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Laboratories, Incorporated, Murray Hill, New Jersey 0'79'74
Synopsis
Crystals of poly-L-lysine have been grown from aqueous solution in the presence of divalent anions. The most stable of these incorporate the HPO; ion and are precipitated by the addition of sodium monohydrogen phosphate to solutions of poly-I.lysine HBr. Precipitation at or slightly above room temperature gives rise to single crystals of a-poly-dysine HPOa in the form of hexagonal lamellae about 150 d thick.
The axes of the helical polypeptide molecules are oriented normal to the planes of the lamellae, and since molecular length is about 1100 A in the a-helical conformation, these helices must be folded. The a parameter of the hexagonal unit cell is 19.55 d for crystals immersed in mother liquor, and the lysine side chains are almost fully extended. Precipitation brought about by heating the same solutions to about 75°C produces microcrystals of @-poly-L-lysine HPOa. A mode of packing of the anions in these crystals is proposed tentatively on the basis of an intersheet spacing determined from x-ray powder diffraction patterns. In general, a crystals are transformed to @ structures on drying; conditions under which the transition can either be forestalled or reversed are discuseed.