title: Modification of chemical and conformational properties of natural organic matter by click chemistry as revealed by ESI-Orbitrap mass spectrometry.
abstract: A click reaction is reported here for the first time as a useful technique to control the conformational stability of natural organic matter (NOM) suprastructures. Click conjugates were successfully formed between a previously butynylated NOM hydrophobic fraction and a hydrophilic polyethylene glycol (PEG)-amino chain. The click products were shown by size exclusion chromatography (HPSEC) hyphenated with Orbitrap mass spectrometry (MS) in electrospray ionization (ESI) (+), while precursors were visible in ESI (-). Despite their increase in molecular weight, HPSEC elution of click conjugates occurred after that of precursors, thus showing their departure from the NOM supramolecular association. This indicates that the click-conjugated NOM molecules were varied in their hydrophilic and cationic character and lost the capacity to accommodate in the original hydrophobic suprastructures. The most abundant product had the C16H30O5N4 formula, a click conjugate of butanoic acid, while other products were short-chained (C4-C8) linear unsaturated and hydroxylated carboxylic acids. Tandem MS revealed formation of triazole rings in clicked conjugates and their two fragmentations at the ester and the C-N alkyl-aryl bonds. The behavior of NOM molecules modified by click chemistry confirms that hydrophobicity and ionic charge of humic molecules play a pivotal role in stabilizing intermolecular forces in NOM. Moreover, the versatility of the click reaction may become useful to decorate NOM molecules with a variety of substrates, in order to alter NOM conformational and chemical properties and diversify its applications in the environment.
authors.affiliation: Centro Interdipartimentale di Risonanza Magnetica Nucleare per l'Ambiente, l'Agroalimentare e i Nuovi Materiali (CERMANU), Università di Napoli Federico II, Via Università 100, 80055, Portici, Italy. antonio.nebbioso@unina.it.
authors.forename: Antonio
authors.initials: A
authors.lastname: Nebbioso
authors.affiliation: Centro Interdipartimentale di Risonanza Magnetica Nucleare per l'Ambiente, l'Agroalimentare e i Nuovi Materiali (CERMANU), Università di Napoli Federico II, Via Università 100, 80055, Portici, Italy.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Piccolo
mesh_terms: D002264:Carboxylic Acids / Q000737:chemistry; D002850:Chromatography, Gel; D057930:Click Chemistry; D006812:Humic Substances / Q000032:analysis*; D057927:Hydrophobic and Hydrophilic Interactions; D008968:Molecular Conformation; D052638:Particulate Matter / Q000032:analysis* / Q000737:chemistry; D011092:Polyethylene Glycols / Q000737:chemistry; D021241:Spectrometry, Mass, Electrospray Ionization; D014230:Triazoles / Q000737:chemistry
chemical_list: D002264:Carboxylic Acids; D006812:Humic Substances; D052638:Particulate Matter; D014230:Triazoles; D011092:Polyethylene Glycols
keywords: Chemical modification; Click chemistry; Conformational modification; Hydrophobic humic acid; Natural organic matter; Polyethylene glycol