Optical properties of gold nanorods: DDA simulations supported by experiments

Simulations of the absorption efficiency using the discrete dipole approximation (DDA) method and taking into account the real shape of gold nanorods are reported. A dominant surface plasma band corresponding to the longitudinal resonance is observed. Its maximum position lambda(max) shifts to the red as the aspect ratio increases. The transversal dipolar and multipolar mode wavelength positions are also discussed. These data are in good agreement with previous theoretical work based on classical electrostatic predictions and assuming that gold nanorods behave as ellipsoidal particles. From the experimental point of view, good agreement with the published data for gold nanorods is obtained.     

Structural study of AOT reverse micelles containing native or modified proteins: influence of surfactant-enzyme interaction

In this paper, the solubilization effect of different proteins in sodium di(2-ethylhexyl)sulfosuccinate (AOT) reverse micelles is studied. From results obtained with chemically modified proteins, it is shown that the nature of the surfactant-protein interaction controls the intermicellar potential, not the location of the proteins within the droplets. By binding hydrophobic molecules onto the surface of -chymotrypsin and ribonuclease, we force these hydrophobic enzymes to interact, via hydrophobic forces, with the droplet's interface. Small-angle X-ray scattering (SAXS) and conductivity measurements suggest that modification of the intermicellar potential is not required when the enzymes are modified. Conversely, electrostatic forces play an important role, as is observed using cytochrome c and its derivatives differing in their superficial charge.     

Size control and growth process of alkylamine-stabilized platinum nanocrystals: a comparison between the phase transfer and reverse micelles methods

Alkylamine-stabilized platinum nanoparticles are synthesized either by the phase-transfer method or in reverse micelles. The phase-transfer method produces nanocrystals that are quite spherical whereas the synthesis in reverse micelles generates a large number of wormlike structures. An alkylamine is used as a stabilizing agent to prevent nanoparticle coalescence, and it is shown that there is an inverse relationship between the alkylamine chain length and the platinum nanoparticle diameter. By comparing alkylamine and alkylthiol analogues, it is found that the integrity of the different crystallites depends on the strength of the interaction between the stabilizing agent and the platinum nanocrystals. The results obtained and the comparison made between the two synthesis methods improve the understanding of the growth mechanisms of platinum nanocrystals in disperse media.     

Tuning of copper nanocrystals optical properties with their shapes

Copper nanocrystals are obtained by chemical reduction of copper ions in mixed reverse micelles. A large excess of reducing agent favors producing a new generation of shaped copper nanocrystals as nanodisks, elongated nanocrystals, and cubes. By using UV-Visible spectroscopy and numerical optical simulations we demonstrate that the optical properties are tuned by the relative proportions of spheres and nanodisks.     

Synthesis of nanosize metallic and alloyed particles in ordered phases

Functionalized reverse micelles have been used to synthesize Copper and Cobalt nanoparticles differing by their size and shape. They can be also used to synthesize Fe–Cu alloy (at 30% Fe) and composite (at 70% Fe) particles. In the case of Fe–Cu system, the magnetic properties are presented.     

On a possible excited state proton transfer in N-formylkynurenine derivatives

It is shown that intramolecular hydrogen bonding between the

and the ortho carbonyl on the side chain of N'formylkynurenine and some parent compounds plays an important role on their spectroscopic properties. The fluorescence emissionλ_max is shifted by about 4000 cm^?1 in going from polar to non-polar solvents. This abnormally red-shifted fluorescence is attributed to an excited state proton transfer from the formamido to the ortho carbonyl of the side chain.     

Nanoparticles of: Synthesis and superparamagnetic properties

By using oil in water micelles, cobalt ferrite particles having an average diameter around 3 nm were synthetised. These nanoparticles are characterized by the presence of cation vacancies and no Fe(II) is observed, as it has been described in literature previously. Chemical interfacial treatment allows to coat the particles with citrate derivatives. The magnetic properties of uncoated and coated particles strongly diluted in a polymer substrate are compared by magnetization measurements and ⁵⁷Fe M?ssbauer spectroscopy. The anisotropy constant is shown to be independent of coating, whereas the magnetization is found to be larger in the uncoated particles. Received 3 February 1998     

Mesostructures of cobalt nanocrystals. 1. Experiment and theory

Solid mesostructures made of cylinders are produced by the slow evaporation of cobalt nanocrystals dispersed in hexane and subjected to an applied field perpendicular to the substrate. Varying the initial nanocrystal concentration is found to be an efficient method for changing the pattern size. The experimental structures and the theoretical predictions based on the minimization of the total free energy are in good agreement. A comparison of experiment with theory allowed us to conclude that the mesostructures form as a result of a liquid-gas phase transition during the evaporation process. Within the theoretical model and the experimental data, it is concluded that the phase ratio of the magnetic to the total volume and the height of the cylinders govern the pattern geometry. In contrast, because of the saturation of the magnetization curve, the mesostructures are not influenced by the field strength.     

Zinc-porphyrin sensitized reduction of simple and functional quinones in vesicle systems

Changes of the surfactant vesicle sizes and of the efficiency of the photoredox reaction between various solubilized Zn porphyrins and duroquinones upon incorporation of the chromophore or upon addition of salts have been examined by quasi-elastic light scattering and laser photolysis techniques. The yields of porphyrin cation and duroqumone anion radicals appear to be independent of the nature of the porphyrin-qumone system. Addition of salts influences both the yield and the ejection of porphyrin cations from the vesicles by screening up the surface charge.     

On the flash photolysis of phenol derivatives in neutral aqueous solutions: effect of nitrous oxide and alcohols on transients

Flash photolysis of N₂O saturated neutral aqueous solution of tyrosine phenol and p-cresol leads to OH adduct formation. This species subsequently undergoes either unimolecular water elimination to form the phenoxyl radical or bimolecular radical-radical recombination. Alcohol addition to neutral aqueous solutions provokes the formation of hydrogen atom adduct.