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Morphosynthesis of alanine mesocrystals by pH control
Yurong Ma1, Helmut Cölfen, Markus Antonietti
1Max-Planck-Institute of Colloids and Interfaces, Colloid Chemistry, Forschungscampus Golm, Am Mühlenberg, D-14424 Potsdam, Germany.
The Journal of Physical Chemistry. B
|June 15, 2006
Summary
DL-alanine crystallization can occur via nanoparticle assembly into mesocrystals, supplementing classical molecule-based crystallization. This finding depends on supersaturation, controlled by temperature or pH, in the absence of additives.
Area of Science:
- Crystallization science
- Materials science
- Physical chemistry
Background:
- Polar organic molecules exhibit complex crystallization behaviors.
- Understanding crystallization mechanisms is crucial for materials design.
- DL-alanine serves as a model system for studying crystallization of polar molecules.
Purpose of the Study:
- To investigate the crystallization modes of DL-alanine without structure-directing additives.
- To analyze the influence of supersaturation (via temperature and pH) on crystallization pathways.
- To elucidate the formation mechanism of DL-alanine mesocrystals.
Main Methods:
- Scanning Electron Microscopy (SEM) for crystal morphology.
- X-ray Diffraction (XRD) for crystal structure.
- Single-crystal analysis.
- Time-resolved conductivity measurements.
- Dynamic Light Scattering (DLS) for precursor analysis.
Main Results:
- Crystallization via mesoscale assembly of nanoparticles (mesocrystals) observed across a wide range of conditions.
- Classical molecule-based crystallization identified at lower supersaturations and pH away from the isoelectric point (IEP).
- Precursor structures and reaction kinetics elucidated through conductivity and DLS.
Conclusions:
- Mesoscale assembly is a significant crystallization pathway for DL-alanine, supplementing classical mechanisms.
- Supersaturation and pH are key factors controlling crystallization modes.
- A formation mechanism for DL-alanine mesocrystals has been proposed.