Department of Chemistry, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8551, Japan.
Japan Science and Technology Agency, Precursory Research for Embryonic Science and Technology, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan.
J Phys Chem B. 2020 May 7;124(18):3734-3742. doi: 10.1021/acs.jpcb.0c01451. Epub 2020 Apr 28.
When an aqueous salt solution freezes, a freeze-concentrated solution (FCS) separates from the ice. The properties of the FCS may differ from those of a supercooled bulk solution of the same ionic strength at the same temperature. The fluorescence and lifetime characteristics of 6-cyano-2-naphthol (6CN) were studied in frozen NaCl solutions in order to provide insight into the solution properties of the FCS. While the photoacidity of 6CN in an FCS is similar to that in solution, several anomalous behaviors are observed. Fluorescence spectra indicate that the solubility of 6CN is significantly enhanced in the FCS (50 mM or higher) compared to that in the bulk NaCl solution where the solubility limit is 250 μM. The high solubility induces the aggregation of 6CN in the FCS, which is not detected in bulk solutions. This trend becomes marked as the initial NaCl concentration decreases and the FCS is confined in a small space. The fluorescence lifetimes of 6CN in the FCS support the spectroscopy results. In addition to the species identified by fluorescence spectroscopy, excimers are assigned from lifetime measurements in the FCS. The excimer formation is also a result of the enhanced solubility of 6CN in the FCS.
当盐水溶液冻结时，会从冰中分离出浓缩冷冻溶液（FCS）。FCS 的性质可能与相同离子强度和温度下的过冷体相溶液的性质不同。为了深入了解 FCS 的溶液性质，研究了 6-氰基-2-萘酚（6CN）在冷冻 NaCl 溶液中的荧光和寿命特性。虽然 6CN 在 FCS 中的光酸性与溶液中的光酸性相似，但观察到了几种异常行为。荧光光谱表明，与在溶解度极限为 250μM 的 bulk NaCl 溶液相比，6CN 在 FCS（50mM 或更高）中的溶解度显著提高。高溶解度导致 6CN 在 FCS 中聚集，而在 bulk 溶液中则无法检测到。随着初始 NaCl 浓度的降低和 FCS 被限制在小空间中，这种趋势变得明显。6CN 在 FCS 中的荧光寿命支持光谱结果。除了通过荧光光谱鉴定的物种外，还从 FCS 中的寿命测量中分配了激基缔合物。激基缔合物的形成也是 6CN 在 FCS 中溶解度增强的结果。
