Hydrogen-bond Basicity Research Articles

Confining Noble Metal (Pd, Au, Pt) Nanoparticles in Surfactant Ionic Liquids: Active Non-Mercury Catalysts for Hydrochlorination of Acetylene

Metal catalysts often encounter the dilemma of rapid deactivation due to reduction or particle aggregation/growth during the reaction. Here we reported an active and stable metal nanoparticles (NPs)/surfactant ionic liquid (IL) system for the catalytic hydrochlorination of acetylene. The NPs of Pd, Au, and Pt with a narrow size distribution and well-defined lattice fringes experienced in situ generation in the reaction medium of anionic surfactant carboxylate ILs (ASC-ILs). Benefiting from the high reactivity of NPs and the self-assembly property of ASC-ILs, an effective redox cycle between Pd0 and PdII was established to reduce the deactivation of metal catalysts. The Pd NPs/surfactant IL systems showed excellent catalytic activity toward acetylene hydrochlorination. An acetylene conversion of 93% and a selectivity of 99.5% were achieved with no discernible deterioration over a reaction time of 55 h. Furthermore, ASC-ILs were endowed with a unique property of the strong hydrogen-bond basicity, which was ...

The transfer of neutral molecules from water and from the gas phase to solvents acetophenone and aniline

We have used literature data to set out equations for the transfer of neutral solutes from water and from the gas phase to the dry solvents acetophenone and aniline. The equations contain five descriptors and can be used to predict further values of the water–acetophenone, gas–acetophenone, water–aniline and gas–aniline partition coefficients for a wide range of solutes with an error of about 0.2 log units. These equations provide information about the solubility properties of the two solvents. It is shown that acetophenone behaves as a typical aprotic aromatic solvent, albeit with a rather large hydrogen-bond basicity. Aniline behaves as a hydrogen-bond acidic solvent, stronger even than ethanol solvent. Since aniline solvent is also a moderately strong hydrogen-bond base, it has rather unusual solubility properties by comparison to other aromatic solvents.

Development of Abraham model correlations for predicting enthalpies of solvation of nonionic solutes dissolved in formamide

ABSTRACTExperimental enthalpy of solution data for 81 solutes dissolved in formamide have been compiled from the published literature and converted to enthalpies of solvation data using standard thermodynamic relationships. Abraham model correlations were derived from the compiled enthalpy of solvation data. The derived mathematical equations describe the observed experimental to within overall standard deviations of 2.3 kJ mol−1. A principal component analysis based on the calculated equation coefficients, and the coefficients for water and 23 organic solvents previously determined, shows that formamide is both a hydrogen-bond acid and a hydrogen-bond base. Of the solvents that we have studied thus far, formamide is the closest to water in terms of enthalpies of solvation of dissolved solutes.

Bifacial Base-Pairing Behaviors of 5-Hydroxyuracil DNA Bases through Hydrogen Bonding and Metal Coordination.

A novel bifacial ligand-bearing nucleobase, 5-hydroxyuracil (U(OH) ), which forms both a hydrogen-bonded base pair (U(OH) -A) and a metal-mediated base pair (U(OH) -M-U(OH) ) has been developed. The U(OH) -M-U(OH) base pairs were quantitatively formed in the presence of lanthanide ions such as Gd(III) when U(OH) -U(OH) pairs were consecutively incorporated into DNA duplexes. This result established metal-assisted duplex stabilization as well as DNA-templated assembly of lanthanide ions. Notably, a duplex possessing U(OH) -A base pairs was destabilized by addition of Gd(III) ions. This observation suggests that the hybridization behaviors of the U(OH) -containing DNA strands are altered by metal complexation. Thus, the U(OH) nucleobase with a bifacial base-pairing property holds great promise as a component for metal-responsive DNA materials.

Gelation and decrystallization of cellulose by TAAHs/DMSO treatment and the role of anions and cations

Compact crystalline cellulose was structurally transformed into a loose regenerated form using treatment with tetraalkylammonium halides in dimethyl sulfoxide (TAAHs/DMSO) and gel formation using water. Swelling of cellulose was affected by the TAAHs content in DMSO and the anion and/or cation type. The cellulose swelling ratio of TAAHs/DMSO was in the order of F− > Cl− > Br− ≈ I− due to differences between hydrogen bond basicity (β) values of TAAHs/DMSO. The swelling ratio varied with the cation size of tetraalkylammonium chlorides (TAACs). For tetraalkylammonium fluorides (TAAFs), swelling ratios were all high and independent of cation size. Decrystallization of cellulose varied with the TAAHs anion and/or cation type in a pattern similar to cellulose swelling ratios. Structural transformation of cellulose, which is due to disruption of hydrogen bonds and van der Waals and hydrophobic interactions in cellulose chains and sheets by anions and cations of TAAHs, was confirmed based on FT-IR, XRD, FE-SEM, TGA, and enzymatic hydrolysis reactions.

Contributions to reversed-phase column selectivity: III. Column hydrogen-bond basicity

Column selectivity in reversed-phase chromatography (RPC) can be described in terms of the hydrophobic–subtraction model, which recognizes five solute–column interactions that together determine solute retention and column selectivity: hydrophobic, steric, hydrogen bonding of an acceptor solute (i.e., a hydrogen-bond base) by a stationary-phase donor group (i.e., a silanol), hydrogen bonding of a donor solute (e.g., a carboxylic acid) by a stationary-phase acceptor group, and ionic. Of these five interactions, hydrogen bonding between donor solutes (acids) and stationary-phase acceptor groups is the least well understood; the present study aims at resolving this uncertainty, so far as possible. Previous work suggests that there are three distinct stationary-phase sites for hydrogen-bond interaction with carboxylic acids, which we will refer to as column basicity I, II, and III.All RPC columns exhibit a selective retention of carboxylic acids (column basicity I) in varying degree. This now appears to involve an interaction of the solute with a pair of vicinal silanols in the stationary phase. For some type-A columns, an additional basic site (column basicity II) is similar to that for column basicity I in primarily affecting the retention of carboxylic acids. The latter site appears to be associated with metal contamination of the silica. Finally, for embedded-polar-group (EPG) columns, the polar group can serve as a proton acceptor (column basicity III) for acids, phenols, and other donor solutes.

Stacking geometry for non-canonical G:U wobble base pair containing dinucleotide sequences in RNA: dispersion-corrected DFT-D study.

Emergence of thousands of crystal structures of noncoding RNA molecules indicates its structural and functional diversity. RNA function is based upon a large variety of structural elements which are specifically assembled in the folded molecules. Along with the canonical Watson-Crick base pairs, different orientations of the bases to form hydrogen-bonded non-canonical base pairs have also been observed in the available RNA structures. Frequencies of occurrences of different non-canonical base pairs in RNA indicate their important role to maintain overall structure and functions of RNA. There are several reports on geometry and energetic stabilities of these non-canonical base pairs. However, their stacking geometry and stacking stability with the neighboring base pairs are not well studied. Among the different non-canonical base pairs, the G:U wobble base pair (G:U W:WC) is most frequently observed in the RNA double helices. Using quantum chemical method and available experimental data set we have studied the stacking geometry of G:U W:WC base pair containing dinucleotide sequences in roll-slide parameters hyperspace for different values of twist. This study indicates that the G:U W:WC base pair can stack well with the canonical base pairs giving rise to large interaction energy. The overall preferred stacking geometry in terms of roll, twist and slide for the eleven possible dinucleotide sequences is seen to be quite dependent on their sequences.

Phase Behavior of Aqueous Biphasic Systems Composed of Ionic Liquids and Organic Salts

This study evaluated the effects of ionic liquids (ILs) on the formation of aqueous biphasic systems (ABS) with organic salts. Phase diagrams, tie lines, and respective tie line lengths were determined at 298 K and atmospheric pressure. Using imidazolium-based ILs, the effects of the IL anions and salt anions, as well as the addition of dipolar aprotic solvents (DAS) on ABS formation were investigated. In general, the IL with hydrogen bond basicity ranging between 0.38 and 0.60 formed ABS with organic salts. However, those below this range were insoluble, and those above this range did not undergo phase separation. The salt anion capacity to induce ABS increased with increased valence and decreased Gibbs free energy of hydration. Moreover, the biphasic area for the IL-based ABS reduced with increased DAS concentration.

Computational characterization of organometallic ligands coordinating metal: Case of azopyridine ligands

Azpy (2-phenylazopyridine), Nazpy (2-pyridylazonaphtol), Mazpy (2,6-diméthyl-2-phenylazopyridine) and Dazpy (2-phenylazo-4,6-dimethylpyridine) are four pyridylazo ligands that are characterized by density functional theory (DFT) theoretical investigation either in gas or in condensed phases. As they display at least three heteroatoms donors of electrons, hydrogen bond basicity has been experimented via energy and geometrical descriptors to determine which of the donors will link to metal so as to form metallic complexes. The pyridinic Nitrogen ( N py ) and that close to the substituent linked to azo group ( N 2) are the most available with almost the same energy to authorize coordination with metal. Before, prediction of Azpy synthesis was undertaken. 1H NMR was also performed. They showed that the conformational trans or E2-azpy was the most stable existing ligand. Nonetheless, this structure undergoes a modification on behalf of the conformational cis or E1-azpy that is the suitable ligand to provide with two nitrogen atoms with the same energy. Regarding this observation, all calculations were undertaken on the conformational E1 of each pyridylazo ligand. Therefore, the results obtained were consistent with the experimental analysis confirming that all of the four ligands are bidentates. In consequence, all the pyridylazo ligands can be assumed to connect to the metal by two nitrogen atoms forming five membered ring regardless the azo group's substituent nature.

Experimental and theoretically study of interaction between organic compounds and tricyanomethanide based ionic liquids

Activity coefficients at infinite dilution (γ1,2∞) for 35 solutes in two new tricyanomethanide containing Ionic Liquids were measured by inverse gas chromatography at temperatures from (318.15 to 368.15)K. Most organic compounds have stronger affinity with 1-butyl-4-methylpyridinium tricyanomethanide than 1-butyl-3-methylimidazolium tricyanomethanide. The retention data were further converted to gas-to-IL and analyzed using the Abraham solvation parameter model. The LSER treatment indicates that the most dominant interaction constants for this family of ILs are strong dipolarity, hydrogen bond basicity and acidity. Quantum chemical gas phase DFT calculations were performed on isolated ion pairs at the 6-311 ++ G(d,p) level basis. It was found that the stacking structure of cation and anion is compact in the [BMIM][TCM] system and relatively loose in the [BMPY][TCM] system allowing a facile restructuring of the ionic liquid [BMPY][TCM] in the process of organic compounds dissolution.

The effect of changing the components of an ionic liquid upon the solubility of lignin

Changing the cation of an ionic liquid was shown to have a significant effect on lignin solubility, with interaction of aromatic cations with the solute being significant. The effect of the anion on lignin solubility was negligible, above a minimum hydrogen bond basicity.

Contact angles and wettability of ionic liquids on polar and non-polar surfaces.

Many applications involving ionic liquids (ILs) require the knowledge of their interfacial behaviour, such as wettability and adhesion. In this context, herein, two approaches were combined aiming at understanding the impact of the IL chemical structures on their wettability on both polar and non-polar surfaces, namely: (i) the experimental determination of the contact angles of a broad range of ILs (covering a wide number of anions of variable polarity, cations, and cation alkyl side chain lengths) on polar and non-polar solid substrates (glass, Al-plate, and poly-(tetrafluoroethylene) (PTFE)); and (ii) the correlation of the experimental contact angles with the cation-anion pair interaction energies generated by the Conductor-like Screening Model for Real Solvents (COSMO-RS). The combined results reveal that the hydrogen-bond basicity of ILs, and thus the IL anion, plays a major role through their wettability on both polar and non-polar surfaces. The increase of the IL hydrogen-bond accepting ability leads to an improved wettability of more polar surfaces (lower contact angles) while the opposite trend is observed on non-polar surfaces. The cation nature and alkyl side chain lengths have however a smaller impact on the wetting ability of ILs. Linear correlations were found between the experimental contact angles and the cation-anion hydrogen-bonding and cation ring energies, estimated using COSMO-RS, suggesting that these features primarily control the wetting ability of ILs. Furthermore, two-descriptor correlations are proposed here to predict the contact angles of a wide variety of ILs on glass, Al-plate, and PTFE surfaces. A new extended list is provided for the contact angles of ILs on three surfaces, which can be used as a priori information to choose appropriate ILs before a given application.

Long-Chain Fatty Acid-Based Phosphonium Ionic Liquids with Strong Hydrogen-Bond Basicity and Good Lipophilicity: Synthesis, Characterization, and Application in Extraction

The development of ionic liquids (ILs) with strong hydrogen-bond basicity is of great importance for the application of ILs in liquid–liquid extractions, but a long-standing problem is that the increase in hydrogen-bond basicity of ILs usually comes along with undesired changes in other properties such as reduced lipophilicity, raised melting point, and difficulty of forming biphasic systems with water. Herein, we provided a promising solution to this problem by synthesizing a class of functional phosphonium ILs with the use of biocompatible saturated/unsaturated long-chain fatty acids (carbon number up to 20) as anion precursors, and we also carried out systematic investigations on their physicochemical properties. These long-chain fatty acid ILs (LCFA-ILs) featured very strong hydrogen-bond basicity, up to the top level of all reported solvents, along with good lipophilicity and a wide liquid range. Moreover, the viscosity of LCFA-ILs exhibited only a slight increase with increasing chain length, and th...

Solvatochromic Parameters of the Binary Mixtures of Imidazolium Chloride Ionic Liquid Plus Molecular Solvent

Imidazolium-based chloride ionic liquids (ILs) have exhibited remarkable performance in several important applications such as biomass dissolution and extraction, but their large viscosity is a non-negligible problem. Adding molecular co-solvents into chloride ILs is effective in reducing viscosity; nevertheless, understanding of the accompanied change of thermodynamic polarity is quite few. Therefore, in this work we reported three Kamlet-Taft solvatochromic parameters, including dipolarity/polarizability π*), hydrogen-bond acidity (α) and hydrogen-bond basicity (β), for the binary mixtures of several imidazolium-based chloride ILs plus either dipolar protic solvents (water and methanol) or dipolar aprotic solvents (dimethyl sulfoxide, N,N-dimethylformamide and acetonitrile). The results demonstrated that those parameters could be altered by the structure of IL and type of co-solvent owing to the solute-solvent and solvent-solvent interactions. The structure of alkyl chain of cation had considerable impact on the π* variation of IL aqueous solution against IL concentration but hardly affected other mixtures. Moreover, remarkable preferential solvation of probes was observed for β and α in the mixtures of IL and dipolar aprotic co-solvents, whereas the hydrogen-bond interactions between IL and dipolar protic co-solvent enabled the preferential solvation to be alleviated and resulted in more linear variation of β and α against the molar fraction of IL. The results not only contribute to a better understanding of the effect of co-solvent on imidazolium-based chloride ILs, but also are instructive for improving the thermodynamic performance of IL-based applications via providing IL+co-solvent mixtures with desirable physicochemical properties.

Physical Ionic Liquid/Polysiloxane Mixtures for Tuning the Polarity and the Selectivity of the Polysiloxane Stationary Phase for GC Analysis

Two novel room-temperature ionic liquids (RTILs), a mono-cationic (tetra-n-octylammonium) and a dicationic (bis-methylpiperidinium-butylidene) room-temperature ionic liquid with the bis[(trifluoromethyl)sulfonyl]imide anion, were individually mixed with OV-1701 polysiloxane to tune the selectivity and the polarity of stationary phases for GC. The interaction properties of the stationary phases were investigated on the basis of polarity calculations and the linear solvation energy relationship. The incorporation of the monocationic RTIL in the OV-1701 increased the dipolarity/polarizability capacities (s) and the hydrogen-bond basicity ability (a) allowing the separation of the m-chloroaniline/p-chloroaniline isomers and the m-xylene/p-xylene isomers which are not usually separated on polysiloxane stationary phase. The mixed stationary phases exhibited a greater selectivity than the OV-1701 phase for the majority of the aromatic compounds tested, demonstrating a kind of synergistic effect of the combination of polysiloxane and RTIL. The addition of RTIL proved to be an original method to modulate the polarity and the selectivity of the stationary phase of intermediate polarity in order to prepare stationary phases dedicated for specific separation with good durability (more than 20 months and more than 1,000 injections) and without any loss of thermal stability.

Determination and Correlation of Solubility of Nonivamide in Different Solvents

The solubility of nonivamide in dimethyl sulfoxide, methanol, acetone, ethyl acetate, methyl tert-butyl ether, acetonitrile, n-hexane and water over the temperature range of 293.2K to 323.2K was measured. The results reveal that the solubility of nonivamide is greatly influenced by the hydrogen-bond basicity of solvent and increases with temperature. The experimental data were correlated with the modified Apelblat equation. The dissolution enthalpy and entropy of nonivamide in different solvents were obtained from the correlation of lnx with 1/T using the van't Hoff equation. The calculated nonivamide solubility is in good agreement with experimental data for most of the solvents.

Rapid evaluation of the interaction energies for hydrogen-bonded uracil and thymine dimers, trimers and tetramers

Hydrogen bonds play an important role in the self-assembled processes of nucleic acid bases. The ability to rapidly and accurately evaluate the interaction energy for hydrogen-bonded nucleic acid base pairs and multimers is critical for correctly understanding the mechanism underlying the assembly and modeling the self-assembled processes of nucleic acid bases. In this paper, the polarizable dipole–dipole interaction model is developed and applied to hydrogen-bonded uracil and thymine base dimers, trimers and tetramers. We regard the chemical bonds NH, CH and CO in uracil and thymine as bond dipoles. The magnitude of the bond dipole moment varies according to its environment. The parameters needed are first determined from the training dimers. Then the polarizable dipole–dipole interaction model together with the parameters is applied to a series of hydrogen-bonded uracil and thymine base dimers, trimers and tetramers. The hydrogen bond distances and the interaction energies obtained from the polarizable dipole–dipole interaction model are compared to those obtained from MP2 calculations. The calculation results show that the polarizable dipole–dipole interaction model produces the equilibrium hydrogen bond distances compared well with those yielded by the MP2/6-31G(d) method and produces the interaction energies in good agreement with those yielded by the counterpoised-corrected MP2/6-311++G(3df,2p) method, demonstrating that the polarizable dipole–dipole interaction model is reasonable and useful.

A theoretical study of the thermodynamic and hydrogen-bond basicity of TEMPO radical and related nitroxides

The use of B3LYP/6-311++G(d,p) and MP2/6-311++G(d,p) calculations on TEMPO and four related nitroxide radicals having another oxygen functionality (ketone, hydroxyl and ether) has allowed to determine the relative basicities (thermodynamic and hydrogen-bonded) of the oxygen lone pair relative to the nitroxide radical. The differences are small, especially the B3LYP ones, but in all cases they favor the radical. This is consistent with experimental results in the case of the hydroxyl group but not in the case of the keto group.

Fluorescence interaction and determination of sulfathiazole with trypsin.

The mechanism of interaction of trypsin with the sulfathiazole was studied through using fluorescence quenching and UV-visible absorption spectra at pH 7.4. The Stern-Volmer quenching constants, binding constants, number of binding sites and the corresponding thermodynamic parameters ΔH(o), ΔS(o) and ΔG(o) were calculated at different temperatures. The effect of common metal ions on the constants was also discussed. The results suggest that sulfathiazole can interact strongly trypsin and that there is the formation of trypsin-sulfathiazole complex and the interaction can be explained on the basis of hydrogen bonds and van der Waals forces. The binding distance (r) between the donor (trypsin) and acceptor (sulfathiazole) was 3.52 nm based on the Förster's non-radiative energy transfer theory. The detection and quantification limits of sulfathiazole were calculated as 2.52 and 8.40 μM in the presence of trypsin, respectively. The relative standard deviation (RSD) was 4.086% for determinations (n = 7) of a sulfathiazole solution with the concentration of 7.54 μM.

Experimental and theoretical study of interaction between organic compounds and 1-(4-sulfobutyl)-3-methylimidazolium based ionic liquids

Activity coefficients at infinite dilution (γ1,2∞) for diverse probe solutes in three homologous 1-(4-sulfobutyl)-3-methylimidazolium based ionic liquids were measured by inverse gas chromatography at temperatures from 323 to 343K. Accordingly, this family of ionic liquid can be ranked according to their interaction with organic compounds as follows: [HSO4]≪[OTf]≪[N(Tf)2]. The retention data were further converted to gas-to-IL and analyzed using the Abraham solvation parameter model. The LSER treatment indicates that the most dominant interaction constants for this family of ILs are strong dipolarity, hydrogen bond basicity and acidity. Then, the ChelpG atomic charges on the cation and the anions obtained by ab initio calculations are used to explain the interactions between methanol, thiophene and benzene and the anions or the cation.