1. A. G. Zavarzina and V. V. Demin, “Acid-base properties of humic acids of different origin as seen from the potentiometric titration data,” Eurasian Soil Sci. 32, 1115–1122 (1999).
2. A. G. Zavarzina, N. G. Vanifatova, and A. A. Stepanov, “Fractionation of humic acids according to their hydrophobicity, size, and charge-dependent mobility by the salting-out method,” Eurasian Soil Sci. 41, 1294–1301 (2008).
3. Yu. A. Zavgorodnyaya, V. V. Demin, A. V. Kurakov, and O. N. Biryukova, “Characteristics of physical-chemical properties of fungal melanin,” Vestn. Mosk. Univ., Ser. 17: Pochvoved., No. 3, 39–47.
4. D. V. Kovalevskii, A. B. Permin, I. V. Perminova, D. V. Konnov, and V. S. Petrosyan, “Condition selection of quantitative 13C NMR spectra of humic acids,” Vestn. Mosk. Univ., Ser. 2: Khim. 41, 39–42 (2000).
5. E. D. Lodygin, V. A. Beznosikov, and R. S. Vasilevich, “Paramagnetic properties of humic substances in taiga and tundra soils of the European Northeast of Russia,” Eurasian Soil Sci. 51, 921–928 (2018).