2 research outputs found
Biotransformation of Hexabromocyclododecanes (HBCDs) with LinBî—¸An HCH-Converting Bacterial Enzyme
Hexabromocyclododecanes (HBCDs) and hexachlorocyclohexanes
(HCHs)
are polyhalogenated hydrocarbons with similar stereochemistry. Both
classes of compounds are considered biologically persistent and bioaccumulating
pollutants. In 2009, the major HCH stereoisomers came under regulation
of the Stockholm convention. Despite their persistence, HCHs are susceptible
to bacterial biotransformations. Here we show that LinB, an HCH-converting
haloalkane dehalogenase from <i>Sphingobium indicum</i> B90A,
is also able to transform HBCDs. Racemic mixtures of α-, β-,
and γ-HBCDs were exposed to LinB under various conditions. All
stereoisomers were converted, but (−)Âα-, (+)Âβ-,
and (+)Âγ-HBCDs were transformed faster by LinB than their enantiomers.
The enantiomeric excess increased to 8 ± 4%, 27 ± 1%, and
20 ± 2% in 32 h comparable to values of 7.1%, 27.0%, and 22.9%
as obtained from respective kinetic models. Initially formed pentabromocyclododecanols
(PBCDOHs) were further transformed to tetrabromocyclododecadiols (TBCDDOHs).
At least, seven mono- and five dihydroxylated products were distinguished
by LC-MS so far. The widespread occurrence of HCHs has led to the
evolution of bacterial degradation pathways for such compounds. It
remains to be shown if LinB-catalyzed HBCD transformations in vitro
can also be observed in vivo, for example, in contaminated soils or
in other words if such HBCD biotransformations are important environmental
processes
Deconvolution of Mass Spectral Interferences of Chlorinated Alkanes and Their Thermal Degradation Products: Chlorinated Alkenes
Chlorinated
paraffins (CPs) are high production volume chemicals
and ubiquitous environmental contaminants. CPs are produced and used
as complex mixtures of polychlorinated <i>n</i>-alkanes
containing thousands of isomers, leading to demanding analytical challenges.
Due to their high degree of chlorination, CPs have highly complex
isotopic mass patterns that often overlap, even when applying high
resolution mass spectrometry. This is further complicated in the presence
of degradation products such as chlorinated alkenes (CP-enes). CP-enes
are formed by dehydrochlorination of CPs and are expected thermal
degradation products in some applications of CPs, for example, as
metal working fluids. A mathematical method is presented that allows
deconvolution of the strongly interfered measured isotope clusters
into linear combinations of isotope clusters of CPs and CP-enes. The
analytical method applied was direct liquid injection into an atmospheric
pressure chemical ionization source, followed by quadrupole time-of-flight
mass spectrometry (APCI-qTOF-MS), operated in full scan negative ion
mode. The mathematical deconvolution method was successfully applied
to a thermally aged polychlorinated tridecane formulation (Cl<sub>5</sub>–Cl<sub>9</sub>). Deconvolution of mass patterns allowed quantifying fractions of
interfering CPs and CP-enes. After exposure to 220 °C for 2,
4, 8, and 24 h, fractions of CP-enes within the respective interfering
clusters increased from 0–3% at 0 h up to 37–44% after
24 h. It was shown that thermolysis of CPs follows first-order kinetics.
The presented deconvolution method allows CP degradation studies with
mass resolution lower than 20000 and is therefore a good alternative
when higher resolution is not available