Chiral Discrimination of Amino Acids by Using a Twisted Carbon Nanobelt: A DFT Study

Beyond the confines of chemistry, molecular chirality and related ideas like symmetry, asymmetry, handedness, symmetry breaking, and chiral recognition have a growing influence in science. In the current study, a twisted carbon nanobelt (TCNB) is used for the chiral discrimination of amino acids (AA) using density functional theory study. The values of interaction energy (<i>E</i>_int) range from −28.55 to −34.45 kcal mol^–1. Two distinct trends of <i>E</i>_int are identified, with the TCNB demonstrating selectivity for <i>R</i>-enantiomers of proline and <i>S</i>-enantiomers of histidine. Similarly, for threonine, the TCNB is selective toward <i>SR</i>-threonine. Chiral discrimination energy is most pronounced for threonine@TCNB (<i>SR</i> and <i>RS</i>) enantiomeric complexes, <i>i</i>.<i>e</i>., 6.90 kcal mol^–1. Quantum theory of atoms in molecules (QTAIM) and noncovalent interaction (NCI) analyses reveal that the <i>S</i> enantiomer in each case has maximum interactions compared to the <i>R</i> enantiomer. Electron density difference (EDD) and natural bond orbital (NBO) analyses indicate charge transfer from amino acids toward the belt, with <i>RS</i>-thre@TCNB having a maximum charge transfer, <i>i</i>.<i>e</i>., 2.260 (e^–). Frontier molecular orbital (FMO) analysis reveals a decline in energy gap upon complexations. The highest decrease in energy gap is seen for <i>R</i>-pro@TCNB (3.42 eV from 3.59 eV), which displays high selectivity of the TCNB toward proline. The current study highlights the selectivity of the TCNB toward chiral molecules, showing a significant chiral discrimination ability for <i>S</i> and <i>R</i> enantiomers of amino acids. This work contributes valuable insights into the molecular interactions and chiral recognition involving twisted carbon nanobelts.