Topography of cyclodextrin inclusion complexes. 15. Crystal and molecular structure of the cyclohexaamylose-7.57 water complex, form III. Four- and six-membered circular hydrogen bonds

Topography of cyclodextrin inclusion complexes. XVI. Cyclic system of hydrogen bonds: structure of α-cyclodextrin hexahydrate, form (II): comparison with form (I)

“…the 'empty' a-CD present in aqueous solution has a conformation that differs from the conformation adopted if guest molecules other than water are included. This even holds for a recently discovered, new crystal form of a-CD hydrate, a-CD.7.57H20 (Chacko & Saenger, 1980) which was obtained from 1.2M aqueous BaCl 2. It displays a 'round' a-CD macrocycle with 2.57 H20 molecules included and disordered over four different, not fully occupied sites, representing 'activated water'.…”

“…Such circular hydrogen bonds have been observed previously (five-and six-membered circles, Saenger, 1979) and again recently in yet another crystal form of hydrated a-CD (a-CD. 7.57H20; fourand six-membered circles, Chacko & Saenger, 1980). The circular hydrogen bonds can be homodromic, running in the same direction, antidromic, with counter-running hydrogen bonds and heterodromic, with hydrogen bonds in randomly alternating sense (Fig.…”

Crystallographic studies of carbohydrates

“…Cyclic systems of hydrogen bonds are common in the cyclodextrin hydrates, where they are classified as homodromic, antidromic and heterodromic, of which the homodromic is the more stable (Saenger, 1979;Chacko & Saenger, 1981). This concept is an extension of the sequential, double-donor and doubleacceptor classification for water trimers (Hankins, Moskovitz & Stillinger, 1970).…”

An Unusual Hydrogen-Bonded Network Associated with Metal-Organic Chains: Structure and Crystal Packing of the Coordination Polymer [Cd(terephthalate)(H2O)3].4H2O

“…Their coordination polyhedron is represented by a distorted tetrahedron with angles in the range 86±135 . Angles varying in this range also occur in some polymorphs of ice as well as in water enclathrated in -cyclodextrin (Chacko & Saenger, 1981). In all cases the OÐHÁ Á ÁO hydrogen-bond distances vary in the range 2.71±2.84 A Ê , i.e.…”