DNA Base Pairs Sensors: DFT, QTAIM and NCI-RDG Study

This work aims to present a theoretical study of sensor candidate formed from Cytosine-Cu-Cytosine at DFT/BP86/ZORA/DZP level using ADF code for the significance of proposing complexes based on DNA that captures toxic adducts in the gas phase as: CO, CO₂, NO, HCN, SO₂, H₂S and NO₂. The interaction between adducts and Cytosine-Cu-Cytosine complex was analyzed by QTAIM based on electronic density ρ(r) and Laplacian of electronic density ？²ρ(r). NCI-RDG analysis was performed and discussed. Interaction of adducts with Cytosine-Cu-Cytosine complex takes place with a transition state, and the energy barrier is lower with CO₂ E(TS) = 0.26 (kcal/mol). Potential energy surface (PES) gives saddle point for the formation of two bonds Cu-N and Cu-C at E = ？6.826 a.u, Cu-N = 1.96 ？ and Cu-C = 2.38 ？ during the interaction of HCN with Cytosine-Cu-Cytosine complex. PES analysis proved that the interaction of NO₂ with Cytosine-Cu-Cytosine achieves stabilization at E = ？6.781 a.u, ${\text{Cu-N}}_{{\text{NO}}_{\text{2}}}$ = 2.057 ？ and ${\text{O}}_{{\text{NO}}_{\text{2}}}$ …H23 = 1.90 ？.