Corrosion behavior of pure titanium in artificial saliva solution

The biocompatibility of commercially pure (cp) titanium stems from its chemical stability within an organism, due to a fine film of impermeable titanium oxide covering the metal surface, which guarantees its resistance to corrosion. Despite its biocompatible characteristic, this material does not promote the formation of a hydroxyapatite layer, therefore, many research groups have sought to alter the material`s surface, introducing modifications that might influence corrosion resistance. The electrochemical behavior of cp Ti, with hydroxyapatite coating and without hydroxyapatite coating, commonly used in implant materials, was investigated using an artificial saliva solution at 25 degrees C and pH=7.4. In the conditions of the study it was observed that the hydroxyapatite layer influences the properties of corrosion resistance. This study of the behavior of cp Ti with and without hydroxyapatite coating, in naturally aerated artificial saliva solution at 25 degrees C, was based on open circuit potential measurements and potentiodynamic polarization curves. At approximately 1x10(-6) A/cm(2) the potential for cp Ti with and without hydroxyapatite coating begins to increase at a faster rate, but at -74mV (SCE) for coated cp Ti and at 180mV (SCE) for uncoated cp Ti the increase in potential begins to slow. This behavior, characterized by a partial stabilization of current density, indicates that in those potential ranges a protective passive film is formed.

Activation of Leishmania (Leishmania) amazonensis arginase at low temperature by binuclear Mn(2+) center formation of the immobilized enzyme on a Ni(2+) resin

In Leishmania, arginase is responsible for the production of ornithine, a precursor of polyamines required for proliferation of the parasite. In this work, the activation kinetics of immobilized arginase enzyme from L. (L.) amazonensis were studied by varying the concentration of Mn(2+) applied to the nickel column at 23 degrees C. The intensity of the binding of the enzyme to the Ni(2+) resin was directly proportional to the concentration of Mn(2+). Conformational changes of the enzyme may occur when the enzyme interacts with immobilized Ni(2+), allowing the following to occur: (1) entrance of Mn(2+) and formation of the metal bridge; (2) stabilization and activation of the enzyme at 23 degrees C; and (3) an increase in the affinity of the enzyme to Ni(2+) after the Mn(2+) activation step. The conformational alterations can be summarized as follows: the interaction with the Ni(2+) simulates thermal heating in the artificial activation by opening a channel for Mn(2+) to enter. (C) 2010 Elsevier Inc. All rights reserved.

Contextual, but not auditory, fear conditioning is disrupted by neurotoxic selective lesion of the basal nucleus of amygdala in rats

The basolateral amygdala complex (BLA) is involved in acquisition of contextual and auditory fear conditioning. However, the BLA is not a single structure but comprises a group of nuclei, including the lateral (LA), basal (BA) and accessory basal (AB) nuclei. While it is consensual that the LA is critical for auditory fear conditioning, there is controversy on the participation of the BA in fear conditioning. Hodological and neurophysiological findings suggest that each of these nuclei processes distinct information in parallel; the BA would deal with polymodal or contextual representations, and the LA would process unimodal or elemental representations. Thus, it seems plausible to hypothesize that the BA is required for contextual, but not auditory, fear conditioning. This hypothesis was evaluated in Wistar rats submitted to multiple-site ibotenate-induced damage restricted to the BA and then exposed to a concurrent contextual and auditory fear conditioning training followed by separated contextual and auditory conditioning testing. Differing from electrolytic lesion and lidocaine inactivation, this surgical approach does not disturb fibers of passage originating in other brain areas, restricting damage to the aimed nucleus. Relative to the sham-operated controls, rats with selective damage to the BA exhibited disruption of performance in the contextual, but not the auditory, component of the task. Thus, while the BA seems required for contextual fear conditioning, it is not critical for both an auditory-US association, nor for the expression of the freezing response. (C) 2009 Elsevier Inc. All rights reserved.