Probing the Relationship between Crystallization and Gelation by Using Ammonium Salts of Bile Acids

Abstract

Hydrogels formed from aqueous solutions of bile acids and their salts are biocompatible materials that promise to be useful in drug delivery, cellular immobilization, and other applications. These materials are considered to result from self-association of the components to give networks of fibrils; however, the molecular structure of the fibrils has not yet been established with certainty. Previous work has shown that ammonium salts of lithocholic acid can form both crystals and hydrogels under the same conditions. Structural analyses of these salts by single-crystal X-ray diffraction revealed that lithocholate anions are invariably arranged in similar ways, leading to the suggestion that the fibrils causing hydrogelation have closely related structures. This hypothesis has now been strengthened by additional studies of the behavior of ammonium salts of lithocholic acid and other bile acids. In this new work, both crystallization and fibril-induced gelation are again observed, and the crystals tend to have fibril-like acicular morphologies that reflect rapid growth by edge-to-edge association of bile anions. When the ammonium cations are small, the crystals have closely related structures. The observation that simple ammonium salts of many bile acids consistently favor the same pattern of molecular organization in crystalline solids reinforces the hypothesis that the fibrils responsible for hydrogelation have analogous internal structures.

Polymorphism of amantadinium niflumate

“…11 Amantadine is a substance used in the treatment of Parkinson's disease and Parkinson's syndromes, as well as a drug against influenza A virus. 16,17 In the CSD there are some crystal structures of amantadine salts with bioactive components such as: indomethacin in conjunction with L-amino acids, 18 sulfamethoxazole, 19 [1-(dibenzylamino)ethyl] phosphonic acid, 20 fumaric acid, 21 oxalic acid, 4-aminobenzoic acid, glutaric acid, saccharin, 22 gemfibrozil, 23 sulfathiazole, 24 resveratrol, 25 and 3,7,12trihydroxycholan-24-oic acid 26 as well as salts with NSAIDs: indomethacin, diclofenac, and mefenamic, meclofenamic, flufenamic, tolfenamic acids. 27 In this paper we present two polymorphic structures of a new salt of niflumic acid with amantadine, which may be a potential new form of medicine exhibiting a synergistic therapeutic effect due to a change in properties.…”