Quantitative structure–transformation relationships of phenylurea herbicides

Abstract

Quantitative relationships between the structure of phenylurea herbicides and their transformation in different matrices have been developed. Experimental data on microbial transformation by pure and mixed cultures of soil micro-organisms in inoculated and native soil, as well as on chemical transformation by hydrolysis in sterile soil and water, were available from previous studies. Around 60 experimental or calculated descriptors were used. Quantum chemical calculations were performed with three different semi-empirical methods. Models developed with multiple linear regression were generally easier to interpret than those derived with partial least-squares projection to latent structures. Quite simple and interpretable models could be found to predict transformation rates by pure cultures from lipophilicity, by mixed cultures from adsorption distribution coefficients, and by chemical or enzymatic hydrolysis from electronic properties. Transformation in inoculated soil could not be predicted, but for native soil the use of a quantum chemical descriptor for reactivity (energy of LUMO) together with molar refraction resulted in a general model.

Prediction of the Fate of Organic Compounds in the Environment From Their Molecular Properties: A Review

“…The polarizability α was involved in many equations (Tables S3, S4, S6 to S9), but the atom self-polarizability (ALP ij ;Berger et al, 2001;Berger et al, 2002;Tehan et al, 2002b;Von Oepen et al, 1991), the second (α 2 ) and third (α 3 ) principal polarizabilities (Dunnivant et al, 1992), and the polarizability of the hydroxyl oxygen atom in an acid (α O ) were also used. Other polarizability terms are specially used in linear solvation energy relationships (LSER) equations (see section 2.8).…”

Quantitative structure–transformation relationships of sulfonylurea herbicides

“…This results in polar groups being closer to each other 15. Therefore, optimisation of the structures of sulfonylureas was done with all three Hamiltonians, using the molecular mechanics correction for peptide bonds (parameter MMOK), as this has been found necessary for calculations with phenylureas 4. Different starting conformations of the sulfonylureas were optimised.…”

“…This includes not only self‐polarisability and superdelocalisability, but also HOMO and LUMO energies. The latter have been described to be of relevance for different relationships, eg for aniline and phenol biodegradation by single strains of microorganism,32 for nucleophilic substitution reaction,35 for transformation of phenylureas in soil,4 and for structure‐activity relationships of sulfonylureas 1…”

“…These compounds have quite a complex structure and transformation, following different reaction pathways, varies significantly with pH 3. We have used a mechanistic approach as previously described for phenylureas 4. Transformation data were generated previously with specially developed multi‐residue methods for sulfonylureas, using either capillary electrophoresis or high‐performance liquid chromatography 3.…”

Investigation of Structure – Biodegradability Relationships in Polychlorinated Biphenyls Using Self-Organising Maps

“…QSAR (Quantitative Structure Activity Relationship) studies are widely used in the pharmaceutical industry and in theoretical organic chemistry in an attempt to find correlations between chemical or biochemical behaviour and molecular structure. Methods which try to establish a relationship between a particular physical or chemical property within a set of molecules, such as efficacy as a drug, and some molecular descriptors are potentially powerful, but rely upon a suitable choice of descrip- tors [20,21]. To assess data of the sort shown in Table 1 using a SOM therefore, the structural features of the PCB and its biodegradability must be encoded in some appropriate manner.…”