Document Type : Research Paper
In the present work, an extensive theoretical calculation study on Histidine-Histidine dipeptide in gas
phase is done by using DFT method with Gaussian 98 program. Through investigations on the molecular
geometries of this molecule it is found that there is six rings in the molecules not two rings. The presence of
four intramolecular hydrogen bonds is responsible for the formation of additional four rings besides two
imidazole rings which gives more stability to the molecule. The quantum theory of atoms in molecules
(QTAIM) proves these strong intramolecular hydrogen bonds in the title dipeptide.