Crystalline state nature

Burdett, J. K. (1979). Application of molecular theories to the structure of the crystalline state. Nature 279, 121-25. 

Tallon, J.L. A hierarchy of catastrophes as a succession of stability limits for the crystalline state. Nature 1989, 342, 658-660. 

A from the surface the density is typically constant and equal to the bulk value. In strong unscreened electric fields several authors [137-140] report a phase transition towards a ferroelectric crystalline state in their simulations. However, it should be kept in mind that these systems, because of the absence of ionic screening, are rather unphysical in nature. 

Adamantane (CAS No 281-23-2) l-tricyclo[3.3.1.1 ]decane is a cage hydrocarbon with a white or almost white crystalline solid nature, like solid wax, at normal conditions. Its odor resembles that of camphor. It is a stable and nonbiodegradable compound that is combustible due to its hydrocarbon nature. It has not been found to be hazardous or toxic to living entities [14, 15]. It should be pointed out that adamantane can exist in gas, liquid, and two solid crystalline states. 

It is important to note that most molecules are not rigid but may prefer a distrinct structure and the conformation of a molecule strongly depends on its specific environment. Hence, the crystal structure of a drug does not have to correspond to the receptor bound conformation. Also, a conformation in solution depends on the nature of the solvent and measuring conditions, and may change when the molecule is bound to the receptor [4]. In addition, different receptors or receptor subtypes can bind the same drug in different conformations. It is a general assumption and observation, but by far not a strict condition, that the conformation in aqueous solution is similar to the bound conformation and is a better representation of the bioactive conformation than an X-ray structure of the isolated molecule in the crystalline state. 

Boryl-borate tautomerism This type of tautomerism is observed for boryloxyalkylphosphines (101), (102) possessing a hydroxyalkyl group and electron-acceptor substituents at the a-carbon atom [Eq. (88)] (851ZV1102 90IZV1133). Mutual transformations take place rapidly and the equivalency of methyne protons in NMR spectra serves as evidence of tautomerism. In the crystalline state these compounds exist in form A. The considerable influence of the nature of the solvent (-4 ppm in DMFA - 10 ppm in C6H6) on the position of the signal in the MP NMR spectrum provides evidence in favor of tautomerism. 

Researchers who have focused more on understanding cause-effect relationships in solution processing have given attention to film drying and pyrolysis behavior, densification processes, and nucleation and growth into the desired crystalline state. Both thermodynamic and kinetic factors associated with the phase transformation from the amorphous state to the crystalline state have been considered.11 119 Control of these factors can lead to improvements in the ability to influence the microstructure. It is noted that in the previous sentence, influence has been carefully chosen, since the ability to manipulate the factors that govern the nature of the phase transformation to the extent that full control of the microstructure is possible remains to be demonstrated. However, trends in characteristics such as film orientation and columnar versus uniaxial grains have certainly already been achieved.120... 

We turn now to a presentation of our own research on the use of built-in or internal chiral auxiliaries for asymmetric induction in photochemical reactions in the crystalline state [28]. This work is a natural outgrowth of the work of Toda and coworkers on the use of external chiral host compounds for the same purpose discussed in Sect. 2.2. In both cases, the primary role of the chiral auxiliary is to guarantee the presence of a chiral space group for the ensuing solid-state photochemical reaction. 

Racemizations in the crystalline state have a long history. It is known that L-a-amino acids slowly racemize in the solid state [62]. As this also happens in solid proteins the implications are manifold, not only in pure chemistry but also in biochemistry, nutrition, food technology, and geology. Therefore, techniques have been developed to determine the dl ratio of amino acids down to 0.1% and inversion rate constants have been determined under acid hydrolysis conditions [63]. One could think of very slow deamination and readdition of the amine or an enolization mechanism. However, such reactions can also be induced by photolysis or radiolysis from natural sources [64]. 

An extracellular RNase of Bacillus subtilis strain H was isolated in crystalline state and its chemical nature studied by Nishimura and coworkers (112). It has a very complicated base specificity (113, 114)-However, with a few exceptions, the phosphodiester bonds of 3 -purine nucleotides are cleaved faster than those of 3 -pyrimidine nucleotides, and those of 3 -nucleotides with 6(4)-keto group are cleaved faster than those of 3 -nucleotides with a 6(4)-amino group. Thus, when adjacent bonds are the same, the following results ... 

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