title: Enumeration of carboxyl groups carried on individual components of humic systems using deuteromethylation and Fourier transform mass spectrometry.
abstract: Here, we report a novel approach to enumeration of carboxylic groups carried by individual molecules of humic substances using selective chemical modification and isotopic labeling (deuteromethylation) and high-resolution electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FTICR MS). Esterification was conducted with a use of thionyl chloride-deuteromethanol reagent under mild conditions to avoid transesterification. The deuteromethylated products were subjected to solid phase extraction using PPL Bond Elute cartridges prior to FTICR MS analysis. An amount of carboxyl groups in the individual molecular component was estimated from the length of identified deuteromethylation series. The method allowed for discerning between compounds with close elemental compositions possessing different protolytic properties. We found that different carboxylic moieties occupy distinct regions in molecular space of humic substances (HS) projected onto Van Krevelen diagram. These locations do not depend on the source of the humic material and can be assigned to carboxyl-rich alicyclic molecules (5 to 6 COOH), hydrolyzable tannins (3-4 COOH), lignins (1 to 2 COOH), condensed tannins and lignans (0 to 1 COOH), and carbohydrates (0 COOH). At the same time, the alignment pattern of these carboxylated species along the structural evolution lines in Van Krevelen diagrams was characteristic to the specific transformation processes undergone by the humic materials in the different environments. The obtained data enable mapping of molecular ensemble of HS with regards to their specific acidic compartments and might be used for directed fractionation of HS. Graphical abstract Selective isotopic labeling followed by FTICR MS enables discerning between humic molecules with close elemental compositions carrying different numbers of carboxylic groups.
authors.affiliation: Department of Chemistry, Lomonosov Moscow State University, Leninskie Gory 1-3, 119991, Moscow, Russia.
authors.forename: Alexander
authors.initials: A
authors.lastname: Zherebker
authors.affiliation: Skolkovo Institute of Science and Technology, 143025, Skolkovo, Moscow Region, Russia.|Orekhovich Institute of Biomedical Chemistry, Russian Academy of Medical Sciences, ul. Pogodinskaya 10, 119121, Moscow, Russia.|Institute for Energy Problems of Chemical Physics of RAS, Leninskij pr. 38-2, 119334, Moscow, Russia.|Moscow Institute of Physics and Technology, 9, Institutskii per., 141700, Dolgoprudnyi, Moscow Region, Russia.
authors.forename: Yury
authors.initials: Y
authors.lastname: Kostyukevich
authors.affiliation: Orekhovich Institute of Biomedical Chemistry, Russian Academy of Medical Sciences, ul. Pogodinskaya 10, 119121, Moscow, Russia.|Institute for Energy Problems of Chemical Physics of RAS, Leninskij pr. 38-2, 119334, Moscow, Russia.|Moscow Institute of Physics and Technology, 9, Institutskii per., 141700, Dolgoprudnyi, Moscow Region, Russia.
authors.forename: Alexey
authors.initials: A
authors.lastname: Kononikhin
authors.affiliation: Skolkovo Institute of Science and Technology, 143025, Skolkovo, Moscow Region, Russia.|Moscow Institute of Physics and Technology, 9, Institutskii per., 141700, Dolgoprudnyi, Moscow Region, Russia.
authors.forename: Oleg
authors.initials: O
authors.lastname: Kharybin
authors.affiliation: Department of Chemistry, Lomonosov Moscow State University, Leninskie Gory 1-3, 119991, Moscow, Russia.
authors.forename: Andrey I
authors.initials: AI
authors.lastname: Konstantinov
authors.affiliation: Department of Chemistry, Lomonosov Moscow State University, Leninskie Gory 1-3, 119991, Moscow, Russia.
authors.forename: Kirill V
authors.initials: KV
authors.lastname: Zaitsev
authors.affiliation: Skolkovo Institute of Science and Technology, 143025, Skolkovo, Moscow Region, Russia. ennikolaev@rambler.ru.|Orekhovich Institute of Biomedical Chemistry, Russian Academy of Medical Sciences, ul. Pogodinskaya 10, 119121, Moscow, Russia. ennikolaev@rambler.ru.|Institute for Energy Problems of Chemical Physics of RAS, Leninskij pr. 38-2, 119334, Moscow, Russia. ennikolaev@rambler.ru.|Moscow Institute of Physics and Technology, 9, Institutskii per., 141700, Dolgoprudnyi, Moscow Region, Russia. ennikolaev@rambler.ru.
authors.forename: Eugene
authors.initials: E
authors.lastname: Nikolaev
authors.affiliation: Department of Chemistry, Lomonosov Moscow State University, Leninskie Gory 1-3, 119991, Moscow, Russia. iperm@med.chem.msu.ru.
authors.forename: Irina V
authors.initials: IV
authors.lastname: Perminova
keywords: 1H NMR spectroscopy; Carboxylic group; FTICR MS; Humic substances; Isotopic labeling; Modification