How does temperature modulate the structural properties of aggregated melamine in aqueous solution—An answer from classical molecular dynamics simulation

Abstract

In this study, classical molecular dynamics simulation of eight melamine molecules is carried out in water over a temperature range of 300 K to 380 K at an ambient pressure to examine the molecular details of melamine aggregation along with the impact of temperature on the aggregated state of melamine in water. It is found that the hydrogen bonds formed between sp3 N-sp2 N of melamine, which is mainly responsible for the aggregation over the sp3 N-sp3 N, are disturbed mainly by the rise in temperature. These outcomes are complemented by the consideration of an average number of hydrogen bonds per melamine and preferential interaction parameter calculations. The impact of temperature is negligible on the orientational probability between the two triazine cores. The π–π stacking interaction between the two triazine rings plays a less significant role on melamine aggregation. Dynamical calculations, by considering cluster structure analyses and dimer existence autocorrelation function, strengthen the fact of destabilization of aggregated melamine in water with the rise in temperature. With free energy of solvation, association constant along with the binding free energy between a melamine pair gives the thermodynamic point of view of the impact of elevated temperature on melamine aggregation. Interestingly, the potential of mean force calculation using an umbrella sampling technique explains the reasons, in depth, of how do sp3 N-sp2 N interactions confirm the decrease in the initial probability of growth of higher order clusters with the increase in temperature.

Switching of Self-Assembly to Solvent-Assisted Assembly of Molecular Motor: Unveiling the Mechanisms of Dynamic Control on Solvent Exchange

“…The KB theory is initially composed by employing the grand-canonical (μVT) ensemble. The associated KB integrals are regarded as the volume integrals over the pair distribution function of species i and j present in the system: ,− where r is the distance between the center of masses of the species, i.e., i and j . G ij ( r ) refers to the KB integral.…”

“…The KB integrals, G mm , G mw , and G mt , are ascertained from the molecular motor–molecular motor, molecular motor–water, and molecular motor–THF radial distribution functions. In the calculation of these distribution functions, COMs of the molecular motor, water, and THF molecules are taken into account. ,, …”

“…In the calculation of these distribution functions, COMs of the molecular motor, water, and THF molecules are taken into account. 74,76,77 Using eq 11, the value of τ mw m is determined for systems S0− S3. From Figure 10(a) it can be seen that the molecular motor preferably interacts with like molecules over water (as the corresponding preferential interaction parameters have positive values) and τ mw m is the highest for system S0; then, it decreases from system S1, and after that, it dramatically decreases from systems S2−S3.…”

“…The angles, i.e., 0°−20°or 160°−180°, between these vector normals relate to the stacking between the two aromatic planes. 74,76,78 Now, to determine the angle between the planes, we have conceded three planes (A1, A2, and A3) of each molecular motor molecule. Then, we have considered all possible combinations among these three planes and have measured the angle between any two planes.…”

“…The above findings show that when two molecular motor molecules are engaged in the π−π stacking, they retain the angle (0−20°). 74,76,78 It is also essential to estimate the distance between the molecular motor molecules to verify that they satisfy the distance criterion along with the specific angle. Next, for the interacting planes (A1−A2 and A1−A3), the distances are measured for all systems.…”