Antibiotic ligands

Fig. 16. The antibiotic ligands (a) monensin, which binds Na+ selectively, and (b) valinomycin and (c) enniatin-B, which bind K+ selectively.

More attention will be given to the AC s than to the AEC s. Furthermore, the discussion will bear principally on synthetic ligands. The very interesting natural antibiotic ligands have been discussed in other chapters (see pp. 86—96) their properties will be used here merely for illustration and comparison purposes since they are more difficult to analyze in terms of strategies because of their complicated structural features. 

Table 10. Stability constants (log Kt) of alkali and alkaline-earth metal cation complexes with some selected natural antibiotic ligands (K, in Imol i)...

The X-ray crystal structures of many of these complexes have now been determined representative examples are. shown in Fig. 4.11 from which it is clear that, at least for the larger cations, coordinative saturation and bond rhrectionality are far less significant factors than in many transition element complexes. Further interest in these ligands stems from their use in biochemical modelling since they sometimes mimic the behaviour of naturally occurring, neutral, macrocydic antibiotics such as valinomycin, monactin, nonactin, nigericin... 

Binding of bidentate sulfur ligands can also be of importance in the inhibition of zinc containing enzymes. An aminopeptidase which is essential for vancomycin antibiotic resistance in... 

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