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Titolo:
Nonlinear dynamics of layer growth and consequences for protein crystal perfection
Autore:
Vekilov, PG; Rosenberger, F; Lin, H; Thomas, BR;
Indirizzi:
Univ Alabama, Ctr Micrograv & Mat Res, Huntsville, AL 35899 USA Univ Alabama Huntsville AL USA 35899 & Mat Res, Huntsville, AL 35899 USA
Titolo Testata:
JOURNAL OF CRYSTAL GROWTH
fascicolo: 2-4, volume: 196, anno: 1999,
pagine: 261 - 275
SICI:
0022-0248(199901)196:2-4<261:NDOLGA>2.0.ZU;2-J
Fonte:
ISI
Lingua:
ENG
Soggetto:
SUPERSATURATED LYSOZYME SOLUTIONS; LIGHT-SCATTERING INVESTIGATIONS; SURFACE-MORPHOLOGY; MOSAIC-VIRUS; CRYSTALLIZATION; KINETICS; MICROGRAVITY; THAUMATIN; TRANSPORT; INSTABILITIES;
Keywords:
protein crystallization; striations; diffraction resolution; microgravity; impurities; slow growth;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
--discip_EC--
Citazioni:
78
Recensione:
Indirizzi per estratti:
Indirizzo: Vekilov, PG Univ Alabama, Ctr Micrograv & Mat Res, Huntsville, AL 35899 USA Univ Alabama Huntsville AL USA 35899 Huntsville, AL 35899 USA
Citazione:
P.G. Vekilov et al., "Nonlinear dynamics of layer growth and consequences for protein crystal perfection", J CRYST GR, 196(2-4), 1999, pp. 261-275

Abstract

In situ high-resolution optical interferometry of lysozyme crystal growth reveals that under steady external conditions, the local growth rate R, vicinal slope p and step velocity are not steady but fluctuate by several times their average values. The variations in p, which is proportional to the local step density, indicate that these fluctuations occur through the dynamic formation of step bunches. Our previous work with unstirred solutions has shown that the fluctuation amplitude of R increases with supersaturation and crystal size (Vekilov et al., Phys. Rev. E 54 (1996) 6650). Based on scaling arguments and numerical simulations, we have argued that the fluctuations are the response of the coupled bulk transport and nonlinear interfacekinetics to finite amplitude perturbations provided by the intrinsically unsteady step generation. In this paper, we emphasize the recently discovered spatio-temporal correlation between the sequence of moving step bunches and striations (compositional variations) in the crystal, visualized by polarized-light microscopy. Hence, these unsteady kinetics have detrimental effects on the perfection of the crystals, and means to reduce and eliminate them should be sought. To this end, based on the above conclusion as to the mechanism of the kinetic unsteadiness, we accelerated the bulk transport towards the interface by forced solution flow. We found that this results in lower fluctuation amplitudes. This observation confirms that the system-dependent kinetic Peclet number, Pe(k), i.e., the relative weight of bulk transport and interface kinetics in the control of the growth process, governs the step bunching dynamics. Since Pe(k) can be modified by either forced solution flow or suppression of buoyancy-driven convection under reduced gravity, this model provides a rationale for the choice of specific transport conditions to minimize the formation of compositional inhomogeneities. Interestingly, on further increase of the solution flow velocities >500 mu m/s, the fluctuation amplitudes in R increased again, while the average growth rate decreased. At low supersaturations, this leads to growth cessation. Thegrowth instability, deceleration and cessation were immediately reversibleupon reduction of the flow velocity. When solutions, intentionally contaminated with similar to 1% of covalent lysozyme dimer were used, these undesirable phenomena occurred at about half the flow rates required in pure solutions. Thus, we conclude that enhanced convective supply of impurities to the interface causes an increase in step-bunching related defects, growth deceleration and, in some cases, cessation. Finally, we correlate the "slow protein crystal growth" to step bunch formation. We show that in the absenceof significant step density variations, the kinetic coefficient for step propagation is as high as 4 x 10(-3) cm/s, which is 1-2 orders of magnitude higher than the previously determined, apparent values for any protein. (C)1999 Elsevier Science B.V. All rights reserved.

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Documento generato il 26/09/20 alle ore 02:34:38