The enclathration of alcohols by cholic acid

Master Thesis


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University of Cape Town

A series of crystalline Cholic acid inclusion compounds were studied with a view to understanding the role of guest molecules in inducing and stabilizing a particular Cholic acid (host) lattice structure. Alcohols in the series CH₃(CH₂nOH (n= 0 to 3 and 2-propanol) were employed as guest molecules and enclathrated in the host lattice of Cholic acid during crystallization. Single crystal structure analyses were performed by X-ray diffraction. Two types of molecular packing were identified. Cholic acid inclusion compounds with methanol, ethanol and 1-propanol are characterized by a 3-D host and guest molecule network stabilized by hydrogen bonds with symmetry of P2₁2₁2₁ space group. The guest molecules 2- propanol and 1-butanol, by nature of their size, induce a molecular packing with a larger guest cavity than that in the P2₁2₁2₁ space structures. Symmetrically defined by the P6₅22 space group, the crystal lattice is characterized by a helix of Cholic acid molecules generated by the six-fold screw axis through the origin and parallel to the c axis. The lattice is stabilized by an intricate hydrogen bonding scheme. The conformation of Cholic acid (particularly that of the flexible side-chain) in the two types of molecular packing was studied. The size and shape of the guest cavities created by the host lattices were examined. Thermal analyses (Thermogravimetric analysis and Differential Scanning Calorimetry) were performed on these compounds to examine the guest content and the strength of host-guest interactions. ₁₂₃₅

Bibliography: pages 220-231.