Complexes des ions Hg2+ avec Le monomère et le dimère de la thymine: 5-methyl-2,4 (1H, 3H) pyrimidinedione

1984 ◽  
Vol 62 (1) ◽  
pp. 22-26 ◽  
Author(s):  
M. M. Petit-Ramel ◽  
G. Thomas-David ◽  
G. Perichet ◽  
P. Pouyet
Keyword(s):  
Experimental Data ◽  
Concentration Distribution ◽  
Mapping Method ◽  
Association Constants ◽  
Chelate Complexes ◽  
Ph Titration ◽  
Complex Species ◽  
Wide Ph Range ◽  
Linear Configuration ◽  
Ph Range

The association constants for Hg2+-complexes involving monomeric (TM) and dimeric (TD) forms of thymine are determined by pH-titration measurements made over a wide pH range 2 < pH < 11. In both systems, the experimental data have been analyzed by a pit-mapping method and the concentration distribution of the various complex species is plotted versus a pH gradient.Because of the tendency of Hg2+ to form two bonds in a linear configuration, non-chelate complexes [Hg(TM)+] (log β101 = 10.65) and [Hg(TM)2] (log β102 = 20.70) are formed with the monomer thymine.Photodimers, obtained after irradiation of monomer thymine at 260 nm in frozen water (−10 °C), are the (meso)-cis, syn forms and can be complexed by the Hg2+ ions in [Hg(TD)] (log β101 = 13.55), [HgH−1 (TD)]− (log β1−11 = 6.73), and [HgH−2 (TD)]2− (log β1−21 = 1.69) species. [Hg(TD)] complex shows an absorption spectrum shifting towards 280 nm, whereas the free dimer ligand absorbs lower than 240 nm only. An irradiation at 280 nm provides the formation of the [Hg (TM)2] complex and consequently the breaking of the cyclobutane cycle in the dimer molecule.

Adsorption of hexavalent chromium on dunite

2011 ◽  
Vol 63 (4) ◽  
pp. 818-824 ◽  
Author(s):  
Antri Demetriou ◽  
Ioannis Pashalidis
Keyword(s):  
Experimental Data ◽  
Ionic Strength ◽  
Metal Ion ◽  
Outer Sphere ◽  
Atmospheric Conditions ◽  
Adsorption Model ◽  
Wide Ph Range ◽  
Ph Range ◽  
Relative Adsorption ◽  
Outer Sphere Complexes

The paper presents and discusses the effect of various physicochemical parameters (e.g. pH, ionic strength, Cr(VI) initial concentration, amount of the adsorbent, temperature and contact time between metal ion and adsorbent) on the adsorption efficiency of Cr(VI) on dunite in aqueous solutions under atmospheric conditions. Evaluation of the experimental data shows that dunite presents increased affinity for Cr(VI) over a wide pH range and Cr(VI) concentration, and the experimental data are well fitted by the Kd adsorption model. The relative adsorption is pH dependent and decreases slightly (about 10%) with increasing pH, because of changes in the surface charge of the solid. The effect of the ionic strength is significant (particularly at low pH), indicating the predominance of outer-sphere complexes. Moreover, adsorption experiments at various temperatures, two different pH values (pH 3 and pH 8) and three different ionic strengths (0.0, 0.1 and 1.0 M NaClO4), indicate an endothermic but spontaneous entropy-driven processes.

Stereoselective effect on ternary complexation of copper ions with N,N′-dimethyltartramide and mandelic acid

1983 ◽  
Vol 61 (9) ◽  
pp. 2151-2153
Author(s):  
Michelle M. Petit-Ramel ◽  
Gaël De Rycke ◽  
André Rio ◽  
Pierre E. Blond
Keyword(s):  
Aqueous Solution ◽  
Concentration Distribution ◽  
Mandelic Acid ◽  
Copper Ions ◽  
Mapping Method ◽  
Ternary Complexes ◽  
Ph Gradient ◽  
Potentiometric Measurements ◽  
Ternary Complexation ◽  
Ph Range

The binary and ternary complexation in aqueous solution between copper(II) ion,N,N′-dimethyltartramide (H2A) and mandelic acid (HB), were studied by potentiometric measurements in the 5–10 pH range at 25 °C and μ = 1 M in NaClO4. The titrations were analyzed using a pit-mapping method and the concentration distribution of the various simple and mixed complexes were plotted versus a pH gradient. A significant stereoselective effect is displayed in the ternary complexes only.

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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