MOLECULAR MODELING STUDY OF URANYL NITRATE EXTRACTION WITH MONOAMIDES II. MOLECULAR MECHANICS AND LIPOPHILICITY CALCULATIONS. STRUCTURE-ACTIVITY RELATIONSHIPS

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Abstract
This report describes the second part of a theoretical approach aimed at establishing structure-activity relationships in a data base made of twenty-two monoamides (A) used as uranium (VI) nitrate extractants. It was found that predominant factors determining the extracting ability of a monoamide are 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 as low as possible ; and Hi) lipophilicity of the ligands, which should be above a minimum threshold value. In the first paper of this series[1], quantum chemistry calculations were reported to account for electronic properties of the ligands. This second paper reports molecular mechanics calculations made on UO2(NO3)2A2 complexes in order to determine the influence of steric effects on the formation of these compounds. Calculations of monoamide lipophilicity using Rekker's method showed that all the molecules of the data base were lipophilic enough and, consequently, that this parameter was not significantly important for the extraction of uranyl nitrate by these monoamides. A quantitative relationship was established between the U(VI) distribution ratio and the two parameters, calculated by quantum chemistry and molecular mechanics methods.