Rogers Ciarán J, Koutsoukos Spyridon, Eisermann Jana, Wylie Luke, Smith Gavin J, Welton Tom, Roessler Maxie M
Department of Chemistry, Imperial College London, Molecular Sciences Research Hub, London, W12 0BZ, UK.
Centre for Pulse EPR Spectroscopy (PEPR), Imperial College London, Molecular Sciences Research Hub, London, W12 0BZ, UK.
Angew Chem Int Ed Engl. 2025 Jul 7;64(28):e202504882. doi: 10.1002/anie.202504882. Epub 2025 May 10.
Ionic liquids (ILs) are a unique class of compounds that have attracted interest for numerous and diverse applications, ranging from solvents for sustainable synthesis to sustainable electrolytes. Understanding their nanostructure and solute-solvent interactions is a prerequisite to harnessing the full potential of ILs. It has been proposed that ILs solvate non-polar solutes via their alkyl chains through the formation of nanoscale structures, such as micelles. Here, we determine the non-covalent interactions responsible for such nanostructuring in ILs. We use pulse electron paramagnetic resonance (EPR), paramagnetic relaxation enhancement (PRE) NMR, molecular dynamics (MD), and density functional theory (DFT) calculations in combination with ILs tailored to probe specific interactions through spin and isotopic labelling. Inter- and intramolecular cation-anion interactions are probed by electron-nuclear double resonance (ENDOR) and F PRE experiments and show that nitroxide solutes associate with the polar domains of the imidazolium cation through weak hydrogen bonding with the imidazolium ring protons, as supported by MD simulations. Thus, this study reveals a less structured nanostructure than a micellar picture might suggest, but with clear IL cation-solute interactions. Our methodology to reveal nanostructure not only has implications for ILs but is also applicable to other soft matter systems.
离子液体（ILs）是一类独特的化合物，已在众多不同的应用中引起了人们的兴趣，从可持续合成的溶剂到可持续电解质。了解它们的纳米结构和溶质 - 溶剂相互作用是充分发挥离子液体潜力的先决条件。有人提出，离子液体通过形成纳米级结构（如胶束），经由其烷基链溶剂化非极性溶质。在此，我们确定了导致离子液体中这种纳米结构形成的非共价相互作用。我们结合使用脉冲电子顺磁共振（EPR）、顺磁弛豫增强（PRE）核磁共振、分子动力学（MD）和密度泛函理论（DFT）计算，并使用通过自旋和同位素标记来探测特定相互作用的定制离子液体。通过电子 - 核双共振（ENDOR）和F PRE实验探测分子间和分子内的阳离子 - 阴离子相互作用，结果表明，如分子动力学模拟所支持的那样，氮氧化物溶质通过与咪唑环质子的弱氢键与咪唑阳离子的极性域缔合。因此，本研究揭示了一种比胶束模型所暗示的结构更松散的纳米结构，但存在明显的离子液体阳离子 - 溶质相互作用。我们揭示纳米结构的方法不仅对离子液体有影响，也适用于其他软物质系统。
