Chiral and Isotope Analyses for Assessing the Degradation of Organic Contaminants in the Environment: Rayleigh Dependence

Abstract

The Rayleigh equation is frequently used to describe isotope fractionation as a function of conversion. In this article we propose to draw a parallel between isotope and enantiomeric enrichments and derive a set of conditions that allow the use of the Rayleigh approach to describe the enantiomeric enrichment-conversion dependencies. We demonstrate an implementation of the Rayleigh equation for the enantioselective enzymatic hydrolysis of Mecoprop-methyl, Dichlorprop-methyl, and dimethyl-methylsuccinate by lipases from Pseudomonas fluorescens, Pseudomonas cepacia, and Candida rugosa. The data obtained for all the studied reactions gave good fits to the Rayleigh equation, with a linear regression R(2) > 0.96. In addition to that, our analysis of four microcosm studies on the hydrolysis of the individual enantiomers of Dichloroprop methyl, Lactofen, Fenoxaprop-ethyl, and Metalaxyl reported in the literature by other research groups revealed a suitability of the Rayleigh dependence. Two dimensional plots describing the isotope fractionation versus enantiomeric enrichment are demonstrated for all studied cases. Processes not accompanied by enantiomeric enrichment (acid and base hydrolysis) and by isotope enrichment (transesterification) are demonstrated, their 2-D plots are either horizontal or vertical which can illuminate concealed degradation pathways.

Enantioselective Dechlorination of Polychlorinated Biphenyls in Dehalococcoides mccartyi CG1

“…In addition, ultrasonication and the release of premature cytoplasmic RDases during the preparation of crude cell extracts might change the enantioselectivity. To test the potential impacts, the enantiomeric enrichment factor ( ER ) calculated with the Rayleigh equation (41) was employed as an indicator to evaluate the distinct enantioselective enzymatic reactions in this study. The different enantiomeric enrichment factors of living cells (in vivo), concentrated whole cells (in vitro), and crude cell extracts (in vitro) may help to exclude the effects of starting biomass on enantioselectivity and confirmed the yet-to-be-identified impacts of crude cell extraction (e.g., ultrasonication) and cytoplasmic RDases on the enantioselectivity of the PCB RDase.…”

Enantioselective stable isotope analysis (ESIA) — A new concept to evaluate the environmental fate of chiral organic contaminants

“…Very recently, individual isotope enrichment factors of α-HCH enantiomers during aerobic biodegradation of α-HCH have been reported by Bashir et al (2013). This ESIA was applied afterwards by Milosevic et al (2013) and Maier et al (2013) for polar herbicides (phenoxy acids), Wang et al (2013) for galaxolide (HHCB), a synthetic polycyclic musk and Jammer et al (2014) for phenoxyalkanoic methyl herbicides. The approach gives perspectives for assessing the environmental fate of any chiral xenobiotic compound.…”

Quantitative structure–activity relationship correlation between molecular structure and the Rayleigh enantiomeric enrichment factor

“…3,4 In compound-specic isotope analysis the Rayleigh equation is used to describe the relationship between the changes in the isotopic composition vs. contaminant concentration during the degradation process. Recently, [7][8][9][10] it was established that the Rayleigh equation is also effective in describing the enantioselective behavior by deriving the enantiomeric enrichment factor (3 ER ), which can be used as an identifying tool for a specic enzymatic reaction (eqn (1)). Recently, [7][8][9][10] it was established that the Rayleigh equation is also effective in describing the enantioselective behavior by deriving the enantiomeric enrichment factor (3 ER ), which can be used as an identifying tool for a specic enzymatic reaction (eqn (1)).…”