Hydrogen-Bonding and the Dissolution Mechanism of Uracil in an Acetate Ionic Liquid: New Insights from NMR Spectroscopy and Quantum Chemical Calculations

Facile synthesis of self-healing and layered sodium alginate/polyacrylamide hydrogel promoted by dynamic hydrogen bond

Hydrogels are widely used in many fields but generally suffer from low mechanical strength and poor self-healing performance. Here, a novel and facile method was developed to prepare a semi-interpenetrating polymer network (semi-IPN) hydrogel with layered structure and improved properties based on sodium alginate (SA) and polyacrylamide (PAM). Systematic characterizations revealed a formation mechanism of layered structure via hydrogen bonds (HBs) promoted self-assembly of SA in the porous PAM matrix. Also, HBs can also display a key role in enhancing self-healing of the hydrogel, by which the hydrogel possesses a self-healing capacity of 99 % with sprayed by a few of water. Moreover, the layered semi-IPN structure makes the tensile strength of PAMSA hydrogel reach 266 kPa. The fabricated PAMSA hydrogel with layered microstructure containing SA provides a protocol to broaden the functionality and variety of the hydrogels.

Recent advances in ionic liquids and nanotechnology for drug delivery

In drug discovery and drug development, it is estimated that around 40% of commercialized and 90% of under-study drugs have inadequate pharmaceutical properties, severely impairing its therapeutic efficacy. Thus, there is a strong demand to find strategies to enhance the delivery of such drugs. Ionic liquids are a novel class of liquids composed of a combination of organic salts that are of particular interest alone or in combination with drug delivery systems. This review is focused on the recent efforts using ionic liquids in drug solubility, formulation and drug delivery with specific emphasis on nanotechnology. The latest developments using hybrid delivery systems obtained upon the combination of drug delivery systems and ionic liquids will also be addressed.

Association of Nucleobases in Hydrated Ionic Liquid from Biased Molecular Dynamics Simulations

We employed metadynamics-based classical molecular dynamics simulations to methylated adenine-thymine (mA-mT) and guanine-cytosine (mG-mC) base pairs to see favorable conformations in various concentrations of hydrated 1-ethyl, 3-methyl imidazolium acetate. We investigated various stacked and hydrogen-bonded conformations of association of base pairs through appropriately chosen collective variables. Stacked conformations more favored in water for both base pairs, whereas Watson-Crick (WC) hydrogen-bonding conformations are favored in pure and hydrated ionic liquids (ILs) except for 0.75 mol fraction IL. We observe that EMIm cations surround the base pairs in WC conformations creating a kind of hydrophobic cavity and protect the hydrogen bonds between base pairs. However, the five-membered heteroaromatic rings of cations stack with the nucleobases in the cation-base-cation (π-π-π) model, which resembles the base-base-base stacking in a DNA duplex. Interestingly, from additional simulations of 0.5 mol fraction hydrated choline dihydrogen phosphate IL, we observe that the stacked conformations become more favored than the WC conformation due to the absence of π-bonds in cations. The calculated values of relative solubility of base pairs in pure and hydrated ionic liquids compared to those in pure water correlate well with the free energy values of WC and stacked conformations.

Biosolvation Nature of Ionic Liquids: Molecular Dynamics Simulation of Methylated Nucleobases in Hydrated 1-Ethyl-3-methylimidazolium Acetate

Solvation free energies of methylated nucleobases were calculated in pure and hydrated 1-ethyl-3-methylimidazolium acetate, [Emim][Ac], ionic liquid, and pure water using classical molecular dynamics simulations using multistate Bennett's acceptance ratio method. The calculated solvation free energies in pure water were compared with the previous experimental and theoretical findings and found to be in agreement. We observe that the solvation free energy of methylated nucleobases is more in the pure ionic liquid compared to that in the pure water and on changing the mole fraction of water in the ionic liquid, the solvation free energy decreases gradually. Comparing the Coulombic and van der Waals contribution to the solvation free energy, electrostatic contribution is more compared to that of the latter for all nucleobases. To obtain the atomistic details and explain the solvation mechanism, we calculated radial distribution functions (RDFs), spatial distribution functions (SDFs), and stacking angle distribution of cations to the nucleobases. From RDFs and SDFs, we find that the acetate anions of the ionic liquid are forming strong hydrogen bonds with the amine hydrogen atoms of the nucleobases. These hydrogen bonds contribute to the major part of the Coulombic contribution to the solvation free energy. Stacking of cations to the nucleobases is primarily due to the van der Waals contribution to the solvation free energy.

Design of task-specific fluorinated ionic liquids: nanosegregation versus hydrogen-bonding ability in aqueous solutions

Fluorinated ionic liquids rich-nanosegregated behaviour reduces the impact of the addition of water upon the ionic liquids's H-bond acceptance ability.

Controlled stabilization of anionic forms of the uracil derivatives: A DFT study

Relative stabilities of the N1/N3/О5/О6 anions of 42 substituted uracils in gas phase and aqueous solutions have been theoretically studied using approximation IEFPCM (SMD) - TPSS/aug-cc-pVTZ. The specific solvation of uracil and its anions has been simulated with the first hydrate shell made up with 5 water molecules. The nonspecific solvation has been accounted in terms of the SMD model. We have found a series of relative stability under conditions of both specific and nonspecific hydration. The series is ranked according to the increase of the relative stability of the N3 anion. In gas phase, the N1 anion is significantly more stable than its N3 counterpart: the ΔG_gas values vary in the range from 19.54 (5OH6СН₃U) to 83.14 (5NO₂6NH₂U) kJ/mol that is caused by a more effective delocalization of the excess charge through the uracil framework in the N1 anion. The hydration pronouncedly diminishes ΔG to the range from -0.02 (5OH6СН₃U) to 38.16 (5Br6NO₂U) kJ/mol due to the fact that the polar solvent is prone to stabilize more polar anionic states of uracils. Therefore, less polar uracil anions are more stable. We have defined the main factor influencing the N1/N3/О5/О6 distribution of anions, viz. the presence of the substituents in 5 and 6 positions of the pyrimidine ring. Herewith, the most favorable mechanism of the influence of 5-substituents has been previously defined as resonant whereas, as we found in this work, the inductive mechanism is more pronounced in the case of 6-substituents.

Facile Cellulose Dissolution and Characterization in the Newly Synthesized 1,3-Diallyl-2-ethylimidazolium Acetate Ionic Liquid

A facile cellulose solvent 1,3-diallyl-2-ethylimidazolium acetate ([AAeim][OAc]) with high electrical conductivity has been designed and synthesized for the first time, via a quaternization reaction and ion exchange method. The dissolution characteristics of cellulose in this solvent were studied in detail. Meanwhile, the co-solvent system was designed by adding an aprotic polar solvent dimethyl sulfoxide (DMSO) in [AAeim][OAc]. The effects of temperature and the mass ratio of DMSO to [AAeim][OAc] on the solubility of cellulose were studied. Furthermore, the effects of regeneration on the molecular structure and thermal stability of cellulose were determined by Fourier transform infrared spectroscopy (FT-IR), thermal gravity analysis (TGA) and X-ray diffraction (XRD). The findings revealed that the synthesized ionic liquid (IL) has a relatively low viscosity, high conductivity and a good dissolving capacity for bamboo dissolving pulp cellulose (Degree of Polymerization: DP = 650). The macromolecular chain of the cellulose is less damaged during the dissolution and regeneration process. Due to the increased number of “free” anions [OAc]⁻ and cations [AAeim]⁺, the addition of DMSO can significantly increase the solubility of the cellulose up to 12 wt % at the mass ratio of 3:1, indicating that the synthesized IL has a potential application in the electrospinning field.

Solvation Structure of Uracil in Ionic Liquids

The local solvation environment of uracil dissolved in the ionic liquid 1-ethyl-3-methylimidazolium acetate has been studied using neutron diffraction techniques. At solvent:solute (ionic liquid:uracil) ratios of 3:1 and 2:1, little perturbation of the ion-ion correlations compared to those of the neat ionic liquid are observed. We find that solvation of the uracil is driven predominantly by the acetate anion of the solvent. While short distance correlations exist between uracil and the imidazolium cation, the geometry of these contacts suggest that they cannot be considered as hydrogen bonds, in contrast to other studies by Araújo et al. (J. M. Araújo, A. B. Pereiro, J. N. Canongia-Lopes, L. P. Rebelo, I. M. Marrucho, J. Phys. Chem. B 2013, 117, 4109-4120). Nevertheless, this combination of interactions of the solute with both the cation and anion components of the solvents helps explain the high solubility of the nucleobase in this media. In addition, favourable uracil-uracil contacts are observed, of similar magnitude to those between cation and uracil, and are also likely to aid dissolution.

Protonic Ammonium Nitrate Ionic Liquids and Their Mixtures: Insights into Their Thermophysical Behavior

This study is centered on the thermophysical characterization of different families of alkylammonium nitrate ionic liquids and their binary mixtures, namely the determination at atmospheric pressure of densities, electric conductivities and viscosities in the 288.15 < T/K < 353.15 range. First, measurements focusing on ethylammonium, propylammonium and butylammonium nitrate systems, and their binary mixtures, were determined. These were followed by studies involving binary mixtures composed of ethylammonium nitrate (with three hydrogen bond donor groups) and different homologous ionic liquids with differing numbers of hydrogen bond donor groups: diethylammonium nitrate (two hydrogen bond donors), triethylammonium nitrate (one hydrogen bond donor) and tetraethylammonium nitrate (no hydrogen bond donors). Finally, the behavior of mixtures with different numbers of equivalent carbon atoms in the alkylammonium cations was analyzed. The results show a quasi-ideal behavior for all monoalkylammonium nitrate mixtures. In contrast, the other mixtures show deviations from ideality, namely when the difference in the number of carbon atoms present in the cations increases or the number of hydrogen bond donors present in the cation decreases. Overall, the results clearly show that, besides the length and distribution of alkyl chains present in a cation such as alkylammonium, there are other structural and interaction parameters that influence the thermophysical properties of both pure compounds and their mixtures.

High Nucleobase-Solubilizing Ability of Low-Viscous Ionic Liquid/Water Mixtures: Measurements and Mechanism

Research on nucleobases has always been on the forefront owing to their ever-increasing demand in the pharmaceutical, agricultural, and other industries. The applications, however, became limited due to their poor solubility in water. Recently, ionic liquids (ILs) have emerged as promising solvents for nucleobase dissolution, as they exhibit >100-fold increased solubility compared to water. But the high viscosity of ILs remains as a bottleneck in the field. Here, by solubility and viscosity measurements, we show that addition of low-to-moderate quantity of water preserves the high solubilizing capacity of ILs, while reducing the viscosity of the solution by several folds. To understand the mechanism of nucleobase dissolution, molecular dynamics simulations were carried out, which showed that at low concentrations water incorporates into the IL-nucleobase network without much perturbing of the nucleobase-IL interactions. At higher concentrations, increasing numbers of IL anion-water hydrogen bonds replace IL-nucleobase interactions, which have been confirmed by (1)H- and (13)C NMR chemical shifts of the IL ions.

Dual functionality of amphiphilic 1-alkyl-3-methylimidazolium hydrogen sulfate ionic liquids: surfactants with catalytic function

A series of amphiphilic 1-alkyl-3-methylimidazolium hydrogen sulfate ILs were synthesized. Their co-catalytic activities have been determined and discussed in terms of their structure and surface properties.

Glucosamine condensation catalyzed by 1-ethyl-3-methylimidazolium acetate: mechanistic insight from NMR spectroscopy

[C₂C₁Im][OAc] could efficiently catalyze GlcNH₂ into deoxyfructosazine (DOF) and fructosazine (FZ), and the underlying catalysis mechanism was investigated by NMR spectroscopy.

Multiscale modeling of the trihexyltetradecylphosphonium chloride ionic liquid

Hierarchical trihexyltetradecylphosphonium cationic and chloride anionic models.

Cholinium-based ionic liquids with pharmaceutically active anions

Ionic liquids with cholinium-based active pharmaceutical ingredients (API-ILs) were preparedviaa simple and sustainable two-step anion exchange reaction. The resulting salts have improved upon the chemical, physical and biopharmaceutical properties of the parent APIs.