Microstructural metrology of tobacco mosaic virus nanorods during radial compression and heating.

We determined stress-induced deformations and the thermal stability of nanorod-shaped tobacco mosaic virus (TMV) capsids in coffee-ring structures by X-ray nanodiffraction. The hexagonal capsids lattice transforms under compression in the outer boundary zone of the coffee-ring into a tetragonal lattice. The helical pitch of the nanorods increases by about 2.5% across the outer boundary zone while the lateral distance between nanorods decreases continuously across the whole coffee-ring structure by about 2% due to compressive forces. The diffraction patterns show a mixture of helical scattering and Bragg peaks attributed to a lattice of nanorods interlocked by their helical grooves. Thermo-nanodiffraction reveals water loss up to about 100 °C resulting in a reduction of the helical pitch by about 6% with respect to its maximum value and a reduction of the nanorods separation by about 0.5 nm. Up to about 200 °C the pitch is increasing again by about 2%. Secondary crystallization in the bulk reaches a maximum at 150-160 °C. At higher temperatures the crystallinity is continuously decreasing up to about 220 °C. Above about 200 °C and depending on the heating history, the nanorods start disintegrating into small, randomly oriented aggregates.

Identification and dynamics of polyglycine II nanocrystals in Argiope trifasciata flagelliform silk.

Spider silks combine a significant number of desirable characteristics in one material, including large tensile strength and strain at breaking, biocompatibility, and the possibility of tailoring their properties. Major ampullate gland silk (MAS) is the most studied silk and their properties are explained by a double lattice of hydrogen bonds and elastomeric protein chains linked to polyalanine ß-nanocrystals. However, many basic details regarding the relationship between composition, microstructure and properties in silks are still lacking. Here we show that this relationship can be traced in flagelliform silk (Flag) spun by Argiope trifasciata spiders after identifying a phase consisting of polyglycine II nanocrystals. The presence of this phase is consistent with the dominant presence of the -GGX- and -GPG- motifs in its sequence. In contrast to the passive role assigned to polyalanine nanocrystals in MAS, polyglycine II nanocrystals can undergo growing/collapse processes that contribute to increase toughness and justify the ability of Flag to supercontract.

Raster microdiffraction with synchrotron radiation of hydrated biopolymers with nanometre step-resolution: case study of starch granules.

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.

Synchrotron radiation microdiffraction of ballistic molten wax microdrops.

Using stroboscopic techniques, diffraction patterns of ballistic paraffin wax microdrops have been observed. The microdrops, generated by a high-temperature ink-jet system, travel through the 1 mum synchrotron radiation beam with a speed of about 1.4 m/s. Diffraction patterns were recorded in flight by a charge couple device with a microchannel plate image intensifier stage, which was activated with the microdrop generation frequency of 1000 Hz during 2 mus. The data show liquid microdrops with a constant temperature up to 8 mm from the ink-jet system capillary exit. The general technique could be adapted for studying fast structural processes, such as protein conformational changes in aqueous microdrops.

High-pressure potato starch granule gelatinization: synchrotron radiation micro-SAXS/WAXS using a diamond anvil cell.

Potato starch granules have been examined by synchrotron radiation small- and wide-angle scattering in a diamond anvil cell (DAC) up to 750 MPa. Use of a 1 microm synchrotron radiation beam allowed the mapping of individual granules at several pressure levels. The data collected at 183 MPa show an increase in the a axis and lamellar period from the edge to the center of the granule, probably due to a gradient in water content of the crystalline and amorphous lamellae. The average granules radius increases up to the onset of gelatinization at about 500 MPa, but the a axis and the lamellar periodicity remain constant or even show a decrease, suggesting an initial hydration of amorphous growth rings. The onset of gelatinization is accompanied by (i) an increase in the average a axis and lamellar periodicity, (ii) the appearance of an equatorial SAXS streak, and (iii) additional short-range order peaks.

Na-cellulose formation in a single cotton fiber studied by synchrotron radiation microdiffraction.

A cotton fiber was kept under slight tension and exposed locally to a stream of aqueous 1 N NaOH microdrops of 50 microm diameter. The resulting "macrodrop" of about 300 microm size was at the origin of the formation of Na-cellulose I domains extending about 550 microm from the center of the macrodrop along the fiber. The phase transformation zone between cellulose I and Na-cellulose I was mapped by scanning synchrotron radiation microdiffraction using a 300 nm x 300 nm beam. A stitching technique was used to limit radiation damage. Subsequent exposure of the NaOH containing macrodrop to a stream of H2O or HCl microdrops converted part of the Na-cellulose I back into cellulose I.

Characterizing the decay of ancient Chinese silk fabrics by microbeam synchrotron radiation diffraction.

Scanning synchrotron radiation microdiffraction with an approximately 1 x 1 microm(2) beam has been used as a novel method for characterizing the decay of several T'ang dynasty (618-907 AD) silk fabrics. The crystalline fraction could be visualized based on beta-sheet 210 reflection intensities, extracted by recursive peak fits from several thousand diffraction patterns recorded during mesh scans. The azimuthal width of the 210 reflection, which is related to the orientation distribution of the crystalline domains within nanofibrils and the macroscopic orientation of the fibers traversed by the beam, was found to be sensitive to the overall state of decay of the fabric. The fine structure of the histogram of azimuthal width was related to the fiber hierarchical microstructure and the fabric morphology. SAXS/WAXS analysis supports the assumption of an initial loss of the random chain network with decay. At a subsequent state of aging, decay proceeds into the nanofibrils and the silk fibers break up into even smaller fractions.

Structural processes during starch granule hydration by synchrotron radiation microdiffraction.

Starch granule hydration has been examined on the level of a single potato starch granule by static and dynamic synchrotron radiation (SR) microdiffraction techniques. A cryofrozen, hydrated granule was mapped through a 5 microm SR-beam in order to investigate its internal organization. The edge of the granule showed fiber texture scattering due to radially oriented amylopectin helices. The variation of fiber texture across the granule center supports the model of concentric shells. The crystalline phase appears, however, to increase strongly toward the granule center due to a random amylopectin fraction, which could be related to crystallization of short-range ordered amylopectin during hydration. During gelatinization, the shell structure breaks down and remaining fiber-textured amylopectin domains belong probably to the swollen starch granule envelope. Hydration of a granule was initiated by a microdrop generator and followed in situ by SR-microdiffraction. A fast hydration process with a half time of about 7 s seems to reflect the porous nature of starch granules. The size of the hydrated domains suggests that this process is limited to the level of amylopectin side chain clusters. Longer hydration times are assumed to involve remaining short-range ordered amylopectin and results in larger domains.

Recent synchrotron radiation microdiffraction experiments on polymer and biopolymer fibers.

The status of synchrotron radiation (SR) microdiffraction techniques developed at the ID13 beamline of the European Synchrotron Radiation Facility (ESRF) is reviewed for polymer and biopolymer fiber applications. Beam sizes in the micrometer-range have been used to study the local structure of whole fibers such as viscose-rayon or poly(p-phenylene terephthalamide). The possibilities for in situ studies during stretching, extrusion, or indentation will be discussed.

X-ray diffraction on spider silk during controlled extrusion under a synchrotron radiation X-ray beam.

The structure of a single thread of Nephila edulis silk has been studied by in situ X-ray diffraction from a living spider. A systematic increase of orientational order with increasing silking speed up to 40 mm s-1 was observed. Within a few mm from the spinnerets exit, crystalline domains with a beta-poly(L-alanine) structure were observed. The data also suggest an increase in crystalline fraction in the immediate vicinity of the spigot exit.

Submicrometre beams from a hard X-ray waveguide at a third-generation synchrotron radiation source.

The use of an X-ray waveguide for scattering experiments at an undulator of a third-generation synchrotron radiation source is discussed. The performance with a perfect crystal monochromator, multilayer monochromator and focusing mirror is explored. A maximum flux of 8 x 109 photons s(-1) at lambda = 0.083 nm was obtained for a 0.15 (V) x 600 (H) micron(2) beam at the exit of the waveguide with a multilayer monochromator. The combination of an Si (111) monochromator and ellipsoidal mirror resulted in a flux of approximately 10(9) photons s(-1) but with a horizontal compression of the beam to approximately 30 micron. The use of the waveguide in diffraction experiments is addressed.

Investigation of the variation in orientation and crystallinity in poly(ethylene terephthalate) containers using microfocus X-ray diffraction.

The microfocus X-ray beamline at the European Synchrotron Radiation Facility has been used to investigate the variation in molecular orientation and crystallinity in the wall of a container fabricated from poly(ethylene terephthalate). Two-dimensional wide-angle X-ray scattering patterns were recorded and displayed in real time as the specimen was tracked across the incident X-ray beam enabling the measurement of textural changes to be made with a spatial resolution of ~2 mum.

Low-angle synchrotron radiation diffraction with glass-capillary optics.

The use of borosilicate-glass-capillary optics at a chosen wavelength for low scattering has been explored using an undulator beam at the ESRF. With a 2.3 mum beam at 0.092 nm wavelength, a silver behenate powder sample was scanned in two dimensions with a 2 mum step width. Scattering from single crystallites with d(001) = 5.83 nm could be observed. The limit for observation, at low angles, was ca s approximately 0.1 nm(-1) (s = 1/d for d approximately 10 nm).