Nanoscale organization of ionic liquids and their interaction with peptides probed by 13C NMR spectroscopy

Validation of Structural Grounds for Anomalous Molecular Mobility in Ionic Liquid Glasses

Ionic liquid (IL) glasses have recently drawn much interest as unusual media with unique physicochemical properties. In particular, anomalous suppression of molecular mobility in imidazolium IL glasses vs. increasing temperature was evidenced by pulse Electron Paramagnetic Resonance (EPR) spectroscopy. Although such behavior has been proven to originate from dynamics of alkyl chains of IL cations, the role of electron spin relaxation induced by surrounding protons still remains unclear. In this work we synthesized two deuterated imidazolium-based ILs to reduce electron-nuclear couplings between radical probe and alkyl chains of IL, and investigated molecular mobility in these glasses. The obtained trends were found closely similar for deuterated and protonated analogs, thus excluding the relaxation-induced artifacts and reliably demonstrating structural grounds of the observed anomalies in heterogeneous IL glasses.

Solvation structure of poly-m-phenyleneisophthalamide (PMIA) in ionic liquids

Polyaramids are a class of high-performance polymers, known for their high mechanical strength and chemical and thermal stability. Their ability to create a network of intermolecular hydrogen bonds causes them to be very poorly soluble in conventional solvents. Hazardous solvents such as N-methylpyrrolidone (NMP) and dimethylacetamide (DMA), in combination with an inorganic salt such as CaCl2, are currently used for the synthesis and processing of polyaramids. Ionic liquids are proposed as suitable greener alternatives. In this work, we studied the solubility and dissolution mechanism of the meta-oriented polyaramid poly-m-phenyleneisophthalamide (PMIA) in a wide range of ionic liquids. It was found that, similarly to cellulose, PMIA could be dissolved readily and in large amounts in ionic liquids containing a strongly coordinating anion (such as chloride, acetate and dialkylphosphate) and an imidazolium cation. Hydrogen bonding between the anion and the amide NH of PMIA is the main solvent-solute interaction. An odd-even effect in solubility occurred when altering the length of the side chains on the imidazolium cation. Furthermore, it was found that the presence of hydrogen bond donating CH moieties on the cation is a necessary condition for dissolution. The exact role of these hydrogen bond donors was investigated by FTIR and 13C NMR spectroscopy. It was found that there is no significant interaction between the hydrogen atoms of the imidazolium ring and the amide carbonyl groups. Rather, the hydrogen bond donors are needed to stabilize the solvation shell around PMIA through alternating cation-anion interactions.

Structural Anomalies in Ionic Liquids near the Glass Transition Revealed by Pulse EPR

Unusual physical and chemical properties of ionic liquids (ILs) open up prospects for various applications. We report the first observation of density/rigidity heterogeneities in a series of ILs near the glass transition temperature ( T_g) by means of pulse electron paramagnetic resonance (EPR). Unprecedented suppression of molecular mobility is evidenced near the glass transition, which is assigned to unusual structural rearrangements of ILs on the nanometer scale. Indeed, pulse and continuous wave EPR clearly indicate the occurrence of heterogeneities near T_g, which exist in a rather broad temperature range of ∼50 K. The two types of local environments are evidenced, being drastically different by their stiffness. The more rigid one suppresses molecular mobility, whereas the softer one instead promotes diffusive molecular rotation. Such properties of ILs near T_g are of general importance; moreover, the observed density/rigidity heterogeneities controlled by temperature might be considered as a new type of tunable reaction nanoenvironment.

"Solvent-in-salt" systems for design of new materials in chemistry, biology and energy research

Inorganic and organic "solvent-in-salt" (SIS) systems have been known for decades but have attracted significant attention only recently. Molten salt hydrates/solvates have been successfully employed as non-flammable, benign electrolytes in rechargeable lithium-ion batteries leading to a revolution in battery development and design. SIS with organic components (for example, ionic liquids containing small amounts of water) demonstrate remarkable thermal stability and tunability, and present a class of admittedly safer electrolytes, in comparison with traditional organic solvents. Water molecules tend to form nano- and microstructures (droplets and channel networks) in ionic media impacting their heterogeneity. Such microscale domains can be employed as microreactors for chemical and enzymatic synthesis. In this review, we address known SIS systems and discuss their composition, structure, properties and dynamics. Special attention is paid to the current and potential applications of inorganic and organic SIS systems in energy research, chemistry and biochemistry. A separate section of this review is dedicated to experimental methods of SIS investigation, which is crucial for the development of this field.

Biological Activity of Ionic Liquids and Their Application in Pharmaceutics and Medicine

Ionic liquids are remarkable chemical compounds, which find applications in many areas of modern science. Because of their highly tunable nature and exceptional properties, ionic liquids have become essential players in the fields of synthesis and catalysis, extraction, electrochemistry, analytics, biotechnology, etc. Apart from physical and chemical features of ionic liquids, their high biological activity has been attracting significant attention from biochemists, ecologists, and medical scientists. This Review is dedicated to biological activities of ionic liquids, with a special emphasis on their potential employment in pharmaceutics and medicine. The accumulated data on the biological activity of ionic liquids, including their antimicrobial and cytotoxic properties, are discussed in view of possible applications in drug synthesis and drug delivery systems. Dedicated attention is given to a novel active pharmaceutical ingredient-ionic liquid (API-IL) concept, which suggests using traditional drugs in the form of ionic liquid species. The main aim of this Review is to attract a broad audience of chemical, biological, and medical scientists to study advantages of ionic liquid pharmaceutics. Overall, the discussed data highlight the importance of the research direction defined as "Ioliomics", studies of ions in liquids in modern chemistry, biology, and medicine.

Microscopic rigidity and heterogeneity of ionic liquids probed by stochastic molecular librations of the dissolved nitroxides

We propose a new potent approach for studying nano/microscopic heterogeneities in ionic liquids exploiting stochastic librations of nitroxides and pulse EPR.

Direct Observation of Self-Organized Water-Containing Structures in the Liquid Phase and Their Influence on 5-(Hydroxymethyl)furfural Formation in Ionic Liquids

Water-containing organic solutions are widespread reaction media in organic synthesis and catalysis. This type of multicomponent liquid system has a number of unique properties because of the tendency for water to self-organize in mixtures with other liquids. The characterization of these water domains is a challenging task because of their soft and dynamic nature. In the present study, the morphology and dynamics of micrometer- and nanometer-scale water-containing compartments in ionic liquids were directly observed by electron microscopy. A variety of morphologies, including isolated droplets, dense structures, aggregates, and 2D meshworks, have been experimentally detected and studied. Using the developed method, the impact of water on the acid-catalyzed biomass conversion reaction was studied at the microscopic level. The process that produced nanostructured domains in solution led to better yields and higher selectivities compared with reactions involving the bulk system.

An unexpected increase of toxicity of amino acid-containing ionic liquids

The influence of the structure of cations and anions on the biological activity of ionic liquids is addressed.