Molecular modeling study of uranyl nitrate extraction with monoamides II. Molecular mechanics and lipophilicity calculations. Structure-activity relationships

This report describes the second part of a theoretical approach aimed at es tablishing structure-activity relationships in a data base made of twenty-t wo monoamides (A) used as uranium (VI) nitrate extractants. It was found th at predominant factors determining the extracting ability of a monoamide ar e of three kinds : i) electron density of the coordinating atoms or groups, which should be as high as possible; ii) steric effects, which should be a s low as possible; and iii) lipophilicity of the ligands, which should be a bove a minimum threshold value. In the first paper of this series([1]), qua ntum chemistry calculations were reported to account for electronic propert ies of the ligands. This second paper reports molecular mechanics calculati ons made on UO2(NO3)(2)A(2) complexes in order to determine the influence o f steric effects on the formation of these compounds. Calculations of monoa mide lipophilicity using Rekker's method showed that all the molecules of t he data base were lipophilic enough and, consequently, that this parameter was not significantly important for the extraction of uranyl nitrate by the se monoamides. A quantitative relationship was established between the U(VI ) distribution ratio and the two parameters, calculated by quantum chemistr y and molecular mechanics methods.