CONTENT Vol. 2 - Humus.ru

15th IHSS Meeting- Vol. 2
alkali-extractable reaction products were analyzed on TSK 2000SW column (Tosoh
Biosciences) using 1100 HPLC system with diode-array detector (Agilent Technologies). 0.1
M Na-phosphate buffer with 0.1% SDS (pH 7.0) was used as an eluent.
3. Results and Discussion
On the basis of preceding adsorption experiments, the concentration of precursor solution was
selected so as to achieve maximal adsorption of monomers and multilayer formation. No
polymerization in the bulk of the reaction mixture occurred during 15 min adsorption period
as revealed by HPLC analysis of supernatants. The total amount of monomers adsorbed per
10 mg of the mineral was 93.9 µg (632.9 µmol). The amount of individual compounds
adsorbed was the following (µg): tyrosin (5.63) < triptophane (6.13) < ferulic acid(9.41) <
vanillic acid(10.31) < hydroxybenzoic acid(13.36) < caffeic acid (22.84) < gallic acid(26.20).
Laccase have lost about 50% of its initial activity upon immobilization.
During reaction period initially white hydroxyaluminum-kaolinite became progressively
brown in color due to oxidation of adsorbed phenolic compounds by laccase. After 72 hours
of incubation high molecular weight (>70 kDa) humic-like polymers were formed on the
mineral surface. Their absorption spectrum in the region of 220–600 nm resembled natural
humates. Humic-like compounds were similar to that obtained in earlier work [4] when
opposite order of adsorption of reaction components on hydroxyaluminum-kaolinite was
applied (first laccase was immobilized, then precursors were added to the mineral). No
polymer formation was observed in abiotic controls.
4. Conclusions
High molecular weight humates can be formed by surface polymerization in presence of
laccase. The order by which phenol oxidase and humus precursors are adsorbed on the
mineral surface do not affect the resulting molecular weight of the product.
Acknowledgements
The work was supported by RFBR 09-04-00570 and by Programme 15 of Presidium RAS.
References
1. G.Guggenberger, K.Kaiser, Geoderma, 113 (2003), p.293.
2. A.G.Zavarzina, in A.Varma, G.Shukla (Eds.), Soil Enzymes, Springer-Verlag, Germany,
Chapter 3, in press.
3. A.Naidja, J. Mol. Cat. A: Chemical, 115 (1997), p.305-316.
4. A.G.Zavarzina, Eurasian Soil Sci., 39 (2006), p.48-53.
Vol. 2 Page - 41 -