A first principles study of thiol-capped Au nanoparticles: Structural, electronic, and magnetic properties as a function of thiol coverage

Abstract

We have studied the stability of thiolated Au 38 nanoparticles (NPs) via density functional theory based calculations varying the coverage from 0 up to 32 molecules. Three different initial core arrangements were considered for the cluster, spherical, tubular, and bi-icosahedral, while thiol groups were attached to the cluster via the sulfur atom either as single molecules or forming more complex staple motifs. After molecular dynamics runs several metastable configurations are found at each coverage thus allowing to analyze the properties of the NPs in the form of ensemble averages. In particular, we address the structural and electronic properties as a function of the number of thiols. The study emphasizes the strong influence of the core structure on the stability of the NPs, and its interplay with the thiol coverage and adsorption geometries. The magnetic properties of the NPs have also been explored via spin-polarized calculations including spin-orbit coupling. No evidence for the existence of a robust intrinsic ferromagnetism is found in any of the structures. © 2013 AIP Publishing LLC. [http://dx

In Situ Formation of Dual‐Phase Thermosensitive Ultrasmall Gold Nanoparticles

“…According to the proposed formation mechanism of gold nanoparticles, an increase in PNPEDMA chain length (molecular weight) should favor the reduction of AuCl 4 À and affect the size ands hape of gold nanoparticles. To confirm this hypothesis, three PNIPAM-b-PNPEDMA diblock copolymers, namely, PNIPAM 180 -b-PNPEDMA 4 ,P NIPAM 180 -b-PNPEDMA 10 ,a nd PNIPAM 180 -b-PNPEDMA 28 ,w ere synthesized to examine the effect of block composition on gold nanoparticle formation.…”

“…The resulting macroCTA was then chain-extended with N-phenylethylenediamine methacrylamide (NPEDMA) to yield aw ell-defined PNIPAM 180 -b-PNPEDMA 4 diblock copolymer with M n and M w /M n ratio of 14.2 kDa and 1.10, respectively (see the Supporting Information, Figures S1 and S2). In at ypical USGNP synthesis, PNIPAM 180 -b-PNPEDMA 4 copolymer (5 mg) was dissolved in water (1 mL) with vigorous stirring, and then HAuCl 4 (82 mL, 0.02 mm)w as quickly added to the polymer solution.O n mixing,t he solution immediatelyc hanged color from orange to dark brown without any precipitate, indicating efficient AuCl 4 À reduction and stabilization of the resulting GNPs by PNIPAM 180 -b-PNPEDMA 4 .A fter 5h reaction time, the Au@ PNIPAM 180 -b-PNPEDMA 4 complex was further purified by dialysis.…”

“…We propose that Au nanoclustersa re possibly preorganized with monodisperse micelles formed by the amphiphilic diblock copolymer,w hich are composed of ah ydrophilic PNIPAM block and ah ydrophobic PNPEDMA block with www.chemeurj.org aC 12 hydrophobic trithioester head group (Scheme 2). First, the hydrophobic sectionc ontaining NPEDMA and trithioester group self-assembles into the cores of micelles in the aqueous solution.O na ddition of HAuCl 4 ,t he PhNH group easily reacts with HAuCl 4 ,t of orm ap rotonated PhNH-/AuCl 4 À salt through ab ase/acid reaction. At the same time, the AuCl 4 À anion acts as an oxidanta nd is capable of oxidizing the PhNH group, [22] which results in the formation of gold nanoparticles, which can be stabilized by the PNPEDMAb lock and trithioester head group.…”

“…On the other hand, it has been recently demonstrated that colloidally stable gold nanoparticles can be conveniently prepared in as ingle step withouta ny external reducing agents by designing certain copolymers that can act as both ar educing agent and as tabilizer simultaneously.P olymers such as polymethylhydrosiloxane, [13] poly(N-vinyl-2-pyrrolidone), [14] poly(sodium acrylate), [15] poly(ethylene oxide), [16] polyallylamine, [17] poly [2-(N,N-dimethylamino)ethyl methacrylate], [18] and polyethylenimine [19] -based homopolymers or copolymers can fulfill the required dual role of reducing AuCl 4 À counterions to zerovalent gold and at the same time stabilizing the resulting gold nanoparticles. However,i ns yntheses with these polymers, large gold nanoparticles (> 3nm) were usually produced.…”

“…Gold nanoparticles (GNPs) have attracted considerable attention in recent years due to their potentiala pplications in aw ider ange of areas, such as catalysis, [1] biosensing, [2] drug delivery, [3] molecular electronics, [4] ands urfacep atterning. [5] In particular, ultrasmall gold nanoparticles (USGNPs) with sizes in the 1-3 nm range are of great interestb ecause of their unique properties compared to those larger than 5nm.…”