Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400 076, India.
Langmuir. 2013 Jun 25;29(25):7709-14. doi: 10.1021/la401564b. Epub 2013 Jun 12.
The behavior of lamellar structures of Aerosol OT (AOT) as hosts, vis-à-vis the flexible normal micelles and rigid nanochannels of Nafion membranes, has been investigated with two different fluorophores, [2,2'-bipyridyl]-3,3'-diol (BP(OH)2) and coumarin 102 (C102). Surprisingly, for BP(OH)2, a rise time is observed at intermediate emission wavelengths and not in the red edge of the fluorescence spectrum. A shoulder at 525 nm is observed in time resolved emission spectra (TRES) at initial times of BP(OH)2 in AOT lamellar structures. This feature is the signature of the monoketo (MK) tautomer, observed for the first time in a microheterogeneous medium. Also, the usually ultrafast single proton transfer in BP(OH)2 is retarded to an considerable extent in lamellar structures. The potential of this medium in promoting unusual intermediates is thus highlighted. This property may be ascribed to the rigidity of lamellar structures, compared to hosts such as regular micelles. However, studies using another fluorophore, coumarin 102 (C102), brings out the fact that these structures are significantly different from the rigid host, Nafion, as well. The absence of excited state proton transfer (ESPT) in this molecule in AOT lamellar structures indicates that it is not protonated, unlike in Nafion. Thus, the interfacial pH of lamellar structures is found to be significantly greater than that of Nafion nanochannels. From the time dependent Stokes shift (TDSS) of the emission spectra of C102, the relaxation time (0.85 ns) of interfacial water in lamellar structures is found to be an order of magnitude faster than that observed in Nafion nanochannels, in which H3O(+) ions have been substituted by different cations. Hence, this study demonstrates that AOT lamellar structures are rather unique hosts and that they behave very differently from conventional rigid and flexible hosts such as normal micelles and Nafion, respectively.
气溶胶 OT（AOT）的层状结构作为主体，与 Nafion 膜的柔性正常胶束和刚性纳米通道相比，其行为已通过两种不同的荧光团[2,2'-联吡啶]-3,3'-二醇（BP（OH)2)和香豆素 102（C102)）进行了研究。令人惊讶的是，对于 BP(OH)2，在中间发射波长处观察到上升时间，而不是在荧光光谱的红色边缘处。在 BP(OH)2 在 AOT 层状结构中的初始时间的时间分辨发射光谱（TRES）中，观察到 525nm 处的肩峰。这个特征是单酮（MK）互变异构体的特征，这是首次在微不均匀介质中观察到。此外，BP(OH)2 中的通常超快单质子转移在层状结构中被大大延迟。因此，突出了这种介质在促进异常中间体方面的潜力。这种性质可能归因于层状结构的刚性，与常规胶束等主体相比。然而，使用另一种荧光团香豆素 102（C102）的研究表明，与刚性主体 Nafion 相比，这些结构也有很大的不同。在 AOT 层状结构中，该分子不存在激发态质子转移（ESPT）表明它没有质子化，与 Nafion 不同。因此，发现层状结构的界面 pH 值明显大于 Nafion 纳米通道的 pH 值。从 C102 的发射光谱的时变斯托克斯位移（TDSS），发现层状结构中界面水的弛豫时间（0.85ns）比在 Nafion 纳米通道中观察到的快一个数量级，在 Nafion 纳米通道中，H3O(+) 离子已被不同的阳离子取代。因此，本研究表明 AOT 层状结构是相当独特的主体，它们的行为与常规刚性和柔性主体（如正常胶束和 Nafion）非常不同。
