Alcohol compounds in Azolla imbricata and potential source implication for marine sediments

Abstract

This study investigated the composition of long-chain alkyl diols, triols, sec-alcohols, hydroxyl acids, and other hydroxylated compounds in Azolla imbricata and compared the organic alcohol components of Azolla filiculoides, Azolla microphylla, and South China Sea (SCS) sediments in order to investigate the possible indication of Azolla being the biological source of diols and triols in SCS sediment. Large amounts of diols, monohydroxy acids, and sec-alcohols with internal hydroxy groups at omega 20 were detected in the three types of Azolla. Among these, 1,omega 20-diol and omega 20-hydroxy acid exhibited strong even-odd predominance distribution, whereas omega 20-sec-alcohol exhibited strong odd-even predominance distribution. In addition, small amounts of diols, triols, and dihydroxy acids with internal hydroxy groups at 9, 10 or omega 9, omega 10 were detected, among which the chain length of C-29 was predominate. Compounds having similar structures as those in Azolla reflected a similar biosynthetic pathway: omega 20-hydroxy acid exhibiting even-odd predominance distribution is decarboxylated to omega 20-sec-alcohol exhibiting odd-even predominance distribution and converted to 1, omega 20-diol with even-odd predominance distribution by acyl reduction; omega 9, omega 10-hydroxy acid is converted to 1,20,21(1, omega 9, omega 10)-triol by acyl reduction, and then converted to 9,10-diol by hydrogenation and dehydration. The alcohol components in A. imbricata were clearly not the biological source of 1,13/1,14/1,15-C-28,C- 30,C- 32 diols and 1,3,4-C27-29 triols in the SCS sediment. Certain marine diatoms might be the source of 1,14-C-28,C- 30 diol in inshore sediment, but the biological source of diols and triols in the SCS sediment requires further investigation.