Ortho-phenylenediamine Based Bis-ureas as the Ion Selective Sensors; A QM/MD Study

Density functional theory dispersion corrected (DFT-D3)calculations and molecular dynamic (MD) simulation were applied to investigate the sensing ability of four types of receptors (RCs) composed of the ortho-phenylenediamine based bis-ureas for selective complexation with the anions such as Cl–, Br–, OAC–, PhCO2–, H2PO4– and HSO4– in the gas phase and DMSO. On the basis of the data obtained from B3LYP-D3/6-31G+(d,p)calculations, RCs-OAC– complexes have the maximum binding energy, whose binding energy is reduced in the presence of DMSO as the solvent. IR vibrational frequencies of the N—H bonds of the RCs showed a red-shift due to their interactions with the anions in the corresponding complexes. Moreover, HOMO-LUMO analysis indicates that due to the complexation process, ionization potential (IP) and electron affinity (EA) values decrease which confirms the electron migration from the anions to the RCs. Natural bond orbital (NBO) analysis indicates that charge transfer occurs from the anions to the RCs due to an n-type mechanism and in comparison to other ions OAC– has stronger orbital interactions with the RCs. 20 ns MD simulations in DMSO, show the specific interactions between OAC– and RC4, which confirm the ability of RC4 as a good candidate to be applied as an anion-selective sensor.