0428同步年報-2021-全

Soft Matter 031 W ater is known as the solvent of life in nature, because it can operate the self-assembly structures and functions of biomolecules. One example that shows the active role of water is found in the hydrophobic gate of trans-membrane proteins. Structural characterizations and theoretical calculations showed that water can open and close the hydrophobic gate by changing the self-assembly structure of the gate. In so doing, water alters also the kinetic barriers required for water and ions to pass through the gate and regulates the water and ion permeabilities of the trans-membrane protein. In contrast, the role of water in synthetic matters is passive. Although synthetic molecules such as dendritic dipeptide, carbon nanotube, pillar arenes, etc . have been synthesized to mimic the tube- like structure of trans-membrane proteins, the synthetic molecules are too rigid to interact dynamically with water. In this case, water is simply a liquid that passes through the tube-like supramolecular structures of synthetic molecules, but lacks the ability to operate the self-assembly structures and functions of synthetic molecules. To make water an active component for synthetic molecules, Chien-Lung Wang (National Yang Ming Chiao Tung University) and Wei-Tsung Chuang (NSRRC) developed a flexible amphiphilic discotic molecule (ADM) and characterized the active role of water in the supramolecular chemistry of this molecule (illustrated in Fig. 1(a) ). 1 Under polarized light in an optical microscope, they found that water induces the self-assembly of the amorphous ADM as shown in Figs. 1(b) and 1(c) , and use of small-angle X-ray scattering at TLS 23A1 confirmed that this water- induced self-assembly (WISA) resulted in the formation of a hexagonal columnar (Col h ) phase of ADM, which contains bulk artificial water channels (AWC). Moreover, on letting water act as the orientation-directing agent, the directional WISA that they developed can further turn these randomly oriented bulk AWC into a well oriented AWC array. The excellent orientation control of the bulk AWC was confirmed with grazing Incidence X-ray diffraction (GI XRD) at TLS 01C2 , TLS 17A1 and TLS 23A1 as shown in Fig. 1(d) . Comparing to the nearly 0 water permeability of the dehydrated ADM, the well oriented AWC array prepared by the directional WISA is salt-rejected and delivered an effective water permeability, 4.34 X 10 7 H 2 O ⸳ nm ⸳ channel -1 ⸳ s -1 , indicating that water not only induces an ordering, but also turns on the function of the ADM. AWC in the literature are tube-like molecules, which provide water transport at the length of several nanometers (~ the The Active Role of Water in Artificial Water Channel Arrays In water-induced self-assembly, water becomes an active component that regulates the supramolecular structures and functions of synthetic functional materials. Fig. 1 : (a) Illustration of the WISA process. POM images of (b) dehydrated amorphous ADM and (c) hydrated ordered phase of ADM. (d) GI XRD patterns of an oriented AWC array of ADM produced from the directional WISA. (e) POM image of the well-aligned AWC array. [Reproduced from Ref. 1]