Crystal packings, inclusion complexes

On the other hand, the crystallization process of diolefin compounds often plays a significant role in determining their topochemical behaviour, by changing their crystal structure or by forming solvent inclusion complexes. Furthermore, topochemical photoreactions of crystals with )8-type packing are accompanied by thermal processes under moderate control by the reacting crystal lattice (see p. 140). These factors seriously complicate the whole reaction scheme. 

Enantioselective photocyclization of 74 occurred efficiently in the inclusion complex with 2a. In particular, the selectivity is very high in the case of 74a. However, control is inefficient in the 1 2 complex 85 composed of 2a and 74c. The host guest ratio probably depends on the packing of the components in the crystal. The packing is... 

Fig. 27 The crystal structure of )0-CD-PEG inclusion complex. The crystal packing structure is head-to-head...

It was found meanwhile that nearly every slim unbranched polymer chain, such as poly(trimethylene oxide) [224], poly(l,3-dioxolane) [225], poly(tetramethylene oxide) [226], polyethylene imine) [227], poly(3-hydroxy propionate), poly (4-hydroxybutyrate) and poly(6-hydroxyhexanoate) [228,229], poly(butylene succinate) [229], polyadipates [230], nylon-6 [231], and even oligomers of polyethylene [232], form a-CD ICs with channel structures. In all of these cases, inclusion is a heterogeneous process, since the guest polymer and its CD complex are almost insoluble in water. Therefore, extensive sonication had to be applied to accelerate the diffusion process. The polymer was also dissolved in an organic solvent, e.g., nylon-6 in formic acid, and this solution was added to the solution of a-CD [231], Alternatively, a monomer, such as 11-aminoundecanoic acid, was included in a-CD and polymerized to nylon-11 by solid state polycondensation within the channels of the IC. Thus, the IC of nylon-11 was formed under conservation of the crystal packing [233-235],... 

In the pharmaceutical industry, SSNMR is commonly used to study polymorphism, hydrogen bonding, crystal packing, and solid-solid interactions. Shelf life or activity decay is often determined by the bioavailability of different polymorphs. Fig. 12 shows very different CP/MAS spectra from two polymorphs of an analgesic, flufenamic acid. It is also used for the study of inclusion complexes, drug-excipient interactions, or the effect of moisture on drug substances or formulations. 

A racemic inclusion crystal is also obtained when the guest molecule is other than chloroform. 1 forms a similar 1 1 molecular cavity inclusion complex with methylene chloride, but in a different space group C2/c (Table III). In marked contrast to the type I crystal, the heterocyclophane in the CH Clo complex takes both "R"- and "S"-confor-mations (Type II, racemic inclusion crystal). A schematic picture of the host-guest packing in the methylene chloride complex is shown in Fig 2. 

CRYSTAL PACKING PATTERNS OF CYCLODEXTRIN INCLUSION COMPLEXES ... 

The packing of each molecule in the crystal is shown in Fig. 3. The 3-CyD dimers are packed in the manner of the brickwork pattern which is one of the cage type packing structures and has been frequently seen in the 3-CyD inclusion complex structure of the triclinic space group PI. 

Cyclodextrins are well known [1] to form a number of crystalline adducts or inclusion complexes with a variety of substances. In the crystalline lattice, cyclodextrins form two types of packing One is a cage type where the cavity of one cyclodextrin molecule is closed on both sides by ad jacent molecules. The other is a channel-type, in which the cyclodextrin rings are packed on top of each other to produce cylinders with infinite centralcavity. Formation of one or the other type crystal structure depends on the size and molecular character of the guest molecule. 

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