References of "Willaert, Ronnie"
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See detailKinetics and Thermodynamics of Glucose Isomerase Crystallization
Sleutel, Mike; Willaert, Ronnie; Gillespie, Christopher et al

in Crystal Growth & Design (2009), 9

A quantitative study using laser confocal microscopy combined with differential interference microscopy on the kinetics and thermodynamics of the crystallization of glucose isomerase is presented ... [more ▼]

A quantitative study using laser confocal microscopy combined with differential interference microscopy on the kinetics and thermodynamics of the crystallization of glucose isomerase is presented. Fundamental crystallization parameters are determined from the kinetics of step advancement and rates of two-dimensional (2D) nucleation. The ruling mass transfer pathway and accompanying activation barriers are discussed. In brief, the solubility exhibits normal temperature dependence and the crystallization enthalpy is the thermodynamic driving force. The diminishing entropic cost for higher PEG concentrations is attributed to water structuring and a decrease in water activity. The prominent step generation mechanism is homogeneous 2D nucleation for high supersaturations. At low driving forces 2D nucleation occurs on anomalously hyperactive sites and the step edge free energies for homogeneous and heterogeneous nucleation are determined. The number of nucleation centers for both mechanisms are estimated and from the density of nucleation centers we obtain for the activation barrier of adsorption ∼3.8 kJ mol-1. No step-step interaction is observed for interstep distances >70 nm. Theoretical fits of step velocity data suggest surface diffusion makes a non-negligible contribution to surface kinetics. From the temperature dependence of the step kinetic coefficient the activation barrier for crystallization was determined to be <22.4 kJ mol-1. [less ▲]

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See detailCounterdiffusion protein crystallisation in microgravity and its observation with PromISS (Protein Microscope for the International Space Station)
Zegers, Ingrid; Carotenuto, Luigi; Evrard, Christine ULg et al

in Microgravity Science and Technology (2006), XVIII

The crystallisation by counterdiffusion is a very efficient technique for obtaining high-quality protein crystals. A prerequisite for the use of counterdiffusion techniques is that mass transport must be ... [more ▼]

The crystallisation by counterdiffusion is a very efficient technique for obtaining high-quality protein crystals. A prerequisite for the use of counterdiffusion techniques is that mass transport must be controlled by diffusion alone. Sedimentation and convection can be avoided by either working in gelled systems, working in systems of small dimensions, or in the absence of gravity. We present the results from experiments performed on the ISS using the Protein Microscope for the International Space Station (PromISS), using digital holography to visualise crystal growth processes. We extensively characterised three model proteins for these experiments (cablys3*lysozyme, triose phosphate isomerase, and parvalbumin) and used these to assess the ISS as an environment for crystallisation by counterdiffusion. The possibility to visualise growth and movement of crystals in different types of experiments (capillary counterdiffusion and batch-type) is important, as movement of crystals is clearly not negligible. [less ▲]

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