Molecular and Crystal Structure of the Bilayer-Forming Lipid-Model Amphiphile, Ditetradecyldimethylammonium Bromide Monohydrate

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Abstract
The conformation and molecular packing of ditetradecyldimethylammonium bromide monohydrate (2C14N+2C1Br−·H2O), C30H62NBr·H2O, has been determined by the X-ray diffraction method. The crystals are triclinic with the space group P\bar1, Z=2, a=2.9827(9), b=0.7847(3), c=0.7480(3) nm, α=104.69(4), β=90.64(7), and γ=90.84(6)°. The structure was determined by direct methods and refined by the least-squares procedure: R=0.07 (Rw=0.07) for 3335 observed reflections. Two amphiphile molecules of the unit cell are related by centrosymmetry and pack tail to tail in a bilayer structure. The hydrocarbon chains tilt about 45° with respect to the bilayer normal. There are statistically four water molecules with half occupancies in a unit cell. Water molecules and bromide anions make hydrogen-bonding networks along the c-axis in the hydrophilic layer. The above molecular and crystal structure of 2C14N+2C1Br−·H2O was quite similar to those of 2C18N+2C1Br−·H2O.