We report the synthesis, for the first time, of small, highly monodisperse Cu 5 clusters in water without any surfactant or protective agent. For this purpose, we used a new approach based on the kinetic control of the reaction, which is achieved with an electrochemical method and using a solution with almost no conductivity (i.e., without added electrolytes commonly used in electrochemical methods). This allows the application of extremely small current densities needed to focus the reaction to synthesize only one selected cluster size. Clusters were characterized by ultraviolet−visible (UV−vis) and fluorescence spectroscopies, atomic force microscopy, electrospray ionization time-of-flight mass spectrometry, X-ray photoelectron spectroscopy, extended X-ray absorption fine structure, and Xray absorption near-edge spectroscopy, showing the presence of only Cu clusters with five atoms. Contrary to what should be expected, such clusters are very stable and remain unaltered in solution, for at least one year, because of their huge band gap (4.07 eV). Moreover, such Cu 5 clusters are extremely stable to UV irradiation, temperature, and pH.

Nanomaterials with very low atomicity deserve consideration as potential pharmacological agents owing to their very small size and to their properties that can be precisely tuned with minor modifications to their size. Here, it is shown that silver clusters of three atoms (Ag -AQCs)-developed by an ad hoc method-augment chromatin accessibility. This effect only occurs during DNA replication. Coadministration of Ag -AQCs increases the cytotoxic effect of DNA-acting drugs on human lung carcinoma cells. In mice with orthotopic lung tumors, the coadministration of Ag -AQCs increases the amount of cisplatin (CDDP) bound to the tumor DNA by fivefold without modifying CDDP levels in normal tissues. As a result, CDDP coadministered with Ag -AQCs more strongly reduces the tumor burden. Evidence of the significance of targeting chromatin compaction to increase the therapeutic index of chemotherapy is now provided.

Subnanometer-sized metal clusters often feature a molecule-like electronic structure, which makes their physical and chemical properties significantly different from those of nanoparticles and bulk material. Considering potential applications, there is a major concern about their thermal stability and susceptibility towards oxidation. Cu clusters of only 5 atoms (Cu₅ clusters) are first synthesized in high concentration using a new-generation wet chemical method. Next, it is shown that, contrary to what is currently assumed, Cu₅ clusters display nobility, beyond resistance to irreversible oxidation, at a broad range of temperatures and oxygen pressures. The outstanding nobility arises from an unusual reversible oxidation which is observed by <i>in situ</i> X-ray Absorption Spectroscopy and X-ray Photoelectron Spectroscopy on Cu₅ clusters deposited onto highly oriented pyrolitic graphite at different oxygen pressures and up to 773 K. This atypical property is explained by a theoretical approach combining different state-of-the-art first principles theories. It reveals the essential role of collective quantum effects in the physical mechanism responsible for the nobility of Cu₅ clusters, encompassing a structural ‘breathing’ through concerted Cu–Cu elongations/contractions upon O₂ uptake/release, and collective charge transfer as well. A predictive phase diagram of their reversible oxidation states is also delivered, agreeing with the experimental observations. The collective quantum effects responsible of the observed nobility are expected to be general in subnanometer-sized metal clusters, pushing this new generation of materials to an upper level.

Subnanometer-sized metal clusters often feature a molecule-like electronic structure, which makes their physical and chemical properties significantly different from those of nanoparticles and bulk material. Considering potential applications, there is a major concern about their thermal stability and susceptibility towards oxidation. Cu clusters of only 5 atoms (Cu₅ clusters) are first synthesized in high concentration using a new-generation wet chemical method. Next, it is shown that, contrary to what is currently assumed, Cu₅ clusters display nobility, beyond resistance to irreversible oxidation, at a broad range of temperatures and oxygen pressures. The outstanding nobility arises from an unusual reversible oxidation which is observed by <i>in situ</i> X-ray Absorption Spectroscopy and X-ray Photoelectron Spectroscopy on Cu₅ clusters deposited onto highly oriented pyrolitic graphite at different oxygen pressures and up to 773 K. This atypical property is explained by a theoretical approach combining different state-of-the-art first principles theories. It reveals the essential role of collective quantum effects in the physical mechanism responsible for the nobility of Cu₅ clusters, encompassing a structural ‘breathing’ through concerted Cu–Cu elongations/contractions upon O₂ uptake/release, and collective charge transfer as well. A predictive phase diagram of their reversible oxidation states is also delivered, agreeing with the experimental observations. The collective quantum effects responsible of the observed nobility are expected to be general in subnanometer-sized metal clusters, pushing this new generation of materials to an upper level.