Aristotle University of Thessaloniki, School of Physics, Section of Solid State Physics, 54124 Thessaloniki, Greece.
Aristotle University of Thessaloniki, School of Physics, Section of Solid State Physics, 54124 Thessaloniki, Greece.
J Struct Biol. 2020 Sep 1;211(3):107557. doi: 10.1016/j.jsb.2020.107557. Epub 2020 Jun 27.
The exoskeleton of crustaceans consists of chitin biopolymers where the embedded inorganic biominerals, mainly CaCO, affect strongly its mechanical properties. Raman and Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopies and Transmission Electron Microscopy (TEM) are applied to investigate the CaCO structure in various parts of the Calappa granulata crab exoskeleton. The shape of the main Raman peak of CaCO reveals the presence of two phases which are identified as calcite and amorphous calcium carbonate (ACC). The relative concentration of the two phases in various parts of the exoskeleton is determined from the area ratio under the corresponding peaks. The results of the Ca L-edge NEXAFS analysis are in line with the Raman findings, since the energy separation of peaks that appear in the lower frequency region of the main L and L peaks due to crystal field splitting, is directly related to the percentage of the ACC phase in the total CaCO mineral content. The C K-edge spectra are used for the determination of the extent of calcification of the exoskeleton. Furthermore, dark and bright field TEM images reveal the presence of nanocrystallites with an average size of 20 nm. The structure of the nanocrystallites, as derived from the Selected Area Electron Diffraction patterns, is calcite. The results suggest that ACC plays a structural role in the exoskeleton of Calappa granulata.
甲壳类动物的外骨骼由几丁质生物聚合物组成，其中嵌入的无机生物矿物质主要为 CaCO，强烈影响其机械性能。拉曼和近边 X 射线吸收精细结构（NEXAFS）光谱和透射电子显微镜（TEM）用于研究 Calappa granulata 蟹外骨骼各个部位的 CaCO 结构。CaCO 的主要拉曼峰的形状表明存在两种相，分别鉴定为方解石和无定形碳酸钙（ACC）。通过对应峰下的面积比确定外骨骼各个部位两种相的相对浓度。Ca L 边 NEXAFS 分析的结果与拉曼发现一致，因为由于晶场分裂，出现在主 L 和 L 峰低频区域的峰的能量分离与 ACC 相在总 CaCO 矿物含量中的百分比直接相关。C K 边谱用于确定外骨骼的钙化程度。此外，暗场和明场 TEM 图像显示存在平均粒径为 20nm 的纳米晶。从选区电子衍射图谱得出，纳米晶的结构为方解石。结果表明，ACC 在 Calappa granulata 的外骨骼中起结构作用。
