Hyperfine splittings from naturally occurring sulfur-33 in electron paramagnetic resonance spectra

Sullivan, Paul D.

doi:10.1021/ja01016a003

Cited by 71 publications

(21 citation statements)

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“…Subsequent triplet-singlet conversion allows for the radical pair to combine and thus form a polysulfide (RSSS n R) product. Such products that are formed through the triplet pathway are therefore enriched in 33 S. Our mechanism is supported by prior ESR measurements (24,25), which show that disulfide radicals have 33 S hyperfine structure values (∼10 G) similar to sulfur nuclei that exhibit MIE. The experimental products also preserve evidence for significant mixing and classical isotope effects that influence Δ 36 S in a mass-dependent manner (21,23), supporting this small anomaly as the cause of 36 S variation reported in ref.…”

Section: Resultssupporting

confidence: 80%

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Evidence of magnetic isotope effects during thermochemical sulfate reduction

Oduro

Harms

Sintim

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

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Thermochemical sulfate reduction experiments with simple amino acid and dilute concentrations of sulfate reveal significant degrees of mass-independent sulfur isotope fractionation. Enrichments of up to 13‰ for 33 S are attributed to a magnetic isotope effect (MIE) associated with the formation of thiol-disulfide, ion-radical pairs. Observed 36 S depletions in products are explained here by classical (mass-dependent) isotope effects and mixing processes. The experimental data contrasts strongly with multiple sulfur isotope trends in Archean samples, which exhibit significant 36 S anomalies. These results support an origin other than thermochemical sulfate reduction for the mass-independent signals observed for early Earth samples.anomalous | sulfur radical | thermolysis | spin-selective | hyperfine coupling S ince the report by Farquhar et al., (1) that significant deviations from the terrestrial fractionation line are observed in samples older than approximately 2.32-2.45 Ga (2, 3), considerable effort has been dedicated to identifying the origin and significance of this signal (4-10). The mass-independent signal in these ancient samples is expressed as variations in both Δ 33 S and Δ 36 S (1).* Given the observations that gas-phase reactions can produce mass-independent signals for both Δ 33 S and Δ 36 S, the first studies on this subject attributed this ancient signal to photolytic reactions in the early atmosphere. Subsequent studies also pointed out that the mass-independent reactions may also be produced by variations in the spectrum of light that drives atmospheric photolytic reactions (10-12), and other studies speculated that liquid phase reactions involving weakly bound transition states may account for these variations (7,13).In a recent report, Watanabe et al. (7) demonstrated that high temperature reduction of sulfate using alanine and glycine as organic substrates caused moderate mass-independent sulfur isotope fractionations. These authors did not identify the origin of the effect, but suggested that it was either a magnetic isotope effect (MIE) (14) or another type of isotope effect accompanying heterogeneous reactions such as adsorption of S-bearing compounds on surfaces of solids (13). Magnetic isotope effects are expressed in rare cases for isotopes with nuclear magnetic moments, like 13 C, 17 O, 29 Si, 199 Hg, 201 Hg, 73 Ge, 235 U, and 33 S (14, 15, 16). The effect is expressed when the lifetime of a radical pair is sufficient for hyperfine coupling between magnetic nuclei and unpaired electrons to influence interconversions between singlet and triplet states. This coupling in turn changes the proportion of reactive intermediates that can participate in spin-selective reactions. The 33 S nucleus has a spin of 3∕2 and a magnetic moment of 0.643 nuclear magnetons and has been implicated in at least one well-characterized example of a 33 S MIE (14,(17)(18)(19). The alternative suggestion relates to a proposal that anomalous isotope effects may be associated with heterogeneous reactions as a resu...

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Section: Resultssupporting

confidence: 80%

“…The mechanistic aspects for the origin of 33 S anomalies via disulfide ion-radical pair reaction routes have been proposed through multiple sulfur isotope measurements and 33 S electron spin resonance (ESR) spectroscopic evidence (24,25).…”

mentioning

confidence: 99%

Evidence of magnetic isotope effects during thermochemical sulfate reduction

Oduro

Harms

Sintim

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

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“…In a higher concentration spectrum (~10 -3 M), the hyperfine splitting was lost but the signal caused by M s = ± 3/2 of 33 S (natural isotopic abundance, 0.75%) became observable. The obtained value of a s was 0.86 mT (29), which was smaller than that (0.92 mT) for thianthrene radical cation (23' + ) (30). This result indicates that the spin density on the sulfur atom of 21" + is lower than that of 23" + and therefore the BCO units are even more effective than the fused benzene rings in delocalizing not only the positive charge but also spin density.…”

Section: Dithiinsmentioning

confidence: 64%

Super-Stabilization of π-Conjugated Cations by Annelation to Bicyclic Frameworks

Komatsu

2007

ACS Symposium Series

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As exemplified by the synthesis of the extraordinarily stable tropylium ion, the annelation of cyclic π-conjugated cations with rigid σ-framework, bicyclo[2.2.2]octene, has been found to be an effective method for creation of unusually stable cationic π-conjugated systems. By using this method, detailed X-ray crystallographic studies have been conducted for the monomeric radical-cation salts of hydrocarbons such as cyclooctatetraene and a series of benzenoid condensed aromatics and of sulfur containing compounds such as thiophene, dithiins, and oligothiophenes. Some of these species can be further oxidized to dications, and also undergo intriguing rearrangements to cationic species with novel structures. The results are well interpreted by the use of theoretical calculations. 32

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“…This idea has been criticized on the grounds that the promotion energy p -+ d is expected to be too high in divalent sulphur to allow a significant participation of the d orbitals to the 7r bonding [5]. However, both models were employed in the present investigation, using the parameters proposed by Sullivan [6] for the p model: as = ~ + 1.20fi and ties = 0"65fi; and those suggested by Longuet-Higgins [2] for the d model, where the sulphur atom closely resembles an ethylene molecule: ~' = c~ee , fi'= fiec and ties = 0"8flee. The effect of twisting the phenyl groups was accounted for by using the expression fi(O)= fi cos O, 0 being the angle of the out-of-plane rotation.…”

Section: Molecular Orbital Calculationsmentioning

confidence: 99%

“…Only the carbon atoms in the heterocyclic ring can display sufficiently high constants to match the experimental values. Because of molecular symmetry the 41.5 M~z coupling was assigned to the carbon atom in position 4 and therefore the 28.6 MrIz coupling had to be attributed to the four remaining carbons (2,3,5,6), which are then accidentally degenerate. The calculated values are 28.3 and 29.2 for C(4) and -26.4 and -26.9 for C(3), C(5) whether the p or the d orbital model is used.…”

Section: Molecular Orbital Calculationsmentioning

confidence: 99%

Proton,¹³C and³³S coupling constants in the electron resonance spectrum of the 2,4,6-triphenylthiapyryl radical

et al. 1970

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The E.S.R. spectrum of the 2,4,6-triphenylthiapyryl radical is interpreted by investigating deutero and ~3S-enriched derivatives. In some spectra of the latter, several laC as well as 3aS satellite lines were detected and their coupling constants determined. The spin density distribution was calculated by using standard p and d-orbital models. Satisfactory results are obtained if the phenyl groups are assumed to be twisted from the heterocyclic plane.

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Hyperfine splittings from naturally occurring sulfur-33 in electron paramagnetic resonance spectra

Cited by 71 publications

References 5 publications

Evidence of magnetic isotope effects during thermochemical sulfate reduction

Evidence of magnetic isotope effects during thermochemical sulfate reduction

Super-Stabilization of π-Conjugated Cations by Annelation to Bicyclic Frameworks

Proton,¹³C and³³S coupling constants in the electron resonance spectrum of the 2,4,6-triphenylthiapyryl radical

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Hyperfine splittings from naturally occurring sulfur-33 in electron paramagnetic resonance spectra

Cited by 71 publications

References 5 publications

Evidence of magnetic isotope effects during thermochemical sulfate reduction

Evidence of magnetic isotope effects during thermochemical sulfate reduction

Super-Stabilization of π-Conjugated Cations by Annelation to Bicyclic Frameworks

Proton,13C and33S coupling constants in the electron resonance spectrum of the 2,4,6-triphenylthiapyryl radical

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Proton,¹³C and³³S coupling constants in the electron resonance spectrum of the 2,4,6-triphenylthiapyryl radical