Formation and stabilization mechanism of mesoscale clusters in solution.

Shuyi Zong,Hongxun Hao,Xin Huang,Jingkang Wang,Qi Liu,Hao Wu

doi:10.1107/s2052252521012987

Abstract

To understand the existence of complex meso-sized solute-rich clusters, which challenge the understanding of phases and phase equilibria, the formation and stabilization mechanisms of clusters in solution during nucleation of crystals and the associated physico-chemical rules are studied in detail. An essential part of the mechanism is the formation of long-lived oligomers between solute molecules. By means of density functional theory simulation and nuclear magnetic resonance experiments, this work showed that the oligomers in solution tend to be π-π stacking dimers. Clusters are formed under the combined effect of diffusion and monomer-dimer reaction. The physically meaningful quantities such as the monomer-dimer reaction rate constants and the diffusion coefficients of both species were obtained by reaction-diffusion kinetics and diffusion-ordered spectroscopy results. The evolution of cluster radius as a function of time, and the qualitative spatial distributions of monomer and dimer densities under steady-state were plotted to better understand the formation process and the nature of the clusters.

Highlights

Crystal nucleation in solution suggests that crystal nuclei might form inside the solute-rich clusters
The contribution of free energy can be regarded as a diffusion driving force that is dependent on the density of monomers and oligomers
The concentrationdependent nuclear magnetic resonance (NMR) shifts combined with dimerization model further confirms the dimerization reaction in OTBN– methanol solution

Summary

Introduction

Crystal nucleation in solution suggests that crystal nuclei might form inside the solute-rich clusters. The crucial role of the solute-rich clusters as locations of crystal nucleation has been supported by experimental evidence in many systems, such as proteins (Vekilov, 2010; Kuznetsov et al, 2001), biominerals (Pouget et al, 2009; Gebauer et al, 2008), polymers (Wang et al, 2009), colloids (Leunissen et al, 2005; Savage & Dinsmore, 2009) and small organic molecules (Aber et al, 2005; Harano et al, 2012). The existence of clusters in solution is spatially and chemically heterogeneous, which is of significance for self-assembly and nanoparticle manufacturing (Elbaum-Garfinkle et al, 2015; Banjade et al, 2015)

Methods

Results

Conclusion