CRYSTAL-LATTICE ENERGY OF AMINO-ACID HYDROHALIDES

Basic relationships concerning thermodynamics of crystalline phases an d the process of their formation, as well as energetics of intermolecu lar interactions in these, were invoked and discussed from the point o f view of their application in studies of stability, features and beha viour of solid systems. Further, electrostatic, dispersive and repulsi ve contributions to the crystal lattice energy of 25 hydrohalides of a minoacids were calculated assuming that each atom of the basic stoichi ometric unit interacts with all atoms from surroundings. Energy of ele ctrostatic interactions was obtained assuming 1+ and 1- charges on cat ion and anion, respectively, and using atomic partial charges resultin g from Mulliken population analysis or fitted so as to reproduce molec ular electrostatic potential (MEP) around molecules, determined on ab initio Hartree-Fock (HF) or density functional theory (DFT) levels. Di spersive and repulsive contributions were evaluated by either Lennard- Jones or Buckingham equations using atomic (ionic) parameters for disp ersive interactions originating from the London or Slater-Kirkwood the ory and those for repulsive interactions resulting from the criterion of minimization of energy on separation of atoms (ions) equal to the s um of their van der Waals radii. Coulombic energies arising from charg es fitted to MEP seem to be the most reliable. These values show a dec reasing tendency with an increase of dimensions of ions (volume of bas ic stoichiometric units).