A Comprehensive Study on Lyotropic Liquid–Crystalline Behavior of an Amphiphile in 20 Kinds of Amino Acid Ionic Liquids

Abstract

We examined the self-organization behavior of a designed amphiphilic molecule in 20 kinds of amino acid ionic liquids composed of 1-butyl-3-methylimidazolium cation and natural amino acid anion ([C4mim][AA]). Addition of [C4mim][AA], regardless of their anion species, to the amphiphile provided homogeneous mixtures showing lyotropic liquid-crystalline (LC) behavior. Upon increasing the component ratio of [C4mim][AA] in the mixtures, a successive change of the mesophase patterns from inverted hexagonal columnar, in some case via bicontinuous cubic, to layered phases was observed. By examining the LC properties at various temperatures and component ratios, we constructed lyotropic LC phase diagrams. Interestingly, the appearance of these phase diagrams is greatly different according to the selection of [AA]. Through comparison, we found that the self-organization behavior of an amphiphile in ionic liquids can be tuned by controlling their ability to form hydrogen-bond, van der Waals, and π-π interactions.

Ionic liquid crystals based on amino acids and gemini surfactants: tunable phase structure, circularly polarized luminescence and emission color

“…4d), implying the appearance of a blended columnar mesophase. This phenomenon may be ascribed to the weak hydrogen-bonding ability of Ile caused by its sterically bulky group, 45 which impeded the formation of ordered LC structures.…”

“…44 Moreover, it has been proven that amino acids can participate in the construction of lyotropic and thermotropic LCs. 45–47 Hence, luminescent amino acids as rigid segments are expected to afford orientational anisotropy in CPL-active ILCs. Additionally, it is crucial to search for appropriate proper surfactants to furnish flexible alkyl chains.…”

Does thermotropic liquid crystalline self-assembly control biological activity in amphiphilic amino acids? – tyrosine ILCs as a case study

“…It is therefore important to further investigate and understand the potential of ILCs as antimicrobial agents. Several groups worldwide have investigated amino acid ILCs (and ILs) and the major focus was put on their thermotropic 25,[32][33][34][35][36][37] and lyotropic phase behaviour 34,[38][39][40][41][42][43][44][45][46] as well as solvation properties. 37,[47][48][49][50][51] Biological properties of amino acid ILCs, on the other hand, remain almost unexplored.…”

Current Topics in Ionic Liquid Crystals

“…Amino acids have been mostly utilized for lyotropic ILCs [149–155] Thermotropic amino acid ILCs are much rarer. In an initial effort, we converted glycine, alanine and phenylalanine into ILCs with C‐terminal head group possessing ambient temperature SmA phases [156] .…”