Experimental and first-principles investigation of the adsorption and entrapping of guanine with SiO2 clusters of sol–gel silicate material for understanding DNA photodamage

Abstract

We report a first principles density functional theoretical (DFT) investigation of guanine (G) adsorption onto SiO₂ clusters, viz., Si₂O₄, Si₃O₆, Si₄O₈ and Si₅O₁₀ in terms of geometry, binding energy (E_B), binding site, energy gap (E_g), and electronic and spectral properties. Guanine entrapped within a Si₉O₁₈ cluster was also studied in terms of geometry, energy gap (E_g), electronic and spectral properties. We observed that the most stable forms of the cluster were Si₅O₁₀ and Si₉O₁₈. Guanine adsorbed onto SiO₂ (G–SiO₂) and guanine entrapped within SiO₂ (GE–SiO₂) were analyzed by the B3LYP/LanL2DZ method. The HOMO–LUMO energies illustrate that charge transfer from ligand to metal (L → M) occurs in G–SiO₂ clusters as guanine to SiO₂. The composite of guanine with nanostructured silica material was prepared by simple precipitation and chemical sol–gel processes. The prepared G–SiO₂ and GE–SiO₂ composites were characterized by FT-IR and FE-SEM with EDX analysis. The resulting experimental evidence is included for better understanding the guanine adsorption and entrapment. The adsorption and entrapping of G–SiO₂ and GE–SiO₂ was also confirmed by UV-vis spectroscopy. Experimental results are compared with the DFT results. Furthermore, the sol–gel silicate material used to protect the DNA base (guanine) from UVA-irradiation has been highlighted.