Showing papers on "Solvent effects published in 2010"
TL;DR: In this article, the adsorption isotherms at different temperatures were determined and modeled with Langmuir, Freundlich and Redlich-Peterson equations, and the effects of solution pH on the adorption were also studied.
787 citations
27 Oct 2010
521 citations
TL;DR: These studies indicate that the solution properties of ionic liquids are similar to those of polar organic solvents, which is of interest for applications in separation science.
443 citations
TL;DR: A detailed study of the thermodynamics of the halogen-bonding interaction in organic solution is presented in this paper, where 19F NMR titrations are used to determine association constants for the interactions of a variety of Lewis bases with fluorinated iodoalkanes and iodoarenes.
Abstract: A detailed study of the thermodynamics of the halogen-bonding interaction in organic solution is presented. 19F NMR titrations are used to determine association constants for the interactions of a variety of Lewis bases with fluorinated iodoalkanes and iodoarenes. Linear free energy relationships for the halogen bond donor ability of substituted iodoperfluoroarenes XC6F4I are described, demonstrating that both substituent constants (σ) and calculated molecular electrostatic potential surfaces are useful for constructing such relationships. An electrostatic model is, however, limited in its ability to provide correlation with a more comprehensive data set in which both halogen bond donor and acceptor abilities are varied: the ability of computationally derived binding energies to accurately model such data is elucidated. Solvent effects also reveal limitations of a purely electrostatic depiction of halogen bonding and point to important differences between halogen bonding and hydrogen bonding.
318 citations
TL;DR: In this article, 28 solvents diversely positioned on the Teas graph were studied for their solubility and electrospinnability for making polymethylsilsesquioxane (PMSQ) solutions.
299 citations
TL;DR: In this article, the effects of the polymerization conditions, such as the solvents and supporting electrolytes, on the morphological structure and electrochromic properties of PEDOT films were systematically studied.
Abstract: Although significant efforts were devoted to improving the properties of conductive polymers, the effects of solvent and supporting electrolytes on the morphology and electrochromic features of electropolymerized materials have been scantly investigated. In this work, the effects of the polymerization conditions, such as the solvents and supporting electrolytes, on the morphological structure and electrochromic properties of PEDOT films were systematically studied. Surprisingly, we find a very significant solvent effect and a small supporting electrolyte effect. We show that morphological properties also strongly correlate with electrochromic properties. Films prepared in propylene carbonate have a smoother structure than those prepared in acetonitrile and this leads to superior electrochromic properties, such as an exceptionally high contrast ratio (71%), transparency in the doped state (80%), and coloration efficiency (193 cm2/C) for the films prepared in propylene carbonate. Significant differences bet...
273 citations
TL;DR: The current understanding of the antioxidant properties of phenols (in homogeneous solutions) is reviewed, with particular emphasis on the role of the solvent.
Abstract: The current understanding of the antioxidant properties of phenols (in homogeneous solutions) is reviewed, with particular emphasis on the role of the solvent. Phenols (ArOH) are known to reduce the rates of oxidation of organic matter by transferring a H atom (from their OH groups) to the chain-carrying ROO* radicals, a mechanism that most likely involves a concerted transfer of the hydrogen as a proton and of one electron between the two oxygen atoms, O-H---O* (proton-coupled electron transfer mechanism). The antioxidant capabilities of phenols are strongly reduced by hydrogen-bond accepting solvents since the hydrogen-bonded molecules ArOH---S are virtually unreactive toward ROO* radicals. The magnitude of these kinetic solvent effects is determined by the solute acidity alpha(2)(H) of ArOH (range 0 to 1) and solvent basicity beta(2)(H) (range 0 to 1). Hydroxyl solvents (alcohols) have a double effect on ArOH. On the one hand, they act as hydrogen-bond accepting solvents and reduce the conventional rates of the ArOH + ROO* reaction. On the other hand, these solvents favour the ionization of ArOH into their phenoxide anions ArO(-), which may react with ROO* very rapidly by electron transfer (sequential proton loss electron transfer mechanism). The overall effect is therefore determined by the ionization degree of ArOH. Other aspects of the kinetics and thermodynamics of ArOH + ROO* are also discussed.
259 citations
TL;DR: In this paper, the effect of CN groups and solvent on the enthalpies of homolytic and heterolytic N-H bond cleavage was studied using DFT/UB3LYP/6-31++G∗∗ method.
Abstract: In this article, we have studied p-phenylenediamine (PPD) and tetracyano-p-phenylenediamine (TCPPD) molecules in order to study the effect of CN groups and the solvent effect on the enthalpies of homolytic and heterolytic N–H bond cleavage. Geometries of the molecules and reaction enthalpies related to hydrogen atom transfer, single electron transfer–proton transfer (SET–PT) mechanism and sequential proton loss electron transfer (SPLET) mechanisms were studied using DFT/UB3LYP/6-31++G∗∗ method. Ab initio MP2/6-31++G∗∗ method was used as the reference for the geometry calculation of the two molecules in vacuum. Solvent contribution to the enthalpies was computed employing integral equation formalism IEF-PCM method. Obtained results show that solvent is able to cause significant change in the reaction enthalpies of the stepwise SET–PT and SPLET mechanisms of hydrogen splitting-off from NH2 group. This may result in the change in thermodynamically preferred mechanism. Solvents also attenuate the CN-substituent effect in the case of SET–PT and SPLET mechanisms.
257 citations
TL;DR: The complexation behavior of a series of paraquats with pillar[5]arene (P5A) host has been comprehensively investigated, showing the nature of the substituents attached to 1,4-bis(pyridinium)butane dramatically affects the molecular recognition behavior.
Abstract: The complexation behavior of a series of paraquats (G1·2PF6–G5·2PF6) and bis(pyridinium) derivatives (G6·2PF6–G14·2PF6) with pillar[5]arene (P5A) host has been comprehensively investigated by 1H NMR, ESI mass and UV-vis absorption spectroscopy. It is found that P5A forms 2 : 1 external complexes with N,N′-dialkyl-4,4′-bipyridiniums (G1–G4·2PF6); while it forms 1 : 1 pseudorotaxane-type inclusion complexes with methylene [–(CH2)n–] linked bis(pyridinium) derivatives possessing appropriate chain lengths (n = 3–6, G7–G10·2PF6). Host–guest association constants in dimethyl sulfoxide (DMSO) were determined, indicating G7–G10·2PF6 axles form stable [2]pseudorotaxanes with P5A wheel in this very high polarity solvent and 1,4-bis(pyridinium)butane (G8·2PF6) was the most suitable axle unit. Meanwhile, the nature of the substituents attached to 1,4-bis(pyridinium)butane dramatically affects the molecular recognition behavior. The introduction of pyridyls (G13·2PF6) increases not only the Ka value (4.5 × 102→7.4 × 102 M−1), but also the charge transfer (CT) absorption (colorless→yellow). Furthermore, the solvent effects have also been investigated, showing they significantly influence the association strength during the course of host–guest complexation. Particularly, the Ka value of P5A–G13·2PF6 in 1 : 1 (v:v) acetone-d6/DMSO-d6 is enhanced by a factor of 7.3 compared with pure DMSO-d6 (7.4 × 102→5.4 × 103 M−1).
249 citations
TL;DR: In this article, density functional theory is applied to the reaction intermediates and barriers involved in the oxygen reduction reaction (ORR) on a platinum fuel cell catalyst and the results show that the solvent effects change significantly the reaction barriers compared with those in the gas-phase environment (without solvation).
Abstract: We report here density functional theory (DFT) studies (PBE) of the reaction intermediates and barriers involved in the oxygen reduction reaction (ORR) on a platinum fuel cell catalyst. Solvent effects were taken into account by applying continuum Poisson−Boltzmann theory to the bound adsorbates and to the transition states of the various reactions on the platinum (111) surface. Our calculations show that the solvent effects change significantly the reaction barriers compared with those in the gas-phase environment (without solvation). The O2 dissociation barrier decreases from 0.58 to 0.27 eV, whereas the H + O → OH formation barrier increases from 0.73 to 1.09 eV. In the water-solvated phase, OH formation becomes the rate-determining step for both ORR mechanisms, O2 dissociation and OOH association, proposed earlier for the gas-phase environment. Both mechanisms become significantly less favorable for the platinum catalytic surface in water solvent, suggesting that alternative mechanisms must be conside...
200 citations
TL;DR: The choice of reaction solvent has a major influence on the surface area and pore volume in conjugated microporous polymer (CMP) networks synthesized by Sonogashira−Hagihara palladium-catalyzed cross-coupling chemistry of aromatic dibromo monomers with 1,3,5-triethynylbenzene as discussed by the authors.
Abstract: The choice of reaction solvent has a major influence on the surface area and pore volume in conjugated microporous polymer (CMP) networks synthesized by Sonogashira−Hagihara palladium-catalyzed cross-coupling chemistry of aromatic dibromo monomers with 1,3,5-triethynylbenzene. Four solvents were evaluated for these reactions: N,N-dimethylformamide (DMF), 1,4-dioxane, tetrahydrofuran (THF), and toluene. Networks synthesized in DMF tend to exhibit the highest surface areas (up to 1260 m2/g), whereas those synthesized in toluene have on average significantly lower surface areas and pore volumes. By judicious choice of reaction solvent, microporous materials can be prepared which combine high surface area with a variety of functional groups of interest in applications such as gas storage, molecular separations, and catalysis.
TL;DR: Tanaka et al. as discussed by the authors reported a very efficient method for the alkoxylation of alkynes using cationic Au complexes of the type [(PR3)Au] +.
Abstract: Hydration and alkoxylation of alkynes are important reactions in organic synthesis, for which mercury(II) salts initially served as catalysts. Due to substantial practical aspects, such as the requirement of strongly acidic reaction media, the quick denaturation of the Hg catalyst and environmental concerns, alternative catalysts were sought for quite some time. In particular, for the addition of water and methanol to unactivated alkynes, Au3] and Pt-containing catalysts 5] were investigated as an alternative but turned out to be less efficient. In 1998, Teles et al. reported a very efficient method for the alkoxylation of alkynes using cationic Au complexes of the type [(PR3)Au] + . In dry methanol, acetals D and E were obtained, whereas in the presence of water, ketones B and C were the only products (Scheme 1). In the case of terminal alkynes, the Markovnikov products were formed with very high selectivity whereas internal alkynes led to product mixtures. Subsequent work by Tanaka et al. and Nolan et al. even further improved that reaction.
TL;DR: In this paper, the singleelectron transfer living radical polymerization (SET-LRP) of water-soluble monomers, N,N-dimethylacrylamide (DMA), initiated with 2-methylchloropropionate (MCP) in dipolar aprotic and protie solvents is reported.
Abstract: The single-electron transfer living radical polymerization (SET-LRP) of water-soluble monomers, N,N-dimethylacrylamide (DMA) and N-isopropylacrylamide (NIPAM), initiated with 2-methylchloropropionate (MCP) in dipolar aprotic and protie solvents is reported. The radical polymerization of acrylamides is characterized by higher rate constants of propagation and bimolecular termination than acrylates. Therefore, the addition of CuCl Is required to mediate deactivation in the early stages of the reaction. Through the use of Cu(0)-wire/Me-TREN catalysis, conditions were optimized to minimize the amount of externally added CuCl required to maintain a linear evolution of molecular weight and narrow molecular weight distribution. By using less CuCl additive, the amount of soluble copper species that must ultimately be removed from the reaction mixture is reduced.
TL;DR: In this article, the solvent effect was taken into account via the polarizable continuum model to identify the radical anion CO2− adsorbed on the surface on defect-free surfaces, it was found to bind as a bridging bidentate configuration with both oxygens coordinating to the 5-fold Ti ions.
Abstract: Binding configurations of CO2 and CO2− on perfect and oxygen-deficient anatase (101) surfaces were explored using first-principles calculations on both cluster and periodic models The solvent effect was taken into account via the polarizable continuum model Analysis of molecular orbitals, charge, and spin density distributions was used to help identify the radical anion CO2− adsorbed on the surface On defect-free surfaces, it is found to bind as a bridging bidentate configuration with both oxygens coordinating to the 5-fold Ti ions Analysis of vibrational frequencies provides a specific signature of the CO2 anion to distinguish it from other species in experiments The reduction potential of adsorbed CO2 on a (101) surface is lower by 024 V than the reduction potential of a CO2 molecule, both in aqueous solution, due to the formation of hybridized orbitals, which facilitates charge transfer to CO2 The reduced (101) surface of TiO2 is much more favorable for CO2 binding with accompanying charge trans
TL;DR: The hydrogenolysis of glycerol was performed in an autoclave at temperatures between 190 and 225 °C and at a H2 pressure of 5 MPa over a CuO/ZnO catalyst prepared by an oxalate gel (OG) method.
TL;DR: It turned out that the appropriate choice of the functional is of prime importance to obtain, not only quantitatively accurate values, but also qualitatively correct evolution of the spectral features with respect to the dihedral angles of the amino group.
Abstract: Using a time-dependent density functional theory approach and taking into account bulk solvent effects, we investigate the absorption and fluorescence spectra of Nile Red. In particular, we have assessed both the planar and twisted intramolecular charge transfer mechanism by using a panel of exchange correlation functionals including both global and range-separated hybrids, refined solvent models and the simulation of vibronic couplings. It turned out that the appropriate choice of the functional is of prime importance to obtain, not only quantitatively accurate values, but also qualitatively correct evolution of the spectral features with respect to the dihedral angles of the amino group. At the light of this study, the interpretation of the experimental data is critically re-examined and compared to typical dual-fluorescent molecules.
TL;DR: The self-assembly of organic molecules has attracted sub-stantial interest as a bottom-up approach to createnano-sized objects and their properties depend strongly on the design, arrangement, and number of molecules in the aggregate.
Abstract: The self-assembly of organic molecules has attracted sub-stantialinterest asa bottom-upapproachto createnano-sizedobjects. Their properties depend strongly on the design,arrangement, and number of molecules in the aggregate. Forsupramolecular polymers, the monomers are entirely heldtogether by non-covalent interactions; these interactions aretypically weak, reversible, and highly sensitive to variablessuch as temperature, concentration, and solvent polarity.
TL;DR: The separation performance of solvent resistant nanofiltration (SRNF) membranes was studied in a systematic way to elucidate the complex mechanisms involved in rejection of solutes.
Abstract: The separation performance of solvent resistant nanofiltration (SRNF) membranes was studied in a systematic way to elucidate the complex mechanisms involved in rejection of solutes. Rejection of three dyes (Sudan II, Sudan Black, Sudan 408) from common organic solvents (methanol, ethanol, acetone, methyl ethyl ketone, toluene and n-hexane) through a polyimide based SRNF membrane, STARMEM™122, was studied. It was found that the rejection of the STARMEM™122 membrane was lower than that indicated by the manufacturer. The experimental observations for Sudan II were not promising for the rejection study as they were lower than expected. Sudan Black and Sudan 408, which are larger solutes than Sudan II, provided more interesting insights. The effects of the solvent on the membrane and solute were studied separately. A higher permeation rate of ketones and alcohols was observed, while permeabilities of non-polar solvents were low which shows that this membrane shows higher affinity toward semi-polar solvents (alcohols, ketones). The effect of the solvent on the solute's rejection, based on the results for Sudan Black and Sudan 408, was studied for solvents in the same chemical groups, since the membrane showed a similar separation performance for solvents with similar functional groups (e.g. alcohols). The effect of solvent on solute molecular size was investigated by using simulation with Molecular Dynamics. It was shown that the effective size of a molecule is dependent on the solvent due to solvation and hydration of the solute by the solvent. The size of the solute in the solvent belonging to a similar family was studied separately. It was clear that the rejection was influenced by molecular size of the solute in the same group of solvents. A surprising negative rejection of solutes was achieved for n-hexane. Although solutes in n-hexane have higher volume compared to those in other solvents, the affinity between the solute and membrane increases the solute permeation in the presence of n-hexane. The affinity of solvent and solute for the membrane was investigated by means of solubility parameters for solvents within the same chemical family. In two different systems including two different solvents and one solute (Sudan Black and methanol, Sudan Black and ethanol), lower rejection (in this case for Sudan Black and methanol) was achieved when the solutes have higher affinity toward the solvent. Finally, it was found that in a system comprising the solvent, solute and membrane, interactions between solvent and membrane have much more effect on separation than solvent–solute interactions.
TL;DR: This new hypothesis suggests that the stereoselectivity is dictated by two interrelated conformational properties of the reactive complex, namely, the conformational preferences of the oxacarbenium pyranose ring, modulating the steric crowding and exposure of the anomeric carbon toward the α or β face.
Abstract: The mechanism of solvent effects on the stereoselectivity of glycosylation reactions is investigated using quantum-mechanical (QM) calculations and molecular dynamics (MD) simulations, considering a methyl-protected glucopyranoside triflate as a glycosyl donor equivalent and the solvents acetonitrile, ether, dioxane, or toluene, as well as gas-phase conditions (vacuum). The QM calculations on oxacarbenium-solvent complexes do not provide support to the usual solvent-coordination hypothesis, suggesting that an experimentally observed β-selectivity (α-selectivity) is caused by the preferential coordination of a solvent molecule to the reactive cation on the α-side (β-side) of the anomeric carbon. Instead, explicit-solvent MD simulations of the oxacarbenium-counterion (triflate ion) complex (along with corresponding QM calculations) are compatible with an alternative mechanism, termed here the conformer and counterion distribution hypothesis. This new hypothesis suggests that the stereoselectivity is dictated by two interrelated conformational properties of the reactive complex, namely, (1) the conformational preferences of the oxacarbenium pyranose ring, modulating the steric crowding and exposure of the anomeric carbon toward the α or β face, and (2) the preferential coordination of the counterion to the oxacarbenium cation on one side of the anomeric carbon, hindering a nucleophilic attack from this side. For example, in acetonitrile, the calculations suggest a dominant B2,5 ring conformation of the cation with preferential coordination of the counterion on the α side, both factors leading to the experimentally observed β selectivity. Conversely, in dioxane, they suggest a dominant (4)H3 ring conformation with preferential counterion coordination on the β side, both factors leading to the experimentally observed α selectivity.
TL;DR: The results show that computationally efficient solvent modeling is possible and can reveal fine details of molecular structure, solvation, and dynamics.
Abstract: Solvent modeling became a standard part of first principles computations of molecular properties. However, a universal solvent approach is particularly difficult for the nuclear magnetic resonance (NMR) shielding and spin−spin coupling constants that in part result from collective delocalized properties of the solute and the environment. In this work, bulk and specific solvent effects are discussed on experimental and theoretical model systems comprising solvated alanine zwitterion and chloroform molecules. Density functional theory computations performed on larger clusters indicate that standard dielectric continuum solvent models may not be sufficiently accurate. In some cases, more reasonable NMR parameters were obtained by approximation of the solvent with partial atomic charges. Combined cluster/continuum models yielded the most reasonable values of the spectroscopic parameters, provided that they are dynamically averaged. The roles of solvent polarizability, solvent shell structure, and bulk permeab...
TL;DR: From the solvent-effected attachment energy calculations it follows that the (100) face becomes morphologically more important compared with that in vacuum, while the (020) and (102 ) are not visible at all.
TL;DR: The correlation of rate and equilibrium constants indicates that the effect of oxidations of two ascorbate derivatives by the TEMPO radical in acetonitrile are very sensitive to the presence of various additives, and has a thermochemical origin rather than being a purely kinetic effect.
Abstract: Ascorbate (vitamin C) is a ubiquitous biological cofactor. While its aqueous solution chemistry has long been studied, many in vivo reactions of ascorbate occur in enzyme active sites or at membrane interfaces, which have varying local environments. This report shows that the rate and driving force of oxidations of two ascorbate derivatives by the TEMPO radical (2,2',6,6'-tetramethylpiperidin-1-oxyl) in acetonitrile are very sensitive to the presence of various additives. These reactions proceed by the transfer of a proton and an electron (a hydrogen atom), as is typical of biological ascorbate reactions. The measured rate and equilibrium constants vary substantially with added water or other polar solutes in acetonitrile solutions, indicating large shifts in the reducing power of ascorbate. The correlation of rate and equilibrium constants indicates that this effect has a thermochemical origin rather than being a purely kinetic effect. This contrasts with previous examples of solvent effects on hydrogen atom transfer reactions. Potential biological implications of this apparently unique effect are discussed.
TL;DR: In this article, the mechanisms by which ionic solvents enhance the rate and selectivity of the reaction are discussed on the basis of correlation studies using empirical parameters and theoretical calculations.
TL;DR: A procedure to predict rate constants for HAT reactions of oxyl radicals (RO•) in various media using the Marcus cross relation and a combined model, referred to as the CR/KSE model, shows remarkable predictive power.
Abstract: Chemical reactions that involve net hydrogen atom transfer (HAT) are ubiquitous in chemistry and biology, from the action of antioxidants to industrial and metalloenzyme catalysis. This report develops and validates a procedure to predict rate constants for HAT reactions of oxyl radicals (RO•) in various media. Our procedure uses the Marcus cross relation (CR) and includes adjustments for solvent hydrogen-bonding effects on both the kinetics and thermodynamics of the reactions. Kinetic solvent effects (KSEs) are included by using Ingold’s model, and thermodynamic solvent effects are accounted for by using an empirical model developed by Abraham. These adjustments are shown to be critical to the success of our combined model, referred to as the CR/KSE model. As an initial test of the CR/KSE model we measured self-exchange and cross rate constants in different solvents for reactions of the 2,4,6-tri-tert-butylphenoxyl radical and the hydroxylamine 2,2′-6,6′-tetramethyl-piperidin-1-ol. Excellent agreement is observed between the calculated and directly determined cross rate constants. We then extend the model to over 30 known HAT reactions of oxyl radicals with OH or CH bonds, including biologically relevant reactions of ascorbate, peroxyl radicals, and α-tocopherol. The CR/KSE model shows remarkable predictive power, predicting rate constants to within a factor of 5 for almost all of the surveyed HAT reactions.
TL;DR: The four Catalán solvent scales (dipolarity, polarizability, acidity and basicity of the medium) are the most appropriate for describing the solvatochromic effects.
Abstract: Two difluoroboron dipyrromethene (BODIPY) based fluorescent dyes – 4,4-difluoro-3-{2-[4-(dimethylamino)phenyl]ethenyl}-8-[4-(methoxycarbonyl)phenyl]-1,5,7-trimethyl-3a,4a-diaza-4-bora-s-indacene (1) and 4,4-difluoro-3-[2-(4-fluoro-3-hydroxyphenyl)ethenyl]-8-[4-(methoxycarbonyl)phenyl]-1,5,7-trimethyl-3a,4a-diaza-4-bora-s-indacene (3) – have been synthesized via condensation of p-N,N-dimethylaminobenzaldehyde and 4-fluoro-3-hydroxybenzaldehyde, respectively, with 4,4-difluoro-8-[4-(methoxycarbonyl)phenyl]-1,3,5,7-tetramethyl-3a,4a-diaza-4-bora-s-indacene (2). UV–vis spectrophotometry and steady-state and time-resolved fluorometry have been used to study the spectroscopic and photophysical characteristics of 1–3 in various solvents. The multi-parameter Kamlet–Taft {π*, α, β} solvent scales and a new, generalized treatment of the solvent effect, proposed by Catalan (J. Phys. Chem. B, 2009, 113, 5951–5960), have been used in the analysis of the solvatochromic shifts of the UV–vis absorption and fluorescence emission maxima of 1–3, and the rate constants of excited-state deactivation via fluorescence (kf) and radiationless decay (knr). The four Catalan solvent scales (dipolarity, polarizability, acidity and basicity of the medium) are the most appropriate for describing the solvatochromic effects. Solvent dipolarity and polarizability are the important causes for the solvatochromism of 1. Conversely, the absorption and emission maxima of 2 and 3 are hardly dependent on the solvent: the small changes reflect primarily the polarizability of the solvent surrounding the dye. Fluorescence decay profiles of 1 can be described by a single-exponential function in aprotic solvents, whereas two decay times are found in alcohols. The fluorescence decays of 2 (lifetimes τ in 1.9–2.9 ns range) and 3 (τ between 3.5 and 4.0 ns) are mono-exponential in all solvents studied. The fluorescence properties of dye 1 are very sensitive to the solvent: upon increasing solvent dipolarity, the fluorescence quantum yields and kf values decrease and the emission maxima become more red-shifted. The kf values of 2 [(1.6 ± 0.3) × 108 s−1] and 3 [(1.5 ± 0.2) × 108 s−1] are practically independent of the solvent properties. The crystal structure of 2 reveals that the BODIPY core is nearly planar with the boron atom moved out of the plane. The angle between the phenyl group at the meso-position and the BODIPY plane equals 80°.
TL;DR: In this paper, polyvinylidene fluoride (PVDF) microporous flat membranes were cast with different kinds of PVDFs and four mixed solvents.
Abstract: Polyvinylidene fluoride (PVDF) microporous flat membranes were cast with different kinds of PVDFs and four mixed solvents [trimethyl phosphate (TMP)–N,N-dimethylacetamide (DMAc), triethyl phosphate (TEP)–DMAc, tricresyl phosphate (TCP)–DMAc, and tri-n-butyl phosphate (TBP)–DMAc]. The effects of different commercial PVDFs (Solef® 1015, FR 904, Kynar 761, Kynar 741, Kynar 2801) on membrane morphologies and membrane performances of PVDF/TEP–DMAc/PEG200 system were investigated. The membrane morphologies were examined by scanning electron microscopy (SEM). The membrane performances in terms of pure water flux, rejection, porosity, and mean pore radius were measured. The membrane had the high flux of 143.0 ± 0.9 L m−2 h−1 when the content of TMP in the TMP–DMAc mixed solvent reached 60 wt %, which was 2.89 times that of the membrane cast with DMAc as single solvent and was 3.36 times that of the membrane cast with TMP as single solvent. Using mixed solvent with different solvent solubility parameters, different morphologies of PVDF microporous membranes were obtained. TMP–DMAc mixed solvent and TEP–DMAc mixed solvent indicated the stronger solvent power to PVDF due to the lower solubility parameter difference of 1.45 MPa1/2 and the prepared membranes showed the faster precipitation rate and the higher flux. The less macrovoids of the membrane prepared with TEP (60 wt %)–DMAc (40 wt %) as mixed solvent contributed to the higher elongation ratio of 96.61% ± 0.41%. Therefore, using TEP(60 wt %)–DMAc (40 wt %) as mixed solvent, the casting solution had the better solvent power to PVDF, and the membrane possessed the excellent mechanical property. The microporous membranes prepared from casting solutions with different commercial PVDFs exhibited similar morphology, but the water flux increased with the increment of polymer solution viscosity. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010
TL;DR: Polyethylene glycol (PEG) was found to be an inexpensive non-toxic and effective medium for the one-pot synthesis of Nsubstituted decahydroacridine-1,8-diones in the presence of ceric ammonium nitrate (CAN) as the catalyst in high yields as mentioned in this paper.
TL;DR: In this article, the effect of the addition of weak acids such as suberic acid, phthalic acid and oxalic acid on the energy requirement of CO2 desorption was investigated experimentally.
Abstract: The effect of the addition of weak acids into CO2-loaded solvents or rich solvents on the energy requirement of CO2 desorption was investigated experimentally. The commercially available CO2 solvent monoethanolamine (MEA) was used to absorb different amounts of CO2. Subsequently, a few weak acids such as suberic acid, phthalic acid, and oxalic acid were added into the solvents to study the effect of acid amount on the rate of CO2 release. It was found that CO2 could be released much faster and in much larger quantity with the addition of weak acids while the other desorption conditions were maintained the same. The amount of CO2 released was found to be proportional to the amount of acid added. Acid addition could be potentially used to reduce the energy requirement for CO2 desorption from solvent.
TL;DR: It is shown that the E(f) parameters of the reference electrofuges can be used to determine N( f) and s(f)* for almost any combination of leaving group and solvent, and the nucleofuge-specific parameters ofThe reference systems can analogously beused to derive the electroFugalities E(F) of other types of carbocations.
Abstract: Chemists are well trained to recognize what controls relative reactivities within a series of compounds. Thus, it is well-known how the rate of ionization of R−X is affected by the stabilization of the carbocation R+, the nature of the leaving group X−, or the solvent ionizing power. On the other hand, when asked to estimate the half-life of the ionization of a certain substrate in a certain solvent, most chemists resign. This question, however, is crucial in daily laboratory practice. Can a certain substrate R−X be handled in alcoholic or aqueous solution without being solvolyzed? Can a biologically active tertiary amine or azole be released by ionization of a quaternary ammonium ion? In this Account, we describe a straightforward means of addressing such experimental concerns. A semiquantitative answer to these questions is given by the correlation equation log k25 °C = sf(Nf + Ef), in which carbocations R+ are characterized by the electrofugality parameter Ef, and leaving groups X− in a certain solvent...
TL;DR: A linker partial dissociation mechanism for the guest uptake and release into and out of 3a is proposed based on the kinetic studies of guest@3a using 2D EXSY analysis, as well as structural analysis of a guests@3b.
Abstract: Two molecules of tetrakis(dihydroxyboryl)-cavitand 1a as an aromatic cavity and four molecules of 1,2-bis(3,4-dihydroxyphenyl)ethane 2 as an equatorial linker self-assemble into capsule 3a via the formation of eight dynamic boronic ester bonds in CDCl3 or C6D6. Capsule 3a encapsulates one guest molecule, such as 4,4′-disubstituted-biphenyl and 2,6-disubstituted-anthracene derivatives, in a highly selective recognition event, wherein the guest substituents are oriented to both aromatic cavity ends of 3a, as confirmed by a 1H NMR study and X-ray crystallographic analysis. Capsule 3a showed a significant solvent effect on guest encapsulation. The association constant (Ka) of 3a with guests in C6D6 was much greater than that in CDCl3 (450−48 000-fold). The encapsulation of guests within 3a in C6D6 was enthalpically driven, whereas that in CDCl3 tended to be both enthalpically and entropically driven. Thermodynamic studies suggest that the small Ka value in CDCl3 arises from the character of CDCl3 as a competi...