Electrochemical Behavior of Carbon Steel in Acidic Medium Containing Cationic Inhibitor

Electrochemical behavior of carbon steel in 1 M acetic acid (CH3COOH) containing tetramethyl ammonium bromide (TMB) as the cationic inhibitor was investigated by potentiodynamic polarization technique and electrochemical impedance spectroscopy (EIS). The aim of this study is to evaluate the inhibition efficiency of cationic inhibitor for carbon steel corrosion. The electrochemical analysis revealed that inhibition efficiency significantly increased with the increasing of inhibitor concentration. Polarization study indicated that TMB acted as a mixed type inhibitor, which inhibited both cathodic and anodic reactions. The changes of impedance parameters by different inhibitor concentration showed a better protection due to formation of a thin film onto the steel surface. This study suggests that TMB is able to inhibit corrosion process of carbon steel in acidic medium with significant inhibition efficiency.

Calcium Salt Precipitation and Mechanisms of Inhibition Under Oral Conditions

Dental calculus contains a range of calcium phosphates, derived from plaque fluid and the saliva. Older deposits tend to contain more hydroxyapatite and 6 tricalcium phosphate. Compounds which inhibit the transformation of calcium phosphate nuclei to hydroxyapatite and its subsequent crystal growth are known to be effective in restricting calculus deposition in vivo. Such compounds include the diphosphonates, polyphosphates, and zinc. Under physiological conditions, apatites tend to be calcium-deficient with matching HP042- groups. If these groups are displaced, then crystal growth is inhibited. This can be demonstrated for heated apatite and FP032- treatment. The latter, however, subsequently hydrolyzes with reformation of the HPO42- groups. Diphosphonates and polyphosphates adsorb upon nuclei, displacing surface phosphate in the process. The treated apatite nuclei will not grow until the adsorbed species are displaced or hydrolyzed. The cationic inhibitor, zinc, is acquired by the dental plaque and oral surfaces and is eluted in the saliva. Zinc is adsorbed upon apatite crystallites with displacement of calcium. When a surface coverage of approximately 3 μmol/m2 is achieved, crystal growth is almost completely inhibited. Post-treatment with calcium desorbs the zinc. Inhibition of hydroxyapatite crystal growth and thence calculus formation thus depends upon displacement of surface ions from seed crystallites. The role of HPO42- groups in this and other physiological apatite processes is of particular interest.

The role of magnesium ions in β-galactosidase-catalysed hydrolyses. Studies on charge and shape of the β-galactopyranosyl-binding site

1. β-d-Galactopyranosyl trimethylammonium bromide is a competitive inhibitor of β-galactosidase, Ki=1.4±0.2mm at 25°C. 2. Tetramethylammonium bromide is not an inhibitor (Ki>0.2m). 3. The kinetics of deactivation of Mg2+-saturated, and of inhibitor-and Mg2+-saturated, enzyme in 10mm-EDTA are similar. 4. The apparent Ki for the glycosylammonium salt is approx. 2.2mm in the absence of Mg2+. 5. It is therefore concluded that Mg2+ and the inhibitor bind independently, and that the Mg2+ does not act as an electrophilic catalyst. 6. Complexant fluorescence measurements indicate binding of 1 Mg2+ ion per 135000-dalton protomer. 7. This stoicheiometry is confirmed by equilibrium dialysis. 8. 1,6-Anhydrogalactopyranose is neither a substrate (kcat./Km< 3×10-2m-1·S-1) nor an inhibitor (Ki>0.2m). 9. Considerations of conformations available to the cationic inhibitor and to the anhydrogalactose indicate that the substrate is bound with the pyranose ring in a conformation not greatly different from the normal chair (C1) conformation.