[en] The mechanism of demethylenation of (methylenedioxy)benzene (MDB), (methylenedioxy)amphetamine (MDA), and (methylenedioxy)methamphetamine (MDMA) by purified rabbit liver cytochrome P450IIB4 has been investigated by using deuterium isotope effects. A comparison of the magnitude and direction of the observed kinetic isotope effects indicates that the three compounds are demethylenated by different mechanisms. The different mechanisms of demethylenation have been proposed on the basis of comparisons of the observed biochemical isotope effects with the isotope effects from purely chemical systems

[en] The fate of monocrotophos in the aqueous and soil environment was examined. Hydrolysis rates for monocrotophos are pH-dependent and follow first-order kinetics. The half lives of monocrotophos in pH 3 and 9 buffer solution at 25 degree C are 131 and 26 days, respectively. N-Methylacetoacetamide and O-desmethylmonocrotophos were the major hydrolytic degradation products detected. There was no observable qualitative or quantitative difference when the aqueous and soil experiments were conducted in the dark or with exposure to sunlight. Soil metabolism studies showed rapid and extensive decomposition of monocrotophos and its soil metabolites to ¹⁴CO₂ and unextractable residues. N-Methylacetoacetamide, N-(hydroxymethyl)monocrotophos, and 3-hydroxy-N-methylbutyramide were detected as soil degradation products. Soil TLC data indicated that monocrotophos was mobile under test conditions. Rotational crops planted at various time intervals after soil treatment contained low, if any, significant residue levels of monocrotophos or its metabolites