Kosuke Ikeya1, Rachel L Sleighter, Patrick G Hatcher, Akira Watanabe. 1. Graduate School of Bioagricultural Sciences, Nagoya University, Chikusa, Nagoya, 464-8601, Japan; Department of Chemistry and Biochemistry, Old Dominion University, Norfolk, VA, 23529, USA.
Abstract
RATIONALE: The green fraction of soil humic acids (HAs), designated Pg, contains 4,9-dihydroxyperylene-3,10-quinone (DHPQ) as a chromophore. Although various naturally occurring DHPQ derivatives are known to occur and Pg-like absorption is observed in the UV-visible spectra of HAs from various types of soils worldwide, the chemical structure of Pg is still unknown. METHODS: For a better understanding of the chemical composition of Pg, the pre-isolated (crude Pg) and purified Pg (G2) samples and three soil HAs with different degrees of humification were analyzed using negative-mode electrospray ionization coupled with Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS) at 12 Tesla. The Pg samples were characterized using H/C-O/C ratios and based on the type and magnitude of the molecular formulae having DHPQ or related compounds as a potential structure. RESULTS: The H/C-O/C diagram indicated that most of the lipids, proteins, other aliphatics, and lignin-like components were removed, while condensed aromatic components were concentrated during the purification process of crude Pg to G2 using Sephadex G-50. More than 27 molecular formulae resembling DHPQ, DHPQ substituted with varying numbers of carboxyl and/or hydroxyl groups, and phenyl-DHPQ derivatives were identified in both Pg samples. The peak magnitudes of these formulae in G2 (accounting for 40% of the total assigned magnitude) were greater than that in the crude Pg (21%). Most of the 27 molecular formulae were also detected in the three soil HAs, suggesting a common existence of Pg-related compounds in various soil HAs. CONCLUSIONS: The important molecular formulae of Pg components were estimated utilizing FTICRMS.
RATIONALE: The green fraction of soil humic acids (HAs), designated Pg, contains 4,9-dihydroxyperylene-3,10-quinone (DHPQ) as a chromophore. Although various naturally occurring DHPQ derivatives are known to occur and Pg-like absorption is observed in the UV-visible spectra of HAs from various types of soils worldwide, the chemical structure of Pg is still unknown. METHODS: For a better understanding of the chemical composition of Pg, the pre-isolated (crude Pg) and purified Pg (G2) samples and three soil HAs with different degrees of humification were analyzed using negative-mode electrospray ionization coupled with Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS) at 12 Tesla. The Pg samples were characterized using H/C-O/C ratios and based on the type and magnitude of the molecular formulae having DHPQ or related compounds as a potential structure. RESULTS: The H/C-O/C diagram indicated that most of the lipids, proteins, other aliphatics, and lignin-like components were removed, while condensed aromatic components were concentrated during the purification process of crude Pg to G2 using Sephadex G-50. More than 27 molecular formulae resembling DHPQ, DHPQ substituted with varying numbers of carboxyl and/or hydroxyl groups, and phenyl-DHPQ derivatives were identified in both Pg samples. The peak magnitudes of these formulae in G2 (accounting for 40% of the total assigned magnitude) were greater than that in the crude Pg (21%). Most of the 27 molecular formulae were also detected in the three soil HAs, suggesting a common existence of Pg-related compounds in various soil HAs. CONCLUSIONS: The important molecular formulae of Pg components were estimated utilizing FTICRMS.
Authors: Morgane Derrien; Yun Kyung Lee; Jae-Eun Park; Penghui Li; Meilian Chen; Sang Hee Lee; Soo Hyung Lee; Jun-Bae Lee; Jin Hur Journal: Environ Sci Pollut Res Int Date: 2017-06-02 Impact factor: 4.223