鯊魚牙齒中礦物成分的固態核磁共振研究

Abstract

固態核磁共振光譜是當今研究分子間結構資訊以及化合物鑑定的重要光譜學，因而在生物礦化的研究中被普遍使用於骨頭、琺瑯質以及軟骨組織的測量。這篇論文裡，我們的研究著重於利用固態核磁共振鑑定大眼長尾鯊（Alopias superciliosus）牙齒中的化合物成分與結構。大眼長尾鯊的下顎有四到五排的牙齒，並且在下顎的不同位置具有顯著的大小與形貌的差異。過去的研究指出這些不同的牙齒處於不同的生長過程，因此我們將樣品依照位置與大小進行個別鑑定與分析。這個研究的主要目的在於辨識牙齒中的化學成分與他們在牙齒生長過程中的角色。利用一維或二維固態核磁共振技術，並以標準礦物的結果作對照，我們可以判定牙齒樣品中的核磁共振訊號。我們期盼礦物組成在牙齒生長過程的量變趨勢以及分子層級上的資訊可以幫助理解生物礦化的機制。 本論文中第一章、第二章提供生物礦化與固態核磁共振光譜原理相關的背景知識。第三章詳述了實驗所使用的藥品列表、標準品合成與儀器鑑定方法。第四章包含牙齒樣品的固態核磁共振光譜的分析。利用二維異核化學位移相關譜（2D HETCOR）做為輔助辨識礦物物種所屬訊號，以及礦物分子化學環境的解析。交叉極化的動態分析（cross polarization kinetics）以及反摺積（deconvolution）的分析顯示礦物組成在牙齒生長過程的量變趨勢。我們在牙齒樣品中辨認出一個化學環境與氟化鈣相似的物種（CaF2-like specie），與無晶相環境有空間相關性。這個存在於無晶相結構的氟化鈣物種在相對新生的牙齒樣品中佔的比例較高。透過比較主要幾種磷灰石（hydroxyapatite, fluorapatite and fluorohydroxyapatite）在新生與成熟的牙齒的含量，可以做為推論鯊魚牙齒發展過程中的生物礦化動力學以及機制的有力資訊。

Solid-state NMR has been demonstrated as a powerful technique in the investigation of detailed molecular information and chemical identification. Thus, it is widely used in biomineralization studies of samples such as bone, enamel, dentin, and cartilage. In this work, we focus on the identification of the structure and composition of the teeth of Alopias superciliosus, a thresher shark, using various solid-state NMR strategies. The Alopias superciliosus teeth samples came in several rows with distinguishable size and morphology, and these dental series comprise teeth that evolved from nascent to mature in embryotic development. Samples of separate rows and sizes were characterized individually for their chemical compositions. The aim of this work is to identify chemical species and their role in the growth of shark’s teeth. With the help of model compounds, hydroxyapatite (Ca10(PO4)6(OH)2, HAp), fluorohydroxyapatite (Ca10(PO4)6(OH)2-xFx, FHAp), and CaF2 were identified in the 1D and 2D solid-state NMR spectra of the teeth samples. These data can provide essential information for a better understanding of the biomineralization of vertebrate teeth at the molecular level. Chapter 1 and 2 provide the background knowledge of this work. In Chapter 3, a complete layout of the chemicals used for solid-state NMR measurement is provided. Synthetic model compounds such as FHAp are characterized with the listed instruments. In Chapter 4, the solid-state NMR spectra of the teeth samples are assigned by 2D HETCOR and the spatial relationships among biominerals species are clarified. Analyses of cross polarization kinetics and peak deconvolution reveal the variation trend of the chemical species of shark teeth at different growth stages. The CaF2-like species, identified in the teeth samples by solid-state NMR but not XRD, is thought to reside in the amorphous phase that constitutes a large portion in teeth at early growth stage. The different amount of hydroxyapatite, fluorapatite, and fluorohydroxyapatite in nascent and mature teeth shed light on the mineralization kinetics and the mechanism of shark teeth development.