The self-assembled structures of atomically precise, ligand-protected noble metal nanoclusters leading to encapsulation of plasmonic gold nanorods (GNRs) is presented. Unlike highly sophisticated DNA nanotechnology, this strategically simple hydrogen bonding-directed self-assembly of nanoclusters leads to octahedral nanocrystals encapsulating GNRs. Specifically, the p-mercaptobenzoic acid (pMBA)-protected atomically precise silver nanocluster, Na4[Ag44(pMBA)30], and pMBA-functionalized GNRs were used. High-resolution transmission and scanning transmission electron tomographic reconstructions suggest that the geometry of the GNR surface is responsible for directing the assembly of silver nanoclusters via H-bonding, leading to octahedral symmetry. The use of water-dispersible gold nanoclusters, Au≈250(pMBA)n and Au102(pMBA)44, also formed layered shells encapsulating GNRs. Such cluster assemblies on colloidal particles are a new category of precision hybrids with diverse possibilities. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Pradeep Thalappil

Department Of Chemistry

Amrita Chakraborty

Ann Candice Fernandez

Ganapati Natarajan

Ganesan Paramasivam

Gold

Hydrogen bonds

Nanoclusters

Nanocrystals

nanorods

Plasmonics

Plasmons

Precious metals

Self assembly

Silver

Supramolecular chemistry

Directed self-assembly

gold nanorod

GOLD NANORODS (GNRS)

MERCAPTOBENZOIC ACIDS

SELF ASSEMBLED STRUCTURES

SILVER NANOCLUSTERS

Tomographic reconstruction

Transmission electron

Nanoribbons

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

Angewandte Chemie - International Edition

We present isomerism in a few supramolecular adducts of atomically precise nanoparticles, [Ag29(BDT)12∩(CD)n]3- (n = 1-6), abbreviated as I where BDT and CD are 1,3-benzenedithiol and cyclodextrins (α, β and γ), respectively; ∩ symbolizes an inclusion complex. The different host-guest complexes of I were characterized in the solution state as well as in the gas phase. The CDs (α, β and γ) encapsulate a pair of BDT ligands protecting the Ag29 core. This unique geometry of the supramolecular adducts makes the system similar to octahedral complexes of transition metals, which manifest various isomers. These isomers of I (n = 2-4) were separated by ion mobility mass spectrometry (IM MS). We proposed structures of all the inclusion complexes with the help of IM MS measurements and molecular docking, density functional theory (DFT), and collision cross section (CCS) calculations. Copyright © 2018 American Chemical Society.

Journal of the American Chemical Society

Isomerism in Supramolecular Adducts of Atomically Precise Nanoparticles

Atomically precise pieces of matter of nanometer dimensions composed of noble metals are new categories of materials with many unusual properties. Over 100 molecules of this kind with formulas such as Au25(SR)18, Au38(SR)24, and Au102(SR)44 as well as Ag25(SR)18, Ag29(S2R)12, and Ag44(SR)30 (often with a few counterions to compensate charges) are known now. They can be made reproducibly with robust synthetic protocols, resulting in colored solutions, yielding powders or diffractable crystals. They are distinctly different from nanoparticles in their spectroscopic properties such as optical absorption and emission, showing well-defined features, just like molecules. They show isotopically resolved molecular ion peaks in mass spectra and provide diverse information when examined through multiple instrumental methods. Most important of these properties is luminescence, often in the visible-near-infrared window, useful in biological applications. Luminescence in the visible region, especially by clusters protected with proteins, with a large Stokes shift, has been used for various sensing applications, down to a few tens of molecules/ions, in air and water. Catalytic properties of clusters, especially oxidation of organic substrates, have been examined. Materials science of these systems presents numerous possibilities and is fast evolving. Computational insights have given reasons for their stability and unusual properties. The molecular nature of these materials is unequivocally manifested in a few recent studies such as intercluster reactions forming precise clusters. These systems manifest properties of the core, of the ligand shell, as well as that of the integrated system. They are better described as protected molecules or aspicules, where aspis means shield and cules refers to molecules, implying that they are "shielded molecules". In order to understand their diverse properties, a nomenclature has been introduced with which it is possible to draw their structures with positional labels on paper, with some training. Research in this area is captured here, based on the publications available up to December 2016. © 2017 American Chemical Society.

Chemical Reviews

Atomically Precise Clusters of Noble Metals: Emerging Link between Atoms and Nanoparticles

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.

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

Highly organized crossed bilayer assemblies of nanowires (NWs) are made using directed hydrogen bonding between the protecting ligand shells of atomically precise cluster molecules anchored on NWs. Layers of quantum clusters remain sandwiched between two neighboring NWs at a defined distance, dictated by the core-size of the cluster, while the orientation of the ligands in space dictates the interlayer geometry. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA.

Advanced Materials

Cluster-Mediated Crossed Bilayer Precision Assemblies of 1D Nanowires

Ambient, structure-and topology-preserving chemical reactions between two archetypal nanoparticles, Ag 25 (SR) 18 and Au 25 (SR) 18, are presented. Despite their geometric robustness and electronic stability, reactions between them in solution produce alloys, Agm Aun (SR)18 (m+n=25), keeping their M25 (SR)18 composition, structure and topology intact. We demonstrate that a mixture of Ag25 (SR)18 and Au25 (SR)18 can be transformed to any arbitrary alloy composition, Agm Aun (SR)18 (n=1-24), merely by controlling the reactant compositions. We capture one of the earliest events of the process, namely the formation of the dianionic adduct, (Ag25 Au25 (SR)36) 2-, by electrospray ionization mass spectrometry. Molecular docking simulations and density functional theory (DFT) calculations also suggest that metal atom exchanges occur through the formation of an adduct between the two clusters. DFT calculations further confirm that metal atom exchanges are thermodynamically feasible. Such isomorphous transformations between nanoparticles imply that microscopic pieces of matter can be transformed completely to chemically different entities, preserving their structures, at least in the nanometric regime. © 2016 The Author(s).

Fulltext

Nature Communications

Structure-conserving spontaneous transformations between nanoparticles

An improvement in the previously reported seed-mediated chemical synthesis of gold nanorods (GNRs) is reported. Monodisperse GNRs have been synthesized in a one-step protocol. The addition of controlled quantity of sodium borohydride (NaBH4) directly into the growth solution produced uniform GNRs, formed by in situ nucleation and growth. In order to arrive at the conclusion, we studied the formation of GNRs with various seeds, of metals of widely differing crystal structures, and there were no variations in the properties of the GNRs formed. The role of NaBH4 in the growth of GNR, which has not been covered in previous reports, is discussed in detail. The dependence of longitudinal plasmon peak on the concentration of NaBH4 is compared with the dependence of residual concentration of NaBH4 in the seed solution, which is added to the growth solution in seed-mediated synthesis. The study shows that NaBH4 plays an important role in the formation of GNRs. This proposed protocol offers a number of advantages: one-step preparation of GNRs, significant reduction in the preparation time to 10 min, high monodispersity of GNRs, and tailorability of the aspect ratio depending on NaBH4 concentration. It is suggested that NaBH4 added to the growth solution leads to in situ formation of the seed particles of the size of 3-5 nm which enables the growth of GNRs. The growth of GNRs suggested here is likely to have an impact on the preparation of other anisotropic structures. Our single-pot methodology makes the procedure directly adaptable production of GNRs and for their synthesis even in undergraduate laboratories.

Journal of Nanoparticle Research

Investigation of the role of NaBH4 in the chemical synthesis of gold nanorods

Atomically Precise Nanocluster Assemblies Encapsulating Plasmonic Gold Nanorods

Journal	Data powered by TypesetAngewandte Chemie - International Edition
Publisher	Data powered by TypesetWiley-VCH Verlag
ISSN	14337851
Open Access	No