Neutral pH Region Research Articles

Dependence of the fluorescence of immobilized 1-hydroxypyrene-3,6,8-trisulfonate on solution pH: Extension of the range of applicability of a pH fluorosensor

1-Hydroxy-3,6,8-pyrenetrisulfonate (HPTS), covalently immobilized on cellulose attached to a plastic strip, has been used as a fluorescent optical pH sensor for the neutral pH region. At near neutral pH, HPTS fluoresces green, i.e., from its conjugate base form, exclusively and independent of whether it was excited in its conjugate base form or acidic (phenol) form, or both. However, the fluorescence of immobilized HPTS also varies in the low pH region from about pH 3 to below pH 1, in that not only the green emission almost completely disappears, but also a second (blue) band appears which can be attributed to the fluorescence of the conjugate acid (the phenol). The proton transfer in the lowest excited singlet state which accounts for the variation of the fluorescence in the low pH region is here evaluated kinetically. The application of this sensor to measure pH over a wide range of pH values is suggested.

A stable reddish purple anthocyanin in the leaf ofGynura aurantiaca cv. ‘Purple Passion’

The anthocyanin (GAA) in the epidermis and hair of the leaf ofGynura aurantiaca cv. ‘Purple Passion’ was isolated and identified as cyanidin tetra-glucoside acylated by three molecules of caffeic acid and one molecule of malonic acid. GAA was also isolated from the lower epidermis of the leaf ofG. bicolor DC. GAA showed a very stable reddish purple color from weakly acid to neutral pH region, but the color of the deacylated compound disappeared rapidly in the same region. This indicated that the attached organic acids must play an essential role in the stabilization of the color.

PH-Sensitive liposomes composed of tocopherol hemisuccinate and of phosphatidylethanolamine including tocopherol hemisuccinate

The ionic single-chain amphiphile tocopherol hemisuccinate (THS) is water-insoluble but on addition of NaOH, forms vesicles which give an aqueous suspension that is pale-colored and milky. Observation of the permeability of the 5(6)-carboxyfluorescein-entrapped THS vesicle membranes indicated them to be pH-sensitive liposomes which are stable in the neutral pH region but become leaky at acidic pH. 1-Palmitoyl-2-oleoyl-phosphatidylethanolamine (POPE) itself is difficult to form stable liposomes near neutral pH in isotonic buffer but when mixed with THS, gives stable liposomes near physiological pH. These liposomes were found to have a pH-sensitivity that depended on the lipid composition. They were unstable in the presence of rat serum but significantly increased their stability when cholesterol was incorporated ( THS/ POPE/ Chol = 2:8:8). This paper discusses why the ionic single-chain amphiphile THS can form liposome-like vesicles by itself like phosphatidylcholine, which has the diacyl chain.

Functional metallomacrocycles and their polymers, 26. Synthesis of 2‐acryloylamino‐9,16,23‐tri‐tert‐butylphthalocyanine and autoxidation of thiol with water‐soluble polymers containing cobalt(II) phthalocyaninate complex

AbstractThe catalytic autoxidation of 2‐mercaptoethanol was studied by using new water‐soluble polymers containing a cobalt(II) phthalocyaninate complex as a catalyst. The phthalocyanine vinyl‐monomer, 2‐acryloylamino‐9,16,23‐tri‐tert‐butylphthalocyanine (APc(t‐Bu)3), was synthesized and copolymerized with three kinds of water‐soluble monomers to result in a favorite electrostatic environment as a catalyst. The resulting cationic polymer containing a cobalt(II) phthalocyaninate complex has high activity as a catalyst for autoxidation of 2‐mercaptoethanol independent of pH. The catalystic system obeys Michaelis‐Menten kinetics with respect to substrate concentration. The rate constant k5 of the rate‐controlling step and the apparent Michaelis constant K were obtained from a Lineweaver‐Burk plot. The cationic environment on the polymeric catalyst enhances enzyme‐like activity in the neutral pH region for autoxidation of 2‐mercaptoethanol, because of the promotion of substrate dissociation and the accumulation of thiolate anions.

好アルカリ性バチルス属細菌が生産する耐熱性アルカリキシラーゼ

Land plants are mainly composed of cellulose, hemicellulose and lignin. Xylans are major components of hemicellulosic polysaccharides, and one of the most abundant biopolymers. The main chain of xylans from all land plants is based on a β-1, 4-D-xylopyranosyl linkage. This main chain is substituted with a variable number of neutral or uronic monosaccharide, short oligosaccharide side chains, or non-saccharide substituents. Most of xylans are consequently heteropolysaccharides containing L-arabinofuranose, D-galactopyranose and D-glucuronopyranose. Lignin is one of the non-saccharide substituents. Structure of xylans varies in the nature and degree of branching of the main chain.So-called xylanases hydrolyze the β-1, 4-linked xylopyranosyl main chain of land plant xylans to produce xylose or xylooligosaccharides. Xylanases can hydrolyze not only soluble xylans but also insoluble ones bound to cellulose. Therefore, xylanases can break down xylans remaining in pulp. A part of lignin can be consequently removed from the pulp by treatment with xylanases. This “bio-bleaching” process would possibly decrease the amount of chlorine used for pulp bleaching. Toxic or carcinogenic chlorinated compounds have been produced from wood components with the chlorine and thrown into environments.Xylanases have been isolated from various bacteria and fungi. Most of microbial xylanases show the enzymic activities at acidic or neutral pH regions. We have investigated alkaliphilic microorganisms, that are one of extremophiles, and their enzymes.Several xylanases have been isolated from alkaliphiles during a course of the investigation. Some of them are alkaline-active and thermostable. These alkaline xylanases might be suitable for the bio-bleaching process, because the pulp is generally processed at a high alkaline pH and high temperature condition. This article reviews the β-1, 4-xylanases produced by alkaliphiles that have been isolated.

The albite-water system: Part I. The kinetics of dissolution as a function of pH at 100, 200 and 300°C

Albite feldspar was hydrolyzed at 100, 200, and 300°C in solutions at pH values ranging from 1.4 to 10.3. The dissolution experiments were carried out in a single-pass tubular flow system. Rates were determined both by the mass loss of the sample and from the reactor output concentration of released Si. All of the measured rates represent limiting rates since the experiments were run at conditions far from equilibrium with respect to albite saturation. The only secondary phase to form was boehmite, precipitation of which mostly occurred under acid conditions. The dissolution rate curves displayed a U-shaped relationship with pH, as evidenced by a decrease in the rates with increasing pH in the acid region, a neutral pH region marked by no pH dependence and a basic pH region where the rates increased with increasing pH. For any given temperature, the absolute values of the slopes ( n) of the log rate vs. pH curves were approximately equal in the acid and basic pH regions. The absolute values of n increased from 0.2 to 0.6 in both the acid and basic pH regions as the temperature increased from 100 to 300°C. The calculated energies of activation were 89, 69, and 85 kJ/mol in the acid, neutral and basic pH regions, respectively. These values reflect the greater dependence of the rates on temperature in the acid and basic pH ranges in comparison to the neutral pH range. The results from this study have been compared to a few published studies in the literature concerning the hydrolysis of albite and other feldspars at 100°C and higher temperatures. A comparison of the rates revealed that the differences in rates are potentially dependent on the design of the experiments. Even after taking into account experimental uncertainties, it appears that static hydrolysis experiments almost always produce measured rates that are lower than those obtained in flow systems. This may be explained by the precipitation of secondary phases and/or chemical affinity considerations.

Synthesis and properties of new cationic-periphery porphyrins, tetrakis(p-(aminomethyl)phenyl)porphyrin and N-methyltetrakis(p-(aminomethyl)phenyl)porphyrin

Two new cationic periphery porphyrins, tetrakis(p-(aminomethyl)phenyl)porphyrin, TAMPP, and N-methyltetrakis(p-(aminomethyl)phenyl)porphyrin, N-MTAMPP, have been synthesized. These porphyrins are protonated in a pH range suitable for studies of binding with nucleic acids. The structure of the N-methylated analogue is significantly different, resulting in a phenonmenon that has not been previously reported: the aryl rings at the methine bridge positions of the porphyrin ring undergo restricted rotational motion. The ability of the aryl rings to rotate may be crucial to allow intercalation of cationic periphery porphyrins. The acidity constants and associated pK a 's for the porphyrins TAMPP and N-MTAMPP were determined by a combination of spectrophotometric and potentiometric methods. The acid-base properties of these new porphyrins are profoundly altered by N-methylation. As a result, the N-methylated species bears an additional positive charge in the neutral pH region where binding studies with nucleic acids are normally carried out. The peripheral aminogroups of the N-methylated porphyrin are more basic as well, by 1.5 pH units at an ionic strength of 0.12 M

Electrostatic effect of chelation with metal ions on streaming potentials in chelating resins containing formazan derivatives

Electrostatic phenomena in chelating resins containing formazan derivatives were studied by measuring streaming potentials. It was found that the adsorption of metal ions can be related to the chelation due to proton replacement in the low pH region whereas it will be changed to adsorption due to electronegativity in the neutral pH region. The electrostatic potentials in the resin phase vary with metal chelation of the formazan groups. Metal chelation lowers the electrostatic energy, enhancing the stability of the resins.

合成高分子表面へのタンパク質の吸着

In this article I have reviewed (blood) proteins adsorption onto synthetic polymer surfaces, i. e., onto polymeric microspheres. First, the surface characteristics of polymeric microspheres (polymer latices) were examined. As a result, hydrogel polymer layers, e. g., poly (acrylamide) (poly-AAm) and poly (2-hydroxyethyl methacrylate) (poly-HEMA) layers were found to exist on the microsphere surfaces of styrene (St) /AAm and St/HEMA copolymers (P (St/AAm) and P (St/HEMA)), respectively. Subsequently, singular and competitive protein adsorption onto polymeric microspheres was investigated as a function of pH and ionic strength, surface characteristics of microspheres, coexistent electrolyte ions. Each protein showed the maximum adsorption near its isoelectric point. The amounts adsorbed onto hydrophilic P (St/AAm) and P (St/HEMA) microspheres were much smaller than that onto hydrophobic polystyrene (PS) microsphere, particularly in the neutral and alkaline pH regions. Fibrinogen adsorbed preferentially from the protein mixture of albumin, γ-globulin, and fibrinogen. Further, the adsorbability of heat-denatured albumin was studied. Compared with the native component of the protein, the denatured components adsorbed preferentially onto microspheres.

Temperature- and pH-dependent changes in the coordination sphere of the heme c group in the model peroxidase N alpha-acetyl microperoxidase-8.

The pH- and temperature-dependent changes in the coordination sphere of the heme c group of N alpha-acetyl microperoxidase-8 (Ac-MP-8) have been studied by examining its optical, resonance Raman, electron paramagnetic resonance, and magnetic circular dichroism spectra. An optical titration indicates that Ac-MP-8 exists in three major ionization forms over the pH 1-12 range that are linked by pK alpha values of approximately 3 and 9. The acid form that is present at pH 1.5 exists as a mixture of five- and six-coordinate high-spin species and most likely has water or buffer ions as axial ligand(s). On titration to pH 7, the His18 residue is deprotonated and becomes the proximal ligand to the iron to give a six-coordinate neutral form that has water as the sixth ligand. This form exists in a thermal high-spin intermediate-spin state equilibrium. On raising the pH to 10, an alkaline form is generated which is predominantly a five-coordinate high-spin species. It is formed by ionization of the proximal His18 residue to its imidazolate form with concomitant dissociation of the water ligand at the sixth site. At concentrations of Ac-MP-8 greater than 10 microM, some six-coordinate low-spin species are formed that are attributed to a dimer in which a His18 residue from a second molecule of Ac-MP-8 coordinates to the sixth site of another to give a bis-His complex. Raising the pH to 11.5 does not produce an appreciable amount of the six-coordinate complex with hydroxide as the sixth ligand. These studies show that Ac-MP-8 is a good water-soluble model for the peroxidases that exhibits minimal aggregation at concentrations below 10 microM in the neutral and alkaline pH regions.

Polarographic behavior of Cd 2+ and Zn 2+—PGA complexes. Polarographic and circular dichroism spectroscopic studies on the Cd 2+ and/or Zn 2+—poly(α-L-glutamic acid) complex in aqueous solution

The helix-coil transition of poly(α-L-glutamic acid) (PGA) induced by Cd 2+ and/or Zn 2+ was investigated by direct current (d.c.) polarography and circular dichroism (CD) spectroscopy as a function of pH and the mixing ratio of glutamic acid residue to Cd 2+ and/or Zn 2+. The diffusion current for Cd 2+ or Zn 2+ declined sharply in the pH range of c. 4–7 due to the formation of the metal ion-PGA helical complex. The helix contents of PGA, estimated by the decrease in polarographic current, are in good agreement with results obtained by circular dichroism in the neutral pH region. The degree of helicity induced by either of these two ions can also be determined independently by polarography. The size of the complex was calculated by the Ilkovič equation and depends strongly on the mixing ratio of glutamic acid to cation. In the neutral pH region, the relationship between the half-wave potentials and the concentration of PGA indicates that two peptide residues coordinate approximately to one Cd 2+.

Enzymatic Properties of Two Calcium-stimulated ATPases in the Neutral and Acidic pH Regions Found in the Membrane Fraction of Human Milk.

Two calcium-stimulated ATPases at optimal pH values of 5.0 and 7.0, which are designated as acid and neutral Ca(2+) -ATPase, respectively, were found in the membrane fraction of human milk, and their enzymatic properties were studied. For maximal activity, neutral Ca(2+)-ATPase required 0.45 mM Ca ion, while acid Ca(2+) -ATPase required 207 mM Ca ion. Neutral Ca(2+) -ATPase activity was not enhanced by adding the Mg ion at more than 0.1 mM. Among the nucleotides, neutral Ca(2+) -ATPase showed a higher substrate specificity to GTP, CTP, ITP, and UTP than to ATP, while ATP was the best substrate for acid Ca(2+) -ATPase. Neutral and acid Ca(2+) -ATPases had apparent Km values of 0.361 and 0.192 mM, and Vmax of 186 and 178 μmol ATP hydrolyzed/mg of protein per min, respectively. Both Ca(2+) -ATPases were potently inhibited by fluoride, lanthanide, vanadate, and p-chloromercuribenzoate, and inactivated by EDTA, EGTA, and CDTA, but were unaffected by N-ethylmaleimide, NaN3, ouabain, oxidized glutathione, or oligomycin, and were inactivated by heating at 60°C for 10 min. These enzymes were concentrated in the membrane fraction of the cream and skim milk membrane.

Isoxazoles. VII: Hydrolysis of 4-Methyl- 5-isoxazolylnaphthoquinone Derivatives in Aqueous Solutions

The kinetics for the degradation of 2-(4-methyl-5- isoxazolylamine)-A/-(4-methyl-5-isoxazolyl)-1,4-naphthoquinone-4- imine (1) in solution were investigated at 70 °C and at a constant ionic strength of 0.5 over a pH range of 1.75 to 12.85. The degradation rates were determined by absorption and second-derivative UV spectrometry. Two degradation products were identified in acidic and neutral pHs; they are 4-/V-(4-methyl-5-isoxazolyl)-1,2-naphthoquinone (2) and 2-methyl- cyanoacetamide (5), respectively. In alkaline pH, two degradation products, 2-hydroxy-A/-(4-methyl-5-isoxazolyl)-1,4-naphthoquinone-4- imine (3) and 5-amino-4-methylisoxazole (4), were isolated. The pathway for degradation of 1 in acidic and neutral pH followed consecutive first-order kinetics since 2 undergoes hydrolysis giving 2-hydroxy-1,4- naphthoquinone (6) ano 2-methylcyanoacetamide (5). No appreciable buffer effect on the degradation of 1 and 2 was observed for any of the buffer species in this study. The pH-rate profiles exhibited specific acid and specific basic catalysis for 1 and specific acio catalysis for 2. The maximum stability for 1 and 2 occurred in the neutral pH region.

O-Carboxymethyl-O-ethyl-β-cyclodextrinによる1-Hexylcarbamoyl-5-fluorouracil (HCFU) の安定性及びバイオアベイラビリティの向上

The possible utility of O-carboxymethyl-O-ethyl-beta-cyclodextrin (CME-beta-CyD) as a novel drug carrier was studied in vitro and in vivo, by using 1-hexylcarbamoyl-5-fluorouracil (HCFU) as a model drug. The chemical instability of HCFU in solution and solid state was improved by CME-beta-CyD complexation. The in vitro release of HCFU from the CME-beta-CyD complex was decelerated in acidic solution, while accelerated at neutral pH regions, showing a typical delayed-release pattern. This pattern was clearly reflected in the blood levels after the oral administration of the complex to dogs, increasing the bioavailability. The present results suggested that CME-beta-CyD is useful as a delayed-release-type carrier for the oral administration of chemically labile HCFU.

NMR and crystallographic studies of a p-sulfonatocalix[4]arene-guest complex

The {sup 1}H and {sup 13}C NMR spectra of a complex formed from tetrasodium p-sulfonatocalix(4)arene (1{sub 4}) and trimethylanilinium chloride (2) in D{sub 2}O showed that 2 is bound to the cavity of cone-shaped 1{sub 4}: in the acidic pH region (pD 0.4) the phenyl moiety resides in the cavity, whereas in the neutral pH region (pD 7.3) both the trimethylammonium and the phenyl moiety are included nonspecifically in the cavity. The difference was accounted for by the change in the electron density in the benzene {pi}-systems induced by the dissociation of OH groups. The complex was crystallized from acidic aqueous solution. The solid-state {sup 13}C NMR (CP-MAS) supports the inclusion of the phenyl moiety in the cavity. The X-ray crystallographic studies established that (1) 1{sub 4} adopts a cone conformation, (2) 1{sub 4} and 2 form a host-guest-type complex with the phenyl moiety inserted into the cavity, (3) not only the hydrophobic force but also the electrostatic force operates for guest inclusion, and (4) the overall structure is similar to that of clays, 1{sub 4} molecules being arranged into bilayers. These findings serve as a useful cross-link between solution complexes and solid-state complexes.

Characterization of the hydrogen peroxide - enzyme reaction for two cytochrome c peroxidase mutants

The bimolecular reaction between Escherichia coli-produced cytochrome- c peroxidase (CcP(MI)) and hydrogen peroxide is identical to that of native yeast cytochrome- c peroxidase (CcP) and hydrogen peroxide in the neutral pH region. Both enzymes have pH-independent bimolecular rate constants of 46 μM −1 · s −1 for the reaction with hydrogen peroxide. A second mutant enzyme, E. coli-produced cytochrome- c peroxidase mutant with phenylalanine at position 191 (CcP(MI, F191)), has a pH-independent bimolecular rate constant for the hydrogen peroxide reaction of 65 μM −1 · s −1, 40% larger than for CcP or CcP(MI). The initial peroxide-oxidation product of CcP(MI, F191) is an oxyferryl porphyrin π-cation radical intermediate in contrast to the oxyferryl amino-acid radical intermediate formed upon oxidation of CcP or CcP(MI) with hydrogen peroxide. The reactions of all three enzymes with hydrogen peroxide are pH-dependent in KNO 3-containing buffers. The reactions are influenced by an ionizable group, which has an apparent p K a of 5.4 in all three enzymes. The enzymes react with hydrogen peroxide when the ionizable group is unprotonated. Both CcP(MI) and CcP(MI, F191) have slightly smaller pH stability regions compared to CcP as assessed by the hydrogen peroxide titer and spectral analysis. The alteration in structural stability must be attributed to differences in the primary sequence between CcP and CcP(MI) which occur at positions −2, −1, 53 and 152.

Synthesis of thiomorpholino buffers for isoelectric focusing in immobilized pH gradients

The two commercially available Immobilines having a pK of 6.2 (2-morpholino ethyl acrylamide) and 7.0 (3-morpholinopropylacrylamide) have been modified and two new buffers have been synthesized: 2-thiomorpholinoethylacrylamide, pK 6.6, and 3-thiomorpholinopropyl acrylamide, pK 7.4. The replacement of an oxygen with a sulfur atom in the morpholino ring is thus seen to shift the pK values of these two bases by +0.4 pH units. In formulations in which the two new bases replaced the standard morpholino derivatives, identical pH profiles and protein patterns were obtained. The reason for this work was to try to close the gap between the pK 7.0 and 8.5 species and to provide the users of immobilized pH gradients with more buffers in the neutral pH region. The two new thiomorpholino derivatives are an important step in this direction.

The effect of organic acids on the dissolution of K-feldspar under conditions relevant to burial diagenesis

AbstractThe mechanism by which secondary porosity in sandstone reservoirs is produced is poorly understood. Previous hypotheses to account for the increased dissolution of framework silicates have invoked the introduction of acidic and/or organic-rich fluids capable of complexing metals. In order to evaluate the relative effects of these factors, the rates of K-feldspar dissolution have been measured at 70°C and 95°C, at pH values of 1, 4, and 9, with and without oxalic acid, at a total pressure of 50 MPa, using direct sampling autoclaves. The presence of oxalic acid increased the dissolution rate of Kfeldspar at pH 4 and 9, but decreased the rate at pH 1 at both temperatures. The maximum increase in dissolution rate was observed at pH 4, 95°C by a factor ∼4. In oxalic-free experiments, the rate of dissolution increased an order of magnitude with each unit decrease in pH in the pH regime 1–4. In the presence of oxalic acid, this dependency of dissolution upon pH decreased to approximately an order of magnitude increase with each decrease in pH by 2pH units. The dissolution process was observed to be stoichiometric under all conditions, indicating that the mechanism by which rates are increased was not due to preferential complexation of aluminium, but rather by an increase in the overall solubility of feldspar in the neutral pH region. This regime of increased rate of reaction of feldspar coincides with that expected to be naturally buffered by the introduction of organic acids into a sandstone reservoir system.

Effects of pH and Ionic Strength on the Binding of Egg White Riboflavin Binding Protein with Flavins1

The effects of pH and ionic strength on the equilibrium constants and rate constants (binding and dissociation rate constants) between riboflavin binding protein (RBP) and flavins (riboflavin, 3-carboxymethylriboflavin [CMRF], and FMN) were studied by fluorometry. The equilibrium constant and the binding rate constant between RBP and riboflavin were pH-independent between pH 6 and 9, and both constants were also independent of the ionic strength, while the constants between RBP and CMRF or FMN were dependent on both pH and ionic strength. The dissociation rate constants between RBP and the flavins used here were not so dependent on pH and ionic strength in the pH region 6 to 9, and the patterns of pH profiles as a whole were similar to each other, although the constants for FMN were about 30-60 times larger than those for CMRF or riboflavin. RBP had lower affinity for FMN than for riboflavin in the neutral pH region, which is based on the small binding rate constant and the large dissociation rate constant for FMN. The former is due to an electrostatic repulsion force between negative net charges of RBP and the phosphate group of FMN, and the latter is due to steric interference by the phosphate group of FMN.

加圧選鉱法による微細な石英とディッカイトの分離

The flotation separation of dickite and quartz finer than 2 μm has been investigated by using a pressure type and a Denver type flotators. Flotation tests were carried out by activating dickite with calcium chloride, followed by adding sodium oleate as a collector.In Denver type flotation, the separation of dickite from quartz can be achieved by the addition of large amounts of calcium chloride and sodium oleate, in neutral pH region. However, in the case of pressure type flotation, dickite can be seiectively floated from quartz by adding Separan AP30 (an anionic polymeric flocculant) and sodium oleate in the presence of proper amounts of calcium chloride at pH 5 to 12. The amounts of calcium chloride and sodium oleate necessary for floating dickite in pressure type fiotation are one tenth and one fortieth, respectively, of those in Denver type flotation.The amounts of calcium ions adsorbed on dickite are larger than those on quartz in neutral to weakly alkaline pH region. The lower the calcium concentration is and the lower the pH value is, the more remarkable the difference in calcium adsorption between dickite and quartz becomes.It is considered from the above results that in pressure type flotation dickite is selectively floated from quartz by the following mechanism: preferential adsorption of calcium species on the dickite surface occurs on the addition of proper amounts of calcium chloride in moderate pH region and induces the adsorption of Separan AP30 and oleate ion by which dickite flocs are formed and the surface becomes hydrophobic.