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

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.