Molecular aggregation in selected crystalline 1:1 complexes of hydrophobic D- and L-amino acids.: II.: The D-norleucine series

The amino acid D-norleucine has been co-crystalized with selected L-amino acids with linear side chains including L-norvaline [D-norleucine-L-zorvaline (1/1), C6H13NO2. C5H11NO2, amino-acid side chain R = CH2CH2CH3] and L-methionine [D-norleucine-L-methionine, C6H13NO2. C5H11NO2S (1/1), R = CH2CH2SCH3], as well as amino acids with branched side chains including L-valine [D-norleucine-L-valine (1/1), C6H13NO2. C5H11NO2, R = CH(CH3)(2)], L-allo-isoleucine [D-norleucine-L-allo-isoleucine (1/1), C6H13NO2. C6H13NO2, R = CH(CH3)CH2CH3] and L-leucine [D-norleucine-L-leucine (1/1), C6H13NO2. C6H13NO2, R = CH2CH(CH3)(2)]. The crystal structures are divided into distinct hydrophilic and hydrophobic layers. The polar is disordered over two positions with nearly equal occupancy. Similarities and differences in both the crystal packing and molecular conformations of D-Nle and the partner molecules are discussed.