Selective behavior

Collectors Fitting into Fattice Cavities. Lattice site fitting of collectors at sohd walls has been invoked as a means of explaining the selective behavior of amines (cationic coUectors) as reagents in the flotation-separation of soluble salt minerals such as KCl and NaCl (22). 

Traditional Safety Engineering approach (control of error by motivational, behavioral, and attitude change) Occupational safety Manual operations Selection Behavior change via motivational campaigns Rewards/punishment Very common... 

A peculiar shape-selective behavior has been observed in a Cu-based MOF containing one-dimensional tunnels with narrow necks at regular distances of... 

A (Figure 4.9). The diameter of such a neck, 2.3 A, is sufficiently large for a linear C-C chain to pass, but too small to also be an equilibrium adsorption position. The largest compound allowed inside the pores is a linear molecule limited in length to four carbon atoms due to the distance between two subsequent necks [103]. Another example of shape-selective behavior is found in a Zn-based MOF able to encapsulate linear hexane while branched hexanes are blocked [104]. 

Guest Selectivity Behavior, Separation of Solvent Mixtures. 58... 

Independent Parallel Reactions of Different Species on the Same Catalyst. One often requires a catalyst that promotes the reactions of one component of a feedstock but does not promote the reactions of other constituents of the mixture. For example, one might desire to dehydrogenate six-membered rings, but not five-membered rings. This type of selectivity behavior may be represented by mechanistic equations of the form... 

Platinum clusters, n = 2-11 react with di oxygen at a rate that is within an order of magnitude of gas kinetic. There is no distinct size selective behavior. Products of these gas phase reactions observed with 7.87 eV ionization laser, are PtpO where for m=l,... 

Lewis Bases. A variety of other ligands have been studied, but with only a few of the transition metals. There is still a lot of room for scoping work in this direction. Other reactant systems reported are ammoni a(2e), methanol (3h), and hydrogen sulfide(3b) with iron, and benzene with tungsten (Tf) and plati num(3a). In a qualitative sense all of these reactions appear to occur at, or near gas kinetic rates without distinct size selectivity. The ammonia chemisorbs on each collision with no size selective behavior. These complexes have lower ionization potential indicative of the donor type ligands. Saturation studies have indicated a variety of absorption sites on a single size cluster(51). 

In summary, reactions with ligands that requi re a bond to be broken before chemisorption is completed show size selective behavior. This applies to hydrogen and nitrogen and likely... 

Table IV shows the striking difference in selectivity behavior between Pt and Pt-MoO catalysts for NO-H2 and NO-H2 and NO-H2-CO reactions. For the NO-H2-CO reaction at 600°C,only 12% of the reacted NO is...

Perhaps the most successful application of Fukui function and local softness is in the elucidation of the region-selective behavior of different types of pericyclic reactions including the 1,3-dipolar cycloadditions (13DC), Diels-Alder reactions, etc. These reactions can be represented as shown in Scheme 12.4. Considering the concerted approach of the two reactants A and B, there are two possible modes of addition as shown in Pathway-I and Pathway-II. 

Inspection of Eq. (13.6) shows that the selectivity behavior of a liquid membrane is specified completely by the membrane selectivity constant, Ky, which in turn is dependent on the equilibrium constant of Eq. (13.5) and on the mobility of ions i and j within the membrane. For the case in which the membrane consists of a neutral carrier [129], the exchange reaction can be presented as ... 

An inspection of Eqs. (2) and (3) shows the selectivity behavior of liquid membranes to be fully specified by Kyot. 

EMF-measurements are, therefore, a method for directly assessing the relative stability of the complexes of the valinomycin group antibiotics in water and water-like solvents (cf. Fig. 11 and Ref. (87)). The selectivity constants of the liquid membranes are in this case independent of the ion-selective behavior of the membrane solvents used. 

It is easy to treat the selectivity behavior of liquid membranes in the presence of the two divalent ions I2+ and J2+ using the assumptions described above in analogy to Eq. (21), the following relation is obtained ... 

In order to investigate the molecular basis of the ion selective behavior of electrically neutral ligands, we made use of model calculations which are summarized in the following. 

The ion selective behavior of a carrier molecule embedded in a given medium, say, a membrane, may be described in terms of the changes in free energy associated with the transfer of a cation from an aqueous solution into the cavity enclosed by the multidentate ligand ... 

These considerations go far to explain the selectivity behavior of a series of macroheterobicyclic ligands (Fig. 9). Table 4 shows that an increase in the number of coordination sites from 6 to 8 or 9 leads to an increased preference for large cations. Ligand VI, with 11 coordination sites is no longer suited for the complexation of even the largest alkali and alkaline earth metal cations. Furthermore, it is clear that a relatively large coordination number (5 6) is required to produce selectivity for divalent ions. 

The discrepancies have to be attributed to differences in AGd, i.e. deformation energy to adjust the size of the preformed cavities to the cationic radii. It seems reasonable to assume a smaller cavity for monensin, because of its shorter skeleton and somewhat higher flexibility (fewer rings) as compared to nigericin. Thus, the differences in selectivity behavior of nigericin and monensin can qualitatively be accounted for. 

The usefulness of this ligand in the construction of Ca2+-sensors has been confirmed. The selectivity behavior of a liquid membrane, which consists of a filter paper impregnated with a 20% solution of the ligand in p-nitroethylbenzene (117), was determined by means of EMF-measure-ments conducted on the cell ... 

Although there is no direct connection between the rules discussed in Chap. 4 for the monovalent-divalent ion selectivity of ligands in liquid membranes and the electrochemical selectivity behavior of these membranes (cf. Eqs. (22) and (31)), the effect of solvent on Na+/Ca2+ selectivity (Fig. 22) is remarkably similar to the calculated effect shown in Fig. 18 (actually for K+/Ba2+ preference). The discrimination against Mg2+ and especially HaO+ is considerably better for the electrode discussed here 117) than for liquid ion-exchange membranes responsive to Ca2+ (123). 

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