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A computational study of the role of water molecules on cation···p interactions
1, 1 , 2, 2 , 2, 2 , * 2, 2
1  Departamento de Química-Física, Facultade de Química, Universidade de Santiago de Compostela. Av. das ciencias s/n 17582, Santiago de Compostela, SPAIN
2  Departamento de Química-Física, Facultade de Ciencias, Universidade de Santiago de Compostela, Av. Alfonso X O Sabio s/n 27002, Lugo, SPAIN

Abstract: Among the different forces observed in biological complexes, the cation···p interaction is a strong, non-covalent binding force which participates in a wide variety of processes such as molecular recognition in biological receptors, enzymatic catalysis, etc. The nature and characteristics of this kind of interaction has been mainly theoretically studied in the gas phase, despite being known that the presence of water molecules modulates the strength of the interaction between metal ions and aromatic species. Besides, most studies have employed benzene as a prototype of aromatic unit. On the other hand, an also simple aromatic system as phenol presents two coordination sites for cations: the aromatic ring and the hydroxyl oxygen, thus allowing a greater variety of structures to be formed than in benzene. The hydroxyl group can also be hydrated and participate in the formation of the hydrogen bond network. In the present work, a study of the interaction between cations and phenol has been carried out to shed light on the effect of successive hydration on the interaction. So, ab initio and DFT methods were employed for studying the stepwise microhydration of phenol···cation complexes, locating the most stable structures and obtaining the corresponding complexation energies. The results suggest that the participation of the hydroxyl group is already relevant in clusters containing a small number of water molecules.
Keywords: cation-pi, ab initio, DFT, non-covalent interactions