Subtle discrimination

The stereochemistry of siderophores is a very important aspect of their role in mediated iron uptake, since it has been shown that very subtle discrimination by microbial iron transport systems takes place between siderophore isomers. In fact, uptake of siderophores by microorganisms shows - at least in part - stereospecific preferences (Section 5.2). 

N-Stearoyltyrosine. The case of N-stearoylserine methyl ester illustrates temperature-dependent enantiomeric discrimination in both monolayers spread from solution and in equilibrium with the bulk phase. Although the IIIA isotherms suggested large differences in the intermolecular associations in homochiral and heterochiral films of SSME, there exist chiral systems in which enantiomeric discrimination as exhibited in film compression properties is much more subtle. N-Stearoyltyrosine (STy) is such a system. 

As can be seen, all the compounds have a strong solubility interaction. Nonetheless Figure 6 shows that they are also well separated, so the more subtle difference between the other four interaction terms are important for their discrimination, ft is worth noting that pentane interacts only via solubility, benzene has a very small hydrogen bonding term, while hydrogen bonding is present in methanol and acetic acid. 

Thus, when one looks sufficiently critically at the ideas currently under discussion one finds that there appears to be no good reason for discarding the conventional tert.-oxonium ion as the propagating species, and that the only clearly identifiable problem is whether propagation through these conventional tert.-oxonium ions goes by the Jaacks mechanism or by the ring-expansion mechanism. This is a difficult matter to resolve experimentally because the direct discrimination between the microcyclic ions (II), (VIII), and (IX) on the one hand and the macrocyclic ion (V) on the other, requires subtle and sensitive techniques. 

Is it so Does a rose consist only of molecules and their interactions We can answer yes, but it is also fair to say that this would represent only a first, gross approximation. First of all, notice that the term consists of does not necessarily imply that life can be explained and understood in terms of molecules and their interactions. Here comes the age-old question of the discrimination between structure and properties, and whereas the structure per se can be seen as consisting of small parts, usually properties and behavior are not - or at least additional qualitative concepts are needed. In turn, this does not necessarily mean that life holds something intrinsically unexplainable or beyond the reach of science. This is an important and subtle point, and I hope to be able to offer some clarifying ideas about that in the chapter dealing with autopoiesis and cognition. 

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