Organic inclusion crystals

Dynamics in Organic Inclusion Crystals of Steroids and Primary Ammonium Salts 505... 

Organic inclusion crystals are attractive substances from the viewpoint of the dynamics of molecular assemblies. The inclusion crystals comprise nanocomposites between host and guest molecules and exhibit supramolecular properties through non-covalent bonds [1], The host molecules provide molecular-level cavities where the guest molecules undergo intercalations and reactions. We have elucidated such dynamics by using the inclusion crystals of steroids and primary ammonium salts (Figure 26.1). 

Figure 26.1 Dynamical properties related to organic inclusion crystals of steroids and primary ammonium salts.

Solvent-drop grinding was next applied as an eco-friendly modification to a previously described preparation of a crystalline organic inclusion compound. Initial work had demonstrated solution-mediated supramolecular organisation and solid-state topochemically controlled reactivity in a system involving l,2-bis(4-pyridyl)ethylene (bpe) 32 and 1,2,4,5-benzenetetracar-boxylic acid (bta) 33 [57]. A single crystal of a 2 1 bpe bta 32 33 cocrystal was... 

Scheme 3 illustrates intriguing enantioselection in organic reactions that proceed in chiral crystalline lattices (5). When inclusion crystals of a ketone and an optically active diol host are treated with BH3-ethyl-enediamine complex, the optically active alcohol is obtained in... 

We have researched the inclusion abilities of bile acid derivatives by using more than one hundred organic compounds as guest candidates. The inclusion phenomena vary from one case to another, indicating that subtle changes in molecular structures induce alteration in their molecular assemblies. In fact, X-ray diffraction studies prove that the steroidal hosts form various assemblies such as monolayers, bilayers, helical tubes, and so on, as shown in Figure 2. Therefore, systematic investigation of inclusion crystals of bile acid derivatives is expected to reveal a relationship between their molecular structures, assemblies and inclusion behavior. 

Figure 11 Packing coefficients in various states organic crystals, protein cores, inclusion crystals, encapsulated hosts and the liquid state.

When chemical reactions are carried out in inclusion complexes, reactions can proceed selectively due to template control effects caused by the host compound. In some cases, reaction occurs only in the inclusion complex, but not in solution, since molecules can be arranged in the appropriate positions for reaction in an inclusion crystal. When an optically active host compound is used, enantiose-lective reactions can be accomplished. For some time we have been studying such selective reactions in inclusion complex crystals in the solid state. However, these reactions have already been published in the book Organic Solid State Reactions [1], In this present chapter, some representative topics and some recent new results of selective thermochemical and photochemical reactions in inclusion crystals are briefly summarized. 

When a mixture of acetophenone 59a (1.0 g, 8.3 mmol), NaBH4 (0.94 g, 24.9 mmol), and water (10 ml) was stirred at room temperature for 2 h, rat-60a was produced. To the water suspension medium of rac-60a was added powdered 8a (3.87 g, 8.3 mmol), and the mixture was stirred for 3 h to give a 2 1 inclusion complex of 8a with (-)-60a.25 Inclusion complex formed was filtered and dried. Heating of the complex in vacuo gave (-)-60a of 95% ee (0.42 g, 85%). From the filtrate left after separation of the inclusion crystals, (+)-60a of 77% ee (0.35 g, 70%) was obtained by extraction with ether. By the same procedure, optically active 60a and 60c-g were prepared (Table 5). Solid state and solvent-free organic reactions have been well established25,263 0. Host-guest inclusion complexation in the solid state has also been reported.260... 

Nakano, K., Sada, K. and Miyata, M. (1996). Novel additive effect of inclusion crystals on polymorphs of cholic acid crystals having different hydrogen-bonded networks with the same organic guest. Chem. Commun., 989-90. [58]... 

Z. Urbanczyk-Lipkowska, F. Toda, Selective Reactions in Inclusion Crystals, in Organic Supramolecular Chemistry, F. Toda, R. Bishop (Eds.), John Wiley Sons, New York 2004, pp. 173-184 F. Toda, Top. Curr. Chem. 2005, 254, 1. 

When the intermolecular forces are relatively strong and directional, crystalline molecular compounds (crystalline molecular complexes) are formed. They have fixed stoichiometries and ordered structures. These two-component molecular crystals are also called cocrystals or maybe adduct crystals. Hydrogen-bonded cocrystals, donor-acceptor crystals (charge transfer crystals), and inclusion crystals (host-guest crystals) are examples of crystalline molecular complexes. Crystalline organic salt is a special case of hydrogen-bonded cocrystal or donor-acceptor crystal, i.e., proton (or electron) transfer from the acid (or donor) to base (or acceptor) occurred. 

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