Hydrogen bonding cooperation in glycine-(water)n clusters studied by density functional theory calculations

Although hydrogen bonds are relatively weak, they play essential roles in life processes. Through cooperative effects, these weak bonds exhibit a significant influence on the structure, function and dynamics of biomolecules. In this work, we study the internal mechanism of cooperativities, involving collective electron and nuclear motions, in multiple H-bonding glycine-(H2O)(n) (n=2 or 3) clusters, using first-principles calculations. Multiplex molecular orbitals aid the coherent carrier-transport through orbital-penetrating. In addition, the infrared spectra and nuclear vibrating patterns reveal that the H-bond donor stretching modes exhibit significant connections across neighboring hydrogen bonds. However, when the anharmonic nuclear motions are taken into account, the cooperative effects are partially ruined due to the nonsynchronized nuclei activities. Additionally, the cooperative contributions to the H-bonding interaction energies are also evaluated. These results give descriptions of cooperativities of multiple hydrogen bonds and provide a more comprehensive insight into conventional intermolecular hydrogen bonding.