Solvent effects, incorporation into crystal

In general, the greater the similarity in size and shape between the solute and liquid-crystalline solvent molecules, the easier it is for the solute to incorporate itself into the liquid-crystalline phase. If the result of a chemical reaction depends on the solvent order, then the largest effects can be expected for those solute molecules which fit best into the liquid-crystal structure. Since the structure of -heptadecyl phenyl ketone is identical to -butyl stearate except for the terminal phenyl and butoxy groups, it exhibits the largest solvent effect of the ketones studied [730]. 

Figure 8.6 Effect of solvent composition on MALDI sample preparation, (a) Polymer incorporation into matrix crystals (b) polymer precipitation.

A few years ago, a largely empirical approach was used to quantify the effect of admixtures and solvents. A theoretical description of the effect of admixtures has been developed only rather recently. Nevertheless, a consistent theory of the effect of admixtures on individual aspects of the process of crystallization is still missing. Various admixtures probably operate with different mechanisms. Some of them are selectively adsorbed on ciystal faces and deactivate individual growth centers, others can change the structural properties of the solution or of the interface they may be incorporated into the crystal lattice or pushed away by the growing crystal and sometimes there exists a chemical Interaction between the micro- and macrocomponents. It is obvious that this situation enables us to give subsequent explanations of individual effects but the prediction Is... 

In 1965, Walter C. McCrone introduced the term pseudo-polymorphism [ 18]. By his definition, pseudo-polymorphic effects included desolvation/dehydration products, second-order transitions and dynamic isomerism however, today the term is generally limited to all phenomena connected with solvates and hydrates. Any substance used in the pharmaceutical industry has the ability to form so-called crystalline hydrates or solvates. In these structures, volatiles (either water or solvent) are not only physisorbed at the solid-air interface but also incorporated into the crystal lattice structure (chemisorbed) as a guest molecule, either in stoichiometric or in non-stoichiometric amounts. Careful consideration must be... 

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