Theoretical Investigation of Structures, Bonding and Electronic Properties for the Complexes of 6-Mercaptopurine and Ag8 Clusters

The Ag clusters have been investigated widely theoretically and experimentally. In particular, it has recently shown that the neutral Ag-8 clusters embedded in an argon matrix have a strong fluorescence signal. As we can know, the metal clusters may have important effects on the structures and properties of biomolecules. More and more attention is paid to the interaction between nanomaterials and biomolecules. In this work, the B3LYP method in density functional theory was used on the complexes between the 6-mercaptopurine (6MP) and Ag-8 clusters combined with 6-311++G** as well as LANL2DZ base sets. The geometries of all the complexes were optimized with full degree of freedom and the structures, chemical bonds, orbital properties as well as Mulliken charges for ten possible complexes were analyzed based on the same theory level. In addition, the influence of temperature and pressure on the stabilities of the four complexes was further explored using standard statistical thermodynamic methods ranging from 50 to 500 K and at 100 kPa or 100 bar. The results show that the complex Ag-8-6MP-7-5 can be the most stable one among the investigated complexes, in which the Ag(11) atom interacts with the S(10) atom forming the strong chemical bond. The Mulliken charges also show that the Ag-S chemical bond is formed and the related charge has transferred. Additionally, the temperature and pressure can significantly influence the stability of the four stable complexes.