A kinetic study of the oxidation of l-methionine by water soluble colloidal MnO2

Modeling of the Inhibitory Effect of Nanoparticles on Amyloid β Fibrillation

Experiments have shown that charged nanoparticles (NP) inhibit, partially or completely, the aggregation of Aβ protein monomers into fibrils. The equilibrium fibril content is found to be inversely proportional to the concentration of NP. In this work, we report a kinetic model for the fibrillation of Aβ protein in the presence of NP. In the model, apart from nucleation, elongation and fragmentation processes, the effect of NP is considered to cause a conformational change to the protein monomer, making the latter incompatible for aggregation. The simulated results explain the growth kinetics of pure Aβ (1-40) protein, and the kinetics in the presence of NP. The NP-monomer interaction considered in the model captures the significant effect of NP on the fibrillation process at a very molar ratio (NP to Aβ monomer) as low as 10^-4. The model predictions are compared with two different NP systems, namely, gold and silica NP. The model can be applied to explain the inhibitory effect of other additives such as small molecules, NP, lipids, and surfactants that show a similar inhibition trend for fibril formation of Aβ and other proteins.

Oxidative degradation of l-histidine by manganese dioxide (MnO2) nano-colloid in HClO4 medium with/without using TX-100 catalyst: a kinetic approach

The kinetics of the oxidative degradation of l-histidine (His) in perchloric acid medium by freshly prepared manganese dioxide (MnO₂) nano-colloid have been investigated with and without using TX-100 catalyst.

Degradation kinetics and estrogenic activity of 17beta-estradiol removal by aqueous manganese dioxide

Natural and synthetic hormones have emerged as a new group of contaminants in soil and water systems. To better understand the processes affecting these compounds in soils and sediments, the kinetics of 17beta-estradiol (E2) transformation by hydrous manganese oxide (delta-MnO(2) were investigated as a function of reactant concentration, MnO(2) concentration, pH and the presence of co-solutes. The reaction of E2 degradation by delta-MnO(2) did not exhibit simple pseudo-first-order kinetics, although a good linear fit (R(2) = 0.97) was obtained during the first 30 min, which was indicative of pseudo-first-order reaction kinetics in the first stage. The initial reaction rate (r(init)) values of E2 degradation were enhanced with increasing E2, MnO(2) and H(+) concentration. The reaction orders for E2, MnO(2) and H(+) concentrations were 0.80, 0.72 and 0.07, respectively. The presence of metal ions and carboxylic acids had an inhibitory effect on r(init) as a result of the decreased number of active surface sites in the presence of co-solutes. The same inhibitory effect on r(init) was also observed in wastewater. Furthermore, the results showed that delta-MnO(2) not only degraded E2 but also removed 62% and 48% of the estrogenic activity originating from E2 in ultrapure water and wastewater, respectively. This study demonstrated that natural manganese oxides in soils and sediments are likely to promote appreciable degradation of E2, and that reaction rates are strongly dependent on solution conditions. However, a combination of methods should be adopted in order to completely remove the estrogenic activity of E2.