Hydrogen Bonding in Tight Environments: Simulated Force Spectroscopy of Nanoconfined Hydrogen-Bonded Complexes

Abstract

The single-molecule force spectroscopy of a prototypical class of hydrogen-bonded complexes is computationally investigated. The complexes consist of derivatives of a barbituric acid and a Hamilton receptor that can form up to six simultaneous hydrogen bonds. The force–extension (F–L) isotherms of the host–guest complexes are simulated using classical molecular dynamics and the MM3 force field, for which a refined set of hydrogen bond parameters was developed from MP2 ab initio computations. The F–L curves exhibit peaks that signal conformational changes during elongation, the most prominent of which is in the 60–180 pN range and corresponds to the force required to break the hydrogen bonds. These peaks in the F–L curves are shown to be sensitive to relatively small changes in the chemical structure of the host molecule. Thermodynamic insights into the supramolecular assembly were obtained by reconstructing, from the force measurements, the Helmholtz free energy profile along the extension coordinate and ...