Abstract
X-ray radiation damage propagation is explored for hydrated starch granules in order to reduce the step resolution in raster-microdiffraction experiments to the nanometre range. Radiation damage was induced by synchrotron radiation microbeams of 5, 1 and 0.3 µm size with ∼0.1 nm wavelength in B-type potato, Canna edulis and Phajus grandifolius starch granules. A total loss of crystallinity of granules immersed in water was found at a dose of ∼1.3 photons nm(-3). The temperature dependence of radiation damage suggests that primary radiation damage prevails up to about 120 K while secondary radiation damage becomes effective at higher temperatures. Primary radiation damage remains confined to the beam track at 100 K. Propagation of radiation damage beyond the beam track at room temperature is assumed to be due to reactive species generated principally by water radiolysis induced by photoelectrons. By careful dose selection during data collection, raster scans with 500 nm step-resolution could be performed for granules immersed in water.
Highlights
Raster-microdiffraction with synchrotron radiation microbeams has become a routine technique for studying hierarchically organized synthetic and biological polymers (Riekel, 2000; Paris, 2008; Riekel et al, 2009)
We quantified radiation damage for a single 50 mmdiameter potato starch granule contained within a water-filled capillary at room temperature (RT) (Fig. 1a) which was exposed at the same position to 200 exposures of 0.1 s each by a 1.1 mm beam
Particle size analysis during amorphization shows too much fluctuation to test this hypothesis. This is compounded by reports on a more complex shape of the 100-peak owing to the presence of two hydrated fractions (Lemke et al, 2004) which makes a particle size determination problematic
Summary
Raster-microdiffraction with synchrotron radiation microbeams has become a routine technique for studying hierarchically organized synthetic and biological polymers (Riekel, 2000; Paris, 2008; Riekel et al, 2009). A $200 nm step-resolution has been demonstrated for radiation-hard poly(p-phenylene terephthalamide) fibres (Muller et al, 2000; Roth et al, 2003) For hydrated biopolymers, such as cellulose or starch, step increments of 4–5 mm have been used at $13 keV in order to avoid spill-over of radiation damage to neighbouring raster-points (Schoeck et al, 2007; Gebhardt et al, 2007; Lemke et al, 2004). This is somewhat larger than the travel range of photoelectrons in organic matter (O’Neill et al, 2002) which is at the origin of secondary radiation damage. Several raster-microdiffraction studies on single B-type starch granules have already addressed the local structure of the polysaccharide chains (Buleon et al, 1997; Waigh et al, 1997; Lemke et al, 2004; Chanzy et al, 2006; Gebhardt et al, 2007) and their superstructure (Waigh et al, 1999)
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