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). 

MF < MC1 < MBr < MI . By contrast for less-ionic halides with significant non-coulombic lattice forces (e.g. Ag) solubility in water follows the reverse sequence MI < MBr < MC1 < MF . For molecular halides solubility is determined principally by weak intermolecular van der Waals and dipolar forces, and dissolution is commonly favoured by less-polar solvents such as benzene, CCI4 or CS2. 

The strong electrostatic lattice forces in ionic compounds give them high melting points. 

Crystal surfaces. Crystal surfaces may be viewed as vast defects inasmuch as the lattice forces are incompletely balanced. The effects of this imbalance are partially offset by distortion of the crystal lattice near the surface, but crystal surfaces still show a strong tendency to adsorb other... 

Several structures of Co(R2Dtc)3 complexes have been reported. The structure of the Co(MorphoDtc)3 complex has been determined both as a CH2C12 (302) and as dibenzene (96b) solvate. The similarity of the CoS6 cores in the two structures suggests that the differences in lattice forces arising from different solvents in the lattice are not significant. 

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... 

The success of altering solubility by manipulating the solid phase of the drug depends on which factor dominates the aqueous solubility behavior, the hydrophobicitiPjjlafg the lattice forces. 

Existence of stripes looks just natural in terms of a static phase separation. At doping the system (LSCO) must screen the excess charge (Sr2+-ions) in AF regions. Therefore stripes of the AF ordered phase must alternate with "metallic domain walls. The stripe arrangement by itself is nothing but an optimization of the competing Coulomb and lattice forces [7]. (The phenomena is well known in physics of surface.)... 

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... 

The above drawbacks of crystalline photoreactions are circumvented in an approach called the ionic auxiliary approach which is outlined below [185-207]. Scheffer and coworkers make a salt of a substrate having a carboxylic acid with a chiral organic amine or vice versa. The chirality of the amine would necessitate that the salt crystallize in a chiral space group. The crystal formed in this fashion would also be able to withstand higher conversions due to stronger lattice forces in these crystals. An example of this type of approach is shown in Scheme 8. Treatment of the dibenzobarralene derivative 18, with the tert-butyl ester of (S)-proline 19, afforded salt 20 irradiation of the crystals of this salt gave diester 21. In this reaction, only one regioisomer 21 is formed, and this product is formed in over 95% ee. More examples are to be found in Chap. 12. 

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