Phototransformation of l-tryptophan and formation of humic substances in water
| Autor: | Enrico Chiavazza, Elisa De Laurentiis, Pier Giuseppe Daniele, Roberto Buscaino, Marco Minella, Chiara Scapuzzi, Davide Vione, Francesco Turci, Ingrid Corazzari, Silvia Berto |
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| Rok vydání: | 2018 |
| Předmět: |
010504 meteorology & atmospheric sciences
Decarboxylation Humic substances 010501 environmental sciences Photochemistry 01 natural sciences law.invention Hydrophobic effect chemistry.chemical_compound law Dissolved organic carbon Environmental photochemistry Environmental Chemistry Dissolved organic matter Formate Organic matter Aromatic amino acids Surface waters Tryptophan Electron paramagnetic resonance 0105 earth and related environmental sciences chemistry.chemical_classification Aqueous solution chemistry Absorption (chemistry) |
| Zdroj: | Environmental Chemistry Letters. 16:1035-1041 |
| ISSN: | 1610-3661 1610-3653 |
| DOI: | 10.1007/s10311-018-0714-y |
| Popis: | Humic substances are poorly known, though they represent a major pool of non-biotic organic carbon on earth. In particular, there is little knowledge on the formation of humic substances by irradiation of organic matter dissolved in waters. Specifically, it is known that humic substances can be formed from proteins by photochemical processes in surface waters, but the role of single amino acids and their transformation pathways are not yet known. Therefore, here we studied the phototransformation of aqueous l-tryptophan under simulated sunlight. Irradiated l-tryptophan solutions were analyzed by absorption, fluorescence, nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) spectroscopies, chromatography, potentiometry and mass spectrometry (MS). The solutions appeared turbid after irradiation; therefore, nephelometry and dynamic laser light scattering were used to characterize the suspended particles. Results show that about 95% of l-tryptophan was degraded in 8-h irradiation, undergoing deamination and decarboxylation of the amino acidic moieties to release ammonium and formate. The MS signal at m/z 146 suggests the formation of 3-ethylindole, while pH-metric and NMR data revealed the presence of hydroxylated compounds. The phototransformation intermediates of l-tryptophan had fluorescence and absorption spectra similar to those of humic substances, they were able to produce ·OH upon irradiation and tended to aggregate by both ionic and hydrophobic interactions. Overall, our findings reveal for the first time the nature of products formed upon phototransformation of l-tryptophan. Interestingly, the transformation of l-tryptophan is quite different from that of the previously studied l-tyrosine, although both compounds produce humic-like materials under irradiation. |
| Databáze: | OpenAIRE |
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