Jump to main content
Jump to site search

Issue 13, 2011
Previous Article Next Article

Decreasing particle size helps to preserve metastable polymorphs. A case study of dl-cysteine

Author affiliations

Abstract

The contribution describes the effect of particle size on the interconversion between the high-temperature (I) and the low-temperature (II) polymorphs of crystalline DL-cysteine (+NH3–CH(CH2SH)–COO) studied by X-ray powder diffraction, Raman spectroscopy, differential scanning calorimetry, scanning electron microscopy. Crystalline DL-cysteine undergoes a phase transition on cooling related to the rotation of its side-chain and a rearrangement of the H-bond network. For the crystals larger than ∼1 μm, the transition could be observed in the range 250–200 K and was characterized by a large (up to 110 K) hysteresis. If (I) was obtained as crystalline particles with characteristic size of ∼1 μm by grinding, no transformation into (II) was observed on cooling down even to 10 K. (I) was preserved down to 200 K, after which another low-temperature phase, (I)′, appeared, which was structurally related to (I), but with strongly disordered (possibly modulated) sulfhydryl side-chains. Nevertheless, (II) could be prepared as small (∼0.1 to 1 μm) particles directly at low temperatures by freeze-drying of DL-cysteine aqueous solutions. The sample could be then preserved as a metastable low-temperature polymorph on heating up to ∼333 K, and transformed completely to (I) at 373 K only. The small particles of (I) obtained by heating from small particles of (II) then transformed completely back to (II) on cooling down to 183 K. The effects are interpreted in terms of kinetic control of the polymorphic transitions and the relation between particle size, nucleation of a new phase, and relaxation of mechanical stresses.

Graphical abstract: Decreasing particle size helps to preserve metastable polymorphs. A case study of dl-cysteine

Back to tab navigation

Publication details

The article was received on 07 Feb 2011, accepted on 11 Apr 2011 and first published on 10 May 2011


Article type: Paper
DOI: 10.1039/C1CE05178D
CrystEngComm, 2011,13, 4417-4426

  •   Request permissions

    Decreasing particle size helps to preserve metastable polymorphs. A case study of DL-cysteine

    V. S. Minkov, V. A. Drebushchak, A. G. Ogienko and E. V. Boldyreva, CrystEngComm, 2011, 13, 4417
    DOI: 10.1039/C1CE05178D

Search articles by author

Spotlight

Advertisements