Effect of poly(ethylene oxide)-silane graft molecular weight on the colloidal properties of iron oxide nanoparticles for biomedical applications.

The size, charge, and stability of colloidal suspensions of magnetic nanoparticles with narrow size distribution and grafted with poly(ethylene glycol)-silane of different molecular weights were studied in water, biological buffers, and cell culture media. X-ray photoelectron spectroscopy provided information on the chemical nature of the nanoparticle surface, indicating the particle surfaces consisted of a mixture of amine groups and grafted polymer. The results indicate that the exposure of the amine groups on the surface decreased as the molecular weight of the polymer increased. The hydrodynamic diameters correlated with PEG graft molecular weight and were in agreement with a distributed density model for the thickness of a polymer shell end-grafted to a particle core. This indicates that the particles obtained consist of single iron oxide cores coated with a polymer brush. Particle surface charge and hydrodynamic diameter were measured as a function of pH, ionic strength, and in biological buffers and cell culture media. DLVO theory was used to analyze the particle stability considering electrostatic, magnetic, steric, and van der Waals interactions. Experimental results and colloidal stability theory indicated that stability changes from electrostatically mediated for a graft molecular weight of 750 g/mol to sterically mediated at molecular weights of 1000 g/mol and above. These results indicate that a graft molecular weight above 1000 g/mol is needed to produce particles that are stable in a wide range of pH and ionic strength, and in cell culture media.

Luminescence rigidochromism and redox chemistry of pyrazolate-bridged binuclear platinum(II) diimine complex intercalated into zirconium phosphate layers.

The direct intercalation of a pyrazolate-bridged platinum(II) bipyridyl dimer ([{Pt(dmbpy)(µ-pz)}(2)](2+); dmbpy = 4,4'-dimethyl-2,2'-bipyridine, pz(-) = pyrazolate) within a zirconium phosphate (ZrP) framework has been accomplished. The physical and spectroscopic properties of [{Pt(dmbpy)(µ-pz)}(2)](2+) intercalated in ZrP were investigated by X-ray powder diffraction and X-ray photoelectron, infrared, absorption, and luminescence spectroscopies. Zirconium phosphate layers have a special microenvironment that is capable of supporting a variety of platinum oxidation states. Diffuse reflectance spectra from powders of the blue-gray intercalated materials show the formation of a low-energy band at 600 nm that is not present in the platinum dimer salt. The nonintercalated complex is nonemissive in room-temperature fluid solution, but gives rise to intense blue-green emission in a 4:1 ethanol/methanol 77 K frozen glassy solution. Powders and colloidal suspensions of [{Pt(dmbpy)(µ-pz)}(2)](2+)-exchanged ZrP materials exhibit intense emissions at room-temperature.

Facet-selective platinum electrodeposition at free-standing polycrystalline boron-doped diamond films.

In the present investigation, electrochemical deposition of platinum particles was carried out on boron doped diamond (BDD) films by using cyclic voltammetry at different potential sweep rates while maintaining the Pt concentration and number of potential cycles during the deposition as constant for all samples. The BDD film surfaces were studied using Raman spectroscopy, X-ray diffraction, and scanning electrochemical microscopy. The deposited particles were characterized by scanning electron microscopy/X-ray energy dispersive analysis, X-ray photoelectron spectroscopy, and cyclic voltammetry before and after methanol oxidation. The platinum nanoparticles are found to be selectively electrodeposited on the (111) facets of the BDD. In addition, the location of the Pt particles on the diamond facets was affected by the potential sweep rate. For higher sweep rates, the particle size was dependent on the facet on which the particles are electrodeposited with smooth (110) facets exhibiting a smaller number of particles but with a larger particle diameter. After methanol oxidation studies using cyclic voltammetry and controlled potential electrolysis for several hours, the platinum particles remained attached to the (111) facets of the BDD, while the particles on the (110) facets of the BDD became agglomerated along grain boundaries. Functional groups present on the (111) facet of the diamond surface play an important role on the stability of the particles attached to the diamond surface. After methanol oxidation, the particles deposited on other facets appeared to lose their adhesion leading to agglomeration on the grain boundaries. BDD appears to be a promising electrocatalyst support material that can help to resist platinum nanoparticle agglomeration in direct methanol and other low temperature fuel cell applications.

Electrochemical and surface characterization of 4-aminothiophenol adsorption at polycrystalline platinum electrodes.

The formation of a self-assembled monolayer (SAM) of 4-aminothiophenol (4-ATP) on polycrystalline platinum electrodes has been characterized by surface analysis and electrochemistry techniques. The 4-ATP monolayer was characterized by cyclic voltammetry (CV), linear sweep voltammetry, Raman spectroscopy, reflection-absorption infrared (RAIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). CV was used to study the dependence of the adsorption time and 4-ATP solution concentration on the relative degree of coverage of 4-ATP monolayers on polycrystalline Pt electrodes. The adsorption time range probed was 24-72 h. The optimal concentration of 4-ATP needed to obtain the highest surface at the lowest adsorption time was 10 mM. RAIR and Raman spectroscopy for 4-ATP-modified platinum electrodes showed the characteristic adsorption bands for 4-ATP, such as nuNH, nuCH(arom), and nuCS(arom), indicating the adsorption on the platinum surface. The XPS spectra for the modified Pt surface presented the binding energy peaks of sulfur and nitrogen. High energy resolution XPS studies, RAIR, and Raman spectrum for platinum electrodes modified with 4-ATP indicate that the molecules are sulfur-bonded to the platinum surface. The formation of a S-Pt bond suggests that ATP adsorption leads to an amino-terminated electrode surface. The thickness of the monolayer was evaluated via angle-resolved XPS (AR-XPS) analyses, giving a value of 8 A. As evidence of the terminal amino group on the electrode surface, the chemical derivatization of the 4-ATP SAM was done with 16-Br hexadecanoic acid. This surface reaction was followed by RAIR spectroscopy.

Proceso descontínuo de síntese de amiloglicosidade por Aspergilus awamori: influência do pH e da concentraçäo inicial de polissacarídeo

Estudou-se a influência da concentraçäo inicial de polissacarídeo (So) e do pH na produçäo de amiloglicosidase por Aspergillus awaamori NRRL 3112. Foram efetuados ensaios descontínuos, a pH 4,0 e 5,0 em fermentador de 10 litros, empregando-se meio de cultura a base de farinha de mandioca. Através do estudo cinético do processo, verificou-se a partir de So = 20g/l, para ambos os valores de pH, um comportamento acentuadamente crescente da atividade enzimática final no caldo, até se atingir um valor máximo para um determinado So. Verificou-se que esta atividade máxima é significativamente maior a pH 5,0, chegando-se a aproximadamente 7000U/1 para So = 93g/1, enquanto que a pH 4,0, obteve-se 2500U/1