Showing papers on "Buffer solution published in 2006"

Systems and methods for manufacturing liposomes

Abstract: The present invention provides apparatus and processes for producing liposomes. By providing a buffer solution in a first reservoir, and a lipid solution in a second reservoir, continuously diluting the lipid solution with the buffer solution in a mixing chamber produces a liposome. A therapeutic agent, such as a nucleic acid, is included in one of the buffer solution or the lipid solution. Upon mixing a liposome encapsulating the therapeutic product is substantially instantaneously formed. Thereafter the liposome solution formed is immediately diluted with buffer solution to enhance homogeneity and maintain small particle size.

Voltammetric Determination of Folic Acid with a Multi-Walled Carbon Nanotube-Modified Gold Electrode

Abstract: The voltammetric behavior of folic acid (FA) at a multi-walled carbon nanotube (MWNT) modified gold electrode has been investigated by cyclic voltammetry, chronoamperometry and chronocoulome- try. The modified electrode exhibits a good promoting effect on the electrochemical reaction of FA. FA can generate a well-defined anodic peak at around 0.83 V (vs. SCE) in 0.1 M H3PO4-NaH2PO4 buffer solution of pH 2.5. The peak results from a 2-electron transfer of FA, and the standard potential of FA is estimated to be 0.79 V (vs. SCE). The parameters affecting the re- sponse of FA, such as solution pH, accumulation time, accumulation potential, and amount of MWNTs are optimized for the determination of FA. Under the opti- mum conditions, the peak current changes linearly with FA concentration in the range from 2.0� 10 � 8 Mt o 1.0� 10 � 6 M. This method has been applied to the determination of FA in drug tablets, and the recovery is 93.9-96.9%. In addition, the influence of some co- existent species is examined. When a Nafion layer is introduced on the gold electrode before deposition of MWNTs, the resulting composite electrode can give better response to FA. At the same time, the interference by some foreign species is suppressed to some extent.

Application of a Single-Wall Carbon Nano-Tube Film Electrode to the Determination of Trace Amounts of Folic Acid

Abstract: Single-wall carbon nano-tubes were used to modify the surface of a glassy carbon electrode (GC) and applied in the determination of folic acid with voltammetry. The experiments demonstrated that the presence of a carbon nano-tube film on the electrode greatly increased the reduction peak current of folic acid. Cyclic voltammetry (CV) and linear sweep voltammetry (LSV) were used in a comparative investigation of the electrochemical reduction of folic acid with the film electrode. Effects of pH on the peak current and the peak potential were studied in the pH range of 4.0–8.0 with Britton-Robinson buffer solution. The reduction peak current was found to be linearly related to folic acid concentration over the range of 1 × 10−8 to 1 × 10−4 mol L−1 with a detection limit of 1 × 10−9 mol L−1 after 5 min accumulation. The film electrode provides an efficient way for eliminating interferences from some inorganic and organic species in the solution. The high sensitivity, selectivity and stability of the film electrode demonstrate its practical application from a simple and rapid determination of folic acid in tablets.

Effects of pH, temperature, and aqueous organic material on the dissolution kinetics of meta-autunite minerals, (Na, Ca)2-1[(UO2)(PO4)]2.3H2O

Abstract: Autunite minerals have been frequently identified in contaminated sediments as the long-term controlling phase of uranium. Under these conditions the mobility of uranium in subsurface pore waters is limited by the rate of dissolution of autunite and meta-autunite group minerals, [(UO2)(PO4)]2 ? xH2O. Single-pass flow-through (SPFT) tests were conducted to quantify the dissolution kinetics of natural calcium meta-autunite, Ca[(UO2)2(PO4)2]2 ? 3H2O, and synthetic sodium meta-autunite, Na2[(UO2)(PO4)]2 ? 3H2O, as a function of pH (7 -10) and temperature (5 ? 70 C) in the presence and absence of aqueous organic material. The data indicate that release of uranium and phosphorus are non-stoichiometric over the range of experimental conditions investigated. In a 0.1 M NH4OH buffer solution, acquisition of valid dissolution rate data was limited by uramphite solubility, NH4[(UO2)(PO4)]2 ? xH2O. Dissolution rates obtained in a 0.01 M TRIS [tris (hydroxymethyl) aminomethane] buffered solution increased by a factor of {approx}100X over the pH interval of 7 to 10 (? = 0.90?0.08), irrespective of temperature. At constant pH the rate data showed a minor increase with temperature. Data from experiments using a more concentrated 0.05 M TRIS buffer exhibited a {approx}35-fold increase in rates compared to those in a 0.01 M TRIS buffermore » at constant temperature and pH. The difference in rate between interlayer cation (Na+ or Ca2+) and uranium release is {approx}10,000 in neutral solutions; however, the difference diminishes to {approx}10 at higher pH values. The combination of structural dissolution and ion exchange explain these trends in interlayer cation behavior. Data presented here illustrate the significance of pH and dissolved organic material on the dissolution of autunite minerals.« less

Enrichment of phosphorylated proteins from cell lysate using a novel phosphate-affinity chromatography at physiological pH.

Abstract: While phosphoproteins have attracted great interest toward the post-genome research (e.g. clinical diagnosis and drug design), there have been few procedures for the specific enrichment of native phosphoproteins from cells or tissues. Here, we describe a simple and efficient protocol to enrich phosphoproteins comprehensively from a complex mixture containing solubilized cellular proteins. This method is based on immobilized metal affinity chromatography using a phosphate-binding tag molecule (i.e. a dinuclear zinc(II) complex) attached on a highly cross-linked agarose. The binding, washing, and elution processes were all conducted without a detergent or a reducing agent at pH 7.5 and room temperature. An additive, 1.0 M CH3COONa, was necessary in the binding and washing buffers (0.10 M Tris-CH3COOH, pH 7.5) to prevent the nonphosphorylated protein from binding. The absorbed phosphoproteins were eluted using a mixed buffer solution (pH 7.5) consisting of 0.10 M Tris-CH3COOH, 10 mM NaH2PO4-NaOH, and 1.0 M NaCl. In this study, we demonstrate a typical example of phosphate-affinity chromatography using an epidermal growth factor-stimulated A431 cell lysate. The total time for the column chromatography (1 mL gel scale) was less than 1 h. The strong enrichment of the phosphoproteins into the elution fraction was evaluated using SDS-PAGE followed by Western blotting analysis.

Conductivity of single-stranded and double-stranded deoxyribose nucleic acid under ambient conditions: The dominance of water

Abstract: We investigate the conductivity of single-stranded and double-stranded herring deoxyribose nucleic acid (DNA) in buffer solution spotted and dried on Au nanocontacts. We find an exponential increase of the conductivity with increasing humidity that is identical for single- and double-stranded DNA within the measurement accuracy. While the small conductivity of dry DNA is comparable to that of a large band-gap semiconductor, we attribute the increase at high humidity levels to water molecules accumulated at the phosphate backbone. For high humidities we observe s-shaped current-voltage characteristics that can be well explained by the dissociation of water attached to the DNA molecules.

Nanostructured electrochemical DNA biosensors for detection of the effect of berberine on DNA from cancer cells

Abstract: Multi walled carbon nanotubes (MWNT) in dimethylformamide (DMF) or aqueous sodium dodecyl sulfate (SDS) solution, colloidal gold nanoparticles (GNP) in phosphate buffer solution (PBS), and a GNP-MWNT mixture in aqueous SDS solution have been investigated for chemical modification of a screen-printed carbon electrode used as the signal transducer of a dsDNA-based biosensor. Differential pulse voltammetry of the DNA redox marker Co[(phen)3]3+ and the guanine moiety anodic oxidation and cyclic voltammetry with K3[Fe(CN)6] as indicator revealed substantial enhancement of the response of the biosensor, particularly when MWNT in SDS solution was used. The biosensor was used in testing of berberine, an isoquinoline plant alkaloid with significant antimicrobial and anticancer activity. Berberine had a very strong, concentration-dependent, effect on the structural stability of DNA from the human cancer cells (U937 cells) whereas non-cancer cells were changed only when berberine concentrations were relatively high 75 and 50 microg mL(-1).

A wide pH range optical sensing system based on a sol–gel encapsulated amino-functionalised corrole

Abstract: The synthesis of a new compound, 10-(4-aminophenyl)-5,15-dimesitylcorrole, and its application for the preparation of optical chemical pH sensors is described. The dye materials were immobilized in a sol–gel glass matrix and characterised upon exposure to aqueous buffer solutions. The response of the sensor is based on the fluorescence intensity changing of corrole owing to multiple steps of protonation and deprotonation. Due to its containing several proton sensitive centers, the 10-(4-aminophenyl)-5,15-dimesitylcorrole based optode shows a wider response range toward pH than that of tetraphenylporphyrin (TPPH2) and 5,10,15-tris(pentafluorophenyl)corrole (H3(tpfc)). It shows a linear pH response in the range of 2.17–10.30. The effect of the composition of the sensor membrane has been studied and the experimental conditions were optimized. The optode showed good reproducibility and reversibility, and common co-existing inorganic ions did not show obvious interference to its pH measurement.

The effect of ionic strength on the electron-transfer rate of surface immobilized cytochrome C.

Abstract: Horse heart cytochrome c was immobilized on four different self-assembled monolayer (SAM) films. The electron tunneling kinetics were studied in the different assemblies as a function of the ionic strength of the buffer solution using cyclic voltammetry. When cytochrome c is electrostatically immobilized, the standard electron exchange rate constant k° decreases with the increase of the solution's ionic strength. In contrast, the protein covalently attached or ligated has a rate constant independent of the ionic strength. The inhomogeneity of electrostatically immobilized cytochrome c increases with the increase of the solution's ionic strength whereas that of the covalently attached protein is independent of the ionic strength. A comparison of these different electron-transfer behaviors suggests that the thermodynamically stable geometry of cytochrome c in the electrostatic assemblies is also an electron transfer favorable one. It suggests that the surface charges of cytochrome c are capable of guiding it into geometries in which its front surface faces the electron-transfer partner. The inhomogeneity observed in this study indicates that a distribution of cytochrome c orientations and thus a distribution of electron transfer rate constants exists.