ИСТИНА

Purpose. The interaction of humic substances (HS) with protein is critically important in technological applications. Although experiments with HS and positively charged proteins increased the knowledge about possible interaction, the colloidal behavior of HS-protein mixture in the system of two immiscible liquids has been neglected. In this context, the main objective of this study was to reveal the interference of HS and globular proteins on its distribution in an aqueous/oil system and the adsorption at liquid/liquid interface. Materials & Methods. Leonardite humic acids (HA) and two types of globular proteins lysozyme from chicken egg white (Lsz) and human serum albumin (HSA) were under the test. The study was performed by radiochemical approach that used tritium labeled compounds obtained with the help of tritium thermal activation method and scintillation phase technique developed for compounds mixtures. Dynamic light scattering and optical microscopy of aqueous solutions supplemented the results. Aqueous phase was prepared in phosphate saline buffer (pH 7.2±0.1, 0.16 M) and p-xylene was chosen as an oil phase. The reaches were performed for fixed concentration of protein that is corresponds to plateau region on the adsorption isotherm of individual compound (0.1 mg/ml for Lsz and 0.06 mg/ml for HSA). HA concentration was varied from 0.2 to 50 μg/ml. Results and discussions. The surface activity of HA-HSA conjugate is given by protein. HSA possess rater high surface activity at the aqueous/oil interfaces to supplant HA in both organic phase and liquid/liquid interface. HSA/HA molar ratio in the adsorption layer was varied from 40 to 2 with HA bulk concentration growth from 0.2 to 15 mg/l. Further increase in HA concentration doesn’t significantly change in the surface molar ratio. HA-Lsz conjugate posses’ higher hydrophobicity and surface activity then free HA. The formation of the conjugates with Lsz/HA ratio 1:1, 1:2 and 1:3 were observed in the HA concentration ranges from 5 to 12 mg/l, from 15 to 23 mg/l and from 26 to 30 mg/l respectively. Conclusions. Our results revealed the difference in colloidal behavior of humic acids – globular proteins conjugates in the aqueous/oil systems for conjugates formed by positively and negatively charged proteins. As it was previously stated by Cooper for electrolytes and observed in our study for humic materials that both electrostatic and hydrophobic interactions play a key role in HA-protein conjugation. Our results suggest that the structure of the HS-protein conjugate and the mechanism of its formation are controlled by surface charge distribution of protein. Colloidal-chemical properties of the HS-protein conjugate are in good correlation with its composition.