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

对光有响应的脂双层膜对于用于光电器件和光学传感器的人工视觉系统的开发具有极大的兴趣。有许多研究使用光敏化合物，如两亲性偶氮苯和螺苯并吡喃衍生物的光控制离子跨脂质双层膜的传输。大多数的研究已经使用的膜电容的变化，由于脂质双层结构的破坏，这是由于光异构化的化合物纳入脂质双层。到目前为止，已经有几个小组报道了光可控的离子传输系统，其中连接光致变色化合物的通道或载体分子被引入到脂质双层膜中。在这些体系中，光致变色反应是通过紫外光（300- 380 nm）照射进行的。由于杯[4]芳烃的醚类衍生物在脂质双层膜中具有Na^+离子载体的作用，因此我们选择杯[4]芳烃作为光敏离子载体的基本骨架。在对叔丁基杯[4]芳烃的醚衍生物中引入二甲氨基偶氮苯作为光致变色化合物，合成了光响应性载体。在偶氮苯衍生物中，二甲氨基偶氮苯在可见光区具有强吸收，这归因于反式异构体的π-π* 跃迁。我们预期，添加了二甲氨基偶氮苯的杯[4]芳烃衍生物介导Na^+离子跨脂双层膜的转运，并且离子转运能力可以通过可见光照射来控制。在本研究中，我们成功地开发了一种基于杯[4]芳烃的光响应离子载体的可见光驱动离子传输系统，其中Na^+穿过脂质双层的通量可以通过光照射（> 400 nm）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).