Nucleotide conjugated (ZnO) 3 cluster: Interaction and optical characteristics using TDDFT.

Binding of four DNA nucleotide units with (ZnO)3 cluster in an aqueous phase has been investigated using density functional theory (DFT) and time dependent-density functional theory (TDDFT) method and the stability order for (ZnO)3 -nucleobases/sugar/phosphate systems is predicted as phosphate > C > A > S > T ∼ G. The order of binding energy for (ZnO)3 -nucleotide hybrid systems is observed to be (ZnO)3  + nuc-C ˃ (ZnO)3  + nuc-A ˃ (ZnO)3  + nuc-G ˃ (ZnO)3  + nuc-T. The binding of nucleotide units with the cluster has been explained on the basis of molecular electrostatic potential (MEP) plots, hydrogen bonding, glycosidic torsion angles, density of state (DOS) plots. The photophysical properties of (ZnO)3 -nucleotide complexes have been studied using TDDFT approach. Among all (ZnO)3 -nucleotide complexes, the absorption spectra of (ZnO)3  + nuc-A and (ZnO)3  + nuc-C complexes are seen to undergo red shift with respect to their bare nucleotide units that would be useful in the optical sensing of the respective nucleotides of DNA. It is interesting to note that binding of the nucleotide unit with the cluster makes it fluorescent, the study reports the fluorescence activity of (ZnO)3  + nuc-T complex.