PubMed Health⌕ Search

Biomedical subjects

H Chanzy

Publications and source records attributed to H Chanzy.

32 records · Page 2Linked to original sources
PubMed1994

Single crystals of V amylose complexed with n-butanol or n-pentanol: structural features and properties.

Rectangular single crystals of amylose complexed with n-butanol or n-pentanol were prepared by adding these precipitants to metastable aqueous solutions of amylose. The crystals were analysed by electron and X-ray diffraction. It was confirmed that the crystals have an orthorhombic P2(1)2(1)2(1) symmetry with cell parameters: a = 2.74 nm, b = 2.65 nm and c (chain axis) = 0.8 nm. Within the unit cell, the amylose chains were organized in antiparallel pairs of parallel 6(5) amylose helices with four molecules of precipitant located between the helices and occupying about 10% of the cell volume. Upon desolvation, the crystals were invariably converted to the hexagonal close-packed VH amylose. The crystals could also be swollen in a series of solvents or solvent mixtures without losing their single crystal characteristics. Such treatments retained the orthorhombic symmetry but resulted in an expansion of their a and b cell parameters while c remained constant at 0.8 nm.

1-Butanol↗
PubMed1993

Morphological and structural features of amylose spherocrystals of A-type.

Amylose spherocrystals of A-type were grown by mixing ethanol with hot aqueous solutions of short chain amylose followed by slow cooling to 4 degrees C. The spherocrystals which had a diameter of the order of 10 microns were observed by scanning electron microscopy and analysed by X-ray diffraction. They were also cross-sectional for transmission electron microscopy and electron diffraction investigation. These techniques showed that each spherocrystal consisted of an assembly of thin elongated single crystal-like domains of A-type amylose radiating from the centre of the spherocrystal. In each of these domains, the chain axis of amylose was found to be aligned with the long axis of the domain, in agreement with the overall positive optical birefringence observed for the spherocrystals. The spherocrystals which were rather fragile broke easily along the boundaries of the crystalline domains. This could explain the susceptibility of these structures to alpha-amylase digestion.

Amylose↗
PubMed1993

Visualization of the adsorption of a bacterial endo-beta-1,4-glucanase and its isolated cellulose-binding domain to crystalline cellulose.

Endo-beta-1,4-glucanase A (CenA), a cellulase from the bacterium Cellulomonas fimi, is composed of two domains: a catalytic domain and a cellulose-binding domain. Adsorption of CenA and its isolated cellulose-binding domain (CBD.PTCenA) to Valonia cellulose microcrystals was examined by transmission electron microscopy using an antibody sandwich technique (CenA/CBD.PTCenA-alpha CenA IgG-protein A-gold conjugate). Adsorption of both CenA and CBD.PTCenA occurred along the lengths of the microcrystals, with an apparent preference for certain crystal faces or edges. CenA or CBD.PTCenA, but not the isolated catalytic domain, were shown to prevent the flocculation of microcrystalline bacterial cellulose. The cellulose-binding domain may assist crystalline cellulose hydrolysis in vitro by promoting substrate dispersion.

Actinomycetales↗
PubMed1992

Single crystals of alpha-chitin.

Single crystals of alpha-chitin were grown by the addition of precipitants to dilute solutions of low molecular weight chitin fractions dissolved in aqueous LiSCN. At temperatures around 200 degrees C, bundles of thin needle-shaped crystals were obtained. Each of these needles was an alpha-chitin single crystal, characterized by a spot electron diffraction pattern which could be indexed along the hk0 reciprocal net corresponding to the Minke and Blackwell unit cell [a = 0.474 nm, b = 1.88 nm, c (fibre axis) = 1.032 nm, space group P2(1)2(1)2(1)]. In a crystal, the a* parameter was along the crystal axis and the b* perpendicular to it.

Chitin↗
PubMed1991

The crystal and molecular structure of VH amylose by electron diffraction analysis.

The crystal and molecular structures of VH amylose were determined by a constrained linked-atom least-squares refinement, utilizing intensities measured from electron diffraction patterns and stereochemical restraints. Hexagonal platelet single crystals were grown from dilute aqueous ethanol solution and their electron diffraction diagrams analysed. These data indicated that the amylose chains were crystallized in a hexagonal lattice with a = b = 13.65 A, c (chain axis) = 8.05 A and space group P6(5)22. The best model obtained using the base plane data coupled with a stereochemical refinement yielded R = 0.24 (R'' = 0.25). It corresponded to a system of left-handed 6-fold helices packed on an hexagonal net but with statistically random up/down chain disorder. A column of six water molecules was present within each helical repeat. Additionally, the gap between each pair of adjacent helices was bridged by two water molecules positioned so as to allow hydrogen bonding with chains of either sense. This proposed crystal structure differs somewhat from previous reports which invoked orthorhombic lattices and requires a regularly alternating arrangement of up and down chains to account for the intensity. Suggestions are made to account for these differences.

Amylose↗
PubMed1991

Liquid crystal-type assembly of native cellulose-glucuronoxylans extracted from plant cell wall.

In numerous plant cell walls, the cellulose microfibrils are arranged in a helicoidal pattern which has been considered as an analog to a cholesteric order. Here, we report on the spontaneous helicoidal organization which occurs in acellular conditions from aqueous suspensions of cellulose. The cellulosic mucilage of mature seeds of quince (Cydonia oblonga L) was studied both in situ (pre-release mucilage) and after water extraction and in in vitro re-assembly (prolonged high speed ultracentrifugation, further progressive dehydration and embedding in LR White methacrylate or hydrosoluble melamine resin). The cellulosic component was characterized by the use of cellobiohydrolase (CBH1) bound to colloidal gold, and the glucuronic acid residues of the xylan matrix were characterized by the use of cationised gold. Inside the seeds, the pre-release mucilage is mostly helicoidal, with the occurrence of more or less ordered domains, which indicate a fluid organization relevant to an actual liquid crystal state. Cytochemical tests revealed the tight association between cellulose and glucuronoxylans, the latter constituting a charged coat around each microfibril. Following the hydration of the seed, a cellulosic suspension was extracted in which microfibrils were totally dispersed. The progressive dehydration of the suspension gave rise to concentrated viscous drops. Ultrastructural observations revealed the occurrence of multidomain organization, from non-ordered to cholesteric-like regions, revealing that the mucilage is at the same time crystalline and liquid. This constitutes the first demonstration that liquid crystal type assemblies can arise from crystalline and biological cellulose in aqueous suspension. It strengthens the hypothesis that a transient liquid crystal state must occur during the cellulose ordering. The possible morphogenetic role of the glucuronoxylans in the cholesteric organization of the cellulose is discussed.

Cell Wall↗
PubMed1990

Single crystals of chitosan.

Lamellar single crystals of chitosan were prepared at 125 degrees C by adding ammonia to a low DP fraction of chitosan dissolved in water. The crystals gave sharp electron diffraction diagrams which could be indexed in an orthorhombic P2(1)2(1)2(1) unit cell with a = 8.07 A, b = 8.44 A, c = 10.34 A. The unit cell contained two anti-parallel chitosan chains and no water molecules. It was found that cellulose microfibrils from Valonia ventricosa could act as nuclei for inducing the crystallization of chitosan on cellulose. This produced a shish-kebab morphology.

Chitin↗
PubMed1990

Single crystals of V amylose complexed with isopropanol and acetone.

Single crystals of amylose complexed with isopropanol or acetone were prepared by adding these precipitants to a metastable aqueous solution of amylose. With both precipitants, similar micrometre sized platelet crystals were obtained. They gave indistinguishable electron diffraction diagrams which could be indexed in an orthorhombic unit cell, with a = 28.26 A, b = 29.30 A, c = 8.01 A and in a space group P2(1)2(1)2(1) or P2(1)2(1)2. Within the unit cell, the amylose chains are organized in antiparallel pairs of parallel 6(5) amylose helices occupying 70% of the cell content, the remaining 30% consisting of isopropanol/acetone and water, with an estimate of 10 isopropanol/acetone molecules for 52 water molecules per unit cell. If the crystals are suspended in pure isopropanol at various temperatures or in pure methanol at room temperature, they undergo a de-solvation process that ultimately converts them into VH amylose. De-solvation with isopropanol left the crystals intact whereas with methanol, they became cracked during the shrinkage. An explanation is proposed for such difference.

1-Propanol↗
PubMed1989

Electron crystallography of linear polysaccharides.

The present article illustrates how the use of electron diffraction data coupled with realistic molecular modeling can yield to unambiguous structural elucidation of linear polysaccharides in the crystalline state. The series of the original ab initio quantitative crystal structure analyses is presented, along with a description of the methods. Pertinent examples showing the unique ability and utility of electron crystallography to yield new structural insights for biologically interesting macromolecules are given.

Crystallography↗
PubMed1988

The double-helical nature of the crystalline part of A-starch.

A new three-dimensional structure of the crystalline part of A-starch is described in which the unit cell contains 12 glucose residues located in two left-handed, parallel-stranded double helices packed in a parallel fashion; four water molecules are located between these helices. Chains are crystallized in a monoclinic lattice with a = 2.124 nm, b = 1.172 nm, c = 1.069 nm and gamma = 123.5 degrees, the c axis being parallel to the helix axis. Systematic absences are consistent with the space group B2. The structure was derived from joint use of electron diffraction of single crystals, X-ray powder patterns decomposed into individual peaks and previously reported X-ray fibre diffraction data after adequate re-indexing. The repeating unit consists of a maltotriose moiety where the glucose residues have the 4C1 pyranose conformation and are alpha(1----4) linked. The conformation of the glycosidic linkage is characterized by torsion angles (phi, psi) which take the values (91.8, -153.2), (85.7, -145.3) and 91.8, -151.3); all the primary hydroxyl groups exist in a gauche-gauche conformation. There are no intramolecular hydrogen bonds. Within the double helix, interstrand stabilization is achieved without any steric conflict and through the occurrence of O(2)...O(6) type hydrogen bonds. The present structure is consistent with both physicochemical and biochemical aspects of the crystalline component of the cereal starch granules.

Amylose↗
PubMed1985

The molecular and crystal structure of dextrans: a combined electron and X-ray diffraction study. II. A low temperature, hydrated polymorph.

The crystal and molecular structure of a dextran hydrate has been determined through combined electron and X-ray diffraction analysis, aided by stereochemical model refinement. A total of 65 hk0 electron diffraction intensities were measured on frozen single crystals held at the temperature of liquid nitrogen, to a resolution limit of 1.6 A. The X-ray intensities were measured from powder patterns recorded from collections of the single crystals. The structure crystallizes in a monoclinic unit cell with parameters a = 25.71 A, b = 10.21 A, c (chain axis) = 7.76 A and beta = 91.3 degrees. The space group is P2(1) with b axis unique. The unit cell contains six chains and eight water molecules, with three chains of the same polarity and four water molecules constituting the asymmetric unit. Along the chain direction the asymmetric unit is a dimer residue; however, the individual glucopyranose residues are very nearly related by a molecular 2-fold screw axis. The conformation of the chain is very similar to that in the anhydrous structure, but the chain packing differs in the two structures in that the rotational positions of the chains about the helix axes (the chain setting angles) are considerably different. The chains still pack in the form of sheets that are separated by water molecules. The difference in the chain setting angles between the anhydrous and hydrate structures corresponds to the angle between like unit cell axes observed in the diffraction diagrams recorded from hybrid crystals containing both polymorphs. Despite some beam damage effects, the structure was determined to a satisfactory degree of agreement, with the residuals R''(electron diffraction) = 0.258 and R(X-ray) = 0.127.

Dextrans↗
PubMed1976

High-angle electron diffraction of frozen hydrated collagen.

By using the techniques developed by Taylor et al. [(1975) J. Mol. Biol. 92, 165-167] (freezing of the hydrated specimen before its insertion into the electron microscope and keeping it frozen throughout the diffraction experiment), it was possible to obtain a high-angle electron-diffraction pattern from collagen fibrils. This pattern is in good agreement with that obtained by high-angle X-ray diffraction. Electron diffraction will be very useful to study collagen, because the diffraction pattern from a carefully selected area of one fibril is now feasible.

Animals↗
PubMedDate not supplied

Structural aspects in semicrystalline samples of the mannan II family.

A series of samples having the mannan II character were prepared by either (i) desincrusting stems of Acetabularia crenulata, or (ii) acetylating these stems, followed by dissolution and recrystallization under deacetylation conditions, or (iii) recrystallizing at low temperature the alkali soluble fraction of ivory nut mannan. The samples were characterized by transmission electron microscopy, X-ray and electron diffraction analysis together with (13)C CP/MAS NMR spectroscopy. Whereas the A. crenulata stems consisted of a mixture of mannan I and mannan II, the recrystallized samples were all of the hydrated mannan II family and occurred in a ribbonlike morphology where the mannan chains were organized with their molecular axis perpendicular to the ribbon long axis. The recrystallized ivory nut mannan samples presented X-ray and electron diffraction diagrams, together with (13)C solid-state NMR spectra recorded at 95% RH, different from those of recrystallized A. crenulata recorded under the same RH conditions. They corresponded therefore to a new allomorph of the mannan II family. Despite this difference, when the recrystallized samples were in an aqueous environment, they revealed an additional well-defined perhydrated phase, which showed the same (13)C solid-state NMR spectrum for both samples. As this phase, which gave 6-band NMR spectra with narrow line-width and low T1, had no counterpart in X-ray diffraction, it was attributed to specific amorphous segments of mannan chains, gaining some mobility when swollen in water. When the samples were totally dried, their NMR spectra lost their resolution, thus indicating the role played by water for the structural organization of the crystalline and amorphous components of mannan II.

Acetylation↗