Comparative Study of Catalytic Activity of Recyclable Au/Fe3O4 Microparticles for Reduction Of 2,4-Dinitrophenol and Anionic, Cationic Azo Dyes.

We synthesized Au/Fe3O4 microparticles. Initially, citrate-capped Fe3O4 micro-sized particles were synthesized by the co-precipitation method with an excess amount of trisodium citrate. Gold ions were reduced on the surface of citrate-capped Fe3O4 and grew as gold sub-microparticles with an average diameter of 210 nm on the surface. The characteristic SPR peak of gold nanoparticles on the surface of Fe3O4 was detected at 584 nm, whereas the absorption in the near-infrared region was increased. SEM images has proved that the synthesized Au/Fe3O4 composite microparticles has an average diameter of 1.7 micrometers. The results of XRD patterns proved the existence of both crystal phases of Fe3O4 and Au particles. To investigate the catalytic activity, the reaction rate constant of reduction of 2,4-dinitrophenol (2,4-DNP) and degradation of Congo red (CR), and methylene blue (MB) with NaBH4 in the presence of Au/Fe3O4 catalyst was monitored by UV-Vis spectroscopy. The initial reaction rate constant calculated from the change in characteristic peak absorptions of 2,4-dinitrophenol was 3.97×10-3 s-1, while the reaction rate constants for the degradation of CR and MB were 9.72×10-3 s-1 and 14.25×10-3 s-1 respectively. After 5 cycles, Au/Fe3O4 microparticles preserved 99 % of the reaction rate constant, exhibiting considerable recycling efficiency in the reduction of nitro groups.

Hydrogen bonding-induced color recovery of gold nanoparticles upon conjugation of amino acids.

Hydrogen bonding-induced redispersion of the aggregated Au nanoparticles upon N-hydroxysuccinimide ester bioconjugations may provide a simple and colorimetric tool as an optical sensor to detect a trace amount of amino acids as low as approximately 10(-6) M in an aqueous solution.

Infrared spectroscopy characterization of normal and lung cancer cells originated from epithelium.

The vibrational spectral differences of normal and lung cancer cells were studied for the development of effective cancer cell screening by means of attenuated total reflection infrared spectroscopy. The phosphate monoester symmetric stretching nu(s)(PO3(2-)) band intensity at ~970 cm(-1) and the phosphodiester symmetric stretching nu(s)(PO2(-)) band intensity at approximately 1,085 cm(-1) in nucleic acids and phospholipids appeared to be significantly strengthened in lung cancer cells with respect to the other vibrational bands compared to normal cells. This finding suggests that more extensive phosphorylation occur in cancer cells. These results demonstrate that lung cancer cells may be prescreened using infrared spectroscopy tools.

Adsorption changes of cyclohexyl isothiocyanate on gold surfaces.

The adsorption and structure of cyclohexyl isothiocyanate (CHIT) on gold surfaces has been investigated by surface-enhanced Raman scattering (SERS) and scanning tunneling microscopy (STM). Depending on the concentration, the spectral changes of the NCS stretching vibration on gold nanoparticles appeared to be more conspicuous than those of cyclohexyl ring modes. Both equatorial and axial chair conformers of CHIT were found to exist at low bulk concentrations near the monolayer coverage limit, whereas the equatorial chair conformer appeared to be dominant at high bulk concentrations. It was also observed that the ring conversion of equatorial to axial conformers can easily occur at higher temperatures, and the mole fraction of the axial form is assumed to increase with increasing temperature from 30 to 60 degrees C. Alternatively, STM imaging revealed that the adsorption of CHIT molecules on Au(1 1 1) leads to the formation of disordered SAMs with a few vacancy islands, as opposed to the formation of well-ordered self-assembled monolayers (SAMs) by cyclohexanethiols.