Rationally Designed Fluorescence .OH Probe with High Sensitivity and Selectivity for Monitoring the Generation of .OH in Iron Autoxidation without Addition of H2O2

The first sensitive fluorescence ^.OH probe ( 1 ) that is capable of monitoring the generation of trace ^.OH in iron autoxidation is presented. The probe 1 was designed by utilizing both the unique aromatic hydroxylation and the electrophilicity of ^.OH, and prepared by incorporating a strong electron‐donating methoxy group into a cyanine fluorochrome to enhance the trapping ability for ^.OH. Reaction of 1 with ^.OH leads to a larger π‐conjugation formation and near‐infrared fluorescence off–on response. The capability of probe 1 has been demonstrated by imaging ^.OH generated in living cells under iron autoxidation as well as various stimuli, which reveals that the basal level of ^.OH in RAW 264.7 cells is lower than that in HeLa cells. The superior analytical performance of probe 1 makes it useful for detecting trace ^.OH in some critical physiological and pathological processes associated with iron autoxidation.     

Interaction of giant extracellular Glossoscolex paulistus hemoglobin (HbGp) with zwitterionic surfactant N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (HPS): effects of oligomeric dissociation

The present work focuses on the interaction between the zwitterionic surfactant N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (HPS) and the giant extracellular hemoglobin of Glossoscolex paulistus (HbGp). Electronic optical absorption, fluorescence emission and circular dichroism spectroscopy techniques, together with Gel-filtration chromatography, were used in order to evaluate the oligomeric dissociation as well as the autoxidation of HbGp as a function of the interaction with HPS. A peculiar behavior was observed for the HPS–HbGp interaction: a complex ferric species formation equilibrium was promoted, as a consequence of the autoxidation and oligomeric dissociation processes. At pH 7.0, HPS is more effective up to 1 mM while at pH 9.0 the surfactant effect is more intense above 1 mM. Furthermore, the interaction of HPS with HbGp was clearly less intense than the interaction of this hemoglobin with cationic (CTAC) and anionic (SDS) surfactants. Probably, this lower interaction with HPS is due to two factors: (i) the lower electrostatic attraction between the HPS surfactant and the protein surface ionic sites when compared to the electrostatic interaction between HbGp and cationic and anionic surfactants, and (ii) the low cmc of HPS, which probably reduces the interaction of the surfactant in the monomeric form with the protein. The present work emphasizes the importance of the electrostatic contribution in the interaction between ionic surfactants and HbGp. Furthermore, in the whole HPS concentration range used in this study, no folding and autoxidation decrease induced by this surfactant were observed. This is quite different from the literature data on the interaction between surfactants and tetrameric hemoglobins, that supports the occurrence of this behavior for the intracellular hemoglobins at low surfactant concentration range. Spectroscopic data are discussed and compared with the literature in order to improve the understanding of hemoglobin–surfactant interaction as well as the acid isoelectric point (pI) influence of the giant extracellular hemoglobins on their structure–activity relationship.     

Mechanisms of air oxidation of ethoxylated surfactants--computational estimations of energies and reaction behaviors

Pathways for formation of previously observed autoxidation products of ethoxylated surfactants have been studied by DFT (B3LYP). In addition to the established radical-chain reaction, several mechanistic possibilities for intramolecular fragmentation of the intermediate radicals have been characterized concerning reaction barriers and energies of transition states. The results can rationalize the formation of previously observed autoxidation products, including several, which have been implicated as strongly allergenic.     

Synthesis and photosensitized oxygenation of cyclopropylidenecyclobutenes

Cyclopropylidenecyclobutenes and -cyclobutanes were conveniently prepared using the Petasis titanocene approach. The cyclobutenes were unreactive to singlet oxygen, reacting sluggishly via a photoinitiated free radical autooxidative epoxidation process, to yield the corresponding spiroketones. By contrast, cyclopropylidenecyclobutanes react rapidly with ¹O₂, via an ‘ene’ process, initially generating a cyclopropyl hydroperoxide, which proceeds to products via Hock cleavage. The inertness of cyclopropylidenecyclobutenes to a ¹O₂ ‘ene’ reaction mode may be attributed to the fact that it would require the formation of the relatively high energy cyclobutadiene moiety.     

The initiation properties of 2-cyano-2-propyl hydroperoxide in oxidation processes

The initiating ability of 2-cyano-2-propyl hydroperoxide in the oxidation reaction of cumene by molecular oxygen has been investigated and compared with the initiating ability of cumene hydroperoxide.

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Die Initiierungseigenschaften von 2-Cyano-2-propyl-hydroperoxid bei Oxydations-prozessen

Zusammenfassung Es wurde die Initiierungsfähigkeit des 2-Cyan-2-hydroperoxypropans in der Oxidation von Cumol mit molekularem Sauerstoff untersucht und mit der Initiierungsfähigkeit des Cumolhydroperoxids verglichen.

     

Fluorescent oligo(N‐phenylmaleimide)s via aerobic radical telomerization initiated by benzylic hydrocarbons: Catalytic effect of CoII/N‐hydroxyphthalimide pair

Radical oligomerization of N‐phenylmaleimide (NPMI) was performed in benzylic hydrocarbons as the solvent. The thermally induced oligomerization occurred only above 130 °C, with the initiation attributed to autoxidation of benzylic hydrocarbons as well as formation and dissociation of charge‐transfer complexes between benzylic hydrocarbons and maleimides. The end‐group analysis on oligo(N‐ethylmaleimide) prepared under similar conditions confirmed that the chain transfer to benzylic hydrocarbons was the primary fashion in forming oligomeric chains, and radical telomerization underlaid the oligomerization with benzylic hydrocarbons as both the solvent, the initiator and the telogen. Co^II/N‐hydroxyphthalimide (NHPI) pairs could catalyze the telomerization at 110 °C. In such a catalytic process, Co^II‐based oxidative complexes oxidized benzylic hydrocarbons and NHPI into benzylic radicals and phthalimide N‐oxyl (PINO), and benzylic hydrocarbons underwent hydrogen atom transfer (HAT) to PINO. Oligo(NPMI)s were formed via HAT with benzylic hydrocarbons and NHPI. These oligo(NPMI)s exhibited fluorescent properties with excitation at 270–350 nm and 400–550 nm and emission at 530–750 nm. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3846–3857     

Radical-Pair Formation in Hydrocarbon (Aut)Oxidation

The reaction profiles for the uni- and bimolecular decomposition of benzyl hydroperoxide have been studied in the context of initiation reactions for the (aut)oxidation of hydrocarbons. The unimolecular dissociation of benzyl hydroperoxide was found to proceed through the formation of a hydrogen-bonded radical-pair minimum located +181 kJ mol⁻¹ above the hydroperoxide substrate and around 15 kJ mol⁻¹ below the separated radical products. The reaction of toluene with benzyl hydroperoxide proceeds such that O−O bond homolysis is coupled with a C−H bond abstraction event in a single kinetic step. The enthalpic barrier of this molecule-induced radical formation (MIRF) process is significantly lower than that of the unimolecular O−O bond cleavage. The same type of reaction is also possible in the self-reaction between two benzyl hydroperoxide molecules forming benzyloxyl and hydroxyl radical pairs along with benzaldehyde and water as co-products. In the product complexes formed in these MIRF reactions, both radicals connect to a centrally placed water molecule through hydrogen-bonding interactions.     

To the core of autocatalysis in cyclohexane autoxidation

Despite their industrial importance, the detailed reaction mechanism of autoxidation reactions is still insufficiently known. In this work, complementary experimental and theoretical techniques are employed to address the radical-chain initiation in the autoxidation of cyclohexane with a particular focus on the "lighting-off" of the oxidation by (added) cyclohexanone. We used a newly developed method to quantify the intrinsic rate of chain initiation as well as the rate enhancement by cyclohexanone and several other (oxygenated) molecules. On the basis of first principles, the hitherto assumed perhemiketale mechanism was found to be many orders of magnitude too slow to account for the observed initiation enhancement by the ketone. Instead, it is shown that the pronounced chain-initiation enhancement by the ketone is attributable to a newly proposed concerted reaction between cyclohexyl hydroperoxide and cyclohexanone, in which the (.)OH radical breaking away from the hydroperoxide abstracts an alphaH atom from the ketone, thereby energetically assisting in the cleavage of the RO--OH bond. This reaction is highly efficient in generating radicals as it quasi-excludes geminate in-cage recombination. As a result, the ketone oxidation product at a level of 1 mol % increases the initiation rate by one order of magnitude, and so acts as a highly efficient "autocatalyst" in autoxidation reactions. An analogous reaction with cyclohexanol, although estimated to be even faster, has only a marginal effect on the overall kinetics, owing to the fast subsequent formation of HO(2) (.) radicals that very rapidly terminate with other ROO(.) radicals. Finally, solid evidence is presented that, also in absence of oxygenates, ROOH initiation is actually a bimolecular reaction, involving concerted H abstraction from the alkane substrate by the nascent (.)OH.