Subcategory: STEM Research
Tandabany Dinadayalane - Clark Atlanta University
DFT calculations at M06-2X/6-31G(d) level have been performed to examine the interactions of two alpha-amino acids (histidine and proline) individually with graphene sheets of two different sizes (62 and 186 carbon atoms). The edges of graphene surfaces were terminated with hydrogen atoms. The conformational analysis was performed for both proline and histidine using MMFF force field as implemented in Spartan ’16. From the conformers generated, we have chosen few low energy and one high energy conformers of proline and histidine to build the complexes with graphene. In case of forming the complexes, we have considered various possible orientations. Binding energies with and without basis set superposition error (BSSE) were calculated. Our aim is to understand the influence of conformers of histidine and proline on binding with graphene in the gas and aqueous phases, and the effect of varying the graphene sheet on their binding affinities. In case of histidine-graphene complexes, the competition between pi-pi and C-H/N-H…pi interactions exists. It should be noted that histidine exhibits higher binding energy than proline. This could be attributed to the presence of pi-electrons and two nitrogen atoms in the five-membered ring of histidine. The most stable complex of proline-graphene shows multiple C-H…pi interactions along with N-H…pi interactions. Graphene size effect is negligible for both amino acids. The solvation effect on binding energies was evaluated by polarizable continuum model (PCM). Inclusion of solvent (water) reduces the binding energy but the trend is retained. HOMO-LUMO energy gaps were calculated at the TPSSh/6-31G(d)//M06-2X/6-31G(d) level. Binding of proline or histidine does not change the band gap of graphene.
Funder Acknowledgement(s): TD acknowledges the NSF HBCU-UP RIA (Grant number 1601071)
Faculty Advisor: None Listed,