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.

Pradeep Thalappil

Department Of Chemistry

Chemical compositions

FUNCTIONAL CONTROL

HIGH-RESOLUTION SEPARATIONS

MIXED-LIGANDS

NOBLE METAL CLUSTERS

REGULAR ARRAY

Systematic variation

THIOLATE LIGANDS

high performance liquid chromatography

Metals

Separation

Ligands

Gold

metal derivative

Palladium

article

chemical analysis

chemical composition

chemical reaction

HIGH RESOLUTION SEPARATION

isolation procedure

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 the American Chemical Society

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. © 2017 The Royal Society of Chemistry.

Nanoscale

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

This communication reports the identification of gas phase isomers in monolayer-protected silver clusters. Two different isomers of Ag11(SG)7- (SG-gulathione thiolate) with different drift times have been detected using combined electrospray ionization (ESI) and ion mobility (IM) mass spectrometry (MS). Surface induced dissociation (SID) of the 3- charge state of such clusters shows charge stripping to give the 1- charged ion with some sodium attachment, in addition to fragmentation. SID and collision induced dissociation (CID) for Ag11(SG)7- suggest different pathways being accessed with each method. SID was introduced for the first time for the study of monolayer-protected clusters. © The Royal Society of Chemistry 2016.

Fulltext

Chemical Communications

Possible isomers in ligand protected Ag11 cluster ions identified by ion mobility mass spectrometry and fragmented by surface induced dissociation

Atomically precise monolayer protected clusters are molecules comprising a few-atom cluster core of a noble metal, typically Au or Ag, surrounded by a protective layer of ligands, exhibiting many special optical, electrical, catalytic, and magnetic properties, and are emerging as important materials in biology, medicine, catalysis, energy conversion and storage, and sensing. The structural diversity of these clusters or aspicules, as we definitively term them, meaning shielded molecules, combining the Greek word aspis (shield) with molecule, is rapidly increasing due to new compositions and modification routes such as ligand-exchange, alloying, or supramolecular functionalization. We present a structural analysis of the most stable cluster of this kind, Au25(SR)18, and propose a Borromean rings diagram for the cluster, showing its topological configuration of three interlocked (Au8S6)-rings. This simplified two-dimensional diagram is used to represent its structure and modifications via ligand or metal atom substitution uniquely. We enumerate and name its isomers with two-ligand or metal atom substituents. Among the several structural insights obtained, the identification of the Borromean rings-interlocked configuration in Au25(SR)18 may explain its high geometric stability and indicate a possible general unified structural viewpoint for these clusters without the division between core and staple motifs. On the basis of our structural analysis, we developed a structure-based nomenclature system that can be applied to both describe and understand the structure and modifications of gold thiolate clusters, AuM(SR)N, and is adaptable to the general case of MM(X)N (M, metal and X, ligand). The application of structural analysis and diagrams to Au38(SR)24 and Au102(SR)44, revealing the possible formation of the cluster core by stacking or growth of rings of metal atoms, is also presented. © 2015 American Chemical Society.

Journal of Physical Chemistry C

A Unified Framework for Understanding the Structure and Modifications of Atomically Precise Monolayer Protected Gold Clusters

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

An efficient method to enhance visible luminescence in a visibly non-luminescent organic-soluble 4-(tert butyl)benzyl mercaptan (SBB)-stabilized Au25 cluster has been developed. This method relies mainly on enhancing the surface charge density on the cluster by creating an additional shell of thiolate on the cluster surface, which enhances visible luminescence. The viability of this method has been demonstrated by imparting red luminescence to various ligand-protected quantum clusters (QCs), observable to the naked eye. The bright red luminescent material derived from Au25SBB18 clusters was characterized using UV-vis and luminescence spectroscopy, TEM, SEM/EDS, XPS, TG, ESI and MALDI mass spectrometry, which collectively proposed an uncommon molecular formula of Au29SBB24S, suggested to be due to different stapler motifs protecting the Au25 core. The critical role of temperature on the emergence of luminescence in QCs has been studied. The restoration of the surface ligand shell on the Au25 cluster and subsequent physicochemical modification to the cluster were probed by various mass spectral and spectroscopic techniques. Our results provide fundamental insights into the ligand characteristics determining luminescence in QCs. © The Royal Society of Chemistry.

Efficient red luminescence from organic-soluble Au25 clusters by ligand structure modification

A silver cluster having the composition Ag9(H 2MSA)7 (H2MSA = mercaptosuccinic acid) was synthesized in macroscopic quantities using a solid-state route. The clusters were purified by PAGE and characterized by UV-vis, FTIR, luminescence, and NMR spectroscopy, TEM, XPS, XRD, TG, SEM/EDAX, elemental analysis, and ESI MS. The solid-state route provides nearly pure Ag9 clusters, and nanoparticle contamination was insignificant for routine studies. Formation of various clusters was observed by modifying the conditions. The effect of ligands on the synthesis was checked. The cluster decomposed slowly in water, and the decomposition followed first-order kinetics. However, it could be stabilized in solvent mixtures and in the solid state. Such materials may be important in cluster research because of their characteristic absorption profiles, which are similar to those of Au25 and Au38. The cluster showed luminescence with a quantum yield of 8 × 10-3 at 5 °C. © 2010 American Chemical Society.

Ag9 quantum cluster through a solid-state route

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

Fluorescence resonance energy transfer between the metal core and the ligand in Au25SG18 (SG-glutathione thiolate) is demonstrated using dansyl chromophores attached to the cluster core through glutathione linkers. The dansyl chromophore functionalization of the cluster has been carried out by two different routes. Efficient energy transfer from the dansyl donor to the Au25 core is manifested by way of the reduced lifetime of the excited state of the former and drastic quenching of its fluorescence. The donor-acceptor separation observed in the two synthetic routes reflects the asymmetry in the ligand binding on the cluster core, which is in agreement with the recent theoretical and experimental results on the structure of Au25. © 2008 American Chemical Society.

Quantum clusters of gold exhibiting FRET

In Situ Reaction Monitoring Reveals a Diastereoselective Ligand Exchange Reaction between the Intrinsically Chiral Au38(SR)24 and Chiral Thiols

ACS Nano

Observation of Cluster Size Growth in CO-Directed Synthesis of Au25(SR)18 Nanoclusters

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

Journal	Journal of the American Chemical Society
ISSN	00027863
Open Access	No