The importance, design and modeling of biodegradable complexants. An extension of the structure-soft character relations.

Complexing Chem. or chelating agents are used in plant cultivation to avail of different phytobiologically useful macro- and microelements. The great majority of the traditional chelators (e.g. EDTA) are, however, essentially non-biodegradable, which can lead to environmentally incalculable consequences. In the present work we sum up our results and conclusions on the modeling of the structure-property relationships of some biodegradable complexes in light of modern plant cultivation criteria. We have systematically investigated some new biodegradable ligands with poliamino-polycarboxylic structure, EDTA analogs, using the molecular modeling method and other possibilities of modern computer techniques. These compounds may be considered as a special group of "soft" chemicals. We established mathematical relations between the steric energy of the complexes and the properties of their components. One can conclude that the new complexes with poliamino-polycarboxylic chelators are less stable, therefore easier degradable than the complexes with EDTA. We have drawn conclusions regarding the regression parameters and the stereochemical properties of the complexes and have interpreted the probable causes of the deviations from the theoretically presumable values. The suitability of some general rules known in the complex chemistry (the Dyrssen-Sillen's diparametric compensatory equation, the van Panthaleon-van Eck's, the Schwarzenbach-Ackermnn's, the Irving-Rosotti's, the Larsson's, the Yatsimirsky's relations, the natural stability rank) and the significance of the differences observed were analyzed in detail.