ITMO Scientists Study Gradient Structures in Cobalt Solution Sediments

The research of oscillating periodic systems is among the most interesting and complex challenges in chemistry in recent years. Such chemical reactions feature oscillating reagent concentrations which results in changes in reaction speed and manyfold periodic precipitation. These phenomena are examples of nonequilibrium processes that are common in nature, like the emergence of tree rings or the growth of bones in living organisms. Prior to the study in question, ITMO scientists have already observed the dynamics of calcium phosphate precipitation and the process of the emergence and formation of bones in the human body, as well as proposed a system that models the growth of bones.

This time, ITMO scientists experimented with cobalt salts. The compounds of this metal have paramagnetic properties, e.g., get magnetised by external magnetic fields, which makes it possible to locally heat the material. Using materials based on such compounds as cell substrates, in turn, makes it possible to locally activate cells. What’s more, in small doses, cobalt is also an element that’s essential for the wellbeing of human bodies. 

In order to study the precipitation process, the scientists put a single-percent agar solution and cobalt chloride in a test tube. When the agar with cobalt chloride jellified, they added an external electrolyte, sodium hydroxide. This launched the diffusion of the solution and the formation of the sediment. As a result, the chemists observed gradient periodical precipitation that featured several phases with various properties. This became the first observation of such systems based on cobalt hydroxide sediments.

“All in all, we’ve registered six phases that differ in color, chemical properties, and composition. In other words, we observed Liesegang rings. Such rings can be naturally occur in the formation of agate, for instance. However, we didn’t expect that the distance between every new ring and the previous one, i.e., the structure diversity ratio, will not correspond with a geometric sequence, as it usually happens. In these structures, every ring is “pressed” into another. It’s also worth mentioning that Liesegang rings usually feature a single phase. In our system we observe a phase gradient as well as phasal transformation of intermediate compounds”, noted Svetlana Ulasevich, the team’s research advisor and associate professor of ITMO’s Infochemistry Scientific Center.

The team described the chemical reactions in the system and studied the effect of various factors on the process of phase emergence. They’ve learned that by controlling the pH level, the concentration of alkali, temperature, and the volume of incoming air, it’s possible to change the proportion of phases in the total volume of the solution’s sediment, i.e., increase and decrease the number of rings of a specific color.

Every such phase that consists of a sediment of a specific color is a chemical compound with unique properties. Oftentimes, such compounds act as a key component when developing new materials. For instance, the sediments of a cobalt solution can be used as substrates for cells in electrochemical devices, as well as thermal sensors, implants, bases for pigments, and antimicrobial coating. What’s more, it is possible to produce such materials in mere weeks with minimal expenses.

“Our next step is to study each precipitation phaseand define the values of the product of its solvability and conductivity. We are also going to conduct tests on cells and learn which of the resulting materials are more biocompatible and how they can affect the behavior of live cultures”, comments Leonid Gudzerov, a member of the research the team and a Bachelor’s student at ITMO’s Infochemistry Scientific Center.