茂名新丛粒藻烷重碳同位素成因之分子内碳同位素组成与分布研究

In the Maoming oil shale, we have discovered and identified the novel series of botryococcanes by NMR analysis, in which a new biosynthetic pathway was proposed to explain the formation of the unique methyl group positioned β to the sole quaternary carbon in these biomarkers. The proposed pathway well explained the carbon numbers and the formation of the novel C33 botryococcanes in the Maoming Basin. However, there are still no satisfied answers for the origin of the unusually heavy carbon isotope of the C33 botryococcane. To uncover the puzzling questions, a new measurement of site-specific natural isotopic fractionation NMR (SSNIF-NMR) will be conducted in this program trying to analyze the intramolecular distribution of stable carbon isotopes in the new C33 botryococcane. As a comparison, the C34 botryococcene extracted from the cultured B race of Botryococcus braunii will be also performed these analysis which has different carbon isotope, chemical structure and biosynthetic pathway. According to the deciphered and calculated results, a connection between the heavy isotopic compositions of the target compound and the paleoclimate/palaeoenvironment through the stable carbon isotopes of the initial carbon source, which can effectively discuss the origin and the formation of the unusually heavy carbon isotopes of the botryococcane in the Maoming Basin, based on the novel structure with a methyl group positioned β to the sole quaternary carbon and atomic level. In the meantime, the intramolecular carbon isotopic composition of basic isoprenoid units and their isotopic fractionations during the isoprenoid formation to the botryococcane can be analyzed, by comparing the intramolecular carbon isotopic composition of isoprenoid units in the C34 botryococcene from the cultured B. brauniii. Besides, according to the calculated results of the intramolecular carbon isotopic composition of isoprenoid units, an isotopic evidence can be offered to the proposed biosynthetic pathway for the novel botryococcane with a cyclobutane ring as intermediate, as well as the conventional biosynthetic pathway with a cyclopropane ring as intermediate for the formation of the C34 botryococcene.

通过NMR解析，我们发现并鉴定了茂名油页岩中含特殊季碳β位甲基结构的新丛粒藻烷系列化合物，提出了有别于常规三元环的四元环生物合成途径，据此合理解释了其碳数分布和结构生成路径。但是，对丛粒藻烷非常重的碳同位素成因尚未有令人满意的答案。本项目拟通过对主峰化合物C33新丛粒藻烷开展特定碳位核磁共振测试，据此天然同位素实测数据开展分子内碳同位素分布分析，并与藻类培养获得的C34丛粒藻烯分子做对比；分析新丛粒藻烷特殊结构与重碳同位素的关系，以此确定茂名盆地丛粒藻生长时期的古环境/古气候因素对重碳同位素的贡献；通过对照分析丛粒藻烷中类异戊二烯C5的碳同位素对初始碳源的表征以及C5形成过程中的同位素分馏，尝试建立C5分子内碳同位素与特定古环境古气候的联系；根据C5的连接方式，还可以对我们提出的新丛粒藻烷四元环生物合成途径提供分子内同位素方面的证据。

基于NMR解析，我们发现并鉴定了茂名油页岩中含特殊季碳β位甲基结构的新丛粒藻烷系列化合物，提出了有别于常规三元环的四元环生物合成途径，合理解释了其碳数分布和结构生成路径。但是，对丛粒藻烷的重碳同位素成因，是新生代EOT事件成因还是火山成因，尚未有确凿的证据。本项目通过进一步精细的分子有机地球化学研究以及新C33丛粒藻烷特定碳位核磁共振的分子内碳同位素分布研究，试图解释丛粒藻烷的重碳同位素成因，主要获得如下进展：①通过精细的分子有机地球化学方法，新发现一系列新丛粒藻烷类化合物：新C32丛粒藻烷、新C31丛粒藻烷醇和1个新C32丛粒藻烷醛、C15与C18类异戊二烯烷基酮，对其碳同位素和成因均进行了一定的研究工作，为分析新丛粒藻烷的重碳同位素成因提供了更多的分子层面上的证据；②通过新C33丛粒藻烷分子内碳同位素分布研究，建立了分子内碳同位素分布的13C-NMR方法，并进行了13C-NMR法与化合物结构法的对比，根据新C33丛粒藻烷特殊季碳β位甲基结构中的碳和甲基化作用来源甲基碳的碳同位素分布研究，发现新丛粒藻的重碳同位素特征很可能受到新生代EOT事件的影响；③发现茂名盆地普遍存在A属丛粒藻生源，其特征生标n-C27，同样具有重碳同位素特征，说明其也受到新生代EOT事件的影响。通过上述研究，丰富了丛粒藻的生物标志化合物分子库，有利于茂名盆地油页岩形成中古生态过程的揭示和油气资源评价；不仅提供了茂名盆地新生代EOT事件的新证据，也提供了盆地中丛粒藻A属、B属和L属的存在以及互相演变的证据，为后面负责人对茂名盆地丛粒藻的属种演变及其对新生代EOT事件的响应方面的继续研究打下了坚实的基础，同时也为丛粒藻的培养提供了新思路，有助于生物燃料油的研发。