Thiolate-Protected Bimetallic Nanoclusters: Understanding the Relationship between Electronic and Catalytic Properties

Heteroatom Doping Promoted Ultrabright and Ultrastable Photoluminescence of Water-Soluble Au/Ag Nanoclusters for Visual and Efficient Drug Delivery to Cancer Cells

Photoluminescence (PL) metal nanoclusters (NCs) have attracted extensive attention due to their excellent physicochemical properties, good biocompatibility, and broad application prospects. However, developing water-soluble PL metal NCs with a high quantum yield (QY) and high stability for visual drug delivery remains a great challenge. Herein, we have synthesized ultrabright l-Arg-ATT-Au/Ag NCs (Au/Ag NCs) with a PL QY as high as 73% and excellent photostability by heteroatom doping and surface rigidization in aqueous solution. The as-prepared Au/Ag NCs can maintain a high QY of over 61% in a wide pH range and various ionic environments as well as a respectable resistance to photobleaching. The results from structure characterization and steady-state and time-resolved spectroscopic analysis reveal that Ag doping into Au NCs not only effectively modifies the electronic structure and photostability but also significantly regulates the interfacial dynamics of the excited states and enhances the PL QY of Au/Ag NCs. Studies in vitro indicate Au/Ag NCs have a high loading capacity and pH-triggered release ability of doxorubicin (DOX) that can be visualized from the quenching and recovery of PL intensity and lifetime. Imaging-guided experiments in cancer cells show that DOX of Au/Ag NCs-DOX agents can be efficiently delivered and released in the nucleus with preferential accumulation in the nucleolus, facilitating deep insight into the drug action sites and pharmacological mechanisms. Moreover, the evaluation of anticancer activity in vivo reveals an outstanding suppression rate of 90.2% for mice tumors. These findings demonstrate Au/Ag NCs to be a superior platform for bioimaging and visual drug delivery in biomedical applications.

Toward Understanding the Correlation between the Charge States and the Core Structures in Thiolate-Protected Gold Nanoclusters

The charge states of thiolate-protected gold nanoclusters (AuNCs) are vital to their stabilities through affecting the number of the valence electrons. However, the origin of the charge states of AuNCs has not been fully understood yet. Herein, through fulfilling the duet-rule derived Au₃(2e) and Au₄(2e) elementary blocks in the grand unified model (GUM), analysis on the substantial crystal structures indicates the charge states of AuNCs can correlate with their core structural packing, especially the number of Au₃(2e) elementary blocks. In addition, aided by the Au₃(2e) block's role in tailoring the population of valence electron, three new AuNCs including Au₁₈(SCH₃)₁₄, Au₃₀(SCH₃)₂₀, and [Au₃₀(SCH₃)₂₁]^- are predicted through controllably specifying the exact number of Au₃(2e) in the core. This work shows that GUM can bridge the gap among the charge states of the cluster, the inner core structure of the cluster, and the detachment of outer ligands via the electron counting rule.

Computational Approaches to the Electronic Properties of Noble Metal Nanoclusters Protected by Organic Ligands

Organometallic nanoparticles composed by metal cores with sizes under two nanometers covered with organic capping ligands exhibit intermediate properties between those of atoms and molecules on one side, and those of larger metal nanoparticles on the other. In fact, these particles do not show a peculiar metallic behavior, characterized by plasmon resonances, but instead they have nonvanishing band-gaps, more along molecular optical properties. As a consequence, they are suitable to be described and investigated by computational approaches such as those used in quantum chemistry, for instance those based on the time-dependent density functional theory (TD-DFT). Here, I present a short review of the research performed from 2014 onward at the University of Modena and Reggio Emilia (Italy) on the TD-DFT interpretation of the electronic spectra of different organic-protected gold and/or silver nanoclusters.