Crystal lattice forces

The tendency for pteridines with hydrogen-bonding substituents to have higher melting points is also in agreement with abnormally strong crystal-lattice forces (Table 1). 

But where there is an equilibrium among two or more conformations of the enzyme in solution, crystallization may select out only one of the conformations. a-Chymotrypsin has a substantial fraction of an inactive conformation present under the conditions of crystallization, but only the active form of the enzyme crystallizes. An allosteric effector molecule that changes the conformation of the protein in solution may have no effect on the crystalline protein, as, for example, with phosphorylase b.5A The enzyme is frozen in one conformation, with the crystal lattice forces preventing any conformational change. On the other hand, the addition of an effector to phosphorylase a causes the crystals first to crack and then to anneal, giving crystals of the enzyme in a second conformation. 

Yalkowsky (1981) has developed equations describing water solubility as a function of both hydrophobicity (locP) and crystal lattice forces. Jain and Yalkowsky (2001) have offered a new general solubility equation, where the molar solubility, %) of a nonelectrolyte can be estimated by... 

PURPOSE AND RATIONALE Solubility assays are gaining growing attention in drug discovery, because many pharmaceutically active compounds can be adjusted to in vivo testing merely with co-solvents. Furthermore, in vitro assays may also lead to false results, simply for precipitation of a compound in the assay media. Solubility assays vary in one main point they are either performed from solids or stock solutions. A nomenclature has been established in the literature which tries to distinguish between these methods. Determinations from stock solutions are often called kinetic solubility whereas thermodynamic solubility stands for solubility of solids (Kerns). Thermodynamic solubility takes the crystal lattice forces into account. Batch to batch variations, polymorphism... 

In many of the recently known host-guest situations (see above), however, both coordinative and crystal lattice forces contribute to the formation of the host-guest compound. Thus, borderline cases must be treated as complex/clathrate hybrids (Fig. 14). According to the nature of the binding, we speak of coordinatoclathrates which demonstrate a certain degree of coordinative participation but have a dominant clathrate character and of clathratocomplexes, just the other way round. The inclusion compounds of l,l -binaphthyl-2,2 -dicarboxylic acid (26a) with different OH-, NH- and CH-acidic guest molecules (cf. Sect. 3) can be quoted as typical examples... 

Cyclopropane wonld have the higher melting point because its cyclic structure gives it a rigid compact shape that would permit stronger crystal lattice forces. 

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