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Issue 63, 2020, Issue in Progress
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Characterization of organophosphatic brachiopod shells: spectroscopic assessment of collagen matrix and biomineral components

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Abstract

The shells of linguloid brachiopods such as Lingula and Discinisca are inorganic–organic nanocomposites with a mineral phase of calcium phosphate (Ca-phosphate). Collagen, the main extracellular matrix in Ca-phosphatic vertebrate skeletons, has not previously been clearly resolved at the molecular level in organophosphatic brachiopods. Here, modern and recently-alive linguliform brachiopod shells of Lingula and Discinisca have been studied by microRaman spectroscopy, Fourier transform infrared spectroscopy, field emission gun scanning electron microscopy, and thermal gravimetric analysis. For the first time, biomineralized collagen matrix and Ca-phosphate components were simultaneously identified, showing that the collagen matrix is an important moiety in organophosphatic brachiopod shells, in addition to prevalent chitin. Stabilized nanosized apatitic biominerals (up to ∼50 nm) permeate the framework of organic fibrils. There is a ∼2.5-fold higher wt% of carbonate (CO32−) in Lingula versus Discinisca shells. Both microRaman spectroscopy and infrared spectra show transient amorphous Ca-phosphate and octacalcium phosphate components. For the first time, trivalent moieties at ∼1660 cm−1 and divalent moieties at ∼1690 cm−1 in the amide I spectral region were identified. These are related to collagen cross-links that are abundant in mineralized tissues, and could be important features in the biostructural and mechanical properties of Ca-phosphate shell biominerals. This work provides a critical new understanding of organophosphatic brachiopod shells, which are some of the earliest examples of biomineralization in still-living animals that appeared in the Cambrian radiation.

Graphical abstract: Characterization of organophosphatic brachiopod shells: spectroscopic assessment of collagen matrix and biomineral components

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Supplementary files

Article information


Submitted
02 Sep 2020
Accepted
29 Sep 2020
First published
20 Oct 2020

This article is Open Access

RSC Adv., 2020,10, 38456-38467
Article type
Paper

Characterization of organophosphatic brachiopod shells: spectroscopic assessment of collagen matrix and biomineral components

O. B. A. Agbaje, S. C. George, Z. Zhang, G. A. Brock and L. E. Holmer, RSC Adv., 2020, 10, 38456
DOI: 10.1039/D0RA07523J

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