Molecular modelling of Me(2+)-(8-hydroxy-quinolinate)2 complexes using ZINDO and ESSF methods

The Me2+ (8-hydroxy-quinolinate)1-2 system was studied using semi-empirical (ZINDO) and molecular mechanics (ESFF) methods for a range of bivalent metals comprising alkaline earth metals (up to Sr2+) and the first two rows of transition metals. The structural validation of the optimisation calculations showed that ESFF is in general an efficient predictor of the structure of the complexes. On the other hand, ZINDO offers an appropriate tool for describing the mechanisms of complex formation for the studied system. The spectral validation based on the comparison of spectral data with predicted molecular geometric parameters shows that ZINDO offers a better tool for describing the mechanisms of complex formation. Finally, the consistent relationship (in relative terms) between SCF energies and equilibrium constants, and between computed charges at the oxygen ligation atom and pH, showed that ZINDO can be used as a tool for the design of chelating agents. For the system studied the CPU times are not prohibitive, even for a metal-comprehensive investigation.