Effect Of pH Variation Research Articles

Synthesis and solvatochromic properties of some new disperse azo dyes derived from 2-anilinoethanol

A series of novel disperse azo dyes based on 2-anilinoethanol were synthesized using aniline derivatives as diazo components. These dyes have been characterized by melting points, FT-IR and 1H NMR spectroscopic methods. The effect of pH variation and solvents polarity on the absorption spectra was examined and a meaningful correlation observed. Also, the effects of substituent with electron-withdrawing and electron-donating groups at their o-, m-, p-position of phenylazoanilinoethanoles were investigated.

Adsorção de boro em solos ácricos em função da variação do pH

A adsorção de B pelo solo é o principal fenômeno que afeta sua disponibilidade e seu potencial de contaminação. Os objetivos deste estudo foram: (a) investigar os efeitos do pH na adsorção de B em amostras superficiais e subsuperficiais de um Latossolo Vermelho Acriférrico (LVwf) e de um Latossolo Amarelo Ácrico (LAw) - ambos com balanço positivo de cargas no horizonte Bw - e de um Nitossolo Vermelho eutroférrico (NVef); (b) avaliar a adequação do modelo de Langmuir em simular os resultados experimentais de adsorção; e (c) correlacionar os atributos químicos, físicos e mineralógicos dos solos com os valores de adsorção máxima (Ads máx) e do coeficiente de afinidade (K L), derivados das isotermas. Experimentos do tipo "batch" foram realizados para determinação da quantidade de boro adsorvido, tendo como eletrólito-suporte soluções de NaCl 0,01 mol L-1 com 0,1; 0,2; 0,4; 0,8; 1,2; 1,6; 2,0; e 4,0 µg mL-1 de B. Houve aumento da adsorção de B com a elevação do pH e da concentração inicial de B adicionado. Maiores quantidades de B foram adsorvidas na amostra superficial do NVef e nos horizontes Bw positivamente carregados dos Latossolos ácricos. A adsorção de B foi representada por isotermas dos tipos C (linear) e L (exponencial) e adequadamente ajustada pelo modelo de Langmuir. Os parâmetros Ads máx e K L estimados por regressão não-linear não se correlacionaram com o pH. No pH natural, teores de matéria orgânica (MO) e de argila foram as variáveis que mais influenciaram a Ads máx nas camadas superficiais. Nas camadas subsuperficiais, a Ads máx correlacionou-se negativamente com os teores de MO e positivamente com os de gibbsita. Teores de (hidr)óxidos de Fe cristalinos e amorfos estiveram correlacionados aos valores de K L obtidos nas amostras subsuperficiais e ao pH natural, bem como à Ads máx das camadas superficiais após aumento do pH.

Biosorption study in a mining wastewater reservoir

An in situ sorption was conducted to assess the behaviour of cations in a mining wastewater reservoir. Sorption experiments on test materials showed that biomass mainly bound uranium, copper, lead, zinc, and nickel, whereas goethite bound arsenic and chromium. Clay minerals bound both barium and rare earth elements. The lacustrine sediments mainly contained iron oxy-hydroxides. Desorption experiments using potentiometric titration were conducted to investigate the effect of pH variations on the stability of the test sorbents after immersion in the lake. Results indicated the presence of weak to very weak acidic functional groups in the sediments attributed to their high content of organic matter affecting the mobility and the behaviour of metals in the lake deposits.

Effect of pH Variations in a Cycling Model on the Properties of Restorative Materials

This study evaluated the effect of cycling various pH demineralizing solutions on the surface hardness, fluoride release and surface properties of restorative materials (Ketac-Fil Plus, Vitremer, Fuji II LC, Freedom and Fluorofil). Thirty specimens of each material were made and the surface hardness measured. The specimens were randomized into five groups according to the pH (4.3; 4.6; 5.0; 5.5 and 6.2) of the demineralizing solution. The specimens were submitted to pH-cycling for 15 days. The specimens remained in the demineralizing solution for six hours and in the remineralizing solution for 18 hours. Then, the surface hardness (SH) was remeasured and the surface properties were assessed. Fluoride release was determined daily. Data from SH and the percentage of alteration in surface hardness were analyzed by analysis of variance (p < 0.05); the Kruskal-Wallis test was performed for the fluoride release results. When hardness was compared, the variation in pH led to a positive correlation for glass ionomer cements and a negative correlation for fluoride release. For polyacid-modified resin composites, a negative correlation was found with regards to fluoride release; no significant correlation was observed for hardness. Surface properties were influenced: an acidic pH led to a greater alteration, except for polyacid-modified resin composites. The pH of the demineralizing solution influenced fluoride release from the tested materials. The pH variation altered hardness and surface properties of glass ionomer cements but did not influence polyacid-modified resin composites.

Chemically Driven Polyacrylonitrile Fibers as a Linear Actuator

A pH sensitive polyacrylonitrile (PAN) fiber, exhibiting soft actuation as a linear actuator, is prepared by electrospinning to investigate the optimum experimental condition of the as-spun fibers and the effect of pH variation on length change of PAN gel fiber. Unbeaded smooth and continuous PAN nanofibers with diameter of ~700 nm are obtained for the 10 wt% PAN fibers at a flow rate of 0.5 mL/h and an electric field of 0.875 kV/cm, suggesting that the value of viscosity is the most significant on the fiber morphology. Diameter and volume changes of PAN filaments are observed as greater than 100% and greater than 720%, respectively for pH activated systems. A typical hysteresis loop is observed for the length change (~38%) of PAN gels with respect to pH variation.

Models for evaluating the effects of variations in pH of rain water on the leaching of fertilizer components in soils

Models for evaluating the effects of variations in pH of rain water on the leaching of fertilizer components in soils

Effect of Extraction and Precipitation Conditions During Soybean Protein Isolate Production on the Genistein Series Content

AbstractThe influence of the conditions for isolation of soy protein on the content of genistein and its conjugated forms was studied. The major components of the genistein series isolated from soybean flour were malonyl genistin (54.3%), genistin (36.9%), and equal amounts (4.4%) of genistein and acetyl genistin. A modification in the conjugation profile of genistein between pH 4.5 and 8.0 and above pH 10 was attributed to the action of β‐glucosidase and the saponification reaction, respectively. A decrease in the content of total genistein in the insoluble flour residue and in the soy protein isolate (SPI) with increasing extraction pH was detected, while in the whey, the total genistein content was not affected by pH. The effect of pH variation during acid precipitation on the content of genistein and its conjugated forms, at a constant extraction pH (8.0), was also studied. Under these conditions, the highest absolute content of total genistein in the SPI was obtained at pH 3.5 and the lowest was obtained at pH 5.6. The total genistein content in the whey followed an inverse trend compared with that of the protein yield. A temperature increase did not substantially affect the distribution of the different genistein forms or their total contents. The content of total genistein was higher in the glycinin than in the β‐conglycinin protein fraction. The effect of the pH during the alcohol/water extraction of the isoflavones was also analyzed. The efficiency of the extraction was lower at pH values between 3.25 and 3.5 than at other pH values.

Effect of pH-variation on insertion and ion channel formation of human calcitonin into planar lipid bilayers

Human calcitonin is the physiological hormone involved in calcium-phosphorus homeostasis. However, its use is limited by its propensity to form aggregates. We find that the type of host lipid has a pronounced influence on human calcitonin fibrillation or incorporation, as assessed by channel formation, in planar lipid membranes at neutral pH. At pH 7, human calcitonin is able to interact and form channels with negatively charged dioleoyl-phosphatidylglycerol (DOPG) bilayers and with zwitterionic palmitoyl-oleoyl phosphatidylcholine (POPC) bilayers containing 15% negatively-charged DOPG, but not with POPC bilayers. At low pH (4.5 and 3.8), the conformational variation of the peptide enables it to insert into POPC and POPC:DOPG but not into DOPG bilayers. The model proposed for human calcitonin interaction and channel formation at acidic pH was based on theoretical predictions of the protonation-deprotonation state of some amino acids, in particular in the fibrillating sequence of peptide molecules; the length of the alpha-helix, and the electrostatic and/or hydrophobic interaction also seem to be relevant. These results may suggest that human calcitonin at low local pH could be involved in osteoclasts' calcium-sensitive permeability through channel formation and/or receptor interaction.

Amperometric sensor for glutathione reductase activity determination in erythrocyte hemolysate

The development of an amperometric sensor for glutathione reductase (GR) activity in erythrocyte hemolysate to contribute to oxidative stress evaluation is presented. In this assay, the reduced form of glutathione, the product of the GR reaction, reacts with 5,5 ′-dithiobis(2-nitrobenzoic acid), producing GSTNB, which is easily reduced in the electrode surface. The current was recorded during 180 s after the sample addition, applying a potential of −300 mV. The sensor presented a suitable sensitivity, a good operational range, and precision. The effects of pH variations and specific uncompetitive inhibitor (safranin-O) in the enzyme activity were also evaluated. The GR activity determination in human erythrocyte hemolysate using this method has provided results that are statistically equal to those obtained by the classical spectrophotometric method, with 95% of confidence. The advantages of this method are the saved time, reagents, and samples and the possibility of its use in the field.

Corrosion et passivation de l'étain dans un milieu simulé à une eau industrielle

The corrosion behaviour of tin in a synthetic medium similar to an industrial water has been studied by using electrochemical methods (plotted potentiodynamic curves and polarization resistance measurement). The effect of pH variation, temperature and concentration of anions in solution has been investigated. The results obtained show that pH variation (around the value 8.2 of the synthetic medium) has no effect on the pitting sensitivity of tin. However, the increasing of temperature in the range of 20–70°C accelerates the corrosion process. The presence of anions Cl– and SO42– leads to pitting corrosion of tin. Cl– ions are more aggressive than SO42– ions, whereas HCO3– ions acted as an inhibitor for pitting corrosion of tin in the studied medium.Key words: tin, corrosion, pitting, industrial water.

Study of the Reaction of Platinum(IV) with Dimethylglyoxime by UV Spectrophotometry

The complex formation of dimethylglyoxime and platinum(IV) in alkaline medium has been investigated by ultraviolet spectroscopy. This study has shown that more than one complex species exists in solution. The effects of pH variation of ammonia buffer solution from 6.0 to 13.0 were investigated with respect to the absorption spectra. The molar ratios method, the Job's method and the method of relative recovery of complex species were used. It was found that the stoichiometric ratio Pt(IV)/dimethylglyoxime was 1:1, 1:2 and 2:1. The molar absorptivity (log ε = 4.1 at 260 nm) and the formation constant of the complex (log K2,1 = 15.0) were obtained. The stability constants of the [Pt(Hdmg)2(NH3)2] complex determined by the molar ratios and Job's method were log β2 = 9.2 ± 0.2 and log β2 = 9.3 ± 0.2, respectively.

The effect of pH and nucleophiles on complement activation by human proximal tubular epithelial cells.

Activation of urinary complement proteins in situ by proximal tubular epithelial cells (PTEC) may contribute to the mediation of tubulointerstitial injury in patients with significant proteinuria. However, the mechanism involved is unclear, and the role of changes in urinary pH and in the concentrations of urea or ammonia requires further clarification. The protein fraction of urine samples from nine patients with proteinuria >1.5 g/day was purified. A cell ELISA involving cultured HK-2 PTEC was used to investigate the capacity of urinary protein to promote the deposition of both C3 and C9 on the cell surface. The effect of variations in pH (5.5-8.0) and in the concentration of urea and ammonia was also examined. C3 was purified and used to further investigate the mechanism of complement deposition. Urine samples from the majority of patients induced deposition of C3 and C9 on the surface of HK-2 cells via the alternative pathway. This process was maximal at acidic pH values. Preincubation of urinary complement or serum with urea or ammonia inhibited C3 deposition. Purified C3 incubated with HK-2 cells showed no evidence of activation in the absence of other complement components. These data suggest that bicarbonate protects against complement-mediated damage in the lumen by increasing the local pH, rather than by inhibiting the generation of ammonia. PTEC appear to activate complement through provision of a 'protected site' on their surface, rather than by the activation of C3 by convertase-like protease(s).

Effect of pH Value on Corrosion Behavior of Steel in CO2-containing Aqueous Media

The dependence of the pH of the medium on the partial pressure of CO2 and temperature in the system constituted by low-carbon steel and NaCl (3%) and the effect of pH variation on the corrosion rate were studied. The mechanism of carbonic acid corrosion of ferrous metals in oxygen-free mineralized aqueous media was analyzed. The possibility of prognosticating the rate of steel corrosion on the basis of partial pressure of CO2 and pH value was considered.

The effect of variations in pH and temperature on stability of melatonin in aqueous solution.

Melatonin (N-acetyl-5-methoxytryptamine) has a diverse range of functions, including the control of neuroendocrine events. A number of studies have shown that melatonin may be of potential benefit for the treatment of insomnia, as well as neurodegenerative disorders. At present, there are numerous dosage forms of melatonin, with the oral route of administration being most popular. Presently, there is little information on the stability of melatonin over a pH range. With the changes in pH in the gastro-intestinal tract, as well as in different experimental conditions, information on the stability of melatonin would be important. We used a high-performance liquid chromatography method to determine the stability of melatonin solutions over a pH range (1.2-12) at room temperature and at 37 degrees C over a period of 21 days. The results show that no melatonin degradation occurred in the first 2 days. From days 3 to 21, there was a gradual decline in melatonin at all pHs, with the decline not exceeding 30%. No decline in melatonin levels occurred in the first 2 days at 37 degrees C. From days 3 to 21, melatonin levels declined gradually, with the decline not exceeding 29%.

The effect of pH variation at the ammonium/ammonia equilibrium in wastewater and its toxicity to Lemna gibba

Laboratory scale batch experiments were performed under controlled conditions at different total ammonia concentrations (10–300 mg N l −1) and controlled pH values of 6.8–8.7 using settled domestic wastewater to measure the effect of the ionised (NH 4 + or ammonium) and un-ionised form (NH 3) on the growth of the duckweed Lemna gibba. Relative growth rates (RGR) varied between 0 and 0.3 per day. The toxicity of total ammonia to duckweed was a result of the effect of both, ionised and un-ionised, forms at low NH 3 concentrations (<1 mg N l −1). At higher NH 3 concentrations, the toxic effect of the ionised form could be disregarded. Relative growth rates of L. gibba decreased linearly with increasing NH 3 concentrations up to a maximum level (8 mg N l −1), above which duckweed died. These data indicate that L. gibba can be used to treat wastewater containing high total ammonia concentrations as long as certain pH levels are not exceeded. Extrapolated relative growth rates resulting from different combinations of pH and total ammonia are given for the examined ranges. Up to a pH of 7.8, a substantial production of 55 kg DW ha −1 per day was achieved. Wastewater treatment using L. gibba becomes impossible at pH levels above approximately 9.8, depending on the temperature.

PH-Dependent Surface-Enhanced Raman Scattering of 8-Hydroxy Quinoline Adsorbed on Silver Hydrosol

Surface-enhanced Raman scattering (SERS) of 8-hydroxy quinoline (HQ) adsorbed on silver hydrosols are compared with the FTIR and normal Raman spectrum in the bulk and in solution. Definite evidence of the charge transfer interaction to the overall contribution in the SER enhancement has been reported. The excitation profile study also supports the evidence of a charge transfer interaction. The effect of pH variation on the SER band intensity is explained in terms of chemisorption of the molecule on bare and chlorinated silver surfaces. The apparent enhancement factor calculations of the principal Raman bands indicate that in the surface-adsorbed state, an HQ molecule is oriented neither flat nor vertical to the silver surface but is tilted.

Effects of pH variation and NaCl on in vitro digestibility of cow's milk proteins in commercially available infant formulas.

Allergenicity and antigenicity of food proteins are generally dependent on their heat-stability and resistance to digestive enzymes. Using the methods of SDS-PAGE and immunoblots, we assessed peptic-digestibility of major milk proteins (casein, beta-lactoglobulin and alpha-lactalbumin) in commercially available infant formulas in acidic pH range (pH 1.5 to 4.0), and we also investigated the effect of NaCl on peptic-digestibility of cow's milk proteins at pH 2.0. The profile of peptic-digestion of casein was similar at pH range from 1.5 to 3.5 where the intact protein of casein rapidly disappeared, whereas slow digestibility of the protein was found at pH 4.0. Beta-lactoglobulin and alpha-lactalbumin were digested at pH range from 1.5 to 2.5 and were almost entirely resistant to peptic digestion at over pH 3.0. In the presence of NaCl at pH 2.0, casein showed a good digestibility by pepsin similar to that in the absence of NaCl, in contrast to beta-lactoglobulin and alpha-lactalbumin both having their peptic-digestibility decreased in the presence of 0.2 M NaCl. As the state of the stomach in new born infants shows low amounts of secretary pepsin and out of optimum pH of peptic activity, low digestibility of beta-lactoglobulin and alpha-lactalbumin in cow's milk based infant formulas at over pH 3.0 is supposed to be responsible for their allergenicity.

Denitrification kinetics of high nitrate concentration water: pH effect on inhibition and nitrite accumulation

The effect of pH variation, within the range 6.5, 7.0, 7.5, 8.5 and 9, on activated sludge denitrification of a synthetic wastewater containing 2700 mg/l NO 3-N was examined using bench-scale Sequencing Batch Reactors. Two major effects were observed. One, at pH values of 6.5 and 7.0, denitrification of a synthetic wastewater containing high nitrate levels was significantly inhibited. Two, denitrification was achieved at higher pH values of 7.5, 8.5 and 9.0, but the accumulation of nitrite increased significantly as mixed liquor pH increased with peak values of 250, 500 and 900 mg/l NO 2-N, respectively. As the pH rose, the specific rate of nitrate reduction increased. At the same time the specific rate of nitrite reduction increased in the absence of nitrate. In the presence of nitrate the specific rate of nitrite reduction remained constant, and the degree to which nitrite reduction increased in the absence of nitrate was a function of increasing pH. While increasing pH from 7.5 to 9.0 affected nitrite intermediate accumulation, the overall time for complete denitrification (reduction of both NO − 3 and NO − 2) was similar for the pH values of 7.5, 8.5 and 9.

Effect of pH Variation by Electrodialysis on the Inhibition of Enzymatic Browning in Cloudy Apple Juice

The pH of cloudy apple juice was reduced temporarily and then returned to its initial value using electrodialysis (ED) technology by water splitting with a bipolar membrane. The juice was treated in a small scale unit at temperatures between 16 and 24 °C and a constant current density of 40 mA/cm2. The pH of the juice was reduced from 3.5 to 2.0 in 30 min. However, this level of acidification required the addition of 12.3 mM K+ (KCl) every 5 min during the treatment. Exogenous K+ compensated for the K+ loss from the juice and maintained the electric charge at neutrality, which favored the accumulation of H3O+ in the juice. The reduction of juice pH to 2.0 resulted in the complete inhibition of polyphenol oxidase (PPO) activity compared with the control. Following acidification, the pH of the juice was returned to its initial value in 60 min by introducing OH- produced by water splitting. The pH adjustment of the juice slightly reactivated the PPO, but browning inhibition was complete and irreversible. The treatment enhanced the color of cloudy apple juice during storage without modifying the flavor or sugar content. However, the ED treatment slightly reduced the malic acid content and substantially reduced the mineral contents. Keywords: Electrodialysis; bipolar membranes; apple juice; enzymatic browning; polyphenol oxidase

Recognition of superpotent sweetener ligands by a library of monoclonal antibodies.

Monoclonal antibodies (mAb) made to the superpotent guanidino sweet tasting ligand, N-(p-cyanophenyl)-N'-(diphenylmethyl)-guanidineacetic acid were examined for their molecular recognition specificities using 14 different sweetener analogues in a competitive radioimmunoassay. The effects of variations in pH on ligand binding was also examined by radioimmunoassay. Photoaffinity labelling of the binding site was accomplished using a radiolabelled azido-derivative of the parent ligand, and L-chain or H-chain labelling was easily identified in several different mAb. For two of the mAb examined in this study (NC6.8 and NC10.14), the analogue binding studies are in agreement with the known Fab-ligand crystal structures. Monoclonal antibodies to this family of sweet tasting compounds may be useful probes for the study of sweet taste chemistry and identification of novel sweet taste ligands from combinatorial chemical libraries.