Evolution from basic to advanced structure of fulvic acid and humic acid prepared by food waste

• Published in: International journal of biological macromolecules 2024-01, Vol.256 (Pt 2), p.128413-128413, Article 128413
• Main Authors: Mu, Daichen, Mu, Linying, Geng, Xinyu, Mohamed, Taha Ahmed, Wei, Zimin
• Format: Article
• Language: English
• Subjects: Advanced structure; Basic structure; Fulvic acid; Humic acid
• ISSN: 0141-8130; 1879-0003
• DOI: 10.1016/j.ijbiomac.2023.128413

Fulvic acid (FA) and humic acid (HA) are common polyacids in nature. However, the evolutionary process of their basic and advanced structures is still unclear. FA and HA were separated into five molecular weight components to investigate the process of evolution from small to large molecules. The primary structure analysis showed that FA were rich in CN, COOH and OH content, while HA were rich in (CH2)n, NH2 and CC. Moreover, with the molecular weight increasing, the structures could complement each other to maintain the hydrophilic or hydrophobic balance. The 2D-COS spectroscopy demonstrated that during the growth of FA, COOH, NH2 and OH firstly respond. On the other hand, during the growth of HA, NH2 and (CH2)n firstly respond. In addition, advanced structure of FA was affected by intramolecular hydrogen bonds and π − π interaction. HA was affected by hydrophobic interactions due to the abundance of hydrophobic groups, primarily (CH2)n and benzene rings. 3D conformational fitting and particle size characterization confirmed that the interaction forces determine that FA and HA become tightly and loosely molecules respectively. This study is to further explore the geochemical formation and evolution process of FA and HA molecules. •Carboxyl and hydroxyl of FA can complement each other to maintain the hydrophilicity.•The C-N, NH2 and COOH contents of HA and FA have obvious thresholds.•The evolution orders of basic structure between FA and HA are different.•Advanced structures are dominated by hydrogen bonding and hydrophobic interactions.•The 3D conformation of FA is loose and that of HA is tight.