Synthesis and the Origin of the Stability of Thiolate-Protected Au₁₃₀ and Au₁₈₇ Clusters

Two stable thiolate-protected gold clusters (Au–SR), Au₁₃₀ and Au₁₈₇ clusters, were synthesized to obtain a better understanding of the size dependence of the origin of the stability of Au–SR clusters. These clusters were synthesized by employing different preparation conditions from those used to synthesize previously reported magic gold clusters; in particular, a lower [RSH] to [AuCl₄^–] molar ratio ([AuCl₄^–]/[RSH] = 1:1) was used than that used to prepare Au₂₅(SR)₁₈, Au₃₈(SR)₂₄, Au₆₈(SR)₃₄, Au₁₀₂(SR)₄₄, and Au₁₄₄(SR)₆₀ (id. = 1:4–12). The two clusters thus synthesized were separated from the mixture by high-performance liquid chromatography with reverse-phase columns. Mass spectrometry of the products revealed the presence of two clusters with chemical compositions of Au₁₃₀(SC₁₂H₂₅)₅₀ and Au₁₈₇(SC₁₂H₂₅)₆₈. The origin of the stability of these two clusters and the size dependence of the origin of the stability of thiolate-protected gold clusters were discussed in terms of the total number of valence electrons

Change in specific interactions between lactose repressor protein and DNA induced by ligand binding: molecular dynamics and molecular orbital calculations

<div><p>Lactose repressor protein (LacR) plays an essential role in controlling the transcription mechanism of genomic information from DNA to mRNA. It has been elucidated that a ligand binding to LacR regulates allosterically the specific interactions between LacR and operator DNA. However, the effect of the ligand binding on the specific interactions has not been clarified at an atomic level. In this study, we performed classical molecular dynamics (MD) and <i>ab initio</i> fragment molecular orbital simulations to elucidate the effect of ligand binding at atomic and electronic levels. The MD simulations for the solvated complexes with LacR-dimer, DNA and ligand demonstrate that the binding of an inducer IPTG to LacR-dimer significantly changes the structure of LacR-monomer to cause strong interactions between LacR-monomers, resulting in weakening the interactions between LacR-dimer and DNA. In contrast, the binding of an anti-inducer ONPF to LacR-dimer was found to enhance the interactions between LacR-dimer and DNA. These findings are consistent with the functions of IPTG and ONPF as an inducer and an anti-inducer, respectively. We therefore proposed a simplified model for the effect of the ligand binding on the specific interactions between LacR-dimer and DNA.</p></div