UMLS:C0847097 - FACTA Search

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Query: UMLS:C0847097 (acidity)
15,165 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The physical, electrophoretic and chromatographic properties (mean diameter, electroosmotic flow, electrophoretic mobility, elution range, efficiency, retention, and hydrophobic, shape, and chemical selectivity) of three surfactant vesicles and one phospholipid vesicle were investigated and compared to a conventional micellar pseudostationary phase comprised of sodium dodecyl sulfate (SDS). Chemical selectivity (solute-pseudostationary phase interactions) was discussed from the perspective of linear solvation energy relationship (LSER) analysis. Two of the surfactant vesicles were formulated from nonstoichiometric aqueous mixtures of oppositely charged, single-tailed surfactants, either cetyltrimethylammonium bromide (CTAB) and sodium octyl sulfate (SOS) in a 3:7 mole ratio or octyltrimethylammonium bromide (OTAB) and SDS in a 7:3 mole ratio. The remaining surfactant vesicle was comprised solely of bis(2-ethylhexyl)sodium sulfosuccinate (AOT) in 10% v/v methanol, and the phospholipid vesicle consisted of 1-palmitoyl-2-oleyl-sn-glycero-3-phosphocholine (POPC) and phosphatidyl serine (PS) in 8:2 mole ratio. The mean diameters of the vesicles were 76.3 nm (AOT), 86.9 nm (CTAB/SOS), 90.1 nm (OTAB/SDS), and 108 nm (POPC/PS). Whereas the coefficient of electroosmotic flow (10(-4) cm2 V(-1) s(-1)) varied considerably (1.72 (OTAB/SDS), 3.77 (CTAB/SOS), 4.05 (AOT), 5.26 (POPC/PS), 5.31 (SDS)), the electrophoretic mobility was fairly consistent (-3.33 to -3.87 x 10(-4) cm2 V(-1) s(-1)), except for the OTAB/SDS vesicles (-1.68). This resulted in elution ranges that were slightly to significantly larger than that observed for SDS (3.12): 3.85 (POPC/PS), 8.6 (CTAB/SOS), 10.1 (AOT), 15.2 (OTAB/SDS). Significant differences were also noted in the efficiency (using propiophenone) and hydrophobic selectivity; the plate counts were lower with the OTAB/SDS and POPC/PS vesicles than the other pseudostationary phases (< or = 75,000/m vs. > 105,000/m), and the methylene selectivity was considerably higher with the CTAB/SOS and OTAB/SDS vesicles compared to the others (ca. 3.10 vs. < or = 2.6). In terms of shape selectivity, only the CTAB/SOS vesicles were able to separate all three positional isomers of nitrotoluene with near-baseline resolution. Finally, through LSER analysis, it was determined that the cohesiveness and hydrogen bond acidity of these pseudostationary phases have the greatest effect on solute retention and selectivity.
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PMID:Characterization of surfactant and phospholipid vesicles for use as pseudostationary phases in electrokinetic chromatography. 1467 70

As an objective method, taste evaluation with an instrument is able to supplement the subjective sensory evaluation and to be applied to the optimization of food processing. Kimchi, a Korean traditional pickle fermented with lactic acid bacteria, is expanding its consumption worldwide. The fermentation control of it has been routinely done by measuring titratable acidity and pH. In this study, an eight-channel taste evaluation system was prepared, followed by an application to the monitoring of Kimchi fermentation. Eight polymer membranes which individually responded to cationic or anionic substances were prepared by mixing electroactive materials such as tri-n-octylmethylammonium chloride, bis(2-ethylhexyl)sebacate as the plasticizer and polyvinyl chloride in the ratio of 1:66:33. Each membrane prepared was separately installed onto the sensitive area of an ion-selective electrode to produce the respective taste sensor. The eight-channel sensor array and a double junction reference electrode were connected to a 16-channel high input impedance amplifier. The amplified sensor signals were stored to a personal computer via a multi-channel A/D converter. Two sensor groups composed of the cation-selective and anion-selective polymer membrane electrodes showed characteristic concentration-dependency to various artificial taste substances. As a whole, the response potentials of the sensor array increased during the fermentation period at 4, 10 and 25 degrees C. Even the response potentials of the anion-selective taste sensors slightly increased possibly due to the protonation of anions by liberated H+ ions, thereby leading to a decrease in the anion concentration. When the signal data were interpreted by principal component analysis (PCA), the first PC at 4 degrees C explained most of the total data variance. A close correlation was found between the values of titratable acidity and the first PC, which indicated a possible applicability of the multi-channel taste sensor of this study to the process monitoring of various pickle.
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PMID:Application of a taste evaluation system to the monitoring of Kimchi fermentation. 1579 27

A conceptual flowsheet has been developed for the separation of (177)Lu from a 300 mg neutron irradiated (176)Yb enriched target. The key component of the process is an extraction chromatographic (EXC) resin containing 2-ethylhexyl 2-ethylhexylphosphonic acid (HEH[EHP]) sorbed onto a 25-53 microm Amberchrom CG-71 substrate. The process is divided into three sections: (1) front-end target removal system, (2) primary separation system and (3) secondary separation system. Each section involves the separation of Yb and Lu using the HEH[EHP] resin followed by concentration and acid adjustment of the Lu-rich eluate using an EXC material containing a diglycolamide extractant. The use of the diglycolamide EXC material is a significant feature of the flowsheet, allowing one to avoid lengthy evaporations and acidity adjustments between successive HEH[EHP] column runs while removing adventitious impurities from the (177)Lu. The overall recovery of (177)Lu is estimated at 73% with an overall decontamination factor from Yb of 10(6). The overall processing time can be as short as 4h.
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PMID:A process for the separation of 177Lu from neutron irradiated 176Yb targets. 1586 44

In this paper, the interaction between 2-sulfophenylazo-rhodanine and protein was investigated by Rayleigh light-scattering technique. Based on this, a novel method for the determination of protein was developed. The effects of different conditions, such as acidity and media, were investigated thoroughly, and the optimum conditions were confirmed. Bis(2-ethylhexyl)sulfosuccinate (AOT) microemulsion, which is introduced into the protein determination, markedly increased the sensitivity of the system by changing the microenvironment. In pH 2.80 Britton-Robinson buffer solution in the presence of AOT microemulsion, the detection limits of bovine serum albumin, human serum albumin, ovalbumin, and gamma-globulin are 5.4, 4.5, 9.8, and 10.1 ng/mL, respectively. The method developed in this paper has been applied to the determination of protein in milk powder with satisfactory results.
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PMID:Determination of protein in milk powder using 2-sulfophenylazo-rhodanine as a probe by the enhanced resonance Rayleigh light-scattering technique. 1704 87

A kinetic study was carried out on the acid hydrolysis of 4-nitrophenylacetate and 4-nitrophenyllaurate in water/HOT/isooctane microemulsions. The substitution of Na+ in the sodium salt of bis(2-ethylhexyl)sulfosuccinate by H+ has permitted us to obtain a functionalized surfactant (HOT) and, consequently, strongly acid microemulsions. The use of HOT-based microemulsions allows us to reach concentrations of H+ in the aqueous core corresponding to a Hammett acidity function of H0 = -2. The rate constant at the interface and the distribution constants of the carboxylic esters throughout the different microenvironments of the microemulsion have been quantified by application of the pseudophase formalism. The results obtained show that the hydrolysis rate constant at the interface increases as the water content of the system decreases. The correlation of the rate constants at the interface of the microemulsion with the Hammett acidity function, H0 (on the basis of the Bunnett-Olsen criterion), has allowed us to confirm that the hydrolysis process takes place via an A2 mechanism for high water contents and through an A1 mechanism for values of W <or= 15 (W = [H2O]/[HOT]).
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PMID:Change in the acid hydrolysis mechanism of esters enforced by strongly acid microemulsions. 1785 67

An ion-exchange process has been used to prepare HOT from NaOT (sodium bis(2-ethylhexyl)sulfosuccinate), where the Na(+) counterion has been replaced by H(+). The acidity function, H(0), of the aqueous core of HOT-based microemulsions decreases with W from H(0) approximately 0.6 at W>20 to H(0)=-1.4 at W=2. On the basis of the H(0) acidity function of the aqueous core and the dependence of H(0) on acid concentration, we have been able to determine the degree of counterion binding (beta) in microemulsions with a value of beta approximately 0.92 which is practically independent of the water content of the system.
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PMID:Degree of counterion binding on water in oil microemulsions. 1791 61

Permeation of seven lanthanides (Ln) and thorium through a supported liquid membrane containing di-(n- octyl)phosphoric (DOPA) or di-(n-pentyl)phosphoric (DPPA) acid as a carrier has been studied as a function of the chemical composition of the system. The results have been compared with a previous study in which di-(2-ethylhexyl)phosphoric acid was used. Metal cations were transported from feed solutions of pH 1.1-4.8 (HNO(3)) into strip solutions of 0.015-0.1 mol l(-1) nitric acid. The ionic strength was kept constant at 0.1 mol l(-1) (HNO(3), KNO(3)). The initial lanthanide concentration and carrier concentration in the liquid membrane were varied from 0.5 to 500 mumol l(-1) and from 0.01 to 0.5 mol l(-1) respectively. To describe the mass transfer of metal cations, permeability coefficients have been determined by inductively-coupled plasma atomic emission spectroscopy or by on-line flow-injection analysis of metal concentrations in strip or feed solution. Probably as the result of a higher solubility of the carrier in aqueous media, transport of Ln with DPPA was not observed. By using DOPA, La, Ce, Pr, and Nd permeated through the membrane while transport of heavier Ln was partly or totally suppressed. This enables these four Ln (separation factor alpha = 3.0 for Nd and Sm) to be separated from the others. Furthermore, at a very low acidity gradient, only La (III) is transported over the membrane (alpha >/= 3.4 for La, Ce and next Ln). The seven elements from La to Tb can be separated from Th(IV) because no evidence of its permeation through the membrane was found under the conditions of Ln transport. In contrast to previous studies on Ln transport with dialkylphosphoric acid carrier, the possibility of participation of species other than Ln(AHA)(3) in the transport has been discussed. The decrease of permeability observed at higher Ln concentrations and higher pH of the feed solution has been explained as the result of formation of species, e.g. polymeric ones, that are unable to permeate through the membrane.
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PMID:Dialkylphosphoric acids as carriers in separation of lanthanides and thorium on supported liquid membranes. 1896 31

The binding properties of neutral or charged chromoionophores and anion ionophores in solvent polymeric membranes were characterized in situ by the so-called sandwich membrane method. Acidity constants (pK(a)) of eight chromoionophores (ETH 5294, ETH 2439, ETH 5350, ETH 5418, ETH 5315, ETH 7061, ETH 7075, ETH 2412) were measured in bis(2-ethylhexyl)sebacate (DOS) and o-nitrophenyloctylether (NPOE) plasticized poly(vinyl chloride) (PVC) membranes commonly used in optical and potentiometric ion sensors. The pK(a) values of all chromoionophores in DOS membranes are by 2-3 orders of magnitude smaller than in NPOE membranes. The weak alkali metal ion binding properties with neutral H(+)-chromoionophore and anion binding with electrically charged chromoionophores were also studied quantitatively. The complex formation constants of the commercially available Co(III)cobyrinate nitrite ionophore and the organomercury chloride ionophore, ETH 9009, were also measured. The very low stability constant observed for ETH 9009 (logbeta(2)=3.60+/-0.03 in PVC-DOS and 3.61+/-0.01 in PVC-NPOE) was explained by the decomposition of the ionophore in contact with chloride samples. On the other hand, the electrically charged nitrite ionophore showed strong complexation with nitrite ions, with logbeta=10.58 and 10.59 in DOS and NPOE membranes, respectively. In contrast to cation ionophores, the stability constant of the NO(2)(-) ionophore does not change with different plasticizers.
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PMID:Quantitive binding constants of H(+)-selective chromoionophores and anion ionophores in solvent polymeric sensing membranes. 1896 23

A new chelating polymeric sorbent has been developed using Merrifield chloromethylated resin anchored with di-bis (2-ethylhexyl) malonamide (DB2EHM). The modified resin was characterized by (13 )C CPMAS NMR spectroscopy, FT-NIR-FIR spectroscopy, CHN elemental analysis and also by thermo gravimetric analysis. The fabricated sorbent showed superior binding affinity for U(VI) over Th(IV) and other diverse ions, even under high acidities. Various physio-chemical parameters, like solution acidity, phase exchange kinetics, metal sorption capacity, electrolyte tolerance studies, etc., influencing the resin's metal extractive behavior were studied by both static and dynamic method. Batch extraction studies performed over a wide range of solution acidity (0.01-10M) revealed that selective extraction of U(VI) could be achieved even up to 4M acidity with distribution ratios (D) in the order of approximately 10(3). The phase exchange kinetics studies performed for U(VI) and Th(IV) revealed that time duration of <15min was sufficient for >99.5% extraction. But similar studies when preformed for trivalent lanthanides gave very low D values (<50), with the extraction time extending up to 60min. The metal sorption studies performed for U(VI) and Th(IV) at 5M HNO(3) was found to be 62.5 and 38.2mgg(-1),respectively. Extraction efficiency in the presence of inferring electrolyte species and inorganic cations were also examined. Metal ion desorption was effective using 10-15mL of 1M (NH(4))(2)CO(3) or 0.5M alpha-hydroxy isobutyric acid (HIBA). Extraction studies performed on a chromatographic column at 5M acidity were found to give enrichment factor values of 310 and 250 for U(VI) and Th(IV), respectively. The practical utility of the fabricated chelating sorbent and its efficiency to extract actinides from acidic waste streams was tested using a synthetic nuclear spent fuel solution. The R.S.D. values obtained on triplicate measurements (n = 3) were within 5.2%.
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PMID:Selective extraction of U(VI) over Th(IV) from acidic streams using di-bis(2-ethylhexyl) malonamide anchored chloromethylated polymeric matrix. 1896 81

Small amounts of polyvinyl alcohol (PVA; 0.5-1.5 wt.%) added to extraction resin was synthesized by suspension polymerization. Their effects on the separation of rare earths (RE) were then investigated by conducting a relative comparison with the performance of pure extraction resin. The supporter and extractant of extraction resin were styrene-divinyl benzene copolymer and 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (HEH[EHP]), respectively. The size of PVA added extraction resin was reduced by 40% particle size of pure extraction resin. Furthermore, a higher level of PVA addition, shorter effluent range and smaller resolution values were shown in the extraction. In constant PVA added extraction resin, more diluted effluent concentration, longer effluent range and bigger resolution values were shown in the extraction. This could be the result of the bonding force between the rare earths and the extraction resin due to the nature of the interaction between the OH(-) group in PVA and the OH(-) group in extractants such as HEH[EHP]. Thus, the bonding force between the RE and extractants was determined by the level of PVA in the resins and the acidity of the effluent solution became another important factor in the extraction performance of the rare earths. As a result, the optimal level of PVA addition and the concentration of effluent for RE (Gd and Tb) separation were determined to be 0.5 wt.% of PVA and 0.05 M HCl of effluent, respectively.
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PMID:Effect of polyvinyl alcohol on rare earths (Gd and Tb) separation by extraction resin. 1897 Apr 17

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