Photoswitched Azobenzene Nanovalves

PhotocontroUed Transport Phenomenon in Lipid Bilayer Membranes. Photocontrolled ion transport across lipid bilayer membranes using photoresponsive compounds such as azobenzene derivatives has been of great interest for potential applications in optoelectronic devices and optical transducers. Most research has exploited membrane capacitance change because of the disruption of membrane structures resulting from photoisomerization of azoben-zene-containing compounds incorporated into the lipid bilayers. Others have used the volumetric change of azobenzene moieties associated with photoisomerization. 

As an extension of Yonezawa s work, Hurst and coworkers reported photo-controlled permeation through a dihexadecyl phosphate (DHP) bilayer containing azobenzene amphiphilic molecules (Lei and Hurst, 1999). The concept 

Hurst and coworkers synthesized an amphiphilic azobenzene derivative, 4-dodecy-4 -(3-phosphate-trimethyleneoxy)azobenzene (DPMA) and incorporated it into DHP vesicles. ions were entrapped in the vesicles during the vesicle formation. Photocontrolled release of ions across the vesicle membrane was conducted by monitoring the K ion concentration released into the solution under UV and visible light irradiation conditions. UV/visible spectroscopic studies confirmed that DPMA molecules were dispersed into the vesicle membrane without aggregation and isomerized reversibly in the vesicle membrane under UV and visible light irradiation. 

Recently Jin (2007) synthesized an azobenzene-modified calix[4]arene, which acts as a photoresponsive ion carrier for the control of Na flux across lipid bilayer membranes. The photoresponsive carrier was synthesized in two steps first reacting hydrazine with calix[4]arene to form monohydrozide calix[4]arene and 

As described earlier, most of the studies on photocontrolled transport phenomenon focused on azobenzene-doped organic platforms such as planar lipid membranes and spherical vesicles, which have an intrinsic disadvantage. Those lipid membranes and vesicles are delicate and unstable, thus limiting their practical applications. Incorporation of the azobenzene moieties into a robust inorganic matrix greatly enhances the system stability and facilitates the device fabrication. For example, azobenzene moieties precisely positioned onto the pore surfaces of mesoporous silica membranes enable novel photocontrolled transport in the resulting composite materials (Liu et al., 2004). 

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