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Structure of low-order hemimorphite produced in a Zn-rich environment by cyanobacterium Leptolingbya frigida

Daniela Medas, Carlo Meneghini, Francesca Podda, Costantino Floris, Mariano Casu, Maria Antonietta Casu, Elodia Musu and Giovanni De Giudici
Structure of low-order hemimorphite produced in a Zn-rich environment by cyanobacterium Leptolingbya frigida
American Mineralogist (May 2018) 103 (5): 711-719


Microbes play a fundamental role in the precipitation of silicate biominerals, thereby affecting the Si geochemical cycle. The fine mechanisms ruling biomineralization are not yet fully understood, and their microscopic structures can offer deep insight into their processes of formation, reactivity and stability. In this study, a Zn silicate biomineral, extracellularly produced by cyanobacterium Leptolingbya frigida, was investigated combining nuclear magnetic resonance (NMR), Zn K-edge X-ray absorption spectroscopy (XAS) and other complementary techniques. (super 29) Si magic angle spinning and (super 29) Si/ (super 1) H cross polarization magic angle spinning analysis, Fourier transform infrared spectroscopy (FTIR) and XAS analysis revealed a poorly crystalline phase closely resembling hemimorphite [Zn (sub 4) Si (sub 2) O (sub 7) (OH) (sub 2) .H (sub 2) O]. Zn K-edge extended X-ray absorption fine structure (EXAFS) provided further structural details, revealing that the Zn-O-Si interatomic distances were 7-8% shorter than the abiotic mineral. (super 13) C NMR spectra analysis was conducted to investigate the composition of the Zn silicate biomineral organic matrix, and results revealed that C atoms occurred in several functional groups such as carbonyl carbons, C rings, O-aliphatic chains, N-aliphatic chains, and aliphatic chains. Under slightly alkaline conditions, bacterial cell walls exhibited fundamental control on the biomineralization process by binding Zn ions and forming Zn-O-Si bonds. In this way, L. frigida cell walls served as a reactive surface for the precipitation of this Zn sorosilicate, hindering the condensation of silicon dimers. Moreover, we found a (super 29) Si NMR band at 85 ppm that could be attributed to a (C (sub 3) H (sub 6) O (sub 3) ) (sub 2) Si complex. This complex could play a role in the control of silicon polymerization, with implications for Si biomineralization processes.

ISSN: 0003-004X
EISSN: 1945-3027
Serial Title: American Mineralogist
Serial Volume: 103
Serial Issue: 5
Title: Structure of low-order hemimorphite produced in a Zn-rich environment by cyanobacterium Leptolingbya frigida
Affiliation: University of Cagliari, Department of Chemical and Geological Sciences, Cagliari, Italy
Pages: 711-719
Published: 201805
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
References: 80
Accession Number: 2018-052687
Categories: Mineralogy of silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 2 tables
N38°49'60" - N41°30'00", E08°15'00" - E09°45'00"
Secondary Affiliation: University of Roma Tre, ITA, ItalyScientific and Technological Park of Sardinia, ITA, Italy
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute. Abstract, copyright, Mineralogical Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 2018
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