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Phases play an important role in the modeling of combinatorial chemistry experiments. The
various sets of starting materials are assigned to different phases that are specified as having
the mode INERT (see section 1.3.1.3) as no reactions are allowed for the compounds assigned
to these phases. Basically, these phases are taken as storage devices where single compounds
from each set of compounds can be drawn to react with other compounds in subsequent
phases. The number of phases in a combinatorial chemistry experiment is given by the number
of different sets of starting materials plus the number of reaction steps that have to be
performed.
Thus, the combinatorial synthesis of esters from a set of acid chlorides and of alcohols requires
three phases (Figure 1-10). The set of acid chlorides is assigned to phase 1, and the alcohols
are assigned to phase 2. Then, one after another, one acid chloride is taken from phase 1, an
alcohol is taken from phase 2, and both compounds are allowed to react to an ester (and HCl)
and are then stored in phase 3.
Figure 1-10. The combinatorial synthesis of esters from acid chlorides and alcohols.
The synthesis of tripeptides from activated amino acids (such as esters) and amino acids
accordingly has to be handled by four phases (Figure 1-11). The first phase stores the activated
amino acids, the second the amino acids. The third phase is used to take dipeptides, and phase
4 to store the tripeptides which result from the reaction of the dipeptides again with activated
amino acids.
Figure 1-11. The combinatorial synthesis of tripeptides.
1.3.1.3 Modes
The starting materials of a reaction can be combined in a variety of ways that are strongly
influenced by the concentration of the species involved. The concentrations govern the kinetic
mode, whether monomolecular or bimolecular reactions can occur. Various settings for the
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