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.

Molecular Signals of Heterogeneous Terrestrial Environments Identified in Dissolved Organic Matter: A Comparative Analysis of Orbitrap and Ion Cyclotron Resonance Mass Spectrometers

“…However, Orbitrap mass analyzers have a ∼10-fold lower mass resolution that limits separation of peaks in the higher mass range ( Supplementary Table S1). Even so, Orbitrap instruments have been successfully applied for characterizing complex natural organic materials ( Supplementary Table S2), including DOM (Pomerantz et al, 2011;Cortés-Francisco and Caixach, 2015;Hawkes et al, 2016), humic and fulvic acids (Galindo and Del Nero, 2015;Nebbioso and Piccolo, 2015), petroleum and bio-oilrelated material (Pomerantz et al, 2011;Zhurov et al, 2013;Rowland et al, 2014;Staš et al, 2015), and extraterrestrial organic materials (Danger et al, 2013;Smith et al, 2014), yet it remains unclear how comparable the results of both instrument types are. Addressing this question is even more pivotal when aiming to compare trends in larger-scale DOM sample sets achieved on different instruments (Swenson et al, 2014).…”

Rate of a Click Chemistry reaction under catalysis by trace‐amounts of copper as evaluated by NMR spectroscopy

“…In addition, such a relatively extended reaction time would not necessarily pose a problem, especially for those applications for which traces of Cu + are tolerated and the purification stage can be bypassed. For instance, this method could be used to optimize the chemical modification of natural organic matter, whose composition already includes traces of several metals.…”

Enhanced washing of polycyclic aromatic hydrocarbons from contaminated soils by the empowered surfactant properties of de novo O-alkylated humic matter

“…This limitation may be overcome by increasing the hydrophobicity of HS through a chemical modification of humic molecules. Different derivatization reactions of HS have been previously performed with various aims: (i) solubility increase in water (Terashima et al 2007 ); (ii) soil aggregates stabilization (Kulikova et al 2021 ); (iii) redox properties change (Volikov et al 2021 ); (iv) alteration of conformational structure (Nebbioso and Piccolo 2015 ). Recently, a phase-transfer catalyzed O-alkylation reaction was reported to vary the hydrophobicity of HS by covalently linking methyl, pentyl, and benzyl residues to the oxygen-containing humic functional groups (Piccolo et al 2023 ).…”