Molecular orbital modeling of aqueous organosilicon complexes

Implications for silica biomineralization

J. D. Kubicki, Peter J. Heaney

Research output: Contribution to journalArticle

23 Citations (Scopus)

Abstract

Researchers recently have proposed that hypercoordinate Si-organic complexes can form in biologically relevant fluids, and they have reported the first evidence for a transient organosilicon complex generated within the life cycle of an organism (Kinrade et al., 2001b, 2002). These interpretations are based upon peak assignments of 29Si NMR spectra that invoke Si-polyol (e.g., Si-sorbitol) complexes with Si in five- and six-fold coordination states. However, ab initio analyses of the proposed organosilicon structures do not reproduce the experimentally observed 29Si NMR chemical shifts (Sahai and Tossell 2001, 2002 and this work). In place of the originally proposed structures, we have modeled one of the observed δ29Si values with a 5-fold Si-disorbitol complex involving 5-membered ring configurations (i.e., Si-O-C-C-O). The calculated δ29Si value of this new structure closely matches the observed δ29Si peaks in the -100 to -102 ppm range. Likewise, 29Si NMR peaks near -144 ppm were well fit by a model complex in which a 6-fold Si was complexed to three sorbitol molecules in 5-membered ring configurations. The ability to reproduce the observed NMR peaks using molecular orbital calculations provides support for the controversial role of hypercoordinate organosilicon species in the uptake and transport of silica by biological systems. The existence of such complexes in turn may explain other puzzles in Si biogeochemistry, such as the persistence of dissolved silica in concentrated biological fluids, the biofractionation of Si isotopes, and fractionation of Ge from Si.

Original languageEnglish (US)
Pages (from-to)4113-4121
Number of pages9
JournalGeochimica et Cosmochimica Acta
Volume67
Issue number21
DOIs
StatePublished - Nov 1 2003

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Biomineralization
biomineralization
Molecular orbitals
Silicon Dioxide
nuclear magnetic resonance
silica
Nuclear magnetic resonance
fold
Sorbitol
modeling
Biogeochemistry
Orbital calculations
Fluids
fluid
Chemical shift
Biological systems
biogeochemistry
Fractionation
Isotopes
Life cycle

All Science Journal Classification (ASJC) codes

  • Geochemistry and Petrology

Cite this

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abstract = "Researchers recently have proposed that hypercoordinate Si-organic complexes can form in biologically relevant fluids, and they have reported the first evidence for a transient organosilicon complex generated within the life cycle of an organism (Kinrade et al., 2001b, 2002). These interpretations are based upon peak assignments of 29Si NMR spectra that invoke Si-polyol (e.g., Si-sorbitol) complexes with Si in five- and six-fold coordination states. However, ab initio analyses of the proposed organosilicon structures do not reproduce the experimentally observed 29Si NMR chemical shifts (Sahai and Tossell 2001, 2002 and this work). In place of the originally proposed structures, we have modeled one of the observed δ29Si values with a 5-fold Si-disorbitol complex involving 5-membered ring configurations (i.e., Si-O-C-C-O). The calculated δ29Si value of this new structure closely matches the observed δ29Si peaks in the -100 to -102 ppm range. Likewise, 29Si NMR peaks near -144 ppm were well fit by a model complex in which a 6-fold Si was complexed to three sorbitol molecules in 5-membered ring configurations. The ability to reproduce the observed NMR peaks using molecular orbital calculations provides support for the controversial role of hypercoordinate organosilicon species in the uptake and transport of silica by biological systems. The existence of such complexes in turn may explain other puzzles in Si biogeochemistry, such as the persistence of dissolved silica in concentrated biological fluids, the biofractionation of Si isotopes, and fractionation of Ge from Si.",
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Molecular orbital modeling of aqueous organosilicon complexes : Implications for silica biomineralization. / Kubicki, J. D.; Heaney, Peter J.

In: Geochimica et Cosmochimica Acta, Vol. 67, No. 21, 01.11.2003, p. 4113-4121.

Research output: Contribution to journalArticle

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