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International audience; Following the first electron micrographs of cotton in 1940, the development of transmission electron microscopy applied to native cellulose has been evolving in a series of successive advances. At first, faced with the weak contrast of the early images, the operators had to use specific electron dense contrasting agents to reveal the ultrastructure of their samples. It was thus found that all native celluloses consisted of microfibrils, with some size variations depending on the sample origin. Following this, a major advance was achieved when the electron microscopes could be adjusted with low electron doses, allowing the recording of diffraction diagrams from the electron beam-sensitive cellulose samples. Under these conditions, one could obtain information of cellulose itself and not, as before, of the contrasting agent. This important development applied to microdiffraction conditions revealed that some large cellulose microfibrils could yield spot diagrams typical of single crystals. Their recording led to a decisive progress for resolving the molecular and crystal structure of the two cellulose allomorphs, cellulose I and I. Using various combinations of diffracted beams to create the images, the so called "diffraction contrast images" could then be developed. These micrographs showed many aspects of the crystalline core of cellulose, including spectacular high-resolution images showing the molecular planes of cellulose in their crystalline environment. Today, electron diffraction, diffraction contrast imaging and low-dose electron microscopy have become major tools to follow the effect of various physical, chemical and biochemical processes at the cellulose crystalline level.

We report magnetic birefringence measurements up to high fields (17.5 T) of dilute aqueous suspensions of rod-like cellulose nanocrystals with well characterized distributions of lengths, widths and thicknesses. We compare these data with three models, one with colinear (1), one with perpendicular cylindrically symmetric tensors for diamagnetic susceptibility and refractive index (2) and one with biaxial diamagnetic anisotropy (3). We find that taking into account polydispersities of length, width, and thickness is essential for accurate fitting and that model 1 is the most appropriate, presumably because of the twisting of the suspended nanocrystal along their long axis. The best-fitted susceptibility anisotropy was Δχz(xy) = χzz–(χxx+χyy)/2 = −2.44 × 10–6 when considering only the crystalline core of nanocrystals and, more appropriately, Δχz(xy) = −0.95 × 10–6 when including crystalline core and skin. The latter value is slightly higher than Δχz(xy) = −0.68(5) × 10–6 deduced from estimations using Pasca...

International audience; Single crystals of amylose V2-propanol, i.e., amylose co-crystallized with water and 2-propanol, were prepared from synthetic linear amylose. When observed under frozen hydrated conditions, these crystals yielded base-plane electron diffraction diagrams containing more than 100 independent diffraction spots, whose intensities were used to solve the crystal structure of this complex. The molecular and crystal structure of amylose V2-propanol clearly indicated that the amylose molecules were organized in 7-fold left-handed helices, with 2-propanol and water molecules located as guests both within and between the helices. The V2-propanol unit cell contains 4 helices, distributed in two antiparallel pairs of parallel helices organized along the P212121 symmetry. The helices are organized along alternating motifs of 4 helices in a close-packed hexagonal arrangement together with 4 others in a nearly square organization surrounding a central column of water and 2-propanol. Whereas the location of the amylose helices is well established in the unit cell, the coordinates of the guest molecules could not be defined with certainty, most likely due to a positional disorder. A tentative model of the guest molecule distribution is presented, which consists of 2 2-propanol and 2 water molecules within the helical cavity together with 4 water molecules and 2 2-propanol molecules between the helices. The mobility of the guest and its description as a continuum, rather than at fixed crystallographic positions, explain why so many structures isomorphous to V2-propanol can be obtained with different guest molecules, while yielding similar electron diffraction diagrams.

Cellulose microfibrils from Valonia ventricosa cell-wall fragments were immersed into molten N-methylmorpholine-N-oxide monohydrate (NMMO·H2O), stabilized with n-propyl gallate and kept at 80 °C. The resulting ultrastructural modifications, which were followed by transmission electron microscopy and electron diffraction analysis, showed that within minutes the solvent slowly penetrated inside the crystalline microfibrils and progressed as a wedge in between the cellulose chains without cutting them. Prior to dissolution, a longitudinal subfibrillation of the initial microfibrils occurred, leading to the observation of highly swollen microfibrils, which could reach diameters up to three times larger than those of the initial samples. This mode of swelling is compared with those occurring in other systems, where the intracrystalline swelling of cellulose has been described at the ultrastructural level.Key words: cellulose swelling, Valonia cellulose, N-methylmorpholine-N-oxide.

Semiconducting diblock copolymers of polyethylene (PE) and regioregular poly(3-hexylthiophene) (P3HT) are demonstrated to exhibit a rich phase behaviour, judicious use of which permitted us to fabricate field-effect transistors that show saturated charge carrier mobilities, ?FET, as high as 2 × 10-2 cm2V-1 s-1 and ON-OFF ratios, Ion/Ioff ?105 at contents of the insulating PE moiety as high as 90 wt %. In addition, the diblock copolymers display outstanding flexibility and toughness with elongations at break exceeding 600 % and true tensile strengths around 70 MPa, opening the path towards robust and truly flexible electronic components. © 2007 WILEY-VCH Verlag GmbH & Co. KGaA

Cellulose whiskers resulting from HCl acid hydrolysis of tunicin were subjected to TEMPO-mediated oxidation under various conditions and the extent of the resulting oxidation was characterized by Fourier-transform infrared spectroscopy (FT-IR), conductimetry, X-Ray diffraction analysis and transmission electron microscopy (TEM). With degree of oxidation of up to 0.1 the samples kept their initial morphological integrity and native crystallinity, but at their surface the hydroxymethyl groups were selectively converted to carboxylic groups, thus imparting a negative surface charge to the whiskers. When dispersed in water these oxidized whiskers did not flocculate and their suspensions appeared birefringent when viewed between cross polarizers, thus indicating a liquid crystalline behavior.

Synchrotron X-ray data have been collected to 1.4 A resolution at the NE-CAT beam-line at the Advanced Photon Source from fibers of cellulose Iβ and regenerated cellulose II (Fortisan) at ambient temperature and at 100 K in order to understand the effects of low temperature on cellulose more thoroughly. Crystal structures have been determined at each temperature. The unit cell of regenerated cellulose II contracted, with decreasing temperature, by 0.25%, 0.22% and 0.1% along the a, b, and c axes, respectively, whereas that of cellulose Iβ contracted only in the direction of the a axis, by 0.9%. The value of 4.6×10−5 K−1 for the thermal expansion coefficient of cellulose Iβ in the a axis direction can be explained by simple harmonic molecular oscillations and the lack of hydrogen-bonding in this direction. The molecular conformations of each allomorph are essential unchanged by cooling to 100 K. The room temperature crystal structure of regenerated cellulose II is essentially identical to the crystal structure of mercerized cellulose II.

The crystal and molecular structure, together with the hydrogen-bonding system in ammonia-mercerized cellulose IIII, has been determined using synchrotron X-ray and neutron fiber diffraction data. The structure has a one-chain monoclinic unit cell with an asymmetric unit that contains only one glucosyl residue and with the hydroxymethyl group in the gt conformation. The hydrogen-bonding system is well-defined with no evidence of disorder. A bifurcated hydrogen bond links a donating secondary alcohol O3 atom to a ring O5 atom (major) and a primary alcohol O6 atom (minor) of an adjacent residue in the same chain. Two hydrogen bonds are present between neighboring chains, perpendicular to the chain direction. A detailed comparison of the crystal structure and hydrogen-bonding system reported here for cellulose IIII and those reported previously for the other cellulose polymorphs is given. The conformation of the chain in cellulose IIII has features similar to that of the center chain in the highly stable cel...

The semiconductors [Pt(NH2dmoc)4][PtCl4], where dmoc denotes (S)-3,7-dimethyloctyl, and [Pt(NH2eh)4][PtCl4], where eh is (R)-2-ethylhexyl, are soluble quasi-one-dimensional compounds with a backbone of linearly arranged platinum atoms. Uniaxially oriented films of those metal complexes of approximately 0.1 μm thickness were deposited from solution on quartz glass slides covered with a friction-deposited orientation layer of approximately 40 nm poly(tetrafluoroethylene) (PTFE). UV/vis spectra recorded with polarized light as well as electron diffraction patterns of [Pt(NH2dmoc)4][PtCl4] indicated that the films were highly ordered, the platinum arrays oriented parallel to the orientation direction of the PTFE molecules. As a consequence, the films exhibited a pronounced anisotropy, among other characteristics, in the electric conductivity, which is of potential use in electronic devices.

The semiconducting material having a quasi-one dimensional chain-structure with a backbone of linearly arranged platinum atoms is studied. It is based on Magnus' green salt. The processing and properties of thin films, fibers and field-effect transistors (FET) comprising semiconducting platinum based chain-structures are also reported.

Cellulose whiskers resulting from the acid hydrolysis of tunicin were subjected to partial silylation by the addition in toluene of a series of alkyldimethylchlorosilanes, with alkyl moieties ranging from isopropyl to n-butyl, n-octyl and n-dodecyl. The samples were characterized by elemental composition, X-ray diffraction analysis, FT-IR, transmission electron microcopy, and their dispersion in organic solvents of various polarities was investigated. As the partial silylation resulted essentially in surface derivatization of the whiskers, the extent of their silylation was characterized by their degree of surface substitution (DSs). With DSs of the order of 0.6/1, the whiskers kept their morphological integrity, but due to their surface silylation, they became readily dispersible in solvents of low polarity such as THF. The resulting suspensions, which did not flocculate, were stable and appeared birefringent when viewed between cross polars. With a DSs greater than 1, the core of the whiskers became silylated, leading to the loss of their whisker character. At this level, it was no longer possible to obtain any birefringent suspension.

The mercerization of homogenized primary wall cellulose extracted fromsugar beet pulp was investigated by transmission electron microscopy (TEM),X-ray diffraction together with 13C CP-MAS NMR, and FT-IR spectroscopy.For samples resulting from acid extraction, mercerization began at 9% NaOH, whereasfor samples purified by alkaline treatment, the mercerization started at 10%NaOH. The change in morphology when going from cellulose I to cellulose II wasspectacular, as all the microfibrillar cellulose morphology disappeared duringthe treatment. This change in morphology was very drastic as soon as the NaOHconcentrations were increased beyond 8 and 9% for the acid and alkalinepreparedsamples, respectively. On the other hand, the conversion was found to be moreprogressive in terms of increasing NaOH concentration when the transformationwas analyzed by X-ray diffraction or spectroscopy. Our observations of themercerization of isolated cellulose microfibrils are consistent with theconceptof cellulose microfibrils made of parallel chains in cellulose I and crystalsofcellulose II consisting of antiparallel chains.

2The aim of this work was to develop a biochemical approach to study (13)-β-d-glucan (callose) biosynthesis using suspension cultures of Arabidopsis thaliana. Optimal conditions for in vitro synthesis of callose corresponded to an assay mixture containing 50 mm Mops buffer, pH 6.8, 1 mm UDP-glucose, 8 mm Ca2+ and 20 mm cellobiose. The enzyme was Ca2+-dependent, and addition of Mg2+ to the reaction mixture did not favour cellulose biosynthesis. Enzyme kinetics suggested the existence of positive homotropic cooperativity of (13)-β-d-glucan synthase for the substrate UDP-glucose, in agreement with the hypothesis that callose synthase consists of a multimeric complex containing several catalytic subunits. Detergents belonging to different families were tested for their ability to extract and preserve membrane-bound (13)-β-d-glucan synthase activity. Cryo-transmission electron microscopy experiments showed that n-octyl-β-d-glucopyranoside allowed the production of micelle-like structures, whereas vesicles were obtained with Chaps and Zwittergent 3-12. The morphology and size of the (13)-β-d-glucans synthesized in vitro by fractions obtained with different detergents were affected by the nature of the detergent tested. These data suggest that the general organization of the glucan synthase complexes and the properties of the in vitro products are influenced by the detergent used for protein extraction. The reaction products synthesized by different detergent extracts were characterized by infrared spectroscopy, methylation analysis, 13C-NMR spectroscopy, electron microscopy and X-ray diffraction. These products were identified as linear (13)-β-d-glucans having a degree of polymerization higher than 100, a microfibrillar structure, and a low degree of crystallinity.

The seed endosperm from the Leguminosae Schizolobium amazonicum was shown to consist of three different parts: (i) the embryo side or interior section; (ii) the seed coat side or exterior section; and (iii) an intermediate zone rich in galactomannan with a 3:1 Man/Gal ratio located between the two sides of the seeds. The exterior section was submitted to a series of hot water and alkaline extractions and the remaining product investigated by monosaccharide analysis, 13 C NMR, X-ray and electron diffraction, together with electron microscopy. After an extraction with 16% NaOH, a linear β(1→4) microfibrillar mannan could be isolated in this portion of the seeds. This is the first time that a pure mannan fraction has been found in the seed of a Leguminosae.

The enzymatic degradation of single crystals of mannan I with the catalytic core domain of a beta-mannanase (EC 3.2.1.78 or Man5A) from Trichoderma reesei was investigated by transmission electron microscopy and electron diffraction. The enzyme attack took place at the edge of the crystals and progressed towards their centres. Quite remarkably the crystalline integrity of the crystals was preserved almost to the end of the digestion process. This behaviour is consistent with an endo-mechanism, where the enzyme interacts with the accessible mannan chains located at the crystal periphery and cleaves one mannan molecule at a time. The endo mode of digestion of the crystals was confirmed by an analysis of the soluble degradation products.

Dispersed cellulose ribbons from bacterial cellulose were subjected to digestion with cloned Cel7A (cellobiohydrolase [CBH] I) and Cel6A (CBH II) from Humicola insolens either alone or in a mixture and in the presence of an excess of β-glucosidase. Both Cel7A and Cel6A were effective in partially converting the ribbons into soluble sugars, Cel7A being more active than Cel6A. In combination, these enzymes showed substantial synergy culminating with a molar ratio of approximately two-thirds Cel6A and one-third Cel7A. Ultrastructural transmission electron microscopy (TEM) observations indicated that Cel7A induced a thinning of the cellulose ribbons, whereas Cel6A cut the ribbons into shorter elements, indicating an endo type of action. These observations, together with the examination of the digestion kinetics, indicate that Cel6A can be classified as an endo-processive enzyme, whereas Cel7A is essentially a processive enzyme. Thus, the synergy resulting from the mixing of Cel6A and Cel7A can be explained by the partial endo character of Cel6A. A preparation of bacterial cellulose ribbons appears to be an appropriate substrate, superior to Valonia or bacterial cellulose microcrystals, to visualize directly by TEM the endo-processivity of an enzyme such as Cel6A.

The relative reactivity of the Iα and Iβ phases of Valonia cellulose toward partial homogeneous acetylation was investigated by FT-IR and CP/MAS 13C-NMR spectroscopy. At the beginning of the acetylation and when only partial reaction was achieved, it was found that the reactivity of the Iα phase was substantially higher than that of the corresponding Iβ component. At a later stage of acetylation, the difference in reactivity between the two phases was less pronounced. In correlation with previous ultrastructural observations (Sassi and Chanzy, 1995), it can be concluded that at equivalent accessibility, the Iα phase of cellulose is indeed more reactive toward acetylation than the Iβ phase. The homogeneous acetylation of cellulose is essentially a surface reaction that affects only the accessible parts located at the surface of the microfibrils. The decrease in the rate of Iα phase disappearance with acetylation time confirms therefore that the microstructure of Valonia is made of domains that are distributed throughout the thickness of its microfibrils.

The cellulose system of the viscous fibrous cellulosic polysaccharide (viscan) in the viscin tissue of the European mistletoe, Viscum album L., was analyzed by chemical and physicochemical techniques including sugar analysis, optical and transmission electron microscopy, X-ray and electron diffraction together with solid state CP/MAS 13C-NMR spectroscopy. The results confirmed that in the elongated thin viscin cells, the cellulose microfibrils (having a diameter of around 3 nm) were tightly coiled with their axes perpendicular to the long axis of the cell. Upon stretching these cells became deformed by more than a hundred fold. In such a deformation, the cellulose microfibrils became unwound to be perfectly aligned along the stretching direction. Based on solid-state CP/MAS 13C-NMR spectroscopic analysis of the viscin tissue, it was found that its cellulose consisted of Iα and Iβ polymorphs in the ratio 1:1.

The crystal and molecular structure and hydrogen bonding system in cellulose II have been revised using new neutron diffraction data extending to 1.2 {angstrom} resolution collected from two highly crystalline fiber samples of mercerized flax. Mercerization was achieved in NaOH/H{sub 2}O for one sample and in NaOD/D{sub 2}O for the other, corresponding to the labile hydroxymethyl moieties being hydrogenated and deuterated, respectively. Fourier difference maps were calculated in which neutron difference amplitudes were combined with phases calculated from two revised X-ray models of cellulose II. The revised phasing models were determined by refinement against the X-ray data set of Kolpak and Blackwell, using the LALS methodology. Both models have two antiparallel chains organized in a P2{sub 1} space group and unit cell parameters: a = 8.01 {angstrom}, b = 9.04 {angstrom}, c = 10.36 {angstrom}, and {gamma} = 117.1{degree}. One has equivalent backbone conformations for both chains but different conformations for the hydroxymethyl moieties: gt for the origin chain and tg for the center chain. The second model based on the recent crystal structures of cellotetraose, has different conformations for the two chains but nearly equivalent conformations for the hydroxymethyl moieties. On the basis of the X-ray data alone, themore » models could not be differentiated. From the neutron Fourier difference maps, possible labile hydrogen atom positions were identified for each model and refined using LALS. The second model is significantly different from previous proposals based on the crystal structures of cellotetraose, MD simulations of cellulose II, and any potential hydrogen-bonding network in the structure of cellulose II determined in earlier X-ray fiber diffraction studies. The exact localization of the labile hydrogen atoms involved in this bonding, together with their donor and acceptor characteristics, is presented and discussed. This study provides, for the first time, the coordinates of all of the atoms in cellulose II.« less

The choice of vinyl polymers as the plastic matrix for the pigment in xerographic toner did not anticipate the deinking thrust which has swept the paper industry. The hydrolytic stability of the carbon-carbon bond in vinyl and diene copolymers has prevented the use of a plastic degradation strategy for toner removal. New toner resins based on alkali degradable plastics have been shown to allow up to 97% toner removal. Based on polyimide and polyesterimide toners (either magnetic or non-magnetic) developed by Xerox, this study uses flash hydrolysis in the presence of 0.5% alkali to repulp. The process operates on 200-300 second batches at 190-210°C. The best results were obtained using alkaline repulping and magnetic deinking coupled with washing. The alkali also inhibits the hydrolytic degradation of cellulose although it negatively impacts the brightness. Thus the use of a polymer resin containing a chemically sensitive function allows conversion of the toner to pigment fragments and water soluble oligomers. The former is best separated by magnetic deinking while the latter is removed by washing.

Individual dendrimer molecules of poly(amidoamine) (PAMAM) from generation 10 (G10) to G5 were imaged by conventional transmission electron microscopy (TEM) after staining with aqueous sodium phosphotungstate. The dendrimers were resolved as separate, beam-stable entities, and their sizes and distribution of sizes were statistically analyzed and compared with data from small-angle X-ray scattering in solution. Aqueous G10 dendrimers were also characterized by examination in the frozen, hydrated state after quench-freezing in liquid ethane (cryo-TEM) and the data compared with the results of the staining experiments. To a first approximation, the dendrimers appeared circular in projection and the diameters conformed to a Gaussian distribution which broadened somewhat with increasing generation number. Cryo-TEM, in general, confirmed the staining experiments but suggested that, in the native state, there is more variability in the shapes of the dendrimers, with polyhedral shapes occurring quite frequently.

The seeds of Cassia spectabilis DC (family: Leguminoseae), an Indian fast growing spreading tree, contain about 40% of endosperm and possess the characteristics of becoming a potential source of commercial gum. The purified galactomannan shows Mw 1.1×10 6 , intrinsic viscosity [ η ] 615 mL/g with k ′=1.706×10 −1 , and a mannose to galactose ratio of 2.65. The hydrolysis of the fully methylated polysaccharide reveals clearly the expected structure of legume galactomannans. The orthorhombic lattice constants of the hydrated gums are as follows: a =9.12 A, b =25.63 A and c =10.28 A. The results of X-ray fiber studies show that the b dimension of the unit cell is very sensitive to relative humidity (RH), galactose substitution and orientation of the films. The probable space group symmetry of the unit cell is P 2 1 2 1 2. Rheological studies of the galactomannan have shown that the transition from semi-dilute to dilute regime occurs at a critical concentration C c * =2.75. The slope of the log–log plot of specific viscosity versus C at zero shear rate is 5.87 in the more concentrated regime. The viscoelastic and critical shear rate behavior indicate the characteristics of a coil polymer. The large dependence of the viscosity on the coil overlap parameter is probably due to polymer–polymer interactions and peculiarity of the galactose distribution along the chain. Above 20 g/L concentration, the rheological behavior of the gum is like the one of a weak-gel.

Filaments ejected by Phaeocystis globosa Scherffel, organized in star-like structures, were observed and analyzed before and after their discharge from cells. Ultrastructural observations obtained after cryofixation and cryosubstitution led to a model for their storage within the cell and for their ejection from the cell. Electron diffraction analysis on the ejected filaments demonstrated their chitinous composition. This technique indicated without ambiguity that each filament was in fact a whisker-like α-chitin crystal, with the axes of the corresponding polymer chains aligned with the filament's axis. X-ray microanalysis of the mats of filaments indicated that the silica content suggested by earlier workers was an artifact resulting from the filtration procedure.

Because cellulases are finding more applications in the textile and detergent industries, their effect on cotton fibres must be evaluated. For this purpose, the action of a recombinant cellulase, endoglucanase V from the fungus Humicola insolens, has been followed by scanning electron microscopy (SEM) in classical longitudinal views as well as in cross-sections of cotton fibres. The experiments were conducted at large enzyme dilution typical of conditions where cellulases are used for biopolishing, i.e. for the removal of defects created by mechanical abrasion. Endoglucanase V appears to restrict its action to the hydrolysis of the loose fibrils created at the surface of the fibres and no indication of extensive enzyme penetration and damage to the interior of the fibres could be detected by SEM. The adsorption sites for endoglucanase V on cotton fibres were examined by transmission electron microscopy (TEM) on ultrathin cross-sections after immuno-gold labeling of the enzyme. This approach showed that the enzymes did not penetrate the fibres but remained at their surface. The use of an immuno-gold labeled cellulase provides a new way to probe the surface features of cotton fibres

Lamellar crystals of inulin were grown by crystallizing sharp fractions of low molecular weight inulin from dilute aqueous ethanol solutions. The crystals were analyzed using three-dimensional electron diffraction and X-ray powder diagrams. Two crystalline polymorphs were observed, depending on the hydration conditions: a hydrated form which indexed on an orthorhombic unit cell, with space group P2 1 2 1 2 1 and with cell dimensions of a = 1.670 nm, b = 0.980 nm and c (chain axis) = 1.47 nm, together with a pseudo-hexagonal semi-hydrated form with unit cell parameters a = 1.670 nm, b = 0.965 nm and c (chain axis) = 1.44 nm. These parameters, together with the density data, indicate that inulin crystallizes along a pseudo-hexagonal six-fold symmetry with an advance per monomer of 0.24 nm. The difference between the hydrated and the semi-hydrated unit cells does not seem to correspond to any change in the conformation of inulin, but rather to a variation in water content.

With the aim of improved understanding of the mechanism of depolymerase action, folded chain lamellar single crystals were partially degraded with PHB-depolymerase A from Pseudomonas lemoignei. Enzymatically degraded single crystals of bacterial poly(3-hydroxybutyrate), PHB, were observed by transmission electron microscopy and were found to be splintered parallel to their long axes. Prior to degradation, the crystals were lamellar with macroscopic dimensions of approximately 2.5 μm by 20 μm and the classical baseplane single crystal diffraction pattern corresponding to bacterial PHB was recorded. When observed by TEM, the partially degraded crystals had been splintered longitudinally to a needlelike morphology. The needlelike fragments of PHB still yielded the same crystalline baseplane diffraction pattern. These results support an “edge attack” model for the degradation of PHB single crystals and explain, at a molecular level, the lack of decrease in molecular weight during the degradation since the dir...

Transglucosylation reactions catalyzed by cellodextrin phosphorylase from Clostridium thermocellum were reinvestigated by using a series of cellobiosyl residues as glycosyl acceptors and α- d -glucopyranosyl phosphate (Glc-1-P) as glycosyl donor. When cellobiose was used as an acceptor, various unsubstituted cellodextrins, ranging from water-soluble products to crystalline precipitates were obtained, depending on the concentration in acceptor. 4-Thiocellobiose, methyl β-cellobioside, and methyl 4-thio-α-cellobioside could also be used as acceptors with the same efficiency as cellobiose. The enzyme showed higher activity when β-cellobiosides bearing strong hydrophobic aglycons were used. A practical preparation of methyl β-cellotrioside, cellotetraoside and cellopentaoside was achieved, using a 1:5 molar ratio of methyl β-cellobioside to the glucosyl donor.

An ultrastructural study of the acetylation of cellulose was achieved by subjecting well characterized cellulose samples fromValonia cell wall and tunicin tests to homogeneous and heterogeneous acetylation. The study involved transmission electron microscopy observations on negatively stained microcrystals as well as diffraction contrast images of the cross sections of wall fragments at various stages of the reaction. These observations showed that the acetylation of crystalline cellulose proceeds by a reduction of the diameters of the crystals while their lengths are reduced to a lower extent. These results were corroborated by electron and X-ray diffraction experiments that showed that during the reaction there was a rapid decrease in the intensities of the equatorial diffraction spots of cellulose, whereas those located on the meridian or close to the meridian stayed constant. A model of acetylation of the cellulose crystal is presented. It is based on a non swelling reaction mechanism that affects only the cellulose chains located at the crystal surface. In the case of homogeneous acetylation, the partially acetylated molecules are sucked into the acetylating medium as soon as they are sufficiently soluble. In heterogeneous conditions the cellulose acetate remains insoluble and surrounds the crystalline core of unreacted cellulose.

The highly crystalline a chitin occurring in the grasping spines of Sagitta was investigated by electron diffraction together with high-resolution electron microscopy. These techniques confirmed the presence of diffraction spots 001 and 0k0 with 1 or k of odd order. These reflections, which should be absent in the P2 1 2 1 2 1 space group, were identified as originating from double diffraction effects resulting from the high perfection of the samples as well as their thicknesses. This study confirms therefore the antiparallelism of the chitin chains in a system that can be considered as a model for α chitin.

The crystalline structures of four Indian seed galactomannans having mannose to galactose ratios ranging from 1.16 to 2.55 have been investigated by wide-angle X-ray diffraction of oriented films. The orthorhombic lattice constants (A) of the polysaccharides are as follows: galactomannans from Trifolium alexandrium, a = 9.02, b = 30.80, c = 10.27; from Medicago sativa (lucerne) a = 9.00, b = 30.66, c = 10.24; from Cassia siamea, a = 9.00, b = 24.81, c = 10.30; and from Cassia saltiana, a = 8.99, b = 24.75, c = 10.30. In agreement with results already published for other seed gums of commercial importance, the values of the b dimension of the unit cell of galactomannans decrease with decreasing galactose content. The values of the a and c dimensions, as found for other galactomannans, are similar to those of mannan I and mannan II, respectively, and can be understood in terms of conformational restrictions on the mannan backbone imposed by the β-(1→ 4) linkage. This similarity suggests that galactomannans of low and high galactose content have a fundamentally related crystal structure.

Lamellar single crystals of some regio-selectively substituted cellulose hetero-esters: cellulose propionate diacetate (CPDA, 2,3-di-O-acetyl-6-O-propionyl cellulose), cellulose acetate dipropionate (CADP, 6-O-acetyl-2,3-di-O-propionyl cellulose), cellulose butyrate diacetate (CBDA, 2,3-di-O-acetyl-6-O-butyryl cellulose) and cellulose acetate dibutyrate (CADB, 6-O-acetyl-2,3-di-O-butyryl cellulose), have been prepared at high temperature in a mixture of dibenzyl ether andn-tetradecane. The CPDA crystals were lozenge-shaped whereas those of CADP, CBDA and CADB had a ribbon morphology. CPDA crystals gave well-resolved electron diffractograms from which the reciprocal lattice parameters a*=0.807 nm−1,b*=0.400 nm−1 andγ*=90° could be determined. Systematic absences occurred at every odd reflection along the two orthogonal axesa*andb*. Thus, the CPDA diffraction pattern is consistent with a pgg symmetry. For CADP, the electron diffraction pattern is consistent with a pmg two-dimensional space group withb the unique axis along the ribbon direction. The diagram yields the reciprocal lattice parameters a* = 0.902 nm−1,b*=0.651 nm−1 andγ*=90°. The CBDA electron diffractogram yields the following cell parameters and two-dimensional space group:a*=0.482 nm−1,b*=0.659 nm−1 andγ*=90°, and a pgg symmetry; and that of CADB:a*=0.834 nm−1,b*=0.645 nm−1 andγ*=90°, and a pmg symmetry.

The frozen-hydrated/cryo-transmission electron microscopy technique has been used to observe polysaccharide aggregates in vitreous ice. Images of kappacarrageenan in the helical state showed fairly large aggregates of a loosely intertwined network of thin rigid rods. Aggregates of agarose in the helical conformation were also visualised. In comparison with those of kappa-carrageenan, the strands of agarose were shorter and less rigid. This difference is discussed in terms of the current knowledge of the gelation of these polysaccharides.

Suspensions of rod-like cellulose crystallites of axial ratio ≈ 20–40, prepared by acid hydrolysis of natural cellulose fibres with sulphuric acid, give stable ordered fluids that display well-formed textures and disclinations characteristic of chiral nematic liquid crystalline phases. The critical volume fraction for phase separation of salt-free suspensions is typically 0.03, with a relatively narrow biphasic region. Because of the negative diamagnetic susceptibility of cellulose, the ordered phase becomes oriented in a magnetic field with its chiral nematic axis parallel to the applied field.

The oriented growth of V amylose n-butanol crystals on cellulose was obtained by seeding solutions of amylose with cellulose microfibrils or microcrystals. In all cases, the lamellar crystals of amylose grew exclusively on the cellulose to give a ‘shish-kebab’ morphology, consisting of a regular system of edge-on amylose crystals organized perpendicular to the cellulose microfibrillar direction. Such behaviour seems to result more from a row nucleation phenomenon rather than from a true epitaxial growth.

Summary: Amylose forms V-type crystalline inclusion complexes with a large varietyofsmallmolecules.Severalauthorshaveproposedmodelsforthesecomplexesbasedonamylosesingleheliceswith6,7and8glucosylunitsperturn.However,sofar,onlyasmall number of crystal structures have been solved and several models are stillhypothetical. We have recently shown that in the unit cell of such complex withisopropanol, the amylose molecules were organized in 7-fold left-handed helices, withisopropanolandwatermoleculeslocatedasguestsbothwithinandbetweenthehelices. Keywords: electron crystallography; inclusion complexes; molecular modeling; singlecrystals; V-amylose; X-ray crystallography Introduction Amylose is an essentially linear homopo-lymer of a(1,4)- D -glucose that can beextracted from native starch. [1] This linearmolecule can also be synthesized in vitro byamylose synthases such as amylosucrase [2] or starch phosphorylase. [3] Amylose can berecrystallized from solution by cooling oraddition of precipitant. Depending on themolecular weight, concentration, tempera-ture and nature of the solvent, differentmorphologies and allomorphic type areobserved for the amylose crystals.

The crystalline structure of native cellulose, with its unique microfibrillar morphology resulting from a complex biogenesis mechanism, has not only been the most studied subject in polymer science, but is still generating great interest along with lively debates and controversies. This issue of Cellulose features such a debate in the form of two articles dealing with the conformational analysis of the glucosidic bond in the cellulose chains. This debate is but the latest incident in a long string of events, which represent the foundation of our current understanding of this important material. This makes this an opportune moment to reflect on some of the major milestones in the history of cellulose structure evaluation, which also often involved debates and controversies. It was in 1913, i.e. close to one century ago, that Nishikawa and Ono showed the first diffraction patterns of two cellulose-based plant materials, namely bamboo and hemp, taking advantage of the discovery of the interference phenomena of X-rays reported 1 year earlier by Laue, Friedrich and Knipping. Following this early report, diffraction diagrams of a large number of cellulose materials were duly recorded and subjected to analysis, as it was felt that the knowledge of the crystalline structure of cellulose was of great importance for the development and improvement of cellulose-based products. While recording diffraction patterns of these specimens, it was soon realized that even the X-ray data sets of the most crystalline samples remained limited and it was therefore hard to deduce from them alone the required structural details. It is only when the diffraction data could be complemented by the occurrence of new techniques that substantial advances toward the structural description of cellulose could be made. The sequential emergence of such techniques explains the succession of steps leading to the present understanding. In the progress toward the molecular description of the crystal structure of cellulose from X-ray diffraction data, a first landmark was the incorporation of the stereochemistry of the glucosyl moieties in the molecular models built by, among others, Meyer and Mark (1928), later revised by Meyer and Misch (1937), who presented a model where the crystal of cellulose consisted of two antiparallel chains. This last model, which remained the established standard for at least two decades, was confronted with a series of conflicting data, resulting from new techniques. In 1958, the recording of electron diffraction diagrams of frozen Valonia cell wall fragments allowed Honjo and Watanabe to obtain diffraction data sets far better H. Chanzy—affiliated with the Universite Joseph Fourier and member of the Institut de Chimie Moleculaire de Grenoble.

The high-temperature crystallization of poly( p -phenylene terephthalamide) (PPTA) from dilute organic solutions was achieved through the introduction of a non-solvent, or precipitating agent, at the desired crystallization temperature. The morphology and crystal structure were examined for crystals produced from PPTA polymer with two different molecular weights ( M w = 46000 and 3430 g mol −1 ), using transmission electron microscopy. For the high-molecular-weight polymer, ribbon-like crystals were produced, while the low-molecular-weight polymer yielded small needles or platelets. In both cases, electron diffraction showed that the Northolt allomorph was obtained. For the high-molecular-weight polymer, the molecular axes were parallel to the ribbon axes in a chain-extended type structure. A hypothesis for the orientation of the low-molecular-weight PPTA in the small platelets, is also given.

The presence of chitin in hyphal cell walls and regenerating protoplast walls ofSaprolegnia monoi¨ca was demonstrated by biochemical and biophysical analyses. α-Chitin was characterized by X-ray diffraction, electron diffraction, and infrared spectroscopy. In hyphal cell walls, chitin appeared as small globular particles while cellulose, the other crystalline cell wall component, had a microfibrillar structure. Chitin synthesis was demonstrated in regenerating protoplasts by the incorporation of radioactiveN-acetylglucosamine into a KOH-insoluble product. Chitin synthase activity of cell-free extracts was particulate. This activity was stimulated by trypsin and inhibited by the competitive inhibitor polyoxin D (Ki 20 μM). The reaction product was insoluble in 1M KOH or 1M acetic acid and was hydrolyzed by chitinase into diacetylchitobiose. Fungal growth and cell wall chitin content were reduced when mycelia were grown in the presence of polyoxin D. However, hyphal morphology was not altered by the presence of the antibiotic indicating that chitin does not seem to play an important role in the morphogenesis ofSaprolegnia.

Deep-sea hydrothermal vent worms live´in tubes made of giant β-chitin crystallites (50 nm in diameter, several μm in length) embedded in a protein matrix. These chitin cyrstallites form a liquid-crystal-like structure differing from the wellknown cholesteric arrangement of classical chitin-protein systems. Furthermore, and in contrast with the latter systems, the vestimentiferan chitin-protein systems are produced by goatskin-shaped glands. Rod-shaped elements in the lumen of these glands were identified by DCTEM and Au-WGA labeling and freeze fracture as chitin crystallites. The main characteristics of these “chitin secreting glands” are described.

Structural studies of substituted 1,3,5-benzenetrisamides, a new family of highly versatile and efficient nucleating and clarifying agents for polymeric materials, are reported. Subtle details of the molecular structure of these species are shown to have a major influence on their solid-state order, morphology, and ability to nucleate specific polymorphs of isotactic polypropylene and induce a broad spectrum of useful mechanical and optical properties in the latter material.

13 C NMR, IR and electron diffraction results show that when annealing conditions ranging from 260°C and 30 min to 280°C and 60 min in a series of mediums ranging from helium gas to various solvents were selected, around 80 % of of the Iα phase could be converted into thr Iβ, whereas a residual 20 % remained unmodified. With polar solvents the transformation occurred at temperatures lower than with nonpolar mediums. Samples of lower crystallinity (bacterial cellulose) were converted more easiliy than highly crystalline samples (Valonia).

Cellulose from the cell wall of the green alga Microdictyon tenuius exhibits two distinct crystalline phases. The major phase has a one-chain, triclinic (P1) structure with unit cell parameters of a=0.674 nm, b=0.593 nm, c (chain axis)=1.036 nm, α=117°, β=113°, and γ=81°. The crystal unit cell of the minor component has two chains and is monoclinic (P2 1 ), with a=0.801 nm, b=0.817 nm, c (chain axis)=1.036 nm, and γ the monoclinic angle=97.3°. The triclinic phase is metastable, and annealing it in dilute alkali at 260°C converts it into the monoclinic form. The triclinic and the monoclinic structures correspond to the Iα and Iβ spectra, respectively

Cellulose samples of various origins were subjected to heat annealing. The initial samples contained various proportions of Iα (triclinic) and Iβ (monoclinic) phases. They could be classified into two families: a family I where the amount of the phase Iα was either small or below detection and a family II where this phase was the major component. The annealing treatment revealed that the Iα phase was metastable as it could be converted totally to the stable Iβ phase