Cavity crystallographic studies

Compounds 139 are tris(oximehydrazone) derivatives with an iron(ll) ion in the center of the cavity [230]. Compound 140 (Fig. 38) has been known for 30 years [231, 232] and was prepared from a tris(2-aldoximo-6-pyridyl)phos-phine that is capped by a BF unit to encapsulate cobalt(ll), zinc(ll), nickel(ll), and iron(II). All four macrocyclic complexes were characterized later by a comparative X-ray crystallographic study [233-236]. 

Pedersen s (1967a) original model, in which the cation is captured in the cavity of the crown ether, has been fully substantiated by X-ray crystallographic studies (Truter, 1973 Dailey, 1978). On the basis of this model, the main features of cation binding can be explained surprisingly well. The size of the cavity can be estimated from CPK molecular models (Table 1). The binding of... 

ID-ROESY studies performed on the complex between (+)-BrPh and /3-CD in solution did not allow one to explain the NOE effect observed on the protons of the maleate counteranion (70). X-ray crystallographic studies performed on the monocrystals obtained from a 1 1 aqueous solution of (+)-BrPh maleate and /3-CD (Fig. 8) provide a plausible explanation for the contradiction maintained in Ref. 70. In particular, as shown in Fig. 8, (+)-BrPh forms with /3-CD, at least in the solid state, not a 1 1 complex but a complex with 1 2 stoichiometry. In this complex the (+)-BrPh molecule is sandwiched between two molecules of /3-CD. The 4-bromophenyl moiety of (+)-BrPh enters the cavity of one of the /3-CD molecules, whereas the cavity of another /3-CD molecule is occupied by the maleate counteranion. Thus, X-ray crystallography may provide useful information on the supra-molecular structure of the selector-selectand complexes and in this way complement well ID-ROESY data. However, the aforementioned possible differences between the structure of the complexes in solution and in the solid phase must be considered. 

Inspection of the crystal structure of compound III bound to the active site of HIV PR revealed lipophilic cavities extending off the Sl/ST subsites adjacent to the /-butyl groups of the benzamidine moiety. The cavities are bordered by flexible loops around Pro81/8T and previous crystallographic studies indicated that both loops can move back by up to 2.5 A, extending the size and... 

Tabushi and Kamitori et al. [22] also reported that a substituted group was intermolecularly included in the cavity of another CD (Fig. 4). They carried out the X-ray crystallographic study of two compounds, 6-O-phenylthio-)0-... 

---