Description: The cause of massive blooms of Ethmodiscus rex laminated diatom mats (LDMs) in the eastern Philippine Sea (EPS) during the Last Glacial Maximum (LGM) remains uncertain. In order to better understand the mechanism of formation of E. rex LDMs from the perspective of dissolved silicon (DSi) utilization, we determined the silicon isotopic composition of single E. rex diatom frustules (δ30SiE. rex) from two sediment cores in the Parece Vela Basin of the EPS. In the study cores, δ30SiE. rex varies from −1.23‰ to −0.83‰ (average −1.04‰), a range that is atypical of marine diatom δ30Si and that corresponds to the lower limit of reported diatom δ30Si values of any age. A binary mixing model (upwelled silicon versus eolian silicon) accounting for silicon isotopic fractionation during DSi uptake by diatoms was constructed. The binary mixing model demonstrates that E. rex dominantly utilized DSi from eolian sources (i.e., Asian dust) with only minor contributions from upwelled seawater sources (i.e., advected from Subantarctic Mode Water, Antarctic Intermediate Water, or North Pacific Intermediate Water). E. rex utilized only ~24% of available DSi, indicating that surface waters of the EPS were eutrophic with respect to silicon during the LGM. Our results suggest that giant diatoms did not always use a buoyancy strategy to obtain nutrients from the deep nutrient pool, thus revising previously proposed models for the formation of E. rex LDMs.

Description: The knowledge of accurate bond strengths is a fundamental basis for a proper analysis of chemical reaction mechanisms. Quantum chemical calculations at different levels of theory have been used to investigate heterolytic Fe–O and Fe–S bond energies of (meta-substituted phenoxy)dicarbonyl(η 5 -cyclopentadienyl) iron [ m -G-C 6 H 4 OFp ( )] and (meta-substituted benzenethiolato)dicarbonyl(η 5 -cyclopentadienyl) iron [ m -G-C 6 H 4 SFp ( )] complexes. In this study, Fp is (η 5 -C 5 H 5 )Fe(CO) 2 , and G is NO 2 , CN, COMe, CO 2 Me, CF 3 , Br, Cl, F, H, Me, MeO, and NMe 2 . The results show that Tao–Perdew–Staroverov–Scuseria and Becke's power-series ansatz from 1997 with dispersion corrections functionals can provide the best price/performance ratio and accurate predictions of Δ H het (Fe–O)'s and Δ H het (Fe–S)'s. The excellent linear free energy relations [ r  = 1.00 (g, 1e), 1.00 (g, 2b)] among the ΔΔ H het (Fe–O)'s and δΔ G 0 of O H bonds of m -G-C 6 H 4 OH or ΔΔ H het (Fe–S)'s and Δp K a 's of S H bonds of m -G-C 6 H 4 SH imply that the governing structural factors for these bond scissions are similar. And, the linear correlations [ r  = −0.97 (g, 1 g), −0.97 (g, 2 h)] among the ΔΔ H het (Fe–O)'s or ΔΔ H het (Fe–S)'s and the substituent σ m constants show that these correlations are in accordance with Hammett linear free energy relationships. The inductive effects of these substituents and the basis set effects influence the accuracy of Δ H het (Fe–O)'s or Δ H het (Fe–S)'s. The ΔΔ H het (Fe–O)'s(g) (1) and ΔΔ H het (Fe–S)'s(g)(2) follow the capto-dative Principle. The substituent effects on the Fe–O bonds are much stronger than those on the less polar Fe–S bonds. Insight from this work may help the design of more effective catalytic processes. Copyright © 2016 John Wiley & Sons, Ltd. The heterolytic Fe–O and Fe–S bond dissociation energies of 12 meta-substituted phenoxydicarbonyl(η 5 -cyclopentadienyl) iron and 12 (meta-substituted benzenethiolato)dicarbonyl(η 5 -cyclopentadienyl) iron were studied using density functional theory methods with large basis sets. The results show that Tao–Perdew–Staroverov–Scuseria and Becke's power-series ansatz from 1997 with dispersion corrections functionals can provide the best price/performance ratio and accurate predictions of Δ H het (Fe–O)′s and Δ H het (Fe–S)'s. Density functional theory methods satisfactorily predict the substituent effects on Δ H het (Fe–O)'s and Δ H het (Fe–S)'s. The ΔΔ H het (Fe–O)'s(g)(1) and ΔΔ H het (Fe–S)'s(g)(2) follow the capto-dative principle. The substituent effects on the Fe–O bonds are much stronger than those on the less polar Fe–S bonds.

Description: The knowledge of accurate bond strengths is a fundamental basis for a proper analysis of chemical reaction mechanisms. Quantum chemical calculations at different levels of theory have been used to investigate heterolytic Fe–O and Fe–S bond energies of para-substituted phenoxydicarbonyl( η 5 -cyclopentadienyl) iron [ p -G-C 6 H 4 O( η 5 -C 5 H 5 )Fe(CO) 2 , abbreviated as p -G-C 6 H 4 OFp ( ), where G = NO 2 , CN, COMe, CO 2 Me, CF 3 , Br, Cl, F, H, Me, MeO, and NMe 2 ] and para-substituted benzenethiolatodicarbonyl( η 5 -cyclopentadienyl) iron [ p -G-C 6 H 4 S( η 5 -C 5 H 5 )Fe(CO) 2 , abbreviated as p -G-C 6 H 4 SFp ( )] complexes. The results show that BP86 and TPSSTPSS can provide the best price/performance ratio and more accurate predictions in the study of Δ H het (Fe–O)'s and Δ H het (Fe–S)'s. The excellent linear free-energy relations [ r  = 0.99 (g, 1a), 1.00 (g, 2b)] among the ΔΔ H het (Fe–O)'s and Δp k a 's of O–H bonds of p -G-C 6 H 4 OH or ΔΔ H het (Fe-S)'s and Δp k a 's of S–H bonds of p -G-C 6 H 4 SH imply that the governing structural factors for these bond scissions are similar. And the linear correlations [ r  = −0.99 (g, 1g), −0.98 (g, 2h)] among the ΔΔ H het (Fe-O)'s or ΔΔ H het (Fe-S)'s and the substituent σ p − constants show that these correlations are in accordance with Hammett linear free-energy relationships. The polar effects of these substituents and the basis set effects influence the accuracy of Δ H het (Fe–O)'s or Δ H het (Fe–S)'s. ΔΔ H het (Fe–O)'s(g) ( ) and ΔΔ H het (Fe–S)'s(g)( ) follow the Capto-dative principle. The substituent effects on the Fe–O bonds are much stronger than those on the less polar Fe–S bonds. Insight from this work may help the design of more effective catalytic processes. Copyright © 2013 John Wiley & Sons, Ltd. The heterolytic Fe–O bond dissociation energies of 12 para-substituted phenoxydicarbonyl( η 5 -cyclopentadienyl) iron and 12 para-substituted benzenethiolatodicarbonyl( η 5 -cyclopentadienyl) iron were studied using Hartree–Fock and density functional theory methods with large basis sets. The results show that BP86 and TPSSTPSS can provide the best price/performance ratio and more accurate predictions in the study of Δ H het (Fe–O)'s and Δ H het (Fe–S)'s. Density functional theory methods satisfactorily predict the remote substituent effects on Δ H het (Fe–O)'s and Δ H het (Fe–S)'s. ΔΔ H het (Fe–O)'s(g) (1) and ΔΔ H het (Fe–S)'s(g)(2) follow the Capto-dative principle. The substituent effects on the Fe–O bonds are much stronger than those on the less polar Fe–S bonds.