Hydrogen-bond Basicity Research Articles

Enhanced extraction of astaxanthin using aqueous biphasic systems composed of ionic liquids and potassium phosphate

Shrimp waste containing a substantial amount of valuable nutrients presents a challenge for food industry. In this work, extraction of astaxanthin from shrimp waste via aqueous biphasic systems (ABS) composed of ionic liquids (ILs) and potassiumphosphate (K3PO4) was investigated. The influence of phosphonium- and ammonium-based ILs and temperature on the phase behavior and astaxanthin extraction was evaluated. The hydrogen-bond basicity of each IL studied shows a negative linear correlation with tie-line lengths of ABS and a positive linear correlation with extraction efficiency (EEAst). In general, lower temperature are favourable for astaxanthin extraction. Tributyloctylphosphonium bromide ([P4448]Br) resulted in the strongest ABS formation ability and bonding interactions between the anion and astaxanthin. Compared with organic solvents, [P4448]Br + K3PO4 ABS achieved higher EEAst of 93.08% at 308 K. The chemical properties provide the possibility of prescreening appropriate ILs for ABS formation and predicting the partition of a target molecule.

Solubility of naftopidil in pure and mixed solvents at 273.15–313.15 K and its correlation with the Jouyban-Acree and CNIBS/R-K models

The dissolution behavior of naftopidil in methanol, ethanol, ethyl acetate, toluene, acetone, acetonitrile and two mixtures of (ethyl acetate + methanol) and (ethyl acetate + ethanol) was studied. In pure and mixed solvents, the solubility was determined experimentally and correlated by some thermodynamic models. The maximum data was obtained at 313.15 K in toluene, and the minimum data was obtained at 273.15 K in acetonitrile. Moreover, there is co-solvence phenomenon in two co-solvent mixtures, the values increased monotonically with the increasing temperature, while increased with increasing co-solvent (ethyl acetate) mass fraction (w) to a maximum value at w = 0.8 and then decreased. The dissolution behavior of naftopidil in pure was explained by the properties of solvents such as the hydrogen bond acidity, hydrogen bond basicity, dipolarity/polarizability, and it was evaluated by Extended Hildebrand Solubility Approach in mixed solvents. Besides, the apparent dissolution standard enthalpy (ΔHsolo), apparent molar standard Gibbs energy (ΔGsolo) and apparent dissolution standard entropy (ΔSsolo) of naftopidil in pure and mixed solvents were also calculated.

Lecithin liposomes and microemulsions as new chromatographic phases

Lecithins are phospholipidic mixtures that can be part of microemulsions and liposomes. In this work, ready-to-use preparations of lecithin have been tested as pseudostationary and mobile phases in EKC and LC, respectively. The selectivity of two EKC systems, one based on lecithin microemulsions (LMEEKC) and another on liposomes (LLEKC), and of a LC system based on lecithin microemulsions (MELC) has been evaluated through the solvation parameter model. In all cases, solute volume and hydrogen-bond basicity are the main descriptors that drive the partition process. While solute volume favors the retention of solutes, hydrogen-bond basicity has the contrary effect. In lecithin-based EKC systems the hydrogen-bond acidity of the solute leads to a higher retention while in the lecithin-based LC system a minor retention is produced. The three lecithin systems have been compared through the solvation parameter model to other chromatographic systems, most of them containing phospholipids. Principal component analysis reveals that lecithin systems cluster together with the other EKC systems based on phospholipids, with an immobilized artificial membrane (IAM) LC system, with the octanol/water reference partition system, and with a SDS-based microemulsion. Thus, they all show similar selectivity. However, the great advantage of using the ready-to use lecithin systems is that the laborious liposome preparation is avoided, and that their commercial availability makes them more affordable than IAM LC columns. Finally, taking into account that lecithin has a high semblance to the mammalian cell membranes composition, the ability of the three lecithin systems to mimic the pass of the solutes through the membranes has been evaluated. Experimental determinations have demonstrated that the skin partition of neutral solutes can be easily emulated, especially using the lecithin-microemulsion EKC method. The model is robust and shows good prediction ability.

Investigation on Preferential Solvation, Transfer Properties and Solvent Effect of Sulfachloropyridazine in Aqueous Co-solvent Solutions of Some Alcohols

The effect of solvent on the solubility of sulfachloropyridazine was studied by making a correlation between the solubility values and solvent’s descriptors for solvent–solute and solvent–solvent interactions with the help of linear solvation energy relationships concept. From analysis of the molecular structure of sulfachloropyridazine, the variation of solubility was well explained in terms of the change in hydrogen bond basicity of mixtures when the mole fraction of methanol (or ethanol or isopropanol) increased in all aqueous binary solvent mixtures. The preferential solvation analysis of sulfachloropyridazine in the three aqueous co-solvent solutions of isopropanol, ethanol and methanol was carried out from solubility values through the method of inverse Kirkwood–Buff integrals. In water-rich compositions of the aqueous co-solvent solutions, the δx1,3 values are negative, indicating that the sulfachloropyridazine was solvated preferentially by the solvent water. In intermediate and alcohol-rich compositions, sulfachloropyridazine was preferentially solvated by the isopropanol, ethanol or methanol. The magnitude of preferential solvation of sulfachloropyridazine is greater in isopropanol solutions than in the other two co-solvent solutions. Analysis results of the KAT-LSER and IKBI methods indicate that the solute mainly acts as a Lewis acid through its –NH2 and > NH functionalities. In addition, the enthalpy, Gibbs energy and entropy of transfer were obtained, which demonstrated that the solubilization ability was more favorable in intermediate composition of the alcohols.

Predicting adsorption coefficients of VOCs using polyparameter linear free energy relationship based on the evaluation of dispersive and specific interactions

Predicting adsorption of volatile organic compounds (VOCs) on activated carbons is of major importance to understand activated carbons' adsorption properties and explore their potential applications. In this study, adsorption of 38 VOCs on a commercial granular activated carbon (GAC) was examined using inverse gas chromatography (IGC) at infinite dilution, and the adsorption coefficients (K), dispersive and specific components of adsorption free energy were calculated. We found that the dispersive interaction was well described by adsorbate's molar polarizability (P), and the specific interactions well by dipolarity/polarizability (S), hydrogen-bond acidity (A) and hydrogen-bond basicity (B). Based on the result, a polyparameter linear free energy relationship (PP-LFER) was established: logK = (0.96 ± 0.23) S + (2.23 ± 0.34) A + (0.84 ± 0.25) B + (0.69 ± 0.050) P + (0.13 ± 0.35); (n = 38, R2 = 0.859, root mean square error (RMSE) = 0.25), which exhibited a more accurate prediction compared to the classical PP-LFER (E, S, A, B and L as descriptors, R2 = 0.765, RMSE = 0.33). Moreover, it overcame the drawbacks of indistinguishable dispersive interaction and unavailable relative contribution of each interaction for classical PP-LFER in explaining adsorption mechanism. As suggested by the developed model, the dispersive interaction was the dominant contribution to the adsorption of VOCs on GAC (42–100%), following by dipole-type interactions (0–30%) and hydrogen bonding (hydrogen-bond acidity 0–32%, hydrogen-bond basicity 0–11%). Additionally, it also accurately predicted the K values of VOCs on other three activated carbons.

Characterization of hydrophilic interaction liquid chromatography retention by a linear free energy relationship. Comparison to reversed- and normal-phase retentions

The Abraham solvation parameter model, a linear free energy relationship (LFER) approach, has been used to characterize a polymeric zwitterionic (sulfobetaine) column in HILIC mode. When acetonitrile (MeCN) is used in the preparation of mobile phases the main solute characteristics affecting the chromatographic behavior of analytes are the molecular size and the hydrogen-bonding (both acidity and basicity) interactions. The former property is more favorable in the acetonitrile-rich mobile phase, reducing thus the retention, but the latter reveals a higher affinity for the water layer adsorbed on the stationary phase, enhancing retention. However, if the aprotic acetonitrile is replaced by methanol, a hydrogen-bond acidic solvent, solute hydrogen-bond basicity does not contribute any more to retention, quite the opposite. Thus, a slightly different selectivity is observed in methanol/water than in acetonitrile/water. Normal-phase mode and HILIC-MeCN share the same main factors affecting retention. For reversed-phase and immobilized artificial membrane (IAM) chromatography, the solute molecular size increase retention because of the lower amount of energy required in the formation of a cavity in the solvated stationary phase. On the contrary, the analyte hydrogen-bond basicity favors interactions with the hydroorganic mobile phase and reduces retention. The determined parameters justify the reversed selectivity commonly observed in HILIC in reference to reversed-phase. In most instances, the least retained solutes in reversed-phase are the most retained in HILIC.

Determination of the hydrogen-bond acidity and basicity for un-dissociated hydrazoic acid, isocyanic acid and isothiocyanic acid

Literature values of water-solvent partition coefficients for un-dissociated hydrazoic acid, isocyanic acid and isothiocyanic acid have been used to obtain properties or ‘descriptors’ of the three acids. These descriptors can be used in linear free energy relationships that we have already obtained to predict further values of partition coefficients for a very large number of solvents. The descriptors include the hydrogen-bond acidity, A, and hydrogen-bond basicity, B, of the acids. We have also used literature values of equilibrium constants for 1:1 complexation of the acids with a number of bases to obtain values of our 1:1 hydrogen-bond acidity, αH2. There is very good agreement between the two sets of hydrogen-bond acidity. Isothiocyanic acid is a strong hydrogen-bond acid about the same as chloroacetic acid, isocyanic acid is about as strong as acetic acid and hydrogen azide is a moderate-to-weak hydrogen bond acid. The hydrogen-bond basicity of the three acids is very small.

Descriptors for terpene esters from chromatographic and partition measurements: Estimation of human odor detection thresholds

We have used gas chromatographic retention data together with other data to obtain Abraham descriptors for 30 terpene esters. These include the air-water partition coefficient, as log Kw, for which no experimental values are available for any terpene ester. The other descriptors are the ester dipolarity, S, the hydrogen bond basicity, B, (the ester hydrogen bond acidity is zero for the esters studied), and L the logarithm of the air-hexadecane partition coefficient. Both S and B are larger than those for simple aliphatic esters, as expected from the terpene ester structures that include ring systems and ethylenic double bonds. These descriptors can then be used to obtain a large number of physicochemical and environmental properties of terpene esters. We have analyzed experimental results on human odor detection thresholds and have constructed another equation for the calculation of these thresholds, to go with a previous equation that we have reported. Then the descriptors for terpene esters can be used to estimate the important odor detection thresholds.

Evaluation of separation properties of stationary phases in supercritical fluid chromatography; deazapurine nucleosides case study

A series of biologically important 7-deazapurine nucleosides was used for evaluation of selectivity of three stationary phases designed for supercritical fluid chromatography. The sorbents of stationary phases tested were diethylamine, diol and 2-picolylamine bonded on ethylene bridged hybrid particles. The highest selectivity for the tested nucleosides showed neutral diol column. All twelve tested nucleosides were baseline resolved in simple mobile phase composed of carbon dioxide/ethanol 79/21 (v/v). The effect of basic isopropylamine and mixed isopropylamine and trifluoroacetic acid mobile phase additives on retention and selectivity was also assessed. The interactions participating in the separation systems were revealed by linear free energy relationship. The obtained results demonstrated the significant contribution of hydrogen bond acidity and basicity on chromatographic behavior of the diol- and 2-picolylamine-based stationary phases.

Porous polymeric resin for adsorbing low concentration of VOCs: Unveiling adsorption mechanism and effect of VOCs’ molecular properties

The adsorption of 20 kinds of VOCs including n-alkanes, alcohols, esters, ketones, aromatics, chlorocarbons and cyclohexane on porous polymeric resin (PP-resin) were studied at low concentration by inverse gas chromatography (IGC). The adsorption partition coefficients and adsorption free energy of VOCs were calculated. A linear solvation energy relationship (LSER) model was employed to understand the adsorption mechanisms of VOCs on PP-resin. The results showed that hydroxyl groups on the surface of PP-resin resulted in the predominantly Lewis basicity on its surface. VOCs were adsorbed on the PP-resin mainly by dispersive interactions. Nevertheless, dipole-dipole/dipole-induced dipole interactions, hydrogen-bond acidity and hydrogen-bond basicity cannot be ignored especially for VOCs with polar groups. Among the adsorbates tested, methanol exhibited the highest specific interaction force (0.909) and cyclohexane was least only 0.038. It was also revealed that dispersive interactions were more important when longer carbon chain or larger molar volume of VOCs were adsorbed.

Catalytic performance of ionic liquid for dehydrochlorination reaction: Excellent activity and unparalled stability

Gas phase catalytic process with the advantages of simply product separation and maximized atom economy, which was a green path used in industrial production. At present, heterogeneous dehydrochlorination catalysts are facing challenge of rapid deactivation caused by released HCl and carbon deposit. In this paper, a series of supported ionic liquid catalysts (SILCs) was synthesized by wet impregnation method and applied to 1, 1, 2-trichloroethane (TCE) dehydrochlorination to produce 1, 1-dichloroethylene (VDC). Tetraarylphosphonium chlorine was the active component with the unique acid resistance and the ability to dissolve coke, which determined the activity and stability of the catalyst. For 6%Tetraphenylphosphonium chloride (TPPC)/SiO2(260 °C, WHSV = 0.19 h−1), the conversion of 1, 1, 2-TCE was ＞99.5%, selectivity of VDC was 86%, and the catalytic activity remained stable within 1100 h. Herein, highly activity for dehydrochlorination was attributed to the strong hydrogen-bond basicity of Cl-, which was decided largely by the interaction between anion and cation of ionic liquid. The reaction mechanism was investigated using FTIR, XPS, TGA-MS, XRF, DFT calculation and two step elimination model induced by alkaline active center is proposed. Such catalysts provide a viable industrial solution to gas dehydrochlorination reaction and design of heterogeneous basic catalysts.

Developing Predictive Models for Carrying Ability of Micro-Plastics towards Organic Pollutants.

Microplastics, which have been frequently detected worldwide, are strong adsorbents for organic pollutants and may alter their environmental behavior and toxicity in the environment. To completely state the risk of microplastics and their coexisting organics, the adsorption behavior of microplastics is a critical issue that needs to be clarified. Thus, the microplastic/water partition coefficient (log Kd) of organics was investigated by in silico method here. Five log Kd predictive models were developed for the partition of organics in polyethylene/seawater, polyethylene/freshwater, polyethylene/pure water, polypropylene/seawater, and polystyrene/seawater. The statistical results indicate that the established models have good robustness and predictive ability. Analyzing the descriptors selected by different models finds that hydrophobic interaction is the main adsorption mechanism, and π−π interaction also plays a crucial role for the microplastics containing benzene rings. Hydrogen bond basicity and cavity formation energy of compounds can determine their partition tendency. The distinct crystallinity and aromaticity make different microplastics exhibit disparate adsorption carrying ability. Environmental medium with high salinity can enhance the adsorption of organics and microplastics by increasing their induced dipole effect. The models developed in this study can not only be used to estimate the log Kd values, but also provide some necessary mechanism information for the further risk studies of microplastics.

Reversed phase HPLC with high temperature ethanol/water mobile phases as a green alternative method for the estimation of octanol/water partition coefficients

High temperature ethanol/water was explored as a green eluent in the reversed-phase liquid chromatographic approximation of pure water retention (log kw) and subsequent estimation of the octanol/water partition coefficient (log P) via the Collander equation and the Leave-One-Out method. As part of this work, linear solvation energy relationships were employed to compare the log kw extrapolated systems based on high temperature ethanol/water, ambient acetonitrile/water, and ambient methanol/water mobile phases. Based on the comparisons of the three organic modifiers, high temperature ethanol/water mobile phases were observed to provide the best estimation of log P. This conclusion is based on a high log P correlation of 0.968 R2 and a near unity cos θ value of 0.997 between LSER coefficient vectors of ethanol/water estimated log P and octanol/water log P systems. The method employed in this work, further, provided high correlation for the hydrogen-bonding basicity term between the two systems.

Limiting Diffusion Coefficients for Ions and Nonelectrolytes in Solvents Water, Methanol, Ethanol, Propan-1-ol, Butan-1-ol, Octan-1-ol, Propanone and Acetonitrile at 298\xa0K, Analyzed Using Abraham Descriptors

We have used literature data on the conductivity of single ions to obtain limiting diffusion coefficients (Do) of ions in water, alcohols, propanone and acetonitrile. We then used literature data on limiting diffusion coefficients of nonelectrolytes in order to set up linear free energy relationships that combine data for ions and nonelectrolytes, as log10 (Do) in the same equation, all values being at 298 K. These equations are for solvents water (N = 377, SD = 0.0474), methanol (N = 96, SD = 0.0332), ethanol (N = 96, SD = 0.0666), propan-1-ol (N = 71, SD = 0.0487), butan-1-ol (N = 53, SD = 0.0600), octan-1-ol (N = 61, SD = 0.0684), propanone (N = 86, SD = 0.0366) and acetonitrile (N = 74, SD = 0.0438) where N is the number of data points, that is ions plus nonelectrolytes, and SD is the standard deviation in log10 (Do). It is shown that solute hydrogen bond acidity, solute hydrogen bond basicity and solute volume all lower the diffusion constants of ions and nonelectrolytes in the various solvents studied.

Solute–Solvent and Solvent–Solvent Interactions and Preferential Solvation of 1,1-Diamino-2,2-dinitroethylene in Aqueous Co-solvent Mixtures of N,N-Dimethylformamide and Dimethyl Sulfoxide

The effects of solvent properties on 1,1-diamino-2,2-dinitroethylene (FOX-7) solubility were investigated from the solubility values in aqueous co-solvent mixtures of N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) in terms of the linear solvation energy relationships with use of mathCAD software. For both aqueous mixtures, the main effect of hydrogen bond basicity was observed based on the solubility variation of FOX-7. The preferential solvation (the difference in composition between the solvation shell of the solute and the bulk composition in a mixture) of FOX-7 in the two aqueous of co-solvent solutions were investigated by using the method of inverse Kirkwood–Buff integrals (IKBI). The values of the preferential solvation parameters (δx1,3) were negative in water-rich mixtures, which are − 3.103×10−2 to − 2.936 × 10−2 for DMF (1) + water (2) mixtures and − 4.470 × 10−2 to − 3.995 × 10−2 for DMSO (1) + water (2) mixtures. However, in the co-solvent compositions ranging from 0.19 or 0.21 to 1 in mole fraction of DMF or DMSO, positive values of δx1,3 were observed. The preference of FOX-7 in water-rich mixtures can be explained based on the higher acidic behavior of FOX-7 molecules, which interact with the proton–acceptor functional groups of DMF and DMSO. KAT-LSER analysis showed that only the hydrogen-bond acceptor basicity of solvents played an important role on the FOX-7 solubility owing to its two amino functional groups. The squared correlation coefficient and F-statistic values are 0.98 and 314 for DMF + water mixture, and 0.96 and 130 for DMSO + water mixture, respectively.

Improving Homogeneous Cationic Gold Catalysis through a Mechanism-Based Approach.

Homogeneous gold catalysis is regarded as a landmark addition to the field of organic synthesis. It is the most effective way to activate alkynes for the addition of a diverse host of nucleophiles. However, the literature reveals that a relatively high catalyst loading is needed in many gold-catalyzed applications (1-10 mol %), which is impractical in large-scale synthesis or multistep synthesis because of the high price and recyclization difficulty of the gold. A more thorough understanding of the factors that operate on homogeneous gold catalysis can provide better guidelines for the future design of more efficient gold-catalyzed reactions. In this Account, we will summarize our group's extensive investigation of factors impacting cationic gold catalysis, namely, the effects of ligands, counterions, additives, and catalyst decay and deactivation, using a mechanism-based approach with the aim of improving the efficiency of homogeneous gold catalysis. Through NMR-assisted kinetic studies, we investigated the above factors. Our systematic ligand effect investigation provided a clearer understanding of how ligands influence each of the three stages in the gold catalytic cycle. On the basis of this study, we synthesized a novel phosphine ligand and achieved parts per million-level gold catalysis by manipulating the electron density of the substituents and the steric strain around phosphorus. Our investigation of counterion effects led to the design of a gold affinity index and hydrogen-bonding basicity index for counterions, which can forecast the reactivity of counterions in cationic gold catalysis. We studied the adverse silver effects in cationic gold catalyst activation and proposed a more efficient practical guide. Our additive effect investigation revealed that additives that are good hydrogen-bond acceptors increase the efficiency of gold-catalyzed reactions in those occurrences where protodeauration is the rate-determining step. The first detailed experimental analysis of gold catalyst decay and the influence of each component in the reaction system (substrate, counterion, solvent) on the decay process was also conducted. We found that high-gold-affinity impurities (halides, bases) in solvents, starting materials, filtration, or drying agents decrease the reactivity of a gold catalyst but that a suitable acid activator can reactivate the gold catalyst and enable the reaction to proceed smoothly at competitively low gold catalyst loadings. The effects of acid additives were also systematically investigated using typical reactions. We are convinced that better mechanistic understandings will offer clearer guidelines for the search for more efficient gold-catalyzed reactions.

Analysis of the retention behavior of selected antiarrhythmics by means of thin-layer chromatography

The retention behavior of ivabradine, its 11 related compounds, diltiazem and verapamil has been examined by thin-layer chromatography using non-polar stationary phase (RP-18) and the following mobile phases: methanol-6.25% aqueous ammonia, tetrahydrofuran - 6.25% aqueous ammonia, and also polar stationary phase (silica gel) with tetrahydrofuran – 6.25% methanolic ammonia as mobile phase. In the examined chromatographic systems, linear relationships were established between the retention coefficients, RM0 and m, and molecular properties of the investigated antiarrhythmic drugs. The Quantitative Structure Retention Relationship (QSRR) modeling was performed with use of the stepwise multiple linear regression, in order to select the most important molecular properties which influence the retention behavior. The developed models revealed that apart from lipophilicity also the molecular volume (V), and the hydrogen bond basicity (B) of the tested compounds are the most important for the retention behavior in the examined chromatographic systems.

Is the interaction between graphene oxide and minerals reversible?

The increased applications and production of graphene oxide (GO) make the necessity to study information on the interaction of GO with minerals. In this work, adsorption and desorption were used to study the reversibility of interaction between GO and goethite/kaolinite. Result showed that the pH value, ionic strength, and temperature had significant effects on the adsorption and desorption behavior of GO. Interaction force was stronger between GO and goethite than that of kaolinite. The interaction may be attributed to the electrostatic, hydrogen-bonding, and Lewis acid base interactions. The irreversible interaction between GO and minerals may be a main mechanism for the observed desorption hysteresis. These results are important for evaluating the fate and health risk of GO in the environment.

Effect of different ionic liquids and anti-solvents on dissolution and regeneration of Miscanthus towards bioethanol

The combined effect of anions of ionic liquids (IL) and anti-solvents on pre-treatment and dissolution mechanisms of biomass are not well studied. To reveal the above effect, three different ionic liquids composed with fixed cation ([EMIM]+) but varied anions were studied for Miscanthus dissolution. Results showed that [EMIM]+[Ac]– was very good in altering the cellulose structure and crystallinity followed by enzymatic digestibility with a sugar yield of 0.98 (g/g of cellulose). The IL [EMIM]+[HSO4]– was very efficient to remove lignin and partially solubilize hemicellulose, however, the sugar yield was low (0.43 g/g of cellulose) compared with [EMIM]+[MeSO3]– and even the untreated Miscanthus. The regenerated biomass with water-acetone mixture (1:1 v/v) as anti-solvent resulted in higher glucose yield. The hydrogen bond basicity (β value) correlated well with cellulose crystallinity, lignin removal, and glucose yield.

Utilizing Water Activity as a Simple Measure to Understand Hydrophobicity in Ionic Liquids.

Ionic liquids (ILs) are regarded as designable solvents finding use in a variety of applications. One of the challenges of the design and selection process is to understand the ionic liquid properties. In this work, we selected seven ILs containing three types of hydrophilic anions and examined several key properties, which are correlated to hydrophobicity. In particular, we measured the hydrogen bond basicity β and water activity aw of IL and IL-water mixtures, and suggested that these two properties are linearly correlated particularly in hydrated ILs. We then used NMR to evaluate the chemical shift of H2O in hydrated ILs. Correlating the outcomes of each of these techniques with respect to understanding the hydrophobicity of the ILs is discussed. It is shown that water activity aw is the most facile technique to represent and understand hydrophobicity of ILs.