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1.
In order to utilize the psyllium husk a medicinally important natural polysaccharide and to develop the novel hydrogels meant for the colon specific drug delivery, we have prepared psyllium and methacrylamide based polymeric networks by using N,N′-methylenebisacrylamide (NN-MBAAm) as crosslinker and ammonium persulfate (APS) as initiator. To study various structural aspects of the polymeric networks thus formed psy-cl-poly(MAAm), these were characterized with SEMs, FTIR, TGA and swelling studies. The swelling studies of networks were carried out as a function of time, temperature, pH and [NaCl]. Equilibrium swelling has been observed to depend on both composition of the polymer and nature of swelling medium. Maximum percent swelling 1262 was observed for the polymeric network prepared with 19.45 × 10−3 mol/L of [NN-MBAAm] at 40 °C in 0.5 M NaOH solution. This article also discusses the release dynamics of tetracycline hydrochloride from the hydrogels, for the evaluation of the drug release mechanism and diffusion coefficients of drug from the polymer matrix. The effect of pH on the release pattern of tetracycline hydrochloride has been studied by varying the pH of the release medium. It has been observed from the release dynamics of drug from the hydrogels that the diffusion exponent ‘n’ have 0.477, 0.423 and 0.427 values and gel characteristic constant ‘k’ have 5.07 × 10−2, 6.34 × 10−2 and 6.38 × 10−2 values, respectively, in distilled water, pH 2.2 buffer and pH 7.4 buffer solution. The values the ‘n’ indicated that the Fickian type diffusion mechanism occurred for the release of tetracycline hydrochloride from drug loaded psy-cl-poly(MAAm) polymers in different release mediums. In Fickian type diffusion mechanism, the rate of polymer chain relaxation is more as compare to the rate of drug diffusion from these hydrogels and release behavior follows Fick’s law of diffusion. In each release medium, the values of the initial diffusion coefficient ‘Di’ for the release of tetracycline hydrochloride was higher than the values of late time diffusion coefficient ‘DL’ indicating that in the start, the diffusion of drug from the polymeric matrix was faster as compare to the latter stages.  相似文献   

2.
A series of hydrogels were synthesized by graft cross-link copolymerization of sodium alginate (SA) and acrylic acid (AA) using N, N-methylene-bis-(acrylamide) as a cross-linker. By study of the swelling kinetics of the hydrogels in different buffer solutions, the overshooting effect was observed in acidic medium, namely the gels firstly swelled to a maximum value following by a gradual deswelling until the equilibrium. The phenomenon is interpreted as a cooperative physical cross-linking caused by the hydrogen bond formation between the carboxyl groups of the hydrogels in a hydrophobic environment. The hydrogen bond formation was further confirmed by FT-IR spectra. The dependence of overshooting effect on the pH of buffer solution was more noticeable in comparison with the composition of hydrogels, demonstrating that the cooperative physical cross-linking caused by the hydrogen bond formation is dominant. Whether or not the overshooting effect appears is not only relative to the pH of buffer solution, but also depends on the pKa of carboxyl groups on the network. The overshoot processes of the hydrogels under acidic medium at pH below the pKa follow a quantitative model proposed by Díez-Peńa et al., and the theoretical curves are in very good agreement with the experimental data. While in pH > pKa buffer solutions, the overshoot phenomenon does not appear arising from the repulsive interaction between the ionized carboxyl groups, the swelling processes follow Schott second-order rate equation.  相似文献   

3.
Accurate and precise determination of phospholipid composition by 31P NMR spectroscopy requires correct assignments and adequate spectral resolution. Because temperature and pH may affect chemical shifts (δ), our first aim was to establish the temperature coefficient (ΔδT) of common phospholipid classes when using sodium cholate as detergent. This parameter can then be used to aid in resonance assignments. The second goal was to investigate the pH dependence of δ so that, in addition to temperature, pH control can be used to minimize spectral overlap. For phosphatidylcholine, sphingomyelin, dihydrosphingomyelin and phosphatidylglycerol, δ values were invariant with pH and temperature. Whereas the ΔδT for phosphatidylinositol was 4 × 10−3 ppm/°C, regardless of pH, these coefficients were highly pH-dependent for phosphatidic acid, phosphatidylethanolamine and phosphatidylserine, exhibiting maximal variations with the deprotonation of the headgroup, particularly for phosphatidic acid. These trends indicate the importance of H-bonding on δ and ΔδT for phospholipid resonances.  相似文献   

4.
Pine needles and their carboxymethyl forms were functionalized by network formation with 2-acrylamido-2-methylpropanesulphonic acid (AAmPSA) in the presence of N,N-methylene bisacrylamide. N-Tetramethylethylene diamine and ammonium persulfate were used as accelerator-initiator systems to prepare these hydrogels. The hydrogels were characterized by FTIR, SEM, and nitrogen analysis and for water uptake capacities before and after metal ion sorption with a view to evaluating their use in the removal of toxic ionic species from waste water. A detailed study of Cr6+ adsorption was carried out as a function of time, temperature, pH, and ionic strength. The thermodynamic parameters of adsorption such as ΔH0, ΔS0, and ΔG0 have been evaluated to understand the underlying mechanism of adsorption. In order to understand their reusability in possible technological applications, biodegradability of these hydrogels and their precursors was studied.  相似文献   

5.
Carboxymethylation of starch provided carboxymethyl starch (CMS) and the modification was followed by grafting CMS with acrylonitrile (AN) using ammonium per sulphate-N,N,N,N-tetramethylethylene diamine as initiator–accelerator system. Crosslinked networks of CMS and AN were obtained using two crosslinkers, viz., N,N-methylenebisacrylamide and ethyleneglycoldimethacrylate. The networks were further reacted with hydroxylamine to generate metal ion active amidoxime groups. The synthesized hydrogels were characterized by FTIR, SEM, nitrogen analysis and swelling studies to evaluate water uptake and the candidate polymers were used as matrices for the sorption of Fe2+ ions, as a model metal ion, as a function of time, temperature, pH and ionic strength. An attempt was made to investigate the thermodynamics of its sorption behaviour.  相似文献   

6.
In order to utilize the psyllium husk, a medicinally important natural polysaccharide, to develop the hydrogels meant for the drug delivery, we have prepared psyllium and polyacrylic acid based polymeric networks by radiation-induced crosslinked copolymerization. Polymeric networks (hydrogels) thus formed were characterized with SEMs, FTIR and swelling studies. Swelling behavior of the hydrogels was studied as a function of monomer concentration in the hydrogels and temperature, pH and [NaCl] of the swelling medium. This paper discusses the swelling kinetics of the hydrogels and release dynamics of anticancer model drug 5-fluorouracil from the hydrogels for the evaluation of swelling and drug release mechanisms. It has been observed from the release dynamics of drug that diffusion exponent ‘n’ have 0.7, 0.8 and 0.7 values and gel characteristics constant ‘k’ have 9.13 × 10−3, 6.22 × 10−3 and 9.01 × 10−3 values for the release of 5-fluorouracil, respectively, in distilled water, pH 2.2 buffer and pH 7.4 buffer. The values of the diffusion exponent show that the release of drug from drug-loaded hydrogels has occurred through Non-Fickian diffusion mechanism. It has also been observed from the swelling and release of drug in the different pH buffer that the polymer matrix is pH responsive and can be exploited for the delivery of anticancer drug to the colon.  相似文献   

7.
A small pond containing the charophyte Chara hispida was monitored over a one-year period for changes in growth, water chemistry, water level and stable isotopic composition. Chara growth was found to be seasonal, with maximum growth occurring from late April to July. During this period, pH rose to > 10 while the dissolved inorganic carbon (DIC) and calcium fell as a result of photosynthesis and calcification. Large gradients in pH, water temperature and irradiance were found within the Chara sward and measurements showed that most growth and photosynthesis occurred within the upper 20 cm of the water column. Chara oospore formation was also found to be seasonal but dependent upon environmental conditions.

δ18Ow rose rapidly during summer as evaporation progressed and this was correlated with the δ18ODIC, and to some extent with δ18Oc of the Chara encrusted calcite. However, extreme isotopic disequilibrium was observed between the δ18Oc and the δ18Ow and also between the δ13Cc and the δ13CDIC. This arose from the high pH allowing atmospheric CO2 to enter the water and combine directly with OH.

It is concluded that, within shallow eutrophic lakes containing Chara swards, inferences of climate (e.g. air temperature) cannot be made from observations of the isotopic composition of Chara carbonates. However in combination with other geochemical data, disequilibrium events may be identifiable in ancient lake basins and taken as evidence for lake shallowing and/or eutrophication.  相似文献   


8.
Because of its novel bioactive properties the production of gymnodimine for use as a pharmaceutical precursor has aroused interest. The dinoflagellate, Karenia selliformis produces gymnodimine when grown in bulk culture using GP + selenium medium but the growth rates (μ) and levels of gymnodimine are low (μ, 0.05 days−1; gymnodimine 250 μg L−1 max). We describe the effects of organic acid additions (acetate, glycolate, alanine and glutamate additions and combinations of these) in enhancing growth and gymnodimine production in axenic cultures. The most effective organic acid combinations in decreasing order were: glycolate/alanine > acetate > glycolate. Glycolate/alanine optimised gymnodimine production by prolonging growth (maximum cell yield, 1.76 × 105 cells mL−1; gymnodimine, 1260 μg L−1; growth rate (μ), 0.2 days−1) compared to the control (growth maximum cell yield, 7.8 × 104 cells mL−1; gymnodimine, 780 μg L−1; μ, 0.17 days−1). Acetate enhanced gymnodimine by stimulating growth rate (μ, 0.23 days−1) and the large concentration of gymnodimine per cell (16 pg cell−1 cf. 9.8 pg cell−1 for the control) suggests a role for this compound in gymnodimine biosynthesis. Amending culture media with Mn2+ additions resulted in slightly decreased growth in control cultures and increased the gymnodimine while in glycolate/alanine cultures growth was stimulated but gymnodimine production decreased. The results suggest that the organic acid can enhance gymnodimine production by either enhancing growth maximum or the biosynthetic pathway.  相似文献   

9.
Guignardia citricarpa is a phytopathogenic fungus and the causal agent of citrus black spot. Incubation in a semi-defined media resulted in formation of exopolysaccharides [EPS(s)]. A medium containing glucose gave rise to a (1→6)-linked β-glucan (200 kD), pustulan, which was characterized by NMR and methylation analysis. A sucrose-containing medium provided a homogalactan (376 kD) and methylation analysis showed nonreducing end- (20%), 6-O- (53%) and 5,6-di-O-substituted Galf units (27%). An HMQC spectrum of the homogalactan showed C-1/H-1 signals at δ 108.2/4.820, 108.3/4.820 and 107.1/5.079, corresponding to three types of β- -Galf units. A DEPT analysis showed inverted signals (CH2) at δ 67.8 and 67.2, corresponding to 6-O-substituted β- -Galf units, whereas a C-5 signal at δ 77.0 suggests 5-O-substitution, confirming a novel structure for a β-galactofuranan.  相似文献   

10.
Graft copolymer of k-carrageenan and N,N-dimethylacrylamide has been synthesized by free radical polymerization using peroxymonosulphate/glycolic acid redox pair in an inert atmosphere. The grafting parameters i.e. grafting ratio, add on and efficiency decrease with increase in concentration of k-carrageenan from 0.6 to 1.4 g dm−3 and hydrogen ion from 3 × 10−3 to 7 × 10−3 mol dm−3, but these grafting parameters increase with increase in concentration of N,N-dimethylacrylamide from 16 × 10−2 to 32 × 10−2 mol dm−3, and peroxymonosulphate from 0.8 × 10−2 to 2.4 × 10−2 mol dm−3. The metal ion sorption, swelling behaviour and flocculation properties have been studied. The intrinsic viscosity of pure and grafted samples has been measured by using Ubbelohde capillary viscometer. Flocculation capability of k-carrageenan and k-carrageenan-g-N,N-dimethylacrylamide for both coking and non-coking coals has been studied for the treatment of coal mine waste water. The graft copolymer has been characterized by Infrared (IR) spectroscopy and thermogravimetric analysis.  相似文献   

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