Erratum: Structural isomerism in gold nanoparticles revealed by X-ray crystallography

Probing the Microstructure in Pure Al & Cu Melts: Theory Meets Experiment

In the present work, a new model of the atomic cluster structure, which is determined by metal Wulff construction with the crystal structure inside, is proposed to describe the structures of metallic melts. The shapes of the structures are determined by surface energies of different crystal plane groups, calculated from density functional theory (DFT), while the size is given by the pair distribution function (PDF) of the experimental high-temperature X-ray diffraction (HTXRD). Taking Aluminum (Al) and Copper (Cu) as the representative examples, we demonstrate that the simulated XRD curves from present models match the experimental results quite well, not only regarding the position and width of the peaks but also the relative intensity of the first and second peaks. These results indicate a successful model to describe the properties of metallic melts. The model also explains a main peak deviation phenomenon between the XRD of metallic melt and the solid ones in pure metal Al. Finally, a physical picture of metallic melt is given, which is mainly composed of atomic cluster structures and free atoms around them.

Structural Oscillation Revealed in Gold Nanoparticles

Oscillation is an intriguing phenomenon in nature. However, structural oscillation has not yet been found in semiconducting nanoparticles, primarily due to the difficulty of structural resolution at the atomic level. The emergence of gold nanoclusters (ultrasmall nanoparticles) has provided an excellent opportunity to address some challenging issues in the nanoparticle field. Herein, two Au₂₈(CHT)₂₀ (CHT: cyclohexanethiolate) structural isomers (Au_28i and Au_28ii for short) were concurrently synthesized by employing a quasi-antigalvanic method, and they could be reversibly transformed into each other for at least 10 cycles, driven by dissolution and crystallization processes. The transformation from Au_28ii to Au_28i is solvent-dielectric-constant-dependent, with a notable deuteration effect from dichloromethane. The markedly different photoluminescence values of these two isomers not only have important implications for the structure-property correlations but also have potential applications in converting, sensing, etc.

Gold Fusion: From Au25(SR)18 to Au38(SR)24, the Most Unexpected Transformation of a Very Stable Nanocluster

The study of the molecular cluster Au₂₅(SR)₁₈ has provided a wealth of fundamental insights into the properties of clusters protected by thiolated ligands (SR). This is also because this cluster has been particularly stable under a number of experimental conditions. Very unexpectedly, we found that paramagnetic Au₂₅(SR)₁₈⁰ undergoes a spontaneous bimolecular fusion to form another benchmark gold nanocluster, Au₃₈(SR)₂₄. We tested this reaction with a series of Au₂₅ clusters. The fusion was confirmed and characterized by UV-vis absorption spectroscopy, ESI mass spectrometry, ¹H and ¹³C NMR spectroscopy, and electrochemistry. NMR evidences the presence of four types of ligand and, for the same proton type, double signals caused by the diastereotopicity arising from the chirality of the capping shell. This effect propagates up to the third carbon atom along the ligand chain. Electrochemistry provides a particularly convenient way to study the evolution process and determine the fusion rate constant, which decreases as the ligand length increases. No reaction is observed for the anionic clusters, whereas the radical nature of Au₂₅(SR)₁₈⁰ appears to play an important role. This transformation of a stable cluster into a larger stable cluster without addition of any co-reagent also features the bottom-up assembly of the Au₁₃ building block in solution. This very unexpected result could modify our view of the relative stability of molecular gold nanoclusters.

pH-Dependent Transmembrane Activity of Peptide-Functionalized Gold Nanostars for Computed Tomography/Photoacoustic Imaging and Photothermal Therapy

Progress in multifunctional nanomaterials for tumor therapy mostly depends on the development of tumor-targeting delivery strategies. One approach is to explore a pH-responsive strategy to target the slightly acidic solid tumor microenvironment. A novel class of pH (low) insertion peptides (pHLIPs) with pH-dependent transmembrane activity can fold and rapidly insert into the lipid bilayer of tumor cells triggered by acidity, facilitating the cellular internalization of nanomaterials synchronously. Here, we innovatively decorated gold nanostars (GNSs) with pHLIPs (GNS-pHLIP) to improve their targeting ability and photothermal therapeutic (PTT) efficiency. The obtained GNS-pHLIP exhibited the excellent characteristics of uniform size and good biocompatibility. As compared to GNS-mPEG, the cellular internalization of GNS-pHLIP was 1-fold higher after a 2 h incubation with cells in media at pH 6.4 than at pH 7.4. Moreover, the tumor accumulation of the GNS-pHLIP was 3-fold higher than that of GNS-mPEG after intravenous injection into MCF-7 breast tumor animal models for 24 h. Furthermore, GNS-pHLIP exhibited stronger signals than the GNS-mPEG through computed tomography (CT) and photoacoustic (PA) imaging. Simultaneously, the desirable targeting efficiency significantly improved the PTT efficacy to tumors, with low side effects on normal tissues. The results clearly demonstrate that the GNS-pHLIP successfully took advantage of the tumor-targeting ability of pHLIPs and the good characteristics of GNSs, which may contribute to the study of tumor imaging and therapy.

Unusual reactivity of dithiol protected clusters in comparison to monothiol protected clusters: studies using Ag51(BDT)19(TPP)3 and Ag29(BDT)12(TPP)4

We report the synthesis and unique reactivity of a new green dithiol protected cluster (DTPC), Ag₅₁(BDT)₁₉(TPP)₃ (BDT and TPP are 1,3-benzenedithiol and triphenylphosphine, respectively). The cluster composition was confirmed by electrospray ionization (ESI) and matrix-assisted laser desorption ionization (MALDI) mass spectrometric studies as well as by other supporting data. Surprisingly, the chemical reactivity between this DTPC and Au₂₅(SR)₁₈ involves only metal ion exchange in Au₂₅(SR)₁₈ without any ligand exchange, while reactions between monothiol protected clusters (MTPCs) show both metal and ligand exchange, an example being the reaction between Ag₂₅DMBT₁₈ and Au₂₅PET₁₈ (where DMBT and PET are 2,4-dimethylbenzenethiol and phenylethanethiol, respectively). The conclusions have been confirmed by the reaction of another DTPC, Ag₂₉(BDT)₁₂(TPP)₄ with Au₂₅BT₁₈ (where BT corresponds to butanethiol) in which only metal exchange happens in Au₂₅BT₁₈. We also show the conversion of Ag₅₁(BDT)₁₉(TPP)₃ to Ag₂₉(BDT)₁₂(TPP)₄ in the presence of a second monothiol, DMBT which does not get integrated into the product cluster. This is completely different from the previous understanding wherein the reaction between MTPCs and a second thiol leads to either mixed thiol protected clusters with the same core composition or a completely new cluster core protected with the second thiol. The present study exposes a new avenue of research for monolayer protected clusters, which in turn will give additional impetus to explore the chemistry of DTPCs.