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標題: | 含鎂非晶態碳酸鈣之製備與鑑定及相轉變探討 Characterization of Structure and Phase Transformation of Magnesium Amorphous Calcium Carbonate |
作者: | Cang-Jie Lin 林蒼傑 |
指導教授: | 陳振中(Chun-Chung Chan) |
關鍵字: | 生物礦化,非晶態碳酸鈣,固態核磁共振,鎂-25固態核磁共振, Biomineralization,Amorphous calcium carbonate,solid-state NMR spectroscopy,Mg-25 NMR, |
出版年 : | 2013 |
學位: | 碩士 |
摘要: | 在碳酸鈣的許多晶態中,方解石和文石是常見的生物礦化物。先前的研究指出,非晶態碳酸鈣不只是生物體內的方解石和文石的前驅物,也是生物體內暫時儲存碳酸鈣時的形態。生物體內的非晶態碳酸鈣含有大量的鎂,且在生物體外的實驗結果指出鎂離子可以穩定非晶態碳酸鈣。然而對於含鎂的非晶態碳酸鈣的結構性質仍然只有非常少的了解,因此我們對於研究此類含鎂的非晶態碳酸鈣的結構性質有濃厚的興趣。在這個研究中,我們利用雙向微量混合器建立一個再現性高的實驗系統,合成出不同含鎂比例的非晶態碳酸鈣。我們利用感應偶合電漿質譜儀和X-ray能量散射光譜儀測量出不同含鎂比例非晶態碳酸鈣的鎂含量在0.2到0.81之間。我們利用13C和25Mg的固態核磁共振技術來測量這種含鎂非晶態碳酸鈣,同時我們也使用傅立葉轉換紅外光光譜儀、掃描式電子顯微鏡和穿透式電子顯微鏡來鑑定我們的樣品。
在pH 8.75時,13C核磁共振光譜中顯示,即使是不同的含鎂比例,還是有部分的碳酸氫根與碳酸根共存。我們在13C同核相關光譜中,發現碳酸根與碳酸氫根的平均距離超過0.6奈米,因此我們排除了碳酸氫根平均散佈在非晶相碳酸鈣中的可能性,而認為碳酸氫根可能是以 cluster 的形式 embed 在碳酸鈣內存在於含鎂非晶態碳酸鈣的球體表面。同時,我們在pH 11.3的條件下合成的25Mg同位素標記樣品中,鎂鈣比為0.2和0.8的非晶態碳酸鈣的25Mg NMR光譜結果幾乎相同,因此我們猜測即使是不同的含鎂量,鎂離子的第一配位層環境依然非常類似。接著,我們利用雙共振技術測量25Mg和13C的平均距離,我們發現鎂在不同ACC中的第二層配位隨著含鎂量上升而上升。總體而言,我們利用固態核磁共振研究含鎂非晶態碳酸鈣的結構性質的資料是迄今最為詳細的。 Of many polymorphs of calcium carbonate, calcite and aragonite are widely found in biominerals. Previous studies show that amorphous calcium carbonate (ACC) is not only a precursor of biogenic calcite or aragonite, but also a temporary storage site of calcium carbonate in some organisms. Biogenic ACC contains substantial amount of Mg. In vitro experiments indeed show that magnesium ions can stabilize ACC. However, the structural feature of Mg-ACC remains poorly known and therefore it would be very interesting to probe the structural ordering in Mg-ACC. In this work, we have established a reliable method based on micro mixing to prepare Mg-ACC with different Mg/Ca ratios. Samples with highly reproducible Mg/Ca ratios ranging from 0.20 to 0.81 have been obtained, as characterized by ICP-MS and EDX. In addition to a series of standard characterizations by FTIR, SEM, and TEM, we have employed 13C and 25Mg solid-state nuclear magnetic resonance to probe the structures of our samples. At pH 8.75, the 13C NMR results show that an appreciable amount of bicarbonate is present in our Mg-ACC samples with Mg/Ca ratios of 0.20 and 0.81. On the basis of 13C homonuclear correlation spectroscopy, we find that the average distance of the carbonate and bicarbonate species is longer than 0.6 nm, hence ruling out the scenario of homogeneous distribution. As such, we suggest that the bicarbonate species are mainly found on the surface of Mg-ACC or embedded in the matrix of amorphous calcium carbonate. . As expected, the 13C NMR signal of bicarbonate is absent for our samples prepared at pH 11.3. In addition, we have obtained the 25Mg NMR spectra for our isotopically enriched samples. The spectral features of our samples with Mg/Ca ratios of 0.20 and 0.8 are more or less the same, suggesting that the first coordination sphere of Mg2+ ions are very similar for different loadings of Mg content. The results are compared with the NMR data obtained for magnesite to shed light on the bonding environment of Mg-ACC. Furthermore, experiments are carried out to probe the average distance between 25Mg and 13C using double techniques in NMR. The results obtained for samples with different loadings of Mg are compared with amorphous magnesium carbonate suggesting that the coordination number of Mg2+ ions increases with higher loadings of Mg content. Overall, our solid-state NMR work represent hitherto the most detailed structural characterization of Mg-ACC. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/60635 |
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