Process synthesis phase change

In this Fourier synthesis, the amplitudes IF" I are obtained from the native intensities of the new protein, and the phases a model are those of the phasing model. During the iterative process of phase improvement (Chapter 7), the phases should change from those of the model to those of the new protein or complex, revealing the desired structure. In Plate 9, we not only knew that our phasing model was similar to the unknown, but we had the added advantage of knowing that its orientation was the same. Otherwise, its phases would not have revealed the unknown structure. 

TRANSLATIONAL CONTROL Eukaryotic cells can respond to various stimuli (e.g., heat shock, viral infections, and cell cycle phase changes) by selectively altering protein synthesis. The covalent modification of several translation factors (nonribosomal proteins that assist in the translation process) has been observed to alter the overall protein synthesis rate and/or enhance the translation of specific mRNAs. For example, the phosphorylation of the protein eIF-2 affects the rate of hemoglobin synthesis in rabbit reticulocytes (immature red blood cells). 

If, after the polymer has been formed, a transformation of one structure into another is possible (e.g., formation of an amorphous polymer with its subsequent crystallization), the kinetic characteristics of these transformations will, in their turn, exert the determining effect on the final structure of the polymer. Specifically, the supramolecular structure of a polymer produced in the course of its synthesis will change, depending on the relationship between the rates of three processes (1) chemical reaction of polymer formation, (2) isolation of polymer in a separate phase, (3) structural transformations inside the polymer phase. In the latter two processes, a significant role is played by the ratio between the rates of the formation and growth of the nuclei of one phase inside the other. This is the kinetic aspect of the problem of controlling the polymer structures during synthesis. 

Often there are significant differences in the phases that exit from one process operation and enter another. For example, hot effluent gases from a reactor are condensed, or partially condensed, often before entering a separation operation, such as a vapor-liquid separator (e.g., a flash vessel or a distillation tower). In process synthesis, it is common to position a phase-change operation, using temperature- and/or pressure-reduction operations, such as heat exchangers and valves. 

Other Industrial Applications. High pressures are used industrially for many other specialized appHcations. Apart from mechanical uses in which hydrauhc pressure is used to supply power or to generate Hquid jets for mining minerals or cutting metal sheets and fabrics, most of these other operations are batch processes. Eor example, metallurgical appHcations include isostatic compaction, hot isostatic compaction (HIP), and the hydrostatic extmsion of metals. Other appHcations such as the hydrothermal synthesis of quartz (see Silica, synthetic quartz crystals), or the synthesis of industrial diamonds involve changing the phase of a substance under pressure. In the case of the synthesis of diamonds, conditions of 6 GPa (870,000 psi) and 1500°C are used (see Carbon, diamond, synthetic). 

Finally, it is appropriate to close this chapter with an example from the roots of fine chemicals the dyestuff, indigo. Manufacture of indigo involves chemistry (see Fig. 2.15) which has hardly changed from the time of the first commercial synthesis more than a hundred years ago (see earlier). Mitsui Toatsu has developed a two-step process in which indole is produced by vapour-phase reaction of ethylene glycol with aniline over a supported silver catalyst (Inoue et al., 1994). Subsequent liquid-phase oxidation of the indole, with an alkyl hydroperoxide in the presence of a soluble molybdenum catalyst, affords indigo. 

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