Association Complexes of Calix[6]arenes with Amino Acids Explained by Energy-Partitioning Methods.

Area of Science:

• Supramolecular Chemistry
• Computational Chemistry

Background:

• Calixarenes form intriguing intermolecular complexes due to versatile noncovalent binding.
• These complexes can accommodate both polar and nonpolar molecules, including within the calixarene cavity.

Purpose of the Study:

• To investigate calix[6]arenes interacting with amino acids.
• To demonstrate how computational methods explain varying noncovalent bond numbers and strengths in calixarene complexes.

Main Methods:

• Symmetry-Adapted Perturbation Theory (SAPT)
• Functional-Group SAPT (F-SAPT)
• Systematic Molecular Fragmentation (SMF)

Main Results:

• Energy partitioning identified various noncovalent bonds, including hydrogen bonds and unconventional ones.
• Repulsive interactions between functional groups were also detected.
• Observed IR red shifts in hydroxy groups were attributed to interactions with the calixarene phenyl ring.

Conclusions:

• F-SAPT analysis of hydrogen bonds and other noncovalent bonds explains enhanced stability in inclusion and outer calixarene complexes.
• Computational tools provide detailed insights into the nature and strength of intermolecular interactions.