Interaction of Glycine with BC2N Nanotubes: Dative Covalent and Hydrogen Bonding

Immobilization of biomolecules on the inorganic nanostructured materials have attracted much attention during the last years as they exhibit unique features derived from combining synergistically the properties of the interacting components. We aimed to investigate the interaction of BC2N nanotubes by glycine using density functional theory. For all the BC2N systems, six initial structural guesses were considered: pure interaction between the NH2 group of Gly and one nanotube B/C/N atom plus H-bonding between the Gly OH group and one nanotube N atoms; interaction between the Gly CO group and one nanotube B/C/N atom plus H-bonding between the Gly OH group and one nanotube N atom. Our DFT results clearly indicate that the most stable adduct results from dative covalent interactions between the Gly NH2 group and the B atoms, which act as Lewis acid sites and the N atoms acting as H-bonding acceptor groups. These findings are consistent with the polar character of BN bonds in BC2N nanotubes. Based on NBO analysis the computed charge transfers values from Gly to the BNNTs, being 0.30 e, confirms the formation of charge transfer complexes for the complexes. The interaction of Gly through the COOH group by means of a simultaneous CO–B dative bond and a OH•••N(BC2N) H-bond was also considered. For the BN/COOH-1 adduct, Gly adsorption on the (4,0) BC2N results in a spontaneous proton transfer from the Gly COOH group to the N nanotube atom, hence forming a COO-/ BC2N -H+ ion pair. Such a proton transfer is attributed to the net charge transfer occurring from Gly to the BC2N, which induces an increase of the COOH acidity and the nanotube basicity up to the point of promoting the proton transfer to a nearby N atom of the nanotube.