Project 4 |
Artificial ionic and water channelsblank Angew. Chem. Int. Ed. 2011, 50(48), 11366-11372 Angew. Chem. Int. Ed. 2012, 51 11674-11676 blank Water is fundamental to life, playing a variety of functions related to its complex dynamic behaviours at the supramolecular level. Most of the physiological processes depend on selective exchanges of ions or molecules between a cell and its environment and water play a crucial role on their translocation events. Artificial ion-channels have been extensively studied with the hope to facilitate the ionic conduction in the bilayer membranes. However, there has been less progress in the area of synthetic water channels. Water channel systems: a) cross section of the helical pore assembled from dendritic dipeptides, 1 and b) oriented dipolar water wires within chiral supramolecular I-quartet assembled from lipophilic ureidoimidazole, 2 selectively transporting water and protons against ions; c) hydrazide-pilar[5]arene, 3 functioning exclusively as highly selective single-molecular water channels. Water molecules and protonated water molecules are represented in red and white CPK models. Violet spheres are representing hydrated cations, non-penetrants for bilayer membrane. blank
These results strongly indicated that water molecules and protons can permeate the bilayer membranes through I-quartet channels. The ion-exclusion phenomena are based on dimensional steric effects whereas hydrophobic and hydrodynamic effects appear to be less important. Water-free I-quartet-"off form" superstructure is reminiscent with closed conformation of the proton gate of the Influenza A M2 protein. The slight conformational adjustments allow the formation water assisted I-quartet-"open form" through protons can diffuse along dipolar oriented water-wire in the open state pore-gate region. These artificial I-quartet superstructures obtained by using a simple chemistry are in excellent agreement with structural X-ray and NMR results as well as theoretical results providing accurate structural issues for water/proton conductance mechanisms through Influenza A M2 proton channel. |