Selective lithium ion recognition in self-assembled columnar liquid crystals based on a lithium receptor

Lithium is recognized as being significantly important due to its various applications in different areas especially in energy technology. In the present study, self-assembled nanostructured liquid-crystalline (LC) materials, that selectively bind lithium cations, have been developed for the first time. Wedge-shaped crown ether derivatives bearing dibenzo-14-crown-4 (DB14C4) or 12-crown-4 moieties are able to act as LC lithium-selective receptors. We have found that complexation of these receptors with lithium perchlorate induces liquid-crystalline columnar phases, while sodium perchlorate is immiscible with both receptors. Remarkably, a receptor consisting of DB14C4 as an effective lithium-selective ligand exhibits high selectivity for LiCl over NaCl, KCl, RbCl and CsCl. The lithium selectivity was demonstrated and investigated by ¹H NMR, ¹H COSY and FT-IR spectroscopic measurements. The preferred coordination number of four and the ideal cavity geometry of the DB14C4 moiety of the receptor are shown to be key factors for the high lithium selectivity. This new design of LC lithium-selective receptors opens unexplored paths for the development of methods to fabricate nanostructured materials for efficient selective lithium recognition.

Molecular recognition at the membrane-water interface: controlling integral peptide helices by off-membrane nucleobase pairing

The aggregation and organization of membrane proteins and transmembrane peptides is related to the interacting molecular species itself and strongly depends on the lipid environment. Because of the complexity and dynamics of these interactions, they are often hardly traceable and nearly impossible to predict. For this reason, peptide model systems are a valuable tool in studying membrane associated processes since they are synthetically accessible and can be readily modified. To control and study the aggregation of peptide transmembrane domains (TMDs) the interacting interfaces of the TMDs themselves can be altered. A second less extensively studied approach targets the TMD assembly by using interaction and recognition of domains at the membrane outside as frequently found in the membrane protein interplay and protein assembly. In the present study, double helical transmembrane domains were designed and synthesized on the basis of a recently reported d,l-alternating peptide pore motif derived from gramicidin A. The highly hydrophobic and aromatic transmembrane peptide was covalently functionalized with a short peptide nucleic acid (PNA) used as specific outer-membrane recognition unit. The PNA sequences were chosen with high polarity to ensure localization within the aqueous phase. To estimate the impact of the membrane adjacent recognition on the TMD assembly by Förster resonance energy transfer (FRET), fluorescence probes were covalently attached to the side chains of the membrane spanning peptide helices. Dimerization of the TMD-peptide/PNA conjugates within unilamellar lipid vesicles was observed. The dimer/monomer ratio of TMDs can be controlled by temperature variation.

Coarse-grained model for mechanosensitive ion channels

In this work, a coarse-grained model for a kind of membrane protein, the mechanosensitive channel of small conductance (MscS), is proposed. The basic structure of the MscS is preserved when the protein is coarse-grained. For the coarse-grained model, the channels show two different states, namely the open and closed states, depending on the model parameters. Under the same membrane tension, the state of the ion channel is found to be critically determined by the protein structure, especially the length of the transmembrane alpha-helix. It is also found that for the protein with certain size, the gating transition occurs when the membrane tension is applied, resembling in a real mechanosensitive channel.