Cellulose synthesized by Acetobacter xylinum in the presence of plant cell wall polysaccharides

Acetobacter xylinum was cultured in Schramm–Hestrin (SH) medium containing glucuronoxylan (xylan medium) or pectin (pectin medium). Loose bundles of cellulose microfibrils were formed in the xylan medium. In contrast the cellulose ribbons formed in the pectin medium were the same as those normally formed in SH medium.The periodic acidthiocarbohydrazidesilver proteinate method indicated that positive reacted substances located along cellulose microfibrils formed in both mediums. Freeze-fracture and deepetching electron microscopy also revealed that polysaccharides exist around cellulose microfibrils. X-ray diffractometry and Fourier Transform In-frared spectroscopy demonstrated that the addition of xylan induced a change in the ratio of cellulose I and I. Electron diffraction analysis revealed that xylan discontinuously affected the crystalline structure of cellulose microfibrils. Pectin did not have this effect. Glucuronoxylan in the medium prevented the assembly of cellulose     

Affinity of Hemicellulose for Cellulose Produced by Acetobacter Xylinum

Cellulose composites were produced by culturing Acetobacter aceti subsp. xylinum (ATCC 53524, agitation tolerant strain) under shaking and agitating conditions in the presence of 2% pine or beech Björkman lignin-carbohydrate complexes (LCCs) or six different types of hemicellulosic polysaccharides including glucuronoxylan, glucomannan, O-acetyl-glucuronoxylan, arabinoglucuronoxylan, arabinogalactan and xyloglucan. Hemicellulosic polysaccharide contents in cellulose composites were similar in spite of the differences in culture, shaking and agitating conditions. On the basis of hemicellulosic polysaccharide contents and X-ray diffraction patterns after extraction by dilute NaOH solution, glucomannan family polysaccharides were found to have the highest affinity to bacterial cellulose. Composites with neutral and acidic LCCs were resistant against alkali while high lability of their delignified carbohydrates against alkali indicates the importance of lignin for formation of cellulose-hemicellulose-lignin framework of plant secondary cell-walls.     

Native Cellulose II Production by Acetobacter Xylinum Under Physical Constraints

Acetobacter xylinum, which normally produces ribbon-like microfibrils of cellulose I, occasionally synthesizes a band-like cellulose (native band, or NB) having a cellulose II crystal structure with a putative folded-chain structure. In contrast to a previous finding of NB production by a mutant strain of A. xylinum, we found that the wild-type strain also produced NB when incubated on agar plate medium. Incubation of the same strain in liquid media of varying viscosity with the addition of polyethylene glycol (PEG) resulted in the production of normal ribbon at low viscosities and NB at high viscosities. This behaviour was independent of the molecular weight of PEG and there seemed to be a critical level in viscosity for the switching from ribbon production to NB production. These findings strongly suggest that NB production is induced by a low mobility of cells in the culture medium due to physical constraints.     

Determination of Intermolecular Acetyl Distribution of Cellulose Triacetate by Reversed Phase High Performance Liquid Chromatography

The chromatographic method for the determination of the intermolecular acetyl distribution of cellulose triacetate (CTA) was established; the key point of the method is a gradient elution by gradually changing the solvent composition of the ternary mixture of chloroform, methanol, and water on a phenyl-bonded silica gel stationary phase. A positive correlation between the retention time and the degree of acetyl substitution was observed under the established chromatographic conditions. The validity of the elution peak width as the measure of intermolecular acetyl distribution was confirmed by the co-injection and fractionation experiments and the comparison of a peak width with a statistically estimated distribution.     

Polyaniline Nanofibrils Array Synthesized within the Anodic Aluminum Oxide Template

Introduction Many methods for the fabrication of nanoparticles have been developed ranging from lithographic techniques to chemical methods. The method termed template synthesis for preparation of a variety of micro- and nano-materials has been explored1-3. The template membranes employed contain cylindrical pores with mono-disperse diameters, that extend through the entire thickness of the membrane. The diameter of this nanocylinder is determined by the diameter of the pores of the template m…     

Structural Parameters of Cellulose Produced by Acetobacter Xylinum and Their Variation in the Course of Drying of Gel Films

The cellulose-producing power of the VKM V-800 Acetobacter xylinum strain under conditions of static culture was studied. The culture medium was optimized with the aim to increase the cellulose yield and obtain highly crystalline cellulose I with molecular weight of about 5 × 10⁵.     

Thermoanalytical studies on complexes of ketoconazole with cyclodextrin derivatives

Inclusion complexation between cyclodextrin derivatives (hydroxypropyl-β-cyclodextrin and methyl-β-cyclodextrin) and a very poorly water-soluble antifungal agent, ketoconazole, was studied. Solid products were prepared by physical mixing, kneading and spray-drying methods in four molecular ratios: 2:1, 1:1, 1:2 and 1:3. The possibility of complex formation between the drug and the cyclodextrins was studied by thermal analysis. Supplementary techniques, such as X-ray diffractometry and Fourier transformation-infrared spectroscopy, were also applied to interpret the results of the thermal study of the products. This revised version was published online in July 2006 with corrections to the Cover Date.     

Occurrence of Polypeptides in Other Organisms Cross-reacting with Antibodies Against A. Xylinum Cellulose Synthase

Antibodies (anti-83 and anti-93) against the cellulose synthase complex from A. xylinum ATCC 53582 have been employed to study the evolutionary conservation of this enzyme complex among various A. xylinum strains, selected species of other cellulose- producing bacteria, algae, and vascular plants. Of the 18 A. xylinum strains examined, the 83 Kd polypeptide clearly is detected only in 4 strains while the 93 Kd polypeptide is observed in all 18 strains. Assuming that the revised acsAB gene (Saxena et al., 1994) encoding the 83 and 93 Kd polypeptides as a single polypeptide holds true for all A. xylinum strains, it is proposed that the cellulose synthase is conserved in A. xylinum but with varying degrees of homology. An unknown regulatory mechanism causing the degradation of the 83 Kd polypeptide in response to agitated culturing conditions has been suggested to explain the absence of the 83 Kd polypeptide in most of the Acetobacter strains examined. A. xylinum cellulose synthase appears to be conserved in phylogenetically related Rhizobium and Agrobacterium species, but not in algae and plants.     

Microstructural Characteristics of Hydrothermally Synthesized LiFePO_4 and Relevant Impacts on the Electrochemical Performance

Phospho-olivine LiFePO 4 has been prepared using a facile hydrothermal method by optimizing the reaction temperatures.Structural and morphological properties of the as-prepared LiFePO 4 powders are systematically characterized using X-ray diffraction (XRD),scanning electron microscopy (SEM),transmission electron microscopy (TEM),infrared spectra,UV-vis spectra,and M ssbauer spectroscopy.It is demonstrated that the samples prepared in the temperature range from 160 to 200 ℃ crystallize in a single phase of phospho-olivine structure.All particles are rod-like,showing dimensions of approximately 150～200 nm in width and 500～600 nm in length with a preferential growth direction of [001].Within the lattice of LiFePO 4 rods,Fe 2+ ions partially disorderly occupy the Li + sites,which increases the cell volume.The electrochemical performance of LiFePO 4 is investigated by charge/discharge experiments.It is found that LiFePO 4 rods prepared at 200 ℃ deliver a specific discharge capacity of 147 mAh g-1,which is apparently superior to those prepared at lower reaction temperatures like 160 and 180 ℃.This observation is explained in terms of the thinner surface noncrystalline layer and lower level of Fe 2+ disorderly occupying the Li + sites.     

Structure and Properties of Electrochemically Synthesized Silver Nanoparticles in Aqueous Solution by High-Resolution Techniques

The aim of this work was to deeply investigate the structure and properties of electrochemically synthesized silver nanoparticles (AgNPs) through high-resolution techniques such as transmission electron microscopy (TEM), scanning electron microscopy (SEM), Zeta Potential measurements, and matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF-MS). Strong brightness, tendency to generate nanoclusters containing an odd number of atoms, and absence of the free silver ions in solution were observed. The research also highlighted that the chemical and physical properties of the AgNPs seemed to be related to their peculiar oxidative state as suggested by X-ray photoelectron spectroscopy (XPS) and X-ray powder diffraction (XRPD) analyses. Finally, the MTT assay tested the low cytotoxicity of the investigated AgNPs.     

New Possibilities of the Acetosulfation of Cellulose

Regioselectively substituted cellulose sulfates in C2/3-, C2/6-, or C6-position of the anhydroglucose unit are accessible by certain synthesis routes. Thereby, products with different properties and various application areas are resulted. Important characteristics of cellulose sulfates regarding their applications are solubility (e.g. in water), rheological behavior, different interaction with low or high molecular cations, thermo reversible gel formation, enzymatic degradability, anticoagulant and antiviral activity. In C6-position substituted cellulose sulfates can be synthesized in principle by acetosulfation. The acetosulfation is a quasi-homogeneous synthesis proceeding under gradually dissolution of the cellulose by using different reactivity of the primary and secondary OH-groups as soon as converting cellulose acetate sulfates. After precipitation of the polymer the acetyl groups are cleaved in alkaline solution. The focus of our study was firstly the investigation of the acetosulfation in different polar aprotic solvents by various sulfating and acetylating agents. In general it should be investigated if C6 substituted cellulose sulfates can be obtained by acetosulfation with different solvents and agents. The products were characterized by ¹³C-NMR and Raman spectroscopy.     

Optical Properties and Photopolymerization of Liquid Crystalline (Acetyl) (Ethyl) Cellulose/Acrylic Acid System

The structure and properties of a chiral nematic phase, which reflects one hand of circularly polarized light in a narrow region of wavelength, of fully acetylated (ethyl) cellulose [(acetyl) (ethyl) cellulose, AEC] in acrylic acid (AA) were studied in comparison with (ethyl) cellulose (EC). AEC mesophase formed right-handed chiral nematic structure while EC formed left-handed one. AEC mesophase showed higher birefringence and reflection intensity. The relationship between the reflection wavelength and the polymer concentration was negatively correlated for both AEC and EC mesophases. The relationship between the reflection wavelength and the molecular weight was also negative for AEC mesophase whereas positive for EC mesophase. AEC mesophase was solidified by photopolymerization of AA moiety. It was revealed that the optical properties of AEC mesophase could be preserved by photopolymerization, since the resulting solid material reflects selectively one hand of circularly polarized light.     

Thermoanalytical studies on complexes of clotrimazole with cyclodextrins

γ-Cyclodextrin and dimethyl-β-cyclodextrin were used as solubilizing agents for a very poorly water-soluble drug, an imidazole derivative antifungal agent, clotrimazole; with the aim of improving the physicochemical properties of the drug. Solid products were prepared by physical mixing, kneading, precipitation and spray-drying methods in 1:1 and 1:2 drug:cyclodextrin molar ratios. Drug interactions were studied by thermoanalytical methods such as DSC, DTA, TG and DTG, X-ray diffractometry and Fourier transformation-infrared spectroscopy. The results demonstrated the formation of inclusion complexes in some products. This revised version was published online in July 2006 with corrections to the Cover Date.     

Studies on the Effect of Structure to Property Stability of Glucomannan

1 INTRODUCTION Directive action of hydrogen bond paves the way for new fields of biological activity, molecular re- cognition and crystal engineering[1]. Hydrogen bond plays an important role in the physical and chemical properties, such as melting point, boiling point, solu- bility, acid strength, viscosity and hardness degree[2]. At present, the popular tools used to investigate hy- drogen bond include wet melting point method, chromatography analysis method, spectrum method and diffract…     

Local structure analysis of the mineral core of reverse micelles in dispersion in hydrocarbons

This paper presents morphological and local structure studies, carried out by means of transmission electron microscopy and X-ray absorption spectroscopy techniques, of the mineral core of organometallic reverse micelles in a dispersion in hydrocarbons. The results obtained for the micelles and their aggregates allowed us to propose a layered structure for the mineral core and the molecular stacking.     

All-cellulose nanocomposites by surface selective dissolution of bacterial cellulose

All-cellulose nanocomposites using bacterial cellulose (BC) as a single raw material were prepared by a surface selective dissolution method. The effect of the immersion time of BC in the solvent (lithium chloride/N,N-dimethylacetamide) during preparation on the nanocomposite properties was investigated. The structure, morphology and mechanical properties of the nanocomposites were characterized by X-ray diffraction, scanning electron microscopy, and tensile testing. The optimum immersion time of 10 min allowed the preparation of nanocomposites with an average tensile strength of 411 MPa and Young’s modulus of 18 GPa. With the longest immersion time of 60 min, the prepared composite sheet turns to express a very high toughness characteristic possessing a work-to-fracture as high as 16 MJ/m³. These biobased nanocomposites show high performances thanks to their unique structure and properties.     

Structural Study of Micro and Nanotubes Synthesized by Rapid Thermal Chemical Vapor Deposition

The structures of micro and nanotubes obtained by pyrolysis of hydrocarbons, hold onto silicon (Si) substrates, are reported in this work. The tubes fabrication experiments were carried out by Rapid Thermal Chemical Vapor Deposition (RTCVD) using propane (C₃H₈) as carbon (C) precursor. Selection of parameters such as temperature of deposition, vacuum conditions or surface cleaning leads to the creation of tubular structures. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), selected area electron diffraction (SAED) and energy dispersive X-ray measurements (EDX) are the microbeam techniques that allow to characterize the tubes found in the studied specimens. Different tube configurations such as isolated nanorods, Y-type junctions or fiber-like layers are evidenced. Metallic catalysis seems to be the mechanism involved in the wires formation since Fe particles are present inside the CNT tubes. Other poly-crystalline inclusions are also evidenced by SAED. The composition of the nanotubes changes from tip to tail in an amorphous matrix. The growth mechanisms leading to tube formation are described.     

Photochromic behaviour of ozonated and photoirradiated cellulose studied by fluorescence spectroscopy

Samples of ozonated pure cotton cellulose have been subjected to three extended periods of irradiation with monochromatic light at 350 nm, with intervening dark periods. The changes during the treatments were monitored using fluorescence spectroscopy. Photochromic behaviour, comprising a fairly rapid emission intensity decrease during irradiation and a slower recovery of the emission intensity in the dark at ambient temperature, was observed. Starting from the completion of the first irradiation/dark treatment the intervening dark reaction almost completely restored the situation prevailing before irradiation. The photochromism observed for a reference sample of cellulose not pretreated with ozone and for microcrystalline cellulose was similar but differed both in amplitude and in fluorescence recovery during the dark periods. The ozonated sample was also irradiated with the entire spectrum of a medium pressure Hg lamp. This treatment caused a strong increase in the emission intensity and a red-shift of the emission maximum. The changes caused by ozonation and irradiation were also studied by diffuse reflectance FT-IR and UV-visible reflectance spectroscopy.     

Applications of FT-IR/microscopy in forensic analysis

The technique of FT-IR/microscopy is applied to a variety of problems faced by the forensics chemist. These are as varied as the identification of drugs and fibers to the assignment of the origin of a paint sample. Our efforts in the effective utilization of FT-IR/microscopy in this area and usage of new data bases to aid in identifications are discussed.     

Experimental Testing of Lateral and Depth Resolution in Imaging Methods

A polymer laminate and a PA-PTFE blend were studied by various imaging methods (FT-IR, Raman, ESEM). Different lateral and depth resolution of the methods were used to gain complementary information on the structure of the materials. Radiation damage caused by the electron beam during ESEM investigation was studied by Raman global imaging.