Pulse radiolytic study of the site of hydroxyl radical attack on aliphatic alcohols in aqueous solution

Asmus, K.‐D.; Moeckel, H.; Henglein, A.

doi:10.1021/j100629a007

Cited by 364 publications

(268 citation statements)

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“…Consistent ratios of 0:5:6:1:1:1:1 were found for the six stable alkoxyamine product peaks observed (Fig. 7) This differs from the ratios of the number of protons on each carbon (2:2:2:2:2:2:3) because all of the protons are not extracted with equal efficiency as has been seen previously (Asmus et al, 1973). As this is a region of changing HPLC gradient, the varying quantum yields of the alkoxyamines in different solvents effect the peak ratios (although by no more than a factor of two) (see Chapter 1, Table I.…”

Section: Octanol As Primary Trapsupporting

confidence: 74%

“…Hydroxyl radical reacts with t-butanol (16) both by extracting a proton from one of the methyl groups (95.7%) and by extracting the proton from the alcohol which rearranges to generate a methyl radical (4.3%) (Asmus et al, 1973). These radicals are trapped by 3-amp and elute at around 18.5 and 19 minutes, respectively, and in the expected ratio.…”

Section: T-butanol As Primary Trapmentioning

confidence: 99%

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Photophysics and photochemistry of natural waters with emphasis on radical probe development and application

Herbelin¹

1994

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The work presented here consists of a literature review and calculations to estimate the importance of photochemistry to carbon cycling in the oceans, followed by a photophysical study of a series of stable nitroxide radical probes that have been used for the quantitative detection of individual carbon-centered radicals and reducing species in natural waters. Two appendices follow. The first contains preliminary experiments utilizing one of the nitroxide probes in an investigation of hydroxyl radical production rates and steadystate concentrations in seawater. The second consists of an investigation of the singlet lifetimes of humic acids (HA), in order to aid in understanding their photochemical cycling and influence on other compounds.The impact of photochemical reactions on global oceanic carbon cycling was calculated from literature values. The results indicate that between 1 and 13% of all dissolved organic carbon in the oceans is oxidized photochemically. This is a significant flux term, much larger than that of riverine input for example.A photophysical study of nitroxide radical probes was undertaken. For all of the compounds studied, steady-state absorption and fluorescence spectra were identical to those of the parent fluorophores. A decrease in fluorescence lifetime and quantum yield of tens-to hundreds-fold was observed for the paramagnetic compounds relative to their diamagnetic counterparts. Very rapid fluorescence quenching rates (3 to 80 x 1010 s-1 ) were calculated for the fluorescamine moiety of the paramagnetic nitroxide compounds in a variety of solvents. Calculated energy minimized geometries were very similar for all compounds which implies that geometric differences are not responsible for the variations found in fluorescence lifetimes and quantum yields between compounds. Calculated Firster and Dexter overlap integrals do not support deexcitation by these mechanisms. Time-resolved absorption measurements resulted in no evidence for transient species due to either intersystem crossing to the triplet state or charge transfer. Of the mechanisms considered, direct internal conversion to the ground state, is most likely given our results.An investigation of the utility of 3-(aminomethyl)-2,2,5,5-tetramethyl-1-pyrrolidinyloxy free radical (3-amp) for detection and quantification of hydroxyl radicals in natural waters found that the addition of primary probe compounds resulted in the generation of secondary carbon-centered radicals that were successfully trapped by 3-amp. Competition kinetics experiments with dimethyl sulfoxide resulted in a natural scavenger rate constant that matched previous literature results for coastal seawater. As expected, the addition of formate resulted in decreases, and the addition of nitrite in increases, in the hydroxyl radical trapping rate by this method. The resulting quantum yield values were about an order of magnitude higher than previous literature results. However, probablyI IYIIIIYYI Wilkl 4 due to the use of different latitudes at which to estimat...

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Section: Octanol As Primary Trapsupporting

confidence: 74%

Section: T-butanol As Primary Trapmentioning

confidence: 99%

Photophysics and photochemistry of natural waters with emphasis on radical probe development and application

Herbelin¹

1994

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“…The fact that a product isotope effect is measurable may indicate that the perturbation by 1-propanol is through insertion between the hydrophobic sites of helix I and helix IV bringing 1-propanol sufficiently close to the yet perturbed metal-binding site to scavenge reactive oxygen species. Three experimental facts would support an assignment that this reactive species is either a hydroxyl radical or a metal-bound equivalent, a complexed hydroxyl radical: (i) the anaerobic reaction of hydrogen peroxide with a hGH-Cu(I) complex, most likely [hGHCu(I)] mbs , is expected to proceed according to Equations 12 and 13 (44 (ii) The most reactive C-H bonds of 1-propanol are the respective C ␣ -H bonds (45). Pulse radiolytic studies have shown that the primary kinetic isotope effect for the reaction of the hydroxyl radical with the C ␣ -H and the C ␣ -D bonds of methanol-h 3 and methanol-d 3 , respectively, is on the order of k H /k D ϭ 2.25 (46), i.e.…”

Section: The Effect Of 1-propanolmentioning

confidence: 67%

Metal-catalyzed Oxidation of Histidine in Human Growth Hormone

Zhao

Ghezzo-Schöneich

Aced

et al. 1997

Journal of Biological Chemistry

109

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In physiological compartments, provided with suitable reducing agents, transition metals are able to catalyze the activation of O 2 to various reactive oxygen species (ROS) 1 which readily attack biomolecules. The metal-catalyzed oxidation (MCO) of proteins plays an important role during oxidative stress and aging where modified proteins may accumulate in tissue (1-9). In addition, MCO also presents a stability problem for the biotechnological manufacturing of proteins (10, 11).A unique feature often observed during MCO of proteins is that only a few amino acid residues within a certain domain of the given protein are modified (2, 12). Such site specificity is attributed to the generation of ROS at specific metal-binding sites, where the highly reactive ROS attack labile functional groups nearby rather than diffuse into the bulk medium. It has been shown that most of the enzymes labile to MCO require metals for activity (13). The oxidation of these enzymes is less sensitive to the inhibition by exogenous ROS scavengers than would be expected on the basis of known rate constants for the reactions of specific ROS with these scavengers. However, one problem associated with all these studies is that neither the oxidizing species nor the intermediary protein-transition metal complexes formed during MCO of proteins have been well characterized. This is most pertinent to copper-catalyzed oxidation (i.e. to the frequently used ascorbate/Cu(II)/O 2 system) involving the Cu(II)/Cu(I) redox couple (2). Here, Cu(II) will most probably require a different geometry and different ligands within the protein ligand sphere than Cu(I). An initial reduction of Cu(II), bound to a metal-binding site, to Cu(I) may change the geometry of the protein-metal complex, and possibly even release Cu(I) from the metal-binding site. On the other hand, the metal may be retained when (i) the protein is flexible enough to adapt to the new geometrical requirements of the reduced metal, or (ii) re-oxidation of the metal by molecular oxygen or reduction products of molecular oxygen such as superoxide or hydrogen peroxide occurs faster than the release of the reduced metal from the metal-binding site.In a recent example for electron transfer coupled ligand dynamics in the model complex Cu(I/II)(TTCN) 2 , we could show that oxidation of tetrahedral [Cu(I)(TTCN) 2 ] ϩ potentially led to the loss of a ligand to yield [Cu(II)(TTCN)(H 2 O) 3 ] 2ϩ before geometrical reorganization around the Cu(II) atom allowed the addition of TTCN to give the final product, octahedral [Cu(II)(TTCN) 2 ] 2ϩ . 2 Analogous mechanisms may lead to kinetic complexities during protein oxidation which may be reflected in oxidation yields and kinetics as well as the nature of the oxidation products.One amino acid particularly affected by MCO is histidine (His) (15-17). There is as yet no detailed mechanism available for His oxidation in proteins, except a crystallographic study which showed the feasibility of metal-catalyzed processes within the metal-binding domain of glutamine syn...

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“…Here, an acetone radical anion is formed which should promptly be protonated giving a strongly reducing alkyl radical (CH 3 ) 2 C • (OH), the same as generated via reaction (4) with 86% yield. 44 The fate of the holes generated in this system is unclear, but at least recombination of holes and electrons is suppressed. One can propose that the holes could be transformed first into hydroxyl radicals (3), which further react with acetone via H-abstraction (see eqn (S1), ESI †) with a rate constant of k = 1.3 × 10 8 dm 3 mol −1 s −1 ).…”

Section: Resultsmentioning

confidence: 99%

High quality reduced graphene oxide flakes by fast kinetically controlled and clean indirect UV-induced radical reduction

et al. 2016

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This work highlights a surprisingly simple and kinetically controlled highly efficient indirect method for the production of high quality reduced graphene oxide (rGO) flakes via UV irradiation of aqueous dispersions of graphene oxide (GO), in which the GO is not excited directly. While the direct photoexcitation of aqueous GO (when GO is the only light-absorbing component) takes several hours of reaction time at ambient temperature (4 h) leading only to a partial GO reduction, the addition of small amounts of isopropanol and acetone (2% and 1%) leads to a dramatically shortened reaction time by more than two orders of magnitude (2 min) and a very efficient and soft reduction of graphene oxide. This method avoids the formation of non-volatile species and in turn contamination of the produced rGO and it is based on the highly efficient generation of reducing carbon centered isopropanol radicals via the reaction of triplet acetone with isopropanol. While the direct photolysis of GO dispersions easily leads to degradation of the carbon lattice of GO and thus to a relatively low electric conductivity of the films of flakes, our indirect photoreduction of GO instead largely avoids the formation of defects, keeping the carbon lattice intact.Mechanisms of the direct and indirect photoreduction of GO have been elucidated and compared.Raman spectroscopy, XPS and conductivity measurements prove the efficiency of the indirect photoreduction in comparison with the state-of-the-art reduction method for GO (hydriodic acid/trifluoroacetic acid). The rapid reduction times and water solvent containing only small amounts of isopropanol and acetone may allow easy process up-scaling for technical applications and low-energy consumption.

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Pulse radiolytic study of the site of hydroxyl radical attack on aliphatic alcohols in aqueous solution

Cited by 364 publications

References 3 publications

Photophysics and photochemistry of natural waters with emphasis on radical probe development and application

Photophysics and photochemistry of natural waters with emphasis on radical probe development and application

Metal-catalyzed Oxidation of Histidine in Human Growth Hormone

High quality reduced graphene oxide flakes by fast kinetically controlled and clean indirect UV-induced radical reduction

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