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Alkaline Media (alkaline + media)
Selected AbstractsSelective Reduction of Fullerene C60 by Metals in Neutral and Alkaline Media.CHEMINFORM, Issue 18 2003Interaction of C60 with KOH Abstract For Abstract see ChemInform Abstract in Full Text. [source] Cover Picture: Tailored Mesoporosity Development in Zeolite Crystals by Partial Detemplation and Desilication (Adv. Funct.ADVANCED FUNCTIONAL MATERIALS, Issue 1 2009Mater. On page 164, Pérez-Ramírez et al. demonstrate that partial detemplation followed by desilication in alkaline media is a powerful and elegant approach for the design of hierarchical zeolites with a tailored degree of mesoporosity. This achievement, illustrated for large beta crystals, is based on the distinct capability of NaOH to extract silicon in template-containing or template-free regions of the zeolite. The introduced mesoporosity enhances the effectiveness of the materials in catalysis due to shorter diffusion lengths. [source] Kinetic characterization of a transient reaction by degeneration of the precursor mechanism: Application to the synthesis of 3,4-diazabicyclo[4.3.0]- non-2-eneINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 5 2006H. Delalu The rate of the oxidation of N -amino-3-azabicyclo[3.3.0]octane by chloramine has been studied by GC and HPLC between pH 10.5 and 13.5. The second-order reaction exhibits specific acid catalysis. The formation of N,N,-azo-3-azabicyclo[3.3.0]octane or 3,4-diazabicyclo[4.3.0]non-2-ene is pH, concentration, and temperature dependent. In alkaline media, the exclusive formation of 3,4-diazabicyclo[4.3.0]non-2-ene is observed. Kinetic studies show that the oxidation of N -amino-3-azabicyclo[3.3.0]octane by chloramine is a multistep process with the initial formation of a diazene-type intermediate, which is converted by hydroxide ions into 3,4-diazabicyclo[4.3.0]non-2-ene. Because it was not possible to follow the rate of change of the intermediate concentration, to determine the kinetics of 3,4-diazabicyclo[4.3.0]non-2-ene formation, a procedure based on the degeneration of the precursor process was adopted. An appropriate mathematical treatment allowed a quantitative interpretation of all the phenomena observed over the given pH interval. The activation parameters were determined. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 327,338, 2006 [source] Ozonation of vinasse in acid and alkaline mediaJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 11 2003MA Martín Santos Abstract The production of ethanol by fermentation and subsequent distillation generates wastewater known as ,vinasse'. This waste is highly polluting on account of its high organic load and antibacterial activity,which arises from the presence of phenolic compounds that reduce the efficiency of the detoxification treatments best suited to this type of waste (eg anaerobic digestion). This can be avoided by using a pre-treatment based on a chemical oxidant (ozone) at an acid or alkaline pH. Ozonation in acid media provides more selective elimination of phenolic compounds and a more readily biodegradable waste (ie an increased BOD5/COD ratio). Copyright © 2003 Society of Chemical Industry [source] Characterization of industrial alkylpolyphosphonates by infusion electrospray ionization-ion trap mass spectrometry with identification of the impurities by tandem capillary zone electrophoresisJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 1 2006Silvia Ortega-Gadea Abstract Technical grade diethylene-triaminepentakis(methylenephosphonic acid) (I), dihexamethylene-triaminepentakis(methylenephosphonic acid) (II), ethylene-diaminetetrakis(methylenephosphonic acid) (III), hexamethylene-diaminetetrakis(methylenephosphonic acid) (IV), amino-tris(methylenephosphonic acid) (V), hydroxyethyl-aminobis(methylenephosphonic acid) (VI), 1-hydroxyethylidene-1,1-diphosphonic acid (VII), and 2-phosphonobutane-1,2,4-tricarboxylic acid (VIII) were characterized by ion trap mass spectrometry with electrospray ionization (ESI-ITMS). Using the negative ion mode and acid and alkaline media, peak series corresponding to the nominal compounds and to impurities with a lower number of phosphonate groups were distinguished in I,V. Each series was constituted by [M , nH + (n , 1)Na], peaks and peaks produced from them by losses of water, H3PO3(or water plus HPO2), and combined losses. For each [M , nH + (n , 1)Na], peak, the number of losses coincided with the number of phosphonate groups not bound to sodium ions minus one (the group bearing the charge). Owing to the hydroxyethyl group, the spectrum of VI was dominated by the formation of intermolecular esters, with both losses and gains of water according to [nM , H ± mH2O],. A series of [M , nH + (n , 1)Na], peaks were observed for VII and VIII, showing in the latter case that the carboxylate groups may also form adducts with sodium ions. Losses of water and H3PO3were observed in VII, whereas losses of water, CO2, and HPO3 were seen in VIII. The reaction pathways leading to the production of the observed ions are described. The nominal compounds and the impurities were also separated and identified by capillary electrophoresis with ESI-ITMS detection. Copyright © 2005 John Wiley & Sons, Ltd. [source] A laser imaging and neutron reflection investigation into the monolayer behaviour of fatty acids used for taste masking microspheresJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 5 2008Sheng Qi Abstract Fatty acid microspheres have been used for taste masking purposes whereby the drug is preferentially released in the lower gastrointestinal tract, although the mechanisms involved are poorly understood. In this study, we use a combination of surface pressure measurements, Brewster angle microscopy (BAM) and neutron reflectivity measurements to study the phase miscibility and escaping tendency from mixed stearic and palmitic acid films with a view to relating this to drug dissolution behaviour. It was noted that mixed systems showed considerably greater film interaction and instability than those composed of the pure lipid, especially in alkaline media. BAM studies were able to identify a range of phase separated structures for both the pure and mixed systems. Neutron reflectivity studies indicated a marked selective dissolution of palmitic acid into the subphase as a function of time and allowed quantification of the rate of dissolution of this species. It is concluded that the fatty acids are interacting within the monolayer and in addition the palmitic acid is escaping the mixed monolayers and dissolving into the alkali subphase. These findings have strong relevance for understanding the mechanism of drug release from the associated microspheres. © 2007 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 97: 1864,1877, 2008 [source] A liquid chromatographic method optimization for the assessment of low and high molar mass carbonyl compounds in winesJOURNAL OF SEPARATION SCIENCE, JSS, Issue 20 2009Luciana C. de Azevedo Abstract Carbonyl compounds (CC) play an important role in beverage aroma since they may affect flavor of wines, brandies, and beers, among others. For this reason, it is necessary to identify and quantify CC through adequate analytical techniques. This study is a proposal of both developing and optimization of a new analytical methodology that allows investigate C1,C8 CC in wines simultaneously by quantifying even those ones that are predominantly present in the adduct form hydroxylalkylsulfonic acids (HASA). The HASA dissociation is undertaken by specific alkaline media (pH 11). The developed methodology employed the LC with UV/VIS detection (, = 365 nm) technique under gradient elution in the way to reach both free-CC and bound-CC quantification. Results showed that binary gradient system using eluent A (MeOH/ACN/H2O 74.5:0.5:25% v/v/v) and eluent B (MeOH) reached the best separation condition of both lower and higher molecular mass CC. This proposed method allowed simultaneous quantification of formaldehyde, acetaldehyde, propanone, furfuraldehyde, butyraldehyde, benzaldehyde, hexanaldehyde, 2-ethyl-hexanaldehyde, E-pent-2-en-1-al, and cyclohexanone , all of them were found in white wine (Moscato Canelli) and red wine (Shiraz) produced in the São Francisco Valley, in the Northeastern Region of Brazil , although this optimized method may probably be suitable for quantification of propionaldehyde, isobutyraldehyde, heptanaldehyde, octanaldehyde, benzaldehyde, and E-hex-2-en-1-al as well. We could not prove if this method is also able to determine the latter CC group since we have not found these substances present in detectable levels in our real samples considered in this study. [source] Selective determination of famotidine in human plasma by high performance liquid chromatography in alkaline media with solid phase extractionJOURNAL OF SEPARATION SCIENCE, JSS, Issue 8 2003Eva Anzenbacherová Abstract A new method is described for the determination of famotidine by solid phase extraction from alkalinized human plasma followed by reversed phase (RP) HPLC in acetonitrile/alkaline buffer with molsidomine as an internal standard. Different acetonitrile/aqueous buffer mobile phases as well as various RP columns were used. Alkaline medium allowed the limit of quantitation to be lowered to 5 ng/mL of plasma as the famotidine gives more intense absorption at about 286 nm (at pH values higher than 7). Moreover, work in alkaline media and at this wavelength is highly selective as peaks corresponding to impurities present in most samples are well separated. A method using a mildly alkaline mobile phase (acetonitrile/10 mM phosphate with 10 mM 1-heptanesulphonic acid, pH 7.5) was successfully used for determination of famotidine in human plasma in a pharmacokinetic study. [source] Chloride-Ion Activities in Simplified Synthetic Concrete Pore Solutions: The Effect of the Accompanying IonsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2000Guillem de Vera Concrete pore solutions are concentrated electrolytes in which the activity of the chemical species must be calculated properly to determine the equilibrium state of such solutions. In this work, the chloride-ion activity coefficients in synthetic concrete pore solutions have been obtained potentiometrically, using different calibrated Cl, ion-selective electrodes (ISEs); also, a discussion about the performance of the different Cl, ISEs in alkaline media is presented. Experimental results are compared with the calculated results, using Pitzer's specific ionic-interaction model, and good agreement is observed between them. [source] ,-Glucosidase-Catalyzed Hydrolysis of Indican from Leaves of Polygonum tinctoriumBIOTECHNOLOGY PROGRESS, Issue 5 2002Thierry Maugard In this article, a HPLC method to identify and quantify the dyes and the indigo precursors produced in Polygonum tinctorium is described. Using this technique, indican has been positively identified in extracts of P. tinctorium. Our work with two cultivars of P. tinctorium has confirmed that the quantity of indican is dependent on the cultivars, harvest period, and age of the leaves. Two enzymes, Novozym 188 (cellobiase) and Novarom G ( , -glucosidase), are compared on the basis of their activities to hydrolyze the indican at several pH values. We observed that Novarom G is more active than Novozym 188 whatever the pH and that optimum pH of both enzymes for indican hydrolysis is 3. Liberated indoxyl can be oxidized in alkaline media and transformed into indigo and indirubin. [source] Metal Aminocarboxylate Coordination Polymers with Chain and Layered StructuresCHEMISTRY - A EUROPEAN JOURNAL, Issue 23 2005Meenakshi Dan Abstract The synthesis and structures of metal aminocarboxylates prepared in acidic, neutral, or alkaline media have been explored with the purpose of isolating coordination polymers with linear chain and two-dimensional layered structures. Metal glycinates of the formulae [CoCl2(H2O)2(CO2CH2NH3)] (I), [MnCl2(CO2CH2NH3)2] (II), and [Cd3Cl6(CO2CH2NH3)4] (III) with one-dimensional chain structures have been obtained by the reaction of the metal salts with glycine in an acidic medium under hydro/solvothermal conditions. These chain compounds contain glycine in the zwitterionic form. 4-Aminobutyric acid transforms to a cyclic amide under such reaction conditions, and the amide forms a chain compound of the formula [CdBr2(C4H7NO)2] (IV). Glycine in the zwitterionic form also forms a two-dimensional layered compound of the formula [Mn(H2O)2(CO2CH2NH3)2]Br2 (V). 6-Aminocaproic acid under alkaline conditions forms layered compounds with metals at room temperature, the metal being coordinated both by the amino nitrogen and the carboxyl oxygen atoms. Of the two layered compounds [Cd{CO2(CH2)5NH2}2],2,H2O (VI) and [Cu{CO2(CH2)5NH2}2],2,H2O (VII), the latter has voids in which water molecules reside. [source] Photooxidation of Pterin in Aqueous Solutions: Biological and Biomedical ImplicationsCHEMISTRY & BIODIVERSITY, Issue 11 2004Franco Studies of the photochemical reactivity of pterin (=2-aminopteridin-4(3H)-one; PT) in acidic (pH,5.0,6.0) and alkaline (pH,10.2,10.8) aqueous solutions have been performed. The photochemical reactions were followed by UV/VIS spectrophotometry, thin layer chromatography (TLC), high-performance liquid chromatography (HPLC), and an enzymatic method for H2O2 determination. PT is not light-sensitive in the absence of molecular oxygen, but it undergoes photooxidation in the presence of O2, yielding several nonpteridinic products. The quantum yields for PT disappearance were found to be 8.2 (±0.6)×10,4 and 1.2 (±0.2)×10,3 in acidic and alkaline media, respectively. H2O2 was detected and quantified in irradiated solutions of PT; and its importance from a biomedical point of view is discussed. The rate constant of the chemical reaction between singlet oxygen (1O2) and PT was determined to be 2.5 (±0.2)×105,l mol,1 s,1 in alkaline medium, and the role of 1O2 in the photooxidation of pterin was evaluated. [source] | |||||||||||||