Study Of pH Effect Research Articles

Porous polyimide framework: A novel versatile adsorbent for highly efficient removals of azo dye and antibiotic

Porous organic frameworks (POFs) have aroused considerable interest owe to its high surface areas, superior chemical and thermal stabilities, good mechanical and abundant porosity. In this study, a porous polyimide (PI) with abundant amine groups was synthesized by the reaction of melamine and pyromellitic dianhydride. And its versatile adsorption performance towards organic pollutants, including azo dye (methyl orange (MO)) and antibiotic (tetracycline (TC)) was investigated. The PI was characterized by Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscope (FE-SEM), thermogravimetric analysis (TGA), and N2 adsorption-desorption techniques. The obtained product possessed high thermal stability and exhibited a high surface area (635.5m2·g−1) and a large pore volume (0.98cm3·g−1). The pH effect study showed that MO adsorption was highly pH-dependent with an optimal pH3, while the TC adsorption was effective in the pH range of 6–8. Batch adsorption experiments were carried out to study adsorption kinetics and adsorption thermodynamics. The result showed that the kinetics experimental data were fitted to pseudo-second-order kinetics model better, and adsorption isotherm could be described by the Langmuir isotherm model perfectly. The maximum adsorption capacities calculated from the Langmuir isotherm model are 609.8 and 155.8mg/g at 318K for MO and TC, respectively. The thermodynamic study showed that the adsorptions of TC and MO on PI were spontaneous (ΔG<0) and endothermic (ΔH>0). Findings in this study demonstrated that the porous PI should be a powerful adsorbent in organic pollutants removal.

Alanine and serine functionalized magnetic nano-based particles for sorption of Nd(III) and Yb(III)

Magnetic nano-based sorbents have been synthesized for the recovery of two rare earth elements (REE: Nd(III) and Yb(III)). The magnetic nano-based particles are synthesized by a one-pot hydrothermal procedure involving co-precipitation under thermal conditions of Fe(III) and Fe(II) salts in the presence of chitosan. The composite magnetic/chitosan material is crosslinked with epichlorohydrin and modified by grafting alanine and serine amine-acids. These materials are tested for the binding of Nd(III) (light REE) and Yb(III) (heavy REE) through the study of pH effect, sorption isotherms, uptake kinetics, metal desorption and sorbent recycling. Sorption isotherms are well fitted by the Langmuir equation: the maximum sorption capacities range between 9 and 18 mg REE <TEX>$g^{-1}$</TEX> (at pH 5). The sorption mechanism is endothermic (positive value of <TEX>${\Delta}H^{\circ}$</TEX>) and contributes to increase the randomness of the system (positive value of <TEX>${\Delta}S^{\circ}$</TEX>). The fast uptake kinetics can be described by the pseudo-second order rate equation: the equilibrium is reached within 4 hours of contact. The sub-micron size of sorbent particles strongly reduces the contribution of resistance to intraparticle diffusion in the control of uptake kinetics. Metal desorption using acidified thiourea solutions allows maintaining sorption efficiency for at least four successive cycles with limited loss in sorption capacity.

English

A positive laccase strain which showed a positive reaction with guaiacol was isolated from Chettaba Forest, which is situated in Constantine, the East of Algeria. It was identified as Chaetomium species (Ref 051A) according to the morphological and ribosomal internal transcribed spacer (ITS) DNA genomic sequence analysis. Laccase activity was determined by using 2,2-azinobis(3- ethylbenzthiazoline-6-sulfonate) diammonium salt (ABTS) as a substrate. Its highest activity was achieved by using potato dextrose broth (PDB) as a culture medium. Metal ion CuSO 4 had no positive effect on laccase production. The laccase activity obtained in submerged fermentation (20 L) was higher than that produced in Erlenmeyer flask (500 ml). The study of pH and temperature effects showed that pH optimum was 5 and 6, and temperature was 35°C. Laccase produced by Chaetomium spp. can be used in industrial production. Keywords: Chaetomium species, guaicol, laccase, 2,2-azinobis(3- ethylbenzthiazoline-6-sulfonate) diammonium salt (ABTS), submerged fermentation

Constant-pH MD Simulations of DMPA/DMPC Lipid Bilayers.

Current constant-pH molecular dynamics (CpHMD) simulations provide a proper treatment of pH effects on the structure and dynamics of soluble biomolecules like peptides and proteins. However, addressing such effects on lipid membrane assemblies has remained problematic until now, despite the important role played by lipid ionization at physiological pH in a plethora of biological processes. Modeling (de)protonation events in these systems requires a proper consideration of the physicochemical features of the membrane environment, including a sound treatment of solution ions. Here, we apply our recent CpHMD-L method to the study of pH effects on a 25% DMPA/DMPC bilayer membrane model, closely reproducing the correct lipid phases of this system, namely, gel-fluid coexistence at pH 4 and a fluid phase at pH 7. A significant transition is observed for the membrane ionization and mechanical properties at physiological pH, providing a molecular basis for the well-established role of phosphatidic acid (PA) as a key player in the regulation of many cellular events. Also, as reported experimentally, we observed pH-induced PA-PA lipid aggregation at acidic pH. By including the titration of anionic phospholipids, the current methodology makes possible to simulate lipid bilayers with increased realism. To the best of our knowledge, this is the first simulation study dealing with a continuous phospholipid bilayer with pH titration of all constituent lipids.

Preparation of activated carbon from peanut shell by conventional pyrolysis and microwave irradiation-pyrolysis to remove organic dyes from aqueous solutions

Activated carbon samples were prepared from peanut shell by conventional pyrolysis (P sample) and microwave irradiation followed by pyrolysis (MW-P sample). These samples as well as peanut shell were characterized by N2 adsorption/desorption isotherms (BET), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM), being applied to remove Direct Black 38 (DB38) and Reactive Red 141 (RR141) dyes from aqueous solutions. In order to evaluate the performance of adsorption process, pH effect, kinetic, equilibrium and desorption studies were carried out in this work. It was found that the MW-P sample exhibited superior characteristics such as texture, surface area, pore volume and pore size than the peanut shell and P sample. In addition, MW-P presented higher values of adsorption capacity, mainly at pH 2.5. The pseudo-second order kinetic model was suitable to represent the adsorption of DB38 and RR141 dyes on the MW-P sample. The Sips isotherm model was adequate to represent the adsorption of DB38 and RR141 on the MW-P sample, being the maximum adsorption capacities of 110.6 and 284.5mgg−1, respectively. The dyes were desorbed from MW-P sample using an alkaline solution. The results demonstrated that the microwave irradiation followed by pyrolysis is an alternative way to prepare an activated carbon with interesting characteristics and high adsorption capacities for organic dyes.

Charge Distribution and the Interactive Effect of pH and Ionic Strength on Phosphate Adsorption Properties of Two Benchmark Soils from Botswana

The constraint imposed by phosphate (PO4) deficiency on soil fertility in Botswana necessitated the study of ionic strength (μ) and pH effects on electric charge distribution and PO4 adsorption of two representative soils: Typic Pellustert and Typic Haplustalf. Electric charge increased with increasing soil pH, but the effect of µ on electric charge distribution was indistinct. The point-of-zero-salt-effect (PZSE) occurred at pH 4.8 in the Pellustert and at almost 6.0 in the Haplustalf. Ionic strength decreased PO4 adsorption in the Pellustert, but increased it in the Haplustalf. The Scatchard and reciprocal linearization of the Langmuir model adequately described PO4 adsorption of the soils under varying µ and pH × µ conditions. The PO4 adsorption maxima (M) and affinity index (b) decreased with increasing µ in the Pellustert, but not in the Haplustalf. The decreasing M and b with increasing µ in the Pellustert was explained by electrostatic repulsion from the highly negative charge surface, whereas the increasing M and b with increasing µ in the Haplustalf was attributed to enhanced access to the surface sorption sites due to compression of diffuse double layer. Under varying pH × µ conditions, PO4 sorption sites were resolved into low- and high-energy sites, depending on the concentration of added PO4. Because b is related to the ease of PO4 detachment from soil surfaces into solution for plant uptake or leaching, PO4 added to this Pellustert at µ > 0.01 would likely leach freely, and hence µ monitoring is imperative for PO4 fertilization strategy of this Pellustert.

Prediction of pH dependent absorption using in vitro, in silico, and in vivo rat models: Early liability assessment during lead optimization

Weakly basic compounds which have pH dependent solubility are liable to exhibit pH dependent absorption. In some cases, a subtle change in gastric pH can significantly modulate the plasma concentration of the drug and can lead to sub-therapeutic exposure of the drug. Evaluating the risk of pH dependent absorption and potential drug–drug interaction with pH modulators are important aspects of drug discovery and development. In order to assess the risk around the extent of decrease in the systemic exposure of drugs co-administered with pH modulators in the clinic, a pH effect study is carried out, typically in higher species, mostly dog. The major limitation of a higher species pH effect study is the resource and material requirement to assess this risk. Hence, these studies are mostly restricted to promising or advanced leads. In our current work, we have used in vitro aqueous solubility, in silico simulations using GastroPlus™ and an in vivo rat pH effect model to provide a qualitative assessment of the pH dependent absorption liability. Here, we evaluate ketoconazole and atazanavir with different pH dependent solubility profiles and based on in vitro, in silico and in vivo results, a different extent of gastric pH effect on absorption is predicted. The prediction is in alignment with higher species and human pH effect study results. This in vitro, in silico and in vivo (IVISIV) correlation is then extended to assess pH absorption mitigation strategy. The IVISIV predicts pH dependent absorption for BMS-582949 whereas its solubility enhancing prodrug, BMS-751324 is predicted to mitigate this liability. Overall, the material requirement for this assessment is substantially low which makes this approach more practical to screen multiple compounds during lead optimization.

HLA-DO inhibition of HLA-DM catalytic function is regulated by acid-promoted HLA-DO inactivation (APP5P.106)

Abstract CD4+ T cells recognize MHC-II-peptides, whose generation is controlled by HLA-DM and its inhibitor, HLA-DO. Activation of DM-DO-expressing cells alters DO:DM in favor of active DM, but the molecular mechanism(s) underlying this process are unclear. DM is known to catalyze exchange of MHC-II-associated invariant chain peptides (CLIP) for antigenic peptides. As expected, We identified the positive correlation between the total CLIP level and DO:DM, and confirmed sufficient DM inhibition in high DO:DM cells. Importantly, super-resolution microscopy shows co-localization of CLIP with only the early endsomal marker but not the lysosomal marker in these cells, indicating the pH regulation of DM inhibition by DO and the presence of active DM in lysosomes. We demonstrated that acid-expose of DM-DO complexes yields active DM, and isolated free functional DM ectodomains using size exclusion chromatography. The study of pH-effects on the interaction between soluble DM and a stabilized DO equivalent (DOaP11A) indicates that the generation of active DM from DM-DO complexes is mainly due to acid-promoted DO denaturation. It is also suggested that free DM ectodomains are subjected to acid-promoted inactivation. Therefore, association by DO may regulate the endosomal pH range of DM activity while extending DM active life span at the lysosomal pH condition. Acidification of endosomes will down-regulate DO:DM via acid-promoted DO inactivation for efficient DM catalysis.

Retention of samarium ions from aqueous solutions by poly(acrylic acid)-enhanced ultrafiltration

Rare earth elements (REE) are widely used in variety of commercial applications, which results in public exposure to them, and it is a matter of concern. Recent studies have demonstrated that the toxicity of (REE) as a group is similar to the toxicity of heavy metals. Many methods were used to remove lanthanides from wastewaters generated from their commercial use. Samarium, a REE, which may be removed from the aqueous solution by polyelectrolyte-enhanced ultrafiltration process, was investigated using poly(acrylic acid) (PAA) with average molecular weight 100,000 Da. The ultrafiltration studies were carried out using a tangential cell system. Polyethersulfone membrane with molecular weight cutoff of 5,000 Da and an effective filtration area of 50 cm2 were used (PES-5). Several parameters, such as transmembrane pressure, PAA concentrations, and pH, have been optimized to improve the retention of the Sm(III) ions. Results shows that the permeate flux increases linearly with increasing transmembrane pressure. It can be seen that with the increase in the concentration of PAA, the Sm(III) ions retention also increases until reaching 80%. A better retention was observed at 2 × 10−4 mol L−1 PAA concentration and 3 bar transmembrane pressure. The pH effect study on samarium ions revealed a maximum retention around 70% for pH 5.

A Combination Turbidity and Supernatant Microplate Assay to Rank‐Order the Supersaturation Limits of Early Drug Candidates

A unique opportunity exists at the drug discovery stage to overcome inherently poor solubility by selecting drug candidates with superior supersaturation propensity. Existing supersaturation assays compare either precipitation‐resistant or precipitation‐inhibiting excipients, or higher‐energy polymorphic forms, but not multiple compounds or multiple concentrations. Furthermore, these assays lack sufficient throughput and compound conservation necessary for implementation in the discovery environment. A microplate‐based combination turbidity and supernatant concentration assay was therefore developed to determine the extent to which different compounds remain in solution as a function of applied concentration in biorelevant media over a specific period of time. Dimethyl sulfoxide stock solutions at multiple concentrations of four poorly soluble, weak base compounds (Dipyridamole, Ketoconazole, Albendazole, and Cinnarizine) were diluted with pH 6.5 buffer as well as FaSSIF. All samples were monitored for precipitation by turbidity at 600 nm over 1 h and the final supernatant concentrations were measured. The maximum supersaturation ratio was calculated from the supersaturation limit and the equilibrium solubility in each media. Compounds were rank‐ordered by supersaturation ratio: Ketoconazole > Dipyridamole > Cinnarizine ∼ Albendazole. These in vitro results correlated well with oral AUC ratios from published in vivo pH effect studies, thereby confirming the validity of this approach. © 2014 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci 103:3022–3032, 2014

Metabolism and Pharmacokinetics of the Anti-Hepatitis C Virus Nucleotide Prodrug GS-6620

The anti-hepatitis C virus nucleotide prodrug GS-6620 employs a double-prodrug approach, with l-alanine-isopropyl ester and phenol moieties attached to the 5'-phosphate that release the nucleoside monophosphate in hepatocytes and a 3'-isobutyryl ester added to improve permeability and oral bioavailability. Consistent with the stability found in intestinal homogenates, following oral administration, intact prodrug levels in blood plasma were the highest in dogs, followed by monkeys, and then were the lowest in hamsters. In contrast, liver levels of the triphosphate metabolite at the equivalent surface area-adjusted doses were highest in hamsters, followed by in dogs and monkeys. Studies in isolated primary hepatocytes suggest that relatively poor oral absorption in hamsters and monkeys was compensated for by relatively efficient hepatocyte activation. As intestinal absorption was found to be critical to the effectiveness of GS-6620 in nonclinical species, stomach pH, formulation, and food effect studies were completed in dogs. Consistent with in vitro absorption studies in Caco-2 cells, the absorption of GS-6620 was found to be complex and highly dependent on concentration. Higher rates of metabolism were observed at lower concentrations that were unable to saturate intestinal efflux transporters. In first-in-human clinical trials, the oral administration of GS-6620 resulted in poor plasma exposure relative to that observed in dogs and in large pharmacokinetic and pharmacodynamic variabilities. While a double-prodrug approach, including a 3'-isobutyryl ester, provided higher intrinsic intestinal permeability, this substitution appeared to be a metabolic liability, resulting in extensive intestinal metabolism and relatively poor oral absorption in humans.

Resistance to heavy metals and bioaccumulation of lead and zinc by Chryseobacterium solincola strain 1YB-R12T isolated from soil

A novel species of the genus Chryseobacterium which was isolated from soil, has been studied for resistance to heavy metals (lead, chromium, nickel, zinc, cadmium, copper and cobalt), antibiotic and its capacities for bioaccumulation of lead and zinc. It exhibited high minimal inhibitory concentration (MIC) values for metal ions tested ranging from 75 mg/l to 500 mg/l and antibiotic resistance to imipenem, cefuroxim, tetracyclin, nalidixic acid, fusidic acid, pipemidic acid, fosfomycin, cefalotin, dibekacin, furans and nitrofurantoin. The strain was able to accumulate more than 90% of lead and zinc during the active growth cycle. Study of pH effect on heavy metal removal indicated that the metal ion accumulation increased with increasing pH. Since Chryseobacterium solincolacouldgrow at the presence of significant concentrations of toxic metals and because of its high metal accumulation capacity in aerobic conditions, may be potentially applicable in situ bioremediation of heavy metals contaminating aqueou...

Formation and inhibition of bromate during ferrate(VI) – Ozone oxidation process

To investigate the feasibility of minimizing the bromate formation with ferrate(VI) during ozonation process, the batched experiments were carried out under several operating variables, such as ferrate(VI) dose (0–5.0mg/L), initial bromide concentration (100–1500μg/L), ozone concentration (1.5, 2.5 and 4.0mg/L), pH (3.0–11.0), temperature (278K, 298K and 313K) and reaction time (0–60min). Compared with ozone oxidation, ferrate(VI)–ozone process can effectively inhibit the bromate formation. Bromate formation can be completely inhibited under the following conditions: ferrate(VI) dose of 1.0 or 2.0mg/L, [O3]⩽2.5mg/L, [Br−]⩽200μg/L, pH⩽9.0 and temperature⩽313K. The inhibiting mechanism took effect by the produced intermediates of ferrate(VI), such as Fe(III), Fe(II), H2O2 and the hydroxides of Fe(III), which had reduction or flocculation effects on BrO3- or HBrO/BrO− that resulted in less bromate formation, and it was further proved by the effect of radical scavenger (t-BuOH). The pH effect study revealed that ferrate(VI) could depress the concentration of bromate below the drinking water standard (10μg/L) in the wide pH range of 3.0–11.0. High ambient temperature also showed a positive effect on the inhibition of bromate formation in ferrate(VI)-ozone process.

PH in atomic scale simulations of electrochemical interfaces

Electrochemical reaction rates can strongly depend on pH, and there is increasing interest in electrocatalysis in alkaline solution. To date, no method has been devised to address pH in atomic scale simulations. We present a simple method to determine the atomic structure of the metal|solution interface at a given pH and electrode potential. Using Pt(111)|water as an example, we show the effect of pH on the interfacial structure, and discuss its impact on reaction energies and barriers. This method paves the way for ab initio studies of pH effects on the structure and electrocatalytic activity of electrochemical interfaces.

A study of pH effects on the bacterial surface physicochemical properties of Acinetobacter baumannii

The first step in the biofilm formation is the bacterial attachment to solid surfaces, which is dependent on the bacteria cell surface physico-chemical properties. The purpose of this work was to analyze the effect of pH on the physicochemical cell surface properties of Acinetobacter baumannii by two different methods. The cell surface properties were evaluated using the microbial adhesion to solvents method (MATS) and contact angle measurements (CAM). MATS technique allowed us to enlighten that A. baumannii was hydrophilic at the different values of pH. It was found that at a desired pH of 6.5, the strain presents a maximum and stable value of electron-donor characteristic, while the electron acceptor character increased as the pH increased. Regardless of the methods employed, the obtained results using MATS and CAM confirmed the influence of the pH on the surface physicochemical properties of A. baumannii. The cell surface electron-donor and electron-acceptor character at pH 6.5 was found to be quite similar using both methods.

New colorimetric chemosensor bearing naphthalendiimide unit with large blue-shift absorption for naked eyes detection of Cu2+ ions

Abstract A naphthalendiimide-based chemosensor was designed for naked-eye detection of Cu 2+ , which displayed high selectivity in the presence of other competitive metal ions. The Cu 2+ recognition gave rise to apparent red-to-yellow color change with the blue-shift maximum absorption wavelength as large as 80 nm, through the intramolecular charge transfer mechanism. The pH effect studies indicated that it can be applied to the analysis of samples from mildly acidic to basic environments.

Photophysical study of some 3-benzoylmethyleneindol-2-ones and estimation of ground and excited states dipole moments from solvatochromic methods using solvent polarity parameters

► Photophysical studies of 3-benzoylmethyleneindol-2-ones in a series of different solvents. ► Ground and excited states dipole moments. ► Analysis of the ground and excited state processes. ► Study of pH effect on 3-benzoylmethyleneindol-2-ones. 3-Benzoylmethyleneindol-2-ones, isatin based chalcones containing donor and acceptor moieties that exhibit excited-state intramolecular charge transfer, have been studied in different solvents by absorption and emission spectroscopy. The excited state behavior of these compounds is strongly dependent on the nature of substituents and the environment. These compounds show multiple emissions arising from a locally excited state and the two states due to intramolecular processes viz. intramolecular charge transfer (ICT) and excited state intramolecular proton transfer (ESIPT). Excited-state dipole moments have been calculated using Stoke-shifts of LE and ICT states using solvatochromic methods. The higher values of dipole moments obtained lead to support the formation of ICT state as one of the prominent species in the excited states of all 3-benzoylmethyleneindol-2-ones. The correlation of the solvatochromic Stokes-shifts with the microscopic solvent polarity parameter ( E T N ) was found to be superior to that obtained using bulk solvent polarity functions. The absorption and florescence spectral characteristics have been also investigated as a function of acidity and basicity (Ho/pH) in aqueous phase.

Adsorption of phenol from aqueous solutions using activated carbon prepared from crofton weed

Abstract Activated carbon derived from crofton weed (ACCW) was evaluated for its ability to remove phenol from an aqueous solution. The kinetics study, adsorption isotherm, pH effect, and thermodynamic study were examined in batch experiments. Adsorption data for phenol uptake by ACCW were analyzed according to Langmuir, Freundlich and Temkin adsorption models. Thermodynamic parameters for the adsorption system were determined at 293 K, 313 K and 333 K (ΔH° = −22.92 kJ mol−1; ΔG° = −2.87 to −5.28 kJ mol−1 and ΔS° = −60.20 J/K·mol). ΔG° v alues obtained were negative, indicated that the adsorption of the phenol on the surface of ACCW was a spontaneous adsorption process. The kinetics process can be described by a pseudosecond-order rate equation very well. These results show that the ACCW could be considered as a potential adsorbent for phenol in aqueous solutions.

Study of pH effects on the evolution of properties of brown-water natural organic matter as revealed by size-exclusion chromatography during photocatalytic degradation

This study shows the effect of pH on the photocatalytic degradation of natural organic matter (NOM). The experiments were carried out in batch reactor (a solar UV-light simulator) with Degussa P-25 titanium dioxide (TiO 2). The NOM degradation was followed by size-exclusion chromatography for dissolved organic carbon (DOC), ultraviolet absorption and fluorescence-detection (SEC-DOC, SEC-UV 254 and SEC-Fl 254/450). Changes in pH values affected the adsorption of NOM onto TiO 2, but did not affect the photodegradation sequence of NOM. For high or low pH values, the degradation of the NOM preferentially removed the larger molecular size fraction in comparison to the middle and small molecular size fractions, resulting in the relative increase of these smaller fractions. This sequence of NOM degradation leads to the evolution of the formation potential for disinfection by-products (DBPs). Specifically, the trihalomethanes and halogenated organic compounds formation potential (THMF and AOXFP) decreased steadily.

Fluorescence and Raman Study of pH Effect on the Adsorption Orientations of Methyl Red on Silver Colloids

We report the fluorescence and surface-enhanced Raman scattering (SERS) analysis of methyl red (MR) isomers (o-MR, m-MR, p-MR) on silver (Ag) colloids at different pH conditions. The changes in simultaneous fluorescence quenching around 400 nm accompanied by enhancement around 540 nm with pH are closely related to energy transfer efficiency and the interaction between the carboxylic group and the Ag surface. The change of SERS signals with pH values can be ascribed to different adsorption orientations of MR on the Ag surface, from near flat (o-MR) to near perpendicular (p-MR).