Showing papers on "Buffer solution published in 1999"

Improved Silica-Guanidiniumthiocyanate DNA Isolation Procedure Based on Selective Binding of Bovine Alpha-Casein to Silica Particles

Abstract: DNA purified from clinical cerebrospinal fluid and urine specimens by a silica-guanidiniumthiocyanate procedure frequently contained an inhibitor(s) of DNA-processing enzymes which may have been introduced by the purification procedure itself. Inhibition could be relieved by the use of a novel lysis buffer containing alpha-casein. When the novel lysis buffer was used, alpha-casein was bound by the silica particles in the first step of the procedure and eluted together with DNA in the last step, after which it exerted its beneficial effects for DNA-processing enzymes. In the present study we have compared the novel lysis buffer with the previously described lysis buffer with respect to double-stranded DNA yield (which was nearly 100%) and the performance of DNA-processing enzymes.

A New Class of Biodegradable Thermosensitive Polymers. 2. Hydrolytic Properties and Salt Effect on the Lower Critical Solution Temperature of Poly(organophosphazenes) with Methoxypoly(ethylene glycol) and Amino Acid Esters as Side Groups

Abstract: The hydrolytic properties of the novel biodegradable thermosensitive poly(organophosphazenes) with methoxypoly(ethylene glycol) (MPEG) and amino acid esters as side groups have been studied by means of gel permeation chromatography and 31P and 1H NMR spectroscopy and by identification of the hydrolysis products. The polymers substituted with α-amino acid esters were hydrolyzed faster than that with β-amino acid ester. The higher content of the amino acid ester in the polymer backbone caused enhanced hydrolysis. The rate of the polymer degradation decreased in the order of methyl > ethyl > benzyl esters. The polymer hydrolysis occurred more rapidly in both acidic and basic buffer solutions than in the neutral solution. The 31P NMR spectra of the polymers with high content of glycine ethyl ester showed that the polyphosphazene backbone underwent fragmentation mostly to small molecules after incubation in the buffer solution of pH 10 for 26 days. Phosphates and ammonia were formed as hydrolysis products in m...

Simultaneous absorption and oxidation of no and so2 by aqueous solutions of sodium chlorite

Abstract: Complete and simultaneous removal of NO and SO2 is achieved in a laboratory bubble column reactor at about room temperature using aqueous solutions of NaClO2 buffered with Na2HPO4and KH2PO4The influence of reaction medium chemistry (pH and concentrations of buffer and NaOH) on NOx and SO2 removal efficiencies was also evaluated. The buffered NaClO2 solution is determined to be more effective in absorbing NOx and SO2 and in controlling chlorine dioxide (ClO2) leakage. The presence of SO2 greatly reduces the scrubbing solution absorption rate for NO as evidenced by shorter breakthrough times, irrespective of the absorbent solution used. The scrubbing solution pH is determined to be very critical in the simultaneous absorption and oxidation of NO and SO2. NO2 control is enhanced significantly as the buffer concentration increases from 0.1 M to 0.5 M, with no NO2 detected in the effluent gas at buffer concentration levels ≥ 0.5 M. Optimal removal efficiencies were observed at the following conditions...

In Vitro Behavior of Silica-Based Xerogels Intended as Controlled Release Carriers

Abstract: We report on the in vitro behavior of room-temperature-prepared xerogels upon immersion in typical physiologic solutions. The effect of various parameters was studied: xerogel composition and particle size; solution composition; and immersion protocol. Three xerogel compositions were tested: a silica xerogel (S100); a Vancomycin–silica xerogel composite (S100V); and a calcium- and phosphorus-containing silica xerogel (S70). The immersion was per-formed integrally (i.e., without solution exchange) or dif-ferentially (i.e., with solution exchange) to model the continuous flow of body fluids past implant surfaces. Four different solutions were used: tris(hydroxymethyl)amino-methane hydrochloric acid buffer solution plus electrolytes (TE); TE supplemented with 3% H2O2; TE supplemented with 10% serum; and serum. Carbonated hydroxyapatite formed on all xerogels. The reaction was faster on S70 than on S100. The silica network fully dissolved for all xerogels in the differential experiment. S70 particles transformed to calcium- and phosphorus-containing “shells” upon differ-ential immersion. The presence of H2 O2 and serum proteins in the immersion solution slowed down the silicon dissolu-tion of both xerogels. Xerogel dissolution was associated with decreased BET surface area and increased mean pore size. The data showed a linear relationship between the dissolution rate and the time-dependent surface area. Re-gardless of this relationship, our data also suggested that the rate-limiting step of the dissolution during integral im-mersion was the diffusion of the dissolved species to the bulk solution.

Electrodeposition of zinc–nickel alloys from ammonia-containing baths

Abstract: This paper describes the use of ammonia-containing baths for Zn–Ni alloy electrodeposition. Buffering properties of the ammonia/ammonium couple limit the local change in pH in the vicinity of the electrode surface caused by simultaneous hydrogen evolution. In addition, it is shown that the divalent zinc and nickel species exist in the form of Zn(NH3)42+ and Ni(NH3)62+ complexes over a large pH range. The electrochemistry of the deposition at pH 10 was investigated by galvanostatic experiments and cyclic voltammetry, and compared with deposition from ammonium chloride baths at pH 5. The Ni content in the alloys were found to be 40–60% higher from the ammonia-containing bath than from the acidic baths. Reduction of divalent ions and hydrogen evolution were shown to occur at potentials 250 mV more cathodic than with baths at pH 5; the deposition mechanism may be affected by complexation of the metal cations by ammonia.

How Polyelectrolyte Adsorption Depends on History: A Combined Fourier Transform Infrared Spectroscopy in Attenuated Total Reflection and Surface Forces Study

Abstract: We present a systematic study of how adsorption history affects the thickness, surface forces, and interfacial rheology of a model cationic polymer. The polymer was quaternized poly-4-vinylpyridine, QPVP (weight-average degree of polymerization nw = 325 and 98% quaternized with ethyl bromide). The main comparisons concerned one-step adsorption from solution at a variable salt concentration up to 0.5 M NaCl, versus two-step adsorption (initial adsorption from buffer solution without added salt, then NaCl added later). The aqueous solutions were buffered at pH = 9.2 such that the surfaces (mica in the case of surfaces forces (SFA) experiments, oxidized silicon in the case of in situ infrared (FTIR-ATR) experiments) in each case carried a large negative charge. The SFA and FTIR-ATR experiments gave consistent estimates of the amount of polymer adsorbed, confirming the expectation that adsorption should be driven by electrostatic attraction to the surface of large opposite charge. The adsorbed amount showed l...

Synthesis, characterization, and enzymatic degradation of network aliphatic copolyesters

Abstract: Network copolyesters were prepared from glycerol (Yg) and sebacic acid (10) with 10–90 mol % of either succinic acid (4), 1,12-dodecanedicarboxylic acid (14), 1,18-octadecanedicarboxylic acid (20), or terephthalic acid (T). Prepolymers prepared by melt-polycondensation were cast from dimethylformamide solution and postpolymerized at 230–250°C for various periods of time to form a network. The resultant films were transparent, flexible, and insoluble in organic solvents. The network copolyesters obtained were characterized by infrared absorption spectra, wide angle X-ray diffraction analysis, density measurement, thermomechanical analysis, differential scanning calorimetry, and tensile test. The enzymatic degradation was estimated by weight loss of the network copolyester films in a buffer solution with Rhizopus delemar lipase at 37°C. The weight loss due to the enzymatic degradation was decreased with increasing comonomer content, and the copolyesters with Yg4, Yg20 and YgT more than 50 mol % were not degraded by lipase enzyme at all. On the contrary, Yg-10/14 films were degraded appreciably over whole range of comonomer composition. With increasing comonomer content, the heat distortion temperature increased gradually, while the tensile strength and Young's modulus were not changed much. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2005–2011, 1999

Fluoride release/uptake of polyacid‐modified resin composites (compomers) in neutral and acidic buffer solutions

Abstract: The aim of the present study was to evaluate the fluoride uptake/release of polyacid-modified resin composites (compomers) in neutral and acidic buffer solutions. Two compomers (Dyract and Compoglass) were tested and the conventional glass-ionomer cement (GIC) Vivaglass Base served as a control. Forty specimens were fabricated from each of the respective materials. Twenty of these specimens were placed in artificial saliva and the other 20 specimens in a fluoridated dentifrice slurry for 5 min. Then, 10 fluoridated and 10 non-fluoridated specimens were immersed in a neutral buffer solution (pH 6.8), and the other specimens were immersed in an acidic solution (pH 4.0). After 1, 2, 3, 4, and 5 days the samples were again placed in either a fluoridated dentifrice slurry or saliva for 5 min, after which time they were transferred to fresh buffer solutions. The fluoride content of the solutions was assessed with a fluoride sensitive electrode. Fluoride release from all the materials decreased continuously during the experiment, with a significantly higher release in the acidic solution compared to the neutral buffer solution. Fluoridation did not result in an increased fluoride release for the compomers. However, the conventional GIC revealed a significantly higher fluoride release after fluoridation. It is concluded that Dyract and Compoglass can not be replenished with fluoride, irrespective of the pH value of the environment.

α-Chymotrypsin superactivity in aqueous solutions of cationic surfactants

Abstract: α-Chymotrypsin (α-CT) activity was tested in aqueous media with the following cetyltrialkylammonium bromide surfactants in the series methyl, ethyl, propyl and butyl, different in the head group size, and for the sake of comparison also with the anionic sodium n -dodecyl sulfate and the zwitterionic myristyldimethylammonium propanesulfonate. N -glutaryl- l -phenylalanine p -nitroanilide hydrolysis rate was monitored at surfactant concentration above the critical micellar one. Only some cationic surfactants gave superactivity and the head group size had a major weight. The highest superactivity was measured in the presence of cetyltributylammonium bromide. The effect of both nature and concentration of three different buffers was also investigated. There is a dependence of enzyme superactivity on buffer type. Michaelis–Menten kinetics were found. The binding constants of substrate with micellar aggregates were determined in the used buffers and the effective improvement of reaction rate (at the same free substrate concentration in the medium) was calculated. k cat significantly increased while K m was little changed after correction to free substrate concentration. The ratio of k cat to K m was between 12 and 35 times higher than in pure buffer, depending on buffer and surfactant concentrations. The increase of α-CT activity (30%) was less important in the presence of 1×10 −2 M tetrabutylammonium bromide, a very hydrophobic salt, unable to micellise. Fluorescence spectra showed differences of enzyme conformation in the presence of various surfactants.

Electrochemical Study of 4-Nitrophenol at a Modified Carbon Paste Electrode

Abstract: A zeolite-modified carbon paste electrode (CPE) has been used for the determination of 4-nitrophenol by differential pulse voltammetry (DPV). The electrochemical reduction of 4-nitrophenol at −1.0 V is carried out in a Britton-Robinson medium at pH 3.5. The cyclic voltammetric (CV) behaviour has been investigated to study the nature of the process. Studies on the effect of pH were carried out over the pH range 2–9 with the Britton-Robinson buffer solution, and the influence of pH on peak height and peak potential was analyzed. A linear relationship between peak intensity and concentration is obtained in the range 0.2–10 mg L−1, with a detection limit of 0.04 mg L−1; a relative standard deviation of 1.5% for a 5 mg L−1 4-nitrophenol concentration and a relative error of 2.6% were also obtained (n=11).

New Tetraazacrown Ethers Containing Two Pyridine, Quinoline, 8-Hydroxyquinoline, or 8-Aminoquinoline Sidearms

Abstract: A series of macrocyclic tetraazacrown ethers containing two pyridine, quinoline, 8-hydroxyquinoline, or 8-aminoquinoline sidearms has been prepared. Crab-like cyclization of bis(alpha-chloroacetamide)s and diamines followed by reduction of the cyclic diamides was used to synthesize the selected crown ethers containing two unsubstituted macroring nitrogen atoms. The preparation of the macrocycles with sidearms was accomplished by reductive amination of the proper aldehydes with the crown ethers using sodium triacetoxyborohydride (NaBH(OAc)(3)) as the reducing agent. The 8-hydroxyquinoline- and 8-aminoquinoline-containing macrocycles were synthesized by reductive amination of 8-acetoxyquinoline-2-carboxaldehyde or 8-nitroquinoline-2-carboxaldehyde followed by removing the acetate groups or reducing the nitro groups to amino groups, respectively. Complexation of ligand 22 with Cu(2+), Co(2+), Ni(2+), Zn(2+), Cd(2+), and Pb(2+) was evaluated potentiometrically in aqueous solution (0.10 M Me(4)NCl) at 25 degrees C. Ligand 22 formed very stable complexes with these metal ions. The UV-vis spectra of 22 and its complexes were examined in an aqueous acetic acid buffer solution (pH 5). The 22-Cu(2+) complex provided a new absorption band at 258 nm.

Packing and stationary phase design for capillary electroendosmotic chromatography (CEC)

Abstract: Reversed-phase stationary phases based on porous silica beads in the range 0.2–3 μm have been prepared to study the dependency of electroosmotic flow (EOF) on particle diameter. Additionally, the influence of the mobile phase composition, i.e. organic modifier content, pH of buffer solution and concentration of buffer salt, on the magnitude of the electroosmotic flow velocity has been investigated. To perform separations in an aqueous acidic mobile-phase, mixed mode stationary phases containing both alkyl chains and strong cationexchange groups have been applied.

Bisphosphonate prodrugs: synthesis and in vitro evaluation of novel clodronic acid dianhydrides as bioreversible prodrugs of clodronate.

Abstract: P,P‘-Diacetyl, P,P‘-dibutyroyl, P,P‘-dipivaloyl, and P,P‘-dibenzoyl (dichloromethylene)bisphosphonic acid dianhydride disodium salts (2a−d) were synthesized and evaluated as novel bioreversible prodrugs of clodronate. The anhydrides were prepared by reacting anhydrous tetrasodium clodronate with a large excess of the corresponding acid anhydride. The dianhydrides 2a−d alone were more lipophilic than the parent clodronate, as determined by drug partitioning between 1-octanol and phosphate buffer at pH 7.4. They also were stable toward chemical hydrolysis in aqueous solutions (pH 7.4 and 2.0). The half-lives for chemical degradation in a buffer solution at 37 °C varied from 0.7 to 286 h and from 15 to 790 h at pH 2.0 and 7.4, respectively. The dianhydrides 2a,b,d underwent complete enzymatic hydrolysis to clodronate in 80% serum at 37 °C after 1 min, although 2c had a half-life of 3.3 h. The aqueous solubility of clodronate decreased considerably in the presence of Ca2+ ions. This is most probably due to fo...

Capillary electrophoresis chiral separation of basic pharmaceutical enantiomers with different charges using sulfated ?-cyclodextrin

Abstract: A negatively charged cyclodextrin, sulfated β-cyclodextrin [β-CD-(SO4−)4], was used as a chiral selector for capillary electrophoresis separations of basic pharmaceutical enantiomers. The charges of the basic enantiomers were controlled by adjusting the buffer pH. At pH 2.5, basic compounds are positively charged and interact stronger with the negatively charged CD than with neutral CDs, owing to the extra electrostatic interaction. This additional interaction is very useful for chiral separations of the enantiomers that interact weakly with the neutral CDs. For example, chiral separations of acebutolol, metanephrine, normetanephrine, nafronyl, labetalol, and nadolol were achieved at this pH. For labetalol and nadolol that have two chiral centers, three of the four isomers were separated. The capillary surface was dynamically coated with poly(vinyl alcohol) (PVA) to reduce the possible interactions between solutes and the capillary wall, to improve efficiency and reduce the electroosmotic flow (EOF) for enhancing resolution. PVA reduced the interactions between the analytes and the chiral selector; nevertheless, peak tailing was observed owing to the electrodispersion for the compounds that interact too strongly with the anionic CD. At pH 11.6, most of the basic test compounds (except those having phenol groups) are neutral and have weaker interactions with the negatively charged CD. The separation efficiency increased dramatically for all analytes at higher pH owing to the absence of electrodispersion. The existence of the neutral PVA polymer in the buffer solution increased the solubility of the neutral hydrophobic amines and reduced the solute–CD complexation. Chiral separations of a large number of compounds were achieved at a single concentration of the charged cyclodextrin. ©1999 John Wiley & Sons, Inc. J Micro Sep 11: 11–21, 1999