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

对光有响应的脂质双分子层膜对于开发用于光电器件和光学换能器的人工视觉系统具有重要意义。利用光响应性化合物，如两亲性偶氮苯和螺苯吡喃衍生物，对离子在脂质双分子层膜上的光控制进行了许多研究。大多数研究使用了由于脂质双分子层结构破坏而引起的膜电容变化，这是由纳入脂质双分子层的化合物的光异构化引起的。到目前为止，有几个研究小组已经报道了光可控离子传输系统，其中通道或载体分子附着于光致变色化合物被纳入脂质双分子层膜。在这些体系中，光致变色反应是通过紫外线（300-380nm）照射进行的。然而，长时间的紫外线照射通常会导致光致变色化合物和脂质分子的光损伤。在本研究中，我们选择杯状[4]芳烃作为光响应离子载体的基本骨架，因为它的醚衍生物已知在脂质双分子层膜中充当Na^+离子载体。为了合成光响应载体，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。在偶氮苯衍生物中，二甲氨基偶氮苯在可见光区有很强的吸收，这是由于其反式异构体的π-π*跃迁。我们期望二甲氨基偶氮苯附加杯形[4]芳烃衍生物介导Na^+离子在脂质双层膜上的传输，并且离子传输能力可以通过可见光照射来控制。在这项研究中，我们已经成功地开发了一种可见光驱动的离子传输系统，该系统使用的是基于萼[4]芳烃的光响应离子载体，其中Na^+通过脂质双分子层的通量可以通过光照射（>400nm）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).