Department of Chemical, Biological & Macromolecular Sciences, S N Bose National Centre for Basic Sciences, Salt Lake, Kolkata, India.
J Fluoresc. 2012 Mar;22(2):753-69. doi: 10.1007/s10895-011-1011-3. Epub 2011 Nov 10.
The self-assembly of non-toxic well-consumed small caffeine molecules into well-defined structures has important implications for future medical applications seeking to target the transport of small drugs in human body. Particularly, the solvation of the microenvironments of the self assembly ultimately dictates the interaction with the drug molecules and their therapeutic efficacy. We present femtosecond-resolved studies of the dynamics of aqueous solvation within self-assembled dimeric structure of caffeine molecules. We have placed small hydrophobic probes 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl) 4H-pyran (DCM), coumarin 500 (C500) into the caffeine dimer to enable spectroscopic examinations of the interior. While molecular modeling and NMR studies of the probes in the caffeine dimers reveal a well-defined location (stacked in between two caffeine molecules), dynamical light scattering (DLS), Fourier transform infrared (FTIR) spectroscopy, densimetric and sonometric experiments explore the structural evolution of the dimer upon complexation with the probes. We have extended our studies in various temperatures in order to explore structural evolution of the self assembled structure and consequently the dynamics of solvation in the interior of the dimer. Picoseconds/femtosecond resolved dynamics and the polarization gated spectroscopic studies unravel the hydration and energetics associated with activated viscous flow of the confined probes. Our studies indicate that the interior of the caffeine dimer is well-solvated; however, the dynamics of solvation is retarted significantly compared to that in bulk water, clearly revealing the dimers maintain some ordered water molecules. We have also explored the consequence of the retarded dynamics of solvation on the photo-induced electron transfer (ET) reaction of a model probe, 2-(p-toluidino) naphthalene-6-sulfonate (TNS) encapsulated in the dimer.
无毒且易消耗的小咖啡因分子自组装成具有明确结构的物质，这对未来旨在靶向人体中小药物运输的医学应用具有重要意义。特别是，自组装微环境的溶剂化最终决定了与药物分子的相互作用及其治疗效果。我们提出了在咖啡因分子自组装二聚体结构中水溶液溶剂化动力学的飞秒分辨研究。我们将小疏水分子探针 4-(二氰基亚甲基)-2-甲基-6-(对二甲氨基苯乙烯基)-4H-吡喃（DCM）、香豆素 500（C500）放入咖啡因二聚体中，以对内部进行光谱检查。虽然探针在咖啡因二聚体中的分子建模和 NMR 研究揭示了一个明确的位置（堆积在两个咖啡因分子之间），但动态光散射（DLS）、傅里叶变换红外（FTIR）光谱、密度和超声实验探索了探针与二聚体络合时二聚体的结构演变。我们在不同温度下扩展了我们的研究，以探索自组装结构的结构演变以及随后二聚体内溶剂化的动力学。皮秒/飞秒分辨动力学和极化门控光谱研究揭示了与受限探针的激活粘性流动相关的水合作用和能量学。我们的研究表明，咖啡因二聚体的内部是良好溶剂化的；然而，与在体相水中相比，溶剂化动力学明显延迟，这清楚地表明二聚体保持一些有序水分子。我们还探索了溶剂化动力学延迟对模型探针 2-(对甲苯基氨基)萘-6-磺酸盐（TNS）在二聚体中包封的光诱导电子转移（ET）反应的影响。
