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Crystals 2017, 7(11), 339;

Microindentation Hardness of Protein Crystals under Controlled Relative Humidity

Graduate School of Nanobioscience, Yokohama City University, Yokohama 236-0027, Japan
Department of Education, Yokohama Soei University, Yokohama 226-0015, Japan
Author to whom correspondence should be addressed.
Academic Editors: Ronald W. Armstrong, Stephen M. Walley and Wayne L. Elban
Received: 9 October 2017 / Revised: 30 October 2017 / Accepted: 31 October 2017 / Published: 4 November 2017
(This article belongs to the Special Issue Crystal Indentation Hardness)
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Vickers microindentation hardness of protein crystals was investigated on the (110) habit plane of tetragonal hen egg-white lysozyme crystals containing intracrystalline water at controlled relative humidity. The time evolution of the hardness of the crystals exposed to air with different humidities exhibits three stages such as the incubation, transition, and saturation stages. The hardness in the incubation stage keeps a constant value of 16 MPa, which is independent of the humidity. The incubation hardness can correspond to the intrinsic one in the wet condition. The increase of the hardness in the transition and saturation stages is well fitted with the single exponential curve, and is correlated with the reduction of water content in the crystal by the evaporation. The saturated maximum hardness also strongly depends on the water content equilibrated with the humidity. The slip traces corresponding to the (11 ̅0)[110] slip system around the indentation marks are observed in not only incubation but also saturation stages. It is suggested that the plastic deformation in protein crystals by the indentation can be attributed to dislocation multiplication and motion inducing the slip. The indentation hardness in protein crystals is discussed in light of dislocation mechanism with Peierls stress and intracrystalline water. View Full-Text
Keywords: protein crystal; lysozyme crystal; indentation; hardness; dislocation; intracrystalline water; relative humidity; Peierls stress; slip protein crystal; lysozyme crystal; indentation; hardness; dislocation; intracrystalline water; relative humidity; Peierls stress; slip

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Kishi, T.; Suzuki, R.; Shigemoto, C.; Murata, H.; Kojima, K.; Tachibana, M. Microindentation Hardness of Protein Crystals under Controlled Relative Humidity. Crystals 2017, 7, 339.

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