NMR spectroscopy in identification of humic substances and prediction their properties

Dashitsyrenova A.D.1, Kalabin G.A.1, Kuschnarev D.F.2, Proydakov A.G.2, Rokhin A.V.2

1Peoples’ Friendship University of Russia, 8/5 Podolskoye Shosse, 113093 Moscow, Russia
2Irkutsk State University,1 K.Marx Street, 664003 Irkutsk, Russia

Humic substances (HS) are natural high molecular weight aromatic systems with irregular structure, have important role in providing vital functions in ecosystems, first of all in plants [1]. Problem on connections of physiological activity (A) of HS with their structural details demands modern analytic methods. 13C NMR-spectroscopy allow to get quantitative data of structural groups, which cannot be done by any chemical or physical methods [2].
The objectives of this study are to assess (i) physiological activity of HS isolated from Gusinoozersk deposit of brown oxidized coal on coleoptiles (Triticum aestivum) [3] and yeast (Saccharomyces cerevisiae) with structural details, (ii) prediction optimal concentration of HS’s solutions on the basis of relaxation parameters 17O NMR of aqua. 
In that way, we received two equations of relationships:
A (coleoptiles)=3.6(С=О)+4.2(СООН)+32.2(СarО)-5.6(СarС,Н)-8.5(СalkО)-2.3(Сalk)
A (yeast)=3.0(C=O)+15.6(COOH)+69.7(CarO)-15.6(CarC,H)-21.8(CalkO)+1.1(Calk), which allow to conclude, that in spite of two different objects, methods and conditions of biotesting, the main effect  have presence of the same structural fragments as carboxyl, aromatic and alkoxy-groups. 
By 17O NMR  were registered and measured relaxation time of 17O water in solutions of HS in systems “HS-NaOH-H2O”.[2] The maximum of 1/217O in HS’s solutions coincides with maximum of physiological activity of HS on coleoptiles and yeast in 0.001%. So, this optimal concentration of HS  has the most structure-forming effect on solution, possessing physiological activity.

References:
1.Orlov D.S. (1990) Humic substances of soils and common theory of humification. Moscow, MSU Publisher, 325p. (in Russian)
2.Kalabin G.A., Kanitskaya L.V., Kuschnarev D.F. (2000). Quantative NMR spectroscopy of natural organic materials and products of its processing. Moscow, Publisher “Chemistry”, 408p (in Russian).
3.Kulikova N.A., Dashitsyrenova A.D., Perminova I.V., Lebedeva G.F Auxin-like Activity of Different Fractions of Coal Humic Acids // Ecology and the Future, #2, р. 11-13, 2003.