Preparation and characterization of microporous layers on titanium by anodization in sulfuric acid with and without hydrogen charging.

The formation of microporous oxide layers on titanium (Ti) by anodization in sulfuric acid (H2SO4) solution and the influence of prior hydrogen charging on their properties are examined using electrochemical techniques, scanning electron microscopy, grazing incident X-ray diffraction, and X-ray photoelectron spectroscopy. When Ti is anodized in 1 M aqueous H2SO4 solution at a high direct current (DC) potential (>150 V) for 1 min, a porous surface layer develops, and the process takes place with spark-discharge. Under these conditions, oxygen evolution at the Ti electrode proceeds vigorously and concurrently with the formation of anodic oxide. The oxygen gas layer adjacent to the Ti surface acts as an insulator and triggers spark-discharge; the latter stimulates the development of pores. In the absence of spark-discharge, the oxide layer has extended surface roughness but low porosity. A porous oxide layer can be prepared by applying a lower DC voltage (130 V) and without spark-discharge, but Ti requires prior hydrogen charging by cathodic polarization in 1 M aqueous H2SO4 solution. Mott-Schottky measurements indicate that the oxide layers are n-type semiconductors and that the charge carrier density in the anodic oxide layer on the hydrogen-charged Ti is lower than in the case of untreated Ti. The hydrogen charging also affects the flat band potential of the anodic oxide layers on Ti by increasing its value. The reduced charge carrier density brought about by hydrogen charging decreases the oxide layer conductivity and creates favorable conditions for its electrical breakdown that stimulates the development of pores. The porous layer on the hydrogen-charged Ti consists of anatase and rutile phases of TiO2; it has the same chemical composition as the porous layer obtained on untreated Ti. X-ray photoelectron spectroscopy measurements show that prior hydrogen charging does not affect the thickness of anodic oxides on Ti. The porous oxide layer on Ti enables the growth of hydroxyapatite, thus revealing good bioactivity in simulated body fluids.

Redox control of the activity of phosphoglycerate kinase in Synechocystis sp. PCC6803.

Phosphoglycerate kinase catalyzes the phosphorylation of 3-phosphoglycerate to 1,3-diphosphoglycerate using ATP within the Calvin-Benson cycle. Recent proteomic analysis of thioredoxin targets in Synechocystis sp. PCC6803 revealed this enzyme as one of the target candidates, and we present here further characterization of the interaction between these proteins. By using the His-tagged recombinant enzyme, we determined that Synechocystis phosphoglycerate kinase is inactivated by oxidation and that the oxidized enzyme is easily reduced and reactivated by thioredoxin, suggesting a role for thioredoxin in the control of the redox state of this enzyme. In addition, thorough analysis of redox-relevant cysteines revealed that a cysteine pair, Cys314 and Cys340, located on the C-terminal domain of the molecule, is critical for redox regulation.