Journal
CHEMISTRY-A EUROPEAN JOURNAL
Volume 20, Issue 33, Pages 10332-10342Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.201402096
Keywords
amphiphiles; crystal growth; hydrophobic interactions; kinetics; self-assembly
Categories
Funding
- Israel Science Foundation
- Minerva Foundation
- Gerhardt M. J. Schmidt Minerva Center of Supramolecular Architecture
- Helen and Martin Kimmel Center for Molecular Design
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Understanding the crystallization of organic molecules is a long-standing challenge. Herein, a mechanistic study on the self-assembly of crystalline arrays in aqueous solution is presented. The crystalline arrays are assembled from perylene diimide (PDI) amphiphiles bearing a chiral N-acetyltyrosine side group connected to the PDI aromatic core. A kinetic study of the crystallization process was performed using circular dichroism spectroscopy combined with time-resolved cryogenic transmission electron microscopy (cryo-TEM) imaging of key points along the reaction coordinate, and molecular dynamics simulation of the initial stages of the assembly. The study reveals a complex self-assembly process starting from the formation of amorphous aggregates that are transformed into crystalline material through a nucleation-growth process. Activation parameters indicate the key role of desolvation along the assembly pathway. The insights from the kinetic study correlate well with the structural data from cryo-TEM imaging. Overall, the study reveals four stages of crystalline self-assembly: 1)collapse into amorphous aggregates; 2)nucleation as partial ordering; 3)crystal growth; and 4)fusion of smaller crystalline aggregates into large crystals. These studies indicate that the assembly process proceeds according to a two-step crystallization model, whereby initially formed amorphous material is reorganized into an ordered system. This process follows Ostwald's rule of stages, evolving through a series of intermediate phases prior to forming the final structure, thus providing an insight into the crystalline self-assembly process in aqueous medium.
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