Structural changes of flavylium salts. IV. Polarographic and spectrometric examination of pelargonidin chloride

1968 ◽  
Vol 21 (1) ◽  
pp. 221 ◽  
Author(s):  
KA Harper
Keyword(s):  
Ring Opening ◽  
Structural Changes ◽  
Equilibrium Mixture ◽  
Ring Cleavage ◽  
Alkaline Solutions ◽  
Similar Reaction ◽  
Anodic Wave ◽  
Wide Ph Range ◽  
Phenolic Group ◽  
Ph Range

Pelargonidin chloride has been examined polarographically and spectrometrically in aqueous methanol over a wide pH range and the molecular changes determined. In strongly acid solutions the flavylium ion is stable, but between pH3 and pH8 ring opening to the α-diketone occurs, the process involving the pseudo-base and its 3-keto tautomer. The pseudo-base is present in the equilibrium mixture from pH3 to pH12 in amount varying with the pH. The anhydrobase, detected in the equilibrium mixture at pH6, is stable above pH7, becoming ionized as the pH is raised. Unlike the anhydrobase of the simpler flavylium salts, the anhydrobase of pelargonidin chloride does not undergo ring cleavage in strong alkali under the conditions of these experiments. Ionization of the phenolic group at C5 was indicated by a, small anodic wave in the polarograms above pH9.5, due to mercuration at C6. A similar reaction, analogous to the known catalytic mercuration of ketones, was observed for phloroglucinol and resorcinol in alkaline solutions.

Effect of ammonium, carbonate and fluoride concentration on the uranium recovery by resins

2005 ◽  
Vol 93 (4) ◽  
Author(s):  
Ana C. Q. Ladeira ◽  
Carlos A. Morais
Keyword(s):  
Exchange Process ◽  
Fluoride Concentration ◽  
Alkaline Solutions ◽  
High Concentration ◽  
Solution Ph ◽  
Uranium Recovery ◽  
Strong Base ◽  
Base Resin ◽  
Wide Ph Range ◽  
Ph Range

SummaryUranium in solution can be precipitated over a wide pH range, from acidity and alkalinity, depending upon the solution and the precipitant used. The precipitate is generally filtered and the solution resultant contains uranium that should be recovered. This work is aimed at the selection of an appropriate resin for uranium recovery from alkaline solutions in the presence of ammonia, carbonate and fluoride. The ability of uranium extraction of 3 types of polymeric strong base resin was assessed. Laboratory solutions were prepared to determine the influence of the ions like ammonia, carbonate and fluoride on the uranium recovery by resins. The uranium concentration was 100 mg/L and the solution pH ranged from 9.2 to 10.4. The results, obtained by batch experiments, showed that excess of carbonate and fluoride completely inhibit uranium uptake in the pH range studied. Even low concentrations of fluoride and carbonate decrease uranium adsorption by resins. The optimum concentration was below 2.5 g/L (0.04 mol/L) and 5.0 g/L (0.26 mol/L) for carbonate and fluoride, respectively. The presence of high concentration of ammonia up to 20 g/L (1.20 mol/L) did not inhibit the uranium exchange process. Among the three types of resins studied IRA 910U was the most promising adsorbent for uranium at the conditions employed in this work.

Structural changes of flavylium salts. III. Polarographic and spectrometric examination of 3,7,4'-trihydroxyflavylium perchlorate

1967 ◽  
Vol 20 (12) ◽  
pp. 2691 ◽  
Author(s):  
KA Harper
Keyword(s):  
Ring Opening ◽  
Structural Changes ◽  
Equilibrium Mixture ◽  
Open Chain ◽  
Enolic Form ◽  
Molecular Changes ◽  
The Stability ◽  
Dihydroxy Compound

The molecular changes undergone by 3,7,4?-trihydroxyflavylium perchlorate in aqueous methanolic solutions with increasing pH were followed by polarography and spectrometry, and the effect of the hydroxyl at C3 observed by comparison with the behaviour of 7,4?- dihydroxyflavylium perchlorate. The trihydroxyflavylium ion is less stable above pH 2 than the dihydroxy compound and forms the open-chain α-diketone, probably via the 3-keto pseudobase. The stability of the enolic form of the pseudobase increases at higher pH and is favoured from pH 5 to pH 9. At pH 6.5 the anhydrobase appears in the equilibrium mixture and at pH 9 becomes stabilized by ionization. Although the α- hydroxychalcone was not detectable at lower pH, at pH 10 ring opening gives the ionized a-hydroxychalcone, rather than the ionized diketone, and equilibrium shifts in this direction as the pH is raised further.

scholarly journals The spectroabsorptiometric and voltammetric behavior of malvin in buffered solutions and its antioxidant properties

2002 ◽  
Vol 67 (1) ◽  
pp. 53-60 ◽  
Author(s):  
Ljubisa Ignjatovic ◽  
Jasmina Dimitric-Markovic ◽  
Dragan Markovic ◽  
Jelisaveta Baranac
Keyword(s):  
Electronic Absorption ◽  
Structural Changes ◽  
Electronic Absorption Spectra ◽  
Antioxidant Properties ◽  
Oxidation Potential ◽  
Molecular Structures ◽  
Wide Ph Range ◽  
Voltammetric Behavior ◽  
Ph Range

In the present work the structural transformations of malvin in aqueous acetate buffer solutions were investigated over a wide pH range under in vitro conditions using electronic absorption spectroscopy. In addition to the spectroabsorptiometric investigation, the voltammetric behavior and the mechanism of the redox process of this molecule were studied, in order to define its antioxidant properties. The electronic absorption spectra reveal that the structural changes of malvin, caused by changes in the pH of the medium, lead to changes in the voltammetric behaviour of this molecule. The dependence of the oxidation potential of malvin on pH, which can be explained by the presence of different electroactive molecular structures of malvin at different pH values, indicates different mechanisms of the electrode process. The voltammetric activity of malvin is compared semiquantitatively with the voltammetric activity of a standard synthetic antioxidant, BHA, and a natural antioxidant, quercetin.

Structural changes of flavylium salts. II. Polargographic and spectrometric investigation of 4'-Hydroxyflavylium perchlorate

1967 ◽  
Vol 20 (4) ◽  
pp. 745 ◽  
Author(s):  
KA Harper ◽  
BV Chandler
Keyword(s):  
Structural Changes ◽  
Polarographic Reduction ◽  
Spectrometric Investigation ◽  
High Ph ◽  
Low Concentration ◽  
Methanolic Solution ◽  
Electrode Reactions ◽  
Wide Ph Range ◽  
Ph Range

4?-Hydroxyflavylium perchlorate is examined polarographically and spectrometrically in aqueous methanolic solution over a wide pH range. In solutions below pH 3 the flavonoid moiety exists solely as the flavylium ion, which establishes an equilibrium with the pseudobase, the anhydrobase, and the 2-hydroxychalcone above this pH. The flavylium ion disappears from solution above pH 5, the anhydrobase remains at a constant low concentration, and the ratio of pseudobase to chalcone fluctuates as the pH is increased. Electrode reactions for the various reductions are the same as those previously described for 7,4?- dihydroxyflavylium perchlorate. Without influencing the polarographic reduction, the presence of mercury in the polarographic cell favours chalcone formation in neutral solutions and suppresses resonance in the chalcone ion at high pH, probably through formation of a mercuric chelate.

Polarographic and spectrophotometric behaviour of some N-p-phenyl substituted benzamidines

1991 ◽  
Vol 56 (12) ◽  
pp. 2791-2799 ◽  
Author(s):  
Juan A. Squella ◽  
Luis J. Nuñez-Vergara ◽  
Hernan Rodríguez ◽  
Amelia Márquez ◽  
Jose M. Rodríguez-Mellado ◽  
...  
Keyword(s):  
Spectrophotometric Study ◽  
Absorption Bands ◽  
Electrochemical Parameters ◽  
Wide Ph Range ◽  
Group A ◽  
Substituent Constants ◽  
Ph Range ◽  
The Waves

Five N-p-phenyl substituted benzamidines were studied by DC and DP polarography in a wide pH range. Coulometric results show that the overall processes are four-electron reductions. Logarithmic analysis of the waves indicate that the process are irreversible. The influence of the pH on the polarographic parameters was also studied. A UV spectrophotometric study was performed in the pH range 2-13. In basic media some variations in the absorption bands were observed due to the dissociation of the amidine group. A determination of the pK values was made by deconvolution of the spectra. Correlations of both the electrochemical parameters and spectrophotometric pK values with the Hammett substituent constants were obtained.

High degradation efficiency of sulfamethazine with the dual-reaction-center Fe-Mn-SiO2 Fenton-like nanocatalyst in a wide pH range

2021 ◽  
Author(s):  
Manoj Kumar Panjwani ◽  
Qing Wang ◽  
Yueming Ma ◽  
Yuxuan Lin ◽  
Feng Xiao ◽  
...  
Keyword(s):  
Wastewater Treatment ◽  
Reaction Center ◽  
Degradation Efficiency ◽  
Heterogeneous Fenton ◽  
Wide Ph Range ◽  
Ph Range

The development of a heterogeneous Fenton-like catalyst, possessing high degradation efficiency in a wide pH range, is crucial for wastewater treatment. The Fe-Mn-SiO2 catalyst was designed, and prepared by a...

scholarly journals Defect-Rich Heterogeneous MoS2/rGO/NiS Nanocomposite for Efficient pH-Universal Hydrogen Evolution

Nanomaterials ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 662 ◽  
Author(s):  
Guangsheng Liu ◽  
Kunyapat Thummavichai ◽  
Xuefeng Lv ◽  
Wenting Chen ◽  
Tingjun Lin ◽  
...  
Keyword(s):  
Graphene Oxide ◽  
Hydrogen Evolution ◽  
Hydrogen Evolution Reaction ◽  
Active Sites ◽  
Reduced Graphene ◽  
Heterogeneous Interfaces ◽  
Wide Ph Range ◽  
Ph Range ◽  
A Current ◽  
Poor Stability

Molybdenum disulfide (MoS2) has been universally demonstrated to be an effective electrocatalytic catalyst for hydrogen evolution reaction (HER). However, the low conductivity, few active sites and poor stability of MoS2-based electrocatalysts hinder its hydrogen evolution performance in a wide pH range. The introduction of other metal phases and carbon materials can create rich interfaces and defects to enhance the activity and stability of the catalyst. Herein, a new defect-rich heterogeneous ternary nanocomposite consisted of MoS2, NiS and reduced graphene oxide (rGO) are synthesized using ultrathin αNi(OH)2 nanowires as the nickel source. The MoS2/rGO/NiS-5 of optimal formulation in 0.5 M H2SO4, 1.0 M KOH and 1.0 M PBS only requires 152, 169 and 209 mV of overpotential to achieve a current density of 10 mA cm−2 (denoted as η10), respectively. The excellent HER performance of the MoS2/rGO/NiS-5 electrocatalyst can be ascribed to the synergistic effect of abundant heterogeneous interfaces in MoS2/rGO/NiS, expanded interlayer spacings, and the addition of high conductivity graphene oxide. The method reported here can provide a new idea for catalyst with Ni-Mo heterojunction, pH-universal and inexpensive hydrogen evolution reaction electrocatalyst.

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