Search results for "aqueous solution"
showing 10 items of 1610 documents
Thermal, spectroscopic and crystallographic analysis of mannose-derived linear polyols
2018
The major diastereomer formed in the Barbier-type metal-mediated allylation of D-mannose has previously been shown to adopt a perfectly linear conformation, both in solid state and in solution, resulting in the formation of hydrogen-bonded networks and subsequent aggregation from aqueous solution upon stirring. Here, a comprehensive study of the solid state structure of both the allylated D-mannose and its racemic form has been conducted. The binary melting point diagram of the system was determined by differential scanning calorimetry analysis, and the obtained results, along with structure determination by single crystal X-ray diffraction, confirmed that allylated mannose forms a true rac…
Metal ions modify DNA-protecting and mutagen-scavenging capacities of the AV-153 1,4-dihydropyridine.
2019
Abstract 1,4-Dihydropyridines (1,4-DHP) possess important biochemical and pharmacological properties, including antioxidant and antimutagenic activities. AV-153-Na, an antimutagenic and DNA-repair enhancing compound was shown to interact with DNA by intercalation. Here we studied DNA binding of several AV-153 salts to evaluate the impact of AV-153 modifications on its DNA binding capacity, the ability to scavenge the peroxynitrite, to protect HeLa and B-cells cells against DNA damage. Affinity of the AV-153 salts to DNA measured by a fluorescence assay was dependent on the metal ion forming a salt in position 4 of the 1,4-DHP, and it decreased as follows: Mg > Na > Ca > Li > Rb > K. AV-153-…
The reduction mechanism of the CO group.
2001
A detailed study of the electrochemical reduction of benzil in aqueous medium between H0=−5 and pH 11 is presented. A global 2e−, 3H+ or 2e−, 2H+ surface reaction leads to cis and trans endiols. Analysis, using the theory of the square schemes with protonations at equilibrium, shows that in all the pH range the reaction is controlled by the second electron uptake, the paths being successively H+, e− and e−, H+. The electrochemical reaction is followed by surface isomerizations whose rate constants vary from 7 to 200 s−1 for the trans/cis and from 1 to 2000 s−1 for the cis/trans transformations.
A Theoretical Study of the Electronic Spectra of N9 and N7 Purine Tautomers
1999
The complete active space (CAS) SCF method and multiconfigurational second-order perturbation theory (CASPT2) have been used to study electronic spectra of the N(9)H and N(7)H tautomers of purine. The calculations include vertical excitation energies, oscillator strengths, dipole moments, and transition moment directions in gas phase. In accord with experiment in nonpolar solvents, the two lowest π → π* excited singlet valence states are predicted to be located at 4.7 and 5.1 eV. The latter is expected to shift to the red in aqueous solutions. A satisfactory interpretation of the electronic spectra above 5.5 eV is obtained if the experimental data are assumed to consist of the superposition…
The Dissociation Constant of Pyruvic Acid: Determination by Spectrophotometric Measurements
1991
Aqueous solutions of sodium pyruvate/hydrochloric acid mixtures were studied with regard to changes in the intensity of optical absorption at 317 nm wavelength, caused by varying pH and temperature. The data were evaluated to determine the pyruvic acid apparent dissociation constant at infinite dilution. Its temperature dependence followed the relation ln Kod = −(0.55 ± 0.47) − (1538 ± 135)/T or, if previous results of Pedersen at two temperatures are included, In Kod = −(0.97 ± 0.35) − (1418 ± 102)T. The effective absorption coefficient for pyruvic acid and its anion differ because the former species is largely hydrated, whereas the latter is not. The known hydration constant and its tempe…
The Existence of Nitrate Radicals in Irradiated TiO 2 Aqueous Suspensions in the Presence of Nitrate Ions
2018
Evidence of the existence of nitrate radical in irradiated aqueous TiO2 suspensions in the presence of nitrate ions are reported for the first time. The joint use of UV/Vis and EPR spectroscopy showed that nitrate radicals are formed by hole induced oxidation of nitrate ions. Photocatalytic degradation of a model alkene compound allowed to highlight the presence of an intermediate organic nitrate deriving from nitrate radical attack to the double bond of the substrate. These results not only allow deeper understanding of photocatalytic processes, but open the route to new green photocatalytic syntheses initiated by nitrate radicals and to new insights in the field of atmospheric chemistry.
Non-Monotonic Concentration Dependence of the Electro-Phoretic Mobility of Charged Spheres in Realistic Salt Free Suspensions
2020
Using super-heterodyne Doppler velocimetry with multiple scattering correction, we extend the opti-cally accessible range of concentrations in experiments on colloidal electro-kinetics. We here meas-ured the electro-phoretic mobility and the DC conductivity of aqueous charged sphere suspensions covering about three orders of magnitude in particle concentrations and transmissions as low as 40%. The extended concentration range for the first time allows the demonstration of a non-monotonic con-centration dependence of the mobility for a single particle species. Our observations reconcile previ-ous experimental observations made on other species over restricted concentration ranges. We com-par…
Chemical properties of rutherfordium (Rf) and dubnium (Db) in the aqueous phase
2016
Recent experimental studies of the chemical characterization of the first two transactinide elements, rutherfordium (Rf) and dubnium (Db), conducted atom-at-a-time in aqueous phases are reviewed. A short description on experimental techniques based on partition methods, specifically automated rapid chemical separation systems, is also given. Perspectives for aqueous-phase chemistry experiments on heavier elements are briefly discussed.
Simultaneous Removal and Recovery of Metal Ions and Dyes from Wastewater through Montmorillonite Clay Mineral
2019
The main objective of this work was to evaluate the potential of Montmorillonite nanoclay (Mt), readily and inexpensively available, for the simultaneous adsorption (and removal) of two classes of pollutants: metal ions and dyes. The attention was focused on two &ldquo
Photocatalytic ozonation under visible light for the remediation of water effluents and its integration with an electro-membrane bioreactor
2018
Abstract Photocatalysis and photocatalytic ozonation under visible light have been applied for the purification of a complex aqueous matrix such as the grey water of Masdar City (UAE), by using N-doped brookite-rutile catalysts. Preliminary runs on 4-nitrophenol (4-NP) solutions allowed to test the reaction system in the presence of a model pollutant and to afford the relevant kinetic parameters of the process. Subsequently, the remediation of grey water effluent has been evaluated in terms of the reduction of total organic carbon (TOC) and bacterial counts. The concentration of the most abundant inorganic ionic species in the effluent has been also monitored during reaction. Photocatalytic…