Solubilities and Single Crystals of Achiral Amphiphiles

Single 3D crystals alone are of limited interest in supramolecular chemistry since their surface is small and the large majority of their monomers is inaccessible to chemical reactions with external molecules. Nevertheless, X-ray diffraction on single crystals is a major tool of supramolecular assembly chemistry, possessing the most detailed information on molecular interactions from crystal 

The simplest and most common synkinons are non-branched, saturated fatty acids from C12 to C18 (trivial names lauroyl Cl2, myristoyl Cl4, palmitoyl or cetyl Cl 6, stearoyl Cl8) and their sodium, ammonium and potassium salts (also known as soaps ). Laurie, myristic, palmitic and stearic acids are barely soluble in water at 20°C (5.5, 2.0,0.7 and 0.3 mg/L) and 60°C (8.7, 3.4, 1.2 and 0.5 mg/L), each ethylene group lowering the solubility by a factor of 2-3. The solubilities of the corresponding sodium and potassium salts are, however, in the order of several grams per litre. Even in highly concentrated emulsions of soaps in distilled water ( 30% w/w), precipitation of solids is often not observed. Bivalent fatty acid salts, however, are just as insoluble as free fatty acids only 1.4 mg of calcium stearate dissolves in 1 L of water.  

The Physical Chemistry of Lipids, Plenum Press, New York, 1986 F. Kaneko, M. Kobayashi, Y. Kitagawa, Y. Matsuura, Acta Cryst., 19SK), C46, 1490 J.H. Dumbleton, T.R. Lomer, Acta Cryst., 1965, 19, 301 F. Brisse, J.-P. Langin, Acta Cryst., 1982, B38, 215 

Acta Chem. Scand., 1968, 22, 811 S. Aleby, E. von Sydow, Acta Cryst., 1960, 13, 487 

Okuyama, Y. Soboi, N. lijima, K. Hirabayashi, T. Kunitake, T. Kajiyama, Bull. Chem. Soc. 

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