Hydrogen Bond Acceptor Basicity Research Articles

Solvent effects on kinetics of an heteroatomic nucleophilic substitution reaction in ionic liquid and molecular solvents mixtures

Rate constants, kA, for the aromatic nucleophilic substitution reaction of 2-chloro-3,5-dinitropyridine with aniline were determined in different compositions of 2-propanol mixed with hexane, benzene, and 2-methylpropan-2-ol and 1-ethyl-3-methylimidazolium ethylsulfate ([Emim][EtSO4]) with dimethyl sulfoxide at 25°C. The obtained rate constants of the reaction in pure solvents are in the following order: 2-methylpropan-2-ol > dimethyl sulfoxide > 2-propanol > hexane > benzene > [Emim][EtSO4]. Molecularmicroscopic solvent parameters corresponding to the selected binary mixtures were utilized to study the kinetics of a nucleophilic substitution reaction in order to investigate and compare the effects of the solvents on a chemical process. The influence of solvent parameters including normalized polarity (ETN), dipolarity/polarizability (π*), hydrogen bond donor acidity (α), and hydrogen bond acceptor basicity (β) on the second-order rate constants were investigated and multiple linear regressions gave much better results with regard to single parameter regressions. The dipolarity/polarizability of media has a positive effect in all mixtures regarding zwitterionic character of the reaction intermediate and the hydrogen bond acceptor basicity of the solvent by stabilizing of activated complex increases the reaction rate.

Solution enthalpies of 1,4-dioxane: Study of solvent effects through quantitative structure–property relationships

Solution enthalpies of 1,4-dioxane have been obtained in 15 protic and aprotic solvents at 298.15K. Breaking the overall process through the use of Solomonov's methodology the cavity term was calculated and interaction enthalpies (ΔintH) were determined. Main factors involved in the interaction enthalpy have been identified and quantified using a QSPR approach based on the TAKA model equation. The relevant descriptors were found to be π* and β, which showed, respectively, exothermic and endothermic contributions.The magnitude of π*’ coefficient points toward non-specific solute–solvent interactions playing a major role in the solution process. The positive value of the β coefficient reflects the endothermic character of the solvents’ hydrogen bond acceptor (HBA) basicity contribution, indicating that solvent molecules engaged in hydrogen bonding preferentially interact with each other rather than with 1,4-dioxane.

Molecular-Microscopic Properties and Preferential Solvation in Protic Ionic Liquid Mixtures

Structural and molecular-microscopic properties of the solvatochromic probes 4-nitroaniline, 4-nitroanisole, and Reichardt’s dye were investigated in binary mixtures of ethylammonium propionate with methanol, ethanol, 1-propanol and 2-propanol. Solvatochromic parameters (α, hydrogen-bond donor acidity; β, hydrogen-bond acceptor basicity; π*, dipolarity/polarizability; \( E_{\text{T}}^{\text{N}} \), normalized polarity parameter) in different binary mixtures of ionic liquid with molecular solvents were determined with UV–Vis spectroscopy. The \( E_{\text{T}}^{\text{N}} \) parameters show nearly ideal trends in all solvent mixtures, but the other parameters show different behavior in the mixtures. The π* parameters show a negative deviation from ideality in the ionic liquid/methanol system. In contrast, the α parameters have severe positive deviations from ideal behavior in ionic liquid/1-propanol and ionic liquid/2-propanol solvent mixtures. A synergistic solvation effect is observed for the π* parameters in IL/methanol mixtures. Specific solute–solvent interactions or solvent–solvent interactions, which cause non-ideal trends in some parameters, are justified and interpreted by the preferential solvation model.

Equilibrium studies of thallium(I) complexes with cytidine 5′-monophosphate in different aqueous solutions of methanol

The protonation equilibria of cytidine 5′-monophosphate (CMP) and its complex formation with Tl(I) ion were studied over a wide pH range (1.5 to 10.5), using a combination of spectrophotometric and potentiometric methods at constant temperature (25°C), different methanol–water mixtures (0 to 50% v/v), and constant ionic strength (0.1moldm−3 sodium perchlorate). Least squares regression calculations are consistent with the formation of TlHL and TlL− species, where L2− represents the fully dissociated ligand. The protonation of CMP and the formation constants of the formed complexes in different media were analyzed in terms of Kamlet, Abboud, and Taft (KAT) parameters. A single-parameter correlation of the formation constants versus α (hydrogen-bond donor acidity), β (hydrogen-bond acceptor basicity) and π* (dipolarity/polarizability) are relatively poor in all solutions, but dual and multi-parameter correlations represent significant improvements with regard to the single-parameter model. Linear correlation is observed when the experimental formation constant values (in logarithm scale) are plotted versus the calculated ones, while the KAT parameters are considered. Finally, the results are discussed in terms of the effect of solvent on protonation and complexation.

Solvatochromic relationship: Prediction of distribution of ionic solutes in aqueous two-phase systems

Partition ratios of several ionic compounds in 20 different polymer/polymer aqueous two-phase systems (ATPS) containing 0.15M NaCl in 0.01M phosphate buffer, pH 7.4, were determined. The differences between the electrostatic properties of the phases in all the ATPS were estimated from partitioning of the homologous series of dinitrophenylated-amino acids. Also the solvatochromic solvent parameters characterizing the solvent dipolarity/polarizability (π*), solvent hydrogen-bond donor acidity (α), and solvent hydrogen-bond acceptor basicity (β) of aqueous media were measured in the coexisting phases of the ATPS. The solute-specific coefficients for the compounds examined were determined by the multiple linear regression analysis using the modified linear solvation energy relationship equation. The minimal number of ATPS necessary for determination of the coefficients was established and 10 ATPS were selected as a reference ATPS set. The solute-specific coefficients values obtained with this reference set of ATPS were used to predict the partition ratios for the compounds in 10 ATPS not included in the reference set. The predicted partition ratios values were compared to those determined experimentally and found to be in good agreement. It is concluded that the presented model of solute–solvent interactions as the driving force for solute partitioning in polymer/polymer ATPS describes experimental observations with 90–95% accuracy.

The conformational analysis of push–pull enaminones using Fourier transform IR and NMR spectroscopy, and quantum chemical calculations. IV. 4-(N,N-dimethylamino)-1,1,1-trifluoro-3-methylbut-3-en-2-one and 4-(N,N-dimethyl-amino)-1,1,1-trifluoropropen-3-en-2-one

IR Fourier spectra of two enaminoketones with general formula (CH3)2NCR1CR2C(O)CF3, R1H, R2CH3 (2); R1CH3, R2H (3) were investigated in various pure solvents. For comparison results of earlier investigated enaminoketone R1H, R2H (1) were also presented. On the basis of NMR and IR spectra it was shown that enaminoketones 1 and 2 presented in solutions as an equilibrium of two conformers, (E–s–Z)⇌(E–s–E), whereas the enaminoketone 3 presented as equilibrium of two isomers, (E–s–Z)⇌(Z–s–Z). Quantum chemical calculations by the DFT methods were carried out to evaluate relative energy and dipole moment of each spatial form. For both (E–s–Z) and (E–s–E) conformer of the 1 and 2 the main influence on the ν˜(CO) vibrations has the solvent’s hydrogen bond donor (HBD) acidity whereas for the 3 influence of the solvent’s polarity/polarizability dominated. Both the solvent’s polarity/polarizability and solvent’s hydrogen bond donor (HBD) acidity influenced on the ν˜(CC) mode of the conformers of the 1 and 2. Solvent influence on the ν˜(CC) vibrations of the 3 depended substantially whether the solvent is aprotic or an alcohol. In the former case the main contribution made the solvent’s hydrogen bond acceptor (HBA) basicity [(E–s–Z) isomer] or the solvent’s polarity/polarizability with solvent’s hydrogen bond donor (HBD) acidity [(Z–s–Z) isomer]. Alcohols influenced on the ν˜(CC) vibrations of both isomers predominantly due to the solvent’s polarity/polarizability.In aprotic solvents the greatest contribution in solvent influence on thermodynamic parameters of both (E–s–Z)⇌(E–s–E) and (E–s–Z)⇌(Z–s–Z) equilibrium made the solvent’s hydrogen bond acceptor (HBA) basicity. Rotation around double CC bond is characterized by higher sensitivity to the solvent’s hydrogen bond acceptor (HBA) basicity compared to the rotation around formally single CCO bond.

Linear Solvation Energy Relationships in the Determination of Specificity and Selectivity of Stationary Phases

The retention of fifty structurally different compounds has been studied using linear solvation energy relationships. Investigations were performed with the use of six various stationary phases with two mobile phases (50/50 % v/v methanol/water and 50/50 % v/v acetonitrile/water). Packing materials were home-made and functionalized with octadecyl, alkylamide, cholesterol, alkyl-phosphate and phenyl molecules. This is the first attempt to compare all of these stationary phases synthesized on the same silica gel batch. Therefore, all of them may be compared in more complex and believable way, than it was performed earlier in former investigations. The phase properties (based on Abraham model) were used to the classification of stationary phases according to their interaction properties. The hydrophilic system properties s, a, b indicate stronger interactions between solute and mobile phase for most of the columns. Both e and v cause greater retention as a consequence of preferable interactions with stationary phase by electron pairs and cavity formation as well as hydrophobic bonds. However, alkyl-phosphate phase has different retention properties, as it was expressed by positive sign of s coefficient. It may be concluded that most important parameters influencing the retention of compounds are volume and hydrogen bond acceptor basicity. The LSER coefficients showed also the dependency on the type of organic modifier used as a mobile phase component.

Solvents Design on the Basis of Molecular-Microscopic Properties of Binary Mixtures for Lycopene Extraction

Lycopene is a natural compound with high-value of nutritional and medical properties. Nowadays, the extrac- tion of Lycopene with mixtures of solvents to obtain more efficiency and less toxicity is interested. In this study, the Lyco- pene extraction in three binary mixtures of solvents (Ethyl-acetate/Ethanol, Hexane/Isopropanol and Benzene/Isopropanol) was measured and then the effects of solvatochromic parameters (π*, dipolarity/polarizability; β, hydrogen-bond acceptor basicity; α, hydrogen-bond donor acidity) and solvophobicity (Sp) parameters on the extraction from tomato tissues have been considered. Among the all parameters, Sp shows the biggest contribution in the extraction that is well justified, knowing that Lycopenes are lypophobic. Our calculation results show that in addition to Sp, another parameter is needed to get the reasonable correlation between the parameters and the extraction. For Ethanol/Ethyle-acetate mixture, β, for Isopropa- nol/Benzene mixture, π* and for Isopropanol/Hexane mixture, α, participated in the correlation equation in addition to Sp.

Solvent Effects on Tautomeric and Microscopic Protonation Constants of Glycine in Different Aqueous Solutions of Methanol and Ethanol

The acid-base equilibria of glycine have been studied in different aqueous solutions of methanol and ethanol (0–45 % v/v) using a potentiometric method. In this study, the macro and micro protonation constants of the amino acid and its tautomeric constant have been determined at 25 °C and constant ionic strength (0.1 mol⋅dm−3 NaClO4). The protonation and the tautomeric constants of glycine in different binary mixtures were analyzed in terms of the Kamlet, Abboud and Taft (KAT) parameters. Single-parameter correlations of the constants versus α (hydrogen-bond donor acidity), β (hydrogen-bond acceptor basicity) and π∗ (dipolarity/polarizability) are poor in all solutions. Multi-parameter correlations show better results, but dual-parameter correlations represent significant improvements with regard to the single- and multi-parameter models. Linear correlation is observed when the experimental protonation constant values are plotted versus the calculated ones when the KAT parameters are considered. Finally, the results are discussed in terms of the effect of the solvent on protonation and tautomeric constants.

Solvatochromic behavior of the electronic absorption spectra of gallic acid and some of its azo derivatives

The electronic absorption spectra of gallic acid and its azo derivatives have been studied in various solvents of different polarities. Multiple regression techniques were applied to calculate the regression and correlation coefficients based on an equation that relates the wavenumbers of the absorption band maxima (υmax−) to the solvent parameters; refractive index (n), dielectric constant (D), empirical Kamlet–Taft solvent parameters, π*(dipolarity/polarizability), α (solvent hydrogen-bond donor acidity) and β (solvent hydrogen-bond acceptor basicity). The fitting coefficient obtained from this analysis allows estimating the contribution of each type of interactions relative to total spectral shifts in solution. The dependence of υmax− on the solvent parameters indicates that the obtained bands are affected by specific and non-specific solute-solvent interactions.

Salt effects on solvent features of coexisting phases in aqueous polymer/polymer two-phase systems

The solvatochromic parameters characterizing the solvent dipolarity/polarizability (π*), solvent hydrogen-bond donor acidity (α), and solvent hydrogen-bond acceptor basicity (β) of aqueous media were measured in the coexisting phases of aqueous Dextran-Ficoll, Dextran-Ucon, Dextran-PEG, PEG-Ucon, Ficoll-Ucon, and Ficoll-PEG two-phase systems (ATPS). Ionic composition of each ATPS included 0.15M KCl, 0.15M KBr, 0.15M NaBr, 0.1M Na2SO4, and 0.1M Li2SO4 in 0.01M sodium phosphate buffer (NaPB), pH 7.4; and 0.01M and 0.11M sodium phosphate buffer, pH 7.4. Partition ratios of sodium salts of dinitrophenylated (DNP) amino acids with aliphatic side-chains (glycine, alanine, norvaline, norleucine, and α-amino-n-caprylic acid) were measured in all ATPSs, and the results were evaluated in terms of the differences between the relative hydrophobicity (parameter E) and the electrostatic properties (parameter C) of the aqueous media of the coexisting phases. It was established that parameter E is described by a linear combination of the differences between the solvent dipolarity/polarizability (Δπ*) and between the solvent hydrogen-bond acidity (Δα) of the media in the coexisting phases. Parameter C depends on the phase forming polymer pair and is shown to be described by a linear combination of three parameters: the differences between the solvent hydrogen-bond acidity (Δα) and between the solvent hydrogen-bond basicity (Δβ) of the media in the coexisting phases, and a measure of the effect of a given salt additive on the hydrogen bonds in water. This effect was represented by a parameter (Kb−l), characterizing the equilibrium between populations of hydrogen bonds with a bent hydrogen bond conformation and with linear hydrogen bond conformation affected by a given salt additive.

Solvent effects in ionic liquids: empirical linear energy–density relationships

Multiparameter linear energy-density relationships to model solvent effects in room temperature ionic liquids (RTILs) are introduced and tested. The model incorporates two solvent dependent and two specific solute-solvent parameters represented by a set of electronic indexes derived from the conceptual density functional theory. The specific solute-solvent interactions are described in terms of the electronic chemical potential for proton migration between the anion or cation and the transition state structure of a specific reaction. These indexes provide a quantitative estimation of the hydrogen bond (HB) acceptor basicity and the hydrogen bond donor acidity of the ionic solvent, respectively. A sound quantitative scale of HB strength is thereby obtained. The solvent dependent contributions are described by the global electrophilicity of the cation and nucleophilicity of the anion forming the ionic liquid. The model is illustrated for the kinetics of cycloaddition of cyclopentadiene towards acrolein. In general, cation HB acidity outweighs the remaining parameters for this reaction.

Do anions influence the polarity of protic ionic liquids?

Polarity studies in two classes of imidazolium-based protic ionic liquids (PILs) possessing [HSO(4)](-), [HCOO](-), [CH(3)COO](-) and [CH(3)CH(2)COO](-) anions were carried out using a solvatochromic method from 298.15 to 353.15 K. For 1-methylimidazolium class of PILs, E(T)(30) was found to be independent over the entire range of temperature, while E(T)(30) was noted to decrease with a rise in temperature in the case of 1-butylimidazolium class of PILs containing [CH(3)COO](-) and [CH(3)CH(2)COO](-) anions. The E(T)(30) value decreases in both the classes upon varying the anions ([HSO(4)](-), [HCOO](-), [CH(3)COO](-) and [CH(3)CH(2)COO](-)). The E(T)(30) value is controlled by hydrogen bond acceptor basicity, β, and dipolarity/polarizability, π*. The E(T)(30) value for PILs varies inversely to the strength of the coulombic interaction between ions in PILs. Strong interactions between ions lead to lower E(T)(30) values. Unlike the poor thermal effect on E(T)(30), the Kamlet-Taft parameters i.e. α, β and π* have pronounced thermal effect in the imidazolium-based PILs. Variation in the Kamlet-Taft parameters is controlled by the stabilization of ions and the degree of proton transfer from Brønsted acid to Brønsted base.

Effect of NaCl additive on properties of aqueous PEG–sodium sulfate two-phase system

The concentrations of all components in the phases of aqueous two-phase polyethylene glycol-sodium sulfate system of a fixed composition with different concentrations of NaCl additive were determined. Solvatochromic solvent features of aqueous media in the phases of all the systems were characterized in terms of solvent dipolarity/polarizability, solvent hydrogen bond donor acidity and hydrogen bond acceptor basicity. Partitioning of a homologous series of dinitrophenylated amino acids with aliphatic alkyl side chain was examined in all the systems, and the differences between the relative hydrophobicity and electrostatic properties of the phases were quantified. These differences were described in terms of solvatochromic solvent features of the phases. The previously reported partition coefficients of twelve different nonionic compounds in all the systems were expressed in terms of solute descriptors. It is demonstrated that two solvatochromic solvent descriptors (solvent dipolarity/polarizability, and solvent hydrogen bond donor acidity) could adequately describe the partitioning of the solutes in all the systems employed.

Cosolvent effects on the diffusions of 1,3-dichlorobenzene, l-carvone, geraniol and 3-fluorophenol in supercritical carbon dioxide

In order to get an insight into solute–cosolvent interactions and to predict the cosolvent effects on diffusions, several cosolvents and solutes with different size, hydrogen-bond donor (HBD) acidity, and hydrogen-bond acceptor (HBA) basicity were chosen, and the molecular diffusion coefficients of the solutes in pure and modified supercritical carbon dioxide were measured by the Taylor–Aris chromatographic peak broadening method. Cosolvent effect parameter, which is defined as the ratio of diffusion coefficient with and without cosolvent, respectively, is introduced to quantitatively compare the strength of different types of interaction between solute and cosolvent, especially hydrogen bonding. For cosolvent without hydrogen-bond ability, the cosolvent effect parameter decreases with the increase of molecular volume and weight of the solutes, in that the strength of dispersion force with cosolvent increases with their size. For cosolvent with only HBA basicity, the solute with higher HBD acidity has smaller cosolvent effect parameter, due to the fact that the strength of hydrogen-bond interaction between the solute and cosolvent only depends on and increases with the HBD acidity of the solute. For amphiprotic cosolvent, the solute with higher HBD acidity has smaller cosolvent effect parameter, it can be inferred from which that HBD acidity rather than HBA basicity of the solute makes a major contribution to the hydrogen-bond interaction between solute and cosolvent. These results are consistent with the interpretation by the Kamlet–Taft solvatochromic parameters (HBD acidity and HBA basicity). Moreover, a nonlinear decrease in diffusion coefficient with the increase of cosolvent concentration is observed, which is typical of the behavior of the system with strong interaction.

Solute-Solvent Interaction Effects on Protonation Equilibrium of Some Water-Insoluble Flavonoids

The protonation constants of three different flavonoids (naringenin, chrysin, and daidzein) were determined in water–DMSO mixed solvents using a potentiometric method at 25.0 (±0.1) °C and 1.00 mol⋅dm−3 tetra-n-butylammonium chloride as supporting electrolyte. The protonation constants were characterized and were analyzed in various solvent media in terms of the Kamlet, Abboud and Taft (KAT) parameters. Single-parameter correlations of the protonation constants versus α (hydrogen-bond donor acidity), β (hydrogen-bond acceptor basicity) or π∗ (dipolarity/polarizability) are poor for all compounds, but the dual-parameter α and π∗ correlation presents significant improvement with regard to the single- and multi-parameter models. A linear correlation is observed when the logarithm of the experimental protonation constants is plotted versus the calculated ones when the KAT parameters are considered. The protonation constants of the flavonoids in water were also calculated by the Yasuda-Shedlovsky extrapolation method at zero percent organic solvent. Finally, the results are discussed in terms of the effect of solvent composition on the protonation constants.

Solvatochromic Probes Absorbance Behavior in Mixtures of 2-Hydroxy Ethylammonium Formate with Methanol, Ethylene Glycol and Glycerol

Solute-solvent and solvent-solvent interactions were investigated for binary mixtures of an ionic liquid (IL) 2-hydroxy ethylammonium formate as with methanol, ethylene glycol and glycerol. The physicochemical properties of the solvent mixtures at 25 °C, over the whole range of mole fractions, were determined using solvatochromic probes. High normal polarity (\(E_{T}^{N}\)) in the alcohol-rich region confirms solute-solvent interactions in this medium. Dipolarity/polarizability (π∗) show a different trend to \(E_{T}^{N}\) with a positive deviation from ideal behavior in IL-glycerol mixtures. However, these deviations for other solvent mixtures are insignificant. Contrary to what is observed for \(E_{T}^{N}\) and π∗, hydrogen-bond donor (HBD) acidity and hydrogen-bond acceptor (HBA) basicity demonstrate similar trends. The applicability of the combined nearly-ideal binary solvent/Redlich-Kister (CNIBS/R-K) equation for the correlation of various parameters provides a simple computational model to correlate and/or predict various solvatochromic parameters for many binary solvent systems.

Protonation Constants of Adenine and Adenosine in Different Aqueous Solutions of Methanol and Ethanol

The protonation constants of adenine (K1 and K2) and adenosine (K2) were determined in binary mixtures of water with methanol or ethanol containing (0, 10, 15, 20, 25, 30, 35, 40, and 45) % (v/v) using a combination of potentiometric and spectrophotometric methods at 25 °C and constant ionic strength (0.1 mol·dm−3 sodium perchlorate). The protonation constants were analyzed using the normalized polarity parameter (ETN) and Kamlet, Abboud, and Taft (KAT) parameters. A very good linear correlation of log K versus the normalized polarity parameter was obtained. Dual-parameter correlation of log K versus π* (dipolarity/polarizability) and α (hydrogen-bond donor acidity) as well as π* and β (hydrogen-bond acceptor basicity) also gives good results in various aqueous organic solvent mixtures. Finally, the results are discussed in terms of the effect of the solvent on the protonation constants.

Solvatochromic Effect Studies on the Stability of Dioxovanadium(V) Complexes with Ethylene Glycol-bis(2-aminoethylether)-N,N,N′,N′-tetraacetic Acid in Different Water + Methanol Mixtures

The stability constants for the reaction of dioxovanadium(V) with ethylene glycol-bis(2-aminoethylether)-N,N,N′,N′-tetraacetic acid (EGTA) and the dissociation constants of EGTA were determined at 25 °C and a constant ionic strength of 0.05 mol·dm−3 sodium perchlorate in ten different compositions of water + methanol by a combination of potentiometric and UV spectrophotometric methods. The Solver, Microsoft Excel 2000 optimization package, has been used to perform nonlinear least-squares curve fitting on the basis of the Gauss−Newton method for calculation of the solvatochromic regression coefficients. Nonspecific and specific solute−solvent interactions were interpreted by correlating the equilibrium data with solvent parameters using the Kamlet−Abboud−Taft (KAT) solvatochromic equation. Finally, the influence of the solvent on the stability of the complex was discussed on the basis of the correlation results and the contribution of α (hydrogen-bond donor acidity), β (hydrogen-bond acceptor basicity), an...

Equilibrium studies of triphenyltin(IV) complexes with glycine, glycyl-glycine, and glycyl-glycyl-glycine in different aqueous solutions of ethanol

The protonation equilibria of glycine (gly), glycyl-glycine (gly-gly), and glycyl-glycyl-glycine (gly-gly-gly) and their formation constants with triphenyltin(IV) chloride were studied over a wide pH range (pH 1–11), using a combination of spectrophotometric and potentiometric methods at constant temperature (25 °C), different ethanol–water mixtures (50%–80%, v/v), and constant ionic strength (0.1 mol dm–3 NaClO4). Least-squares regression calculations are consistent with the formation of ph3SnHL+, ph3SnL, and ph3SnH–1L– complex species, where L– represents the fully dissociated form of each ligand. The stability constant of the formed complexes in different media were analyzed in terms of Kamlet, Abboud, and Taft (KAT) parameters. Single-parameter correlations of the stability constants versus α (hydrogen-bond donor acidity), β (hydrogen-bond acceptor basicity), and for π* (dipolarity/polarizability) are relatively poor in all solutions, but multi-parameter correlations represent significant improvements with regard to the single- and dual-parameter models. Linear correlation is observed when the experimental logβxyz values are plotted versus the calculated ones, while all the KAT parameters are considered. Also, the stability constant values of the formed complexes are determined in zero percent of organic solvent using the Yasuda–Shedlovsky extrapolation approach. Finally, the results are discussed in terms of the effect of solvent on complexation.