Preparation and Antiviral Activity of La₂CuO₄ and Y₂Cu₂O₅ with Mechanistic Insights from First-Principles

Copper oxide is a representative inorganic antiviral material. However, the highly active Cu₂O phase transforms gradually into CuO, which results in reduced antiviral activity. For this study, we aimed at developing a material with high antiviral activity based on CuO. To this end, La₂CuO₄ and Y₂Cu₂O₅ were synthesized respectively by combining CuO with La₂O₃ and Y₂O₃. Their antiviral properties were investigated. For comparison, Al₂CuO₄ and the simple oxides of each constituent element were also prepared and evaluated. The ternary oxides synthesized using citric acid combustion method and the solid-state reaction method were confirmed to be single-phase. Surface analysis revealed the presence of Cu⁺ on La₂CuO₄ and Y₂Cu₂O₅. The amount of ion release from these materials was found to be low. Antiviral activity tests were conducted against the nonenveloped bacteriophage Qβ and the enveloped bacteriophage Φ6, following ISO-standard evaluation methods. La₂CuO₄ and Y₂Cu₂O₅ exhibited stronger antiviral activity against Qβ than either CuO, La₂O₃, or Y₂O₃. Detailed analyses suggested that the enhanced activity was attributable to strengthened electrostatic interactions and an improved ability to inactivate proteins. In contrast, La₂O₃ and Y₂O₃ showed relatively high antiviral activity against Φ6, primarily because of their strong affinity for phosphate groups. First-principles calculations indicate that (i) the surfaces of these ternary oxides containing Cu²⁺ are cation-rich and (ii) the surface formal charge of copper is predominantly monovalent. These findings suggest that the unique surface states because of their crystal structures play a crucially important role in the antiviral performance of La₂CuO₄ and Y₂Cu₂O₅. The antiviral activity of La₂CuO₄ against Qβ exhibited high long-term stability, surpassing the reported performance of Cu₂O. The present study is expected to provide promising new materials with improved antiviral activities compared to conventional CuO.