THE CRYSTAL POLYMORPHISM OF TETROLIC ACID (CH3C-CCOOH) - A MOLECULAR-DYNAMICS STUDY OF PRECURSORS IN SOLUTION, AND A CRYSTAL-STRUCTURE GENERATION

The possible configurations of two molecules of tetrolic acid in a sol vent box containing 326 carbon tetrachloride molecules are studied by molecular dynamics with the GROMOS package and force field over period s of up to 2000 picoseconds. The cyclic hydrogen-bended dimer was the most persistent configuration, but events leading to the cleavage one hydrogen bond and thus the formation of a precursor to the crystal cat ermer motif were found to occupy up to 10 % of the simulation times. T he experimental bond-breaking enthalpy was correctly reproduced. Two d ifferent crystal structure generation procedures were employed to repr oduce the two observed polymorphic crystal structures and to predict o ther possible polymorphs; in all cases, some unobserved structures had more cohesive packing energies than the observed ones. The possible a pplication of molecular dynamics in the study of the preliminary steps in crystal nucleation is discussed.