3 research outputs found
Intrinsic Chemiluminescence Generation during Advanced Oxidation of Persistent Halogenated Aromatic Carcinogens
The ubiquitous distribution coupled
with their carcinogenicity
has raised public concerns on the potential risks to both human health
and the ecosystem posed by the halogenated aromatic compounds (XAr).
Recently, advanced oxidation processes (AOPs) have been increasingly
favored as an “environmentally-green” technology for
the remediation of such recalcitrant and highly toxic XAr. Here, we
show that AOPs-mediated degradation of the priority pollutant pentachlorophenol
and all other XAr produces an intrinsic chemiluminescence that directly
depends on the generation of the extremely reactive hydroxyl radicals.
We propose that the hydroxyl radical-dependent formation of quinoid
intermediates and electronically excited carbonyl species is responsible
for this unusual chemiluminescence production. A rapid, sensitive,
simple, and effective chemiluminescence method was developed to quantify
trace amounts of XAr and monitor their real-time degradation kinetics.
These findings may have broad biological and environmental implications
for future research on this important class of halogenated persistent
organic pollutants
Mechanism of Intrinsic Chemiluminescence Production from the Degradation of Persistent Chlorinated Phenols by the Fenton System: A Structure–Activity Relationship Study and the Critical Role of Quinoid and Semiquinone Radical Intermediates
We
found recently
that intrinsic chemiluminescence (CL) could be
produced by all 19 chlorophenolic persistent organic pollutants during
environmentally friendly advanced oxidation processes. However, the
underlying mechanism for the structure–activity relationship
(SAR, i.e., the chemical structures and the CL generation) remains
unclear. In this study, we found that, for all 19 chlorophenol congeners
tested, the CL increased with an increasing number of chlorine atoms
in general; and for chlorophenol isomers (such as the 6 trichlorophenols),
the CL decreased in the order of meta- > ortho-/para-Cl-substituents
with respect to the −OH group of chlorophenols. Further studies
showed that not only chlorinated quinoid intermediates but also, more
interestingly, chlorinated semiquinone radicals were produced during
the degradation of trichlorophenols by the Fenton reagent; and the
type and yield of which were determined by the directing effects,
hydrogen bonding, and steric hindrance effect of the OH- and/or Cl-substitution
groups. More importantly, a good correlation was observed between
the formation of these quinoid intermediates and CL generation, which
could fully explain the above SAR findings. This represents the first
report on the structure–activity relationship study and the
critical role of quinoid and semiquinone radical intermediates, which
may have broad chemical and environmental implications for future
studies on remediation of other halogenated persistent organic pollutants
by advanced oxidation processes
Unusual Double Beckmann Fragmentation Reaction under Physiological Conditions
Pyridinium aldoximes,
which are best-known as therapeutic antidotes
for organophosphorus chemical warfare nerve-agents and pesticides,
have been found to markedly detoxify polyhalogenated quinones, which
are a class of carcinogenic intermediates and recently identified
disinfection byproducts in drinking water. However, the exact chemical
mechanism underlying this detoxication remains unclear. Here we demonstrate
that pralidoxime can remarkably facilitate the dechlorination/hydroxylation
of the highly toxic tetrachloro-1,4-benzoquinone in two-consecutive
steps to generate the much less toxic 2,5-dichloro-3,6-dihydroxy-1,4-benzoquonine,
with rate enhancements of up to 180 000-times. On the contrary,
no accelerating effect was noticed with <i>O</i>-methylated
pralidoxime. The major reaction product from pralidoxime was identified
as its corresponding nitrile (2-cyano-1-methylpyridinium chloride).
Along with oxygen-18 isotope-labeling studies, a reaction mechanism
was proposed in which nucleophilic substitution coupled with an unprecedented
double Beckmann fragmentation reaction was responsible for the dramatic
enhancement in the detoxification process. This represents the first
report of an unusually mild and facile Beckmann-type fragmentation
that can occur under normal physiological conditions in two-consecutive
steps. The study may have broad biomedical and environmental significance
for future investigations of aldoxime therapeutic agents and carcinogenic
polyhalogenated quinones