Growth of organic crystals via attachment and transformation of nanoscopic precursors

Yuan Jiang,Adrian Moise,Denis Gebauer,Zihao Lu,Matthias Kellermeier,Rose Rosenberg,Helmut Cölfen,Michael Przybylski

doi:10.1038/ncomms15933

Abstract

A key requirement for the understanding of crystal growth is to detect how new layers form and grow at the nanoscale. Multistage crystallization pathways involving liquid-like, amorphous or metastable crystalline precursors have been predicted by theoretical work and have been observed experimentally. Nevertheless, there is no clear evidence that any of these precursors can also be relevant for the growth of crystals of organic compounds. Herein, we present a new growth mode for crystals of DL-glutamic acid monohydrate that proceeds through the attachment of preformed nanoscopic species from solution, their subsequent decrease in height at the surface and final transformation into crystalline 2D nuclei that eventually build new molecular layers by further monomer incorporation. This alternative mechanism provides a direct proof for the existence of multistage pathways in the crystallization of molecular compounds and the relevance of precursor units larger than the monomeric constituents in the actual stage of growth.

Highlights

A key requirement for the understanding of crystal growth is to detect how new layers form and grow at the nanoscale
This is explored by three independent methods: electrospray ionization mass spectrometry (ESI-MS), analytical ultracentrifugation (AUC) and in situ atomic force microscopy (AFM) on an inert silicon substrate
ESI-MS serves primarily to explore the range of species present, while it cannot provide a quantitative description of their relative abundance

Summary

Introduction

A key requirement for the understanding of crystal growth is to detect how new layers form and grow at the nanoscale. We present a new growth mode for crystals of DL-glutamic acid monohydrate that proceeds through the attachment of preformed nanoscopic species from solution, their subsequent decrease in height at the surface and final transformation into crystalline 2D nuclei that eventually build new molecular layers by further monomer incorporation This alternative mechanism provides a direct proof for the existence of multistage pathways in the crystallization of molecular compounds and the relevance of precursor units larger than the monomeric constituents in the actual stage of growth. Driven by the reduction of interfacial surface area, the nanodroplets aggregate and/or grow by inclusion of monomers to yield larger solvent-rich mineral droplets that later dehydrate into amorphous nanoparticles[33] and crystallize[31] While this pathway envisages a vital role of PNCs and/or nanoscopic liquid intermediates in the process of phase separation, it does not (yet) consider their possible relevance during the later stages of growth. This is explored by three independent methods: electrospray ionization mass spectrometry (ESI-MS), analytical ultracentrifugation (AUC) and in situ AFM on an inert silicon substrate

Methods

Results

Conclusion