Department of Physics, NanoPhotonics Centre, Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, United Kingdom.
Department of Chemistry, Melville Laboratory for Polymer Synthesis, University of Cambridge, Cambridge CB2 1EW, United Kingdom.
Proc Natl Acad Sci U S A. 2022 Dec 6;119(49):e2212497119. doi: 10.1073/pnas.2212497119. Epub 2022 Dec 1.
Nanoconfined few-molecule water clusters are invaluable systems to study fundamental aspects of hydrogen bonding. Unfortunately, most experiments on water clusters must be performed at cryogenic temperatures. Probing water clusters in noncryogenic systems is however crucial to understand the behavior of confined water in atmospheric or biological settings, but such systems usually require either complex synthesis and/or introduce many confounding external bonds to the clusters. Here, we show that combining Raman spectroscopy with the molecular nanocapsule cucurbituril is a powerful technique to sequester and analyze water clusters in ambient conditions. We observe sharp peaks in vibrational spectra arising from a single rigid confined water dimer. The high resolution and rich information in these vibrational spectra allow us to track specific isotopic exchanges inside the water dimer, verified with density-functional theory and kinetic population modeling. We showcase the versatility of such molecular nanocapsules by tracking water cluster vibrations through systematic changes in confinement size, in temperatures up to 120° C, and in their chemical environment.
纳米受限少分子水团簇是研究氢键基本方面的宝贵体系。不幸的是，大多数水团簇实验必须在低温下进行。然而，在非低温系统中探测水团簇对于理解大气或生物环境中受限水的行为至关重要，但这些系统通常需要复杂的合成和/或向团簇引入许多混杂的外部键。在这里，我们表明，将拉曼光谱与分子纳米胶囊葫芦脲结合使用是一种在环境条件下隔离和分析水团簇的强大技术。我们观察到振动光谱中源自单个刚性受限水二聚体的尖锐峰。这些振动光谱中的高分辨率和丰富信息使我们能够跟踪水二聚体内特定的同位素交换，并用密度泛函理论和动力学群体建模进行了验证。我们通过跟踪水团簇振动，展示了这种分子纳米胶囊的多功能性，这些振动通过限制尺寸、温度高达 120°C 以及化学环境的系统变化来实现。
