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Aging of thiolate protected gold nanoparticles (AuNPs) results in reduced reactivity in the disulfide exchange as monitored by electron paramagnetic resonance (EPR) spectroscopy with a bisnitroxide disulfide incoming ligand. Factors determining the reactivity of the aged particles were investigated. The presence of different binding sites on the surface of AuNPs and a surface reorganization process during aging can explain observed reactivity trends. [ABSTRACT FROM AUTHOR]

Optically active polyaniline nanorods and hierarchically structured gold microspheres are synthesized using tetrachloroaurate as an efficient oxidant of aniline in the presence of a chiral inducing agent camphorsulfonic acid. The chiral organization of the resultant polyaniline nanorods is strongly affected by the ratio of aniline to AuCl 4−, with the highest optical activity being observed for the ratio around 5:2. The particle size and size distributions of the gold microspheres are influenced by the concentration of the oxidant tetrachloroaurate. [ABSTRACT FROM AUTHOR]

Electron spin−echo envelope modulation (ESEEM) spectroscopy was used to investigate intramolecular and intermolecular complexes of cyclodextrins (CDs) with a nitroxide group. The interaction with solvent molecules (D2O) was followed through the 2H modulation depth. Competition experiments with adamantane-type guests were used to confirm complexation. The shielding of the nitroxide group from solvent upon inclusion into a CD cavity made this technique more sensitive to complexation than cw EPR spectroscopy. ESEEM analysis of a series of CDs mono and bis spin-labeled on the primary rim of the cavity showed that only one compound formed a self-inclusion complex. This suggests that significant linker length/flexibility is required for formation of inclusion complexes in functionalized CDs. DEER (double electron−electron resonance) experiments confirmed that the self-inclusion complex of the spin-labeled CD was intra- rather than intermolecular. [ABSTRACT FROM AUTHOR]

New nanocomposites containing functionalized acrylate monomers and Au nanoparticles (NPs, 1.5−3 nm core diameter, 1−2 wt %) have been developed for an all-optical fabrication of periodic bulk structures by holographic photopolymerization. The Au NPs were coated with ethyl 11-mercaptoundecanoate to ensure good solubility in low-polarity organic media. The materials with only 1.5 wt % Au NPs show unusually high amplitude of the refractive index modulation in the diffraction volume gratings (0.0073). Both volume and surface relief gratings are formed during the holographic exposure. The proposed mechanism of the refractive index contrast amplification (as compared to monomer mixture without NPs) includes interception of free radicals by Au nanoparticles. This slows down the free-radical photopolymerization, thus promoting the increase in lateral periodic redistribution of the components in the interference pattern. The redistribution of both NP and monomers provides high efficient grating formation with the spatial period of 0.5−4.5 μm. The formation of the surface relief coincident with the interference pattern is also observed. The introduction of 1.5 wt % Au NPs into the prepolymer mixture more than doubles the surface relief depth (from ca. 150 to 400 nm for the period 4.2 μm), thus proving the NP influence on the structure and, consequently, on the shrinkage of the polymer matrix. [ABSTRACT FROM AUTHOR]

This paper describes the synthesis of gold nanoparticles stabilized by two series of new dendritic disulfide ligands with alkene groups at their peripheries. Intraparticle cross-linking of the alkene groups around the periphery of each nanoparticle was achieved by Grubbs' metathesis. It was demonstrated that cross-linking of the organic ligand has no effect on the size or morphology of the inorganic gold core as determined by TEM and UV−vis measurements. However, the introduction of cross-linking at the surface of the ligand enhances the stability of the gold nanocore toward chemical etchant agents (NaCN) and thermal treatment. The impact of cross-linking on nanoparticle stability is greater when the cross-linking is closer to the nanoparticle surface (i.e., using lower generation dendritic ligands). Attempts to perform further synthetic transformation on the hybrid materials in order to remove the gold core led to insoluble products composed predominantly of the dendritic ligand. [ABSTRACT FROM AUTHOR]

Using EPR spectroscopy and spin-labeled ligands, we have studied product distribution in the ligand exchange reactions of Au nanoparticles. When the incoming ligand was used in excess, the exchanged nanoparticles had uniform composition of the organic shell. Preparative GPC was employed to fractionate these materials according to the diameter of the Au core, as confirmed by TEM, UV, and EPR measurements. When the exchange reaction was carried out with less than a stoichiometric amount of the incoming ligand, nanoparticles with polydisperse composition of the organic shell were formed. This was established by the EPR analysis of the exchange reaction mixtures following their GPC fractionation. The GPC separation of these mixtures is controlled by both Au core size and shell composition. [ABSTRACT FROM AUTHOR]

EPR spectroscopy and spin-trapping experiments showed that polymer-encapsulated Au nanoparticles promote aldehyde oxidation viaa radical pathway by initiating formation of acyl radicals. [ABSTRACT FROM AUTHOR]

EPR spectroscopy and spin-trapping experiments showed that polymer-encapsulated Au nanoparticles promote aldehyde oxidation viaa radical pathway by initiating formation of acyl radicals. [ABSTRACT FROM AUTHOR]

Stirring of perthiolated β-cyclodextrin in water yields cross-linked hollow capsules ca.50 nm in diameter, which can be used for encapsulation and controlled release of large molecules as shown using Reichardt’s dye. [ABSTRACT FROM AUTHOR]

Low temperature (‘cold’) atmospheric pressure plasmas have gained much attention in recent years due to their biomedical effects achieved through the interactions of plasma-induced species with the biological substrate. Monitoring of the radical species in an aqueous biological milieu is usually performed via electron paramagnetic resonance (EPR) spectroscopy using various nitrone spin traps, which form persistent radical adducts with the short-lived radicals. However, the stability of these nitroxide radical adducts in the plasma-specific environment is not well known. In this work, chemical transformations of nitroxide radicals in aqueous solutions using a model nitroxide 4-oxo-TEMPO were studied using EPR and LC-MS. The kinetics of the nitroxide decay when the solution was exposed to plasma were assessed, and the reactive pathways proposed. The use of different scavengers enabled identification of the types of reactive species which cause the decay, indicating the predominant nitroxide group reduction in oxygen-free plasmas. The 2H adduct of the PBN spin trap (PBN-D) was shown to decay similarly to the model molecule 4-oxo-TEMPO. The decay of the spin adducts in plasma-treated solutions must be considered to avoid rendering the spin trapping results unreliable. In particular, the selectivity of the decay indicated the limitations of the PTIO/PTI nitroxide system in the detection of nitric oxide. [ABSTRACT FROM AUTHOR]