A combination of FTIR and DFT to study the microscopic structure and hydrogen-bonding interaction properties of the [BMIM][BF4] and water

Aqueous Ionic Liquid Mixtures as Minimal Models of Lipid Bilayer Membranes

We introduce aqueous ionic liquid (IL) mixtures, specifically mixtures of 1-butyl-3-imidazoliumtetrafluoroborate (BMImBF4), with water as a minimal model of lipid bilayer membranes. Imidazolium-based ILs are known to form clustered nanoscale structures in which local inhomogeneities, micellar or lamellar structures, are formed to shield hydrophobic parts of the cation from the polar cosolvent (water). To investigate these nanostructures, dynamic light scattering (DLS) on samples with different mixing ratios of water and BMImBF4 was performed. At mixing ratios of 50% and 45% (v/v), small and homogeneous nanostructures can indeed be detected. To test whether, in particular, these stable nanostructures in aqueous mixtures may mimic the effects of phospholipid bilayer membranes, we further investigated their interaction with myelin basic protein (MBP), a peripheral, intrinsically disordered membrane protein of the myelin sheath. Using dynamic light scattering (DLS), continuous wave (CW) and pulse electron paramagnetic resonance (EPR), and small-angle X-ray scattering (SAXS) on recombinantly produced, "healthy" charge variants rmC1WT and double cysteine variant C1S17CH85C, we find that the size and the shape of the determined nanostructures in an optimum mixture offer model membranes in which the protein exhibits native behavior. SAXS measurements illuminate the size and shape of the nanostructures and indicate IL-rich "beads" clipped together by functional MBP, one of the in vivo roles of the protein in the myelin sheath. All the gathered data combined indicate that the 50% and 45% aqueous IL mixtures can be described as offering minimal models of a lipid mono- or bilayer that allow native processing and potential study of at least peripheral membrane proteins like MBP.

Thermostability improvement of sucrose isomerase PalI NX-5: a comprehensive strategy

OBJECTIVE

To increase the thermal stability of sucrose isomerase from Erwinia rhapontici NX-5, we designed a comprehensive strategy that combines different thermostabilizing elements.

RESULTS

We identified 19 high B value amino acid residues for site-directed mutagenesis. An in silico evaluation of the influence of post-translational modifications on the thermostability was also carried out. The sucrose isomerase variants were expressed in Pichia pastoris X33. Thus, for the first time, we report the expression and characterization of glycosylated sucrose isomerases. The designed mutants K174Q, L202E and K174Q/L202E, showed an increase in their optimal temperature of 5 °C, while their half-lives increased 2.21, 1.73 and 2.89 times, respectively. The mutants showed an increase in activity of 20.3% up to 25.3%. The Km values for the K174Q, L202E, and K174Q/L202E mutants decreased by 5.1%, 7.9%, and 9.4%, respectively; furthermore, the catalytic efficiency increased by up to 16%.

CONCLUSIONS

With the comprehensive strategy followed, we successfully obtain engineered mutants more suitable for industrial applications than their counterparts: native (this research) and wild-type from E. rhapontici NX-5, without compromising the catalytic activity of the molecule.

Interfacial Water and Microheterogeneity in Aqueous Solutions of Ionic Liquids

In this work, aqueous solutions of two prototypical ionic liquids (ILs), [BMIM][BF4] and [BMIM][TfO], were investigated by UV Raman spectroscopy and small-angle neutron scattering (SANS) in the water-rich domain, where strong heterogeneities at mesoscopic length scales (microheterogeneity) were expected. Analyzing Raman data by a differential method, the solute-correlated (SC) spectrum was extracted from the OH stretching profiles, emphasizing specific hydration features of the anions. SC-UV Raman spectra pointed out the molecular structuring of the interfacial water in these microheterogeneous IL/water mixtures, in which IL aggregates coexist with bulk water domains. The organization of the interfacial water differs for the [BMIM][BF4] and [BMIM][TfO] solutions, being affected by specific anion-water interactions. In particular, in the case of [BMIM][BF4], which forms weaker H-bonds with water, the aggregation properties clearly depend on concentration, as reflected by local changes in the interfacial water. On the other hand, stronger water-anion hydrogen bonds and more persistent hydration layers were observed for [BMIM][TfO], which likely prevent changes in IL aggregates. The modeling of SANS profiles, extended to [BPy][BF4] and [BPy][TfO], evidences the occurrence of significant concentration fluctuations for all of the systems: this appears as a rather general phenomenon that can be ascribed to the presence of IL aggregation, mainly induced by (cation-driven) hydrophobic interactions. Nevertheless, larger concentration fluctuations were observed for [BMIM][BF4], suggesting that anion-water interactions are relevant in modulating the microheterogeneity of the mixture.

Structures and non-covalent interaction behaviours of binary systems containing the ionic liquid 1-(2'-hydroxylethyl)-3-methylimidazolium bis(trifluoromethylsulfonyl)imide and chloroform

Mixtures of ionic liquids (ILs) and molecular solvents can overcome the drawbacks (high viscosity, high polarity, and high cost) of pure ILs and extend their practical use. The structural and interaction properties of ILs form the bases for understanding their properties. In this work, the structural properties of the mixtures of an IL, 1-(2'-hydroxylethyl)-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C2OHMIM][Tf₂N]), with chloroform, a molecular solvent of weak polarity, in various concentrations were analysed using Fourier transform infrared spectroscopy and density functional theory calculations. Excess spectra were used to analyse the infrared spectra. The IL forms a stable ion cluster-CDCl₃ complex with CDCl₃ in the concentration range investigated. In the ion cluster-CDCl₃ complex, the hydrogen atom of CDCl₃ forms hydrogen-bonds with the fluorine atoms of the anion. In addition, the chlorine atom of CDCl₃ forms a halogen-bond with the oxygen atom of the anion. All the hydrogen and halogen-bonds identified between the [C2OHMIM][Tf₂N] ion cluster and CDCl₃ exhibit low strength, closed shells, and electrostatically dominant interactions.

Influence of Hydration on the Structure and Interactions of Ethaline Deep-Eutectic Solvent: A Spectroscopic and Computational Study

Deep-eutectic solvents (DESs) are regarded as alternative green solvents to ionic liquids. In this work we report the structural properties and hydrogen bonding (H-bonding) interactions of an aqueous DES system. The used DES, ethaline (ETH), is composed of choline chloride and ethylene glycol (EG) in 1 : 2 molar ratio. The investigations were carried out by FTIR spectroscopy combined with quantum chemical calculations. Excess spectroscopy and two-dimensional correlation spectroscopy (2D-COS) were used to explore the data in detail. The results showed that, upon mixing, ETH transforms to EG dimers and trimers and D₂ O clusters transform to various ETH-D₂ O complexes. Theoretical calculations show that water molecules insert between the anion and cation of ETH, break the strong doubly ionic Cl^-… H-O_Ch+ H-bond, share charges of the ions and form H-bond with them, thus modulate the interaction properties of ETH. This study deepens our molecular-level understanding of the system and would shed light on its applications.

Solvation of anions in acetonitrile solutions: FTIR and quantum chemical study for Br-, ClO4-, AsF6-, and CF3SO3. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2020;229:117873. [PMID: 31813727 DOI: 10.1016/j.saa.2019.117873]

Anion solvation in acetonitrile solutions was comparatively studied using FTIR spectroscopy and quantum chemical calculations at the RTF + MP2/6-311G** level of theory with solvation model density (SMD) corrections. Infrared spectra for all stable anionic complexes X^-(CH₃CN)_n (where X^- = Br^- (monatomic halide), ClO₄^- (polyatomic tetrahedral), AsF₆^- (polyatomic octahedral), CF₃SO₃^- (polyatomic ethane-like) and n = 1-8) were calculated and subsequently used in the analysis of the FTIR spectra of (Bu₄N)X and LiX acetonitrile solutions across a wide range of concentrations. Spectroscopic manifestations of solvation were established for all X^- examined. The results for all four anions under investigation were generalized to reveal the regularities of anion solvation by acetonitrile.

Excess spectroscopy and its applications in the study of solution chemistry

Characterization of structural heterogeneity of liquid solutions and the pursuit of its nature have been challenging tasks to solution chemists. In the last decade, an emerging method called excess spectroscopy has found applications in this area. The method, combining the merits of molecular spectroscopy and excess thermodynamic functions, shows the ability to enhance the apparent resolution of spectra, provides abundant information concerning solution structures and intermolecular interactions. In this review, the thinking and mathematics of the method, as well as its developments, are presented first. Then, research progress related to the exploration of the method is thoroughly reviewed. The materials are classified into two parts, small-molecular solutions and ionic liquid solutions. Finally, potential challenges and the perspective for further development of the method are discussed.

The effect of introducing an ether group into an imidazolium-based ionic liquid in binary mixtures with DMSO

Combined DFT and FTIR investigations reveal interesting hydrogen bonding interactions between dimethyl sulfoxide and an ether-functionalized imidazolium-based ionic liquid.

The structure and hydrogen-bond properties of N-alkyl-N-methyl-pyrrolidinium bis(trifluoromethylsulfonyl)imide and DMSO mixtures

Mixing ionic liquids (ILs) with molecular solvents can extend the practical applications of ILs and overcome the drawbacks of neat ILs. Knowledge on the structure and hydrogen-bond interaction properties of IL-molecular solvent mixtures is essential for chemical applications. In this work, the structure and hydrogen-bond features of N-alkyl-N-methyl-pyrrolidinium bis(trifluoromethylsulfonyl)imide ([CnMPyr][Tf2N], n = 3, 4, 6 and 8) and DMSO mixtures were studied using Fourier transform infrared spectroscopy (FTIR) and density functional theory (DFT) calculations. Excess infrared absorption spectroscopy and two-dimensional correlation spectroscopy (2D-COS) were employed to extract structural information on the mixtures from the C-D systematic stretching vibrational (νs(C-D)) region of the methyl groups in DMSO-d6. It was found that the mixing process of [CnMPyr][Tf2N] and DMSO is non-ideal and interaction complexes form between [CnMPyr][Tf2N] and DMSO-d6. They are ion cluster-DMSO-d6 complexes and ion pair-DMSO-d6 complexes. In the mixing processes, the species present in pure DMSO gradually decrease from DMSO dimer to DMSO monomer with an increase in ILs. Besides, the ion cluster-DMSO complexes gradually increase, while the ion pair-DMSO complexes decrease due to the strong electrostatic interaction between the cation and anion. In the ion cluster-DMSO complexes and ion pair-DMSO complexes, the ring hydrogen atoms of the methylene group directly attached to the nitrogen atom are the preferred interaction sites of the [CnMPyr]+ cations. All the hydrogen bonds in the identified complexes are closed-shell, electrostatically dominant and weak.