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Nature and Size of Included Guest Molecule Determines Architecture of Crystalline Cyclodextrin Host Matrix
Author(s) -
Saenger Wolfram
Publication year - 1985
Publication title -
israel journal of chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.908
H-Index - 54
eISSN - 1869-5868
pISSN - 0021-2148
DOI - 10.1002/ijch.198500008
Subject(s) - chemistry , crystallography , tetragonal crystal system , molecule , zigzag , ionic bonding , matrix (chemical analysis) , crystal (programming language) , crystal structure , stereochemistry , nanotechnology , ion , geometry , organic chemistry , mathematics , chromatography , computer science , programming language , materials science
Owing to its annular shape, the cyclic hexasaccharide α‐cyclodextrin (α‐CD) can form inclusion complexes in aqueous solution. If these are crystallized, the guest molecules are invariably accommodated in the cavities of the host. Depending on size and molecular or ionic character of the guest, different crystal modifications are formed belonging to the herringbone or brick‐type cage structures or to the channel structures. Small molecular guests lead to herringbone cages, small aromatic guests crystallize in brick‐type cages whereas ionic and long molecular guests are enclosed in infinite channels. Thus, there is a clear dependence of crystal packing on the physical properties of the guest molecule. Polyiodide cocrystallizes with α‐CD in different channel forms with iodine atoms arranged linearly in the channels. The packing of the channels is in tetragonal, hexagonal or sheet‐like arrays, depending on counterions which are located in voids between the channels. If a α‐CD is replaced by the larger β‐CD (channel diameters 5 and 6.2 Å resp.), polyiodide now adopts a zigzag structure — a clear case of an influence of host matrix geometry on guest configuration.