Free-radical destruction of beta-lactam antibiotics in aqueous solution

Many pharmaceutical compounds and metabolites are being found in surface and ground waters, indicating their ineffective removal by conventional wastewater treatment technologies. Advanced oxidation/reduction processes (AO/RPs), which utilize free-radical reactions to directly degrade chemical contaminants, are alternatives to traditional water treatment. This study reports the absolute rate constants for reaction of three beta-lactam antibiotics (penicillin G, penicillin V, amoxicillin) and a model compound (+)-6-aminopenicillanic acid with the two major AO/RP reactive species: hydroxyl radical ((*)OH) and hydrated electron (e(-)aq). The bimolecular reaction rate constants (M(-1) s(-1)) for penicillin G, penicillin V, amoxicillin, and (+)-6-aminopenicillanic acid for (*)OH were (7.97 +/- 0.11) x 10(9), (8.76 +/- 0.28) x 10(9), (6.94 +/- 0.44) x 10(9), and (2.40 +/- 0.05) x 10(9) and for e(-)aq were (3.92 +/- 0.10) x 10(9), (5.76 +/- 0.24) x 10(9), (3.47 +/- 0.07) x 10(9), and (3.35 +/- 0.06) x 10(9), respectively. To provide a better understanding of the decomposition of the intermediate radicals produced by hydroxyl radical reactions, transient absorption spectra were observed from 1 to 100 micros. In addition, preliminary degradation mechanisms and major products were elucidated using (137)Cs gamma irradiation and LC-MS. These data are required for both evaluating the potential use of AO/RPs for the destruction of these compounds and studies of their fate and transport in surface waters where radical chemistry may be important in assessing their lifetime.     

Plasma-chemical decomposition of methane during diamond synthesis

Using a mass spectrometric sampling method, we have observed the decomposition of CH₄ in an rf plasma usedfor diamond deposition. The gas samples were extracted through an orifice located downstream of the plasma zone and analyzed online. For the experiments a dilute mixture of H₂ and CH₄ containing 0.1–3% CH₄ has been used. CH₄ is converted to C₂H₂ and C₂H₄ quantitatively. Small amounts of heavier hydrocarbons are formed. A comparison of the experimental results with a recent kinetic model treating a purely thermal environment is made and the differences between our experiment and the model are explained. The role of acetylene as a species formed in an atmosphere rich in atomic hydrogen is proposed. The electron impact dissociation process is suggested as the rare-determining step in the plasma-chemical decomposition of methane.     

Surface modification of Mitoxantrone-loaded PLGA nanospheres with chitosan

The purpose of this research was to develop polylactic-co-glycolic acid (PLGA) nanospheres surface modified with chitosan (CS). Mitoxantrone- (MTO-) loaded PLGA nanospheres were prepared by a solvent evaporation technique. The PLGA nanospheres surface was modified with CS by two strategies (adsorption and covalent binding). PLGA nanospheres of 248.4 ± 21.0 nm in diameter characterized by the laser light scattering technique, scanning electron microscopy (SEM) are spherical and its drug encapsulation efficiency is 84.1 ± 3.4%. Zeta potential of unmodified nanospheres was measured to be negative −21.21 ± 2.13 mV. The positive zeta potential of modified nanospheres reveals the presence of CS on the surface of the modified nanospheres. Modified nanospheres were characterized for surface chemistry by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FT-IR). FT-IR spectra exhibited peaks at 3420 cm⁻¹ and 1570 cm⁻¹, XPS spectra shows the N 1s (atomic orbital 1s of nitrogen) region of the surface of the nanospheres, corresponding to the primary amide of CS. In vitro drug release demonstrated that CS-modified nanospheres have many advantages such as prolonged drug release property and decreased the burst release over the unmodified nanospheres, and the modified nanospheres by covalent binding method could achieve the release kinetics of a relatively constant release. These data demonstrate high potential of CS-modified PLGA nanospheres for the anticancer drug carrier.     

Interaction of chitosan with benzoic acid in solution and films

Chitosan films are prepared from solutions containing benzoic acid. Depending on preparation conditions, films of two types can be prepared: homogeneous optically transparent films and biphasic films containing fractal inclusions in a transparent matrix. The presence of ionic interaction between chitosan and benzoic acid in films is confirmed with the use of IR spectroscopy. The algorithm of the analysis of fractal dimensionality based on halftone images is suggested.     

Plasma-chemical reactions in weakly decomposed CCl4

For the case of weak feed gas decomposition, where the concentration of CCl₄ exceeds those of decomposition and built-up products, the emission of CCl* is shown to originate from dissociative excitation of CCl₄. With electron concentration measured independently, the kinetics of CCl₄ decomposition has been extracted from the time dependence of the CCl* intensity. Supported by EPR determinations of radical concentrations in rapidly flowing CCl₄ and CCl₄/O₂ afterglows, the primary decomposition reaction is shown to be the electron impact dissociation into CCl₃ and Cl. Its rate constant (k ₁=4×10^–8 cm³s^–1) indicates strongly that dissociative electron attachment is the main reaction channel at least at r.f. power densities just above the threshold of a self-maintaining discharge. At extremely low mean electron energies the emission of a continuum is observed, which is tentatively ascribed to the radiative CCl₃-Cl recombination.     

New way to crosslink chitosan in aqueous solution

In this paper, the reaction between o-phthaldialdehyde and free NH₂ of chitosan is investigated; at a very low molar ratio between the two reactants ([dialdehyde]/[NH₂] ∼ 2.5 × 10⁻⁴), an increase of the apparent molecular weight is obtained as evidenced from the rheological behaviour. Then, three non-ionic polysaccharides (galactomannan, maltodextrins, methylcellulose) are oxidised to 10% with sodium metaperiodate to obtain polyaldehydic derivatives able to react with free NH₂ of chitosan after their direct dissolution into chitosan solution at a molar ratio [monosaccharide units]/[NH₂ ] ∼ 0.6. Stable swollen porous gels are obtained with an excellent yield in the presence of a reducing agent (NaBH₃CN) chosen to reduce the Schiff base; nearly no influence of the structure of the initial non-ionic polysaccharides is observed when the polysaccharides are oxidized in the same conditions. Different parameters for the reaction of oxidized methylcellulose (Me-ox) with chitosan are tested: influence of the degree of oxidation (up to 50%), and of the oxidised methylcellulose concentration. The larger is the degree of oxidation or the Me-ox concentration, the lower is the degree of swelling (i.e., the larger is the degree of chitosan cross-linkage). The swollen gels formed immediately after reaction are isolated and re-swell in aqueous acidic conditions, a good solvent of initial chitosan, to purify the gel and determine the yield of the reaction and the swelling degree. At the end, preliminary tests of biodegradability of these new gels are performed using specific enzymatic degradation with lysozyme and cellulase in the case of chitosan/Me-ox cogels chosen as example.     

Surface modification using photocrosslinkable chitosan for improving hemocompatibility

Immobilization of the anticoagulative or antithrombogenic biomolecule has been considered as one of the important methods to improve the blood compatibility of artificial biomaterials. In this study, a novel immobilization reaction scheme was utilized to incorporate O-butyrylchitosan (OBCS) onto the activated glass surface with an aim to develop an anticoagulative substrate. Activation of the glass surface was carried out by silanization and then OBCS was grafted to the silanized surface via a radiation grafting technique. The OBCS-grafted glass surfaces were characterized by electron spectroscopy for chemical analysis (ESCA) and atomic force microscopy (AFM). The blood compatibility of the OBCS-grafted glass was evaluated by platelet rich plasma (PRP) contacting experiments and protein adsorption experiments in vitro. These results have demonstrated that the surface with immobilized OBCS shows much less platelet adhesive and fibrinogen adsorption compared to the control surface. Therefore, the novel reaction scheme proposed here is very promising for future development of an anticoagulative glass substrate.     

Macromolecular effects upon enzymatic degradation of chitosan in solution

Macromolecular effects were revealed in the course of enzymatic degradation of chitosan in an acetic acid solution under the action of hyaluronidase, a nonspecific enzyme. It was shown that the concentration of chitosan in the initial solution determines its supramolecular organization and, hence, the degree of enzymatic degradation.     

Preparation and characterization of chitosan nanocomposites with vermiculite of different modification

In this study, the biopolymer chitosan/vermiculite (VMT) nanocomposites were prepared by the solution mixing process of the cationic biopolymer chitosan with three different modified VMT (HVMT, NVMT, and OVMT), which was treated by hydrochloride, sodium, and cetyl trimethyl ammonium bromide (CTAB), respectively. Wide-angle X-ray diffraction (WAXD), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA) have been employed in the characterization of chitosan/HVMT, chitosan/NVMT, and chitosan/OVMT nanocomposites. Both WAXD data and TEM images of chitosan nanocomposites indicated that the silicate layers were disorderedly dispersed into the chitosan matrix in nano scale. The thermal stability of chitosan/HVMT nanocomposites have the greatest improvements compared to that of neat chitosan, chitosan/NVMT and chitosan/OVMT nanocomposites. It provides a potential approach to prepare high performance and low-cost chitosan nanocomposite.     

Plasma-chemical synthesis and properties of polymer semiconductors and prospects for their use

The properties and structures of semiconducting polymers prepared by chemical and electrochemical techniques and plasma-synthesized polymer semiconductors were compared. The advantages and disadvantages of these techniques were considered. The potential areas of application of semiconducting polymer films prepared by plasma polymerization were demonstrated.     

Inhibition of mild steel corrosion in HCl solution using chitosan

The efficiency of chitosan (a naturally occurring polymer) as a corrosion inhibitor for mild steel in 0.1 M HCl was investigated by gravimetric, potentiodynamic polarization, electrochemical impedance spectroscopy measurements, scanning electron microscopy, and UV–visible analysis. The polymer was found to inhibit corrosion even at a very low concentration. Inhibition efficiency increases with a rise in temperature up to 96 % at 60 °C and then drops to 93 % at 70 °C, while it slightly increases with an increase in chitosan concentration. Polarization curves indicate that chitosan functions as a mixed inhibitor, affecting both cathodic and anodic partial reactions. Impedance results indicate that chitosan was adsorbed on the metal/solution interface. Adsorption of chitosan at the mild steel surface is found to be in agreement with Langmuir adsorption isotherm model. Chemical adsorption is the proposed mechanism for corrosion inhibition considering the trend of protection efficiency with temperature. Calculated kinetic and thermodynamic parameters corroborate the proposed mechanism.     

Dispergation and modification of multi-walled carbon nanotubes in aqueous solution

Multi-walled carbon nanotubes (MWCNTs) are widely applied in development of composite materials. However, their properties are directly influenced by the degree of uniformity of dispersion of MWCNTs in the material’s matrix. In this paper, the dispersing of raw MWCNTs (R-MWCNTs) and decorated MWCNTs (D-MWCNTs) was studied in aqueous solution. The D-MWCNTs were obtained by chemical modification method by treatment of initial MWCNTs with the mixture of concentrated nitric and sulfuric acids (3: 1 vol/vol). To achieve a good dispersion of the MWCNTs, a method utilizing ultrasonic processing and surfactant (polyvinylpyrrolidone, PVP) was employed. MWCNTs were characterized by Fourier transform infrared spectroscopy (FT–IR) and X-ray diffraction (XRD). The prepared MWCNTs suspensions were investigated by UV spectroscopy, zeta potential measurements, surface tension and transmission electron microscopy (TEM). The D-MWCNTs have better dispersibility in aqueous solution; this attributed to the functional groups formed on their surface during chemical modification. The PVP surfactant in a certain concentration of 0.6 g/L has the maximum dispersing effect on MWCNTs in aqueous solution, the optimum concentration ratio of PVP and MWCNTs was 3: 1.     

Chemiluminescence accompanying chitosane destruction in hydrochloric acid solution containing hydrogen peroxide

The chemiluminescence (CL) accompanies the destruction of chitosane (CTS) in the presence of H₂O₂. The CL kinetics has a complex character and can be described as a sum of two exponentials. The photoluminescence monitoring and IR spectra of the reaction mixture indicate the formation of carbonyl groups in the course of CTS destruction. The enhancement of the CL intensity by Fe²⁺ suggests the reaction of Fe²⁺ with hydroperoxides accumulated with CTS decomposition. The macroradicals ROO^· are assumed to be transformed through the cleavage of the glycoside bond via a six-membered cyclic intermediate to form the terminal peroxide radical and ketone.     

Plasma-chemical processes for the preparation of pure hydrogen

The current status and prospects of the commercial and pilot production of high-purity hydrogen (>99.9999%) in quasi-equilibrium and nonequilibrium plasmas with the extraction of hydrogen using palladium membranes are surveyed. It was concluded that plasma-chemical processes with the use of a quasi-equilibrium arc plasma for the production of hydrogen with acetylene and carbon black or as a syngas constituent are currently most promising.     

ESR study on carboxymethyl chitosan radicals in an aqueous solution

Carboxymethyl chitosan (CMCTS) at a highly concentrated aqueous solution forms hydrogel by ionizing irradiation. To study on radiation-induced reaction mechanism of CMCTS in an aqueous solution, CMCTS radicals formed by reactions with OH radical were observed by ESR method. As a result of ESR spectral analysis, CMCTS radicals were identified as radicals on carboxymethyl groups.     

Adsorption of chromium from aqueous solution using chitosan beads

A basic investigation on the removal of Cr(III) and Cr(VI) ions from aqueous solution by chitosan beads was conducted in a batch adsorption system. The chitosan beads were prepared by casting an acidic chitosan solution into an alkaline solution. The influence of different experimental parameters; pH, agitation period and different concentration of Cr(III) and Cr(VI) ions was evaluated. A pH 5.0 was found to be an optimum pH for Cr(III) adsorption, and meanwhile pH 3.0 was the optimum pH for the adsorption of Cr(VI) onto chitosan beads. The Langmuir and Freundlich adsorption isotherm models were applied to describe the isotherms and isotherm constants for the adsorption of Cr(III) and Cr(VI) onto chitosan beads. Results indicated that Cr(III) and Cr(VI) uptake could be described by the Langmuir adsorption model. The maximum adsorption capacities of Cr(III) and Cr(VI) ions onto chitosan beads were 30.03 and 76.92 mg g⁻¹, respectively. Results showed that chitosan beads are favourable adsorbents. The Cr(III) and Cr(VI) ions can be removed from the chitosan beads by treatment with an aqueous EDTA solution.     

壳聚糖及其衍生物溶液浇铸膜的结构研究

用偏光显微镜小角光散射、扫描电镜和大角度X-光衍射技术研究了壳聚糖及其衍生物丁酸壳聚糖、苯甲酸壳聚糖的溶液浇铸膜的结构。用低于液晶临界浓度的稀溶液能制备具有液晶织构的膜。观察到指纹状织构、正光性滴状织构和负光性滴状织构．后两种滴状织构内分子自组织构型分别为辐射型和双极型。     

Plasma surface modification of chitosan membranes: characterization and preliminary cell response studies

Surface modification of biomaterials is a way to tailor cell responses whilst retaining the bulk properties. In this work, chitosan membranes were prepared by solvent casting and treated with nitrogen or argon plasma at 20 W for 10-40 min. AFM indicated an increase in the surface roughness as a result of the ongoing etching process. XPS and contact angle measurements showed different surface elemental compositions and higher surface free energy. The MTS test and direct contact assays with an L929 fibroblast cell line indicated that the plasma treatment improved the cell adhesion and proliferation. Overall, the results demonstrated that such plasma treatments could significantly improve the biocompatibility of chitosan membranes and thus improve their potential in wound dressings and tissue engineering applications.     

Selective tryptophan modification with rhodium carbenoids in aqueous solution

A new transition metal-based reaction has been developed for the selective modification of tryptophan residues on protein substrates. After activation of vinyl-substituted diazo compounds by Rh2(OAc)4, the resulting metallocarbenoid intermediates were found to modify indoles in aqueous media despite competing reactions with water. Both N- and 2-substituted indole products were observed in the reaction. Following initial small-molecule studies, the reaction was performed on two protein substrates. Both myoglobin and subtilisin Carlsberg were modified readily in aqueous solution, and the tryptophan selectivity of the reactions was confirmed through MS analyses of trypsin digest fragments. It was also demonstrated that myoblobin concentrations as low as 10 muM still led to appreciable levels of modification. Reconstitution experiments confirmed that myoglobin retained its ability to bind heme following modification.     

Surface modification in natural fluorapatite after uranyl solution treatment

Natural fluorapatite samples were contacted with uranyl nitrate solutions (from 10⁻² to 10⁻⁶M), adjusted to pH 6.0, then, shaken for times varying between 15 minutes to 72 hours, at room temperature. After that, the solid and liquid phases were separated by centrifugation and the solid was dried at 80°C overnight. The uranium analysis of the solid samples and solutions revealed that uranium was incorporated over fluorapatite. Selected solid samples produced by contacting treatments were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. XRD patterns showed the growth of uranyl species in the fluorapatite. Imaging by SEM at 20000x showed the location of uranyl compounds in a crystalline layer in the surface of fluorapatite grains. This layer was well defined for the 10⁻² M of U-contacting solution, but a saturation value was attained at 64% of uranium uptake yield. In the case of 10⁻⁴ M and lower U-contacting solution, the uranium uptake yield was near of 90% after 45 minutes. This fact suggests that natural fluorapatite has excellent properties to immobilize uranium compounds in a solution. Afterwards, the pregnant fluorapatite mineral was regenerated using an alkaline-leaching process. The uranium separated in this way is concentrated and can be handled to a final disposition.