Cluster disintegration

The cluster disappeared from the spectra after reduction in H2 at 200 °C, while the elemental Cl signal still had substantial intensity, indicating that the rhodium chlorine cluster disintegrated but that chlorine was still present on the support. The work is described in the case study on rhodium catalysts in Chapter 9. 

In the hypothesis, Points 5 and 8 above (alternative structures) have come under criticism, first by Skovborg et al. (1992) and then by Natarajan et al. (1994). However, Skovborg noted that alternating structures may account for some of his nucleation data. A further criticism of the labile cluster hypothesis is that the energy barrier for agglomeration of clusters is far larger than cluster disintegration (Radhakrishnan and Trout, 2002). 

Fe/S clusters in regulatory enzymes have been proposed to act as sensors in such a manner that, upon detection of a measurand, the cluster disintegrates and activity stops. Putative examples are NO sensing by the [2Fe-2S] cluster in the terminal enzyme of heme synthesis, ferrochelatase [8], and 02 sensing by the [4Fe-4S] cluster in the regulatory enzyme of purine nucleotide biosynthesis, glutamine 5-phosphoribosyl-l-pyrophosphate amidotransferase [9], This is of course not a catalytic activity, since the cluster is destroyed in the action. 

Glass beads can be used as an illustration of hydrophobia interactions. Thus, glass beads covered with dichloro-dimethylsilane can be regarded as solid hydrocarbon particles. Only hydrophobic interactions are possible. In a structured solvent such as water or formamide, the beads cluster together. When the polarity of the solvent is decreased by addition of alcohols the clusters disintegrate [79]. 

A plot of the product ratio (4+5) 6 as a function of pressure is presented in Figure 4.4-5. This plot exhibits a dramatic spike at pressures near the critical pressure which the authors attribute to the onset of solute-solvent clustering disintegration of the caged pair is inhibited because the viscosity at the molecular level is much greater than the bulk viscosity. 

Seo HC, Edvardsen RB, Maeland A D, Bjordal M, Jensen MF, Hansen A, Flaat M, Weissenbach J, Lehrach H, Wincker P, (2004). Hox cluster disintegration with persistent anteroposterior order of expression in Odcopleura dioica. Nature 431 67 -71. 

As the temperature increases from ambient to the critical point, the electrolytic conductance of water rises sharply and is almost independent of the pressure. Macroscopically, this is due to the decrease in water viscosity over this range. The primary cause for the fall in viscosity is a disintegration of water clusters. 

The FD region at the top is characterized by the dominance of the fluid over the movement of particles, as already shown in Fig. 11. When the fluid-dominated FD regime is first formed, the clusters of fast fluidization are disintegrated to form an essentially one-phase structure in which the particles are, however, not completely discretely suspended, that is, at a much higher concentration as compared to the ef computed for the broth before Upt. This is shown by the fluctuating voidage considerably above zero, as can be seen in the upper right-hand side of Fig. 11. 

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