The crystallization of amylose from dilute solutions in the presence of a series of linear saturated fatty acids (C3 to C20) was investigated by varying the fatty acid concentration, crystallization temperature and solvent composition (DMSO:water in various ratios). The morphology and structure of the resulting model lamellar crystals were characterized by transmission electron microscopy as well as electron and X-ray diffraction. By adequately controlling the crystallization parameters, all fatty acids could induce the formation of both 6- and 7-fold V-amylose single helices, indicating that the amylose conformation was independent of the chain length of the complexing molecule. Three allomorphs (V6, V6 and V7) were identified individually or in mixtures. Higher concentrations of fatty acid and DMSO and a higher temperature promoted the formation of the more compact V6 structure. V6 and V7 preferentially formed with lower concentrations of fatty acids and DMSO and at lower temperatures. In the case of C5-C20 fatty acids, V7 was only obtained in the presence of DMSO. The polymorphism of V-amylose complexes with linear saturated fatty acids thus appears to be a more general phenomenon than previously reported in the literature.

Chain-folded lamellar crystalline complexes of amylose with aliphatic diols were prepared and characterized by transmission electron microscopy as well as electron and X-ray diffraction. Four allomorphs were identified, depending on the complexing diol and crystallization conditions, that consisted of orthorhombic lattices of antiparallel 6-or 7-fold amylose single helices. Straightchain n-diols (ethane-1,2-diol, butane-1,4-diol, hexane-1,6-diol) yielded 6-fold helical complexes regardless the length of the linear chain, whereas a bulkier branched diol (2-methylpentane-2,4diol) induced the formation of 7-fold helices. Butane-1,3-diol, that contains a straight carbon chain with one end and one side hydroxyl group, induced both 6-and 7-fold helical conformations depending on the crystallization conditions. When a diol induced more than one allomorph, an adequate control of its concentration and crystallization temperature allowed targeting a specific crystalline form. Upon drying, all allomorphs were converted into more compact pseudohexagonal structures. The dried form of a given complex generally retained the same helical conformation as the hydrated one.

Lamellar single crystals of V‐amylose were prepared from dilute aqueous solutions in the presence of selected bicyclic compounds. Transmission electron microscopy images as well as electron and X‐ray diffraction patterns revealed that two allomorphs containing 7‐fold amylose single helices were formed depending on the complexing agent. On the one hand, trans‐decalin and (−)‐β‐pinene induced the crystallization of an orthorhombic unit cell isomorphous to that of V2‐propanol crystals reported in the literature (referred to as V7II). On the other hand, (+)‐camphor and (−)‐borneol yielded a new compact pseudo‐hexagonal structure (referred to as V7I). Cis‐decahydro‐1‐naphthol and decahydro‐2‐naphthol induced the formation of both allomorphs. V7I was favored at a higher crystallization temperature compared to V7II. Upon drying in vacuum, both V7I and V7II converted into the hexagonal anhydrous allomorph V7a but the initial structures were recovered by rewetting the crystals in water at room temperature. In addition, washing the crystals with methanol resulted in a transition from a 7‐fold to a 6‐fold helical conformation of amylose. The results suggest that both water and complexing agent play an important role on the formation and stability of V‐amylose crystals.

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