Showing papers on "Buffer solution published in 2008"

Synthesis and Characterization of Positive-Charge Functionalized Mesoporous Silica Nanoparticles for Oral Drug Delivery of an Anti-Inflammatory Drug?

Abstract: We synthesized mesoporous silica nanoparticles (MSN) with different densities of surface positive charges. The positive surface charge was generated by incorporating trimethylammonium (TA) functional groups into the framework of MSN (MSN–TA) via direct co-condensation of a TA-silane and tetraethoxysilane (TEOS) in the presence of a base as a catalyst. These MSN–TA samples have well-defined hexagonal structures with an average particle diameter of 100 nm, pore size of 2.7 nm, and surface area of about 1000 m2 g−1. Anionic drug molecules, Orange II (a fluorescent tracing molecule), and sulfasalazine (an anti-inflammatory prodrug used for bowel disease), were effectively loaded into these MSN–TA samples and remained inside of the MSN–TA under acidic environment (pH 2–5). The amounts of loading of both Orange II and sulfasalazine were increased with increasing positive charge densities resulting from the increasing number of TA groups. When these drug-loaded MSN–TA nanoparticles were placed in physiological buffer solution (pH 7.4), a partial negative surface charge on the MSN–TA was generated due to the deprotonation of silanol groups, and the strong electrostatic repulsion triggered a sustained release of the loaded molecules. MSN–TA as a nanovehicle for pH-dependent loading and controllable release of anionic drug molecules can be used as an oral delivery drug systems targeting at intestine. These drugs can be remained trapped in the nanovehicle when passing through the stomach's acidic environment and be released in intestine where the environmental pH is close to neutral.

Temperature- and pH-Responsive Dense Copolymer Brushes Prepared by ATRP

Abstract: Dual responsive molecular brushes consisting of statistical copolymers of di(ethylene glycol) methyl ether methacrylate (MEO2MA) and either methacrylic acid (MAA) or N,N-dimethylaminoethyl methacrylate (DMAEMA) were synthesized by grafting from poly(2-(2-bromoisobutyroyloxy)ethyl methacrylate (PBIEM) macroinitiators using atom transfer radical polymerization (ATRP). Copolymer brushes with controlled composition and molecular weights ranging from Mn = 600 000 to 1 400 000 with polydispersity indexes (Mw/Mn) between 1.18 and 1.45 were obtained. The lower critical solution temperature (LCST) of MEO2MA-stat-MAA decreased with the increasing molar fraction of MAA in the copolymer in deionized water but increased in buffer solution at pH 7. At pH 9, the hydrophilicity of polymer increased with ionization of carboxylic acid to further raise the LCST. On the other hand, the LCST of MEO2MA-stat-DMAEMA copolymers increased with increasing DMAEMA content at pH 4, 7, and 9. A bottle-brush terpolymer prepared from all...

Derivative voltammetric direct simultaneous determination of nitrophenol isomers at a carbon nanotube modified electrode

Abstract: Cyclic voltammetry was used to investigate the electrochemical reduction of nitrophenol isomers at a glassy carbon electrode modified with carbon nanotubes, and a derivative voltammetric technique was adopted to improve the resolution and enhance the determination sensitivity. In 0.1 mol L−1 HAc–NaAc buffer solution (pH 5.0), the modified electrode showed a good electrocatalytic response towards nitrophenol isomers. Through a derivative technique, the peak currents increased significantly and the reduction peaks of nitrophenol isomers could be separated, so the method could be applied to direct simultaneous determination without preseparation. The linear calibration ranges were 4.0 × 10−6 to 2.0 × 10−3 mol L−1 for o-nitrophenol, 1.0 × 10−5 to 1.0 × 10−3 mol L−1 for m-nitrophenol and 2 × 10−6 to 4.0 × 10−3 mol L−1 for p-nitrophenol, with detection limits of 5.0 × 10−7, 6.0 × 10−6 and 4.0 × 10−7 mol L−1, respectively.

Do bioactive glasses convey a disinfecting mechanism beyond a mere increase in pH

Abstract: AIM: To test whether bioactive glasses kill microbiota via mineralization or the release of ions other than sodium. METHODOLOGY: Flame-spray synthesis was applied to produce nanometric glasses of different sodium content and constant Ca/P ratio: 28S5, 45S5 and 77S. Calcium hydroxide and nanometric tricalcium phosphate (TCP) were used as controls. Apatite induction was monitored by Raman spectroscopy. Bovine dentine disks with adherent Enterococcus faecalis cells were exposed to test and control suspensions or buffered solutions for 1 h, 1 day and 1 week. Colony-forming units were counted and disks were inspected using scanning electron microscopy. Suspension supernatants and solutions were analysed for their pH, osmolarity, calcium and silicon content. RESULTS: Sodium containing glasses induced pH levels above 12, compared with less than pH 9 with sodium-free 77S. Calcium hydroxide, 45S5 and 28S5 killed all bacteria after 1 day and lysed them after 1 week. TCP caused the highest apatite induction and substantial calcification on bacteria adhering to dentine, but did not reduce viable counts. 77S achieved disinfection after 1 week without visible apatite formation, whilst the buffer solution at pH 9 caused only minimal reduction in counts. CONCLUSION: Bioactive glasses have a directly and an indirectly pH-related antibacterial effect. The effect not directly linked to pH is because of ion release rather than mineralization.

Voltammetric Behaviour of Sulfamethoxazole on Electropolymerized-Molecularly Imprinted Overoxidized Polypyrrole

Abstract: In this work, preparation of a molecularly imprinted polymer (MIP) film and its recognition properties for sulfamethoxazolewere investigated. The overoxidized polypyrrole (OPPy) film was prepared by the cyclic voltammetric deposition of pyrrole (Py) in the presence of supporting electrolyte (tetrabutylammonium perchlorate-TBAP) with and without a template molecule (sulfamethoxazole) on a pencil graphite electrode (PGE). The voltammetric behaviour of sulfamethoxazole on imprinted and non-imprinted (NIP) films was investigated by differential pulse voltammetry (DPV) in Britton-Robinson (BR) buffer solutions prepared in different ratio of acetonitrile-water binary mixture, between the pH 1.5 and 7.0. The effect of the acetonitrile-water ratio and pH, monomer and template concentrations, electropolymerization cycles on the performance of the MIP electrode was investigated and optimized. The MIP electrode exhibited the best reproducibility and highest sensitivity. The results showed that changing acetonitrile-water ratio and pH of BR buffer solution changes the oxidation peak current values. The highest anodic signal of sulfamethoxazole was obtained in BR buffer solution prepared in 50% (v/v) acetonitrile-water at pH 2.5. The calibration curve for sulfamethoxazole at MIP electrode has linear region for a concentration range of 25.10-3 to 0.75 mM (R²=0.9993). The detection limit of sulfamethoxazole was found as 3.59.10-4 mM (S/N=3). The same method was also applied to determination of sulfamethoxazole in commercial pharmaceutical samples. Method precision (RSD87%) were satisfactory. The proposed method is simple and quick. The polypyrrole (PPy) electrodes have low response time, good mechanical stability and are disposable simple to construct.

Decarbonation of MgAl-LDHs (layered double hydroxides) using acetate-buffer/NaCl mixed solution.

Abstract: By using acetate-buffer (sodium acetate and acetic acid)/NaCl mixed solutions, the deintercalation of carbonate ions (CO(2-)3) was conducted on MgAl--LDHs at different Mg/Al ratios-LDH2 (LDH with Mg/Al approximately 2) and LDH3 (LDH with Mg/Al approximately 3). When only an acetate-buffer solution was used, decarbonation did not take place even if the buffer solution was made acidic enough to dissolve LDH itself; however, the addition of NaCl to the buffer solution caused deintercalation of the carbonate ions from the MgAl-LDHs and the reaction was conducted without any morphological and weight change at 25 degrees C. Under the optimum conditions, full decarbonation was attained for the two MgAl-LDHs in minutes, and the obtained LDHs contained Cl(-) in the interlayer space without incorporation of any acetate anions due to their extremely low anion selectivity of acetate ion. The allowable range for the concentration of the decarbonation solution is wide, and the change in pH due to the decarbonation reaction is slight because of the buffering effect. The decarbonation was affected by the Mg/Al ratio of the LDH; i.e., the present LDH2 was slightly more difficult to decarbonate than LDH3, probably due to the higher layer-charge density of LDH2.

The effect of tri-calcium phosphate (TCP) addition on the degradation of polylactide-co-glycolide (PLGA).

Abstract: This paper investigates the effects of alpha-tri-calcium phosphate (alpha-TCP) addition on the properties of polylactide-co-glycolide (PLGA). Samples with additions of 5, 10, 15, 20, 30 and 40 wt% alpha-TCP were prepared via a hotpressing method. Long-term in vitro studies (up to 60 days) were carried out in pH 7.4 phosphate-buffered saline (PBS). Degradation properties were investigated by monitoring pH, water uptake and mass loss. Dissolution of calcium was analysed with inductively coupled plasma spectroscopy (ICP). Internal changes of the sample structure were studied with X-ray microtomography (microCT). Change in the mechanical properties was assessed in tensile tests prior to degradation. With an addition of 40 wt% alpha-TCP, the onset of mass loss could be retarded by 18 days; at the end of the study the pH of the buffer solution was reduced to only 4.3 in comparison to 3 for pure PLGA. Although degradation properties seemed to be strongly dependent on the amount of alpha-TCP added, all samples appeared to show faster internal degradation when assessed with microCT.

Controlled release of bovine serum albumin from hydroxyapatite microspheres for protein delivery system

Abstract: Desorption behavior of a model protein (bovine serum albumin, BSA) on commercial hydroxyapatite (HAp) microspheres and its control were investigated for protein delivery system. The desorption behavior related strongly to the phosphate concentration in phosphate buffer solution: the amount of desorbed BSA increased when the phosphate concentration increased. In physiological buffer solution, which contains 10 mM phosphate, the initial burst release of BSA was observed: 70% of BSA was rapidly desorbed after 0.5 h, and 80% after 24 h. In contrast, the extremely low release profile of BSA was observed in distilled water. For the controlled release of BSA in physiological condition, the BSA-loaded HAp microspheres were encapsulated with a biodegradable polymer, poly(lactic acid-co-glycolic acid) (PLGA) by a solid-in oil-in water (S/O/W) emulsion solvent evaporation method. The initial burst was significantly reduced, and the BSA release was remarkably prolonged by the encapsulation.

Direct electrochemistry and electrocatalytic activity of cytochrome c covalently immobilized on a boron-doped nanocrystalline diamond electrode.

Abstract: Cytochrome c (Cyt c) was covalently immobilized on a boron-doped nanocrystalline diamond (BDND) electrode via surface functionalization with undecylenic acid methyl ester and subsequent removal of the protecting ester groups to produce a carboxyl-terminated surface. Cyt c-modified BDND electrode exhibited a pair of quasi-reversible and well-defined redox peaks with a formal potential (E0) of 0.061 V (vs Ag/AgCl) in 0.1 M phosphate buffer solution (pH 7.0) and a surface-controlled process with a high electron transfer constant (ks) of 5.2 ± 0.6 s-1. The electrochemical properties of as-deposited and Cyt c-modified boron-doped microcrystalline diamond (BDMD) electrodes were also studied for comparison. Investigation of the electrocatalytic activity of the Cyt c-modified BDND electrode toward hydrogen peroxide (H2O2) revealed a rapid amperometric response (5 s). The linear range of response to H2O2 concentration was from 1 to 450 μM, and the detection limit was 0.7 μM at a signal-to-noise ratio of 3. The sta...