Crystals growing from contaminated solutions usually exhibit an altered surface topography and a reduction in step kinetics. In most cases, these effects are supersaturation dependent. The prevalent interpretation is that the crystal surface undergoes a self-purifying transition by moving from an impurity-saturated state at low supersaturation towards an effective state of impurity-repulsion at high driving forces [e.g. 1,2]. However, in recent years, motivated by in situ observations, we have perceived two models which can trigger the accelerated recovery of impurity poisoned surfaces. These events constitute an alternative route towards the self-purification scenario that would normally occur at higher supersaturation values.

One of the routes is linked to a non-classical growth mechanism. In this case the accelerated recovery of impurity poisoned surfaces is triggered when mesoscopic protein clusters, present in supersaturated solutions [e.g. 3,4], merge with the crystal surface and lead to a crystalline mound (i.e. multilayer island [e.g. 3,5]) relatively devoid of impurities. This was monitored in situ for lysozyme crystals growing from highly impure solutions (≈ 94.5% purity). When steps of areas free of multilayer islands and steps generated on areas enclosed by macrosteps are compared significant changes in step morphology and growth kinetics are observed. The freshly formed areas due to the solidification of a cluster on the crystal surface yield faster advancing steps with a morphology that more closely resembles the pure case [2]. This observation strongly suggests that these areas have a locally reduced surface impurity concentration surrounded by areas with high impurity coverage. The de novo formation of an impurity free terrace leads to an acceleration in the step velocity which reduces the terrace exposure time (compared to the surrounding regions) diminishing the probability that an impurity molecule will bind to the surface [6]. Eventually, a new steady-state will be established that is characterized by a higher lateral growth rate and quasi-pure morphology. These cluster-sedimentation events can therefore be considered as local hotspots of self-purification that grow in size with a velocity set by the rate of advancement of a macrostep across the impure surface. Once the edges of the surface are reached, the surface is effectively cleansed from impurity poisoning.

The second model was conceptualized when the growth dynamics of 2D islands and spiral hillocks of lysozyme crystals growing from purified and contaminated solutions were compared [7]. The morphology and step dynamics of spiral hillocks are less affected by the presence of impurities in the growth solution as compared to steps generated by 2D nucleation. Thus, when crystal growth is dominated by spiral hillocks, fewer impurities are adsorbed onto the crystal surface and a more pure crystal lattice should be formed. This mechanism also operates under forced flow [8] indicating its general nature.

[1] Weaver  M. L., et al. Cryst. Growth Des. 2010, 10, 2954–2959. [2] Van Driessche, A.E.S., et al.  Cryst. Growth Des. 2009, 9, 3062–3071. [3] Gliko O., et al., J. Am. Chem. Soc. 2005, 127, 3433–3438. [4] Pan W., et al., J. Phys. Chem. B 2010, 114, 7620-7630. [5] Kuznetsov Y.G., et al., Phys. Rev. B 1998, 58, 6097–6103. [6] Sleutel M., et al., Cryst. Growth Des. 2013, 13, 688–695. [7] Sleutel M., et al., Cryst. Growth Des. 2012, 12, 2367–2374. [8] Maruyama M., et al., Cryst. Growth Des. 2012, 12, 2856–2863.

• Legal notice:
  

  Copyright (c) Pielaszek Research, all rights reserved.
  The above materials, including auxiliary resources, are subject to Publisher's copyright and the Author(s) intellectual rights. Without limiting Author(s) rights under respective Copyright Transfer Agreement, no part of the above documents may be reproduced without the express written permission of Pielaszek Research, the Publisher. Express permission from the Author(s) is required to use the above materials for academic purposes, such as lectures or scientific presentations.
  In every case, proper references including Author(s) name(s) and URL of this webpage: https://science24.com/paper/29703 must be provided.

1. Direct measurement of growth kinetics of elementary steps on ice basal faces
2. Thermodynamic stabilities of two types of quasi-liquid layers on basal faces of ice crystals
3. Atomic or molecular resolution investigation of soluble crystals in liquid by frequency-modulation (non-contact) AFM
4. Gypsum crystal growth: from fast growth in the laboratory to ultraslow growth in Nature
5. Growth Mechanism of Lysozyme Crystals in The International Space Station Based on The Analysis  of  In-Situ Interferometric Observation
6. Unexpected growth behaviour: a first step to understand crystalline growth of non-model proteins?
7. Rocky protein crystals grown in silica gel
8. In situ observations of impurity effects during protein crystal growth
9. Precipitation process and phase stability of calcium sulfate; The role of temperature, salinity and time of reaction
10. The attachment/detachment process of lysozyme molecules on a monoclinic lysozyme crystal surface studied by single-molecule visualization
11. Effects of carboxylated ε-poly-L-lysine on crystallization of ice
12. In-situ observation of emergences of quasi-liquid layers from ice basal faces by advanced optical microscopy
13. Thermodynamic stabilities of two types of quasi-liquid layers on basal faces of ice crystals