Barriers for Extrusion of a Guest from the Interior Binding Cavity of a Host: Gas Phase Experimental and Computational Results for Ion-Capped Decamethylcucurbit[5]uril Complexes

Abstract

Factors affecting the extrusion of guests from metal ion-capped decamethylcucurbit [5]uril (mc5) molecular container complexes are investigated using both collision-induced dissociation techniques and molecular mechanics simulations. For guests without polar bonds, the extrusion barrier increases with increasing guest volume. This is likely because escape of larger guests requires more displacement of the metal ion caps and, thus, more disruption of the ion-dipole interactions between the ion caps and the electronegative rim oxygens of mc5. However, guests larger than the optimum size for encapsulation displace the ion caps prior to collision-induced dissociation, resulting in less stable complexes and lower dissociation thresholds. The extrusion barriers obtained for guests with polar bonds are smaller than those obtained for similarly sized guests without polar bonds. This is likely because the partial charges on the guest allow electrostatic interactions with the ion cap and rim oxygens of mc5 during extrusion, thus stabilizing the extrusion transition state and reducing the extrusion barrier. Results from this study demonstrate simple principles to consider for designing host−guest complexes with specific guest-loss behaviors. Similar trends are observed between the experimental and computational results, demonstrating that molecular mechanics simulations can be used to approximate the relative stability of mc5 molecular container complexes and likely those of other similar complexes.

Supramolecular gating of guest release from cucurbit[7]uril using de novo design

“…2. They are therefore expected to extend t 1/2 purely through a kinetic effect by providing an additional energy barrier to the escape event rather than by stabilizing ADA in the cavity, which is consistent with experimental observations of a CB5 derivative capped by metal cations 44 . This kinetic barrier effect can be understood as an extension of the portal's 'constrictive binding' often described in CB7 45 .…”

Collision Cross-Section Measurements of Collision-Induced Dissociation Precursor and Product Ions in an FTICR-MS and an IM-MS: A Comparative Study

“…Computational modeling was performed using the Spartan ’18 Parallel Suite (Wavefunction, Inc., Irvine, CA). Spartan’s conformer distribution algorithm, using the MMFF force field supplied in the computational package (parameters for Rb + and Cs + were added to the force field), and Monte Carlo searching were used to identify low energy structures for canonical and zwitterionic LE+M + and fragments and 222+M + systems. Single-point energy calculations were then performed on the resulting MMFF structures at the B3LYP-D3/6-31+G* level of theory for LE+M + and fragments and M06-2X/6-31+G* for 222+M + , to obtain more accurate energies and Boltzmann weight scoring.…”

Ion Mobility and Fourier Transform Ion Cyclotron Resonance Collision Cross Section Techniques Yield Long-Range and Hard-Sphere Results, Respectively

“…We began with a Monte Carlo conformation search using the Merck molecular force field (MMFF94) within the Spartan’18 software package (Wavefunction, Inc., Irvine, CA). Since MMFF94 does not include parameters for rubidium and cesium, user-selected parameters for those ions were inserted into the force field . For cucurbit­[ n ]­uril and derivatives, the number of structures that need to be considered is relatively small because the host molecules are rigid.…”

“…Since MMFF94 does not include parameters for rubidium and cesium, user-selected parameters for those ions were inserted into the force field. 37 For cucurbit[n]uril and derivatives, the number of structures that need to be considered is relatively small because the host molecules are rigid. We used Spartan's Monte Carlo search algorithm to generate starting structures.…”