非晶態碳酸鈣於仿生條件的相穩定與演化

生物礦化指生物體內產生礦物質的過程，舉凡在貝殼、珍珠、珊瑚、骨頭、牙齒……等礦物可發現此現象；從奈米尺寸到宏觀世界，將硬物質和軟物質、無機與有機材料組合起來。本研究採取仿生條件提供無晶相碳酸鈣ACC的相演化環境，接續嘗試以原子力顯微鏡與cryo-TEM追蹤成核過程，並提供微脂體鍍膜限制空間和鎂離子以抑制晶體的長晶和相轉變，水溶液中能長時間穩定的含鎂非晶態碳酸鈣。改良系統以脂質模板(lipid templating)進行實驗，於室溫無溶劑環境隨Aging時間增加，以IR與XRD觀察到含鎂非晶態碳酸鈣; MgACC高度選擇性單一相轉變至Mg-calcite現象，並且以HR-FETEM追蹤到晶體由無晶相轉變成部分晶格紋路，進而再轉變為高度有序晶格紋路，SAED說明為奈米尺度的單晶Mg-calcite。於室溫無水溶液之Aging過程以SEM鑑定由奈米粒子聚集成鉅觀球體，將球體進行FIB後TEM的暗場結果得知奈米單晶具有高度有序位相的排列。後續以同輻光源XANES量測Ca的L edge與熱分析(TGA、DSC)實驗，說明lipid模板系統製備之MgACC經歷室溫下以較低活化能脫去結構水的固態相轉變路徑。為解釋水合能高的含MgACC能於Aging過程脫去結構水產生晶相，進而提出假設為lipid藉由鍵結鎂將結構水帶出礦物，在SEM-EDS表面量測得較多鎂含量得以之支持。固態NMR鑑定得知lipid因為與碳酸鈣鍵結造成兩種磷的環境，同輻XANES P-K edge說明lipid的phosphate與MgACC具有化學吸附關係。隨Aging時間增加，lipid-Mg-calcite球體外隨著含鎂量較高之lipid首先生成lipid與奈米粒子組成之有機膠體纖維柱狀型態，引發球體的黏附與融合而於Aging時間增加得到數百~數千微米尺度骨針狀晶型，近似生物體骨骼的相轉變與晶型演化現象。最終以洋菜膠與天門冬胺酸提供限制空間條件，促使ACC相轉成calcite與具有掌性之vaterite碳酸鈣，說明碳酸鈣形貌具有多變特徵。

關鍵字

生物礦化；含鎂方解石；介晶體；自組裝；固態相轉變

並列摘要

Biomineralization refers to the biological process through which highly ordered inorganic materials with hierarchical structures are formed in living organisms. Currently, the mechanisms of biomineralization remains largely unknown. In this work, we used AFM to track the mineralization process of magnesium containing amorphous calcium carbonate (MgACC). The lipid templating method was used to synthesize and stable the MgACC for more than fifteen hours. For a longer setting time of lipid-MgACC in the solution, high Mg-calcite was also observed. The XRD and FT-IR measurements showed that lipid-MgACC powder would transform to high Mg-calcite during the aging process without heating and solvent. HR-TEM and SAED were used to characterize the fringes of Mg-calcite in this aging process. The nano-sized crystallinities of Mg-calcite could self-assemble to form spherical particles of 20 m with aging. Focused ion beam milling and dark field TEM imaging were performed to observe the amorphous region and highly co-orientated nano-crystallites of Mg-calcite inside the microspheres. From Ca-L edge XANES and low temperature crystallization peak as revealed by the TGA-DSC measurements, we infer that lipids helped remove the structure water of Mg-ACC in the aging process. On the basis of all the experimental data, it is suggested that the Mg-calcite crystallization process occurred via the solid-state transformation pathway. We hypothesize that lipid bound Mg-containing nanoparticles were extruded with the structure water and formed the lecithin organogel fiber. The fibers were highly adhesive for the spherical Mg-calcite. As the aging time increased, the microspheres of Mg-calcite aggregated along the fiber and consequently fused to form the long spicule. Lastly, chiral morphology of calcium carbonate was obtained in agarose gel in the presence of aspartic acids, demonstrating the versatile morphology of calcium carbonate.

並列關鍵字

Biomineralization ； High magnesium calcite ； Mesocrystal ； Self-assembly ； Spicule ； Solid-state transformation.

參考文獻

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非晶態碳酸鈣於仿生條件的相穩定與演化

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