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It has been established that the correct choice of the plasticizer and the measurement conditions makes it possible to achieve better analytical characteristics of verapamil-sensitive electrodes based on commercially available components in comparison with the best described in the literature. Particularly, the effect of pH on the verapamil-sensitive electrodes response was found to manifest itself in much more acidic media than might be expected from protolytic equilibrium and is due to the non-exchangeable extraction of verapamil into the membrane phase. The best parameters of selectivity, lower detection limit (4 x 10.sup.-8 M), and potential reproducibility (0.15-0.22 mV) are achieved when using ortho-nitrophenyloctyl ether as a plasticizer and creating conditions that exclude non-exchangeable extraction of verapamil into the membrane. The proposed methods for the determination of verapamil in dosage forms are characterized by simplicity, rapidity, and high metrological characteristics., Author(s): Faisal A. Salih [sup.1] [sup.2] , Andrei D. Novakovskii [sup.1] [sup.3] , Vladimir V. Egorov [sup.1] [sup.3] Author Affiliations: (1) grid.17678.3f, 0000 0001 1092 255X, Belarusian State University, Chemistry [...]

This study explores electrochemical interactions of a pharmaceutical drug, kojic acid (5-hydroxy-2-hydroxymethyl-4 H-pyran-4-one, KA), with bioactive iron Fe(III) at different pH systems by using cyclic voltammetric technique. For this study buffers relevant to physiological pH of blood and digestive system have been selected. Bioactive iron was found to form an electroactive complex [Fe(III)L3] in the presence of KA at all studied pH, whereas electrochemical behavior of KA was also changed by complex formation. This electrochemical investigation reveals that under the experimental conditions, [Fe(III)L3] complex undergoes a diffusion controlled, one electron redox process that is quasi-reversible in nature. It was also found that [Fe(III)L3] complex undergoes coupled chemical reaction according to EC (an electron transfer reaction followed by a chemical reaction) mechanism, and this interaction is pH dependent. Modified Nicholson and Shain, Gileadi, and Kochi methods were used to determine standard heterogeneous electron transfer rate constant (k (0) ) of [Fe(III)L3] complex. It was found to be in the range of [10.sup.-3] to [10.sup.-5] cm/s. Key words: kojic acid, bioactive iron Fe(III), cyclic voltammetry, electron transfer reactions, coupled chemical reactions La presente etude explore les interactions electrochimiques d'un medicament pharmaceutique, l'acide kojique (5-hydroxy-2-hydroxymethyl-4H-pyran-4-one; AK), avec le fer sous sa forme bioactive Fe(III) dans des systemes a diferents pH au moyen d'une technique de voltamperometrie cyclique. Dans le cadre de cette etude, nous avons selectionne des tampons compatibles avec les pH physiologiques du sang et du systeme digestif, soit des tampons de pH 4,0, 5,5, 6,0, 6,7, 7,0 et 7,4. L'etude montre que l'ingestion concomitante d'AK et de Fe(III) peut induire des variations marquees de la biodisponibilite des ions Fe(III). Nous avons observe que le fer bioactif forme un complexe electroactif, le [Fe(III)L3], en presence d'AK a toutes les valeurs de pH etudiees et que la formation de ce complexe modifie egalement le comportement electrochimique de l'AK. Le nombre d'electrons (n) impliques dans le processus d'oxydoreduction du complexe [Fe(III)L3] a ete determine a tous les pH etudies et se situe dans la plage de 0,998 a 1,005. Cette etude electrochimique revele que, dans les conditions experimentales, le complexe [Fe(III)L3] subit un processus d'oxydoreduction monoelectronique regi par la diffusion, de nature quasi reversible. Nous avons egalement decouvert que le complexe [Fe(III)L3] subit une reaction chimique couplee selon le mecanisme de transfert d'electron suivi d'une reaction chimique (EC), et que cette interaction est dependante du pH. Nous avons utilise des donnees de voltamperometrie cyclique pour extraire des informations sur la cinetique heterogene du complexe [Fe(III)L3]. La constante de vitesse de transfert electronique heterogene k (0) ) a ete determinee par trois methodes diferentes : la methode Nicholson & Shain modifiee, la methode Gileadi et la methode Kochi. La constante de vitesse heterogene standard se situe entre [10.sup.-3] et [10.sup.-5] cm/s. [Traduit par la Redaction] Mots-cles : acide kojique, fer bioactif Fe(III), voltamperometrie cyclique, reactions de transfert d'electrons, reactions chimiques couplees, 1. Introduction Kojic acid (5-hydroxy-2-hydroxymethyl-4H-pyran-4-one, KA) is a natural organic acid. It is biodegradable, environment friendly, and a fungal secondary metabolite that has been studied extensively by researchers for its [...]

Microfluidic technology has gained significant scientific interest in the characterization of crude oil emulsions that are often formed in the process of oil production. Microfluidic platforms can be used to mimic the pores of natural rock and study multiphase displacement, as well as emulsion formation at a microscale level. This paper focuses on the applications of microfluidics to probe the stability of emulsified droplets against coalescence (e.g., in the presence of additives, electric field) for both water-in-oil (W/O) and oil-in-water (O/W) emulsion systems. Additionally, this study summarizes the recent efforts made to identify the effects of various experimental factors, including crude oil composition, aging, salinity, and pH on the interfacial properties of water-oil interface and their ultimate roles in the formation and stability of emulsions. Finally, main findings and some recommendations for future work related to the potential of microfluidics in different aspects of crude oil emulsion studies are discussed. Key words: microfluidics, oil production, crude oil emulsions, demulsifiers, asphaltenes, coalescence, salinity, interfacial elasticity. Les technologies microfluidiques suscitent un interet scientifique grandissant pour la caracterisation des emulsions de petrole brut qui se forment souvent dans le processus de production du petrole. II est possible d'employer des plateformes microfluidiques pour imiter les pores de la roche naturelle et etudier le deplacement multiphasique, ainsi que la formation d'emulsion a l'echelle microscopique. Dans ce bref article de synthese, nous nous sommes interesses aux applications de la microfluidique pour evaluer la stabilite a la coalescence des gouttelettes emulsifiees (par exemple, en presence d'additifs, de champ electrique, etc.) dans des systemes d'emulsion eau-dans-l'huile (E/H) et huile-dans-l'eau (H/E). Nous resumons egalement dans cette etude les efforts recents deployes pour determiner les effets de divers facteurs experimentaux, dont la composition, le vieillissement, la salinite et le pH du petrole brut sur les proprietes interfaciales a l'interface eau/huile et le role ultime de ces facteurs dans la formation et la stabilite des emulsions. Enfin, nous discutons des principales constatations et nous formulons quelques recommandations pour les travaux futurs quant au potentiel de la microfluidique dans les differents aspects des recherches sur les emulsions de petrole brut. Mots-cles : microfluidique, production de petrole, emulsions de petrole brut, desemulsifiants, asphaltenes, coalescence, salinite et elasticite interfaciale., Introduction Microfluidics is a unique technology, which deals with fluid flow at the microscale. Microfluidic platforms consist of channels with dimensions of 10-100 [micro]m, which manipulate [10.sup.-9] to [10.sup.-18] L [...]

Monte Carlo multi-track chemistry simulations were carried out to study the effects of high dose rates on the transient yields of hydronium ions ([H.sub.3][O.sup.+]) formed during low linear energy transfer (LET) radiolysis of both pure, deaerated and aerated liquid water at 25 [degrees]C, in the interval ~1 ps - 10 [micro]s. Our simulation model consisted of randomly irradiating water with N interactive tracks of 300-MeV incident protons (LET ~ 0.3 keV/[micro]m), which simultaneously impact perpendicularly on the water within a circular surface. The effect of the dose rate was studied by varying N. Our calculations showed that the radiolytic formation of [H.sub.3][O.sup.+] causes the entire irradiated volume to temporarily become very acidic. The magnitude and duration of this abrupt 'acid-spike' response depend on the value of N. It is most intense at times less than ~10-100 ns, equal to ~3.4 and 2.8 for N = 500 and 2000 (i.e., for dose rates of ~1.9 * [10.sup.9] and 8.7 * [10.sup.9] Gy/s, respectively). At longer times, the pH gradually increases for all N values and eventually returns to the neutral value of seven, which corresponds to the non-radiolytic, pre-irradiation concentration of [H.sub.3][O.sup.+]. It is worth noting that these early acidic pH responses are very little dependent on the presence or absence of oxygen. Finally, given the importance of pH for many cellular functions, this study suggests that these acidic pH spikes may contribute to the normal tissue-sparing effect of FLASH radiotherapy. Key words: liquid water, radiolysis, absorbed dose rate, yields (G values), multiple track model, Monte Carlo multi-track chemistry simulations, hydronium and hydroxide ions, pH, acid spike, FLASH effect. Nous avons realise des simulations Monte Carlo de la trajectoire des particules pour etudier les effets de debits de dose eleves sur les rendements transitoires des ions hydronium ([H.sub.3][O.sup.+]) formes lors de la radiolyse a faible transfert d'energie lineaire (TEL) de l'eau liquide pure, dans des conditions degazees et aerees a 25 [degrees]C, dans l'intervalle d'environ 1 ps a 10 [micro]s. Notre modele de simulation consistait a irradier l'eau de maniere aleatoire avec des protons incidents de 300 MeV decrivant N trajectoires interactives (TEL ~ 0,3 keV/[micro]m) et percutant perpendiculairement l'eau sur une surface circulaire. Nous avons etudie l'effet du debit de dose en faisant varier la valeur N. Nos calculs ont montre que la formation radiolytique d'especes [H.sub.3][O.sup.+] provoque temporairement une acidification tres marquee de l'ensemble du volume irradie. L'ampleur et la duree de cette reponse d'acidification abrupte (<< pic d'acidite >>) dependent de la valeur N. L'intensite culmine a des valeurs de temps inferieures a environ 10 a 100 ns, ou le pH se situe a environ 3,4 et 2,8 pour N = 500 et 2000, respectivement (c.-a-d. pour des debits de dose d'environ 1,9 * [10.sup.9] et 8,7 * [10.sup.9] Gy/s, respectivement). A des temps plus longs, le pH augmente progressivement pour toutes les valeurs de N et revient ultimement a la neutralite (pH = 7), ce qui correspond a la concentration non radiolytique des especes [H.sub.3][O.sup.+] presentes avant l'irradiation. Il importe de souligner que ces reponses rapides d'acidification du pH dependent tres peu de la presence ou de l'absence d'oxygene. Enfin, etant donne l'importance du pH dans de nombreuses fonctions cellulaires, cette etude permet de penser que ces pics d'acidite contribuent peut-etre a l'effet d'epargne des tissus sains qui caracterise la radiotherapie FLASH. [Traduit par la Redaction] Mots-cles : eau liquide, radiolyse, debit de dose absorbee, rendements (valeurs G), modele a trajectoires multiples, simulations Monte Carlo de la trajectoire des particules, ions hydronium et hydroxyde, pH, pic d'acidite, effet FLASH., 1. Introduction Understanding the radiation-induced physicochemical processes in aqueous systems is critical for many areas of basic and applied chemistry, biology, medicine, space radiobiology, etc., as well as a variety [...]

The hydrogen ion concentration ([[H.sup.+]]) in intracellular cytoplasmic fluid (ICF) must be maintained in a narrow range in all species for normal protein functions. Thus, mechanisms regulating ICF are of fundamental biological importance. Studies on the regulation of ICF [[H.sup.+]] have been hampered by use of pH notation, failure to consider the roles played by differences in the concentration of strong ions (strong ion difference, SID), the conservation of mass, the principle of electrical neutrality, and that [[H.sup.+]] and bicarbonate ions [HC[O.sub.3.sup.-]] are dependent variables. This argument is based on the late Peter Stewart's physical-chemical analysis of [[H.sup.+]] regulation reported in this journal nearly forty years ago (Stewart. 1983. Can. J. Physiol. Pharmacol. 61:1444-1461. Doi:10.1139/y83-207). We start by outlining the principles of Stewart's analysis and then provide a general understanding of its significance for regulation of ICF [[H.sup.+]]. The system may initially appear complex, but it becomes evident that changes in SID dominate regulation of [[H.sup.+]]. The primary strong ions are [Na.sup.+], [K.sup.+], and [Cl.sup.-], and a few organic strong anions. The second independent variable, partial pressure of carbon dioxide (PC[O.sub.2]), can easily be assessed. The third independent variable, the activity of intracellular weak acids ([[A.sub.tot]]), is much more complex but largely plays a modifying role. Attention to these principles will potentially provide new insights into ICF pH regulation. Key words: strong ion, acid-base, Stewart, buffer, sodium-hydrogen exchanger. La concentration des ions [H.sup.+] ([[H.sup.+]]) dans le liquide intracellulaire (LIC) doit se maintenir a l'interieur d'une fourchette etroite chez toutes les especes pour que les proteines fonctionnement normalement. Par consequent, les modes d'action regulant le LIC sont d'une importance biologique fondamentale. Les etudes portant sur la regulation de la [[H.sup.+]] du LIC ont ete entravees avec l'utilisation de la notation par le pH, l'echec de prendre en compte les roles joues par les differences de concentration des ions forts (IF), la loi de conservation de masse, le principe d'electroneutralite et le fait que la [[H.sup.+]] et la [HC[O.sub.3.sup.-]] constituent des variables dependantes. Cet argument est fonde sur l'analyse physico-chimique portant sur la regulation de la [[H.sup.+]] rapportee dans le journal de feu Peter Stewart il y a pres de quarante ans. Nous commencons par esquisser les principes de l'analyse de Stewart pour ensuite tenter d'aider la comprehension generale sur sa signification quant a la regulation de la [[H.sup.+]] dans le LIC. Le systeme peut de prime abord sembler complexe, mais il devient evident que les variations dans les IF dominent la regulation de la [[H.sup.+]]. Les principaux IF sont les ions [Na.sup.+], [K.sup.+] et [Cl.sup.-], avec quelques anions organiques forts. On peut facilement evaluer la PC[O.sub.2], deuxieme variable independante. La troisieme variable independante que constitue l'activite d'acides faibles intracellulaires ([[A.sub.tot]]) est beaucoup plus complexe, mais joue largement un role de modification. Une attention particuliere a ces principes pourrait eventuellement fournir de nouvelles idees quant a la regulation du pH dans le LIC. [Traduit par la Redaction] Mots-cles : ion fort, acide-base, Stewart, tampon, echangeur sodium-hydrogene., Introduction Close to 40 years ago in this journal the late Peter Stewart laid out the principles of a quantitative physical-chemical approach to understanding the determinants of hydrogen ion concentration [...]

A pH-responsive supramolecular nanoparticles was constructed through the electrostatic interaction from anionic sulfobutyl ether-[beta]-cyclodextrin ([SBE.sub.7]-[beta]-CD) and two positively charged chitosan (CS-75% and CS-95%). The prepared nanoparticles were characterized by UV-vis absorption spectra, x-ray diffraction, dynamic light scattering, transmission electron microscopy, and zeta potential. It was found that the CS/[SBE.sub.7]-[beta]-CD nanoparticles can be disassembly by increasing pH value and reassembled by reducing to the original pH value. To explore the potential of the obtained nanoparticles as a drug delivery vehicle, a negatively charged anticardio cerebrovascular drug sodium ferulate (SF) was loaded. The result indicated that the SF could be efficiently encapsulated in its nanoparticle nucleus under simulated gastric conditions with lower pH (pH 2.0), while effective release is triggered in a simulated intestinal environment with higher pH (pH 8.5). The assembly/disassembly behavior and drug loading/release property make CS/[SBE.sub.7]-[beta]-CD nanoparticles promising candidates for pH stimulation responsive drug delivery system, which has a broad application prospect in the treatment of cardiovascular and cerebrovascular diseases, diabetes and other chronic diseases. KEYWORDS chitosan, pH-controlled release, sodium ferulate, sulfobutyl ether-[beta]- cyclodextrin, supramolecular nanoparticles, 1 | INTRODUCTION In the past few decades, controllable supramolecular nanoassembly constructed by several kinds of weak noncovalent interactions [1,2] have attracted considerable research interest because of their ease of [...]

Electrodes of the composition Ti/TiO.sub.2,SbO.sub.x were obtained by single-stage plasma electrolytic oxidation in aqueous electrolytes with antimony hydroxocomplexes. The surface morphology and composition of TiO.sub.2,SbO.sub.x layers deposited on titanium were studied by scanning electron microscopy, X-ray diffraction analysis, and X-ray photoelectron spectroscopy. The obtained layers contain anatase TiO.sub.2 and up to 1 at % of antimony as Sb.sub.2O.sub.3 and Sb.sub.2O.sub.5. The resulting Ti/TiO.sub.2,SbO.sub.x electrodes were tested as pH sensors. They have close to Nernst electrode function in the pH range from 2 to 10 (53 ± 1 mV/pH). In the acid-base titration of strong (HCl) and weak (CH.sub.3COOH) acids with Ti/TiO.sub.2,SbO.sub.x electrodes, potential jumps are obtained that are not inferior in magnitude to the potential jump for a glass electrode. A possibility of using Ti/TiO.sub.2,SbO.sub.x electrodes to determine the alkalinity of technogenic waters is shown., Author(s): M. S. Vasilyeva [sup.1] [sup.2], V. S. Rudnev [sup.1] [sup.2], N. E. Zabudskaya [sup.1] [sup.2], A. Yu. Ustinov [sup.1] [sup.2], L. A. Zasukhina [sup.1], G. I. Marinina [sup.1] Author [...]

Krill are abundant and ecologically important zooplankton that inhabit dynamic environments characterized by strong natural variability, but global ocean change is shifting the range of conditions that they experience. Laboratory tests reveal that krill are sensitive to ocean acidification despite residing in naturally low pH areas, showing the importance of modulating factors for determining their responses. This study combines laboratory manipulations with field observations across a strong natural water chemistry gradient in Puget Sound, Washington, USA to investigate the effects of pH and oxygen on adult female North Pacific krill, Euphausia pacifica. Enzyme activities of the Electron Transport System (ETS) and aminoacyl-tRNA synthetases (AARS) were used as indices of zooplankton metabolism and growth, respectively, and were paired with traditional incubation methods. Acclimation to pH and oxygen conditions in the laboratory did not reveal effects on respiration rate, ETS, or AARS activity of krill. However, field observations showed that respiratory potential, as estimated by ETS activity, decreased with decreasing oxygen, declining 9% (95% confidence interval 2.5-15%) over the range of conditions we observed (3.9-8.1 mg O.sub.2 L.sup.-1). This reduction would depress the metabolic potential of krill in areas of stressful conditions (concurrent low pH), though krill also displayed a high degree of inter-individual variability. Although differences in age structure suggest different patterns of recruitment between E. pacifica populations in areas with stressful conditions and those without, populations persist at stressful sites. Lower temperature of waters with low oxygen and pH, as well as high food concentrations, may contribute to these populations' success., Author(s): Anna K. McLaskey [sup.1] [sup.2] [sup.3] , Julie E. Keister [sup.3] Author Affiliations: (1) grid.17091.3e, 0000 0001 2288 9830, Institute for the Oceans and Fisheries, University of British Columbia, [...]

Protonated form of poly(sulfonic acid diphenyl aniline) (p-PSDA) was synthesized through oxidative chemical polymerization of sodium salt of diphenylamino-4-sulfonic acid in hydrochloric acid and then, its deprotonated form (PSDA) was obtained by neutralization with aqueous ammonium hydroxide solution. The samples were characterized by thermal analysis and Fourier Transform Infrared, Ultraviolet-visible, ¹H-NMR spectroscopy techniques. Their dispersive surface energies as well as surface acidity and basicity were determined by inverse gas chromatography at temperatures between 313 and 353 K. The dispersive surface energy of p-PSDA was found to be considerably lower but it increased with temperature while that of PSDA was close to those of conventional polymers and decreased slightly with temperature. According to the Schreiber's procedure, the surfaces of p-PSDA and PSDA were found to be acidic and amphoteric, respectively. It was observed from the electron microscope images p-PSDA chains can form self-organized circular polydisperse micro-sized aggregates in aqueous solutions while PSDA cannot self-organize to form individual aggregates., INTRODUCTION The intrinsically conducting polymers (ICP) have been used in the fields of conducting composites, conducting textiles, rechargeable batteries, corrosion protection of metals, ion exchange membranes, photovoltaics, memory devices, light [...]

Reversed phase HPLC separation and isolation of isomers of 3-chloro-2-hydroxy-4-naphthoquinone-1-oxime was investigated. At pH 7 with acetonitrile as a mobile phase, no separation occurs. Using various buffer solutions the pH of the mobile phase was maintained and the effect was studied between pH ~2.5 and ~10.5. Two distinct peaks are observed in chromatograms in the pH range studied. These peaks are assigned to para-tautomer 3,3-chloro-2-hydroxy-4-naphthoquinone-1-oxime and ortho-tautomer 4,3-chloro-4-hydroxy-2-naphthoquinone-1-oxime. Tautomeric equilibrium was found in acidic pH of mobile phase, whereas at pH 6.8 and basic pH of mobile phase the tautomers are well separated from each other. Isolation of the tautomers was carried out by preparative HPLC technique. The solids of tautomers 3 and 4 were obtained as ammonium acetate adducts. Keywords: naphthoquinoneoxime, keto-enol tautomerism, separation of isomers, pH effect, HPLC, 3-chloro-2-hydroxy-4-naphthoquione-1-oxime DOI: 10.1134/S1061934814120144, Naphthoquinones are important constituents of plant families such as Plumbaginaceae, Juglandaceae, Ebenaceae and many commercially important tropical hardwood species. The first report of HPLC separation of non-isoprenoid naphthoquinones was published [...]