The Structural Arrangement and Relative Abundance of Aliphatic Units May Effect Long-Wave Absorbance of Natural Organic Matter as Revealed by 1H NMR Spectroscopy

Perminova, I.V.; Shirshin, E.A.; Konstantinov, A.I.; Zherebker, A.Y.; Dubinenkov, I.V.; Lebedev, V.A.; Kulikova, N.A.; Nikolaev, E.N.; Bulygina, E.; Holmes, R.M.

Авторы: Perminova Irina V., Shirshin Evgeny A., Konstantinov Andrey I., Zherebker Alexander Ya, Dubinenkov Ivan V., Lebedev Vasily A., Kulikova Natalia A., Nikolaev Eugene N., Bulygina Ekaterina, Holmes Robert Max
Журнал: Environmental Science and Technology
Том: 52
Номер: 21
Год издания: 2018
Издательство: American Chemical Society
Местоположение издательства: United States
Первая страница: 12526
Последняя страница: 12537
DOI: 10.1021/acs.est.8b01029
Аннотация: The objective of this study was to shed light on structural features which underlay intensity of long wave absorbance of natural organic matter (NOM) using 1H NMR spectroscopy. For this purpose, a set of the NOM samples was assembled from arctic and non-arctic sampling sites (the Kolyma river basin and Moscow region, respectively). It was to assure a substantial difference in the humification degree of the isolated organic matter - the biogeochemical proxy of the long-wave absorbance of NOM. The assembled NOM set was analyzed using solution-state 1H NMR spectroscopy. The distribution of both backbone and exchangeable protons was determined using acquisition of spectra in three different solvents. The substantially higher contribution of non-functionalized aliphatic moieties CHn (e.g., materials derived from linear terpenoids, MDLT) in the arctic NOM samples was revealed as compared to the non-arctic ones. The latter were characterized with the higher content of CHα protons adjacent to electron-withdrawing groups which belong to carboxyl rich alicyclic moieties (CRAMs) or to aromatic constituents of NOM. We have calculated a ratio of CHn to CHα protons as a structural descriptor which showed significant inverse correlation to intensity of long wave absorbance assessed with a use of E4/E6 ratio and the slope of absorption spectrum. The steric hindrance of aromatic chromophoric groups of the NOM ensemble by bulky non-functionalized aliphatic moieties (e.g., MDLT) was set as a hypothesis for explanation of this phenomenon. The bulky aliphatics might increase a distance between the interacting groups resulting in inhibition of electronic (e.g., charge-transfer) interactions in the NOM ensemble. The obtained relationships were further explored using Fourier transform mass spectrometry as complementary technique to 1H NMR spectroscopy. The data obtained on correlation of molecular composition of NOM with 1H NMR data and optical properties were very supportive of our hypothesis that capabilities of NOM ensemble of charge transfer interactions can be dependent on structural arrangement and relative abundance of non-absorbing aliphatic moieties.
Добавил в систему: Жеребкер Александр Яковлевич

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The Structural Arrangement and Relative Abundance of Aliphatic Units May Effect Long-Wave Absorbance of Natural Organic Matter as Revealed by 1H NMR Spectroscopyстатья