Buffer solution

Abstract: High-strength bioactive glass-ceramic A-W was soaked in various acellular aqueous solutions different in ion concentrations and pH. After soaking for 7 and 30 days, surface structural changes of the glass-ceramic were investigated by means of Fourier transform infrared reflection spectroscopy, thin-film x-ray diffraction, and scanning electronmicroscopic observations, in comparison with in vivo surface structural changes. So-called Tris buffer solution, pure water buffered with trishydroxymethyl-aminomethane, which had been used by various workers as a "simulated body fluid," did not reproduce the in vivo surface structural changes, i.e., apatite formation on the surface. A solution, ion concentrations and pH of which are almost equal to those of the human blood plasma--i.e., Na+ 142.0, K+ 5.0, Mg2+ 1.5, Ca2+ 2.5, Cl- 148.8, HCO3- 4.2 and PO4(2-) 1.0 mM and buffered at pH 7.25 with the trishydroxymethyl-aminomethane--most precisely reproduced in vivo surface structure change. This shows that careful selection of simulated body fluid is required for in vitro experiments. The results also support the concept that the apatite phase on the surface of glass-ceramic A-W is formed by a chemical reaction of the glass-ceramic with the Ca2+, HPO4(2-), and OH- ions in the body fluid.

Abstract: The degradation kinetics of curcumin under various pH conditions and the stability of curcumin in physiological matrices were investigated. When curcumin was incubated in 0.1 M phosphate buffer and serum-free medium, pH 7.2 at 37 degrees C, about 90% decomposed within 30 min. A series of pH conditions ranging from 3 to 10 were tested and the result showed that decomposition was pH-dependent and occurred faster at neutral-basic conditions. It is more stable in cell culture medium containing 10% fetal calf serum and in human blood; less than 20% of curcumin decomposed within 1 h, and after incubation for 8 h, about 50% of curcumin is still remained. Trans-6-(4'-hydroxy-3'-methoxyphenyl)-2,4-dioxo-5-hexenal was predicted as major degradation product and vanillin, ferulic acid, feruloyl methane were identified as minor degradation products. The amount of vanillin increased with incubation time.

Abstract: α-MnO2 was synthesized by a very simple coprecipitation technique and tested as active electrode material for an electrochemical supercapacitor. The powder presents a poorly crystallized cryptomelane phase with a chemical composition of K0.05MnO2H0.10·0.15H2O. Different aqueous electrolytes were tested including 0.1 M Na2SO4, 0.5 M K2HPO4/KH2PO4 buffer solution, 0.3 M H2SO4, and 1 M NaOH, but interesting pseudocapacitance behavior was only observed in the case of 0.1 M Na2SO4. Further testing using this electrolyte showed that an average capacitance of 166 F/g can be reproducibly obtained within a voltage range −0.4/+0.5 V vs Hg/Hg2SO4 using a sweep rate of 2 mV/s. This interesting value is mainly due to the chimisorption of Na+ ions and/or protons at the surface of the α-MnO2 electrode. Nearly all the Mn surface atoms are involved in the pseudocapacitive process. Therefore, the high specific capacitance seems to be related to the high surface area of the MnO2 powder rather than intercalation of Na+ ions ...

Abstract: The use of total lipid phosphate as a measure of biomass was evaluated in soils with different organic matter content. Lipids were extracted with a one-phase mixture of chloroform, methanol, and a buffer, and digested with either persulfate or perchloric acid to liberate lipid-bound phosphate. This procedure was evaluated by varying the extraction buffer, the extraction and digestion times, the amount of soil extracted, and the amount of lipid material digested. An extraction period of 2 h was sufficient to yield maximum lipid phosphate. Neither sonication, vigorous mixing, nor longer extraction periods increased the amount of lipid phosphate extracted. However, the amount of lipid phosphate recovered was dependent on the choice of buffer. When organic soil was used, citrate buffer in the extraction mixture gave higher amounts of lipid phosphate than acetate buffer, Tris, H2O or phosphate buffer. In a sandy loam with low organic matter content, citrate or phosphate buffers performed equally well. When 13 soils of different organic matter content were examined, the two digestion methods showed a good linear correlation (r2 = 0.991). Substrate-induced respiration (SIR) and ATP contents of the different soils correlated well with the total lipid phosphate. Based on these measurements, a conversion factor of 500 μmol lipid phosphate·g−1 biomass-C (perchloric acid digestion) was calculated.