含鎂非晶相碳酸鈣的化學組成分析－熱力學參數探討與模擬

Modeling of the Chemical Composition of Mg-stabilized Amorphous Calcium Carbonate by Thermodynamic Parameters

張君宇(Chun-Yu Chang)

指導教授 ： 陳振中

國立臺灣大學/理學院/化學研究所/碩士(2017年)

https://doi.org/10.6342/NTU201704272

摘要

含鎂非晶相無序結構碳酸鈣 (MgACC) 在生物體中常被用來做為前驅物儲存，鎂的進入使得 ACC 相轉的瓶頸步驟脫水反應不易發生，大幅提高 ACC 的穩定度。不同物種及不同組織中 MgACC 的含鎂量差異甚大，含鎂量可從 5% 至 54%，組成的差異除了影響 ACC穩定度外，也調控了相轉晶相 calcite 中的鎂含量。生物體如何精準的控制 MgACC 含鎂量一直是科學家的疑問，本研究建立熱力學平衡的模型嘗試探討影響 MgACC 的含鎂量的因子，首先從 NMR 光譜研究 MgACC 的結構，發現 MgACC 是由無序結構碳酸鎂 (AMC) 和無序結構碳酸鈣 (ACC) 以奈米團簇聚集而成，因此在熱力學討論中，MgACC 的沉澱可以視為 AMC 和 ACC 兩種物種的平衡。實驗上利用微量混合器和緩衝溶液建立一個準確且可重複的系統，在不同 pH 值下製備不同含鎂量的 MgACC 樣品，並量測 AMC 和 ACC 的溶解度平衡常數，帶入熱力學平衡系統進行計算，擬合結果與實驗有良好的吻合，可得知在本研究中 MgACC 的生成確實是由熱力學平衡調控。除此之外，我們亦觀察到 AMC 溶解度隨 pH 值改變，其原因亦可用熱力學參數粒徑大小來解釋。因此我們或許可以透過這個模型進一步去了解生物體內調控含鎂量的機制。

關鍵字

碳酸鈣 ； 熱力學模型 ； 碳酸鎂

並列摘要

Amorphous calcium carbonate(ACC) has been established as the key precursor phase in the biogenic mineralization process of calcareous materials. Most biogenic ACCs contain Mg 2+ ions and the Mg content is rather specific in different species and tissues. It has long been an enigma how organisms control the Mg content of biogenic ACC. Using a pH buffer and a micromixer, Mg-stabilized amorphous calcium carbonates(MgACCs) were synthesized under well-controlled chemical conditions. In this study, we develop a thermodynamic equilibrium model to investigate the composition of MgACCs under different pH conditions. Solid-state NMR data revealed that there are two types of carbonate ions in MgACC, whose short range orders were identical to those of ACC and amorphous magnesium carbonate(AMC). Thus, the precipitation of MgACC could be contributed from the combination of ACC and AMC in our model. This model also include a set of ten chemical equilibria with the database of Pitzer equations. We successfully rationalize the chemical composition of MgACC with the combination of equilibrium model and thermodynamic parameters.

並列關鍵字

calcium carbonate ； magnesium carbonate ； thermodynamic model

參考文獻

參考文獻

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