For the first time, cobalt oxide films that are highly protective against localized corrosion and depicting a wide variety of bright and uniform colors due to light interference, have been successfully electrogenerated on polycrystalline cobalt disk electrodes under potentiostatic polarization in a mild aqueous bicarbonate medium. Open circuit potential measurements have shown the formation of a film with a bilayered structure, organized as a thin Co 3 O 4 outer layer and a thick CoO inner layer. The existence of Co 3 O 4 as a thin outer layer, previously postulated from galvanostatic reduction experiments, has been confirmed from XPS analysis. Raman spectroscopy, performed using a very low laser intensity, has shown that the films are mainly composed of CoO. The broadness of the Raman bands observed is associated to the amorphous character of the film, a result that has been confirmed by spectroscopic ellipsometry and X-ray diffraction analysis. Overall film thicknesses, well controlled by the anodization duration, were determined and correlated using mechanical (atomic force microscopy and profilometry) and spectroscopic (specular UV-vis-NIR reflectance and ellipsometry) techniques. Spectroscopic ellipsometry, using a simple amorphous dispersion model, has proved efficient for measuring thicknesses of films ranging from 31 to 290 nm with very low standard deviations. The real part of the complex refractive indices of these films, ranging from 1.8 to 2.2 (at λ ) 632.8 nm) depending on the anodization duration, is in good agreement with values reported in the literature for CoO. The film with the highest refractive index, and consequently the more densely packed structure, was obtained following a 30-minute anodization period.

No abstract

No abstract

The thermal stability of L-5-methyltetrafolic acid (L-5-MTHF) was investigated in model/buffer systems and food systems. L-5-MTHF degradation followed first-order reaction kinetics with relatively greater (P < 0.01) stability at pH 4 compared to pH 6.8 in the buffer systems. This was confirmed using cyclic voltammetry. The stability (for example, k-values) of L-5-MTHF in an oxygen controlled environment improved (P < 0.001) proportionally when in the presence of increasing molar ratios of sodium ascorbate (NaAsc). The addition of NaAsc to L-5-MTHF after heat treatment was also effective at returning thermally oxidized L-5-MTHF back to its original form. A scheme was developed to explain the degradation and regeneration of L-5-MTHF. The importance of antioxidant protection of L-5-MTHF from thermal oxidation was extended using 2 distinct food systems; namely skim milk and soy milk, both with known antioxidant capacities. We conclude that the antioxidant activity of food components can enhance the stability of L-5-MTHF.