Ajito K, Ueno Y, Kim JY, Sumikama T. Capturing the Freeze-Drying Dynamics of NaCl Nanoparticles Using THz Spectroscopy.
J Am Chem Soc 2018;
140:13793-13797. [PMID:
30351129 DOI:
10.1021/jacs.8b07828]
[Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Sodium chloride (NaCl) aqueous solution becomes NaCl hydrate, NaCl·2H2O, at low temperature, which is different from potassium chloride and is a typical complex model for studying the freeze-drying process in foods and pharmaceuticals. Here, we detected unit-cell-sized NaCl particles in ice as precursor substances of NaCl·2H2O during freezing of NaCl solution by using terahertz (THz) spectroscopy. In the freezing process, Na+ and Cl- ions form two types of metastable unit-cell-sized NaCl particles on the pathway to the well-known NaCl·2H2O crystal production, which are not listed in the phase diagram of freezing of NaCl solution but have absorption peaks in THz spectra. This finding of single unit-cell-sized particles signifies the importance of studying the freeze-drying process in-depth and offers a new possibility for the development of freeze-drying technology for the manufacture of nanometer-sized particles such as ultrafine pharmaceutical powders, which more readily dissolve in water.
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