Quantitative infrared analysis of mixtures of isotopically labeled gases

Rochkind, Mark M.

doi:10.1021/ac60260a034

Cited by 27 publications

(22 citation statements)

References 12 publications

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“…This peak was nearly absent following identical treatment of EFE reactions containing unlabeled 2OG. In analysis of reactions carried out under 18 O 2 , a new peak at m/z 136 (+2 units) had approximately the same intensity as the peak at m/z 134. We could not detect 18 O-labeled malate in analysis of EFE reactions lacking L-Arg, suggesting that it resulted from incorporation (into malate by PEPC/MD) of a -13 C 18 O 16 Ounit from the C1-derived (bi)carbonate product of the ethylene pathway.…”

Section: Transfer Of Oxygen From O2 To C1-derived (Bi)carbonatementioning

confidence: 81%

“…The observed origins of the oxygen incorporated into the ω-OH-acid products derived from 2OG, 2OA and 4-OH-2OG provide evidence for radical-carbonate coupling and imply that the first case above-stable carbonate coordination with free rotation-is operant. Approximately half of each ω-OHacid product harbored 18 O when generated in reactions under 18 O 2 in solvent of natural isotopic abundance (Fig. 4C and figs.…”

Section: Evidence Of Radical-carbonate Coupling and Concertedpolar Fr...mentioning

confidence: 99%

“…The 648 and 644 cm −1 features are also absent from spectra of gas taken from control reactions lacking L-Arg (yellow) or containing the Fe/2OG L-arginine 3-hydroxylase, VioC [from the biosynthetic pathway to viomycin (24)], in place of EFE (purple). Incorporation of 18 O from 18 O 2 into CO 2 is thus strictly associated with ethylene production. Comparison of the spectra from reactions containing 2OG 13 C-labeled either only at C1 (blue) or at C1-C4 (green) further validates this conclusion.…”

Section: Transfer Of Oxygen From O2 To C1-derived (Bi)carbonatementioning

confidence: 99%

“…In the spectra from reactions with 1-[ 13 C]-2OG (blue), features of both 16 O= 13 C= 18 O (from C1) and 16 O= 12 C= 18 O (from C2) are visible, and the peak of the 12 C mixed-oxygen isotopolog is slightly more intense, presumably because C2 is converted directly to CO 2 and need not lose an oxygen atom to enter the gas phase, as the C1-derived (bi)carbonate must do. In the corresponding spectra from the reaction with 1,2,3,4-[ 13 C 4 ]-2OG (green), only the peak for the 16 O= 13 C= 18 O mixed-oxygen isotopolog-now from both C1 and C2-is present, and it is correspondingly more intense than in the spectrum from the reaction with 1-[ 13 C]-2OG.…”

Section: Transfer Of Oxygen From O2 To C1-derived (Bi)carbonatementioning

confidence: 99%

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Hybrid radical-polar pathway for excision of ethylene from 2-oxoglutarate by an iron oxygenase

Copeland

Zhou

Schaperdoth

et al. 2021

Science

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Microbial ethylene-forming enzyme (EFE) converts the C3-C4 fragment of the ubiquitous primary metabolite, 2-oxoglutarate (2OG), to its namesake alkene product. This reaction is very different from the simple decarboxylation of 2OG to succinate promoted by related enzymes and has inspired disparate mechanistic hypotheses. We show that EFE produces stereochemically random (equal cis and trans) 1,2-[2H2]-ethylene from (3S,4R)-[2H2]-2OG, appends an oxygen from O2 upon the C1-derived (bi)carbonate, and can be diverted to ω-hydroxylated monoacid products by modifications to 2OG or the enzyme. These results implicate an unusual radical-polar hybrid mechanism involving iron(II)-coordinated acylperoxycarbonate and alkylcarbonate intermediates. The mechanism explains how EFE accesses a high-energy carboxyl radical to initiate its fragmentation cascade, and it hints at new capabilities of 2OG-dependent enzymes that may await discovery and exploitation.

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Section: Transfer Of Oxygen From O2 To C1-derived (Bi)carbonatementioning

confidence: 81%

Section: Evidence Of Radical-carbonate Coupling and Concertedpolar Fr...mentioning

confidence: 99%

Section: Transfer Of Oxygen From O2 To C1-derived (Bi)carbonatementioning

confidence: 99%

Section: Transfer Of Oxygen From O2 To C1-derived (Bi)carbonatementioning

confidence: 99%

See 2 more Smart Citations

Hybrid radical-polar pathway for excision of ethylene from 2-oxoglutarate by an iron oxygenase

Copeland

Zhou

Schaperdoth

et al. 2021

Science

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“…To confirm mechanistic aspects of the reaction chemistry, experiments were performed using CD 3 CHO as the substrate, under the same conditions as described earlier, specifically using the pin anode. An analysis of the difference spectrum obtained for such experiments shows evidence for the products CD 2 CO (2266.2, 2259.9, 2112.5, 861.0 and 849.2 cm −1 ), CD 3 H (1287.2, 1000.0 cm −1 ), DCCO (1989.9 cm −1 ), CCO (1973.7 and 1969.2 cm −1 ), HCO • (1863.5 cm −1 ), DCO • (1924.4 cm −1 ), and CO (2138.7 cm −1 ), the CD 2 = CHOD isotopomer of vinyl alcohol (2674.2, 2411.2, 1608.6, and 926.2 cm −1 ), and the ionic compounds Ar 2 H + (904.3 cm −1 ) and Ar 2 D + (643.2 cm −1 ) . Some additional very weak bands due to H/D atom addition chemistry may also be present but are insignificant relative to the major products that are observed.…”

Section: Resultsmentioning

confidence: 98%

Fourier transform infrared matrix‐isolation analysis of acetaldehyde fragmentation products after charge exchange with Ar^•+ under varied ionization density conditions

et al. 2011

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The products of the Ar(•+) charge exchange ionization of acetaldehyde have been isolated and compared with related photoionization results and computational work. Acetaldehyde has been used to assess the effect of varied ion density in the ionization region of the electron bombardment matrix isolation apparatus. The amount of acetaldehyde destruction has been measured for constant gas-sample composition and constant ionization current for two anode geometries: a pin anode and a plate anode. For the same ionization current, a pin-shaped anode demonstrates higher precursor molecule destruction efficiency (85%) than the plate-shaped anode (30%), resulting in substantial effect on the yield and quantity of isolated products. When the plate anode is used, the observed infrared products correspond to matrix-isolated carbon monoxide (CO), methane (CH(4)), ketene (CH(2)CO), ethynyloxy radical (HCCO), formyl radical (HCO(•)), acetyl radical (CH(3)CO(•)), vinyl alcohol (H(2)C = CH-OH), and cationic proton-bound dimer, Ar(2)H(+). When the pin anode is used, the same products are observed with different relative proportions and new absorption features corresponding to dicarbon monoxide (CCO) and methyl radical (CH(3)(•)) are observed. The surprising observation of infrared absorptions corresponding to vinyl alcohol along with low yield of products anticipated through the analysis of photoelectron-photoionization coincidence measurements suggests that the initially formed fragmentation products are able to further react within the matrix-isolation environment to influence observed product yields. Related experiments, using the isotopomer CD(3)CHO, suggest that the observed products are formed via radical-radical reactions that occur under the high pressure conditions of the matrix isolation environment.

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Matrix Isolation Spectroscopy in Atmospheric Chemistry

Viswanathan

Sankaran

Sundararajan

2000

Encyclopedia of Analytical Chemistry

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There is a growing concern about our environment and it has been realized that quick and definite measures are required if we are to preserve our planet for posterity. The rising level of greenhouse gases in the atmosphere and its consequent effect on the global climatic conditions, the depletion of stratospheric ozone, acid rain, and photochemical smog are some of the issues that have been addressed by scientists and policy makers the world over. Solutions to most environmental problems can be obtained only through collective efforts and, to ensure that such efforts are effective, it is necessary that policies and legislation are made based on scientific data on our ever‐changing environment. The data must provide information on the nature of trace constituents present in the different layers of the atmosphere, their concentrations, and their chemistry. A variety of experimental techniques have been used for this purpose, such as fluorescence spectroscopy, infrared (IR) and ultraviolet/visible (UV/VIS) absorption, Raman scattering, and photoacoustic spectroscopy. All these techniques exhibit some combination of the following features: multielement detection, low detection limits (DLs), specificity for an unequivocal identification of species, accuracy, and precision. One of the experimental techniques that has found important applications in the study of the atmosphere is matrix isolation (MI) spectroscopy. In this technique, the molecules of interest are diluted in a large excess of an inert gas and sprayed onto a cold substrate held at 10 K. Under these conditions, the molecules are trapped, isolated from each other and only surrounded by inert gas atoms. Such cold, isolated molecules yield spectra that have narrow spectral widths. Furthermore, if the trapped species are reactive molecules or radicals, they are likely to have extended lifetimes in the inert cage, thus allowing their chemistry and spectroscopy to be studied at leisure. These features of MI have made it particularly useful in the study of atmospheric chemistry. The high‐resolution capability enables one to use this technique as an analytical tool, as closely lying spectral features of different molecules can now be resolved – a feature that has been employed to identify and estimate trace constituents in the upper tropospheric and stratospheric samples. In conjunction with gas chromatography (GC), MI and Fourier transform infrared (FTIR), referred to as GC/MI/FTIR, offers a powerful tool with which to resolve isomeric forms of environmentally hazardous chemicals such as polycyclic aromatic hydrocarbons (PAHs), dioxins, and polychlorinated biphenyls (PCBs). Such isomeric resolution is essential, as it is well known that only certain isomeric forms are biologically active, whereas the others are not. In this respect, GC/MI/FTIR even scores over GC mass spectroscopy (MS). Analytical spectroscopy of matrix‐isolated species is also done using fluorescence spectroscopy, where again the advantage of high resolution enables one to resolve isomeric forms of compounds. Where the species of interest is a free radical, electron spin resonance (ESR) is the technique of choice to study the trapped species. This is a particularly powerful tool, as free radicals are known to play an important role in a number of atmospheric processes. Another aspect of MI spectroscopy is its ability to study reaction intermediates, a feature that has been employed to study the reaction mechanisms of atmospherically important chemical and photochemical reactions. All these aspects of the technique are discussed in this article, using examples.

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Quantitative infrared analysis of mixtures of isotopically labeled gases

Cited by 27 publications

References 12 publications

Hybrid radical-polar pathway for excision of ethylene from 2-oxoglutarate by an iron oxygenase

Hybrid radical-polar pathway for excision of ethylene from 2-oxoglutarate by an iron oxygenase

Fourier transform infrared matrix‐isolation analysis of acetaldehyde fragmentation products after charge exchange with Ar^•+ under varied ionization density conditions

Matrix Isolation Spectroscopy in Atmospheric Chemistry

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Quantitative infrared analysis of mixtures of isotopically labeled gases

Cited by 27 publications

References 12 publications

Hybrid radical-polar pathway for excision of ethylene from 2-oxoglutarate by an iron oxygenase

Hybrid radical-polar pathway for excision of ethylene from 2-oxoglutarate by an iron oxygenase

Fourier transform infrared matrix‐isolation analysis of acetaldehyde fragmentation products after charge exchange with Ar•+ under varied ionization density conditions

Matrix Isolation Spectroscopy in Atmospheric Chemistry

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Product

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Fourier transform infrared matrix‐isolation analysis of acetaldehyde fragmentation products after charge exchange with Ar^•+ under varied ionization density conditions