PC-SAFT can be applied for estimating high-pressure phase equilibria and it provides accurate predictions of volumetric data of mixtures in the particularly wide range of conditions.

Effect of UVC Irradiation on the Oxidation of Histidine in Monoclonal Antibodies

We oxidized histidine residues in monoclonal antibody drugs of immunoglobulin gamma 1 (IgG1) using ultraviolet C irradiation (UVC: 200–280 nm), which is known to be potent for sterilization or disinfection. Among the reaction products, we identified asparagine and aspartic acid by mass spectrometry. In the photo-induced oxidation of histidine in angiotensin II, 18O atoms from H218O in the solvent were incorporated only into aspartic acid but not into asparagine. This suggests that UVC irradiation generates singlet oxygen and induces [2 + 2] cycloaddition to form a dioxetane involving the imidazole Cγ − Cδ2 bond of histidine, followed by ring-opening in the manner of further photo-induced retro [2 + 2] cycloaddition. This yields an equilibrium mixture of two keto-imines, which can be the precursors to aspartic acid and asparagine. The photo-oxidation appears to occur preferentially for histidine residues with lower pKa values in IgG1. We thus conclude that the damage due to UVC photo-oxidation of histidine residues can be avoided in acidic conditions where the imidazole ring is protonated.

Phase equilibria of binary and ternary polymer solutions using modified UNIQUAC-based local composition model

In the present research, a modification on UNIQUAC activity coefficient model was done based on the local composition concept. The model was applied for binary and ternary systems containing different polymers and protic solvents. The newly modified model was compared with several local composition models such as Wilson, NRTL, UNIQUAC, polymer-NRTL, UNIQUAC-LBY and UNIQUAC-DMD in vapor–liquid. Also, comparison of the model with NRTL, UNIQUAC and UNIQUAC-LBY was done for liquid–liquid equilibrium data. In the presented model, a Freed-FV term was added to activity coefficient expression to consider the free volume effects in the mixture. Also, new surface and volumetric structural parameters were applied for studied alcoholic and aqueous solutions. AARD % of the new model (known as M-UNIQUAC-LBY model) was 1.98% for 28 vapor–liquid equilibrium data set (314 data points) of binary polymer–solvent systems. Moreover, RMSD % of 14 studied liquid–liquid systems in equilibria (155 tie-lines) was equal to 10.6431. The results of presented model were superior to previously presented ones in both VLE and LLE. Therefore, it can be successfully utilized to predict phase equilibria in mixtures, which contain pertinent components for industrial applications.

Consistent transport properties in multicomponent two-temperature magnetized plasmas

Aims.We present a fluid model that has been developed for multicomponent two-temperature magnetized plasmas in chemical non-equilibrium for the partially to fully ionized collisional regimes. We focus on transport phenomena with the aim of representing the atmosphere of the Sun.Methods.This study is based on an asymptotic fluid model for multicomponent plasmas derived from kinetic theory, yielding a rigorous description of the dissipative effects. The governing equations and consistent transport properties are obtained using a multiscale Chapman-Enskog perturbative solution to the Boltzmann equation based on a dimensional analysis. The mass disparity between free electrons and heavy particles is accounted for, as well as the influence of the electromagnetic field. We couple this model to the Maxwell equations for the electromagnetic field and derive the generalized Ohm’s law for multicomponent plasmas. The model inherits a well-identified mathematical structure leading to an extended range of validity for the Sun’s atmospheric conditions. We compute consistent transport properties by means of a spectral Galerkin method using the Laguerre-Sonine polynomial approximation. Two non-vanishing polynomial terms are used when deriving the transport systems for electrons, whereas only one term is retained for heavy particles.Results.In a simplified framework where the plasma is fully ionized, we compare the transport properties for the lower solar atmosphere to conventional expressions for magnetized plasmas attributed to Braginskii, showing a good agreement between both results. For more general partially ionized conditions, representative of the lower solar atmosphere, we compute the muticomponent transport properties corresponding to the species diffusion velocities, heavy-particle and electron heat fluxes, and viscous stress tensor of the model for a helium-hydrogen mixture in local thermodynamic equilibrium. The model is assessed for the 3D radiative magnetohydrodynamic simulation of a pore at the Sun photosphere. The resistive term is found to dominate mainly the dynamics of the electric field at the pore location. The battery term for heavy particles appears to be higher at the pore location and at some intergranulation boundaries.