Dynamics of Alkyl Chains in Monolayer-Protected Au and Ag Clusters and Silver Thiolates:  A Comprehensive Quasielastic Neutron Scattering Investigation

Abstract

Temperature-dependent dynamics of monolayer-protected Au and Ag nanoclusters and silver thiolates have been investigated with quasielastic neutron scattering. The simplest motion in these systems is the uniaxial rotation of the chain, which evolves slowly with temperature. While longer chain monolayers (above C 8 ) on Au clusters are rotationally frozen at room temperature, dynamic freedom exists in lower chain lengths. In the superlattice solids of Ag clusters, the dynamics evolve slowly, and at superlattice melting, all the chains are dynamic. The data are consistent with a structure in which the monolayers form bundles on the planes of metal clusters and such bundles interdigitate, forming the cluster assemblies. In thiolates, the dynamics is distinctly different in long-and short-chain systems. It arises abruptly at the melting temperature in C 12 but a bit sluggishly in C 18 , whereas in C 6 and C 8 , it evolves with temperature. The data are correlated with temperature-dependent infrared spectroscopy, which preserves some of the progression bands even after the bulk melting temperature, but loses them completely above 498 K, suggesting a possible partially ordered phase in this temperature window. Our studies have established the fact that (a) no rotational freedom exists in several of the alkyl chain monolayers on metal cluster solids at room temperature, (b) simple uniaxial rotation explains the dynamics of these systems, (c) the dynamics evolves slowly, and (d) such motions arise abruptly in long-chain layered thiolates which are similar to planar thiolates. We find that longer chains can possess conformational defects at higher temperatures, which slow the rotational dynamics.

Molecular Dynamics of POPC Phospholipid Bilayers through the Gel to Fluid Phase Transition: An Incoherent Quasi-Elastic Neutron Scattering Study

“…The intermediate dynamics are characterized by a time ( = ℏ/Γ) of 6-7 ps, which is the typical time of both the conformational dynamics in the lipid chains and the rotational diffusion of methyl groups [11,35,36]. In Figure 4, the experimental EISF med , derived by the line shape analysis, for the POPC at = 248 and 273 K, are shown and compared with the results obtained at = 298 K for the liquid phase.…”

Label-free fluorescence assay for protein kinase based on peptide biomineralized gold nanoclusters as signal sensing probe

“…Due to these unique properties, the synthesis strategies of AuNCs in water solution by some soft landing such as arylthiolates (Arnold and Reilly, 1998;Pradeep et al, 2004), dendrimers (Bao et al, 2007;Gröhn et al, 2000) have been reported in large volumes, and the AuNCs have been widely used in the fields of chemistry, biology, and materials (Wu and Jin, 2010). Recently, AuNCs have been successfully prepared and widely applied to fluorescence assay of enzyme.…”

Molecular motion in restricted geometries

“…It is therefore of interest to study the dynamical behaviour of these chains. Here we report the dynamics of alkyl chains in both isolated and superlattice systems with varying chain lengths, using QENS [22][23][24][25]. Isolated MPCs investigated are 6, 12 and 18 carbon n-alkyl chain thiolate-protected 4 nm diameter gold clusters while the superlattices are their silver analogues.…”