Supported protecting agents

After supporting these sols on activated carbon, however, the obtained particle size depends on the capability of the protective agent to maintain the particle dimension. The obtained three catalysts, having different characteristics, are summarized in Table 3. As it is shown, mean size of gold nanoparticle obtained by TEM measurement did not always match with X-ray powder diffraction (XRPD) data. This result is not surprising as TEM measurements represent particle sizes, whereas from X-ray diffraction (XRD) it is possible to obtain crystallite dimensions that do not necessarily coincide with the size of... 

In general, consumers use herbal products as therapeutic agents for treatment and cure of diseases and pathological conditions, as prophylactic agents to prevent disease over the long term, and as protective agents to maintain health and well-being. Additionally, herbs and phytomedicinals can be used as adjunct therapy, to support... 

Using the latter two methods, it was possible to determine k, for the Pt-Carbowax catalyst to be 1 s-1 and for the Ru02/sodium dodecylsulfate catalyst to be 0.1s 1. These data have been supported by independent pulse radiolytical and laser photolysis studies. Work is in progress to check the influence of different protective agents, dependence of the catalyst activity on pH, E0 of the relay and ionic strength. 

Table 13.1 Protecting agents for different supporting materials.

In summary, the tested encapsulation method is applicable for other components and different concentrations (aromas, antioxidants, or other oil substances). Other possible supports may be proposed to replace maltodextrin and acacia gum as modified starch (Buffo et al., 2002), proteins, gums, or protective agents. 

Since our synthesis supports a high local concentration of the protecting agent at the reduction center, consequently the resulting colloid particles are rather small (55 - 300 metal atoms). Electron micrographs also show generally a very narrow particle size distribution. 

Figure 14.6. For example, in the impregnation method, the size of the Pt nanoparticles is controlled by the structure of the support material which acts as the confining medium to restrict reaction, diffusion, and aggregation processes. In the colloidal method, the Pt size is controlled either by electrostatic hindrance or the addition of a protecting agent, which will adhere onto the surface of Pt nanoparticles. For the ion-exchange mefliod, the surface groups of flie support material provide the anchorage sites for the Pt particles and control the dispersion and distribution of the Pt nanoparticles. In this section, some examples of Pt deposition methods will be discussed.

It was recently reported that the colloidal Pt nanoparticles may be protected by glycol, which serves as both a solvent and the protecting agent [71, 102]. For example, Kongkanand and co-workers [102] used ethylene glycol as a reducing agent to prepare well-dispersed Pt catalysts supported by polymer-wrapped CNTs. In their procedure, the CNTs were sonicated in A,7V-dimethyIformamide for 15 h to break up the nanotube bundles into individual CNTs. However, polymer such as... 

Ever since the introduction of levodopa there have been concerns that it may be neurotoxic, particularly towards neurons in the substantia nigra, which are in any case depleted in Parkinson s disease. There is a plausible mechanism for this, through generation of free radicals. The evidence from cell culture studies, animal studies, and clinical data has been reviewed, and the authors concluded that the culture experiments are confounded by lack of ascorbate in the medium, which would act as an important protective agent, as it appears to do in vivo in animals, notably in primates [95 ]. The clinical data have failed to support the idea that levodopa accelerates striatal neuronal loss. However, the evidence is contradictory, and it seems unlikely that even after 50 years we shall get a definitive answer. 

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