The role of specific molecular fractions in synchronous fluorescence spectrum of lignite humic acids

conference paper

English

The aim of this work was to investigate the role of specific sequentially extracted molecular fractions (water-soluble components, free and bonded lipids) in the secondary structure of humic acids (domains) and to assess consequent changes of optical properties using synchronous fluorescence spectroscopy (SFS). The advantage of applied extraction technique relies in the selective removal of humic constituents and identification of labile diagnostic molecules without the profound structural alteration of more drastic degradation methods. In principle, the sequential extraction included three steps: hot water extraction in which mostly hydrophilic molecules were removed (alcohols, acids); second step included the extraction by dichloromethane and methanol (fatty acids, alkanes, steroids, and tricyclic diterpenic acids, mid-chain and hydroxyl-substituted carboxylic acids) and third step the transesterification by boron trifluoride and methanol solution (removing of di- and tri-hydroxyalkanoic acids, alfa, beta and omega-hydroxy fatty acids, alkanoic acids, alfa, omega-alkanedioic acids, n-alkanols, phenolic acids and sterols).2 After each extraction step a part of the solid rest of humic acids was removed, titrated by NaOH to pH 13 and freeze-dried. Further, each fraction was then dissolved in water and measured on synchronous fluorescence spectroscopy (delta lambda=20 nm). As demonstrated recently, the main problem of fluorescence measurement of humic substances can be seen in the inner filter effect (quenching) caused by interactions among self assembled humic molecules. Hydrophobic effect is the driving force causing pressing of individual amphiphilic molecules together which results in creation of highly conjugated system of unsaturated bonds. As a result typical fluoresce spectrum seems to indicate a system of specific fluorophores which supported the conventional approach to interpret individual peaks as a superposition of particular fluorophores; in line with our results traditional view can be swapped by the finding that the character of fluorescence spectrum is a function of conformation arrangement of humic molecules.

humic acids, synchronous fluorescence spectroscopy, fractionation

ČECHLOVSKÁ, H.; FASUROVÁ, N.; PEKAŘ, M.; KUČERÍK, J.

2006

6. 12. 2006

Brno

80-214-3320-5

The book of abstracts

192

192

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