Eugenia Zelaya

Synthesis and characterization of gold at gold(i)-thiomalate core at shell nanoparticles.

In this paper, the synthesis of gold at gold(I)-thiolate core at shell nanoparticles is described for the first time. The chemical nature and structure of these nanoparticles were characterized by a multi-technique approach. The prepared particles consist of gold metallic cores, about 1 nm in size, surrounded by stable gold(I)-thiomalate shells (Au at Au(I)-TM). These nanoparticles could be useful in medicine due to the interesting properties that gold(I)-thiomalate has against rheumatoid arthritis. Furthermore, the described results give new insights in the synthesis and characterization of metallic and core at shell nanoparticles.

New findings for the composition and structure of Ni nanoparticles protected with organomercaptan molecules.

Here we explore the synthesis of alkanethiol-coated Ni NPs following the one-phase reaction method by Brust et al. The reduction of NiCl2 with NaBH4 in the presence of dodecanethiol (C12SH) yields a complex product that is difficult to identify as illustrated in the figure of merit. We synthesized Ni(II) dodecanethiolate (C12S) (without the addition of NaBH4) for comparison and performed an exhaustive characterization with TEM, HR-TEM, AFM, MFM, XPS, XRD, UV-vis, magnetism, and FT-IR. It is found that the organic coating is not quite a well-organized self-assembled monolayer (SAM) surrounding the Ni cluster as previously reported. XPS and XRD data show slight differences between both syntheses; however, Ni(II) thiolate appears to be more stable than reduced Ni when exposed to ambient air, indicating the propensity of metallic Ni to oxidize. It has been shown that irradiating with TEM electrons over various metal thiolates leads to nanoparticle formation. We irradiated over Ni(II) thiolate and observed no evidence of NP formation whereas irradiating a reduced Ni sample exhibited an ~3.0 nm nanoparticle diameter. Magnetism studies showed a difference between both samples, indicating ferromagnetic character for the reduced Ni sample. According to our results, the product of the synthesis is comprised of ultrasmall metallic clusters embedded in some form of Ni(II) C12S. In this work, we open a discussion of the chemical nature of the core and the shell in the synthesis of Ni NPs protected with organomercaptan molecules.

Surface chemistry of thiomalic acid adsorption on planar gold and gold nanoparticles.

The self-assembly of thiomalic acid (TMA) on Au(111) and on preformed Au nanoparticles (AuNPs) protected by weak ligands has been studied by X-ray photoelectron spectroscopy (XPS) and electrochemical techniques. Results show that TMA is adsorbed on the Au(111) surface as thiolate species with a small amount of atomic sulfur (∼10%) and a surface coverage lower than that found for alkanethiols due to steric factors. The amount of atomic sulfur markedly increases when the TMA is adsorbed on AuNPs by the ligand exchange method. We propose that the atomic sulfur is produced as a consequence of C-S bond cleavage, a process that is more favorable at defective sites of the AuNPs surface. The bond scission is also assisted by the presence of the electron-withdrawing carboxy moiety in the α-position relative to the C-S bond. Moreover, the high local concentration of positively charged species increases the stability of the negatively charged leaving group, leading to a higher amount of coadsorbed atomic sulfur. Our results demonstrate that the terminal functionalities of thiols are conditioning factors in the final structure and composition of the adlayers.

Role of the capping agent in the interaction of hydrophilic Ag nanoparticles with DMPC as a model biomembrane

The interaction of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) Langmuir monolayers as a model biomembrane with small silver nanoparticles (AgNPs) similar in size but coated with different capping molecules such as citrate (CIT-AgNPs) and 4-mercaptobenzoic acid (MBA-AgNPs), both negatively charged at physiological pH, is studied using a multi-technique approach. Both CIT-AgNPs and MBA-AgNPs expose carboxyl groups and have similar zeta potentials, but differ in the aliphatic or aromatic nature of the capping agent. Results show that AgNPs exhibit quite different behaviors: CIT-AgNPs weakly adsorb on DMPC, while MBA-AgNPs irreversibly adsorb on the interface and remain there upon monolayer compression. It is also shown that there is a cooperative effect of many ligands in the interactions between MBA-AgNPs and DMPC, as MBA molecules in solution are unable to strongly adsorb on the phospholipid monolayer surface. We propose an explanation based on the surface charge density and on the chemical nature of the capping molecule based on XPS studies and on DFT calculations.

Supramacromolecular organization of gold nanocrystals capped with amphiphilic hyperbranched polyethyleneimine

The supramolecular structural aspects of hetero-assemblies constituted of gold nanoparticles capped with amphiphilic unimolecular micelles were studied using synchrotron-based small angle X-ray scattering (SAXS). Experimental results revealed that straightforward transfer of citrate-capped Au nanoparticles from an aqueous environment to a toluenic solution of amphiphilic hyperbranched polymers results in the spontaneous integration of the nanocrystals into the extended hydrophilic domains of self-assembled supramolecular structures. In this way, we were able to self-organize metal-polymer nanoarchitectures in solution displaying interesting thermoactive functions, i.e.: hybrid assemblies exhibiting negative thermal expansion coefficients. We consider that this strategy has potentiality to realize self-organized supramolecular hetero-assemblies as it provides an alternative methodology to spontaneously integrate nanoscale building blocks into preformed supramolecular objects.