| Synthesized membrane channel could mimic biological channel capableof transporting substance across membrane. Great attention has beenfocused on synthesized nanopores as the applications it has, likeseparating ion, biological detection, drug delivery and even DNAsequencing. Among the possible models, constructing self-assembledchannels with shape-persistent macro-cycles has become more importantbecause the size of channel is controllable and residues could be easilymodified. We used single channel planar lipid bilayer electrophysiologytechnique to study the material transportation properties of a series ofself-assembled macro-cycles, based on the result of which we thenapplied molecular dynamics (MD) and ab initio calculations to furtherexplain channel's stability and mechanism of substance transportation.The self-assembled macro-cycles, named as L3and D+L-3, are from ourcollaborate lab, Bing Gong's Lab at Department of Chemistry, Universityat Buffalo, The State University of New York. This series of compoundsconsisting of an inner ring and side chains linked to the inner ring. Theinner ring is formed by the linkage of urea linkage and benzene, while the side chains are attached to the inner ring via amido bond. This seriesmolecular could pack up onto one another into self-assemblednanochannel in solvent with weak polarity and phospholipid bilayer. Inliposome water conductance assay experiment, the proton permeability ofphospholipid bilayer increased after D+L-3was added. L3did not showsimilar result. In mice blood hemolysis experiments, L3and D+L-3givesnegative result, which means that L3and D+L-3could not form channelsthat could conduct Na+, Cl-, etc. To further detect the electrophysiologicalproperties of D+L-3nanotubes, we designed and implemented planarlipid bilayer experiments in hopes of analyzing single-channel ion currentrecording, the result of which agreed with hemolysis experiment.Meanwhile, we implemented molecular dynamics simulation aboutD+L-3, the structure of which was build up empirically with thecomparison of D+L-3to parameterized compound within CHARMMgeneral force field topology file, it has been found that in NPT ensemble(295K,1atom) D+L-3stacked up structure is stable in chloroform. Inthe simulation where D+L-3tube was inserted into POPC lipid bilayer,water molecule could form a single file within the channel and they arequite likely to stay in the gap between two adjacent D+L-3molecules.For now, the simulation result agrees with the electrophysiologyexperiment result. We speculated that the mechanism of protontransportation is in strong relation to the orderly arranged water molecule within the D+L-3nanotube. Yet, this assumption still needs theverification of more delicate experiments and more reliable quantummechanics calculation. Based on the combination of electrophysiologyexperiments and simulation, we build up a systematic method inexploring the substance transportation properties of self-assemblednano-channels. With this method, we study a series of moleculerepresented by D+L-3. In doing so, we acquired a further understandingabout how to modify side chain to increase channel's stability, how tomodify inner residues to realize functional tenability. |
