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DIATOM SILICA BIOMINERALIZATION: AT NANOSCALE LEVEL A CHEMICALLY UNIFORM PROCESS
Author(s) -
Vrieling E. G.,
Gieskes W. W.C.,
Beelen T. P. M.,
Van Santen R.A.
Publication year - 2000
Publication title -
journal of phycology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.85
H-Index - 127
eISSN - 1529-8817
pISSN - 0022-3646
DOI - 10.1046/j.1529-8817.1999.00001-207.x
Subject(s) - frustule , small angle x ray scattering , diatom , materials science , biomineralization , nanoscopic scale , scattering , amorphous solid , matrix (chemical analysis) , chemical engineering , silicon , synchrotron , crystallography , chemical physics , nanotechnology , optics , biology , composite material , chemistry , physics , metallurgy , engineering , botany
Using a high‐brilliance synchrotron X‐ray source, combined small‐ and wide‐angle X‐ray scattering (SAXS and WAXS) was applied to study nanoscale characteristics, in particular pore size in the range of 3 to 65 nm, of a variety of unialgal cultures of centric and pennate diatoms, and of mixed diatom populations sampled in the field. Results of scattering analysis were compared with details of pore size, structure and orientation visible at the electron microscopic level. WAXS patterns did not reveal any crystalline phase or features of microcrystallinity (resolution 0.07 to 0.51 nm), which implies a totally amorphous character of the SiO 2 matrix of the frustule material. SAXS data (resolution 3 to 65 nm) provided information on geometry, size, and distribution of pores in the silica. Overall, two pore regions were recognized that were common to the silica of all samples: the smallest (d less than 10 nm) regularly spaced and shaped spherically, the larger (up to 65 nm) being cylinders or slits. Apparently, at a nanoscale level diatomaceous silica is quite homologous among species, in agreement with the chemical principles of silica polymerization under the conditions of pH and precursor concentrations inside the silicon deposition vesicle. The final frustule “macro”‐morphology is of course species‐specific, being determined genetically. Synthetically‐derived MCM‐type silicas have a similarly organized pore distribution in an amorphous silica matrix as we found in all diatom species studied. We therefore suggest that organic molecules of a kind used as structure‐directing agents to produce these artificial silicas play a role in the nucleation of the silica polymerization reaction and the shaping of pore morphology inside the silicon deposition vesicle of diatoms. Structure‐directing molecules now await isolation from the SDV, followed by identification and characterisation by molecular techniques.