We present the synthesis, separation, and characterization of covalently-bound multimers of paramercaptobenzoic acid (p-MBA) protected gold nanoclusters. The multimers were synthesized by performing a ligand-exchange reaction of a pre-characterized Au 102 (p-MBA) 44 nanocluster with biphenyl-4,4'dithiol (BPDT). The reaction products were separated using gel electrophoresis yielding several distinct bands. The bands were analyzed by transmission electron microscopy (TEM) revealing monomer, dimer, and trimer fractions of the nanocluster. TEM analysis of dimers in combination with molecular dynamics simulations suggest that the nanoclusters are covalently bound via a disulfide bridge between BPDT molecules. The linking chemistry is not specific to Au 102 (p-MBA) 44 . The same approach yields multimers also for a larger monodisperse p-MBA-protected cluster of approximately 250 gold atoms, Au ∼250 (p-MBA) n . While the Au 102 (p-MBA) 44 is not plasmonic, the Au ∼250 (p-MBA) n nanocluster supports localized surface plasmon resonance (LSPR) at 530 nm. Multimers of the Au ∼250 (p-MBA) n exhibit additional transitions in their UV-vis spectrum at 630 nm and 810 nm, indicating the presence of hybridized LSPR modes. Well-defined structures and relatively small sizes make these systems excellent candidates for connecting ab initio theoretical studies and experimental quantum plasmonics. Moreover, our work opens new possibilities in the controlled synthesis of advanced monodisperse nanocluster superstructures. † Electronic supplementary information (ESI) available: Details of syntheses and purification; additional images of PAGE runs; mass spectrum of Au 102 ( p-MBA) 44 ; 1 H NMR spectra of clusters; TEM analysis of cluster sizes; additional TEM images; core-to-core distance and angle distributions from simulations; additional multimer size statistics; additional UV-vis spectra for Au ∼250 ( p-MBA) n multimers and aggregates. See
Water-soluble gold nanoclusters with welldefined molecular structures and stability possess particular biophysical properties making them excellent candidates for biological applications as well as for fundamental spectroscopic studies. The currently existing synthetic protocols for atomically monodisperse thiolate-protected gold nanoclusters (AuMPCs) have been widely expanded with organothiolates, yet the direct synthesis reports for water-soluble AuMPCs are still deficient. Here, we demonstrate a wet-chemistry pHcontrolled synthesis of two large water-soluble nanoclusters utilizing p-mercaptobenzoic acid (pMBA), affording different sizes of plasmonic AuMPCs on the preparative scale (∼7 mg). AuMPCs are essentially homogenous in size and are stable in solution and the solid state. Number of characterization methods were used to gain detailed information about the size, symmetry, molecular composition, and structure of these systems, i.e., high-resolution transmission electron microscopy, powder X-ray diffraction, NMR, UV−vis, thermogravimetry, and polyacrylamide gel electrophoresis. On the basis of the conducted experimental analyses and computationally aided predictions it can be evidenced that both clusters exhibit twinned face-centered cubic symmetry with the molecular composition of Au 210−230 (pMBA) 70−80 and Au 426−442 (pMBA) 112−115 , referred from now on as Au250 and Au500, respectively. For future reference, toxicity of both gold clusters in various concentrations on cultures of Gram-positive and Gram-negative bacteria was investigated.
Interactions between an atomically precise gold nanocluster Au102(p-MBA)44 (p-MBA = para mercaptobenzoic acid) and a fluorescent organic dye molecule (KU, azadioxatriangulenium) are studied. In solution, the constituents form spontaneously a...
Five nucleic acid binding cyanine dyes were synthesized and their photophysical properties were evaluated. Changing a single heteroatom in the chromophore causes major differences both in brightness and photostability between...
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