Biocompatible pH-Degradable Functional Capsules Based on Melamine Cyanurate Self-Assembly

Development of adaptive self-regulating materials and chemical-biological systems-self-healing, self-regulating, etc.-is an advanced modern trend. The very sensitive pH-controlled functionality of supramolecular assemblies is a very useful tool for chemical and biochemical implementations. However, the assembly process can be tuned by various factors that can be used for both better functionality control and further functionalization such as active species, e.g., drugs and dyes, and encapsulation. Here, the effect of a dye, sodium fluorescein (uranine) (FL), on the formation of a self-assembled melamine cyanurate (M-CA) structure is investigated and calculated with density functional theory (DFT) and molecular dynamics. Interestingly, the dye greatly affects the self-assembly process at early stages from the formation of dimers, trimers, and tetramer to nucleation control. The supramolecular structure disassembly and subsequent release of trapped dye occurred under both high- and low-pH conditions. This system can be used for time-prolonged bacterial staining and development of supramolecular capsules for the system chemistry approach.

Morphological aspect of crystal nucleation in wall-confined supercooled metallic film

In this paper, we simulate the nucleation and growth of crystalline nuclei in a molybdenum film cooled at different rates confined between two amorphous walls. We also compare the results for the wall-confined and wall-free systems. We apply the same methodology as in the work (Kirova and Pisarev 2019J. Cryst. Growth528125266) which is based on reconstructing the probability density function for the largest crystalline nucleus in the system. The size of the nucleus and the asphericity parameter are considered as the reaction coordinates. We demonstrate that in both the free and confined systems there are two mechanisms of crystal growth: the attachment of atoms to the biggest crystal from the amorphous phase and the merging of the biggest crystal cluster with small ones (coalescence). We show that the attachment mechanism is dominant in the melt cooled down at a slower rate, and the mechanism gradually shifts to coalescence as cooling rate increases. We also observe the formation of long-lived crystal clusters and demonstrate that amorphous walls do not affect their geometric characteristics. However, system confined between walls demonstrates higher glass-forming ability.

Collective behaviour of a glass-forming film of pure aluminium

The previously discovered features of the temperature behaviour of four-point spatial correlators allow us to study transitions to metastable states. Similar integral characteristics simultaneously study microscopic effects (vortex formation and clustering) and the effect of these phenomena on the thermodynamics of the whole system. It is shown that spatial and temporal behaviour of correlators in supercooled liquid samples determine the signs of the glass transition in a system before its relaxation. After the liquid sample is supercooled below a certain boundary, particle motion correlations on the coordination spheres sharply increase, similar to the situation in a crystal. The study was carried out using the embedded atom method model of aluminium using the molecular dynamics method.