Influence of Structural Flexibility on Ion-Receptor Interactions in Octamethyl Calix[4]pyrrole Complexed with Prolinate
Year: 2026
Type: preprint
Abstract: We present cryogenic ion vibrational spectroscopy of deprotonated L-proline ([Pro-H]-) complexed with octamethyl calix[4]pyrrole (omC4P). Density functional theory calculations reveal two low-energy binding motifs. In the lowest energy structure, the carboxylate group interacts with only three NH groups of omC4P, with the NH group of the fourth pyrrole pointing away from the binding site. In another geometry, slightly higher in energy, the ion binds to all four NH groups. The experimental IR spectrum matches the lowest energy isomer, featuring a free NH stretching signature at 3439 cm-1 alongside strongly red-shifted NH stretching modes involving the three strong hydrogen-bonding NH groups. This three-point binding motif represents a departure from the typical four-point binding observed with smaller anions, demonstrating how the charge distribution of the guest and the structural flexibility of the receptor affect binding of larger anions. Despite the reduced number of hydrogen bonds, the three-point binding motif is lower in energy due to shorter, stronger hydrogen bonds, and it is the dominant motif of [Pro-H]-·omC4P in vacuo.
Source: ChemRxiv
Authors: Lane M. Terry, J. Mathias Weber
Language: English
Subfield: Organic Chemistry
Field: Chemistry
Domain: Physical Sciences
Open Access status: green
Awards: G2586609609, G2796167598, MRI Collaborative Consortium: Acquisition of a Shared Supercomputer by the Rocky Mountain Advanced Computing Consortium, G4591728458, G4958434179, MRI Collaborative Consortium: Acquisition of a Shared Supercomputer by the Rocky Mountain Advanced Computing Consortium, Cryogenic Ion Spectroscopy Studies of Ion-Receptor Interactions in Water Soluble Molecular Recognition Complexes and Their Hydrated Clusters, G8929392486
OpenAlex ID: W7213940892