Structural features of tundra and taiga soil humic acids according to IR EXPERT analytical system data

Abstract

The purpose of this work is to identify the most probable structural fragments of the tundra and the taiga soil humic acids on the basis of computer analysis of their IR spectra. Humic acid (HA) samples were isolated from 11 northern soils of the Komi Republic, Russia. IR spectra were registered in KBr by Bruker FTIR spectrometer Vector-22. IR EXPERT information-analytical system was used for analysis of these spectra. This system is a combination of an extensive database (more than 50,000 correlation records of “IR spectrum–structure–structural fragments–accompanying information”) and software modules that allow solving various spectral-structural tasks. The procedure of working with new IR spectra of humic acid involved two stages. Comparison of the sample IR spectrum with all spectra in IR-EXPERT databases was followed by decomposition of the closest spectral analogs into the set of fragments which is individual for each HA. This unique representation makes it possible to associate a spectrum with a combination of structural fragments rather than with the exact structure. That is what we need for HA. The analysis of the obtained ten-vertex fragments shows that all HA samples contain linear, slightly branched, conjugated chains of double C–C bonds, as well as the fragments of aromatic amines and amides. Using only IR spectroscopy data and the IR EXPERT system, we were able to show that humic acids of these northern soils are predominantly aliphatic and contain a large number of oxygen-containing groups, which allows one to predict their high reactivity when interacting with ecotoxicants.