INTERACTIONS BETWEEN METAL-CATIONS AND THE IONOPHORE LASALOCID .13. STRUCTURE OF 1 1 AND 2/1 LASALOCID ANION-DIVALENT CATION COMPLEXES IN METHANOL/

The successive formation of complexes MA(+) and MA(2) of alkaline-eart h cations M(2)+ with lasalocid HA is observable in methanol. Knowing t he corresponding formation constants, it was possible to access NMR pa rameters specific to these two types of species for the four alkaline- earth cations. C-13 and H-1 chemical shifts are reported for MA(+) and MA(2); H-1-H-1 coupling constants for MA(+) only. Experiments at low temperature and experiments using the paramagnetic cation Mn2+ determi ned the coordination sites. All these data show an appreciable variabi lity of coordination in the series of alkaline-earth cations. Computat ions using the semi-empirical quantum methods AM1 and PM3 and Monte-Ca rlo simulations in methanol according to BOSS, mainly on MgA(+) and Ba A(+) fully confirmed these findings.