Inclusion geometry

Another example of a cyclodextrin-based artificial enzyme is shown in Fig. 2.15. A phosphodiester is hydrolyzed through cooperative interactions with two imidazolyl groups. The relative positions of the imidazolyl groups and the inclusion geometry of the hydrophobic substrate are structurally well-matched. This artificial enzyme can be regarded as a model of ribonucle-ase A. 

Figure 17. Proposed inclusion geometries for a-alkyldibenzyl ketones in the / -CD cavity.

The effects of complexation and stabilization of 2, 3 -dideoxy-adenosine (I) with 2-hydroxypropyl-beta-cyclodextrin (II) were studied, and the results of kinetic studies and pKa determinations are reported. Although hydrolysis is 100% suppressed in both the protonated and neutral complexes, due to the small binding constants, the maximum stabilization attainable in a 0.1 M solution of II at 25 °C was approximately 5-fold at pH 5 and 2-fold at pH 2. Possible inclusion geometries are considered in an attempt to account for the kinetic data. 

The different shifts observed for the (/ )- and (5)-guests are especially remarkable. They can be interpreted to be due to diastereomeric host/guest complexes with different stabilities and inclusion geometries. 

Some authors have proposed a generalized HBG equation that includes all possible types of inclusion geometry [20] ... 

The micro-electromechanical methodology stemming from the category of the Theory of Elasticity to be presented in this section is capable of modeling inclusions of ellipsoidal geometry. Such a description of the inclusion geometry allows us to consider fibrous and lamellar inclusions by means of one or two semiaxes approaching infinity, respectively. 

Figure 6. Preferred inclusion geometry of lithocholic acid in D2O/CD3OD (1 1, v/v).

---