Department of Chemistry, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India.
J Phys Chem B. 2011 Apr 7;115(13):3578-87. doi: 10.1021/jp112263s. Epub 2011 Mar 15.
Aqueous mixtures of poly(ethylene glycol) (PEG) of different compositions offer widely varying physicochemical properties that may support porphyrin aggregation. Aggregation behavior of a common water-soluble porphyrin, meso-tetrakis(4-sulfonatophenyl)porphyrin (TPPS), is investigated within aqueous PEG mixtures constituted of PEGs of average molecular weights 200 (PEG200), 400 (PEG400), 600 (PEG600), and 1000 (PEG1000) using UV-vis molecular absorbance, steady-state fluorescence, and resonance light scattering techniques. No aggregation of TPPS is observed in neat PEGs; addition of 10 wt % water to PEG at pH 1.0 is found to trigger TPPS into significant J-aggregation. The J-aggregation is observed to be most efficient within an aqueous mixture of 90 wt % PEG1000 at pH 1.0. The effect of ionic liquids, 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF(6)]) and 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF(4)]), as additives on the J-aggregation efficiency of TPPS within aqueous mixtures of PEG400 at pH 1.0 is investigated and compared with the effect of salts NaCl, NaPF(6), and NaBF(4) as additives on the J-aggregation of TPPS under the same conditions. In an aqueous mixture of 10 wt % PEG400 at pH 1.0, ionic liquids are observed to increase the J-aggregation efficiency more than the salts at lower concentrations. The efficiency of J-aggregation decreases upon further addition of [bmim][BF(4)] due to reduced dissociation of this ionic liquid in the mixture. While the three salts show limited solubility, the two ionic liquids are completely miscible in a 90 wt % PEG400 mixture in water at pH 1.0. The J-aggregation efficiency of TPPS increases rapidly and reaches a maximum before decreasing gradually as more and more ionic liquid is added to the mixture. The results draw attention to the unique dual role of ionic liquids as additives in affecting the J-aggregation of TPPS within aqueous mixtures of PEG as well as to their proficiency over common salts in J-aggregation.
不同组成的聚乙二醇（PEG）的水溶液提供了广泛变化的物理化学性质，这些性质可能支持卟啉聚集。使用紫外可见分子吸收、稳态荧光和共振光散射技术，研究了一种常见的水溶性卟啉，即间四（4-磺酸钠苯基）卟啉（TPPS）在由平均分子量为 200（PEG200）、400（PEG400）、600（PEG600）和 1000（PEG1000）的 PEG 组成的水溶液中的聚集行为。在纯 PEG 中未观察到 TPPS 的聚集；在 pH 值为 1.0 时，向 PEG 中添加 10wt%的水被发现会引发 TPPS 形成显著的 J-聚集。在 pH 值为 1.0 的 90wt%PEG1000 水溶液中，观察到 J-聚集最有效。研究了离子液体 1-丁基-3-甲基咪唑六氟磷酸盐([bmim][PF6])和 1-丁基-3-甲基咪唑四氟硼酸盐([bmim][BF4])作为添加剂对 pH 值为 1.0 的 PEG400 水溶液中 TPPS 的 J-聚集效率的影响，并将其与盐 NaCl、NaPF6和 NaBF4作为添加剂在相同条件下对 TPPS 的 J-聚集的影响进行了比较。在 pH 值为 1.0 的 10wt%PEG400 水溶液中，与盐相比，离子液体在较低浓度下更能提高 J-聚集效率。由于混合物中这种离子液体的离解减少，进一步添加 [bmim][BF4]会降低 J-聚集效率。虽然这三种盐的溶解度有限，但在 pH 值为 1.0 的 90wt%PEG400 混合水中，这两种离子液体完全互溶。随着向混合物中添加越来越多的离子液体，TPPS 的 J-聚集效率迅速增加，达到最大值，然后逐渐降低。结果表明，离子液体作为添加剂在影响 PEG 水溶液中 TPPS 的 J-聚集方面具有独特的双重作用，并且在 J-聚集方面优于普通盐。
