Different Values Of pH Research Articles

Smart pH-responsive Co-polymeric Hydrogels for Controlled Delivery of Capecitabine: Fabrication, Optimization and In Vivo Toxicology Screening.

Despite exhibiting promising anticancer potential, the clinical significance of capecitabine (a potent prodrug of 5-fluorouracil used for the treatment of colorectal cancer) is limited owing to its acidic and enzymatic hydrolysis, lower absorption following the oral administration, poor bioavailability, short plasma half-life, and poor patient compliance. The present study was aimed to fabricate the capecitabine as a smart pH-responsive hydrogel network to efficiently facilitate its oral delivery while shielding its stability in the gastric media. The smart pH-sensitive HP-β-CD/agarose-g-poly(MAA) hydrogel network was developed using an aqueous free radical polymerization technique. The developed hydrogels were characterized for drug-loading efficiency, structural and compositional features, thermal stability, swelling behaviour, morphology, physical form, and release kinetics. The pH-responsive behaviour of developed hydrogels was established by conducting the swelling and release behaviour at different pH values (1.2 and 7.4), demonstrating significantly higher swelling and release at pH 7.4 as compared with pH 1.2. The capecitabine-loaded hydrogels were also screened for acute oral toxicity in animals by analysing the body weight, water and food intake, dermal toxicity, ocular toxicity, biochemical analysis, and histological examination. The characteristic evaluations revealed that capecitabine (anticancer agent) was successfully loaded into the hydrogel network. The range of capecitabine loading was from 71.22% to 90.12%. An interesting feature of hydrogel was its pH-responsive behaviour which triggers release at basic pH (94.25%). Optimum swelling (95%)was seen at pH 7.4. Based upon regression coefficient R2(0.96 - 0.99) the best-fit model was zero-order. The extensive toxicity evaluations evidenced a good safety profile with no signs of oral, dermal, or ocular toxicities, as well as no variations in blood parameters and histology of vital organs. Our findings conclusively evinced that the developed hydrogel exhibited excellent pharmaceutical and therapeutic potential and thus can be employed as a pH-responsive system for the controlled delivery of anticancer agents.

Studies of the influence factors on the coloring properties of black carrot powder

The article presents materials on the infl uence of storage conditions on the technological and consumer properties of natural anthocyanin dye extracted from black carrots. The solubility of the dye in various media was studied. It was found that anthocyanins do not completely dissolve in alcohol, the solubility point of the powder dye and the ratio of water to alcohol were determined. The dependence of the maximum optical density on acidity was studied when black carrot powder was dissolved in water and water with alcohol. Studies have been performed on changes in the color of an aqueous solution at diff erent pH values of an aqueous suspension prepared in accordance with GOST 2119.3-91 (ISO 787-9-81) General test methods for pigments and fillers. Determination of the pH of an aqueous suspension. Changes in the properties of the dye under different storage temperature conditions and the influence of light exposure were studied.

Fe/ZnO nanorod photoanode and pyrocatechol violet sensitizer based dye sensitized solar cells

A ZnO and Fe/ZnO nanorods have been prepared and used in dye sensitized solar cells. The prepared ZnO and Fe/ZnO nanorods were characterized by XRD, SEM and SEM-EDS. Additionally, the pyrocatechol violet solutions with different pH values have been prepared, characterized and used in dye sensitized solar cells. The dyes which have different pH values were characterized via UV-Vis absorbance and cyclic voltammetry techniques. The Fe doping to ZnO nanorods increased the solar cell efficiency by 20-35%. The pyrocatechol violet dye can be binded to Fe atoms on the ZnO surface and the possible mechanism was discussed in detailed. The efficiency of champion solar cell is obtained 1.39% with Fe/ZnO photoanode and pH 7.5 pyrocatechol violet dye solution.

Characterisation and applications of synthesised cation exchanger guar gum sulphonic acid (GSA) resin for removal and recovery of toxic metal ions from industrial wastewater

The chemically modified guar gum sulphonic acid (GSA) resin was used for removal and pre-concentration of Zn2+, Cd2+, Fe2+, Pb2+ and Cu2+ ions in aqueous solutions and steel industry effluent from Jodhpur, India. This type of ion exchange resin represents a new class of hybrid ion exchangers with higher stability, reproducibility and selectivity for toxic metal ions. The characterisation of the resin was carried out by determining the ion exchange capacity, elemental analysis, FT-IR spectra and thermal analysis (TGA). The distribution coefficients (Kd) of toxic metal ions were determined for differentpH values. The adsorption of different metal ions on GSA resin follows the order: Cu2+ > Fe2+ > Zn2+ > Cd2+ > Pb2+. The adsorbency of different metal ions on the GSA resin was studied for up to 10 cycles.

Interaction of Copper-Containing Preservatives with Wood. Part 1. Mechanism of the Interaction of Copper with Cellulose

Summary In the present work, the state of the copper ions absorbed by cellulose from aqueous solutions with different pH values has been studied by electron spin resonance (ESR), X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray analysis (EDXA) methods. It has been shown that the curve of copper sorption has a S-like shape characteristic for weak acid sorbents. At all pH values in ESR-spectra, an anisotropic Cu(II)-signal is registered. At pH > 4, the anisotropy of ESR-spectra decreases. At pH = 10, complexes connected by exchange interactions and diamagnetic clusters are formed. After the leaching of specimens, the ESR-signal practically disappeared. The decrease of the copper content in cellulose did not correlate with the change of the integral intensity of the spectra. The changes in ESR-spectra of copper-containing cellulose after leaching were explained by the formation of the Cu(II) diamagnetic clusters.

Decomposition of nitrite under various pH and aeration conditions

Studies on the decomposition/oxidation of nitrite at differentpH values and aeration flow rates were investigated using abench-scale batch reactor. The conditions were pH 2.85, 3.50,5.80, 7.0, and 11.6, and with or without aeration at airflowrates of 1.50, 2.25, and 3.25 L min-1.Decomposition/oxidation of nitrite may be described by apseudo-first order expression, and the rate constants fornitrite decomposition/oxidation ranged from 1.2 ×10-6 s-1 to 1.12 × 10-4 s-1 depending on the experimental conditions. The rate ofdecomposition/oxidation of nitrite was found to increase for lowpH conditions and for high airflow rates. The experimentalresults showed that the dominant reaction in thedecomposition/oxidation of nitrite in low pH solutions and inthe presence of some aeration was most probably thedecomposition of nitrous acid to NO and NO2. Oxidation ofnitrite to nitrate appeared to proceed in a smaller proportionin comparison to the breakdown of nitrous acid to nitrogen oxidecompounds. Results from this study showed that emissions ofnitrogen oxides from nitrite-containing solutions are possible ifthe solutions were agitated and the pHs of the solutions wereless than 6.

The distribution of phosphate over iron-bound and calcium-bound phosphate in stratified sediments

Release of phosphate from, and adsorption ontosediments is calculated as a chemical equilibriumbetween dissolved o-phosphate and two solidphosphates, i.e. iron- and calcium-bound phosphate.Organic phosphates play a minor role, if any at all.Using chemical equilibrium equations, the distributionof the two solid inorganic phosphates is calculatedfrom the accumulated phosphate quantity as function oftime and depth in sediment layers of shallow lakes orwetlands. It is shown that this distribution dependson water depth, pH, Ca2+ concentration in thewater, Fe(OOH) concentration in the sediments andmaximal binding capacity of the sediments. Bycomparing values of dissolved phosphate at differentpH values, it is shown that acidification, whichusually takes place in hypolimnia, will cause releaseof phosphate, which is not necessarily dependent onthe redox potential. The release does depend on pH,Ca2+ concentration in the water, CaCO3concentration in the sediments and the saturationstage of the two P-pools in the surface layers ofthese sediments.

Comparative studies on the adsorption and association of 3-methylxanthine and 7-methylxanthine at a charged interface

A systematic comparative study of the adsorption and association of 3-methylxanthine (3MXan) and 7-methylxanthine (7MXan) at mercury-solution interfaces in acidic, neutral, and alkaline buffer solutions was undertaken by ac voltammetry. At bulk concentrations of3MXan above a threshold value, the stacking interactions between vertically oriented molecules lead to a slow reorientation aroundEecm, and the molecules adopt a perpendicular orientation. The association of the adsorbed molecules of7MXan is hindered and is not effective in promoting base-base stacking interactions. The enhanced surface activity of3MXan compared to7MXan results from the different position of the methyl group in the purine moiety. The effect of some divalent metal ions on adsorption stages and association of the investigated compounds has been studied. The results indicate that the complexation of methylated xanthine enhances the stacking interactions and hence would be expected to facilitate the formation of perpendicularly stacked layers ofM(II)-MXan complexes on the electrode surface. The adsorption parameters of the investigated compounds have been computed in absence and presence of Cu(II) at differentpH values. The results are compared with the behaviour of xanthine.

Thermodynamic characterisation of RNAase a in the presence of urea and GuHCl

It is presented a study concerning the influence of guanidinium chloride (GuHCl) and urea on thermal stability of Bovine Pancreatic Ribonuclease A (RNAase A) at differentpH values. As expected, at increasing the denaturant concentration, the protein thermostability decreases. This is shown by a decrease of both the thermodynamic parameters, temperature and heat effect, characterising the denaturation process. In order to analyse the calorimetric curves we adopt a statistical thermodynamic approach. The individual one-dimensional DSC profiles have been expanded into another dimension by varying the GuHCl concentration, so that a heat capacity surface is defined for eachpH. By means of the ICARUS program, developed in our laboratory, we accomplish a two dimensional deconvolution of the experimental data linking the binding equilibrium to the denaturation process. This analysis provides a well founded and complete statistical thermodynamic characterisation of denaturation process of RNAase A in the presence of GuHCl and allows to calculate the thermodynamic parameters associated to the binding of denaturant molecule.

Voltammetric determination of As(III) in an aqueous zwitterionic complexing medium

The polarographic behaviour and determination of As(III) in aqueous complexing electrolytes (bicine buffer solutions) ofpH values varying from 1.13–11.96 have been investigated at 25°C (direct current and differential pulse polarographic techniques). Using DC polarographic measurements, it was shown that reduction of As(III) takes place along one or three waves depending upon thepH value of the solution. Microcoulometric experiments have been performed at the limiting region of the different waves obtained at differentpH values. Cyclic voltammograms were recorded using a HDME to investigate the nature of reduction. Schemes for the mechanism of reduction occurring at the DME have been deduced. Kinetic parameters and wave characteristics for the reduction of As(III) have been calculated. A method for DPP determination of As(III) in bicine buffer solution ofpH 1.41 is reported. The detection limit of the method is 6.60×10−8M As(III).

The pH Dependence on the Formation Process of Tungsten Oxide Gel

In order to investigate the pH-effect on gelation process of tungstic acid, the simultaneous measurements of transmitted-light intensities were carried out for specimens with several different-pH values (pH=1.3 ∼ 1.6), prepared by adding different amounts of NaOH aqueous solution into ion-exchanged tungstic acid. The transmitted-light intensity decreased faster, as the pH-value of the specimen became lower. Moreover, it was found that the transmitted-light intensities of the different-pH specimens showed a unique time dependence when the observation time was scaled by t 1/2 (the time when the transmitted-light intensity became the middle value of the initial and the final intensity). This result indicates that, though the light-scattering mechanism in tungstic acid might change during gelation process, the mechanism of gelation process itself is same irrespective of pH-values. In addition, the critical pH value for the gelation was extrapolated to be 1.71 from 1/ t 1/2 vs. pH value curve.

Polarographic behaviour and determination of As(III) in aqueous complexing electrolytes

The polarographic behaviour and determination of As(III) in aqueous complexing electrolytes viz. universal and citrate buffer solutions ofpH varying from 2.20–12.0 and 1.5–4.96, respectively, have been investigated atT=25°C. It was shown that reduction of As(III) takes place along one, two or three waves depending upon thepH value. Microcoulometric experiments have been performed at the limiting region of the different waves obtained at differentpH values. Schemes for the mechanism of reduction occurring at theDME have been deduced. A method for analytical determination of As(III) on both the micro- and macro-scales in universal and citrate buffer solutions, respectively, in the presence of a trace of triton-x-100 is reported.

Spectrophotometric and potentiometric determination of acidic constants of oxo-phenyl pyridinium monoxime and dioxime

The UV absorption spectra of 1-(1-hydroxyimino-2-oxo-2-phenyl) pyridinium chloride (compound I) and 1-(1-hydroxyimino-2-oxo-2-phenyl)-4-hydroxyiminomethyl pyridinium chloride (compound II) in water solution at differentpH values have been measured. The spectral changes, with changingpH, in aqueous solutions are attributed to the dissociation of individual functional groups of the compounds. The mixed acidic constants (pK′a) of the investigated monoxime and dioxime, have been determined spectrophotometrically in the series ofBritton-Robinson's buffer solutions in thepH range 3.0–5.19 and 7.70–9.90 (t=25±0.5°C,I=0.2). The followingpK′a values have been obtained for monoximepK′a1=4.30 and for dioximepK′a1=4.28,pK′a2=8.36.

Polarographic behaviour of 2,2?-dipyridyl-2-pyridylhydrazone (DPPH) and pyridine-2-aldehyde-2-quinolylhydrazone (PAQH) at the dropping mercury electrode

The polarographic behaviour of 2,2′-dipyridyl-2-pyridylhydrazone (DPPH) and pyridine-2-aldehyde-2-quinolylhydrazone (PAQH) atdme were studied in aqueousBritton-Robinson buffers containing 50% ethanol. The polarograms consist of one irreversible wave in the acidic and alkaline medium. Two electrons are consumed in the splitting of the N-N bond. The effect ofpH on the limiting current andE as well as the reduction mechanism are discussed and compared with similar compounds. The values of the kinetic parameters for the electrode reaction at differentpH values are also computed from the polarographic results.

Polarographic behaviour of 1,3-bis[(2-pyridyl)methyleneamino]thiourea (PMAT) in absence and presence of Triton X-100

The polarographic behaviour of 1,3-bis[(2-pyridyl)methyleneamino]thiourea (PMAT) in solutions of varyingpH has been studied both in the absence and presence of Triton X-100 (T.X-100). The mechanism for the reduction process is discussed. The adsorption effect of electrochemically inactive T.X-100 on the polarographic waves ofPMAT has been investigated. The values of the kinetic parameters for the electrode reaction at differentpH values have been computed. The applicability of the polarographic method for determination ofPMAT is also discussed.

Effect of Essential Fatty Acid Deficiency on the Arrhenius Plot of Acetylcholinesterase from Rat Erythrocytes

Arrhenius plot of erythrocyte acetylcholinesterase was studied at dif ferent pH values in four groups of rats. Two groups were fed EFA-sulficient diets with lard or corn oil as the dietary fat. The other two groups were fed EFA-deficient diets: a basic, fat-free diet, and the same supplemented with hydrogenated beef fat. The Arrhenius plot of membrane-bound acetylcholinesterase from EFA-sufficient animals was found to have a breakpoint about 20°at pH 8.0, with lower activation energy at higher temperatures. The enzyme from EFA-deficient animals exhibited a breakpoint about 28°,the activation energies being lower than that of the enzyme from EFA sufficient animals above and below this point. Solubiization of the membrane with Triton X-100 led to a shift in the breakpoint and to an increase in the activation energies in the enzyme from EFA-deficient animals. No changes were detected with prepara tions from EFA-suflicientanimals after the treatment. After reconstitution of mem brane-like material from the soluble EFA-deficient preparation, the distinctive enzymatic behavior was restored. The results indicate that the Arrhenius plot of the acetyicholin esterase is changed when the enzyme is bound to an EFA-deficient membrane. J. Nutr. 104: 1265—1272,1974. INDEXING

Photooxidation of lysozyme at different wavelengths (author's transl)

The photooxidation of lysozyme in the presence of methylene blue, riboflavine, and bengal rose at differentpH values and wavelengths was studied. Monochromatic irradiation at shorter wavelengths (345 and 365 nm) is - in contrast to visible light - characterized by higher energy yields and lower oxygen consumption. This behavior suggests that the mechanism of photooxidation depends on the wavelength. The specific destruction of amino acid residues is also wavelength-dependent. Using visible light of 448 and 621 nm for riboflavine and methylene blue, respectively, we have confirmed the selective destruction of histidine and tryptophan atpH 7,0. The energy yield for the destruction of tryptophan in lysozyme is much larger than in other proteins. This result is likely related to the exposed location of tryptophan-62 and tryptophan-63 in lysozyme, which is also evident from the kinetic analysis of the corresponding dose-effect relationships. If lysozyme is irradiated with light of 365 nm in the presence of riboflavine only cystine, tyrosine, and methionine are destroyed.

Resistance of Escherichia coli to penicillins. VI. Purification and characterization of the chromosomally mediated penicillinase present in ampA-containing strains.

The chromosomally mediated penicillinase present in three strains of Escherichia coli K-12 has been purified and characterized. Two of the strains carried the ampA gene and the third the wild-type allele. The purification involves release of the enzyme by spheroplast formation, dialysis, chromatography on sulfoethyl cellulose, and chromatography on hydroxylapatite. Enzyme from the two mutants appeared homogeneous in polyacrylamide gel electrophoresis. Enzyme from the wild-type strain gave two bands. Immunologically, the enzymes from all three strains were identical. Ultracentrifugation gave a homogeneous peak with a sedimentation coefficient of 3.4S. Gel filtration gave an estimated molecular weight of 29,000. The N-terminal amino acid residue was found to be alanine. Complete amino acid analysis showed a lack of cysteine. Ultraviolet spectra were recorded at three different pH values. The extinction coefficient at 280 nm is 21.0 for a 1% solution at pH 6.8. The optimal pH is 7.3. With enzyme from one of the resistant mutants, the following K(m) and turnover number values were obtained: for penicillin G, 12 mum and 2,080; for d-ampicillin, 6 mum and 83; for cephalosporin C, 217 mum and 18,400. The effect of different salts on the enzyme activity was tested. Under many conditions the enzyme was found to be unstable.

The co-precipitation of manganese by iron(III) hydroxide

Radioactive manganese and iron were used to study the precipitation of iron(III) and managanese hydroxides at differentpH values from their pure solutions as well as in the presence of each other. It was noticed that there was always some entrainment of mangenese by iron(III) hydroxide even at lowpH values at which the iron itself was incompletely precipitated. The amount of manganese entrained at various concentrations of manganese and iron at the intermediatepH values from 3 to 7 were determined. There is a criticalpH value (i.e. between 4.5 and 4.7) at which there is a change in the course of entrainment from adsorption process to the incorporation phenomena. The effect of aging of the precipitate in its mother liquor to reduce the entrainment was also investigated.