Angelw. Chem. Int. ed.: if you are an organic molecule, how can you get close to water molecules?

Solute solvent interaction plays an important role in chemistry Chemical reaction is highly sensitive to the change of solvent environment And the most abundant solvent on our planet is water Therefore, it is of great significance to study the interaction between water and its dissolved substances, which will undoubtedly lead to the progress of many scientific fields and industrial applications Corrosion science, drug delivery or polymer synthesis may benefit from an in-depth understanding of solvation However, it is a challenging work to image the solvation process of single molecule At present, the experimental technology can not image the solvation process of each molecule in its natural three-dimensional environment Scanning probe microscopy has high resolution, but it can only observe the molecules on the surface of the substance The application of atomic force microscopy (AFM) in liquid environment provides a great possibility for the imaging of three-dimensional solvated structure of polarized surface The technology can obtain high resolution in liquid state and generate three-dimensional solvation map However, due to the interaction of AFM front-end and the fluidity of small organic molecules in liquid environment, it seems impossible to extend this method to study the solvation of individual molecules Scanning tunneling microscope is a valuable tool to solve this problem in UHV and low temperature Karina Morgenstern and her team at Ruhr University in Germany have now designed a unique method to image azo dye 5 - (4-nitrophenylazo) salicylicacid using a scanning tunneling microscope to try to understand how water molecules embrace and solvate it step by step to form a solvent shell NPAs molecules on the gold surface (source: angel Chem Int ed.) were previously studied separately for water and organic molecules, and few in-depth studies have been conducted on the structure resulting from the combination of the two The interaction between water and organic molecules is mainly intermolecular, and previous studies have shown that these interactions are only weakly affected by the gold surface To observe this process, the team fixed azo dyes to the surface of inert gold and used heavy water to obtain better contrast Then cool the assembly to about 27K (- 246 ℃) Although these conditions are extreme, they cannot fully reflect what happens in water at room temperature But these results will open a window for researchers to understand how the hydrophilic and hydrophobic functional groups of molecules affect the formation of solvation Single water molecules connected to NPAs (source: angelw Chem Int ed.) researchers found that the first water molecules first stick to carboxylic acids and nitro groups With the continuous addition of water molecules, a solvation network is gradually formed, and first around these two groups Only at this time, the hydroxyl group will prevent the carboxylic oxygen from forming its own hydrated shell earlier due to the hydrogen bond between the molecules When the ratio of water to azo dye reaches 70:1, the whole molecule is completely enclosed in the hydrated shell NPAs hydration (source: angelw Chem Int ed.) a process in which a specific functionalized azo dye is used to demonstrate how a single water molecule adsorbs hydrophilic and hydrophobic groups of the molecule This technique reveals the solute / solvent interaction at the sub molecular scale Theoretically, it can be applied to any type of molecule, and can also be extended to other solvent molecules This method is of great significance to understand the solvation process at the single molecule level Paper link: http://onlinelibrary.wiley.com/doi/10.1002/anie.201711062/abstract corresponding author: http://www.ruhr-uni-bochum.de/pc1/