A thermosensitive chitosan/poly(vinyl alcohol) hydrogel containing nanoparticles for drug delivery

The synthesis and characterization of a thermosensitive chitosan (CS)/poly(vinyl alcohol) (PVA) hydrogel containing nanoparticles with different charges for drug delivery were reported. Through the electrostatic effect of –N⁺(CH₃)₃ and –COO⁻, the nanoparticles of N-(2-hydroxyl) propyl-3-trimethyl ammonium chitosan chloride(HTCC)–carboxymethyl chitosan (CM) were prepared. The nanoparticles with different charges were obtained by the different ratio of –N⁺(CH₃)₃ and –COO⁻, which were suitable for drug delivery with opposite charges, such as propranolol and diclofenac sodium, respectively. The release of the positive drug was the slowest with the hydrogels containing negative nanoparticles. Similarly, the release of the negative drug was the slowest with the hydrogels containing positive nanoparticles. However, the releases of the two drugs were both the fastest with the pure hydrogels. It indicated the addition of nanoparticles was helpful to slow the suitable drug release. Though the nanoparticles did not reinforce the gel strength, the electrostatic effect between nanoparticles and drugs reduced the burst release. Therefore, the composite gels are attractive for applications as carriers for drug delivery.     

Correlation between crosslinking efficiency and spatial inhomogeneity in poly(acrylamide) hydrogels

Summary Elasticity and light scattering measurements were carried out on poly(acrylamide) (PAAm) hydrogels prepared from acrylamide (AAm) and N,N’-methylenebisacrylamide (BAAm) monomers under various reaction conditions. Elasticity tests showed that the crosslinking efficiency of BAAm ε_xl, that is the fraction of BAAm forming effective crosslinks decreases as the initial monomer concentration C_o is decreased. At C_o=3%, ε_xl was found to be 10^-2–10^-3, indicating that 99 to 99.9% of BAAm used in the hydrogel preparation are wasted in elastically ineffective links. Debye-Bueche analysis of the light scattering data showed that, irrespective of the gel synthesis conditions, the correlation length ξ, that is, the extension of inhomogeneities in the hydrogels is 10¹ nm. The extent of frozen concentration fluctuations in the hydrogels represented by 〈η²〉 decreases with increasing crosslinking efficiency of BAAm. The combination of the light scattering and the elasticity data of gels shows a direct correlation between the fraction of wasted crosslinker molecules during gelation and the spatial gel inhomogeneity.     

Synthesis of Crosslinked Chitosan with Epichlorohydrin Possessing Two Novel Polymeric Ligands and Its Use in Metal Removal

One of the major applications of chitosan and its derivatives is based on its ability to bind strongly toxic metal ions. In this work, two novel polymeric ligands were synthesized to investigate the adsorption properties of Cu(II), Pb(II), Zn(II) and Ni(II) ions in an aqueous solution. To prevent the reaction between as the C₂ amine group of chitosan and ECH, the C₂ amine group was protected N-benzylidene chitosan (CTB). After the reaction with ECH to give N-benzaldehyde crosslinked chitosan (CCTB), the Schiff base was removed in a dilute ethanol hydrochloride solution to obtain CCTS which has free amine group. CCTS–ECH was synthesized by the reaction of CCTS and ECH. Then, CCTS–ECH was reacted with (2-hydroxyphenylimino)methylbenzene-1,4-diol (HBD) and N,N′-bis(2,5-dihydroxybenzylidene)-1,4-diaminobenzene (DHDB) to give ligands CCTS–ECH–HBD and CCTS–ECH–DHDB. The batch experiments showed that two novel polymeric ligands can be effectively used to remove Cu(II) from water.     

Assembly, characterization of Ag nanoparticles in P(AAm-co-NVP)/CS semi-IPN, and swelling of the resulting composite hydrogels

Silver nanoparticles (AgNPs) with controlled size and size distribution were prepared by an in situ chemical reduction route based on a microreactor template composed of poly(acrylamide-co-N-vinylpyrrolidone)/chitosan semi-interpenetrating network hydrogels, P(AAm-co-NVP)/CS semi-IPN, in the presence of sodium hypophosphite. The characterization of structures and morphologies of the as-fabricated P(AAm-co-NVP)/CS–Ag nanocomposite hydrogels was conducted on a Fourier transformation infrared spectroscopy (FTIR), scanning electron microscope (SEM), transmission electron microscope (TEM), and UV–vis spectrometer. The effect of various component proportions of the reactants on formation of AgNPs and swelling of the resulting P(AAm-co-NVP)/CS–Ag nanocomposite hydrogels was investigated. The experimental results indicated that the Ag grains were uniformly dispersed within P(AAm-co-NVP)/CS hydrogel networks in a spherical shape, and were stabilized by the semi-IPN structure and a complexation and/or electrostatic interaction between Ag⁺ cations and chemical functional groups, such as –OH, –CONH₂, –NH₂ or –C=O based on the semi-IPN structure reactor templates. The size of the majority of AgNPs ranges from 12 to 25 nm, depending on the three-network templates, the presence of functional groups as well as feed ratios of N-vinylpyrrolidone, acrylamide, and chitosan. Thermogravimetric analysis (TGA) provides the stability of the resulting nanocomposite hydrogels. The nanocomposite hydrogels demonstrate reduced swelling in comparison with the P(AAm-co-NVP)/CS ones. The kinetics modeling confirms that transport mechanism of the samples follows anomalous diffusion mode, and the kinetic parameters vary with the component ratios, and the maximal theoretical water volume S _∞ is well in agreement with the experimental values.     

Simple preparation of immobilized-metal affinity chromatography media

Immobilized-metal affinity chromatography (IMAC) media was prepared. Iminodiacetic acid (IDA) was optimally coupled to the oxirane-activated gel at pH 13.0 and 60 °C in 0.1–0.15 g of IDA per ml of 2M Na₂CO₃ for 5–7 hours. The amount of coupled IDA was 600–800 micromoles per gram of dried gel by determining zinc (II) ion with atomic absorption spectroscopy. Adsorption and desorption of protein sample to IDA-coupled media was made and the result is compatible to ones reported previously. The efficiency of column chromatography was discussed on partially purifying β-galactosidase from E. coli as the protein sample by zinc (II) ion chelate affinity column.     

Conductometric titration of chitosan sulfate polyanions in the presence of extraneous electrolytes

The possibility of determining the concentration of basic substance and H ₂SO₄ and Na₂SO₄ impurities in technical-grade chitosan sulfate (CS) was demonstrated. Water-ethanol solution containing 80±10% ethanol of the volume of the titratable mixture is the optimum medium for titration of technical-grade CS. Translated from Khimicheskie Volokna, No. 2, pp. 21–23, March–April, 1997.     

Study IR spectroscopic study of sorption of Cu<Superscript>2+</Superscript> ions on granulated chitosan

Formation of insoluble compounds, in particular, the basic salt (CuOH)₂SO₄ and copper hydroxide, is a side process that reduces the concentration of copper ions in the solution and causes overstatement of the data on sorption. Formation of chitosan sulfate salt is a competing side process. Side processes and the structural inhomogeneity of chitosan and the sorption products obtained in heterogeneous conditions make it impossible to calculate the stoichiometric composition of chitosan copper complexes. Articles based on the Proceedings of the All-Russian Scientific and Technical Conference on Current Technologies and Equipment in the Textile Industry (Moscow State Textile University, November, 2007) __________ Translated from Khimicheskie Volokna, No. 2, pp. 17–9, March–April, 2008.     

Effect of Zr/Si molar ratio and sulfation on structural and catalytic properties of ZrO<Subscript>2</Subscript>–SiO<Subscript>2</Subscript> mixed oxides

ZrO₂–SiO₂ mixed xerogel and aerogel samples with varied molar ratios were prepared by sol–gel method followed by oven drying and supercritical drying using n-propanol as a solvent, respectively. Sulfation was carried out to further enhance the acidic properties of the mixed oxides. Effect of drying, Zr/Si molar ratio and sulfation have been studied and correlated with the structural, textural and catalytic properties of ZrO₂–SiO₂ mixed oxides. Both xerogel and aerogel mixed oxides have different structural and textural features, however, the total number of acid sites per unit surface area (0.0021–0.0029 mmol NH₃ m⁻²) and thus the catalytic activity for cyclohexanol conversion (31–41%) was found in the similar range. Sulfated mixed oxide aerogel and xerogel samples showed significant enhancement of cyclohexanol conversion (91–99%).     

Effects of Acylation and Crosslinking on the Material Properties and Cadmium Ion Adsorption Capacity of Porous Chitosan Beads

Abstract

Chitosan is a novel glucosamine biopolymer derived from the shells of marine organisms. This biopolymer is very attractive for heavy metal ion separations from wastewater because it is selective for toxic transition metal ions over less toxic alkali or alkane earth metal ions. Highly porous, 3-mm chitosan beads were prepared by an aqueous phase-inversion technique for casting gel beads followed by freeze drying. In the attempt to simultaneously improve material properties and adsorption capacity, chitosan was chemically modified by 1) homogeneous acylation of amine groups with nonanoyl chloride before bead casting, and 2) heterogeneous crosslinking of linear chitosan chains with the bifunctional reagent glutaric dialdehyde (GA) after bead casting but before freeze drying. The random addition of C₈ hydrocarbon side chains to about 7% of the amine groups on uncrosslinked chitosan beads via N-acylation improved the saturation adsorption capacity from 169 to 216 mg Cd²⁺/g-bead at saturation (pH 6.5, 25°C) but only slightly reduced solubility in acid solution. Crosslinking of the N-acylated chitosan beads with 0.125 to 2.5 wt% GA in the crosslinking bath increased the internal surface area from 40 to 224 m²/g and rendered the beads insoluble in 1 M acetic acid (pH 2.36). However, crosslinking of the N-acylated chitosan beads reduced the saturation adsorption capacity to 136 mg Cd²⁺/g-bead at 0.75 wt% GA and 86 mg Cd²⁺/g-bead at 2.5 wt% GA. Crosslinking also significantly reduced the compression strength. There was no clear relationship between internal surface area and adsorption capacity, suggesting that the adsorbed cadmium was not uniformly loaded into the bead.     

Relaxation patterns of endlinking polydimethylsiloxane near the gel point

While the rheological behavior at the gel point (GP) itself is well known, many questions remain about the approach to the gel point (from either side). For studying this phenomenon, rheological experiments were performed on crosslinked polydimethylsiloxanes (PDMS) and characteristic patterns in the relaxation behavior were abstracted into a phenomenological model for the relaxation time spectrum. The well known power law with slope-n and cutoff at the longest relaxation time λ _max governs the relaxation near the gel point. Beyond the gel point, an additional box-like contribution appears in the spectrum. The relaxation exponent n decreases with increasing extent of crosslinking. The longest relaxation time λ _max and equilibrium modulus G_e show power-law scaling with the distance from the gel point, |p − p_c|. For samples with imbalanced stoichiometric ratios r ≥ 1, the function n (p − p_c) is independent of r. Samples with strong crosslinker deficiency (r = 0.5) exhibit a different functional form for n (p − p_c) from those with r ≥ 1. The power law relaxation with decreasing n in the terminal zone was found previously for a different crosslinking system. It seems to be a common pattern for partially crosslinked materials from polymeric precursors. Received: 11 December 1997/Revised version: 18 December 1997/Accepted: 18 December 1997     

Biologically active amphiphilic derivatives of chitosan

Amphiphilic N-derivatives of chitosan containing C₁₂ alkyl and carboxyl groups were obtained. It was shown that the compounds obtained have fungicidal activity and form intermolecular associates in solutions. __________ Translated from Khimicheskie Volokna, No. 6, pp. 57–58, November–December, 2005.     

Novel hydroxyapatite/tussah silk fibroin/chitosan bone-like nanocomposites

The nanocomposite particles of hydroxyapatite–tussah silk fibroin (HA–TSF) and HA–chitosan (HA–CS) were developed by biomimetic synthesis using Ca(NO₃)₂ and Na₃PO₄ as the precursors of inorganic phase in the presence of TSF and CS. Both nanocomposite particles were carbonate-substituted HA with low crystallinity. TSF and CS induced preferential alignment of HA crystallites along the direction of c-axis, and the induction effect of TSF was more than of CS. HA–TSF and HA–CS nanocomposite particles were found to be needle-like in the shape with a typical size of 100–200 nm in length and about 20 nm in width, and 115–250 nm in length and about 25 nm in width, respectively, as the result of the preferential arrangement of HA crystallites along c-axis intensified by TSF and CS. Based on both nanocomposite particles, the bone-like nanocomposites of HA–TSF/CS and HA–CS/TSF with the same compositions were prepared by isostatic pressing using CS and TSF concentrated solutions as adhesive composition, respectively. However, the two bone-like nanocomposites exhibited significantly different mechanical properties. The compressive strength, compressive modulus, and bending strength of HA–TSF/CS composite were significantly higher than of HA–CS/TSF composite. The fracture mechanism of both composites was analyzed by SEM observation. The study result indicates that HA–TSF/CS nanocomposite is an ideal candidate for bone substitute materials.     

Fabrication and properties of superabsorbent complex gel beads composed of hydrolyzed polyacrylamide and chitosan

A novel method for preparing complex beads composed of hydrolyzed polyacrylamide (HPAM) and chitosan, based on the electrostatic attraction between ? COO^? of HPAM and Al³⁺ and between ? COO^? and ? NH₃⁺ of chitosan, was established. In the two‐stage crosslinking process, first Al³⁺ was used as a crosslinking agent for the crosslinking of HPAM molecules, which were used as the skeleton structure of the gel beads. In the second stage, chitosan diffused into the skeleton structure. The gel beads were characterized with scanning electron microscopy, inductively coupled plasma mass spectrometry, Fourier transform infrared spectroscopy, and thermogravimetric analysis. There was a chitosan component in the gel beads, and these gel beads had porous and rough surfaces. The swelling properties of the HPAM–chitosan gel beads were measured in water, in acidic, neutral, and alkaline buffers, and in different saline solutions. The swelling ratio was as high as 3675 g/g in water and 170 g/g in a 0.15 mol/L NaCl solution. The beads showed pH sensitivity in buffers of different pH values and salt sensitivity in different saline solutions. The order of the equilibrium absorbency of the gel beads in different saline solutions was Na⁺ > K⁺ > Mg²⁺ > Ca²⁺ > Al³⁺. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Copolymerization of 4-cyanophenyl acrylate with methyl methacrylate: synthesis, characterization and determination of monomer reactivity ratios

A novel acrylic monomer, 4-cyanophenyl acrylate (CPA) was synthesized by reacting 4-cyanophenol dissolved in methyl ethyl ketone with acryloyl chloride in the presence of triethylamine as a catalyst. Copolymers of CPA with methyl methacrylate (MMA) at different composition was prepared by free radical solution polymerization at 70 ± 1 °C using benzoyl peroxide as an initiator. The copolymers were characterized by FT-IR, ¹H-NMR and ¹³C-NMR spectroscopic techniques. The solubility tests were checked in various polar and non polar solvents. The molecular weight and polydispersity indices of the copolymers were estimated by using gel permeation chromatography. The glass transition temperature of the copolymers increases with increases MMA content. The thermal stability of the copolymer increases with increases in mole fraction of CPA content in the copolymer. The copolymer composition was determined by using ¹H-NMR spectra. The monomer reactivity ratios determined by the application of linearization methods such Fineman–Ross (r ₁ = 0.535, r ₂ = 0. 0.632), Kelen–Tudos (r ₁ = 0.422, r ₂ = 0.665) and extended Kelen–Tudos methods (r ₁ = 0.506, r ₂ = 0. 0.695).     

A Novel Nanocomposite Matrix Based on Silylated Chitosan and Multiwall Carban Nanotubes for the Immobilization of Urease

A nanocomposite matrix made up of silylated chitosan and multiwall carbon nanotubes (CHIT–SiO₂–MWCNTs) was fabricated to investigate the immobilization of urease (Urs). Urs enzyme was covalently immobilized with the CHIT–SiO₂–MWCNTs matrix using glutaraldehyde as a linker. The resulting Urs/CHIT–SiO₂–MWCNTs biomatrix was characterized with Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and cyclic voltammetry (CV) taking CHIT–SiO₂–MWNTs as a reference. The influence of various parameters on Urs enzyme activity within the matrix was investigated including pH, temperature, and time. The Michaelis–Menten constant and apparent activities for the Urs enzyme were calculated to be 0.51 mM and 89.02 mg/cm², respectively; indicating CHIT–SiO₂–MWCNTs nanocomposite matrix has a high affinity to immobilize Urs enzyme.     

Preparation of core–shell latex particles by emulsion co-polymerization of styrene and butyl acrylate,and evaluation of their pigment properties in emulsion paints

A series of core–shell polymeric particles with poly(n-butyl acrylate-co-methacrylic acid-co-ethylene glycol dimethylacrylate) as core and poly(styrene-co-methyl methacrylate) as shell were prepared by seeded emulsion polymerization. The role of ethylene glycol dimethylacrylate (EGDMA) is to crosslink the core so as to avoid any probability of gel formation and to bind both the core and the shell phase together. The spherical morphology of the core–shell structure was achieved at 60:40 core to shell ratio. The core–shell morphology was confirmed by SEM and TEM analyses. GPC analysis of the particles reveals that the polymer shows a bimodal mode. The first peak has M _w = 382700 and M _n = 245200 with polydispersity index of 1.6, and the second peak has M _w = 21200 and M _n = 14800 with polydispersity index of 1.4. These core–shell latexes were applied as a pigment/binder in emulsion paint and the paint properties like gloss, rock hardness, washability, opacity, etc. were compared with the standard. The results show that these core–shell latexes can provide similar hiding power with 17% reduction of TiO₂ in the paint formulation.     

Radical polymerization of (trimethylsilylethynyl)styrene and thermal properties of polystyrene with ethynyl group

The radical polymerizations of 2-, 3-, and 4-(trimethylsilylethynyl)styrenes (1 a – c) and copolymerizations of 1 a – c (M₁) with styrene (M₂) have been studied. Copolymerization parameters were determined as r₁ = 1.22 and r₂ = 0.54 for 1 a, ₁ = 1.10 and r₂ = 0.90 for 1 b, and r₁ = 1.42 and r₂ = 0.38 for 1 c. The deprotection of the trimethylsilyl groups in poly[(trimethylsilylethynyl)styrene] (2 a – c) and poly[(trimethylsilylethynyl)styrene-co-styrene] (4 a – c) using (C₄H₉)₄NF smoothly proceeded to yield poly(ethynylstyrene) (3 a – c) and poly(ethynylstyrene-co-styrene) (5 a – c), respectively, which underwent curing reactions at elevated temperature to form crosslinking polystyrenes. Received: 31 March 1997/Revised: 2 June 1997/Accepted: 3 June 1997     

Volatile compounds produced by irradiation of butterfat

Anhydrous butterfat was irradiated at 6 megarads in a special glass reaction flask, and the headspace and total condensate samples were examined by wide-range (−180C to 125C) gas chromatography combined with mass spectrometry. The nature and amounts of volatile compounds were not greatly influenced by whether the butterfat was irradiated under oxygen or under vacuum, nor (apart fromn-alkanoic acids) by storage for 1 and 9 weeks. Carbon dioxide was produced in greatest amount. Of the remaining compounds, aliphatic hydrocarbons predominated both in number and amount. Aliphatic oxygenated compounds including carbonyl compounds were isolated in relatively small amounts. The following compounds were identified positively: C_1–13 n-alkanes; C_4–9 2-methylalkanes; C_2–14 alk-l-enes; C_2–9 alk-l-ynes; C_2–5 n-alkanoic acids; C_1–5 n-alkan-l-ols and propan-2-ol; C_2–8 n-alkanals and 2-methylbut-2-enal; C_3–5,7 alkan-2-ones; C_1–4 n-alkyl formates, vinyl and isoamyl formate, methyl acetate and methyln-hexanoate; and carbon dioxide. Visiting Scientist from Division of Dairy Research, C.S.I.R.O., Highett, Victoria, Australia.     

Spectroscopic and conformational study of chitosan acid salts

The efficient procedure for preparation of chitosan acid salts in isopropyl alcohol under mild condition has been demonstrated. The salts were prepared by dissolving chitosan into ascorbic acid, p-amino benzoic acid and p-nitro benzoic acid, respectively, and then washed with an isopropyl/water mix-solvent. The prepared crystal salt and molecular conformation of modified chitosan derivatives are characterized by using ultraviolet, Fourier transform infrared (FTIR), ¹H nuclear magnetic resonance (NMR), X-ray diffraction and Circular dichroism (CD) techniques. The formation of salts was confirmed by FTIR (∼1,523–1,557 cm⁻¹) and NMR (∼7–8 ppm) with respect to the bonding between NH₂ group on chitosan and COOH group on acid. The CD spectra of chitosan salts showed negative at (253, 285 and 295 nm band) in chitosan ascorbic acid, p-amino benzoic acid and p-nitro benzoic acid salt respectively in DMSO, indicating that the polymer adopted a helical secondary structure. The polymers are highly soluble in a wide pH range, which opens new perspectives for the biomedical application of chitosan based-materials.