Chitosan versus Carboxymethyl Chitosan Cryogels: Bacterial Colonization, Human Embryonic Kidney 293T Cell Culturing and Co-Culturing.

The potential of chitosan and carboxymethyl chitosan (CMC) cryogels cross-linked with diglycidyl ether of 1,4-butandiol (BDDGE) and poly(ethylene glycol) (PEGDGE) have been compared in terms of 3D culturing HEK-293T cell line and preventing the bacterial colonization of the scaffolds. The first attempts to apply cryogels for the 3D co-culturing of bacteria and human cells have been undertaken toward the development of new models of host-pathogen interactions and bioimplant-associated infections. Using a combination of scanning electron microscopy, confocal laser scanning microscopy, and flow cytometry, we have demonstrated that CMC cryogels provided microenvironment stimulating cell-cell interactions and the growth of tightly packed multicellular spheroids, while cell-substrate interactions dominated in both chitosan cryogels, despite a significant difference in swelling capacities and Young's modulus of BDDGE- and PEGDGE-cross-linked scaffolds. Chitosan cryogels demonstrated only mild antimicrobial properties against Pseudomonas fluorescence, and could not prevent the formation of Staphylococcus aureus biofilm in DMEM media. CMC cryogels were more efficient in preventing the adhesion and colonization of both P. fluorescence and S. aureus on the surface, demonstrating antifouling properties rather than the ability to kill bacteria. The application of CMC cryogels to 3D co-culture HEK-293T spheroids with P. fluorescence revealed a higher resistance of human cells to bacterial toxins than in the 2D co-culture.

Metal-chelate sorbents based on carboxyalkylchitosans: Ciprofloxacin uptake by Cu(II) and Al(III)-chelated cryogels of N-(2-carboxyethyl)chitosan.

Here we propose a metal-chelate approach to removal of fluoroquinolones from aqueous solutions using their ability to bind strongly divalent and trivalent metal ions immobilized in a polymer matrix. Metal-affine sorbents for ciprofloxacin uptake have been fabricated via chelation of Cu(II), Al(III), and Fe(III) ions by supermacroporous cryogel of carboxyalkyl chitosan derivative (N-(2-carboxyethyl)chitosan, CEC) cross-linked with hexamethylene diisocyanate in aqeous medium. We have shown that virgin CEC cryogel adsorbed ciprofoxacin in a cationic form via electrostatic interactions at pH > pICEC, but the efficacy of recovery was below 50% and strongly pH-dependent. Modification of CEC cryogel with Cu(II) and Al(III) ions improved the ciprofloxacin (CIP) recovery by up to 98% in the pH range 7-10, the sorption capacity and affinity for CIP of metal-chelate sorbents increased with metal content and reached maximum values of 280 and 390 mg/g for Cu(II) and Al(III)-chelated cryogels, respectively. The metal-chelated CEC cryogels were efficient for ciprofloxacin removal from solutions with environmentally relevant concentration (50 µg/L) and were applicable as monolith sorbents under dynamic conditions.

Cryogels of carboxyalkylchitosans as a universal platform for the fabrication of composite materials.

Here we report a new simple method for fabrication of supermacroporous beads and monoliths via cross-linking of carboxyalkylated chitosan derivatives with hexamethylene diisocyanate in aqueous solution at subzero temperature. These materials provide high filtration rate and good mass-transfer that in combination with high binding capacity toward metal ions allows their application as a universal platform for fabrication of composite catalysts, sorbents, and metal-affine chromatography stationary phases. Using N-(2-carboxyethyl)chitosan (CEC), we have demonstrated that optimum chitosan carboxylation degree for cryogels synthesis is close to 1.0. Cu(II)-chelated CEC cryogels have shown high efficiency as metal-affinity sorbents for ciprofloxacin recovery. Co(II)-chelated CEC cryogels have been used for fabrication of Co(II) ferrocyanide-containing composite with the distribution coefficient for 137Cs of 140,000 ml/g and the adsorption capacity of ˜1 mmol/g. Composite Pd-catalysts supported on CEC cryogel provided tenfold higher reaction rate in 4-nitrophenol reduction in comparison with Pd-catalyst supported on chitosan beads.

Chitosan Gels and Cryogels Cross-Linked with Diglycidyl Ethers of Ethylene Glycol and Polyethylene Glycol in Acidic Media.

Here we show that the efficacy of the chitosan interaction with diglycidyl ethers of glycols significantly depends on pH and the nature of acid used to dissolve chitosan. In solutions of hydrochloric acid, cross-linking with diglycidyl ethers of ethylene glycol (EGDGE) and polyethylene glycol (PEGDGE) at room and subzero temperatures yields mechanically stable chitosan gels and cryogels, while in acetic acid solutions only weak chitosan gels can be formed under the same conditions. A combination of elemental analysis, FT-IR spectroscopy, and solid state 13C and 15N NMR spectroscopy was used to elucidate possible differences in the mechanism of chitosan cross-linking in alkaline and acidic media at room and subzero temperatures. We have proved that in acidic media diglycidyl ethers of glycols interacted with chitosan mainly via hydroxyl groups at the C6 position of the glucosamine unit. Besides, not only cross-linkages but also grafts were formed at room temperature. The cryo-concentration effect facilitates cross-linkages formation at -10 °C and, despite lower modification degrees compared to those of gels obtained at room temperature, supermacroporous chitosan cryogels with Young's moduli up to 90 kPa can be fabricated in one step. Investigations of chitosan cryogels biocompatibility in a mouse model have shown that a moderate inflammatory reaction around the implants is accompanied by formation of a normal granulation tissue. No toxic, immunosuppressive, and sensitizing effects on the recipient's tissues have been observed.

Quantum chemistry and experimental studies of hydrothermal destruction of Co-EDTA complexes.

Hydrothermal oxidation, a promising method for removal of cobalt radionuclides from EDTA-containing liquid radioactive waste streams, is in the focus of the present study. It has been demonstrated that Co(III)-EDTA complexes, which are very stable under normal conditions, undergo oxidation as a result of the electron transfer from the EDTA carboxyl group to Co(III) ions under elevated temperature. The electron transfer reaction follows the first-order rate law with an activation energy of 91.8 kJ/mol at рH 12 and time of Co(III) ions half-conversion of 0.2 s at 200 °C. The rate of EDTA oxidation is proportional to the concentration of Co(III) ions and solution pH. Based on quantum chemistry simulations, possible intermediate structures formed upon the electron transfer from EDTA to Co(III) ions have been suggested. It has been shown that the introduction of hydrogen peroxide provides a continuous generation of Co(III) ions and a sequential decarboxylation of the EDTA until complete degradation of the chelate structure. The pathways of cobalt immobilization have been clarified.

Decontamination of spent ion-exchangers contaminated with cesium radionuclides using resorcinol-formaldehyde resins.

The origin of the emergence of radioactive contamination not removable in the process of acid-base regeneration of ion-exchange resins used in treatment of technological media and liquid radioactive waste streams has been determined. It has been shown that a majority of cesium radionuclides not removable by regeneration are bound to inorganic deposits on the surface and inside the ion-exchange resin beads. The nature of the above inorganic inclusions has been investigated by means of the methods of electron microscopy, IR spectrometry and X-ray diffraction. The method of decontamination of spent ion-exchange resins and zeolites contaminated with cesium radionuclides employing selective resorcinol-formaldehyde resins has been suggested. Good prospects of such an approach in deep decontamination of spent ion exchangers have been demonstrated.

Metal ion binding by pyridylethyl-containing polymers: experimental and theoretical study.

Binding of Cu(2+), Ni(2+) and Ag(+) ions to polyallylamine (PAA), polyethylenimine (PEI), poly(N-2-(2-pyridyl)ethylallylamine) (PEPAA), poly(N-2-(2-pyridyl)ethylethylenimine) (PEPEI), and N-2-(2-pyridyl)ethylchitosan (PEC) has been investigated using batch sorption experiments, spectrophotometric titration, ESR, and XPS to elucidate how the structure of polymer precursors affects the ion binding efficiency of their pyridylethylated derivatives. It has been shown that pyridylethylation increases the sorption capacities of PAA and PEI cross-linked with epichlorohydrin toward Ag(+) and Ni(2+) ions, but does not improve or decrease that toward Cu(2+) ions. PEC was the most efficient material for Ag(+) ion sorption with the sorption capacity of 1.21 mmol g(-1). The highest sorption capacity for Ni(2+) (0.62 mmol g(-1)) was found for PEPEI. According to density functional theory (DFT) calculations, lower Cu(2+) binding efficiency to PEPEI results from the "looser" structure of this complex in comparison with unmodified PEI. DFT calculations have also suggested that the Cu(2+) ion is four-coordinated in the complexes with PEPAA and PAA and five-coordinated in all other complexes, which have the structures of distorted square pyramids with Cu-N bond lengths varying significantly depending on the ligand nature. The results of the theoretical investigations of the Cu(2+) complex structures were supported by the ESR data, which revealed the decrease of A‖ and the increase of g‖ values with increasing deviation from the square planar geometry of complexes in the ligands in the order PEI < PEPEI < PEPAA.

Polymer-inorganic coatings containing nanosized sorbents selective to radionuclides. 2. Latex/tin oxide composites for cobalt fixation.

Colloidal tin oxide with an average particle size of 3.5 nm, which was ex-situ synthesized by the sol-gel method, has been attached to the surface of amino-functionalized poly(acrylate-co-silane) latex particles with a diameter of 100 nm to yield a composite with selective sorption properties toward Co(2+) ions. Electrokinetic properties and the colloidal stability of the synthesized latex/SnO2 composites have been evaluated in dependence on SnO2 content and pH; the sorption capacity and distribution coefficients of composites for Co(2+) ions were in accordance with the SnO2 content and its sorption performance as an individual compound. Composite coatings obtained by casting latex/SnO2 dispersions on quartz sand spiked with (57)Co radionuclide have efficiently eliminated radionuclides migration from the surface when the SnO2 volume fraction in the film was 3.5-4.7%. Furthermore, at these SnO2 loadings, the composite coatings retained the coherent structure of the original latex coating with SnO2 particles homogeneously distributed over the film thickness. The presence of competing Ca(2+) ions in the leaching media at a concentration of above 0.01 mol/L results in a decrease of the distribution coefficients of the latex/SnO2 composite and significantly higher (57)Co leaching. The value of the distribution coefficient of the sorption material to be used in latex composite coatings to prevent migration of radionuclides shall be close to 10(6) mL/g.

Polymer-inorganic coatings containing nanosized sorbents selective to radionuclides. 1. Latex/cobalt hexacyanoferrate(II) composites for cesium fixation.

Here we present a new approach to improve fixation of radionuclides on contaminated surfaces and eliminate their migration after nuclear accidents. The approach consists in fabrication of latex composite coatings, which combine properties of polymeric dust-suppressors preventing radionuclides migration with aerosols and selective inorganic sorbents blocking radionuclides leaching under contact with ground waters and atmospheric precipitates. Latex/cobalt hexacyanoferrate(II) (CoHCF) composites selective to cesium radionuclides were synthesized via "in situ" growth of CoHCF crystal on the surface of carboxylic or amino latexes using surface functional groups as ion-exchange centers for binding precursor ions Co(2+) and [Fe(CN)6](4-). Casting such composite dispersions with variable content of CoHCF on (137)Cs-contaminated sand has yielded protective coatings, which reduced cesium leaching to 0.4% compared to 70% leaching through original latex coatings. (137)Cs migration from the sand surface was efficiently minimized when the volume fraction of CoHCF in the composite film was as low as 0.46-1.7%.