Sectroscopic study of stability and molecular species of 12-tungstophosphoric acid in aqueous solution

2008 ◽  
Vol 86 (10) ◽  
pp. 996-1004 ◽  
Author(s):  
Ivanka Holclajtner-Antunović ◽  
Danica Bajuk-Bogdanović ◽  
Marija Todorović ◽  
Ubavka B Mioč ◽  
Joanna Zakrzewska ◽  
...  
Keyword(s):  
Nmr Spectroscopy ◽  
Molecular Species ◽  
Ph Value ◽  
Equilibrium Composition ◽  
Keggin Structure ◽  
Special Importance ◽  
Keggin Anion ◽  
Ph Values ◽  
Ir And Nmr Spectroscopy ◽  
Ph Range

The various molecular species of 12-tungstophosporic acid (WPA) in aqueous solutions of different pH values (from 1 to 11.5) were investigated by UV, IR, and NMR spectroscopy. The dependence of the attained equilibrium composition in solution on time, concentration of WPA, and type of buffer used was studied. Obtained results indicate that the buffer type and pH value greatly determine the equilibrium composition in the solution. The Keggin structure of the WPA is sustained only up to pH 1.5. With further increase in pH, the decomposition of Keggin anion does not lead directly to the monovacant lacunary anion. Between 1.5 and 2.0, the structures with 2 phosphorus atoms from the Dawson series are dominant as intermediate species. In the pH range 3.5–7.5, WPA is present in the form of the monovacant lacunary Keggin anion. These results are of special importance for the biomedical and catalytic applications of heteropoly compounds (HPCs) and for an improved understanding of the mechanism of their functioning.Key words: heteropolyacids of the Keggin structure, hydrostability, UV, IR and NMR spectroscopy.

scholarly journals pH-dependent thermodynamic intermediates of pHLIP membrane insertion determined by solid-state NMR spectroscopy

2018 ◽  
Vol 115 (48) ◽  
pp. 12194-12199 ◽  
Author(s):  
Sarah A. Otieno ◽  
Samuel Z. Hanz ◽  
Bianca Chakravorty ◽  
Anqi Zhang ◽  
Lukas M. Klees ◽  
...  
Keyword(s):  
Solid State ◽  
Nmr Spectroscopy ◽  
Solid State Nmr ◽  
Membrane Surface ◽  
Multistage Model ◽  
Solid State Nmr Spectroscopy ◽  
Ph Values ◽  
Lipid Dynamics ◽  
Ph Range ◽  
Α Helix

The applications of the pH low insertion peptide (pHLIP) in cancer diagnosis and cross-membrane cargo delivery have drawn increasing attention in the past decade. With its origin as the transmembrane (TM) helix C of bacteriorhodopsin, pHLIP is also an important model for understanding how pH can affect the folding and topogenesis of a TM α-helix. Protonations of multiple D/E residues transform pHLIP from an unstructured coil at membrane surface (known as state II, at pH ≥ 7) to a TM α-helix (state III, pH ≤ 5.3). While these initial and end states of pHLIP insertion have been firmly established, what happens at the intervening pH values is less clear. However, the intervening pH range is most relevant to pHLIP−cell interactions in the acidic extracellular tumor environment (and in the endosomes within cells). Here, using advanced solid-state NMR spectroscopy with palmitoyl-2-oleoyl-sn-glycerol-3-phosphocholine unilamellar vesicles as the model membrane, we systematically examined the state of pHLIP−membrane interactions (in terms of the membrane locations of D/E residues, as well as lipid dynamics) at the intervening pH values of 6.4, 6.1, and 5.8, along with the known states at pH 7.4 and 5.3. Thermodynamic intermediate states distinct from the initial and end states were discovered to exist at each of the intervening pH examined. They support a multistage model of pHLIP insertion in which the D/E titrations occur in a defined sequence at distinct intermediate pH values. This multistage model has important ramifications in pHLIP applications.

scholarly journals Zinc adsorption in highly weathered soils

2008 ◽  
Vol 43 (1) ◽  
pp. 131-139 ◽  
Author(s):  
José Carlos Casagrande ◽  
Marcio Roberto Soares ◽  
Ernesto Rinaldi Mouta
Keyword(s):  
Ionic Strength ◽  
Ph Value ◽  
Batch Adsorption ◽  
Adsorption Mechanisms ◽  
Ionic Strength Effect ◽  
Ph Values ◽  
Effects Of Ph ◽  
Ph Range ◽  
Highly Weathered Soils ◽  
Zinc Adsorption

The objective of this work was to assess the effects of pH and ionic strength upon zinc adsorption, in three highly weathered variable charge soils. Adsorption isotherms were elaborated from batch adsorption experiments, with increasing Zn concentrations (0-80 mg L-1), and adsorption envelopes were constructed through soil samples reactions with 0.01, 0.1 and 1 mol L-1 Ca(NO3)2 solutions containing 5 mg L-1 of Zn, with an increasing pH value from 3 to 8. Driving force of reaction was quantified by Gibbs free energy and separation factor. Isotherms were C-, H- and L-type and experimental results were fitted to nonlinear Langmuir model. Maximum adsorption ranged from 59-810 mg kg-1, and Zn affinity was greater in subsoil (0.13-0.81 L kg-1) than in the topsoil samples (0.01-0.34 L kg-1). Zinc adsorption was favorable and spontaneous, and showed sharply increase (20-90%) in the 4-6 pH range. No effect of ionic strength was observed at pH values below 5, because specific adsorption mechanisms predominated in the 3-5 pH range. Above pH 5, and in subsoil samples, Zn was adsorbed by electrostatic mechanisms, since ionic strength effect was observed. Despite depth and ionic strength effects, Zn adsorption depends mainly on the pH.

scholarly journals A study of 12-tungstosilicic and 12-molybdophosphoric acids in solution

2008 ◽  
Vol 73 (2) ◽  
pp. 197-209 ◽  
Author(s):  
Danica Bajuk-Bogdanovic ◽  
Ivanka Holclajtner-Antunovic ◽  
Marija Todorovic ◽  
Ubavka Mioc ◽  
Joanna Zakrzewska
Keyword(s):  
Nmr Spectroscopy ◽  
Aqueous Solutions ◽  
Special Importance ◽  
Molybdophosphoric Acid ◽  
Physiological Conditions ◽  
Tungstosilicic Acid ◽  
Ir And Nmr Spectroscopy ◽  
Wide Range ◽  
Catalytic Applications ◽  
Anion Type

The behaviour of two heteropolyacids (HPAs) with quite different stability in aqueous solutions was systematically investigated by UV, IR and NMR spectroscopy and potentiometric titration. It was shown that the Keggin structure of 12-tungstosilicic acid (H4SiW12O40, WSiA) anion was sustained over a wide range of pH from 1.0 to 7.0, while the same anion type of 12-molybdophosphoric acid (H3PMo12O40, MoPA) was present only at pH 1.0. This means that under physiological conditions WSiA is dominantly present in the form of a Kegginanion, whereas the structure of MoPA is completely decomposed to molybdate and phosphate. The obtained results are of special importance for bio-medical and catalytic applications of these compounds and for a better understanding of the mechanism of their action.

Effect of pH on the Fine Structure of Pectic Acid

1970 ◽  
Vol 28 ◽  
pp. 130-131
Author(s):  
George F. Leeper
Keyword(s):  
Molecular Weight ◽  
Fine Structure ◽  
Molecular Species ◽  
Phosphotungstic Acid ◽  
Ph Value ◽  
Water Soluble ◽  
Pectic Acid ◽  
Molecular Weights ◽  
Ph Values ◽  
Elementary Fibrils

Elementary fibrils, about 35 Å wide, have been demonstrated for cellulose by a variety of techniques. More recently, they have been demonstrated for xylan, chitin, and mannan. However, their existence has not been previously reported for any of the water soluble polysaccharides.Pectic acid molecules of about 200,000 molecular weight and enzymatically abbreviated derivatives with molecular weights of 60,000 and 9,000 were negatively stained at various pH values with 2% phosphotungstic acid to demonstrate elementary fibrils. The width and degree of fasciation of these elementary fibrils varies with pH. Pectic acid elementary fibrils exhibit a 64 Å dimensional stability above a certain pH value which varies inversely with molecular weight. Below this pH, elementary fibrils exhibit a marked increase in width. At still lower pH values, the elementary fibrils are no longer demonstrable, presumably because of their dissociation to a molecular species.

Isotope Effects of Uranium by Ion Exchange in the System Dowex 50 / α-Hydroxyisobutyrate

1974 ◽  
Vol 29 (3-4) ◽  
pp. 190-194 ◽  
Author(s):  
Jorma Aaltonen ◽  
Klaus G. Heumann ◽  
Pikka Pietilä
Keyword(s):  
Ion Exchange ◽  
Isotope Effect ◽  
Separation Factor ◽  
Ph Value ◽  
Isotope Effects ◽  
Uranyl Ions ◽  
Distribution Factor ◽  
Ph Values ◽  
Ion Exchange Column ◽  
Ph Range

In this investigation the isotope effect of uranium in the system Dowex 50 resin/ α- hydroxyisobutyrate solution was studied by mass spectrometry. A recycle ion exchange column was used for the separation experiments. The dependence of the isotope effect on the pH value and on the concentration of the α-hydroxyisobutyrate solution used as eluent was investigated. In the case of a 0.07 ᴍ and a 0.22 ᴍ α-hydroxyisobutyrate solution the elementary separation factor of uranium was calculated to be 1.00019 and 1.00006, respectively. In both cases an enrichment of 235U in relation to 238U was found in the solution.In addition the distribution factor of the uranyl ions in the investigated system was determined in the pH range between 2 and 6. The distribution factor depends strongly on the pH value. With increasing pH values the distribution factor decreases.The results obtained for the elementary separation factor and the distribution factor are compared with other investigations.

UV-Photolyse von 5-Joduracil / UV Photolysis of 5-Iodouracil

1972 ◽  
Vol 27 (5) ◽  
pp. 501-504 ◽  
Author(s):  
E. Gilbert ◽  
G. Wagner ◽  
D. Schulte-Frohlinde
Keyword(s):  
Main Product ◽  
Ph Value ◽  
Product Distribution ◽  
Reaction Products ◽  
Value Addition ◽  
Uv Photolysis ◽  
Ph Values ◽  
Constant Ph ◽  
Ph Range

UV Photosylis (254 nm) of 5-iodouracil in aqueous, oxygenated solution in presence of KI, FeSO4, KBr and K2SO4 was investigated over a pH-range of 1—6. Uracil, isodialuric acid, and isobarbituric acid were identified as photoproducts.At a constant pH-value (pH=1) at high KI-concentrations (10-1 mole/1) the main product is uracil. With decreasing KI-concentrations the yield of uracil decreases and isobarbituric acid appears as a photoproduct. On further decreasing KI-concentrations (< 10-2 mole/1) the yield of isobarbituric acid decreases and the formation of isodialuric acid commences.UV Photolysis of iodouracil at constant KI-concentrations (10—1 mole/1) and increasing pH (pH = 1—6) yields similar results with one exception. At higher pH-values on account of isodialuric acid at least four further compounds are formed. The yield of these products increases with increasing pH value. Addition of KBr and K2SO4 has no effect on the product distribution.The possible mechanisms for the formation of the reaction products are discussed.

scholarly journals Sorption of heavy metals by natural biopolymers

2017 ◽  
Vol 35 (7-8) ◽  
pp. 595-601 ◽  
Author(s):  
Natalya V Efimova ◽  
Alla P Krasnopyorova ◽  
Galina D Yuhno ◽  
Anastasia A Scheglovskaya
Keyword(s):  
Functional Group ◽  
Ph Value ◽  
Kinetic Properties ◽  
Hydrolysis Lignin ◽  
Second Order Reaction ◽  
Equilibrium Solutions ◽  
Sorption Equilibrium ◽  
Ph Values ◽  
Ph Range ◽  
Modified Lignin

The sorption properties of modified hydrolysis lignin towards Cu[Formula: see text], Zn[Formula: see text], Ni[Formula: see text], Co[Formula: see text] ions in the pH range from 2 to 8 at temperature of 298.15 K solution are studied. The analysis of kinetic curves of ions sorption on modified lignin at pH 7 shows that sorption equilibrium in heterogenic system ion–metal–sorbent is attained in 30–60 min. Obtained results indicate good equilibrium kinetic properties of sorbent. Supposed that reaction between sorbate and functional group of sorbent are the second-order reaction and they interact between each other in ratio 1:1. The character of the obtained electrokinetic curve suggests that the zeta potential of modified lignin strongly depends on the pH. The dependencies of cations metals sorption coefficients on the pH value of water phase are S-shaped. Maximal extraction of studied cations is observed at pH values of equilibrium solutions close to neutral ones.

Influence of Ionic Strength and pH-value on the Silicon Dioxide Polishing Behaviour of Slurries Based on Pure Silica Suspensions

2010 ◽  
Vol 1249 ◽  
Author(s):  
Ulrich Kuenzelmann ◽  
Kathrin Estel ◽  
Johann W Bartha ◽  
Erwin-Peter Meyer ◽  
Herbert Barthel
Keyword(s):  
Ionic Strength ◽  
Fumed Silica ◽  
Ph Value ◽  
Acidic Ph ◽  
Experimental Conditions ◽  
Ph Values ◽  
Pure Silica ◽  
Silica Sols ◽  
Ph Range ◽  
Silica Suspensions

AbstractIn this study, the effect of the addition of electrolytes in a given ionic strength to various high-purity silica suspensions was investigated by measurement of the removal rates (RR's) in CMP processes on oxide layers under the same experimental conditions. As so-called slurries the following suspensions were used: i) silica sols produced by the Stöber process, ii) conventional silica sols based on alkali silicate as well as iii) suspensions of fumed silica, with the same SiO2 concentration in each suspension. Ionic strength of the added electrolyte was adjusted to e.g. 0.065 mol/l, with the electrolytes being HCl, NH4Cl, KOH, or binary mixtures of these substances.These investigations revealed significant differences of the polishing behaviour between the different types of silica dispersions as slurries. While for the Stöber sols investigated, the RR's are highest in the acidic range and almost negligible in the alkaline pH range, fumed silica suspensions show an entirely different behaviour: RR is very low for acidic pH-values, and increases with the alkalinity of the slurry. In contrast to these observations, the RR's of slurries based on conventional silica sols are highest around the neutral point, and show a decrease for both more alkaline and acidic pH-values. In comparison to the other two types of material, these suspensions have a high amount of electrolyte background, originating from their manufacturing process.A model is developed to explain these results in a comprehensive manner. It involves effects of the electrolyte type and the ionic strengths as well as influences of the particle size.

scholarly journals Appearance of Platelet-Clumping Substance after Acidification of Plasma

Blood ◽  
1968 ◽  
Vol 31 (3) ◽  
pp. 348-357 ◽  
Author(s):  
HIROH YAMAZAKI ◽  
HIROSHI MURASE ◽  
TATSUO SHIMAMOTO ◽  
TAKIO SHIMAMOTO
Keyword(s):  
Calcium Ions ◽  
Standard Error ◽  
Room Temperature ◽  
Ph Value ◽  
Platelet Rich Plasma ◽  
Final Concentration ◽  
Ringer’S Solution ◽  
Ph Values ◽  
Edta Plasma ◽  
Ph Range

Abstract 1. The pH values of heparinized plasma from ten normal rabbits were from 7.53 to 7.80. The average pH and standard error was 7.69 ± 0.03. These plasmas did not show platelet-clumping activity when exposed to the platelet-saline suspension from the same or other normal rabbits. The platelet-clumping substance was not observed in all ten cases after alkalinization of the plasma to pH values ranging from 8.32 to 9.40. On the contrary, immediately after acidification of the plasmas, the platelet-clumping substance appeared at pH values from 4.90 to 6.82 at room temperature. The range of the lower pH value, in which the platelet-clumping substance was observed, was 4.90-5.60 (5.15 ± 0.07 in average) and the upper range was 5.95-6.82 (6.27 ± 0.12 in average). The pH range at which the strongest clumping of platelets appeared was 5.22-5.95 (5.61 ± 0.07 in average). The platelet-clumping substance did not disappear after the pH of the acidified plasma was reneutralized to the original value. 2. No clumping was found after the addition of citrated, oxalated, EDTA-plasma or serum even when they were acidified. After the pH value of the citrated, oxalated or EDTA-plasma was changed from 4.85 ± 0.39 to 7.55 ± 0.03 and in the presence of calcium ions (10 mM.), platelet-clumping activity was observed. After the addition of citrate (0.38 percent in final concentration), oxalate (0.2 percent in final concentration), or EDTA (0.1 percent in final concentration) to the heparinized plasma the platelet-clumping substance did not disappear. In the case of serum, the platelet-clumping activity did not appear after the pH changes. 3. The platelet-clumping substance in the acidified plasma was heat-labile; it was detected after BaSO4-adsorption and defibrination; it was stable in storage at 4 C., and it was not dialyzable against Ringer’s solution for 72 hours. It induced platelet clumping not only in citrated platelet-rich plasma but also in the platelet-saline suspension. 4. The properties of the platelet-clumping substance in the acidified plasma were compared with that of substances known to have platelet-clumping activity and the experimental evidences showing the differences to ADP, thrombin, ADP-cofactor and thrombocyte agglutinating factors have been detailed.

scholarly journals The Influence of pH Values on the Rheological, Textural and Release Properties of Carbomer Polacril® 40P-Based Dental Gel Formulation with Plant-Derived and Synthetic Active Components

Molecules ◽  
2020 ◽  
Vol 25 (21) ◽  
pp. 5018
Author(s):  
Yuliia Maslii ◽  
Olena Ruban ◽  
Giedre Kasparaviciene ◽  
Zenona Kalveniene ◽  
Anna Materiienko ◽  
...  
Keyword(s):  
Ph Value ◽  
Textural Properties ◽  
Active Pharmaceutical Ingredient ◽  
Application Site ◽  
Structural Viscosity ◽  
Active Components ◽  
Value Evaluation ◽  
Ph Values ◽  
Thixotropic Behavior ◽  
Ph Range

The physicochemical properties, especially pH value of dental medicines, have significant influence on the health of oral cavity tissues. The pH of formulations should correspond to the value of saliva pH (5.5–8.0). For carbomer-based gels, the required pH value is obtained by neutralizing them with alkaline components, which leads to their structuring (thickening). This affects the physical properties of the gel, its residence time at the application site and the rate of release of active pharmaceutical ingredient. Therefore, the main purpose of this study is to evaluate the rheological, textural, and biopharmaceutical properties of Carbomer Polacril® 40P-based dental gel depending on the pH value. Evaluation of the rheological properties of gel preparations were performed by measuring the structural viscosity of the samples as a function of pH and temperature. The textural properties of the gel were evaluated by performing tests regarding back extrusion and spreadability. Carbomer Polacril® 40P-based gels haven’t shown noticeable thixotropic behavior, and were characterized by plastic flow in the whole studied pH range. The structural viscosity at the selected average pH value hasn’t differed at storage (25 °C) and application (37 °C) temperature. Texture studies of dental gels have shown a strong correlation with rheoparameters. Their rheological behavior and textural properties haven’t changed significantly between the pH range of 5.5–6.6. The relatively narrow range of working pH values does not affect the change in the viscosity of the preparation significantly and, consequently, does not affect the release of APIs from the developed Carbomer Polacril® 40P-based dental gel.

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