Effect of chlorine atoms on inhibition effect between amide herbicides and urease enzyme: molecular mechanism and structure-activity relationship

Amide herbicides (AHs) disturbed urease (UA) activity and soil microbial community and caused soil nutrient changes. Activity of UA was inhibited by AHs via groups of chlorine, benzene ring, and peptide bond (-N-/-CO-). Differences of surface charge distribution were mainly derived from position to connected -Cl, distance of -O- from ether group and -N from peptide bond, difference of structure/length for hydrocarbon chain, and different regions of negative charge enrichment. Developmental toxicity for alachlor was strongest related to smaller structure and weaker steric hindrance effect; mutagenicity for propanil was weakest possibly related to missing ether group. Molecular mechanism and structural activity relationship for inhibition of AHs and UA were based on functional groups, amino acids with high frequency, hydrogen bonds, hydrophobic interactions, binding area (BA) of butachlor (396.3 Å2), absolute value of binding energy (|BE|) of propanil (2.93 kJ/mol; which was highest), and quantitative structural relationship between BA and |BE|, which was negative correlation. Binding area for AHs and UA had negative correlation for density with correlation coefficient (r) as -0.937 (p ≤ 0.01). Absolute value of binding energy for AHs and UA had positive correlation for density with r as 0.847 (p ≤ 0.05), and negative correlation for molecular weight with r as -0.973 (p ≤ 0.001). Results provided technological support and theoretical foundation for toxic effects of soil enzyme activity, health effects, risk regulation, and control of AHs.