Excess molecular susceptibility

Johnson et al. reported a systematic investigation of magnetism in the cluster carbonyls of osmium. The experimental quantity of most direct interest was the excess molecular susceptibility (Xems) of the Os cluster compounds, which is the difference between the experimentally determined magnetic susceptibility of the molecular complex (Fig. 8) and the sum of the diamagnetic corrections of those species from which the high-nuclearity cluster is composed. 

Figure 9. Magnetism in osmium cluster carbonyls. The variation of the high-temperature (298 K) excess molecular susceptibility, as a function of cluster nuclearity. Taken from Johnson et...

Electrophilic Aromatic Substitution. The Tt-excessive character of the pyrrole ring makes the indole ring susceptible to electrophilic attack. The reactivity is greater at the 3-position than at the 2-position. This reactivity pattern is suggested both by electron density distributions calculated by molecular orbital methods and by the relative energies of the intermediates for electrophilic substitution, as represented by the protonated stmctures (7a) and (7b). Stmcture (7b) is more favorable than (7a) because it retains the ben2enoid character of the carbocycHc ring (12). 

Some workers avoid delay. Pai)adium-on-carbon was used effectively for the reductive amination of ethyl 2-oxo-4-phenyl butanoate with L-alanyl-L-proline in a synthesis of the antihyperlensive, enalapril maleate. SchifTs base formation and reduction were carried out in a single step as Schiff bases of a-amino acids and esters are known to be susceptible to racemization. To a solution of 4,54 g ethyl 2-oxO 4-phenylbutanoate and 1.86 g L-alanyl-L-proline was added 16 g 4A molecular sieve and 1.0 g 10% Pd-on-C The mixture was hydrogenated for 15 hr at room temperature and 40 psig H2. Excess a-keto ester was required as reduction to the a-hydroxy ester was a serious side reaction. The yield was 77% with a diastereomeric ratio of 62 38 (SSS RSS)((55). 

At the molecular level, the buffering capacity of the cellular solution may block the pollutant in its course. Pollutants that generate acids or bases may be neutralized by acid-base buffers. Excess calcium or other cations may complex fluoride, and redox systems may buffer S02, 03, or PAN, or the free radicals they generate. On another level, enzyme structure determines whether the pollutant will penetrate and react with an active site, and the functioning of an enzyme, apparently through effects on its structure, also modifies its susceptibility to the pollutant (6). Moreover, inhibition of a susceptible enzyme may not affect a pathway the enzyme affected may not be rate-limiting in a particular pathway, and considerably greater inhibition must occur before it is. 

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