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Issue 22, 2012
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The crystalline state of methylene blue: a zoo of hydrates

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A re-investigation of the crystalline state of methylene blue has led to the identification of five different hydrates with clearly distinct structures. These include the already known pentahydrate, a hydrate with 2.2–2.3 equivalents of water, two dihydrates, and a monohydrate. Contrary to older reports, no trihydrate was found. The preparation and characterization of the hydrates as well as the transformations between them are reported. The applied analytical methods include X-ray powder diffraction (XRPD), infrared spectroscopy (ATR-IR), thermogravimetry (TGA), differential scanning calorimetry (DSC), dynamic water vapor sorption (DVS) and solution calorimetry (SolCal). A phase diagram of temperature vs. composition has been established, and the stability domains of the different hydrates as a function of water activity and temperature have been determined based on data from DSC, SolCal and suspension equilibration experiments. Four out of the five hydrates are thermodynamically stable within a certain range of temperature and humidity.

Graphical abstract: The crystalline state of methylene blue: a zoo of hydrates

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Publication details

The article was received on 13 Jan 2012, accepted on 19 Mar 2012 and first published on 05 Apr 2012

Article type: Paper
DOI: 10.1039/C2CP40128B
Citation: Phys. Chem. Chem. Phys., 2012,14, 8074-8082

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    The crystalline state of methylene blue: a zoo of hydrates

    T. Rager, A. Geoffroy, R. Hilfiker and J. M. D. Storey, Phys. Chem. Chem. Phys., 2012, 14, 8074
    DOI: 10.1039/C2CP40128B

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