Enhanced radiation crosslinking of carboxymethylated chitosan in the presence of acids or polyfunctional monomers

Carboxymethylated chitosan (CMCt) hydrogels were synthesized by γ-ray radiation-induced crosslinking in the presence of acids or polyfunctional monomers. Compared with that of CMCt hydrogels synthesized without additives, the gel fraction was improved and the gelation dose was decreased obviously after incorporating acids or polyfunctional monomers into CMCt hydrogels. The diffusion behavior of water in the CMCt gels prepared at different conditions was Fickian diffusion, and the swelling of the CMCt gels displayed characteristic pH sensitivity, which was analyzed by fluorescence molecular probes. Preliminary mechanism of radiation-induced crosslinking of CMCt in the presence of acids or polyfunctional monomers was discussed based on the FTIR and sol-gel analysis. Furthermore, it was found that CMCt hydrogels were hydrodegradable with high temperature (>60 °C), and incorporating polyfunctional monomers into the CMCt hydrogels also could improve the thermal stability of the CMCt hydrogels obviously.     

Effects of synthesis-solvent on swelling and elastic properties of poly(N-isopropylacrylamide) hydrogels

Thermosensitive N-isopropylacrylamide (NIPA) hydrogels were synthesized by a free radical copolymerization with N,N′-methylenebisacrylamide (MBAA) in four solvents: water, ethanol, acetone and N,N-dimethylformamide. The swelling and elastic properties of the hydrogels were affected by the synthesis-solvents; the hydrogels (e.g. NIPA/MBAA = 1000/50 mol/m³-pre-gel solution) synthesized in water have smaller swelling volume and larger shear modulus at 10 °C than those synthesized in amphiphilic solvents. The network structure of hydrogels was estimated in terms of the conversion and two sorts of effective crosslinking density based on the Flory theory and the concentration of crosslinker. The hydrogels synthesized in water can have the microscopic inhomogeneous network arising from the entanglement of polymer chains, while the hydrogels synthesized in amphiphilic solvents can have the homogeneous network arising from the polymer concentration lower than the pre-gel solution and can be similar in network structure to the lightly crosslinked hydrogel synthesized in water.     

Separation of C1-C5 aliphatic carboxylic acids on a highly sulfonated styrene-divinylbenzene copolymer resin column with a C6 aliphatic carboxylic acid solution as the mobile phase

Simultaneous separation of C₁-C₅ aliphatic carboxylic acids (formic, acetic, propionic, iso-butyric, butyric, iso-valeric and valeric acids) on a highly sulfonated styrene-divinylbenzene copolymer resin column (TSKgel SCX,  mm i.d.) was performed with C₆ aliphatic carboxylic acids (3-methyl-n-valeric, iso-caproic and caproic acids) solutions as the mobile phases. Using 0.05 mM sulfuric acid at pH 4.0 as the mobile phase, although good separation of these C₁-C₅ acids was achieved, peaks of the C₅ acids (iso-valeric and valeric acids) with large hydrophobicity tailed strongly. In contrast, using 1 mM C₆ acids at pH ca. 4.0 as the mobile phases, although vacant peaks corresponding to the C₆ acids in the mobile phase appeared, the peak shapes of the C₅ acids were improved greatly. Excellent simultaneous separation, symmetrical peaks and relatively high-sensitivity conductimetric detection for these C₁-C₅ acids were achieved on the TSKgel SCX column in 15 min with 1 mM iso-caproic acid at pH 4.0 as the mobile phase.     

Preparation of composites and nanocomposites based on bentonite and poly(sodium acrylate). Effect of amount of bentonite on the swelling behaviour

A series of composite and nanocomposite hydrogels were synthesized by copolymerization reaction of partially neutralized acrylic acid (SA) on bentonite micropowder (BT) using N,N′-methylenebisacrylamide (MBA) as a crosslinker and potassium persulfate (I) as an initiator in aqueous solution. The influences of Na⁺-BT, organoBT (O-BT), and the content of the BT in the copolymeric gels on the swelling behaviour in deionized water and saline solution (0.2 wt.% NaCl_(aq)) were investigated. Results showed that the equilibrium swelling (W_∞) was decreased by adding a small amount of the BT, however, at higher BT contents, the W_∞ increased with the increase of the amount of clay. It was found that a concentration of 14 wt.% Na⁺-BT gave the best results absorption (955 g/g). Moreover, the amount of swelling for these absorbents in saline solution was smaller than that in deionized water. These hydrogels were characterized by X-ray diffraction and scanning electron microscopy. Finally, the thermogravimetric analysis indicated that introduction of clay to the polymer network resulted in an increase in thermal stability.     

Swelling behaviour of thermo-sensitive hydrogels based on oligo(ethylene glycol) methacrylates

The thermo-sensitive swelling behaviour of hydrogels based on 2-(2-methoxyethoxy)ethyl methacrylate (MEO₂MA) and synthesized by free radical polymerization has been investigated. The homopolymer hydrogel presents a low critical solution temperature (LCST) close to room temperature, which can be modulated by copolymerization with longer oligo(ethylene glycol) side chain methacrylates (OEG_xMA). Then, three series of copolymeric hydrogels synthesized with MEO₂MA and several low ratios of OEG_xMA with M_n = 475 g mol⁻¹ (OEG₈MA), M_n = 1100 g mol⁻¹ (OEG₂₃MA) and M_n = 2080 g mol⁻¹ (OEG₄₅MA) were studied. In addition to conventional tetra(ethylene glycol) dimethacrylate (TEGDMA) crosslinker, the use of biodegradable oligo(caprolactone) dimethacrylate (OCLDMA) was also tested. The hydrophilic/hydrophobic balance, function of the short and the long OEG side chains, establishes a swelling behaviour depending on monomer composition, side chain length and temperature. The swelling at equilibrium increases with increasing the amount of OEG_xMA in the copolymer and, at the same time, the collapsing moves progressively to higher temperature. The temperature dependent volumetric response of some of these hydrogels can be compare with the most extended thermo-sensitive hydrogel, which is based on poly(N-isopropylacrylamide) (P(N-iPAAm)). Therefore, they are potential candidates to replace it in applications where biocompatibility is required.     

New 2-aminoethylimidazole-based dicarboxylic acid receptor derived from cholestane

A new facial amphiphile cholestane-based receptor 1 containing a 2-imidazolylethylamino moiety at the 3α and 7α positions of cholestane was synthesized. Recognition selectivity of the new receptor 1 with various dicarboxylic acids was assessed by ¹H NMR titration. Maleic acid showed the highest binding constant among all the tested acids (K_a = 9.36 × 10⁴ M⁻¹).     

Pyrenyl-appended imidazolium receptor for selective fluorescence sensing of oxalic acid

A new fluorescent imidazolium-based cholestane receptor 4 bearing a pyrene moiety was synthesized. The binding ability of 4 toward various dicarboxylic acids was examined by UV-vis and fluorescence spectroscopy. Receptor 4 showed the highest binding constant for oxalic acid among all the tested dicarboxylic acids (K_a = 5.06 × 10⁴ M⁻¹). Oxalic acid formed a complex with 4 with a 1:2 ratio in ethanol.     

Investigation of swelling and network parameters of poly(ethylene glycol)-crosslinked poly(methyl vinyl ether-co-maleic acid) hydrogels

The influence of poly(ethylene glycol) (PEG) plasticiser content and molecular weight on the physicochemical properties of films cast from aqueous blends of poly(methyl vinyl ether-co-maleic acid) was investigated using thermal analysis, swelling studies, scanning electron microscopy (SEM) and attenuated total reflectance (ATR)-Fourier transform infrared (FTIR) spectroscopy. FTIR spectroscopy revealed a shift of the CO peak from 1708 to 1731 cm⁻¹, indicating that an esterification reaction had occurred upon heating, thus producing crosslinked films. Higher molecular weight PEGs (10,000 and 1000 Da, respectively), having greater chain length, producing hydrogel networks with lower crosslink densities and higher average molecular weight between two consecutive crosslinks. Accordingly, such materials exhibited higher swelling rates. Hydrogels crosslinked with a low molecular weight PEG (PEG 200) showed rigid networks with high crosslink densities and, therefore, lower swelling rates. Polymer:plasticizer ratio alteration did not yield any discernable patterns, regardless of the method of analysis. The polymer-water interaction parameter (χ) increased with increases in the crosslink density. SEM studies showed that porosity of the crosslinked films increased with increasing PEG MW, confirming what had been observed with swelling studies and thermal analysis, that the crosslink density must be decreased as the M_w of the crosslinker is increased. Hydrogels containing PMVE/MA/PEG 10,000 could be used for rapid delivery of drug, due to their low crosslink density. Moderately crosslinked PMVE/MA/PEG 1000 hydrogels or highly crosslinked PMVE/MA/PEG 200 systems could then be used in controlling the drug delivery rates. We are currently evaluating these systems, both alone and in combination, for use in sustained release drug delivery devices.     

Glass transition temperature modification of acrylic and dienic type copolymers of 4-chloromethyl styrene with incorporation of (Me3Si)3C- groups

The new functional styrenic monomer, 4-trisylmethyl styrene (TsiMS) [Tsi=trisyl=tris(trimethylsilyl)methyl], was synthesized by reacting 4-chloromethyl styrene (CMS) with trisyllithium (TsiLi) in tetrahydrofuran (THF) solvent in the presence of copper chloride (CuCl). Attempt for the free radical polymerization of TsiMS by α,α^′-azobis(isobutyronitrile) (AIBN) as an initiator at 70 ± 1 °C failed for several periods of times. This result showed that the trisyl group is a highly sterically hindered substituent and, subsequently, TsiMS becomes resistant for polymerization. Therefore, for preparation of new methacrylic, acrylic and dienic copolymers of TsiMS, we firstly synthesized the copolymers of CMS with different monomers such as methyl methacrylate (MMA), ethyl methacrylate (EMA), methyl acrylate (MA), ethyl acrylate (EA), n-butyl acrylate (BA) and isoprene (IP) by free radical polymerization method in toluene solution at 70 ± 1 °C using AIBN initiator to give the copolymers I-VI in good yields. The copolymer compositions were obtained using related ¹H NMR spectra and the polydispersity indices of the copolymers determined using gel permeation chromatography (GPC). The trisyl groups were then covalently attached to the obtained copolymers as side chains by reaction between excess of TsiLi and benzyl chloride bonds of CMS units, to give the copolymers - in 80-92% yields. All the resulted polymers were characterized by FT-IR, ¹H NMR and ¹³C NMR spectroscopic techniques. The solubility of all the copolymers was examined in various polar and non-polar solvents. The glass transition temperature (T_g) of all copolymers was determined by differential scanning calorimetry (DSC) apparatus. The T_g value of copolymers containing bulky trisyl groups was found to increase with incorporation of trisyl groups in polymer structures. The presence of trisyl groups in polymer side chains, create new macromolecules with novel modified properties.     

Mesogens based on palladium orthometallated complexes with carboxylato bridges: tuning and shaping a non-planar molecule

The binuclear cyclopalladated compounds [Pd₂(μ-OH)₂(Lⁿ)₂] (1) derived from imines HLⁿ = p-C_nH_2n + 1O-C₆H₄-CHN-C₆H₄-OC_nH_2n + 1-p (n = 6,10) react with carboxylic acids to give the derivatives [Pd₂(μ-ox)₂(Lⁿ)₂] (2) with a planar core for oxalic acid, and [Pd₂(μ-OOCR)₂(Lⁿ)₂] (3-7) compounds with a non-planar ridge tent structure for other RCOOH acids: (3) R = C_mH_2m + 1 (m = 1, 3, 5, 7, 9, 11, 13, 15, 17); (4) R = CH₂(OCH₂CH₂)_pOCH₃ (p = 1, 2); (5) R = CH₂-C₆H₄-OC_qH_2q + 1-p (q = 2, 4, 6, 8, 10, 12); (6) R = C₆H₄-OC_rH_2r + 1-p (r = 4, 10); (7) R = C*H(OH)CH₃. The acids used were designed to explore the effect on the thermal properties of the compounds prepared of systematic variations in the type of carboxylato ligand, which induce structure, packing, and polarity changes, and in the length of the carboxylato chain. Most of the complexes prepared, even when far from planar, show liquid crystal behavior and display nematic, smectic A and smectic C phases.     

Effect of different electrolytes on the swelling properties of calyx[4]pyrrole-containing polyacrylamide membranes

Calix[4]pyrrole (1) was synthesized and characterized and this macrocycle was incorporated in polyacrylamide gels. The presence of meso-octamethyl-porphyrinogen inside of gel was checked using infrared spectroscopy, differential scanning calorimetry, and swelling studies. The swelling degree of these hydrogels in equilibrium with different electrolytes (NaCl, LiCl, KCl, CaCl₂ and AlCl₃) was measured in a concentration range 0.1-0.5 mol dm⁻³. Although no significant alterations in the swelling degree can be found for the different 1:1 electrolytes, when the cation charge of unsymmetrical electrolytes increases, the gel swells in a significant way. This swelling process is enhanced by the presence of calyx[4]pyrrole. The effect of alkaline hydrolysis of polaycrylamide-based hydrogels was also studied. The hydrolysed hydrogels collapse in the presence of the electrolytes; this behavior is dependent on the hydrolysis degree, electrolyte charge and calyx[4]pyrrole presence and concentration; the latter leads to polyacrylamide with tailor-made properties.     

Intramolecularly coordinated organoantimony(III) carboxylates

The reactions of organoantimony chlorides L^1,2SbCl₂1 and 2 ([2,6-(ROCH₂)₂C₆H₃]⁻, R = Me; L¹ and R = t-Bu; L²) with silver salts of selected carboxylic acids resulted to corresponding organoantimony carboxylates L^1,2Sb(OOCR′)₂, 1a-c (for L¹) and 2a-c (for L²), where R′ = CH₃ for 1a, 2a; R′ = CHCH₂ for 1b, 2b and R′ = CF₃ for 1c, 2c. All compounds were characterized by the help of elemental analysis, ESI-MS, ¹H and ¹³C NMR spectroscopy. The solid state structure investigation using single crystal X-ray diffraction techniques (2a, c) and IR spectroscopy revealed significant differences in coordination mode of both O,C,O chelating ligand and carboxylic groups in this set of compounds. The structure of all compounds in solution of non-coordinating solvent (CDCl₃) was determined by means of variable temperature ¹H, ¹³C, ¹⁹F NMR spectroscopy and IR spectroscopy.     

Structurally simple chiral thioureas as chiral solvating agents in the enantiodiscrimination of α-hydroxy and α-amino carboxylic acids

C₂-Symmetrical chiral thioureas (S,S)-1 and (S,S)-2 were prepared in good yield by the reaction of 2 equiv of inexpensive (S)-1-phenylethylamine, or the corresponding naphthyl analog, with 1 equiv of thiophosgene in the presence of excess triethylamine. The presence of asymmetric elements in (S,S)-1 and (S,S)-2, and their capacity to act as receptors for anionic species via hydrogen bonding were exploited in the development of ¹H NMR spectroscopic enantiodiscrimination of chiral carboxylic acids. In particular, the diastereomeric complexes derived from thioureas (S,S)-1 and (S,S)-2 with ammonium salts of the chiral acids gave rise to well separated signals of the α-hydrogens and simple integration provides the corresponding enantiomeric ratios. Furthermore, it was observed that C_α-H in the (R) enantiomers of the chiral α-hydroxy and α-amino carboxylic acids studied in this work consistently appears downfield relative to the same signals in the (S) enantiomers.     

An enhanced immobilization of BSA biomolecule on anionic hydrogels: swelling and adsorption modeling

The three-dimensional structure of hydrogels plays a leading role in several areas of applications. The hydrogels are more and more used as systems of immobilized and controlled release of biomolecules in biotechnology and bio-pharmacy industries. To improve protein adsorption capacity in poly(acrylamide) hydrogels, maleic acid co-monomer was included into the reaction mixture during hydrogel synthesis. So, hydrogels of poly(acrylamide) and its copolymers with diprotic maleic acid were prepared by copolymerization and chemical crosslinking with N,N′-methylene bis-acrylamide. Swelling behavior in distilled water, in physiological saline and in bovine serum albumin (BSA) solutions was studied. Influence of initial BSA concentration on hydrogel swelling and BSA adsorption was investigated. The high amount of maleic acid present in the hydrogels has a significant effect on the swelling behavior and BSA adsorption. Results showed that the pH sensitivity of hydrogels resulted in the high amount of adsorbed BSA. The adsorption isotherms were described by Langmuir and Freundlich models. The thermodynamic parameter (ΔG _ads ⁰ ) was determined for all obtained hydrogels. We demonstrated the favorable character and reversibility of the BSA adsorption process.     

OH-radical induced degradation of 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) and 4-chloro-2-methylphenoxyacetic acid (MCPA): A pulse radiolysis and gamma-radiolysis study

The reactions of OH, H and e_aq⁻ with 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) and 4-chloro-2-methylphenoxyacetic acid (MCPA) were studied by pulse radiolysis. The site of OH-radicals addition to the aromatic ring of 2,4,5-T was found to be—C1: ∼18%, C2/C4/C5: total ∼28% and C3/C6: total ∼41%. The overall rate constants with OH-radicals were k(OH+2,4,5-T)=6.4 (±0.5)×10⁹ mol dm⁻³ s⁻¹ and k(OH+MCPA)=8.5 (±0.8)×10⁹ mol dm⁻³ s⁻¹. The radiation induced decomposition of the pesticides, chloride- and product formation (phenolic compounds, aliphatic acids) was studied by gamma radiolysis as a function of dose. A mechanism for acetate formation is discussed. The presence of oxygen during irradiation affected the decomposition rate only indiscernibly, however, chloride elimination, ring fragmentation (formation of aliphatic acids), TOC- and toxicity reduction were strongly enhanced. For complete removal of 500 μmol dm⁻³ herbicides a dose of ∼4 kGy was required. Using air saturation during irradiation a reduction of 37-40% of the TOC was observable at 5 kGy, detoxification (luminescence inhibition <20%) was achieved with 10 kGy.     

Synthesis and decarboxylation of N-acyl-α-triphenylphosphonio-α-amino acids: a new synthesis of α-(N-acylamino)alkyltriphenylphosphonium salts

4-Phosphoranylidene-5(4H)-oxazolones 1 undergo hydrolysis in THF in the presence of HBF₄ at room temperature to give N-acyl-α-triphenylphosphonioglycines 3 (R² = H) in very good yields. 4-Alkyl-4-triphenylphosphonio-5(4H)-oxazolones 2 react with water in CH₂Cl₂/THF solution without any acidic catalyst at 0-5 °C in a few days yielding N-acyl-α-triphenylphosphonio-α-amino acids 3 (R² = Me) or α-(N-acylamino)alkyltriphenylphosphonium salt 4 (R² = CH₂OMe). α-Triphenylphosphonio-α-amino acids 3, on heating up to 105-115 °C under reduced pressure (5 mmHg) or on treatment with diisopropylethylamine in CH₂Cl₂ at 20 °C undergo decarboxylation to give the corresponding α-(N-acylamino)alkyltriphenylphosphonium salts 4, usually in very good yields.     

Determination of sulfur-containing amino acids by capillary electrophoresis dynamic reaction cell inductively coupled plasma mass spectrometry

Capillary electrophoresis dynamic reaction cell™ inductively coupled plasma mass spectrometry (CE-DRC-ICP-MS) for the determination of sulfur-containing amino acids is described. The sulfur-containing amino acids studied include l-cysteine, l-cystine, dl-homocystine and l-methionine. The species studied were well separated using a 70 cm length×75 μm i.d. fused silica capillary while the applied voltage was set at +22 kV and a 10 mmol l⁻¹ disodium tetraborate buffer (pH 9.8) containing 0.1 mmol l⁻¹ EDTA and 0.5 mmol l⁻¹ Triton X-100 was used as the electrophoretic buffer. The sulfur-selective electropherogram was determined at m/z 48 as by using its reaction with O₂ in the reaction cell. The method avoided the effect of polyatomic isobaric interferences at m/z 32 caused by and on by detecting as the oxide ion at m/z 48, which is less interfered. The detection limit of various species studied was in the range of 0.047-0.058 μg S ml⁻¹, which corresponded to the absolute detection limit of 1.3-1.6 pg S based on the injection volume of 27 nl. We determined the concentrations of selected sulfur-containing amino acids in urine and nutritive complement samples. The recovery was in the range of 92-128% for various species.     

Hydrothermal synthesis of two copper helical coordination polymers with acentric three-dimensional framework constructing from mixed pyridine carboxylates

Two copper helical coordination polymers, [Cu(2-pc)(3-pc)]_n1 and [Cu(2-pc)(4-pc)]_n2 (2-pc=2-pyridine carboxylate, 3-pc=3-pyridine carboxylate, 4-pc=4-pyridine carboxylate) have been hydrothermally synthesized directly from pyridine carboxylic acids and copper nitrate. The crystal structure were determined by single-crystal X-ray diffraction with the following data: compound 1, orthorhombic, P2₁2₁2₁, a=6.591(3) Å, b=8.692(5) Å, c=20.548(9) Å, V=1177.2(9) Å³, Z=4; compound 2, orthorhombic, Pna2₁, a=21.160(10) Å, b=9.095(5) Å, c=6.401(3) Å, V=1231.9(11) Å³, Z=4. The acentric three-dimensional (3D) framework of 1 is constructed from right-handed helical Cu(2-pc) chains and left-handed Cu(3-pc) helices. As for 2, Cu(2-pc) helical chains, in which left- and right-handed helices are coexisting, and Cu(4-pc) zigzag chains combined together to form acentric 3D architecture of 2 as well. Additionally, besides general spectral characterization, we first introduce generalized 2D correlation spectroscopy to explore the coordination polymers and ascertain the stretching vibration location of carboxylate groups of compounds 1 and 2.     

Reentrant phase transition and network parameters of hydrophobically modified poly[2-(diethylamino)ethylmethacrylate-co-N-vinyl-2-pyrrolidone/octadecyl acrylate] hydrogels

Hydrophobically modified poly[2-(diethylamino)ethylmethacrylate-co-N-vinyl-2-pyrrolidone/octadecyl acrylate] [P(DEAEMA-NVP/OA)] hydrogels with different OA content were prepared by free-radical crosslinking copolymerization of corresponding monomers in tert-butanol. The swelling equilibrium of the hydrogels was investigated as a function of temperature and hydrophobic comonomer content in pure water. An interesting feature of the swelling behavior of the P(DEAEMA-NVP/OA) hydrogels was the reentrant phase transition where the hydrogels collapse once and reswell as temperature increased. The average molecular mass between crosslinks and polymer-solvent interaction parameter (χ) of the hydrogels were calculated from equilibrium swelling values. The enthalpy (ΔH) and entropy (ΔS) changes appearing in the χ parameter for the hydrogels were determined by using the Flory-Rehner theory. It was observed that the experimental swelling data of the hydrophobic hydrogels at different temperature agreed with the Flory-Rehner theory, that provided that the sensitive dependence of χ parameter on both temperature and polymer concentration is taken into account.     

Microporous hydrogels of cellulose ether cross-linked with di- or polyfunctional glycidyl ether made for the delivery of bioactive substances

Hydrogels were prepared by the cross-linking reactions of carboxymethyl cellulose with di- or polyfunctional glycidyl ether to investigate the effects of different cross-linker’s chain length and the number of epoxy groups on the properties of the gels. Fourier transform infrared spectra showed a new peak at ν = 1,740 cm⁻¹ assigned to the absorption of carbonyl groups in the new ester structure formed by the cross-linking of –COONa with the epoxy compounds. The interior morphology data indicated microporous network structures which correlated with the swelling of hydrogels. The swelling data in water, urea, sucrose, urine and aspartame showed increases in swelling with an increase in chain length of the cross-linker but decreased with the number of epoxy groups on the cross-linker. Collectively, the gels were ionic strength sensitive. The rheology experiments showed that gel point (t _gel) increased with the chain length of the cross-linker but reduced with increase in number of epoxy groups on the cross-linker. Dynamic oscillatory measurements indicated stronger material functions in gels prepared with polyfunctional epoxy cross-linkers. The hydrogels prepared with difunctional epoxy groups had higher loading capacity and faster release of bovine serum albumin compared with hydrogels based on polyfunctional epoxy group cross-linkers.