Glutathione-Coated Au₂₉(SG)₂₇: Structural Determination Based on Different Combination Styles Confirmed by Experiments

Glutathione-coated small-sized gold nanocluster denoted as Au₂₉(SG)₂₇ has potential applications in bio therapeutics. Because it is difficult to obtain an accurate atomic structure experimentally, its structure is predicted by the density functional theory. The atomic structure of Au₂₉(SG)₂₇ is speculated to contain a ring motif (for low Au/S ratio), Au₄ core, and staple motifs (by "divide and protect" method). In the structural optimization, we proposed the four various combination styles and took the second and third combinations, respectively, when N ≤ 6 and N > 6 (N is the number of Au atoms in the ring motif). All stable isomers are sorted by energy, and the structure with the lowest energy (isomer 1) consists of a Au₇(SCH₃)₇ ring motif and Au₄ core-attached staple motifs as Au₄Au₈(SCH₃)₉Au₁₀(SCH₃)₁₁. Then, we calculated and analyzed the atomic and electronic structures of isomer 1. The electronic transition of highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) is mainly the transition from the d orbital to p orbital, which is within the gold core or between the gold core and ring motif. The ultraviolet-visible absorption spectrum calculated by time-dependent density functional is in good agreement with the experimental measurement to confirm the atomic structure of Au₂₉(SG)₂₇ predicted by the combination-style strategy.