A tailor-made design of lipidic bicontinuous cubic matrices using amino acid ionic liquids as self-assembly media

Abstract

Lipidic bicontinuous cubic (Q_II) matrices are a class of liquid-crystalline matrices with three-dimensional (3D) continuity and periodicity. Owing to their unique nanostructures, they have attracted extensive attention as matrices for various bio-functional molecules such as enzymes, DNA, and membrane proteins. In the present study, we have succeeded in developing novel Q_II matrices using monoolein (MO) as an amphiphile and amino acid ionic liquids (AAILs) as solvents. By employing various AAILs, it has been found that the design of AAILs plays a key role in inducing Q_II liquid-crystalline phases. It is noteworthy that the excellent designability of AAILs enables the development of Q_II matrices showing various unique behaviors that are totally different from those of conventional Q_II matrices containing water as a solvent. For example, the AAIL-based Q_II matrices preserve the 3D nanostructures even in a low temperature region (lower than 0 °C). It is also possible to design Q_II matrices that preserve the nanostructures for a long period of time under conventional conditions using these AAILs; on the other hand, for water-based Q_II matrices, special conditions, such as relative humidity over 90%, are required for preserving the nanostructures; moreover, the cubic lattice constant can be controlled from 88 to 100 Å by tuning the AAILs. Herein, we not only present the results showing the advantages of the AAIL-based Q_II matrices in terms of their nanostructure design, but also describe our finding of a primary result showing that the AAIL-based Q_II matrices have great potential to be used as a matrix for some proteins to form secondary structures. Considering the recent significant progress made in the design of biocompatible ionic liquids, we believe that the present matrix design will lead to the development of a new technology for controlling the functions and behavior of various bio-functional molecules.