Crystalline structures choleic acids

Insight into the photochemical reactions between deoxycholic or apocholic acid ( choleic acids ) and guest molecules in crystalline inclusion complexes has been obtained by X-rzy studies. The choleic acids form channels with wall structures determined by the nature of the guest molecule. Guest ketones of various types react photochemically by addition to the choleic acid at a site determined by the orientation of the ketone molecule in relation to the host (e.g. deoxycholic acid reacts at C-5 or C-6 with linear aliphatic ketones, but at C-16 with cyclohexanone).12... 

This hitherto neglected area is now receiving major attention and the crystalline structures of many common and uncommon bile acids [43,44,48,49], their alkaline and alkaline metal salts [7,51,53] have been defined. Choleic acids have been the subject of much activity in this field. A summary of the earlier work on choleic acids can be found in Sobotka [42] and Small [5]. 

The crystalline structure of cholanic acids and their alkaline metal salts has unfortunately been neglected. The major crystallographic work was carried oUt by Kratky, Giacomello, and co-workers (76-79) 30 years ago and was oriented toward solving the structure of the choleic acids. These substances, isolated by Wieland and Sorge (80), are mixed crystals of deoxy-cholic acids (or certain other bile acids such as a and apocholic acids) obtained on crystallization from organic solvents. A summary of the work on choleic acid appears in Sobotka (28). 

The structure of the space unit cell of deoxycholic acid (Fig. lOA) crystallized from acetone (79) has the following dimensions a = 25.8 A, b = 13.5 A, and c = 7.2 A. Since the lattice parameters did not change appreciably with various choleic acids of long-chain aliphatic substances such as alcohols, fatty acids, and esters (Fig. lOB), it was deduced that there were holes in the crystalline lattice of deoxycholic acids that could accommodate aliphatic compounds. The so-called coordination numbers or molecular ratios of the deoxycholic acid and its guest molecule are related to the number of carbons in the aliphatic chain of the guest compounds and therefore the chain length of the molecule. 

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