The detection and measurement of lipid oxidation in biological systems and some biologic effects of this oxidation are reviewed. The role of lipid oxidation in the process of photocarcinogenesis and the protective effect of antioxidants against this process also are discussed. The mechanism of such protection is unknown and studies directed at elucidating the mechanism of antioxidant effect in photocarcinogenesis and in some other pathological conditons believed to involve lipid oxidation are needed. In addition to this, epoxidation of lipids observed in monolayer studies requires further investigation, particularly in the presence of some other unsaturated molecules. The possible significance of such a study--particularly in the presence of polycyclic aromatic hydrocarbon carcinogens, where formation of epoxides is generally accepted as active intermediates--is also discussed. In addition, present knowledge on the role of lipid peroxides in the destruction of proteins and biomembranes, in chemically induced toxicity and in generation of singlet oxygen is presented.
Hybrid polymer/metal organic framework (MOF) membranes have been prepared using either a mixed matrix membrane (MMM) or in situ growth (ISG) approach and were evaluated for application in organic solvent nanofiltration (OSN).
Experimental studies on the mechanism
of copper-catalyzed amination
of aryl halides have been undertaken for the coupling of piperidine
with iodobenzene using a Cu(I) catalyst and the organic base tetrabutylphosphonium
malonate (TBPM). The use of TBPM led to high reactivity and high conversion
rates in the coupling reaction, as well as obviating any mass transfer
effects. The often commonly employed O,O-chelating ligand 2-acetylcyclohexanone
was surprisingly found to have a negligible effect on the reaction
rate, and on the basis of NMR, calorimetric, and kinetic modeling
studies, the malonate dianion in TBPM is instead postulated to act
as an ancillary ligand in this system. Kinetic profiling using reaction
progress kinetic analysis (RPKA) methods show the reaction rate to
have a dependence on all of the reaction components in the concentration
range studied, with first-order kinetics with respect to [amine],
[aryl halide], and [Cu]total. Unexpectedly, negative first-order
kinetics in [TBPM] was observed. This negative rate dependence in
[TBPM] can be explained by the formation of an off-cycle copper(I)
dimalonate species, which is also argued to undergo disproportionation
and is thus responsible for catalyst deactivation. The key role of
the amine in minimizing catalyst deactivation is also highlighted
by the kinetic studies. An examination of the aryl halide activation
mechanism using radical probes was undertaken, which is consistent
with an oxidative addition pathway. On the basis of these findings,
a more detailed mechanistic cycle for the C–N coupling is proposed,
including catalyst deactivation pathways.
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