PubMed Health⌕ Search

Biomedical subjects

C Riekel

Publications and source records attributed to C Riekel.

16 recordsLinked to original sources
PubMed2003

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.

Animals↗
PubMed2002

Two-dimensional x-ray waveguides and point sources.

We show that resonant coupling of synchrotron beams into suitable nanostructures can be used for the generation of coherent x-ray point sources. A two-dimensionally confining x-ray waveguide structure has been fabricated by e-beam lithography. By shining a parallel undulator beam onto the structure, a discrete set of resonant modes can be excited in the dielectric cavity, depending on the two orthogonal coupling angles between the beam and the waveguide interfaces. The resonant excitation of the modes is evidenced from the characteristic set of coupling angles as well as the observed far-field pattern. The x-ray nanostructure may be used as coherent x-ray point sources with a beam cross section in the nanometer range.

Journal Article↗
PubMed2001

Spider silk fibre extrusion: combined wide- and small-angle X-ray microdiffraction experiments.

The major and minor ampullate silks from live Nephila senegalensis (Tetragnathidae) and the major ampullate silk from Euprostenops spp. (Pisauridae) spiders were investigated in situ by X-ray diffraction during forced silking. Wide- (WAXS) and small-angle (SAXS) scattering patterns were obtained at the same time. WAXS data show that the thread at the exit of the spigots already contains beta-sheet poly(alanine) crystallites. SAXS data suggest the presence of microfibrils with an axial repeating period of approximately 8 nm for both Nephila and Euprostenops. Minor ampullate (MI) Nephila silk, however, does not show this axial repeat which is probably due to a higher amount of crystal forming poly(alanine). A microfibrillar morphology, connected by a network of random polymer chains, can explain the presence of highly oriented crystallites, an oriented halo and a diffuse background in the WAXS patterns. At high reeling speeds, bound water is co-extruded with the fibre. It can be squeezed out of the fibre by friction at a needle. Under natural conditions it is the spider's tarsal claws which might serve to squeeze out the water to improve the mechanical properties of the thread during dragline production.

Animals↗
PubMed2001

Twisted plywood pattern of collagen fibrils in teleost scales: an X-ray diffraction investigation.

The distribution and orientation of collagen fibrils, and apatite crystals, in the scales of a bony fish (Leuciscus cephalus) were investigated by X-ray diffraction. The small-angle diffraction patterns obtained with a microfocus scanning setup from most of the examined areas exhibit a distribution of intensity of the collagen reflections according to five preferential orientations, at 36 degrees from one another. It is suggested that the peculiar small-angle X-ray diffraction pattern is due to a plywood arrangement of collagen fibrils in successive layers parallel to the surface of the scale. The fibrils are strictly aligned in each layer and the alignment rotates by 36 degrees in successive layers, according to a discontinuous twist that generates a symmetric plywood pattern. The large spread of the wide-angle reflections does not allow one to distinguish the five directions of orientation in the intensity distribution of the 002 reflection of apatite. However, the patterns recorded from the less ordered regions of the scales display two different orientations of the 002 reflection and allow one to infer a preferential distribution of the apatite crystals with their c-axes parallel to the collagen fibrils. Although much electron microscopic evidence of plywood arrangements in calcified, as well as uncalcified, tissues has been reported, these are the very first diffraction data which unambiguously confirm the presence of these peculiar structures and suggest that this kind of investigation represents a powerful tool with which to study plywood arrangements in biological tissues.

Animals↗
PubMed2001

Microstructural homogeneity of support silk spun by Eriophora fuliginea (C.L. Koch) determined by scanning X-ray microdiffraction.

Scanning X-ray microdiffraction (SXD) permits the 'imaging' in-situ of crystalline phases, crystallinity and texture in whole biopolymer samples on the micrometre scale. SXD complements transmission electron microscopy (TEM) techniques, which reach sub-nanometre lateral resolution but require thin sections and a vacuum environment. This is demonstrated using a support thread from a web spun by the orb-weaving spider Eriophora fuliginea (C.L. Koch). Scanning electron microscopy (SEM) shows a central thread composed of two fibres to which thinner fibres are loosely attached. SXD of a piece of support thread approximately 60 microns long shows in addition the presence of nanometre-sized crystallites with the beta-poly(L-alanine) structure in all fibres. The crystallinity of the thin fibres appears to be higher than that of the central thread, which probably reflects a higher polyalanine content of the fibroins. The molecular axis of the polymer chains in the central thread is orientated parallel to the macroscopic fibre axis, but in the thin fibres the molecular axis is tilted by about 71 degrees to the macroscopic fibre axis. A helical model is tentatively proposed to describe this morphology. The central thread has a homogeneous distribution of crystallinity along the macroscopic fibre axis.

Animals↗
PubMed2000

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.

Algorithms↗
PubMed2000

Bacterial poly(3-hydroxybutyrate): an optical microscopy and microfocus X-ray diffraction study.

Two-dimensional spatially resolved microfocus X-ray diffraction has been used to investigate spherulites of pure bacterial poly(3-hydroxybutyrate) (PHB) and of a blend of natural and synthetic atactic PHB (a-PHB) crystallized at a relatively high temperature (Tc = 140 degrees C). Both samples investigated contained practically two-dimensional spherulites, characterized by wide extinction bands (band spacing > 80 microns). The X-ray diffraction patterns confirmed that the unit cell alpha-axis is oriented along the spherulite radius in PHB and that the same is true for the a-PHB containing blend. Comparison of the matrix of diffraction patterns with the polarized optical micrograph of the scanned sample area indicated a very clear correlation between pattern changes and banding, yielding a straightforward picture of the structural variations within the spherulite.

Bacteria↗
PubMed2000

Evidence for diet effects on the composition of silk proteins produced by spiders.

Silks are highly expressed, secreted proteins that represent a substantial metabolic cost to the insects and spiders that produce them. Female spiders in the superfamily Araneoidea (the orb-spinning spiders and their close relatives) spin six different kinds of silk (three fibroins and three fibrous protein glues) that differ in amino acid content and protein structure. In addition to this diversity in silks produced by different glands, we found that individual spiders of the same species can spin dragline silks (drawn from the spider's ampullate gland) that vary in content as well. Freely foraging ARGIOPE: argentata (Araneae: Araneoidea), collected from 13 Caribbean islands, produced dragline silk that showed an inverse relationship between the amount of serine and glycine they contained. X-ray microdiffraction of the silks localized these differences to the amorphous regions of the protein that are thought to lend silks their elasticity. The crystalline regions of the proteins, which lend silks their strength, were unaffected. Laboratory experiments with ARGIOPE: keyserlingi suggested that variation in silk composition reflects the type of prey the spiders were fed but not the total amount of prey they received. Hence, it may be that the amino acid content (and perhaps the mechanical properties) of dragline silk spun by ARGIOPE: directly reflect the spiders' diet. The ability to vary silk composition and, possibly, function is particularly important for organisms that disperse broadly, such as Argiope, and that occupy diverse habitats with diverse populations of prey.

Amino Acids↗
PubMed2000

Histological structure of human nail as studied by synchrotron X-ray microdiffraction.

Three layers (characterized by different orientations of the keratin molecules) from the outer to the inner side of human nail were observed by synchrotron X-ray microdiffraction. These layers are associated with the histological dorsal, intermediate and ventral plates. The hair-like type alpha-keratin filaments (81 A in diameter), are only present in the intermediate layer (accounting for approximately 2/3 of the nail width) and are perfectly oriented perpendicular to the growth axis, in the nail plane. Keratin filaments of stratum corneum (epidermis) type, found in the dorsal and ventral cells, are oriented in two privileged directions; parallel and perpendicular to the growth axis. This "sandwich" structure in the corneocytes and the strong intercellular junctions, gives the nail high mechanical rigidity and hardness, both in the curvature direction and in the growth direction. Lipid bilayers (49 A thick) parallel to the nail surface fill certain ampullar dilations of the dorsal plate and intercellular spaces in the ventral plate. Using X-ray micro-diffraction, we show that onychomycosis disrupts the keratin structure, probably during the synthesis phase.

Female↗
PubMed2000

Study of the keratinization process in human hair follicle by X-ray microdiffraction.

Synchrotron X-ray micro-diffraction studies along the follicle and the hair fibre allowed us to follow the keratinization process and the progressive organization of the keratin: i) molecular organization appeared progressively in the follicle; the formation of alpha-helices was completed inside the follicle. ii) supramolecular organization appeared only outside the follicle, far from the bulb; filament structure was observed far from the follicle. Comparisons between structures observed for in vitro and in vivo grown hair, whatever in the bulb or in the fibre, indicate there is no evidence of any structural difference. More, no variation in the transition in vivo/in vitro zone has been observed. In vitro and in vivo fibres exhibited the same structure.

Hair↗
PubMed1999

Protein microcrystals and the design of a microdiffractometer: current experience and plans at EMBL and ESRF/ID13.

There is a growing demand for the examination of protein microcrystals at third-generation synchrotron sources. After successful pilot experiments at EMBL/ESRF, which proved that protein microcrystals are often suitable for data collection, operation of the microfocus beamline ID13 was made more user-friendly and suitable for macromolecular crystallography experiments. Given the excellent quality of the beamline microfocusing optics, the key element for successful experiments becomes the handling and visualization of microcrystals. To address this, a microdiffractometer has been designed to allow maximum precision combined with ease of usage and is currently under construction.

Cryoprotective Agents↗
PubMed1998

Submicrometre resolution phase-contrast radiography with the beam from an X-ray waveguide.

Experimental data with unprecedented submicrometre resolution obtained in a phase-contrast radiography experiment in a magnifying configuration are presented. The term 'phase contrast' here indicates that the phase retardation of coherent light in matter was utilized as the contrast mechanism. The coherent and divergent beam exiting an X-ray waveguide was used in a lensless configuration to magnify spatial variations in optical path length up to several hundred times. The defocused image of a nylon fibre was measured with a resolution of 0.14 micro m at the object. Sufficient contrast was found for exposure times of 0.1 s, i.e. in the regime for real-time studies.

Journal Article↗
PubMed1997

Third-generation synchrotron x-ray diffraction of 6-microm crystal of raite, approximately Na3Mn3Ti0.25Si8O20(OH)2.10H2O, opens up new chemistry and physics of low-temperature minerals.

The crystal structure of raite was solved and refined from data collected at Beamline Insertion Device 13 at the European Synchrotron Radiation Facility, using a 3 x 3 x 65 microm single crystal. The refined lattice constants of the monoclinic unit cell are a = 15.1(1) A; b = 17.6(1) A; c = 5.290(4) A; beta = 100.5(2) degrees; space group C2/m. The structure, including all reflections, refined to a final R = 0.07. Raite occurs in hyperalkaline rocks from the Kola peninsula, Russia. The structure consists of alternating layers of a hexagonal chicken-wire pattern of 6-membered SiO4 rings. Tetrahedral apices of a chain of Si six-rings, parallel to the c-axis, alternate in pointing up and down. Two six-ring Si layers are connected by edge-sharing octahedral bands of Na+ and Mn3+ also parallel to c. The band consists of the alternation of finite Mn-Mn and Na-Mn-Na chains. As a consequence of the misfit between octahedral and tetrahedral elements, regions of the Si-O layers are arched and form one-dimensional channels bounded by 12 Si tetrahedra and 2 Na octahedra. The channels along the short c-axis in raite are filled by isolated Na(OH,H2O)6 octahedra. The distorted octahedrally coordinated Ti4+ also resides in the channel and provides the weak linkage of these isolated Na octahedra and the mixed octahedral tetrahedral framework. Raite is structurally related to intersilite, palygorskite, sepiolite, and amphibole.

Journal Article↗
PubMedDate not supplied

Aspects of X-ray diffraction on single spider fibers.

Diffraction patterns of silk from several spider species have been obtained by synchrotron radiation using a beam size > or = 10 microm. Single fiber diffraction patterns were obtained for fiber diameters down to a few microns. Diffraction patterns recorded with a 10 microm wide X-ray beam displayed fiber texture. The presence of two fractions of different crystallinity was confirmed for a single Nephila clavipes fiber. The orientation distribution of the polymer chains of the crystalline fraction along the fiber axis was found to be about 23 degrees full-width at half maximum (fwhm). The azimuthal spread of the short-range order fraction was about 86 degrees fwhm.

Animals↗
PubMedDate not supplied

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.

Kinetics↗