Quantum-chemical modeling of sorption interactions of histidine enantiomers with carbon nanotubes

Abstract

In this study, the elementary act of adsorption of monomers and dimers of histidine enantiomers on a dextrorotatory model CNT-(7,6) chirality from an aqueous solution was studied using quantum chemistry methods to interpret the adsorption isotherm of L- and D-histidine on carbon nanotubes mkNANO MKN-SWCNT S1 and identify the mechanism of sorption sorbent-sorbate interactions. Quantum chemical modelling of the structures was carried out using the GAUSSIAN 09 program by the B3LYP/6-31G(d,p) GD3 method; the influence of the environment was considered using the Tomasi polarization continuum model (PCM). The results of quantum chemical modelling have established a greater number of point interactions of nitrogen and oxygen atoms of the D-isomer with the dextrorotatory CNT, which determines the higher adsorption energy of the D-histidine monomer and dimer on the CNT compared to the L-isomer. It was shown that enantiomers are attached to nanotubes mainly by van der Waals forces and π-π interactions between the imidazole ring of histidine and the carbon nanotube. The contribution of π-π stacking interactions to the adsorption value was assessed using quantum chemistry methods. The formation of 4 different L-amino acid dimers is possible on the surface of CNT: 2L1, 2L2, 2L3, 2L4 and also for the D isomer: 2D1; 2D2; 2D3; 2D4. The results of quantum chemical modelling showed that dimers 2L4 and 2D4 have the highest adsorption energy on CNT. Quantum chemistry methods were also used to calculate the average energy of intermolecular H bonds in seven, eight, and thirteen particle clusters of L-histidine, as well as in seven- and nine-particle clusters of the D-enantiomer. The calculation showed that this value increases with increasing cluster size. This led to a significant contribution of hydrogen bonding to the decrease in the energy of the sorption system during cluster adsorption.