ИСТИНА

Big attention to the study of gels and gel-like state is explained by their wide applications in daily practice and industrial processes. Understanding of the general laws of the gelling phenomenon plays a key role in the design of new «smart» nanostructures, which can be obtained by self-assembly and can respond to external stimuli. One of the interesting systems capable of forming hydrogel at sufficiently small content of reagents is an aqueous solution of silver nitrate and cysteine (CSS) whose gelation is initiated by the introduction of a salt. We discuss our mesoscopic model of CSS in order to study the formation of gel-state at large scales. The model is based on the experimentally established fact that silver mercaptide molecules (SM) form clusters and larger aggregates at the stage of maturation of CSS. We confirm the possibility of the formation of silver-thiol oligomers that was earlier supported by experimental data indirectly. For this aim, we study the morphology of clusters, which were step-by-step formed from 2-22 molecules of SM with using of molecular mechanics methods and DFT. The estimation of a number of free functional groups on the surface of SM clusters confirms our assumption that SM clusters play a role of supramonomers in a gel-network formation. Their self-assembly is due to the formation of hydrogen bonds between the carboxyl and amino groups as well as the formation of silver-thiol oligomers. To simulate the introduction of a salt initiator into CSS we study the coordination of functional groups of cysteine by metal ion. It has been found that a metal ion can simultaneously coordinate C(O)OH, NH2 and thiol groups. These results have been used to develop a coarse-grained model of CSS on the base of the dissipative particle dynamics method (DPD) and differentiate the interactions of SM molecules (coordinated and not coordinated by the metal ions) with solvent molecules. Using the developed DPD model, we report our results on the phase behavior of the solution depending on SM and salt concentrations. Acknowledgement. The work was supported by the Ministry of Education and Science of the Russian Federation (Project № 4.2246.217/ПЧ). The authors also express their gratitude to the Russian Academy of Sciences MSC for providing computing resources of cluster MVS-100k.