Showing papers on "Buffer solution published in 2004"

Adsorption of Lysozyme over Mesoporous Molecular Sieves MCM-41 and SBA-15: Influence of pH and Aluminum Incorporation

Abstract: The adsorption of lysozyme on the mesoporous molecular sieves MCM-41 and SBA-15 from buffered solutions with different pH values has been studied as a model protein adsorption system. The amount adsorbed depends on the solution pH as well as on the pore volume and the composition of the adsorbent. The adsorption isotherms at pH 6.5 to 10.5 fitted the Langmuir model (type L isotherm), while the isotherms recorded at pH 12 are of the S type. The maximum amount adsorbed was observed for AlSBA-15 at pH 9.6 and amounted to 47.2 μmol/g (580 mg/g). The stability of SBA-15 toward to the buffer solution is higher for SBA-15 as compared to MCM-41, which is probably a consequence of the higher wall thickness of the former material. Diffuse reflectance Fourier transform infrared spectra of the adsorbed lysozyme confirm that the adsorption of the enzyme did not result in denaturation of Lz.

DNA extraction from archival formalin-fixed, paraffin-embedded tissues: heat-induced retrieval in alkaline solution

Abstract: Based on the antigen retrieval principle, our previous study has demonstrated that heating archival formalin-fixed, paraffin-embedded (FFPE) tissues at a higher temperature and at higher pH value of the retrieval solution may achieve higher efficiency of extracted DNA, when compared to the traditional enzyme digestion method. Along this line of heat-induced retrieval, this further study is focused on development of a simpler and more effective heat-induced DNA retrieval technique by testing various retrieval solutions. Three major experiments using a high temperature heating method to extract DNA from FFPE human lymphoid and other tissue sections were performed to compare: (1) different concentrations of alkaline solution (NaOH or KOH, pH 11.5–12) versus Britton and Robinson type of buffer solution (BR buffer) of pH 12 that was the only retrieval solution tested in our previous study; (2) several chemical solutions (SDS, Tween 20, and GITC of various concentrations) versus BR buffer or alkaline solution; and (3) alkaline solution mixed with chemicals versus BR buffer or single alkaline solution. Efficiency of DNA extraction was evaluated by measuring yields using spectrophotometry, electrophoretic pattern, semiquantitation of tissue dissolution, PCR amplification, and kinetic thermocycling-PCR methods. Results showed that boiling tissue sections in 0.1 M NaOH or KOH or its complex retrieval solutions produced higher yields and better quality of DNA compared to BR buffer or chemical solutions alone. The conclusion was that boiling FFPE tissue sections in 0.1 M alkaline solution is a simpler and more effective heat-induced retrieval protocol for DNA extraction. Combination with some chemicals (detergents) may further significantly improve efficiency of the heat-induced retrieval technique.

Buffer Loading for Counteracting Metal Salt-Induced Signal Suppression in Electrospray Ionization

Abstract: The decrease in the sensitivity of electrospray ionization mass spectrometry caused by the presence of metal salts, such as sodium chloride, in the sample matrix is well known and is particularly problematic for biological samples. We report here that addition of high levels of ammonium acetate can improve analyte signal in aqueous electrospray solutions and counteracts the signal suppression caused by sodium chloride. A ∼3-fold improvement in S/N is obtained by adding 8 M ammonium acetate to aqueous solutions of cytochrome c without added sodium chloride. No organic solvents or acids are added into the electrospray solutions. The signal-to-noise ratios of cytochrome c and ubiquitin (10-5 M) ions formed from aqueous solutions containing 2.0 × 10-2 M sodium chloride are improved by factors of ∼7 and 11, respectively, by adding 7 M ammonium acetate to the solution. We propose that this effect is a result of the precipitation of Na+ and Cl- from solution within the evaporating electrospray droplets prior to ...

Cadmium ion adsorption on different carbon adsorbents from aqueous solutions. Effect of surface chemistry, pore texture, ionic strength, and dissolved natural organic matter

Abstract: Adsorption of Cd(II) species at pH = 5 was studied on three carbon adsorbents: granular activated carbon, activated carbon fiber, and activated carbon cloth As-received and oxidized adsorbents were used Cd(II) adsorption greatly increased after oxidation due to the introduction of carboxyl groups The use of a buffer solution to control the pH introduced some changes in the surface chemistry of carbons through the adsorption of one of the compounds used, biphthalate anions The increase in ionic strength reduced Cd(II) uptake on both as-received and oxidized carbons due to a screening of the electrostatic attractions between the Cd(II) positive species and the negative surface charge, which in the case of as-received carbons derived from the biphthalate anions adsorbed and in the oxidized ones from the carboxyl groups Tannic acid was used as a model compound for natural organic matter Its adsorption was greatly reduced after oxidation, and most of the carbon adsorbents preadsorbed with tannic acid showed an increase in Cd(II) uptake In the case of competitive adsorption between Cd(II) species and tannic acid molecules, there was a decrease in Cd(II) uptake on the as-received carbon whereas the contrary occurred with the oxidized carbons These results illustrate the great importance of carbon surface chemistry in this competitive adsorption process Finally, under all experimental conditions used, when the adsorption capacity of carbons was compared under the same conditions it increased in the following order: granular activated carbon < activated carbon fiber < activated carbon cloth

Synthesis and degradation behavior of poly(propylene carbonate) derived from carbon dioxide and propylene oxide

Abstract: High molecular weight and regular molecular structure poly(propylene carbonate) (PPC) was successfully synthesized from carbon dioxide and propylene oxide. The PPC copolymer structure was an exact alternating copolymer as evidenced by the 13C-NMR technique. Degradative behavior of the PPC was conducted by soil burial and buffer solution immersion (pH = 6) tests, respectively. The results showed that the weight loss of soil buried in PPC films increased more slowly than that immersed in the buffer solution after 6-month exposure. However, the weight loss of sample immersed in the buffer solution increased rapidly during the first 2 months and reached a value of 4.59%. Water sorption measurement also revealed that the PPC membranes immersed in buffer solution were more hydrophilic than those in soil burial tests. The degradation mechanism of PPC membranes was correlated with the sample morphologies, FTIR, and 1H-NMR spectra. The SEM morphologies were consistent with the weight loss and water sorption measurements. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1840–1846, 2004

Kinetic resolution of (R,S)-sec-butylamine using omega-transaminase from Vibrio fluvialis JS17 under reduced pressure.

Abstract: The kinetic resolution of (R,S) sec-butylamine with the ω-transaminase (TA) from Vibrio fluvialis JS17 was performed under reduced pressure (e.g., 150 torr) to selectively remove an inhibitory product (2-butanone). The evaporation kinetics of 2-butanone at 150 torr in the buffer solution followed the first-order rate law, and the evaporation rate constant was 2.19 1/h, and independent of pH, while the evaporation kinetics of sec-butylamine is dependent on pH. A simple mathematical model of the evaporation of sec-butylamine allowing the estimation of its concentration in the reaction media was developed. The evaporation rate constant of its free amine form and the protonated amine form were 1.00 1/h, and nearly zero, respectively. Although the optimum pH of the ω-TA activity for sec-butylamine is 9.0, the optimal pH of the enzyme reaction under reduced pressure was pH 7.0, due to the higher evaporation rate of sec-butylamine at higher pH above 7.0. Using the recombinant Escherichia coli BL21 overexpressing ω-TA, 400 mM racemic sec-butylamine was resolved successfully to 98% ee of (R)-sec-butylamine with 53% conversion at 150 torr and pH 7.0. © 2004 Wiley Periodicals, Inc.

Comparison of US Pharmacopeia Simulated Intestinal Fluid TS (without pancreatin) and Phosphate Standard Buffer pH 6.8, TS of the International Pharmacopoeia with Respect to Their Use in In Vitro Dissolution Testing

Abstract: Introduction Buffer solutions suitable for dissolution tests are described as such only in The United States Pharmacopeia (USP);The International Pharmacopoeia (IntPh),for example,broadly describes the composition of buffer solutions without specifying their fields of applicability. In this study Simulated Intestinal Fluid (SIFsp),which is described in The 26th United States Pharmacopeia (USP 26) as an 0.05 M buffer solution containing potassium dihydrogen phosphate (the pancreatin is omitted from the composition for most dissolution testing applications),and Phosphate Standard Buffer pH 6.8 TS, which is described in Volume 1 of The International Pharmacopoeia,Third Edition,(IntPh 3) as a mixture of 0.025 M potassium dihydrogen phosphate buffer solution and 0.025 M di-sodium hydrogen phosphate buffer solution,were investigated with respect to their interchangeability as dissolution test media. Both are pH 6.8 phosphate buffers,and they have similar osmolalities (114 mOsmol/kg) and buffer capacities (18 mEq/L/pH/unit). However, in the USP medium potassium (50mM) dominates over sodium (22mM) whereas in the IntPh buffer sodium (49.7mM) dominates over potassium (25mM). [Note: For the current investigations the IntPh phosphate buffer media was used as monographed in the 3rd edition,Volume 1. With the publication of Volume 5 the composition of the buffer pH 6.8 medium has been changed. Volume 5 describes a 0.04 M disodium hydrogen phosphate buffer solution for Buffer pH 6.8.]. The applicability and the interchangeability of these two compositionally similar but not identical buffers as dissolution media was investigated for products containing one of three drug substances: Metronidazole,a typical BCS Class 1 drug,and indometacin and ibuprofen,two drugs belonging to BCS Class 2. In each case several commercial products currently available on the German market were investigated. Products included uncoated,film coated,and sugar coated tablets as well as hard gelatin capsules.

Heat-Treated Transition Metal Hexacyanometallates as Electrocatalysts for Oxygen Reduction Insensitive to Methanol

Abstract: Highly active catalysts for electrochemical reduction of oxygen insensitive to the presence of methanol were prepared from transition metal hexacyanometallate precursors by heat-treatment with carbon black under an inert atmosphere. The catalytic activity for oxygen reduction was examined with the floating electrode technique under an air atmosphere at room temperature. The electrolyte used in most of the measurements was 1 M sodium phosphate buffer solution (pH 7.5), whereas acid and alkaline solutions were also used in addition to the neutral buffer solution to examine the catalytic activity of the prepared catalyst over a wide range of pH. Remarkable enhancements in the catalytic activity were observed for samples heat-treated at temperatures higher than 500°C. Among several 3d-transition metals incorporated in the inorganic precursor, the combination of cobalt and iron incorporated at neighboring sites gave the highest activity, comparable to that of platinum black catalyst (Pt/C). The catalytic activity for oxygen reduction was not affected by the presence of 2.5 M methanol in the electrolyte, while that of Pt/C was severely impaired by the presence of methanol. The catalysts prepared from the inorganic precursors were characterized by X-ray diffraction (XRD), infrared (IR), and X-ray photoelectron spectroscopy (XPS) measurements. The XRD and IR data indicated that the cyanide structure of the inorganic precursor was decomposed when heating beyond 500°C. The XPS data indicated that the oxidation states of cobalt and iron are close to metallic ones and two types of nitrogen forming new bonding are present in the heat-treated samples. The same structural and spectral changes were observed for samples heat-treated without carbon black. From these results, the evolution of the high catalytic activity by heat-treating the inorganic precursors is discussed.

Factors affecting the temporal stability of semipermanent bilayer coatings in capillary electrophoresis prepared using double-chained surfactants.

Abstract: Surfactants such as didodecyldimethylammonium bromide (DDAB) adsorb onto fused-silica capillaries to form semipermanent bilayer coatings. However, such coatings must be regenerated between runs to maintain efficiency and reproducibility. In this paper, chemical and physical factors affecting the stability of DDAB coatings are investigated. Chemical factors such as ionic strength and the nature of the buffer anion (e.g., from acetate to phosphate), which decrease the critical micelle concentration of DDAB, improve the coating stability. Increasing buffer pH also increases the coating stability. Finally, reducing the capillary diameter and reducing the volume of buffer flushed through the capillary enhance the coating stability. Using 50 mM acetate, pH 5.0, in a 25-μm-i.d. capillary, cationic proteins were separated with efficiencies of 1.05 million plates/m and a run-to-run migration time reproducibility of 0.6−0.8% RSD for 10 successive runs without regeneration of the DDAB coating between runs.

Studies on Flue Gas Desulfurization by Chemical Absorption Using an Ethylenediamine−Phosphoric Acid Solution

Abstract: This paper presented a novel flue gas desulfurization (FGD) process. In this method, organic amine was used to absorb sulfur dioxide in flue gas. The vapor−liquid equilibrium model of absorption of sulfur dioxide in the flue gas by an organic amine was established, and the vapor−liquid equilibrium of the sulfur dioxide−ethylenediamine−phosphoric acid−water system was first predicted. For a 0.3 mol·L-1 ethylenediamine buffer solution system, the predicted results fit the experimental results well. It is indicated that the model is preferable to predict vapor−liquid equilibrium under the experimental conditions. Using an ethylenediamine−phosphoric acid aqueous solution as the absorbent, some technology conditions such as the temperature, gas−liquid ratio, pH value, concentration of the desulfurization reagent, and liquid flow rate in absorption and deabsorption were experimentally researched on the ⌀ 30 mm × 600 mm packed tower in the laboratory. The optimized conditions were finally specified after experim...

In-situ observation of nanowire growth from luminescent CdTe nanocrystals in a phosphate buffer solution.

Abstract: One-dimensional (1D) structures of metal and semiconductor materials, often referred to as nanowires, have become a focus of interdisciplinary research in recent years both as a model system for studies of 1D quantum confinement effects and also because of their potential applications in electronics and photonics. A number of direct synthetic methods for the production of nanowires of controlled composition, uniform thickness, and variable aspect ratios has been developed, including the use of hard (alumina membrane) and soft (rodlike micelle) templates, seed-mediated growth in solution, and a catalyst-mediated phase-separation approach. An alternative approach to obtain wires makes use of the assembly of nanoparticles preformed from colloidal suspensions. In a recent paper, Kotov and co-authors showed the feasibility of the spontaneous organization of CdTe nanocrystals (NCs) into crystalline nanowires, during a several-day aging process, which was promoted by the removal of stabilizer ligands through an intermediate methanol washing step. We present here further details about the formation and properties of CdTe nanowires, which were found to grow much faster in a standard physiological phosphate buffered solution. Our results include the in situ observation of the growth process using a confocal microscope. Luminescence and Raman spectroscopy data evidence the occurrence of recrystallization processes during the nanowire formation. CdTe NCs—building blocks for the nanowires—were synthesized in aqueous solution, using thioglycolic acid as stabilizer, following a previously reported approach. Postpreparative size-selective precipitation was applied to the crude solution of NCs to remove the species that had not reacted and separate the strongly emitting fractions of NCs with a narrow size distribution (photoluminescence quantum yield of 20–25%). The selected fractions were dissolved in water, providing stock solutions of CdTe NCs of two different sizes (i.e. , 2.4 nm and 3.5 nm in diameter) with a concentration of 0.05m referred to Te. The CdTe nanowires were obtained by addition of the stock solution of the CdTe NCs to the standard physiological phosphate buffered solution at pH 7.2, followed by incubation at 4 8C in 8-well chambered borosilicate coverslips (Nunc, USA) at ambient conditions for a period of up to 24 h. Incubation at low temperatures was performed to minimize the chances of a possible bacterial contamination, which might be important for potential biomedical applications. However, it was also found that an increase of the incubation temperature to 37 8C did not significantly alter either the dynamics or the pattern of the nanowire formation. As the self-assembled CdTe nanowires retain the luminescence of the NC building blocks, their formation in the chambered coverslips could be followed in situ with a confocal microscope. Different volume ratios of the CdTe NC stock solution and the phosphate buffer were tested, namely, 1:1, 1:5, 1:10, 1:50, 1:100, and 1:1000. Extremely diluted solutions precluded the formation of the nanowires, and highly concentrated solutions did not allow the observation of the wires due to a very strong background luminescence signal. The optimum volume ratio was found to be 1:50, which was used in all further experiments. Figure 1 shows typical confocal images of several nanowires assembled from the red-emitting (3.5-nm size) and green-emitting (2.4-nm size) CdTe NCs. The growth of the nanowires started after 45–60 minutes of incubation; “nucleation patches” emerged (Figure 1a) and continued to grow progressively, with the maximum number and length (up to 70– 80 mm) of observed nanowires being reached after 6–8 h. The nanowires assembled from red-emitting NCs often formed branching structures, bundles, and 3D-resolved networks (Figure 1b–d). Green-emitting NCs, in general, yielded mainly isolated nanowires (Figure 1e), which were less stable in time and more subject to spontaneous aggregation (Figure 1 f). Prolonged incubations (18 h and more) resulted in the formation of dark precipitates, which confirmed the presumed mechanism that the nanowire assembly occurs as a result of a partial destabilization of the CdTe NC ligand shells. At the conditions of our experiments, the destabilization is apparently promoted by the reduction of the electrostatic repulsion of CdTe NCs, due to the electrolytic properties of the phosphate buffer solution. The choice of proper NC concentrations allowed reasonably slow growth rates and, thus, a controllable nanowire formation. Noteworthy, the formation of nanowires was significantly inhibited by the addition of 0.1–3% v/w bovine serum albumin protein, which played the role of an additional capping ligand for the CdTe NCs in solution because of the residual sulfur groups. Once formed in the buffer solution, the nanowires retained their luminescence for at least 10–12 h. This result is in good agreement with our recently reported data on the compatibility of luminescent CdTe NCs with phosphate buffered saline solutions. [a] Dr. A. L. Rogach Department of Physics and CeNS Ludwig-Maximilians-Universit"t M#nchen, 80799 Munich (Germany) Fax: (+49)89-2180-3441 E-mail : andrey.rogach@physik.uni-muenchen.de [b] Dr. N. Gaponik Institute of Physical Chemistry, University of Hamburg 20146 Hamburg (Germany) [c] Dr. Y. P. Rakovich, Prof. J. F. Donegan Physics Department Trinity College Dublin 2 (Ireland) [d] Dr. Y. Volkov, Dr. S. Mitchell, Prof. D. Kelleher Dublin Molecular Medicine Centre and Department of Clinical Medicine Trinity College Dublin 8 (Ireland) Supporting information for this article is available on the WWW under http://www.chemphyschem.org or from the author.

Amino acid analysis using disposable copper nanoparticle plated electrodes

Abstract: A disposable copper nanoparticle-plated screen-printed carbon electrode (designated as Cun-SPE100-nm) provides a new material for the determination of native amino acids. All 20 underivatized amino acids can be sensitively determined at 0.0 V vs. Ag/AgCl in pH 8 phosphate buffer solution. The precisely controlled copper nanoparticles can boost up the CuIIO/CuI2O redox signal on the working surface without any prior pretreatment procedure. The formation of a reversible 1:1 CuIIO–amino acid complex on the Cun-SPE100-nm was proposed to play a key role in the reaction mechanism. Stable detection responses were obtained for all amino acids by flow injection analysis with detection limits (S/N = 3) that lie in the range of 24 nM–2.7 µM. Selected amino acids from six representative chemical natures were separated by HPLC and detected at the Cun-SPE100-nm with promising results.

Dissolution Kinetics of Synthetic Amorphous Silica in Biological-Like Media and Its Theoretical Description

Abstract: Different types of synthetic amorphous silica have been dissolved under biological-like conditions in a buffer system. The buffer solution named TRIS buffer provides a system with comparable pH value, buffer capacity, and osmotic pressure as it can be found in extracellular fluid. Additionally, the phospholipid l-α-dipalmitoylphosphatidylcholine (DPPC) has been used in several dissolution experiments to simulate conditions which are found in extracellular lung fluid. The molybdic acid method (used as standard procedure) and partly ICP−OES have been applied to determine the total amount of silica dissolved. The dissolution of nanodisperse silica shows a strong size effect, which leads to a significant higher silica concentration when compared with the bulk phase. At longer dissolution time a slight decrease of solubility can be observed. The Gibbs free energy of cluster formation is calculated numerically for the dissolution process to predict the temporal development of silica concentration. Theoretical c...

Substrate Binding Favors Enhanced NO Binding to P450cam

Abstract: Ferric cytochrome P450cam from Pseudomonas putida (P450cam) in buffer solution at physiological pH 7.4 reversibly binds NO to yield the nitrosyl complex P450cam(NO). The presence of 1R-camphor affe...

Adsorption of Co2+, Ni2+, Cu2+, and Zn2+ onto amorphous hydrous manganese dioxide from simple (1-1) electrolyte solutions.

Abstract: The adsorption of Co2+, Ni2+, Cu2+, and Zn2+ onto amorphous hydrous manganese dioxide (δ-MnO2) has been studied using two methods, viz., isotherms at constant pH in the presence of buffer solution and pH variation in the absence of buffer solution from a fixed metal ion concentration. While the adsorption isotherm experiments were carried out in 0.5 M NaCl only, pH variation or batch titration experiments were carried out in 0.5 M NaCl, 0.01 M NaCl, and 0.01 M KNO3 solutions. The complex nature of adsorption isotherms at constant pH values indicates that adsorption of all the cations is non-Langmuirian (Freundlich) and takes place on the highly heterogeneous oxide surface with different binding energies. The proton stoichiometry derived from isotherms at two close pH values varies between 0.3 and 0.8. The variation of fractional adsorption with pH indicates that the background electrolyte solution influences the adsorption of cations through either metal-like or ligand-like complexes with Cl−, the former showing a low adsorption tendency. The proton stoichiometry values derived from the Kurbatov-type plot varies not only with the electrolyte solution but also with the adsorbate/adsorbent ratio. The variation of fractional adsorption with pH can be modeled either with the formation of the SOM+ type or with a combination of SOM+ and SOMOH type complexes, depending upon the cation and electrolyte medium. The equilibrium constants obtained from Kurbatov-type plots are found to be most suitable in these model calculations. Adsorption calculated on the basis of ternary surface metal–chlorocomplex formation exhibits very low values.