Effects of crystal packing and hydration on the conformation of enniatin B

Abstract

The effects of crystal packing forces and of hydration on the conformations of the ion carrier enniatin B, cyclo-{O-CH[-CH(CH3)2]-C'O'-N(CH3)-CH[CH(CH3)2]-C'O'-}3, in two different crystal structures belonging to the trigonal space group R3 have been analyzed theoretically by the empirical forcefield method. In one structure the central cavity of the ion carrier shrinks owing to crystal packing forces, while the c axis of the equivalent hexagonal unit cell is extended due to the presence of water molecules in the interlayer space. In the other crystal structure, a water molecule occupies the cavity and counterbalances the crystal packing forces, and therefore the observed molecular conformation resembles more closely the calculated conformation of the isolated single molecule than is the case for the first structure.