The second is the
hydrogen bonded complex via the interactions of the hydroxyl group and the zeolite acid site having weak interaction energies, 20.7
and 23.9 kcal/mol for glycine and L-alanine, respectively. The zwitterion form is not found in the acidic H-ZSM-5 due to the acid–base
reaction, but the glycine zwitterion is found to be stably adsorbed on the Na-ZSM-5 with the adsorption energy of 24.8 kcal/mol.