In situ observation of the internal structure and composition of biomineralized Emiliania huxleyi calcite by solid-state NMR spectroscopy
In situ observation of the internal structure and composition of biomineralized Emiliania huxleyi calcite by solid-state NMR spectroscopy
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DOI：
10.1021/ja803985d
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发表时间：
2008-10-08
影响因子：
15
通讯作者：
Schmidt, Asher
中科院分区：
文献类型：
--
作者：
Gertman, Ronen;Ben Shir, Ira;Schmidt, Asher
生物矿化，特别是生物在环境条件下形成碳酸钙结构，具有广泛的基础和应用价值。生物体精细地控制着生物材料形成的各个方面：组成、多形态、形态和宏观特性。虽然在分子水平上对所得生物矿物进行原位表征是一项艰巨的任务，但固态魔角旋转核磁共振是实现这一目的的最强大的分析技术之一。在这项研究中，它被用来阐明由赫胥黎Emiliania huxleyi形成的生物方解石的结构和组成。赫胥黎Emiliania huxleyi是一种单细胞藻类，其特征是其精美的雕刻方解石细胞覆盖物被称为球石。菌株371 （CCMP）在富含N-15和c -13的培养基中生长和收获，并使用生物合成标记来提高核磁共振测量的灵敏度。晶体和界面方解石环境分别通过直接和间接（交叉极化）13c激发进行选择性探测。利用13c旋转回波双共振（REDOR）核磁共振（NMR）鉴定了不同的晶体环境，特别是在P和N基团掺入浓度高达1.4%时的结构缺陷位点。基于redor的几何约束表明，缺陷部位的P原子和N原子距离碳酸碳晶体为3.2和2.3（+/- 0.2）埃。生物成因方解石中的磷和氮部分被鉴定为小的，非质子化的部分，归因于无机离子，如PO43-和NO3-。与这些缺陷相邻的碳酸盐在化学上与大块结晶碳酸盐难以区分，但它们的直接环境经历了刚性降低，这反映在大量的T-1（(CO32-)- c -13）缩短中。另一方面，界面碳酸盐存在于结构/化学扰动的环境中，这反映在非均相线展宽上。本研究首次直接揭示了E - huxleyi生物成因方解石中P/N部分作为结构缺陷的结合证据，以及邻近结晶碳酸盐的状态。
Biomineralization, particularly the formation of calcium carbonate structures by organisms under ambient conditions, is of vast fundamental and applied interest. Organisms finely control all aspects of the formation of the biomaterials: composition, polymorph, morphology, and macroscopic properties. While in situ molecular-level characterization of the resulting biominerals is a formidable task, solid-state magic angle spinning NMR is one of the most powerful analytical techniques for this purpose. It is employed in this study to elucidate the structure and composition of biogenic calcite formed by Emiliania huxleyi, a unicellular alga distinguished by its exquisitely sculptured calcite cell coverings known as coccoliths. Strain 371 (CCMP) was grown and harvested from N-15- and C-13-enriched growth medium, with biosynthetic labeling to enhance the sensitivity of the NMR measurements. Crystalline and interfacial calcite environments were selectively probed using direct and indirect (cross-polarized) 13 C excitation, respectively. Different crystalline environments, in particular structural defect sites at concentrations of up to 1.4% with P and N moieties incorporated, were identified using 13 C rotational-echo double-resonance (REDOR) NMR. REDOR-derived geometrical constraints show that the P and N atoms at the defect sites are 3.2 and 2.3 (+/- 0.2) angstrom apart from a crystalline carbon carbonate. The phosphorus and nitrogen moieties within the biogenic calcite are identified as small, non-protonated moieties, attributed to inorganic ions such as PO43- and NO3-. The carbonates adjacent to these defects are chemically indistinguishable from bulk crystalline carbonates, yet their immediate environments experience reduced rigidity, as reflected by substantial T-1((CO32-)-C-13) shortening. Interfacial carbonates, on the other hand, reside in structurally/chemically perturbed environments, as reflected by heterogeneous line broadening. This study is the first to directly unravel evidence on the incorporation of P/N moieties as structural defects within E huxleyi biogenic calcite, and on the state of the adjacent crystalline carbonates.