松粉热解脂肪酸生物标志物的特征及其地球化学意义

Characteristics and Geochemical Significance of the Fatty Acid Biomarkers from the Pyrolysis of Pine Pollen

现代松粉的温 -压热模拟实验中 ,产出的轻质烃和氯仿抽提物芳烃馏份的GC MS分析均检出大量偶数碳优势明显的脂肪酸类分子生物标志物。轻烃主要为C16、C18烷酸及其甲、乙酯 ;芳烃组分相对比较复杂 ,包括饱和脂肪酸 (酯 )、不饱和脂肪酸 (酯 )和脂肪酸内酯。前者碳数分布为C15～C3 0 ,以C16、C18碳酸 (酯 )相对丰度占绝对优势为特征 ,后者碳数分布为C2 0 ～C3 0 ,以C2 6、C2 8和C3 0 脂肪酸内酯为主。在 2 5 0℃以下样品中检测出相对丰度较高的不饱和C18碳酸 (酯 )。脂肪酸酯化合物在极低的温度条件下便可排出 ,并分别在 2 0 0～ 30 0℃和 30 0～ 4 0 0℃之间形成两次产出高峰 :花粉内质体中的游离态脂肪酸及不饱和脂肪酸形成低温阶段的第一次高峰 ;花粉壁脂质结构中的脂肪酸及饱和脂肪酸在较高温度阶段形成第二次高峰。原样及低温样品以脂肪酸酯为主 ,2 5 0℃及其以上温度条件下因水解产生较多的脂肪酸 ,随温度继续升高 ,脂肪酸酯易发生脱羧反应而生成链烷烃。 4 0 0℃以后因强烈降解脂肪酸酯含量大大降低 ,这与 35 0～ 4 5 0℃之间奇数碳优势正构烷烃在轻质烃和饱和烃中的大量产出相吻合。研究表明 ,植物花粉是沉积有机质中饱和及不饱和C16、C18脂肪酸酯的重要母源之一。

A large number of fatty acids in the light hydrocarbons and aromatic fractions of the extracts from thermally simulated samples of modern pine pollens were identified by GC MS analysis. These biomarkers are clearly even carbon predominated. The major components of light hydrocarbons are palmitic (C 16 ), stearic (C 18 ), methyl esters (C 16 , C 18 ) and ethyl esters (C 16 , C 18 ). Aromatic hydrocarbons are relatively complex, consisting of saturated fatty acids, unsaturated fatty acids and fatty acid internal esters. The carbon number of the light hydrocarbons is from C 15 to C 30 , and the relative distribution of C 16 , C 18 acids (esters) is of absolute predominance. The carbon number of aromatic hydrocarbons is from C 20 to C 30 , and the main components are C 26 , C 28 and C 30 . Lower abundance of C 18 unsaturated fatty acid was identified at low temperature stage (<250℃). The expulsion of fatty acids (esters) occurred at very low temperature stages. There are two expulsion peak stages from 200℃ to 300℃ and from 300℃ to 400℃. The controlling factor is probably due to difference in hermal stabilization of different fatty acids. The free state fatty acids (esters) in the cytoplasm of pine pollens and the unsaturated fatty acid are easily banished at low temperature stage. Saturated fatty acids and the fatty acids in the lipoid of the wall of pollens would be degraded at the higher temperature stage. Original pollens and the simulated samples at low temperature stage mainly contain fatty esters. Simulated samples at 250℃ and higher temperatures contain more fatty acids due to hydrolysis. Fatty acids (esters) can be easily decarboxylated to produce chain hydrocarbons as the simulation temperature continuously rises. The contents of fatty acids (esters) remarkably drop down because of strong pyrolysis at the higher temperature stage over 400℃. This is consistent with the appearance of large quantity of odd carbon n alkanes in light hydrocarbons and saturated hydrocarbons at 350～450℃ stage. The studies indicate that plant pollens are one of the important origins of C 16 , C 18 saturated and unsaturated fatty acids (esters) in sedimentary organic matters.