bluuebunny/crossref_metadata_2025 huggingface dataset:
Present and Future Role of Chitin and Chitosan in Food
Authors: Agulló Enrique , Rodríguez María Susana , Ramos Viviana , Albertengo Liliana
Published: October 2003

The conversion of processed discarded material into valuable by‐products and alternative specialty materials has been identified as a timely challenge for food research and development associated with numerous applications of chitinous products. Chitin, chitosan, calcareous chitin, and chitosan, N‐acetylated chitosan, N‐methylene phosphonic chitosan (NMPC), and N‐lauryl‐N‐methylene phosphonic chitosan (LMPC) are being studied as a result of their broad range of food applications. These biopolymers offer a wide range of unique applications including formation of biodegradable films, immobilization of enzymes, preservation of foods from microbial deterioration, as additives (clarification and deacidification of fruits and beverages, emulsifier agents, thickening and stabilizing agents, color stabilization), and dietary supplements. This review summarizes some of the most important developments in this field.
Effect of Chemical Crosslinking on the Swelling and Shrinking Properties of Thermal and pH‐Responsive Chitosan Hydrogels
Authors: Goycoolea Francisco M. , Heras Angeles , Aranaz Inmaculada , Galed Gemma , Fernández‐Valle María E. , Argüelles‐Monal Waldo
Published: October 2003

The ability to form a gel through the physical or chemical crosslinking of chitosan has been well documented. In an attempt to mimic biological systems, thermal and pH‐sensitive chitosan cylindrical hydrogels were produced by a combination of physical and chemical crosslinking processes. To this end, chitosan hydrogels prepared from alkali chitin were molded in cylinders and, once washed, were further crosslinked with glutaraldehyde at stoichiometric ratios, R (= [CHO]/[NH2]), of 1.61 and 3.22 × 10−2. Variation in swelling as a result of stepwise changes in temperature between 40 and 2 °C at pH values of 7.0, 7.6, and 8.0 revealed that the system responds in markedly different manners dependent upon the pH. At pH 7.0, cooling from 40 to 2 °C results in contraction of the gel network structure. While raising the temperature from 2 to 40 °C leads to a rapid swelling response (i.e., ca. a twofold increase in the amount of solvent uptake). Subsequent cooling to 2 °C is accompanied by a new contraction cycle. At pH ≥ 7.6 the temperature dependence of the swelling–contraction behavior is exactly the opposite of that observed at pH 7.0. Very similar trends were observed for the gels at both degrees of crosslinking. The swelling–shrinking behavior observed in gels of pH ≥ 7.6, is similar in kind to that of uncrosslinked gels and is interpreted in terms of a lower critical solution temperature (LCST) volume phase transition, driven by hydrophobic association, presumably involving residual acetyl groups in the chitin. The results at pH 7.0 suggest that the slight ionization of the NH groups leads to destruction of the hydrophobic hydration thus effectively reversing the negative thermal shrinking.

Evolution of the swelling ratio, S, as a function of time and temperature for crosslinked chitosan hydrogels. Circles represent S values recorded at pH 7.0 and triangles those at pH 7.6.

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Evolution of the swelling ratio, S, as a function of time and temperature for crosslinked chitosan hydrogels. Circles represent S values recorded at pH 7.0 and triangles those at pH 7.6.
Recovery of Metal Ions by Chitosan: Sorption Mechanisms and Influence of Metal Speciation
Authors: Navarro Ricardo , Guzmán Javier , Saucedo Imelda , Revilla Javier , Guibal Eric
Published: October 2003

Chitosan is characterized by a high affinity for metal ions due to its high content of amine groups. The sorption mechanism depends on both the protonation of these amine groups and the speciation of metal ions. Metal cations may be adsorbed at pH close to neutrality by chelation mechanism while metal anions can be adsorbed in acidic solutions through ionic interactions with protonated amine groups. Several examples are considered. The first example focuses on Cd sorption, which proceeds by a chelation mechanism on free non‐protonated amine groups in neutral media. In acidic solutions the protonation of amine groups limits the ability of amine groups to complex Cd. The cross‐linking of chitosan with glutaraldehyde also results in a dramatic decrease of sorption properties due to the decrease in the density of complexation sites available for sorption. The sorption of vanadium(V) and molybdenum(VI) illustrates the high capacity of chitosan for the sorption of oxo‐anions. They are very efficiently sorbed in acidic solutions by ionic interactions. The correlation of sorption capacities with the distribution of metal species shows that the sorbent has a greater affinity for highly charged anionic species. The sorption of complex anionic species such as chloro‐complexes of Pd and Pt; and that of copper complexed with organic ligands have also been studied. The optimum conditions for sorption are obtained when anionic complexes predominate in the solution. The chemical modification of chitosan, obtained by grafting of sulfur compounds, allows modifying the sorption mechanism: the ion‐exchange polymer is transformed to a dual ion‐exchange and chelating polymer.

Copper sorption isotherm in presence of sodium citrate (0.004 M) (RNH: fraction of protonated amine groups; ACuC: total fraction of anionic copper complexes; Cu‐FAL: total fraction of copper‐free anionic ligands).

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Copper sorption isotherm in presence of sodium citrate (0.004 M) (RNH: fraction of protonated amine groups; ACuC: total fraction of anionic copper complexes; Cu‐FAL: total fraction of copper‐free anionic ligands).
Controlled Chemical Modifications of Chitosan. Characterization and Investigation of Original Properties
Authors: Auzély Rachel , Rinaudo Marguerite
Published: October 2003

The main techniques developed to characterize chitosan are recalled. The interaction of chitosan with oppositely charged surfactants was investigated giving very important surface activity effects. A few chemical modifications are described and the new properties obtained are mentioned: alkylation gives amphiphilic polymers having interesting thickening behavior; grafting cyclodextrin (chit‐CD) gives a polymer able to include hydrophobic molecules; grafting adamantane gives an amphiphilic polymer able to specifically interact with chit‐CD forming a temporary network with gel‐like behavior.

The viscosities of adamantane‐chitosan, cyclodextrin‐chitosan, and unmodified chitosan solutions studied here.

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The viscosities of adamantane‐chitosan, cyclodextrin‐chitosan, and unmodified chitosan solutions studied here.
Chitosan: An Attractive Biocompatible Polymer for Microencapsulation
Authors: Peniche Carlos , Argüelles‐Monal Waldo , Peniche Hazel , Acosta Niuris
Published: October 2003

Chitosan is a weak cationic polysaccharide composed essentially of β(1 → 4) linked glucosamine units together with some N‐acetylglucosamine units. It is obtained by extensive deacetylation of chitin, a polysaccharide common in nature. Chitosan is a biocompatible, biodegradable, and nontoxic natural polymer that exhibits excellent film‐forming ability. As a result of its cationic character, chitosan is able to react with polyanions giving rise to polyelectrolyte complexes. Therefore, because of these interesting properties, it has become the subject of numerous scientific reports and patents on the preparation of microspheres and microcapsules. The techniques employed to microencapsulate with chitosan include, among others, ionotropic gelation, spray drying, emulsion phase separation, simple and complex coacervation, and polymerization of a vinyl monomer in the presence of chitosan. The aim of this work is to review some of the more common techniques used and to put forward the results obtained by our research group in preparing chitosan‐based microcapsules: for taste masking and improving the stability of a nutritional oil, the sustained release of drugs, as well as the preparation of chitosan superparamagnetic microcapsules for the immobilization of enzymes.

Scanning electron micrograph of some superparamagnetic chitosan particles and magnetic hysteresis loop of the microparticles.

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Scanning electron micrograph of some superparamagnetic chitosan particles and magnetic hysteresis loop of the microparticles.
Use of the Interpolyelectrolyte Complexes of Poly(acrylic acid)‐Chitosan as Inductors of Tolerance Against Pathogenic Fungi in Tomato (Lycopersicon esculentum Mill. var. Floradade)
Authors: Ortega‐Ortíz Hortensia , Benavides‐Mendoza Adalberto , Flores‐Olivas Alberto , Ledezma‐Pérez Antonio
Published: October 2003

The interpolyelectrolyte complexes of poly(acrylic acid)‐chitosan were investigated as inductor of systemic resistance potentially useful in the organic production of vegetables. These complexes, which are water soluble, were tested in tomato (Lycopersicon esculentum Mill. var. Floradade). The seed treatments were carried out using solutions consisting of 0.1 vol.‐% of the complex and 5 g · L−1 NaCl in water. The data showed that this treatment produced a higher resistance to the attack by Fusarium oxysporum and Phytophthora capsici pathogens in tomato seedlings.

Formation of the interpolyelectrolyte complex of poly(acrylic acid) and chitosan.

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Formation of the interpolyelectrolyte complex of poly(acrylic acid) and chitosan.
UV Spectrophotometry: Improvements in the Study of the Degree of Acetylation of Chitosan
Authors: Pedroni Viviana Isabel , Gschaider María Elena , Schulz Pablo Carlos
Published: October 2003

A simple and rapid method for determining the degree of N‐acetylation (DA) of chitosan by ultraviolet spectrophotometry using double beam equipment is proposed. D‐Glucosamine (GlcN) hydrochloride and N‐acetylglucosamine (GlcNAc) were used as model substances, and chitosan solutions in different solvents were studied. The best results were obtained from 0.1 M HCl solutions, with high reproducibility and in good agreement with those given by conductometric titration, FT‐IR, 1H NMR and elemental analysis.

Correlation between DA obtained by UV and DA obtained by conductometric titration.

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Correlation between DA obtained by UV and DA obtained by conductometric titration.
Preparation of Crosslinked Chitosan/Silk Fibroin Blend Films for Drug Delivery System
Authors: Rujiravanit Ratana , Kruaykitanon Sopon , Jamieson Alexander M. , Tokura Seiichi
Published: October 2003

Crosslinked chitosan/silk fibroin blend films were prepared by a solution casting technique using glutaraldehyde as crosslinking agent. Drug release characteristics of the blend films with various blend compositions were investigated. Theophylline, diclofenac sodium, amoxicillin trihydrate, and salicylic acid were used as model drugs. The release studies were performed at 37 °C in buffer solutions at pH 2.0, 5.5, and 7.2. It was found that the blend films with 80% chitosan content showed the maximum amount of model drug release at pH 2.0 for all the drugs studied here. This result corresponded to the swelling ability of the blend films. From a swelling study, the maximum degrees of swelling of the drug‐loaded blend films were obtained at this pH and blend composition. The amount of drugs released from the films with 80% chitosan content, from the highest to the lowest values, occurred in the following sequence: salicylic acid > theophylline > diclofenac sodium > amoxicillin.

Comparison of the amounts of drug released from chitosan and the blend film with 80% chitosan content at pH 2.0: (filled) chitosan film, and (blank) blend film with 80% chitosan content (SAL = salicylic acid, THEO = theophylline, DFS = diclofenac sodium, AMX = amoxicillin).

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Comparison of the amounts of drug released from chitosan and the blend film with 80% chitosan content at pH 2.0: (filled) chitosan film, and (blank) blend film with 80% chitosan content (SAL = salicylic acid, THEO = theophylline, DFS = diclofenac sodium, AMX = amoxicillin).
Methylation of Chitosan with Iodomethane: Effect of Reaction Conditions on Chemoselectivity and Degree of Substitution
Authors: Curti Elisabete , de Britto Douglas , Campana‐Filho Sérgio Paulo
Published: October 2003

N,N,N‐trimethylchitosan (TMC) was prepared by reacting purified chitosan with iodomethane, in the presence of sodium hydroxide, water and sodium iodide, at room temperature. The reaction medium was N‐methyl‐2‐pyrrolidone. Different samples of TMC were obtained by adding to the reaction medium a fixed volume (5.5 mL) of aqueous NaOH solutions at different concentrations (15, 20, 30 and 40 wt.‐%) and carrying out the reactions for 9 or 24 h. The features observed in the 1H and 13C NMR spectra of these chitosan derivatives, in respect of the chemical shift, number and relative intensity of the signals, depended strongly on the excess of NaOH and H3CI added to the reaction medium, but when the lowest excess was employed, the characteristics of the derivative were not affected by the reaction time to the same extent. The average degree of quaternization of these N‐methylated derivatives of chitosan ranged from 10.5% to 44.8%, according to the reaction conditions. Increasing the excess of NaOH, in reactions carried out for 9 h, resulted in TMC samples with progressively higher content of trimethylated sites however, the reaction yields were correspondingly lower and O‐alkylation was favored in these cases.

1H NMR spectrum of sample [AX]24h dissolved in D2O (Cp = 10 g/L).

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1H NMR spectrum of sample [AX]24h dissolved in D2O (Cp = 10 g/L).
Diffusion Through Membranes of the Polyelectrolyte Complex of Chitosan and Alginate
Authors: Cárdenas Adriana , Argüelles‐Monal Waldo , Goycoolea Francisco M. , Higuera‐Ciapara Inocencio , Peniche Carlos
Published: October 2003

The swelling of membranes of the polyelectrolyte complex (PEC) between chitosan and alginate shows a similar pattern to that of other PECs. However, if the swelled membranes are dried, a second swelling process is seen which exhibits Fickian behavior. The apparent activation energy was estimated to be 32.8 kJ · mol−1. The release rate of model solutes was highly dependent on their molecular weight and the pH of the medium.

Arrhenius type plot of the temperature dependence of the apparent diffusion coefficients for the membrane of the polyelectrolyte complex between chitosan and alginate in water.

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Arrhenius type plot of the temperature dependence of the apparent diffusion coefficients for the membrane of the polyelectrolyte complex between chitosan and alginate in water.
Synthesis and Unusual Swelling Behavior of Combined Cationic/Non‐Ionic Hydrogels Based on Chitosan
Authors: Yazdani‐Pedram Mehrdad , Tapia Cristian , Retuert Jaime , Arias José Luis
Published: October 2003

Hydrogel‐forming copolymers based on chitosan grafted with different amounts of polyacrylamide were synthesized and its swelling capacity determined in distilled water, sodium chloride solutions, as well as in buffer solutions at pH 1.2 and 8.0. The resulting products are highly efficient as hydrogel‐forming materials with swelling at equilibrium going approximately from 300 to 3 000 times the volume of the dry solid polymer in all the investigated media. The products, different to usual hydrogels, swells considerably more and quickly in electrolyte‐containing solutions compared to in distilled water. This has been attributed to their structure that contains non‐ionic polyacrylamide macromolecules grafted onto the trunk polymer chitosan, which is cationic in nature. In‐vitro drug‐release behavior of formulations containing grafted copolymers have been tested using theophylline as a water‐soluble drug and the results were compared with similar formulations containing unmodified chitosan. It was found that tablets based on formulations containing grafted chitosan show higher erosion and swelling compared with those of the matrix based on unmodified chitosan, leading to a higher fraction of theophylline released. It can be concluded that formulations based on the synthesized copolymers are potentially useful for fluid absorbency and as prolonged drug‐release matrices.

The swelling of one of the hydrogels studied here.

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The swelling of one of the hydrogels studied here.
Drug Delivery Systems Based on Porous Chitosan/Polyacrylic acid Microspheres
Authors: Peniche Carlos , Fernández Mar , Gallardo Alberto , López‐Bravo Antonio , Román Julio San
Published: October 2003

Porous microspheres have been prepared by suspension free radical polymerization of acrylic acid (AA) in the presence of chitosan (CHI). The microspheres were characterized by FTIR and environmental SEM. The PAA content of the microspheres was estimated to be in the range 45–50 wt.‐%. The swelling degree of these particles is almost constant in the range 2 < pH < 5, but it increases considerably as the pH is raised from 5 to 10. The release profiles of microspheres loaded with meclofenamic acid (MF) were determined at pH 2, 7.4, and 10. The in vitro release of MF at different pHs was modulated by the solubility of the drug. These microcapsules are biodegradable and presented good biocompatibility and biodegradability during in vivo experiments.

ESEM microphotograph of the porous PAA/CHI microspheres.

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ESEM microphotograph of the porous PAA/CHI microspheres.
Effect of Chitosan and Temperature on Spore Germination of Aspergillus niger
Authors: Plascencia‐Jatomea Maribel , Viniegra Gustavo , Olayo Roberto , Castillo‐Ortega Maria Monica , Shirai Keiko
Published: October 2003

Inhibition of radial growth and spore germination of Aspergillus niger in media with added chitosan were detected. The highest radial growth inhibition (73%) was determined at 24 h with 3 g · L−1 of chitosan, and the percent inhibition of spore germination was 40% after 13 h of inoculation. Further, the CC50, that is, the concentration at which spore germination is inhibited by 50%, was estimated by probit analysis (3.5 g · L−1). The activation energies, EA were estimated by an Arrhenius model in control and amended chitosan media, obtaining 35.6 and 36.6 kcal · mol−1, respectively. These values were in the same order of magnitude because chitosan as inhibitor was more effective at low temperature (≤ 18 °C). Hence synergism of temperature and chitosan were only observed at 12 and 18 °C. Therefore, the maximal percentage of germinated spores, Smax was also affected by low temperatures in chitosan‐amended media with estimated values lower than 70% at temperatures < 37 °C whereas in control media Smax reached values close to 100%. Scanning electron micrographs showed that chitosan produced spore aggregation and morphological anomalies affecting swelling, germ tube emergence, and polarization.

Germinated spores percentages of Aspergillus niger in Czapeck media at several chitosan concentrations and 30 °C.

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Germinated spores percentages of Aspergillus niger in Czapeck media at several chitosan concentrations and 30 °C.
Synergistic Effects ofD‐Glucosamine and Collagen Peptides on Healing Experimental Cartilage Injury
Authors: Hashida Masaki , Miyatake Katsuyuki , Okamoto Yoshiharu , Fujita Kotaro , Matumoto Takayuki , Morimatsu Fumiki , Sakamoto Koji , Minami Saburo
Published: October 2003

We investigated the synergistic wound‐healing effects ofD‐glucosamine (GlcN) and collagen peptide ($\overline M _{\rm w}$: 10 000 Daltons soluble collagen (S‐Co)) on injured cartilage. A injured cartilage model in rabbit was surgically created. Under general anesthesia, three holes at articular cartilage of the medial trochlear (one hole) and trochlear sulcus (two holes) of a distal femur were created using a high‐speed orthopedic drill. After surgery, rabbits were orally administered with collagen peptide (S‐Co group), GlcN (G group), or both (CoG group) for 2 or 3 weeks. In addition, glycine (Gly group) was administered as a control for the S‐Co group in three rabbits. Control rabbits were provided with water ad lib. After 2 weeks, the holes were filled by fibroblasts and chondroblasts in the treatment group, whereas in the control group, the holes were not filled completely unlike for the treatment group. Even three weeks later, only a small change was seen in the control group. In the group receiving collagen and GlcN, the holes were completely filled by proliferating chondroblasts, remodeling of bony trabeculae was also observed. Image analysis of Safranin O‐ and Alcian blue‐stained specimens showed increased production of proteoglycans and glycosaminoglycans, respectively, not only in the injured site, but also in the normal cartilage in the treated groups. The most enhanced healing of injury and increase in Safranin O and Alcian blue positive materials was observed in the CoG group. As a result, simultaneous administration of collagen and GlcN gave a fairly enhanced healing on restoration of cartilage injuries.

Artificial cartilage injury at the stifle joint of a rabbit. a: proximal hole in trochlear sulcus; b: distal hole in trochlear sulcus; c: medial hole in medial trochlear ridge.

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Artificial cartilage injury at the stifle joint of a rabbit. a: proximal hole in trochlear sulcus; b: distal hole in trochlear sulcus; c: medial hole in medial trochlear ridge.
Effects of Chitin/Chitosan and Their Oligomers/Monomers on Migrations of Macrophages
Authors: Okamoto Yoshiharu , Inoue Aika , Miyatake Katsuyuki , Ogihara Kikumi , Shigemasa Yoshihiro , Minami Saburo
Published: October 2003

The effects of chitin/chitosan and their oligomers/monomers on the migrations of mouse peritoneal macrophage (PEM) and the rat macrophage cell line (rMp) were evaluated in vitro. In direct migratory assay using the blind well chamber method, the migratory activity of PEM was enhanced significantly by chitin and chitosan oligomers (NACOS and COS, respectively), but reduced by chitin, chitosan, and the chitosan monomer (GlcN). The migratory activity of rMp was increased significantly by chitin, chitosan, and the polymers, NACOS and GlcN.
A Layer‐by‐Layer Film of Chitosan in a Taste Sensor Application
Authors: dos Santos David S. , Riul Antonio , Malmegrim Roger R. , Fonseca Fernando J. , Oliveira Osvaldo N. , Mattoso Luiz H. C.
Published: October 2003

Chitosan is alternated with sulfonated polystyrene (PSS) to build layer‐by‐layer (LBL) films that are used as sensing units in an electronic tongue. Using impedance spectroscopy as the principle method of detection, an array using chitosan/PSS LBL film and a bare gold electrode as the sensing units was capable of distinguishing the basic tastes – salty, sweet, bitter, and sour – to a concentration below the human threshold. The suitability of chitosan as a sensing material was confirmed by using this sensor to distinguish red wines according to their vintage, vineyard, and brands.

PCA Plot for red wine samples obtained from impedance measurements at 1 kHz for the sensor array comprising a 3‐bilayer chitosan/PSS film and a bare gold electrode.

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PCA Plot for red wine samples obtained from impedance measurements at 1 kHz for the sensor array comprising a 3‐bilayer chitosan/PSS film and a bare gold electrode.
Chemical Modification and some Aligned Composites of Chitosan in a Filament State
Authors: Hirano Shigehiro , Zhang Min , Yamane Hideki , Kimura Yoshiharu , Matsukawa Kojiro , Nakagawa Masuo
Published: October 2003

The mono‐filaments (> 10 m in length) of chitosan and the blends of chitosan‐collagen, chitin‐collagen and chitin‐silk fibroin were wet‐spun. The mono‐filaments were chemically N‐modified with each of n‐fatty acid anhydrides, intra‐molecular carboxylic anhydrides, fragrant aldehydes and transition metal ions. The mono‐filament was aligned on a straight line with the mono‐filament of silk fibroin or poly(ethylene terephthalate) (PET), and a bundle of one to three mono‐filaments was coated with a medium of sericin (Se), chitosan or N‐acylchitosan to give rise to novel silk‐mimic filament composites. The filaments coated with a medium of sericin exhibited 26–27 denier for the titer, 2.46–3.36 gf · denier−1 for the tenacity and 11.8–25.0% for the elongation. The apparent density (denier · μm−1 in the filament diameter) of the filament composites was about 3–4 times higher than that of the mono‐filaments. Portion of fragrant aldehydes in Schiff's base was slowly hydrolyzed at room temperature by contacting with atmospheric moisture in the open air, and released from the fragrant filaments and composites. The filament composites coated with a chitosan medium were thrombogenic, and those coated with N‐acylchitosans were antithrombogenic.

An illustrated model for a silk‐mimic filament composite, N0(N2I‐FI).

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An illustrated model for a silk‐mimic filament composite, N0(N2I‐FI).
Water‐Soluble N‐(n‐Fatty acyl)chitosans
Authors: Hirano Shigehiro , Yamaguchi Yasuhiro , Kamiya Mitsutomo
Published: October 2003

Chitosan was partially N‐acylated by treatment with n‐fatty acid anhydrides in a homogeneous solution in 2 vol.‐% aqueous acetic acid‐methanol (1:2 v/v). The degree of substitution (d.s.) for N‐acyl groups in the water‐soluble N‐acylchitosan derivatives was in the range of 0.42–0.82 for N‐acetyl, 0.37–0.76 for N‐propionyl, 0.52–0.71 for N‐butyryl and 0.54–0.64 for N‐pentanoyl and ca. 0.58 for N‐hexanoyl, respectively.

Water soluble N‐(n‐fatty acyl)chitosans.

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Water soluble N‐(n‐fatty acyl)chitosans.
Metal dusting
Authors: Grabke H. J.
Published: October 2003

This introductory review paper summarizes shortly the research on metal dusting, conducted in the MPI for Iron Research during the last dozen years. Metal dusting is a disintegration of metals and alloys to a dust of graphite and metal particles, occurring in carburizing atmospheres at aC > 1 and caused by the tendency to graphite formation. The cause of destruction is inward growth of graphite planes into the metal phase, or in the case of iron and low alloy steels into cementite formed as an intermediate. The kinetics of metal dusting on iron and steels was elucidated concerning dependencies on time, temperature and partial pressures. High alloy steels and Ni‐base alloys are attacked through defects in the oxide scale which leads to pitting and outgrowth of coke protrusions, after initial internal formation of stable carbides M23C6, M7C3 and MC. A dense oxide layer prevents metal dusting, but formation of a protective Cr‐rich scale must be favored by a fine‐grain microstructure and/or surface deformation, providing fast diffusion paths for Cr. Additional protection is possible by sulfur from the atmosphere, since sulfur adsorbs on metal surfaces and suppresses carburization. Sulfur also interrupts the metal dusting mechanism on iron and steels, causing slow cementite growth. Under conditions where no sulfur addition is possible, the use of high Cr Nickelbase‐alloys is recommended, they are largely protected by an oxide scale and if metal dusting takes place, its rate is much slower than on steels.
Lanthanidocene Catalysts for the Homo‐ and Copolymerization of Ethylene with Butadiene
Authors: Boisson Christophe , Monteil Vincent , Ribour David , Spitz Roger , Barbotin Fanny
Published: October 2003

Alkylation of lanthanidocene chloride complexes was performed with BuLi, Mg(Bu)(Oct), or an equimolar mixture of BuLi and AlH(iBu)2. In the case of the latter, chain transfer reactions were observed between neodymium and aluminium, and higher activities were obtained. The use of the silylene‐bridged complex, [Me2Si(3‐Me3SiC5H3)2]NdCl, in combination with BuLi and AlH(iBu)2 provided an efficient and unique catalyst for the copolymerization of ethylene with butadiene. Copolymers with high butadiene contents (up to 62 mol‐%) were synthesized. The microstructure of butadiene units was mostly trans‐1,4, and copolymers exhibited a strong alternating character. The influence of butadiene content on the thermal properties of the copolymers was also investigated.

Copolymerization of ethylene with butadiene using 4/BuLi/AlH(iBu)2 (▪) and 2/BuLi/AlH(iBu)2 (▴).

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Copolymerization of ethylene with butadiene using 4/BuLi/AlH(iBu)2 (▪) and 2/BuLi/AlH(iBu)2 (▴).
Photocrosslinking Polymerization of Methacrylate Modified Triethoxysilanes Polycondensates and Multifunctional Methacrylates
Authors: Pavlinec Juraj , Moszner Norbert
Published: October 2003

Densely crosslinked polymer networks were prepared by fast, visible light‐induced polymerization at 20–22 °C. The two methacrylate functionalized triethoxysilanes polycondensates (MSiP) either alone, or in a mixture with methacrylate modified oxozirconium clusters, were polymerized separately and as comonomers to multimethacrylate monomers in a weight ratio of 1:0.9. Pure organic networks based on 1,6‐bis(2‐hydroxy‐3‐methacryloyloxyethoxycarbonylamino)‐2,2,4‐trimethylhexane (UDMA) were used for comparison in the same ratio to other comonomers. The networks based on organic bifunctional monomers showed high, around 85% conversion of double bonds. Nevertheless the non‐reacted monomer that migrates to the toluene amounts from 5.6 to 11.65 wt.‐%. Copolymerization of UDMA with tetrafunctional components resulted in networks with higher residual unsaturation up to 27.7%. This result points out the important role that functionality and the spacer structure between the monomer double bonds play in the extent of reaction. Based only on modified inorganic SiOSi nano‐structures the networks are characterized by nearly complete building up of MSiP in the network, extreme crosslinks density, and mostly less than 1 wt.‐% of soluble substances. However, residual unsaturations exceeded 22%. The advantage of copolymerization of MSiP with proper organic comonomers as potential solvent free matrices for dental composites was demonstrated by a network consisting of MSiP II and UDMA. The 13.7% of unreacted double bonds and 99.65 wt.‐% gel content approximated efforts to minimize residual unsaturation and maximize monomer conversion in cured networks.

Monomers used for the synthesis of the densely crosslinked polymer.

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Monomers used for the synthesis of the densely crosslinked polymer.
Simulation‐Assisted Evaluation of Acetylene Effect on Macromolecular Crosslinking Rate under Polyethylene Irradiation
Authors: Shyichuk Alexander , Tokaryk Galina
Published: October 2003

Gel content data on acetylene accelerated radiation crosslinking (R.A. Jones, J. Polym. Sci., Part B: Polym. Phys. 1994, 32, 2049) have been used to illustrate a new method to determine macromolecular crosslinking and scission yields. The sol‐gel analysis data have been plotted as log(sol) versus log(dose) resulting in quite linear plots having different slopes. The linear approximations with the least squares method resulted in gel‐points with a high accuracy. Computer simulations have shown the plot slope to be dependent on relative rate of competitive macromolecular scission. The scission/crosslink ratios have been found from the plot slopes using simulation software GelSim6. As a result acetylene gas has been found to be accelerating both crosslinking and scission rates: 60 times and 130 times, respectively. Obviously, the radiation yield of radicals is increased due to acetylene inhibiting the recombination of primarily induced radicals in a cage.

Gel content vs. irradiation dose data plotted as log(sol) versus log(dose). Numbers near the curves indicate concentrations of acetylene gas (mmol · kg−1).

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Gel content vs. irradiation dose data plotted as log(sol) versus log(dose). Numbers near the curves indicate concentrations of acetylene gas (mmol · kg−1).
Prediction of Sol Fraction and Average Molecular Weights after Gelation for Non‐Linear Free Radical Polymerizations Using a Kinetic Approach
Authors: Costa Mário Rui P. F. N. , Dias Rolando C. S.
Published: October 2003

Mass balance equations in terms of the moment generating function of the distribution of mole concentrations of polymer species for free radical copolymerizations of mono/divinyl monomers could be numerically solved after gel point using open source code ACDC, needed for extremely stiff two‐point boundary value problems. For the first time, it became possible to compare the error of earlier well‐known approximated estimation methods for the weight fraction of sol and average molecular weights to this accurate mathematical solution. It turns out that predictions by the pseudo‐kinetic method are reasonable only when equal reactivity of double bonds prevails, causing early gelation in the batch reactor. Otherwise the discrepancies between the exact and approximate solutions are quite important.

Comparison between predicted number‐average and weight‐average degrees of polymerization of sol in batch non‐linear free radical polymerizations of model system III.

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Comparison between predicted number‐average and weight‐average degrees of polymerization of sol in batch non‐linear free radical polymerizations of model system III.
Signatures of a Concentration‐Dependent Flory χ Parameter: Swelling and Collapse of Coils and Brushes
Authors: Baulin Vladimir A. , Halperin Avi
Published: October 2003

The quality of solvents of polymers is often described in terms of the Flory χ parameter typically assumed to depend only on the temperature, T. In certain polymer‐solvent systems fitting the experimental data enforces the replacement of (χT) by a concentration‐dependent χeff. In turn, this modifies the swelling and collapse behavior. These effects are studied, in the framework of a mean‐field theory, for isolated coils and for planar brushes. The ϕ dependence of χeff gives rise to three main consequences: (i) shift in the cross‐over between Gaussian and self‐avoidance regimes; (ii) a possibility of first‐order collapse transition for isolated flexible coils; (iii) the possibility of a first‐order phase transition leading to a vertical phase separation within the brush. The discussion relates these effects directly to thermodynamic measurements and does not involve a specific microscopic model. The implementation for the case of poly(N‐isopropylamide) (PNIPAM) brushes is discussed.

ϕ vs. z plots, for brushes with N = 300, σ/a2 = 18 (σ/R = 0.019) characterized by different χeff.

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ϕ vs. z plots, for brushes with N = 300, σ/a2 = 18 (σ/R = 0.019) characterized by different χeff.
Reconstruction of the Chain Length Distribution for Vinyl‐Divinyl Copolymerization Using the Numerical Fractionation Technique
Authors: Papavasiliou Georgia , Teymour Fouad
Published: October 2003

A proposed theory for evaluating the chain length distribution (CLD) using the numerical fractionation (NF) technique was extended to the vinyl‐divinyl (VDV) copolymerization. The CLD is reconstructed for this system, in which pendant double bond propagation leads to crosslinking and gel formation. The method was earlier developed for a non‐linear free‐radical polymerization scheme where chain transfer to polymer and termination by combination resulted in gel formation. The VDV study presented indicates that the proposed method of weighted summation (WS) accurately predicts the resulting CLDs evaluated using NF.

Comparison of the overall polymer NF and the direct solution CLDs near the gel point.

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Comparison of the overall polymer NF and the direct solution CLDs near the gel point.
Dynamics of a Spreading Nanodroplet: A Molecular Dynamic Simulation
Authors: Yaneva Jacqueline , Milchev Andrey , Binder Kurt
Published: October 2003

The spreading of polymer nanodroplets upon a sudden change from partial to complete wetting on an ideally flat and structureless solid substrate has been studied by molecular dynamic simulations using a coarse‐grained bead‐spring model of flexible macromolecules. Tanner's law for the growth of the lateral droplet radius {R(t) ∝ t0.1} is found to hold as long as the droplet does not disintegrate into individually moving chains. The data for the contact angleθfollowing from Tanner's law correspond to a dependence on time {θ(t) ∝ t−0.3}. Our analysis of the mean square displacements of the polymer centers of mass reveals several dynamic regimes during the process of spreading. PACS numbers: 68.10.Gw, 05.70.Ln, 61.20.Ja, 8.45.Gd.

Molecular dynamics results for the average mean square displacement of all polymer chains plotted vs. time for a broad range of values forεwall.

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Molecular dynamics results for the average mean square displacement of all polymer chains plotted vs. time for a broad range of values forεwall.
Segmentation of Heteropolymer Sequences Specifying Subsequences with Different Composition and Statistical Properties
Authors: Gusev Leonid V. , Vasilevskaya Valentina V. , Makeev Vsevolod Ju. , Khalatur Pavel G. , Khokhlov Alexei R.
Published: October 2003

We have studied the segmentation of two‐letter AB heterosequences composed of subsequences with different composition and distribution of A and B monomer units along the chain. Our approach is based on the segmentation function S(k) introduced in the present work and on the Jensen–Shannon divergence measure determined with respect to the probabilities of the lengths of uniform blocks of A and B monomer units. It is shown that the function S(k) is extremely sensitive to the sequence statistics. Even visual analysis of S(k) allows judgment on some features of sequence statistics. In particular, function S(k) is constant for random copolymers, it is an oscillating function for random block copolymers and shows monotonic growth up to some constant value for proteinlike copolymers. However, due to significant fluctuations observed for short sequences, the function S(k) can be effectively used only for segmentation of a heterosequence composed of very long subsequences. On the other hand, we find that the Jensen–Shannon divergence measure does not allow one to judge the type of statistics, but is extremely efficient for segmentation of a heterosequence. Therefore, the two introduced functions, being mutually complementary, provide an effective approach for recognizing and segmentation of heterosequences. As an example, the methods developed are applied for concatenating sequences of different proteins.

Segmentation function S(k, l, x) as a function of parameter k and starting number x of “window” for a sequence composed of elastin and ribonuclease sequences.

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Segmentation function S(k, l, x) as a function of parameter k and starting number x of “window” for a sequence composed of elastin and ribonuclease sequences.
Computer Simulation of a Gold Nanoparticle Coated by Thiol‐Terminated Hydroquinonyl Oligoethers
Authors: Yin Kailiang , Xia Qing , Xu Duanjun , Xi Haitao , Sun Xiaoqiang , Chen Chenglung
Published: October 2003

Molecular dynamics simulations were carried out to investigate the structure of a gold‐nanoparticle including 169 Au atoms coated by 42 thiol terminated hydroquinonyl oligoether chains. Three nanoparticle systems were constructed and investigated for structural comparison. The simulation showed that in all three nanosystems thiol‐chains self‐assembled on the surface of the gold cluster to form a stable gold nanoparticle. The configurations of the thiol chains and stacking of the phenylene rings were analyzed. The thiol‐chains are bundled into groups. Each group contains no more than four chains, in which phenylene rings in the thiol‐chains are correlated in parallel and perpendicular forms. Simple quantum mechanical calculations are carried out to elucidate the correlation of the phenylene rings.

A snapshot of a TTOE‐Au nanoparticle.

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A snapshot of a TTOE‐Au nanoparticle.
Evolution of Molecular Weight and Long Chain Branch Distributions in Olefin–Diene Copolymerization
Authors: Nele Márcio , Soares João B. P. , Pinto José Carlos
Published: October 2003

A model for olefin–diene copolymerization and long chain branch formation was developed. The model shows that the number‐average molecular weight and branching density increases linearly with time in a semi‐batch polymerization, while the polydispersity depends on the diene content in the polymer and on the polymerization time. For low diene fractions or low polymerization times, the polydispersity increases linearly with time. For higher diene contents, the polydispersity increases exponentially with polymerization time after a critical polymer concentration is reached. The calculated distributions of branched species indicate that diene content influences the amount of highly branched chains produced in the polymerization, markedly broadening the distribution of molecular weight and leading to gel formation.

Weight distribution of branched species after 30 min of polymerization.

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Weight distribution of branched species after 30 min of polymerization.
New type of travelling wave solutions
Authors: Schneider K. R. , Shchepakina E. A. , Sobolev V. A.
Published: October 2003

We study the existence of combustion waves for an autocatalytic reaction in the non‐adiabatic case. Based on the fact that the reaction system has canard solutions separating the slow combustion regime from the explosive one, we prove by applying the geometric theory of singularly perturbed differential equations the existence of a new type of travelling waves solutions, the so‐called canard travelling waves. Copyright © 2003 John Wiley & Sons, Ltd.
The diffraction in a class of unbounded domains connected through a hole
Authors: Shestopalov Yu. V. , Smirnov Yu. G.
Published: October 2003

In this paper, the unique solvability, Fredholm property, and the principle of limiting absorption are proved for a boundary value problem for the system of Maxwell's equations in a semi‐infinite rectangular cylinder coupled with a layer by an aperture of arbitrary shape. Conditions at infinity are taken in the form of the Sveshnikov–Werner partial radiation conditions. The method of solution employs Green's functions of the partial domains and reduction to vector pseudodifferential equations considered in appropriate vectorial Sobolev spaces. Singularities of Green's functions are separated both in the domain and on its boundary. The smoothness of solutions is established. Copyright © 2003 John Wiley & Sons, Ltd.
Unsaturated incompressible flows in adsorbing porous media
Authors: Fasano A. , Solonnikov V.
Published: October 2003

We study a free boundary problem modelling the penetration of a liquid through a porous material in the presence of absorbing granules. The geometry is one dimensional. The early stage of penetration is considered, when the flow is unsaturated. Since the hydraulic conductivity depends both on saturation and on porosity and the latter change due to the absorption, the main coefficient in the flow equation depends on the free boundary and on the history of the process. Some results have been obtained in Fasano (Math. Meth. Appl. Sci. 1999; 22:605) for a simplified version of the model. Here existence and uniqueness are proved in a class of weighted Hölder spaces in a more general situation. A basic tool are the estimates on a non‐standard linear boundary value problem for the heat equation in an initially degenerate domain (Rend. Mat. Acc. Lincei 2002; 13:23). Copyright © 2003 John Wiley & Sons, Ltd.
The solution of Lyumkis energy transport model in semiconductor science
Authors: Chen Li , Hsiao Ling
Published: October 2003

The existence and uniqueness of $ (W_{\hskip -3.5pt p}^{2,1}(Q_{\tau}))^{2}\times L_{q}(0,\tau;W_{\hskip -2.5pt q}^{1}(\Omega))$ solution to Lyumkis energy transport model is discussed for N+2<p≤q<∞ and 1≤N≤3. Copyright © 2003 John Wiley & Sons, Ltd.
Integration of [U‐13C]glucose and 2H2O for quantification of hepatic glucose production and gluconeogenesis
Authors: Perdigoto Rui , Rodrigues Tiago B. , Furtado Alexandre L. , Porto Armando , Geraldes Carlos F. G. C. , Jones John G.
Published: October 2003

Glucose metabolism in five healthy subjects fasted for 16 h was measured with a combination of [U‐13C]glucose and 2H2O tracers. Phenylbutyric acid was also provided to sample hepatic glutamine for the presence of 13C‐isotopomers derived from the incorporation of [U‐13C]glucose products into the hepatic Krebs cycle. Glucose production (GP) was quantified by 13C NMR analysis of the monoacetone derivative of plasma glucose following a primed infusion of [U‐13C]glucose and provided reasonable estimates (1.90 ± 0.19 mg/kg/min with a range of 1.60–2.15 mg/kg/min). The same derivative yielded measurements of plasma glucose 2H‐enrichment from 2H2O by 2H NMR from which the contribution of glycogenolytic and gluconeogenic fluxes to GP was obtained (0.87 ± 0.14 and 1.03 ± 0.10 mg/kg/min, respectively). Hepatic glutamine 13C‐isotopomers representing multiply‐enriched oxaloacetate and [U‐13C]acetyl‐CoA were identified as multiplets in the 13C NMR signals of the glutamine moiety of urinary phenylacetylglutamine, demonstrating entry of the [U‐13C]glucose tracer into both oxidative and anaplerotic pathways of the hepatic Krebs cycle. These isotopomers contributed 0.1–0.2% excess enrichment to carbons 2 and 3 and ∼0.05% to carbon 4 of glutamine. Copyright © 2003 John Wiley & Sons, Ltd.
A new dimension of 1H‐NMR spectroscopy in assessment of liver graft dysfunction
Authors: Singh H. K. , Yachha S. K. , Saxena Rajan , Gupta Ashish , Nagana Gowda G. A. , Bhandari M. , Khetrapal C. L.
Published: October 2003

High‐resolution 1H‐NMR spectroscopy of serum and urine samples of an 11‐year‐old male living related orthotopic liver transplant recipient is reported. Serum glutamine increased to abnormal levels along with simultaneous abnormal excretion of urinary glutamine post‐transplantation. High levels of glutamine in both blood and urine and concomitant reduced urea levels in urine were found to be evidence of impairment in urea cycle and compatible with persistently abnormal graft function. Thus glutamine levels in serum and urine, and urea in the urine as observed by 1H‐NMR spectroscopy highlight their important roles in monitoring liver graft function; increased glutamine levels lead to brain damage, if untreated. Copyright © 2003 John Wiley & Sons, Ltd.
Correlation between the occurrence of 1H‐MRS lipid signal, necrosis and lipid droplets during C6 rat glioma development
Authors: Zoula Sonja , Hérigault Gwénaël , Ziegler Anne , Farion Régine , Décorps Michel , Rémy Chantal
Published: October 2003

The aim of this study was to investigate the possible correlation between the 1H MRS mobile lipid signal, necrosis and lipid droplets in C6 rat glioma. First, the occurrence of necrosis and lipid droplets was determined during tumor development, by a histological analysis performed on 34 rats. Neither necrosis nor lipid droplets were observed before 18 days post‐implantation. At later stages of development, both necrosis and lipid droplets were apparent, the lipid droplets being mainly located within the necrotic areas. Using a second group of eight rats, a temporal correlation was evidenced between mobile lipid signal detected by in vivo single‐voxel one‐ (136 ms echo time) and two‐dimensional J‐resolved 1H MR spectroscopy, and the presence of necrosis and lipid droplets on the histological sections obtained from the brains of the same rats. Finally, spatial distribution of the mobile lipid signal was analyzed by chemical‐shift imaging performed on a third group of eight animals, at the end of the tumor growth. The spectroscopic image corresponding to the resonance of mobile lipids had its maximum intensity in the center of the tumor where necrotic regions were observed on the histological sections. These necrotic areas contained large amounts of lipid droplets. All these results suggest that mobile lipids detected in vivo by 1H MRS (136 ms echo time) in C6 rat brain glioma arise mainly from lipid droplets located in necrosis. Copyright © 2003 John Wiley & Sons, Ltd.