부산대학교 도서관

• H 4 SiO 4 0 complexation with organic ligands can increase Si coordination number. • This coordination change provokes extreme Si isotope fractionation. • Calculated and measured equilibrium fractionation factors are in excellent agreement. • Δ e q 30 Si of −19‰ between Si(IV) and Si(VI), and −10‰ between Si(IV) and Si(V). • Strong impact of Si coordination change on Si isotopes signatures in silica biominerals? A combination of theoretical predictions and isotopic equilibration experiments using the three-isotope method have been performed to assess Si isotope fractionation among minerals, and aqueous species in the presence of dissolved catechol. Aqueous Si in abiotic ambient temperature aqueous solutions is dominated by the IV-coordinated H 4 SiO 4 0 species, but the presence of aqueous catechol provokes the formation of a VI-fold Si-catechol complex. Results show an equilibrium Si fractionation factor of ∼19‰ between the VI-fold coordinated Si-catechol complex and the IV-fold coordinated aqueous silicic acid, an amplitude never previously observed for silicon. The fractionation between V-fold Si-organo complexes (with diolate, glyconate or methyllactate groups) and silicic acid has also been estimated through theoretical predictions to be about −10‰. These extreme fractionations can be used to improve our ability to interpret the Si isotope compositions of natural solids, and in particular those associated with marine silica biomineralization processes (e.g. sponge spicules). [ABSTRACT FROM AUTHOR]