Electronic and optical properties of wet-spun films of Li- and Na-hyaluronate

The uv absorption of Na-hyaluronate (NaHA) films and the refractive indices, water content, and swelling of LiHA films have been measured as a function of relative humidity. Three peaks are observed in the uv absorption of NaHA (at about 250, 310, and 330 nm) for water content above 10 water molecules per disaccharide. The absorptivity of the 250, 310, and 330 nm peaks increase as the water content increases, indicating a change in the electronic properties of the HA molecule. The refractive indices, water content, and swelling of LiHA films are used to determine the optical polarizability via the Lorentz–Lorenz relation. The polarizability of LiHA is found to have a similar dependence on water content as NaHA, though the changes observed are larger in magnitude. © 1994 John Wiley & Sons, Inc.     

Properties of reaction centers of Rhodopseudomonas sphaeroides in dried gelatin films.: Linear dichroism and low temperature spectra

Methods of preparing dried gelatin films containing purified reaction centers of Rhodopseudomonas sphaeroides are described. The spectral properties of reaction centers in solution are essentially maintained in dried gelatin films. These films are uniform and have excellent optical properties, showing little particulate scattering at temperatures down to about 4K. Film contraction on cooling to 90K is less than 1% in linear dimension. Linear dichroism spectra are reported for films at room and low temperature. Reaction centers show a moderate amount of linear dichroism in unstretched gelatin films; the magnitude of the linear dichroism becomes much greater when the films are stretched. In stretched films, linear dichroic ratios ($\text{A}{}_{\mathrm{\parallel }}\text{A}{}_{\mathrm{\perp }}$; absorbance measured with electric vector parallel and perpendicular to stretching direction) between 1.7 and 2.2 were obtained for the 860 nm absorption band of the bacteriochlorophyll component that undergoes primary photooxidation. The relative polarizations of light-induced absorption changes of reaction centers in stretched films are similar to those reported by Vermeglio and Clayton ((1976) Biochim. Biophys. Acta 449, 500–515) and support their hypothesis that absorbance decreases, maximal near 860 and 810 nm, and an increase near 790 nm are associated with the respective disappearance and appearance of discrete bands characteristic of the reduced and oxidized bacteriochlorophyll dimer. This interpretation is also supported by the polarization of the absolute absorption spectrum near 810 and 860 nm. An absorption band near 540 nm, ascribed to the Q_x transitions of two molecules of bacteriopheophytin in the reaction center, is split at low temperatures into two bands having similar polarizations. This splitting is probably not due to exciton coupling of the two molecules, since excition theory predicts different polarizations.     

Effect of transglutaminase and 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide on the solubility of fish gelatin–chitosan films

The possibility of decreasing the water solubility of the films made from fish gelatin and chitosan by modification with TGase was investigated. The effectiveness of enzymatic treatment was also compared with chemical crosslinking using EDC. The treatment of the components with TGase in concentration of 0.2 mg/ml of the film-forming solution limited the solubility of the films at 25 °C from 65% to 28% at pH 6 and from 96% to 37% at pH 3. After 15 min of heating at 100 °C, the modified films were soluble in 23% at pH 6 and in 41% at pH 3. Further decrease of the solubility of the fish gelatin–chitosan films was achieved when enzymatic modification was conducted in the presence of 5–10 mM DTT; the solubility was about twice lower than that without DTT at both studied temperatures and pH values. Generally, the composite films modified with EDC in concentration of 30 mM were distinctly less soluble than films made from the components modified with TGase in the presence of DTT.     

N-acetylchitosan gel: A polyhydrate of chitin

N-Acetylchitosan gel, a polyhydrate of chitin, and partially O-acetylated N-acetylchitosan gel were produced by a facile acetylation of chitosan with acetic anhydride in 10% acetic acid and in aqueous acetic acid/methanol at room temperature. Under the same conditions, a series of N-acylchitosan gels was produced in reaction with the other carboxylic anhydrides. The gels thus produced were colorless, transparent and rigid, and stable on heating. The gels were insoluble in cold and boiling water, formic acid, aqueous acids, and the other solvents examined. Significant changes in specific rotation occurred in the acylation of chitosan and its aggregation.     

Mechanical properties of chitosan/bamboo charcoal composite films made with normal and surface oxidized charcoal

Chitosan/bamboo charcoal composite films were prepared by blending chitosan with either virgin bamboo charcoal or bamboo charcoal modified by nitric acid oxidation to provide more hydrophilic regions on the bamboo charcoal surface. Investigation of the physical properties of these composite films revealed that the tensile strength and Young’s modulus of the chitosan films were enhanced in a dose-dependent manner by the inclusion of modified bamboo charcoal at up to 1% (w/w), whilst the elongation at break was increased by inclusion of modified bamboo charcoal at up to 0.5% (w/w). In contrast, chitosan composites with virgin bamboo charcoal at up to 0.5% or 1.0% (w/w) showed no enhancement of the tensile strength or Young’s modulus, respectively, and both parameters were reduced with higher levels of virgin bamboo charcoal. Oil, and especially water, absorption of the composite films displayed a marked and dose-dependent increase compared to those of the pure chitosan film.     

Effect of water on the structure of bacteriorhodopsin and photochemical processes in purple membranes

Visible and infrared spectra of bacteriorhodopsin films under different humidities at room and low temperatures are investigated. On dehydration of purple membranes at room temperatures an additional chromophore state with the absorption band at 506 nm is revealed. The photocycle of purple membranes in the dry state is devoid of the 550 nm intermediate and involves the long-lived intermediate at 412 nm. As water is removed, the 550 nm intermediate becomes undetectable. The analysis of the infrared spectra shows that dehydration does not affect the ordering of the main network of the interpeptide hydrogen bonds which stabilizes the -helical conformation (slightly distorted in the initial humid dark- and light-adapted state); light adaptation (cis-trans isomerization) of bacteriorhodopsin results in an increase of sorbed water in purple membranes. Dehydration of purple membranes decreases the reaction rate of cis-trans isomerization.     

Chitosan pyrolysis and adsorption properties of chitosan and its carbonizate

Chitosan was characterized by Fourier transform infrared spectroscopy (FTIR), ¹³C-nuclear magnetic resonance (NMR), X-ray diffraction (XRD), and elemental analysis (EA). The thin chitosan films obtained by the casting method were heated in vacuum from room temperature to 600 °C. The progress of thermal degradation and carbonization process was monitored by FTIR spectroscopy in a vacuum cell, which allows the elimination of the influence of atmospheric humidity on the chitosan and carbonizate properties. The adsorption of water on the degassed chitosan and its carbonizate as well the oxidation process was also investigated by FTIR spectroscopy. The surface morphology of initial chitosan and obtained carbonaceous material was observed using atomic force microscopy (AFM). Detailed characterization of raw material and carbonization conditions is necessary for tailoring reproducible adsorbent properties.     

Kinetics and mechanisms of depolymerization of alginate and chitosan in aqueous solution

The kinetics and mechanisms of depolymerization of aqueous chitosan and alginate solutions at elevated temperatures have been investigated. Chitosan salts of different degree of acetylation (F_A), type of counterions (-glutamate, -chloride) and degree of purity were studied. One commercially available highly purified sodium alginate sample with high content of guluronic acid (G) was also studied. Furthermore, the influence of oxygen, H⁺ and OH⁻ ions on the initial depolymerization rates was investigated. Depolymerization kinetics was followed by measuring the time courses of the apparent viscosity and the intrinsic viscosity. The initial rate constants for depolymerization were determined from the intrinsic viscosity data converted to a quantity proportional to the fraction of bonds broken. The activation energies of the chitosan chloride and chitosan glutamate solutions with pH close to 5 and the same degree of acetylation, F_A = 0.14, were determined from the initial rate constants to be 76 ± 13 kJ/mol and 80 ± 11 kJ/mol, respectively.The results reported herein suggest that the stability of aqueous chitosan and alginate solutions at pH values 5–8 will be influenced by oxidative–reductive depolymerization (ORD) as the primary mechanism as long as transition metal ions are presented in the samples. Acid – and alkaline depolymerization will be the primary mechanisms for highly purified samples.     

Interaction of chitosans and their N-acylated derivatives with lipopolysaccharide of gram-negative bacteria

The interactions of lipopolysaccharide (LPS) with the natural polycation chitosan and its derivatives--high molecular weight chitosans (80 kD) with different degree of acetylation, low molecular weight chitosan (15 kD), acylated oligochitosan (5.5 kD) and chitooligosaccharides (biose, triose, and tetraose)--were studied using ligand-enzyme solid-phase assay. The LPS-binding activity of chitosans (80 kD) decreased with increase in acetylation degree. Affinity of LPS interaction with chitosans increased after introduction of a fatty acid residue at the reducing end of chitosan. Activity of N-monoacylated chitooligosaccharides decreased in the order: oligochitosan --> tetra- > tri- --> disaccharides. The three-dimensional structures of complexes of R-LPS and chitosans with different degree of acetylation, chitooligosaccharides, and their N-monoacylated derivatives were generated by molecular modeling. The number of bonds stabilizing the complexes and the energy of LPS binding with chitosans decreased with increase in acetate group content in chitosans and resulted in changing of binding sites. It was shown that binding sites of chitooligosaccharides on R-LPS overlapped and chitooligosaccharide binding energies increased with increase in number of monosaccharide residues in chitosan molecules. The input of the hydrophobic fragment in complex formation energy is most prominent for complexes in water phase and is due to the hydrophobic interaction of chitooligosaccharide acyl fragment with fatty acid residues of LPS.     

Preparation and characterization of chitosan membranes by using a combined freeze gelation and mild crosslinking method

When gelification is performed by freezing–thawing repeated cycles, the resultant gel-like polymer systems are called cryogels. This work aims to assess the effect of the addition of glutaraldehyde and 18 Crown Ether-6 on surface properties and protein loading of dried chitosan cryogel films. Residual water content of treated chitosan membranes ranged between 11.93 and 13.86%, while their water activities vary from 0.5 to 0.7 (measured from 4 to 60 °C). Based on thermal data, water evaporation peak and degradation temperatures of chitosan membranes shifted to a higher temperature for crosslinked samples. X-ray diffractograms provide high values of crystallinity for all the samples (70.67–92.86%), the highest value being for the glutaraldehyde-treated membrane. Candida rugosa lipase can be immobilized successfully on chitosan membranes. Lipase immobilized on glutaraldehyde-crosslinked chitosan yielded the highest efficiency in terms of total coupled protein and protein loading efficiency.     

Determination of the degree of acetylation of chitosans by first derivative ultraviolet spectrophotometry

The degree of acetylation of chitosan can be determined in acetic acid solutions (～0·01m) containing 1 g dry chitosan per litre by first derivative ultraviolet spectrophotometry at 199 nm. At this wavelength, the N-acetylglucosamine absorbance readings are linearly dependent on concentration and are not influenced by the presence of acetic acid. Correction factors for the contribution of glucosamine in highly deacetylated chitosans can be easily derived. Typical results for the chitosan of Euphausia superba are: degree of acetylation, 42·6; relative standard deviation, 1·3%; confidence limits, ±0·7. This method is simpler, more precise and faster than the infrared method. Sonication of chitosan solutions leads to immediate chain degradation and to detectable deacetylation after more prolonged periods of time, especially when the pH is 1·0.     

Chitosan–caffeic acid–genipin films presenting enhanced antioxidant activity and stability in acidic media

The use of chitosan films has been limited due to their high degradability in aqueous acidic media. In order to produce chitosan films with high antioxidant activity and insoluble in acid solutions caffeic acid was grafted to chitosan by a radical mechanism using ammonium cerium (IV) nitrate (60 mM). Genipin was used as cross-linker. This methodology originated films with 80% higher antioxidant activity than the pristine film. Also, these films only lost 11% of their mass upon seven days immersion into an aqueous solution at pH 3.5 under stirring. The films surface wettability (contact angle 105°), mechanical properties (68 MPa of tensile strength and 4% of elongation at break), and thermal stability for temperatures lower than 300 °C were not significantly influenced by the covalent linkage of caffeic acid and genipin to chitosan. Due to their characteristics, mainly higher antioxidant activity and lower solubility, these are promising materials to be used as active films.     

Crystallization behavior and environmental biodegradability of the blend films of poly(3-hydroxybutyric acid) with chitin and chitosan

Crystallization behavior and environmental biodegradability were investigated for the films of bacterial poly(3-hydroxybutyric acid) (PHB) blends with chitin and chitosan. The blend films showed X-ray diffractive peaks that arose from the PHB crystalline component. It was suggested that the lamellar thickness of the PHB crystalline component in the blends was large enough to show detectable X-ray diffractive peaks, but this was too small to show observable melting endotherm in the DSC thermogram and the crystalline band absorption in the FT-IR spectrum. In the PHB/chitin and PHB/chitosan blends, thermal transition temperatures of PHB amorphous region observed by dynamic mechanical thermal analysis were almost the same as that of neat PHB. Both the PHB/chitin and the PHB/chitosan blend films biodegraded in an environmental medium. Several blend films showed faster biodegradation than the pure-state component polymers.     

The photochemistry of some main chain liquid crystalline 4,4'-stilbene dicarboxylate polyesters.

Several aspects of the photochemistry and photophysics of four main chain liquid crystalline polyesters with a rigid trans-stilbene 4,4'-dicarboxylate mesogen as chromophore and flexible spacer groups are reported. The three polymers with the longest 'spacer' groups are liquid crystalline at room temperature, two have smectic phases. Chromophore aggregation has a dramatic effect on the photophysics and photochemistry of these polymers. Each of the polymers in poor solvents or as films has greatly perturbed UV-Vis absorption and fluorescence spectra due to aggregation of the stilbene chromophore. These effects are more pronounced upon annealing above the glass transition temperature, T(g), and in the mesophase. Film fluorescence is excitation wavelength dependent and is suppressed at elevated temperatures. The stilbene 'environment' in both films and solution is clearly heterogeneous and energy transfer processes relatively slow. The dominant photochemical reaction upon direct excitation above 300 nm is 2 + 2 photocycloaddition rendering polymer films insoluble. No significant trans-to-cis photoisomerization can be detected upon initial irradiation of the polymer films. There is evidence for the formation of aldehyde and carboxylate functionality upon irradiation in the presence of air. Loss of the aggregate UV-Vis absorption and fluorescence occurs during irradiation. Difference UV-Vis spectra of irradiated films suggest preferential initial consumption of dimeric aggregates. Loss of stilbene UV-Vis absorption upon irradiation above 300 nm can be partly photoreversed upon subsequent 254 nm irradiation. The rate of stilbene chromophore loss from films increased significantly above Tg and in the smectic phase above room temperature.     

Degradation behavior of chitosan chains in the 'green' synthesis of gold nanoparticles

The degradation behavior of chitosan chains in the synthesis of Au nanoparticles by a 'green' method was investigated in this paper for the first time. UV-vis absorption spectra suggested the formation of Au nanoparticles and TEM images showed that their sizes were between 10 and 50nm. During the process of synthesis, the intrinsic viscosity [eta] of chitosan was observed to decrease gradually, implying that the chitosan chains degraded under the reaction conditions. Further studies showed that the degree of degradation of the chitosan chains was changed with different reaction temperatures, reactant ratios, and the molecular weights of chitosan.     

Effect of molecular weight of chitosan on antimicrobial properties and tissue compatibility of chitosan-impregnated bacterial cellulose films

Bacterial cellulose-chitosan (BC-C) films were developed by immersing purified BC pellicles in 1.5 ~ 2.0% (w/v) acetic acid solutions containing chitosan of varying molecular weights. Effects of different molecular weight of chitosan on physical, biological and antimicrobial properties of the composite films were investigated. The cumulative chitosan absorption capacities with M_w of 141,000, 199,000, and 263,000 were 38.43, 24.65, and 23.89 mg/cm³ of dry BC film, respectively. The cumulative release profiles of chitosan from the films strongly depended on molecular weight of chitosan and pH of solution. The order of release of chitosan from the BC-C films was dependent on molecular weight as follows: M_w 141,000 > M_w 199,000 > M_w 263,000. All BC-C films showed the antimicrobial abilities against Staphylococcus aureus and Aspergillus niger but had no inhibitory effect on the growth of Escherichia coli. The BC-C films supported for adhesion, spreading and proliferation of both human skin keratinocytes and fibroblasts. The antibacterial activity against S. aureus of the BC-C with the highest Mw chitosan (263,000) was higher than those of the others. On the other hand, the BC-C films with the lowest M_w chitosan (141,000) promoted the growth of human skin cells more than those of the others.     

Effect of water vapor pressure on the thermal decomposition of 2-chloroethylphosphonic Acid

Decomposition of 2-chloroethylphosphonic acid (Ethephon) was studied in dried films at various water vapor pressures (0.6 to 86.9 millimeters Hg, 3.2 to 93.9% relative humidity) and temperatures (20, 30, 40, and 50 C) at pH 6.3 and 7.0. The rate of decomposition could be determined equally well by [¹⁴C]Ethephon or ethylene measurements. The rate increases at increasing water vapor pressures at a constant temperature and pH, up to an optimum. The optimum vapor pressure for decomposition approximately doubles for each 10 C increase. The activation energy for the decomposition reaction in water vapor pressures of 3.2 to 12 millimeters Hg is 8.7 and 14.3 kilocalories per mole at pH 6.3 and 7.0, respectively.     

Diffusion of KCl in an amylose film

A method has been developed measuring the diffusion coefficient of KCl in amylose films. The films were soaked in potassium chloride solutions, then immersed in pure water and conductivity measured as a function of time. Different concentrations of the soaking solution were used and the measurements were made at several temperatures. The diffusion coefficient of KCl was found to be independent of the soaking solution KCl concentration, but found to increase with increasing temperature. The diffusion coefficient values were about one quarter of those found in water and varied from 4.8×10⁻¹⁰ to 11×10⁻¹⁰ m² s⁻¹. The activation energy of diffusion was close to that found in water. Two values for the activation energy were obtained, 20.1 and 14 kJ mol⁻¹, indicating a change in the film structure at 45 °C. Amylose films swelled equally in KCl-solutions and water. The thickness of amylose films doubled and the increase in mass was 100–200% corresponding the decrease of amylose content from about 87 to 37%, when the conditions changed from normal humidity conditions to water.     

Behavior of Freezable Bound Water in the Bacterial Cellulose Produced by Acetobacter xylinum: An Approach Using Thermoporosimetry

The aim of the study is to examine thermal behavior of water within reticulated structure of bacterial cellulose (BC) films by sub-ambient differential scanning calorimetry (DSC). BC films with different carbon source, either manitol (BC (a)) or glycerol (BC (b)), were produced by Acetobacter xylinum using Hestrin and Shramm culture medium under static condition at 30 ± 0.2°C for 3 days. BC samples were characterized by electron scanning microscopy and X-ray diffraction spectroscopy. The pore analysis was done by B.H.J. nitrogen adsorption. The pre-treated with 100% relative humidity, at 30.0 ± 0.2°C for 7 days samples were subjected to a between 25 and −150°C-cooling–heating cycle of DSC at 5.00°C/min rate. The pre-treated samples were also hydrated by adding 1 μl of water and thermally run with identical conditions. It is observed that cellulose fibrils of BC (a) were thinner and reticulated to form slightly smaller porosity than those of BC (b). They exhibited slightly but non-significantly different crystalline features. The freezable bound water behaved as a water confinement within pores rather than a solvent of polymer which is possible to use thermoporosimetry based on Gibb–Thomson equation to approach pore structure of BC. In comparison with nitrogen adsorption, it was found that thermoporosimetry underestimated the BC porosity, i.e., the mean diameters of 23.0 nm vs. 27.8 nm and 27.9 nm vs. 33.9 nm for BC (a) and BC (b), respectively, by thermoporosimetry vs. B.H.J. nitrogen adsorption. It may be due to large non-freezable water fraction interacting with cellulose, and the validity of pore range based on thermodynamic assumptions of Gibb–Thomson theory.     

Environmentally friendly films based on chitosan and tetrahydrocurcuminoid derivatives exhibiting antibacterial and antioxidative properties

Environmentally friendly films exhibiting both antibacterial and antioxidative properties were elaborated from chitosan and tetrahydrocurcuminoids (THCs). Two tetrahydrocurcuminoids, THC1 (5-hydroxy-1,7-bis(4-hydroxy-3-methoxyphenyl)hept-4-en-3-one) and THC2 (5-hydroxy-1,7-bis(4-hydroxy-3,5-dimethoxyphenyl)hept-4-en-3-one), were incorporated into a chitosan film. THC1 could be prepared from natural curcumin extracted from turmeric roots (Curcuma longa L.). The resulting tetrahydrocurcuminoid–chitosan films exhibited a high free-radical scavenging activity against 2,2-diphenyl-1-picrylhydrazyl (DPPH) in methanol, which was due to a progressive release of the THCs into the solvent. The release kinetics was governed both by molecular interactions between chitosan and THCs and probably by electrostatic forces between the ammonium units in chitosan and the aromatic rings in THCs. These interactions were clearly evidenced by the presence of new absorption bands in the visible regions of the electronic absorption spectra of the THCs. The molecular nature of these interactions was shown using glucosamine, the main monomer of chitosan. When associated with THCs, chitosan retained its bioactivity against Listeria innocua; THCs alone were not bioactive enough against listerial strains.