Gohres John L, Kitchens Christopher L, Hallett Jason P, Popov Alexander V, Hernandez Rigoberto, Liotta Charles L, Eckert Charles A
School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, USA.
J Phys Chem B. 2008 Apr 17;112(15):4666-73. doi: 10.1021/jp077552p. Epub 2008 Mar 22.
Local compositions in supercritical and near-critial fluids may differ substantially from bulk compositions, and such differences have important effects on spectroscopic observations, phase equilibria, and chemical kinetics. Here, we compare such determinations around a solute probe dissolved in CO2-expanded methanol and acetone at 25 degrees C from solvatochromic experiments with molecular dynamics simulations. UV/vis and steady-state fluorescence measurements of the dye Coumarin 153 in the expanded liquid phase indicate preferential solvation in both the S0 and S1 states by the organic species. Simple dielectric continuum models are used to estimate local compositions from the spectroscopic data and are compared to molecular dynamics simulations of a single C153 molecule dissolved in the liquid phase at bubble point conditions. The simulations provide information about the local solvent structure around C153. They suggest the presence of large solvent clustering near the electron-withdrawing side of the probe. Preferential solvation exists in both the S0 and S1 states, but a large disagreement between simulation and experiment exists in the S1 state. Potential reasons for this disparity are discussed.
超临界和近临界流体中的局部组成可能与整体组成有很大差异，这种差异对光谱观测、相平衡和化学动力学有重要影响。在此，我们将25℃下溶解在二氧化碳膨胀甲醇和丙酮中的溶质探针周围的此类测定结果，通过溶剂化显色实验与分子动力学模拟进行比较。在膨胀液相中对染料香豆素153进行的紫外/可见和稳态荧光测量表明，在S0和S1态中，有机物种都存在优先溶剂化现象。使用简单的介电连续介质模型从光谱数据估计局部组成，并与在泡点条件下溶解在液相中的单个C153分子的分子动力学模拟结果进行比较。模拟提供了关于C153周围局部溶剂结构的信息。结果表明，在探针吸电子侧附近存在大量溶剂团簇。在S0和S1态中都存在优先溶剂化现象，但在S1态中模拟与实验结果存在很大差异。本文讨论了这种差异的潜在原因。
