Piezoluminescence at the air-water interface through dynamic molecular recognition driven by lateral pressure application
Piezoluminescence at the air-water interface through dynamic molecular recognition driven by lateral pressure application
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DOI：
10.1021/la0477845
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发表时间：
2005-02-01
期刊：
影响因子：
3.9
通讯作者：
Kikuchi, J
中科院分区：
文献类型：
--
作者：
Ariga, K;Nakanishi, T;Kikuchi, J
以1,6,20,25-四氮[6.1.6.1]副环烷为环核的类固醇环烷通过柔性的l -赖氨酸间隔剂与四个类固醇基团（胆酸或胆酸）相连，以Langmuir单层形式散布在水中。胆甾类环烷的pi-A等温线包括一个过渡到凝聚相，其极限面积类似于2 nm(2)。该值接近胆酸部分直立构象的类固醇环烷的横截面积，强烈提示在压缩单层后，腔体从二维腔体转变为三维腔体。用水溶液荧光探针（6-（对甲苯基）萘-2-磺酸盐（TNS））对该单层进行表面反射荧光光谱分析，发现TNS荧光强度在分子面积为2 nm处突然增加(2)。来访者探针的有效结合将在三维腔体完成后发生。反复压缩和膨胀引起荧光强度的周期性变化。这表明在动态空腔形成过程中，通过捕获和释放TNS客体产生了压电致发光效应。通过分析TNS与类固醇环烷的结合行为，发现其结合常数在（5-9）× 10(4) M-1范围内，与脂质双分子层介质（K = 5.1 × 10(4) M-1）中观察到的结果相似。随着压力的增加，凝聚相内的荧光强度显著增加，表明抑制结合TNS的分子运动可能延缓了非发射过程。类似的单层实验用胆碱型类固醇环烷的单层进行，胆碱型类固醇环烷在水中不能形成开放构象。pi-A等温线的相变和荧光强度的变化都可以忽略不计，证实了腔的动态特性对于有效的压力诱导来宾结合和随之而来的发光是必不可少的。
The steroid cyclophanes with a cyclic core consisting of a 1,6,20,25-tetraaza[6.1.6.1]paracyclophane connected to four steroid moieties (cholic acid or cholanic acid) through a flexible L-lysine spacer were spread on water as Langmuir monolayers. The pi-A isotherm of the cholic-type steroid cyclophane includes a transition to the condensed phase with a limiting area of similar to2 nm(2). This value is close to the cross-sectional area of the steroid cyclophane with a standing-up conformation of the cholic acid moieties, strongly suggesting that the cavity converts from a two-dimensional cavity to a three-dimensional cavity upon compressing the monolayer. Surface-reflective fluorescence spectroscopy of the monolayer using an aqueous fluorescent probe (6-(p-toluidino)naphthalene-2-sulfonate (TNS)) showed an abrupt increase in the TNS fluorescence intensity at a molecular area of 2 nm(2). Efficient binding of the guest probe would occur upon the completion of the three-dimensional cavity. Repeated compression and expansion induces periodic changes in the fluorescence intensity. This indicates a piezoluminescence effect through the catch and release of the TNS guest upon dynamic cavity formation. Analyses of the binding behavior of TNS to the steroid cyclophane resulted in binding constants in the range of similar to(5-9) x 10(4) M-1 which are similar to that observed in lipid bilayer media (K = 5.1 x 10(4) M-1). The fluorescence intensity within the condensed phase was significantly increased with increasing pressure, suggesting that suppression of the molecular motion of the bound TNS may retard the nonemission process. Similar monolayer experiments were carried out with the monolayer of the cholanic-type steroid cyclophane that cannot form an open conformation on water. Both the phase transition in the pi-A isotherm and the change in the fluorescence intensity were negligible, confirming that the dynamic characteristic of the cavity is indispensable for the efficient pressure-induced binding of the guest and the consequent luminescence.