What can you learn from a molecular probe? New insights on the Behavior of C343 in homogeneous solutions and AOT reverse micelles
What can you learn from a molecular probe? New insights on the Behavior of C343 in homogeneous solutions and AOT reverse micelles
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DOI：
10.1021/jp0572636
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发表时间：
2006-07-06
影响因子：
3.3
通讯作者：
Levinger, Nancy E.
中科院分区：
文献类型：
--
作者：
Correa, N. Mariano;Levinger, Nancy E.
研究了溶剂化动力学实验中常用的分子探针C343在均相介质、水相和非水相反胶束体系中的行为。在均匀介质中，Kamlet和塔夫脱溶剂化显色比较方法从吸收和发射谱带定量溶质-溶剂相互作用，表明染料的溶剂化显色行为不仅取决于介质的极性，而且取决于溶剂的氢键性质。具体地，在基态下，分子显示出溶剂的极性极化率（pi*）和氢键受体（β）能力的红移以及介质的氢供体能力（α）的蓝移。羧酸基团使C343对β比对π * 极性参数表现出更大的敏感性;这种敏感性在激发态增加，而对α的依赖性消失。这表明C343与具有高氢键受体能力（高β）和低氢键供体特征（低α）的溶剂形成稳定的氢键复合物。非极性溶剂中的光谱揭示了J-聚集体的形成。根据Kamlet-Taft分析的信息，使用吸收、发射和时间分辨光谱，使用C343探索由水或极性溶剂/1，4-双-2-乙基己基磺基琥珀酸钠（AOT）/异辛烷组成的RM。螯合的极性溶剂包括乙二醇（EG）、甲酰胺（FA）、N，N-二甲基甲酰胺（DMF）和N，N-二甲基乙酰胺（DMA）。C343以低浓度溶解在AOT RM系统中，以单体形式存在，并且当以其质子化形式引入RM样品时，C343保持质子化，从而使其驻留在界面而不是水池中。染料的溶致变色行为取决于封装在RM中的特定极性溶剂，揭示了溶剂和表面活性剂之间的不同类型的相互作用。EG和水与AOT磺酸盐基团形成氢键，破坏了它们的整体氢键结构。虽然水仍然很好地从非极性区域隔离，EG似乎渗透到界面的油侧。在水性AOT RM中，C343既不与磺酸盐基团也不与水相互作用，可能是因为染料中的分子内氢键。DMF和DMA主要通过偶极偶极力相互作用，与AOT钠反离子的强相互作用破坏了它们的本体结构。FA也与Na+抗衡离子相互作用，但保留其存在于本体溶剂中的H-键网络。令人惊讶的是，FA似乎是唯一的极性溶剂以外的水形成的“极性溶剂池”与宏观性质类似的散装。
The behavior of C343, a common molecular probe utilized in solvation dynamics experiments, was studied in homogeneous media and in aqueous and nonaqueous reverse micelles (RMs). In homogeneous media, the Kamlet and Taft solvatochromic comparison method quantified solute-solvent interactions from the absorption and emission bands showing that the solvatochromic behavior of the dye depends not only on the polarity of the medium but also on the hydrogen-bonding properties of the solvent. Specifically, in the ground state the molecule displays a bathochromic shift with the polarity polarizability (pi*) and the H-bond acceptor (beta) ability of the solvents and a hypsochromic shift with the hydrogen donor ability (alpha) of the media. The carboxylic acid group causes C343 to display greater sensitivity to the beta than to the pi* polarity parameter; this sensitivity increases in the excited state, while the dependence on alpha vanishes. This demonstrates that C343 forms a stable H-bond complex with solvents with high H-bond acceptor ability (high beta) and low H-bond donor character (low alpha). Spectroscopy in nonpolar solvents reveals J-aggregate formation. With information from the Kamlet-Taft analysis, C343 was used to explore RMs composed of water or polar solvents/sodium 1,4-bis-2-ethylhexylsulfosuccinate (AOT)/isooctane using absorption, emission, and time-resolved spectroscopies. Sequestered polar solvents included ethylene glycol (EG), formamide (FA), N, N-dimethylformamide (DMF), and N, N-dimethylacetamide (DMA). Dissolved in the AOT RM systems at low concentration, C343 exists as a monomer, and when introduced to the RM samples in its protonated form, C343 remains protonated driving it to reside in the interface rather than the water pool. The solvathochromic behavior of the dye depends the specific polar solvent encapsulated in the RMs, revealing different types of interactions between the solvents and the surfactant. EG and water H-bond with the AOT sulfonate group destroying their bulk H-bonded structures. While water remains well segregated from the nonpolar regions, EG appears to penetrate into the oil side of the interface. In aqueous AOT RMs, C343 interacts with neither the sulfonate group nor the water, perhaps because of intramolecular H-bonding in the dye. DMF and DMA interact primarily through dipoledipole forces, and the strong interactions with AOT sodium counterions destroy their bulk structure. FA also interacts with the Na+ counterions but retains its H-bond network present in bulk solvent. Surprisingly, FA appears to be the only polar solvent other than water forming a "polar-solvent pool" with macroscopic properties similar to the bulk.