The interaction of four solvatochromic pyridiniophenolates with α-cyclodextrin was investigated by means of UV-visible and ¹H-NMR spectroscopies, and supported theoretically by molecular simulation studies. By inserting different substituents into the hydrophobic cavity of α-CD, we were able to identify the separate contributions of the donor and acceptor moieties of these dyes to their solvatochromic behaviour in water.

¹H-NMR evidence suggested that insertion of the less hindered phenoxide group inside the hydrophobic host cavity took place for three complexes. Steric hindrance prevented this in the case of one betaine, leading instead to the encapsulation of an aryl substituent of the pyridinium ring. The fact that in this case no UV-Vis spectral changes were observed points to a negligible influence of this pyridinium substituent to the solvatochromic behaviour of the dye.

We carried out docking of all betaines into the α-CD host, followed by molecular dynamics simulations in water, employing the CHARMM27 force field in a a 20-Å-radius sphere built with TIP3P water molecules. The resulting structures were compared with the experimental data. The theoretical results agreed with the spectroscopic evidence, indicating that UV-Vis spectral changes were observed only when the phenoxide donor lodged inside the more hydrophobic microenvironment of the cyclodextrin host.

• Legal notice:
  

  Copyright (c) Pielaszek Research, all rights reserved.
  The above materials, including auxiliary resources, are subject to Publisher's copyright and the Author(s) intellectual rights. Without limiting Author(s) rights under respective Copyright Transfer Agreement, no part of the above documents may be reproduced without the express written permission of Pielaszek Research, the Publisher. Express permission from the Author(s) is required to use the above materials for academic purposes, such as lectures or scientific presentations.
  In every case, proper references including Author(s) name(s) and URL of this webpage: https://science24.com/paper/8303 must be provided.