Two-step framework

The Two-Step Framework and Primary Versus Secondary Mechanisms... 

THE TWO-STEP FRAMEWORK AND PRIMARY VERSUS SECONDARY MECHANISMS... 

Scheme 9). Although cyanohydrin acetonide 64 could conceivably have been used, the silyl ether 75 was chosen. This compound is readily available from (l)-malic acid, and can undergo electrophilic activation under far more mild conditions than compound 64. Alkylation of the 1,3-diol synthon 75 with bromide 76 created the C11-C26 framework of roflamycoin, in 85% yield. A two-step conversion of the terminal siloxy group to the primary iodide (78) proceeded in 80% overall yield. 

Separations in hydrophobic interaction chromatography have been modeled as a function of the ionic strength of the buffer and of the hydrophobicity of the column, and tested using the elution of lysozyme and ovalbumin from octyl-, butyl- and phenyl-Sepharose phases.2 The theoretical framework used preferential interaction analysis, a theory competitive to solvophobic theory. Solvophobic theory views protein-surface interaction as a two-step process. In this model, the protein appears in a cavity in the water formed above the adsorption site and then adsorbs to the phase, with the free energy change... 

The difference of the polyolefins and the PVC in the catalytic degradation can be seen in Fig. 3 the decomposition of PVC takes place at least in two steps, the first is due to the release of HC1 with 300 °C characteristic temperature, the second peak corresponds to the pyrolysis of the residual hydrocarbon framework (440 - 470 °C temperature range). 

The high activity of Cr-Cl catalyst may result probably from the formation of more active species such as Cr02+ complex cation during the ammoxidation reaction. Some authors [7] assumed that Cr(V) species occurred inside the zeolite structure as complex cation such as Cr02+ coordinated to two framework oxygen atoms and suggest the following two step process as the most probable pathway of chromate formation ... 

In reaction (b) an ionic exchange and solubilization of the aluminum species takes place. In reaction (c) only the solubilization of neutral aluminum species takes place. If the chemical treatment with acid in the two-step process also involves the solubilization of framework aluminum, reaction (a) takes place. 

When the two-step process is repeated on the same material, the thermal treatment following the chemical dealumina t ion results in further expulsion of aluminum from the framework into zeolite cages or channels. The solubilization of non-framework aluminum during the first chemical treatment appears to facilitate further framework dealumination during the subsequent thermal treatment due to the altered steric and electrostatic parameters in the zeolite channels. The newly formed non-framework aluminum species can be readily solubilized by acid treatment. This cyclic method has allowed the almost total removal of aluminum from mordenite (5). 

An attempt has been made by Tsouris and Tavlarides[5611 to improve previous models for breakup and coalescence of droplets in turbulent dispersions based on existing frameworks and recent advances. In both the breakup and coalescence models, two-step mecha-nisms were considered. A droplet breakup function was introduced as a product of droplet-eddy collision frequency and breakup efficiency that reflect the energetics of turbulent liquid-liquid dispersions. Similarly, a coalescencefunction was defined as a product of droplet-droplet collision frequency and coalescence efficiency. The existing coalescence efficiency model was modified to account for the effects of film drainage on droplets with partially mobile interfaces. A probability density function for secondary droplets was also proposed on the basis of the energy requirements for the formation of secondary droplets. These models eliminated several inconsistencies in previous studies, and are applicable to dense dispersions. 

The general criteria for the use of food additives in the EU are described in Annex II of the Framework Directive 89/107/EEC. The authorization of a new food additive in the EU involves a two-step procedure a safety evaluation is completed by the European Food Safety Authority (EFSA) and the food additive is included in the appropriate Directive by the Commission and the Commission adopts a specification of the purity criteria for the food additive. 

During the calcination at 773 K, the sol particles were converted into oxide particles within the interlayer region and rigid pillared layered framework formed in the sol-PILM sample. A two-step procedure is proposed to modify the micropore openings of the solid to enhance the ability of recognizing different molecules. 

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