Theoretical binding affinities and IR spectra of β-cyclodextrin to non-essential amino acids

Department of Chemistry, Department of Biomedical Engineering, Zhejiang University. Hangzhou 310027,
People's Republic of China
E-mail : wushi@zju.edu.cn
Department of Biomedical Engineering, Jiamusi University, Jiamusi 154007, People's Republic of China
Manuscript received 23 November 2006, accepted 10 January 2007

AMl method is used to study the structures and characters of the complexes formed by β-cyclodextrin (β-CD) and non-essential amino acids to obtain the binding energies. On the basis of the AM1 optimized geometries, the IR spectra of the complexes are computed using AMl method. It is indicated that β-CD can form the supra-molecular complexes with the non-essential amino acids, leading to the decrease of the total energy for the complex. The binding energies of the complexes are affected by the relative position of the functional groups between the guests and the host, as well as the electron-donating abilities of the groups. Especially, β-CD shows the chiral binding affinity to tbe nonessential amino acids due to its chiral characteristics. β-CD can bind o-alanine best. The polar groups on the guest molecules are located near the small rim of β-CD, which effectively forms the hydrogen bonds. The changes of the IR absorptions are caused by the different amino acids. The stretching vibration frequencies of the O-H and N-H bonds on the guest molecules are reduced with the formation of the complexes.