Department of Chemistry, The University of South Alabama, Mobile, Alabama 36688, United States.
Department of Chemistry and Physics, Ave Maria University, Ave Maria, Florida 34142, United States.
J Phys Chem B. 2023 Feb 16;127(6):1429-1442. doi: 10.1021/acs.jpcb.2c07872. Epub 2023 Feb 6.
The replacement of unsaturation with a cyclopropane motif as a (bio)isostere is a widespread strategy in bacteria to tune the fluidity of lipid bilayers and protect membranes when exposed to adverse environmental conditions, e.g., high temperature, low pH, etc. Inspired by this phenomenon, we herein address the relative effect of the cyclopropanation, both and configurations, on melting points, packing efficiency, and order of a series of lipid-like ionic liquids via a combination of thermophysical analysis, X-ray crystallography, and computational modeling. The data indicate there is considerable structural latitude possible when designing highly lipophilic ionic liquids that exhibit low melting points. While cyclopropanation of the lipid-like ionic liquids provides more resistance to aerobic degradation than their olefin analogs, the impact on the melting point decrease is not as pronounced. Our results demonstrate that incorporating one or more cyclopropyl moieties in long aliphatic chains of imidazolium-based ionic liquids is highly effective in lowering the melting points of such materials relative to their counterparts bearing linear, saturated, or thioether side chains. It is shown that the cyclopropane moiety effectively disrupts packing, favoring formation of conformer in the side chains, resulting in enhancement of fluidity. This was irrespective of the configuration of the methylene bridge, although marked differences in the effect of - and -monocyclopropanated ILs on the melting points were observed.
用环丙烷基取代不饱和键作为（生物）等排体是细菌中广泛使用的一种策略，可调节脂质双层的流动性，并在暴露于不利环境条件（如高温、低 pH 等）时保护膜。受此现象启发，我们通过热物理分析、X 射线晶体学和计算建模相结合的方法，研究了环丙烷化（顺式和反式）对一系列类脂离子液体的熔点、堆积效率和有序性的相对影响。数据表明，在设计具有低熔点的高亲脂性离子液体时，具有相当大的结构自由度。虽然环丙烷化的类脂离子液体比其烯烃类似物更能抵抗有氧降解，但对熔点降低的影响并不明显。我们的结果表明，在基于咪唑鎓的离子液体的长脂肪链中引入一个或多个环丙基基团，可有效地降低这些材料的熔点，与具有线性、饱和或硫醚侧链的同类物相比。结果表明，环丙烷基有效地破坏了堆积，有利于侧链中环构象的形成，从而提高了流动性。这与亚甲基桥的构型无关，尽管顺式和反式单环丙烷化 IL 对熔点的影响有明显差异。
