Although various complex, bulky ligands have been used to functionalize plasmonic gold nanoparticles, introducing them to small, atomically precise gold clusters is not trivial. Here, we demonstrate a simple one-pot procedure to synthesize fluorescent magic number Au25 clusters carrying controlled amounts of bulky calix[4]arene functionalities. These clusters are obtained from a synthesis feed containing binary mixtures of tetrathiolated calix[4]arene and 1-butanethiol. By systematic variation of the molar ratio of ligands, clusters carrying one to eight calixarene moieties were obtained. Structural characterization reveals unexpected binding of the calix[4]arenes to the Au 25 cluster surface with two or four thiolates per moiety. © 2014 American Chemical Society.

Pradeep Thalappil

Department Of Chemistry

Calixarenes

Cluster surfaces

Clusters

Functionalizations

Gold Nanoparticles

ONE-POT PROCEDURES

Structural characterization

Systematic variation

Binary mixtures

Gold

Ligands

Phenols

Gold compounds

Fulltext

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Journal of Physical Chemistry Letters

ConspectusNanoparticles exhibit a rich variety in terms of structure, composition, and properties. However, reactions between them remain largely unexplored. In this Account, we discuss an emerging aspect of nanomaterials chemistry, namely, interparticle reactions in solution phase, similar to reactions between molecules, involving atomically precise noble metal clusters. A brief historical account of the developments, starting from the bare, gas phase clusters, which led to the synthesis of atomically precise monolayer protected clusters in solution, is presented first. Then a reaction between two thiolate-protected, atomically precise noble metal clusters, [Au25(PET)18]- and [Ag44(FTP)30]4- (PET = 2-phenylethanethiol, FTP = 4-fluorothiophenol), is presented wherein these clusters spontaneously exchange metal atoms, ligands, and metal-ligand fragments between them under ambient conditions. The number of exchanged species could be controlled by varying the initial compositions of the reactant clusters. Next, a reaction of [Au25(PET)18]- with its structural analogue [Ag25(DMBT)18]- (DMBT = 2,4-dimethylbenzenethiol) is presented, which shows that atom-exchange reactions happen with structures conserved. We detected a transient dianionic adduct, [Ag25Au25(DMBT)18(PET)18]2-, formed between the two clusters indicating that this adduct could be a possible intermediate of the reaction. A reaction involving a dithiolate-protected cluster, [Ag29(BDT)12]3- (BDT = 1,3-benzenedithiol), is also presented wherein metal atom exchange alone occurs, but with no ligand and fragment exchanges. These examples demonstrate that the nature of the metal-thiolate interface, that is, its bonding network and dynamics, play crucial roles in dictating the type of exchange processes and overall rates. We also discuss a recently proposed structural model of these clusters, namely, the Borromean ring model, to understand the dynamics of the metal-ligand interfaces and to address the site specificity and selectivity in these reactions.In the subsequent sections, reactions involving atomically precise noble metal clusters and one- and two-dimensional nanosystems are presented. We show that highly protected, stable clusters such as [Au25(PET)18]- undergo chemical transformation on graphenic surfaces to form a bigger cluster, Au135(PET)57. Finally, we present the transformation of tellurium nanowires (Te NWs) to Ag-Te-Ag dumbbell nanostructures through a reaction with an atomically precise silver cluster, Ag32(SG)19 (SG = glutathione thiolate).The starting materials and the products were characterized using high resolution electrospray ionization mass spectrometry, matrix assisted laser desorption ionization mass spectrometry, UV/vis absorption, luminescence spectroscopies, etc. We have analyzed principally mass spectrometric data to understand these reactions.In summary, we present the emergence of a new branch of chemistry involving the reactions of atomically precise cluster systems, which are prototypical nanoparticles. We demonstrate that such interparticle chemistry is not limited to metal clusters; it occurs across zero-, one-, and two-dimensional nanosystems leading to specific transformations. We conclude this Account with a discussion of the limitations in understanding of these reactions and future directions in this area of nanomaterials chemistry. © 2017 American Chemical Society.

Accounts of Chemical Research

Interparticle Reactions: An Emerging Direction in Nanomaterials Chemistry

Ion mobility mass spectrometry studies on Aun-Lyz adducts showed gradual unfolding of the protein structure during binding of Au+ to the protein. The change of the charge state envelope in Aun-Lyz from that of Lyz in ESI MS data confirmed the relaxation of the protein structure. This Au+ binding occurs at cysteine sites through the breakage of disulfide bonds and this ruptures the H-bonded folded network structure of the protein leading to ∼30% change in helicity. Nearly 15% loss in the total H-bonding occurred during the attachment of 8 Au to the protein as calculated by a molecular dynamics simulation. Different Aun-Lyz structures were simulated, which confirmed significant unfolding of the protein. The structural insights were used to understand similar unfolding in the solution state as seen via circular dichroism (CD) and Fourier transform infrared (FTIR) spectroscopy. This open structure is indeed necessary to accommodate a cluster core inside a protein cavity during luminescent cluster synthesis. These studies unambiguously establish noble metal binding-induced conformational changes of protein structures to accommodate the clusters. © 2017 American Chemical Society.

Journal of Physical Chemistry C

Gold-Induced Unfolding of Lysozyme: Toward the Formation of Luminescent Clusters

We present the first example of intercluster reactions between atomically precise, monolayer protected noble metal clusters using Au25(SR)18 and Ag44(SR)30 (RS- = alkyl/aryl thiolate) as model compounds. These clusters undergo spontaneous reaction in solution at ambient conditions. Mass spectrometric measurements both by electrospray ionization and matrix assisted laser desorption ionization show that the reaction occurs through the exchange of metal atoms and protecting ligands of the clusters. Intercluster alloying is demonstrated to be a much more facile method for heteroatom doping into Au25(SR)18, as observed by doping up to 20 Ag atoms. We investigated the thermodynamic feasibility of the reaction using DFT calculations and a tentative mechanism has been presented. Metal core-thiolate interfaces in these clusters play a crucial role in inducing these reactions and also affect rates of these reactions. We hope that our work will help accelerate activities in this area to establish chemistry of monolayer protected clusters. © 2015 American Chemical Society.

Journal of the American Chemical Society

Intercluster Reactions between Au25(SR)18 and Ag44(SR)30

We present the first example of dimer formation in the monolayer protected atomically precise cluster system, Au25(SR)18, using ion mobility mass spectrometry. These transient species are shown to be important in explaining chemical reactivity between clusters. © 2016 The Royal Society of Chemistry.

Chemical Communications

[Au25(SR)18]22-: A noble metal cluster dimer in the gas phase

In this paper is reported the synthesis and detailed mass spectrometric and spectroscopic characterization of highly luminescent Au and Ag clusters protected with mixed proteins. Taking advantage of the aggregation tendency of the protein, lysozyme (Lyz), an inter-protein conjugate was made from a physical mixture of two proteins, bovine serum albumin (BSA) and Lyz. Based on matrix-assisted laser desorption/ionization mass spectrometry data, the new cluster is assigned as ∼Au<inf>36</inf>@BSA-Lyz. This specific system showed a very high red luminescence and the calculated quantum yield was 42% which is the highest to date for such cluster systems. A similar study on an Ag system showed the formation of ∼Ag<inf>35</inf>@BSA-Lyz when a similar metal and protein concentration was used. By varying the concentration of the Ag precursor, different compositions of the cluster protected by the mixed protein were achieved. Such a system with a high quantum yield can be used for various applications such as sensors for ultralow levels of analytes, fluorescent tags and for tracking biomolecules in real systems. © The Royal Society of Chemistry 2015.

RSC Advances

Noble metal clusters protected with mixed proteins exhibit intense photoluminescence

This report describes the precise and systematic synthesis of PdAu 24 clusters protected with two types of thiolate ligands (-SR1 and -SR2). It involved high-resolution separation of metal clusters containing a distribution of chemical compositions, PdAu24(SR1) 18-n(SR2)n (n = 0, 1, 2,⋯, 18), to individual clusters of specific n using high-performance liquid chromatography. Similar high-resolution separation was achieved for a few ligand combinations as well as clusters with other metal cores, such as Au25 and Au38. These results demonstrate the ability to precisely control the chemical composition of two types of ligands in thiolate-protected mono- and bimetallic metal clusters. It is expected that greater functional control of thiolate-protected metal clusters, their regular arrays, and systematic variation of their properties can now be achieved. © 2013 American Chemical Society.

Separation of precise compositions of noble metal clusters protected with mixed ligands

Ligand exchange offers an effective way to modify the properties of the recently prepared quantum clusters of gold. To tune optical and photoluminescence properties of one of the most stable quantum clusters of gold, AU25SG18 (SG-glutathione thiolate), we functionalized it by the exchange of - SG with functionalized -SG and with an altogether different ligand, namely, 3-mercapto-2-butanol (MB). The products were characterized by various techniques such as optical absorption (UV - vis), Fourier-transform infrared (FT - IR), nuclear magnetic resonance (NMR), X-ray photoelectron (XPS), and luminescence spectroscopies, mass spectrometry, and thermogravimetry (TG). Analyses of the TG data helped to establish the molecular composition of the products. Ligand exchange reaction was monitored by NMR spectroscopy, and it was found that the exchange reaction follows a first order kinetics. The XPS study showed that after the exchange reaction there was no change in the chemical nature of the metal core and binding energy values of Au 4f7/2 and 4f5/2, which are similar in both the parent and the exchanged products. Photoluminescence studies of these clusters, done in the aerated conditions, showed that the excitation spectrum of the MB-exchanged product is entirely different from the acetyl- and formyl-glutathione exchanged products. The inherent fluorescence and solid-state emission of these clusters were observed. This intense emission allows optical imaging of the material in the solid state. The emission is strongly temperature dependent. The synthesis of a diverse variety of clusters and their chemical stability and intense luminescence offer numerous applications in areas such as energy transfer, sensors, biolabeling, and drug delivery. © 2008 American Chemical Society.

Ligand exchange of Au25SG18 leading to functionalized gold clusters: Spectroscopy, kinetics, and luminescence

Protected but Accessible: Oxygen Activation by a Calixarene-Stabilized Undecagold Cluster

The Journal of Physical Chemistry C

Stabilization of Thiolate-Protected Gold Clusters Against Thermal Inversion: Diastereomeric Au38(SCH2CH2Ph)24–2x(R-BINAS)x

RSC Adv.

Complexation of calix[4]arene protected gold nanoparticles with pyridinium and bipyridinium compounds

Mixed-monolayer-protected Au25 clusters with bulky calix[4]arene functionalities

Journal	Journal of Physical Chemistry Letters
ISSN	19487185
Open Access	No