Chemistry, Physics and Technology of Surface

ISSN 2518-1238 (Online), ISSN 2079-1704 (Print)

One of the tasks for creating of a medicinal product which contains hydrogel of vitreous humor (VH), nanosized silica and zinc compound is studying of the regularities of complex formation of hyaluronic acid and protein, as a main macromolecular components of VH, with zinc ions.

We have found that after mixing solutions of VH and zinc sulfate the growth of optical density in UV range of the spectrum is observed, apparently due to light scattering as a result of increasing quantity of macromolecular aggregates. It has been proved that this effect is not a consequence of the formation of insoluble compounds due to changes in pH of the medium and thus can be explained by the interaction (complexation) of VH components with zinc ions.

In order to determine the regularities of complex formation, the spectrophotometric titration of VH and separately solutions of purified sodium hyaluronate and model protein – bovine serum albumin (BSA) – with zinc ions was carried out. To constant amount of VH (dilution 1:5) increasing amounts of zinc sulfate solution were added, after that UV spectrum was recorded. As it turned out, after addition of zinc sulfate in the concentrations range 2.5–5.0 mass. % the growth of optical density almost immediately becomes maximal and does not depend on the amount of titrant, which can be explained by saturation of all active centers of VH, which include carboxyl groups of hyaluronic acid and electron donor groups of protein: NH₂-groups, amide bond, thiogroups, etc. In the range 0–0.5 mass. % of zinc sulfate (0–17.5 mmol/l of Zn²⁺) there is a gradual increase in optical density, which makes it possible to calculate equilibrium parameters in the system VH + n Zn²⁺ ↔ VH · (Zn²⁺)_n. For BSA which also demonstrated a gradual increase of optical density in UV range, in order to determine the stoichiometry of  BSA · (Zn²⁺)_n complex the method of molar ratios was used, and it was found that there were about 400 ions of Zn²⁺ per one BSA molecule. In the case of purified sodium hyaluronate, the method of spectrophotometric titration proved to be unsuitable or complexation does not occur at all. Consequently, the interaction of VH with zinc ions is carried out mainly due to the protein component rather than hyaluronan. Dimensional characteristics of aggregates formed as a result of the interaction between VH or BSA and zinc ions were investigated by the method of dynamic light scattering (DLS).

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