Photocontrol of ion flux across a lipid bilayer membrane by visible light

对光有响应的脂质双层膜对于开发用于光电子器件和光学换能器的人工视觉系统具有重要意义。已有许多研究利用光响应性化合物，如两亲性偶氮苯和螺苯并吡喃衍生物来控制离子在脂类双层膜上的传输。大多数研究都使用了由于脂质双层结构的破坏而引起的膜电容的变化，这是由于结合到脂质双层中的化合物的光异构化造成的。到目前为止，已经有几个小组报道了光可控离子传输系统，其中连接光致变色化合物的通道或载体分子被结合到脂质双层膜中。在这些体系中，光致变色反应是在紫外光(300-380 nm)照射下进行的。在本研究中，我们选择杯[4]芳烃作为光响应性离子载体的基本骨架，因为杯[4]芳烃的醚衍生物在脂类双层膜中可以作为钠离子载体。为了合成光敏载体，将二甲氨基偶氮苯作为光致变色化合物引入对叔丁基杯[4]芳烃的醚衍生物中。在偶氮苯的衍生物中，二甲氨基偶氮苯在可见光区有较强的吸收，这归因于反式异构体的π-π*跃迁。我们认为，添加杯[4]芳烃衍生物的二甲氨基偶氮苯可以介导钠离子在脂质双层膜上的迁移，并且离子迁移能力可以通过可见光照射来控制。在这项研究中，我们成功地利用杯[4]芳烃基光响应型离子载体开发了一种可见光驱动的离子传输系统，其中通过脂质双层的钠离子通量可以通过光(&gt；400 nm)的照射来控制。

Lipid bilayer membranes that respond to light are of great interest for the development of the artificial visual systems for use in optoelectronic devices and optical transducers. There are many studies of the photocontrol of ion transport across lipid bilayer membranes using photoresponsive compounds such as amphiphilic azobenzene and spirobenzopyran derivatives. Most of the studies have used changes in membrane capacitance due to the disruption of lipid bilayer structures, which results from the photoisomerization of the compounds incorporated into the lipid bilayers. So far, several groups have reported photocontrollable ion transport systems, where channel or carrier molecules attaching photochromic compounds were incorporated into lipid bilayer membranes. In these systems, photochromic reaction has been conducted by irradiation of UV light (300-380nm). The prolonged UV irradiation, however, usually results in photodamage to photochromic compounds and lipid molecules.In the present study, we have chosen calix[4]arene as a basic skeleton of a photoresponsive ion carrier because its ether derivatives are known to act as Na^+ ion carriers in lipid bilayer membranes. For the synthesis of a photoresponsive carrier, dimethylaminoazobenzene was introduced as a photochromic compound to an ether derivative of p-tert-butylcalix[4]arene. Among azobenzene derivatives, dimethylaminoazobenzene has an intense absorption in the visible region, which is attributed to the π-π* transition of the trans isomer. We expected that the dimethylaminoazobenzene appended calix[4]arene derivative mediates Na^+ ion transport across a lipid bilayer membrane, and the ion transport ability can be controlled by irradiation of visible light. In this study, we have succeeded to develop a visible light-driven ion transport system using a calix[4]arene-based photoresponsive ion carrier, where Na^+ flux across a lipid bilayer can be controlled by irradiation of light (>400nm).