Crystal structure of octakis(2,3,6-tri-O-methyl)-#gamma#-cyclodextrincentre dot4.5 H_2O:evidence for conformational flexibility of permethylated cyclodextrins

摘要

Octakis(2,3,6-tri-O-methyl)-#gamma#-CD(TRIMEG)cocrystallized at 18degC with 4.5 water molecules in the orthorhombic space group P2_12_12_1,unit cell dimensions #alpha#unit cell dimensions #alpha#=10.7879(3),b=29.0580(9),c=32.2909(11)A.The TRIMEG macrocycle is in a 'round'form with all glucose units oriented syn,and one O-6-CH_3 methoxy group points "toward"the molecular cavity.The TRIMEGcentre dot4.5 H_2O molecules are stacked to form infinite cylinders with the central cavities aligned into channels filled for each TRIMEG by 4.5 water molecules distributed over 15 partially occupied sites. This structure differs from the two known structures of TRIMEG in which two diametrically opposed glucoses are oriented anti to yield an 'elliptical'form,and their O-6CH_3 groups are directed 'toward'the cavity and close it at this side to form a bowl-shaped molecule.