Metal ion-biomolecule interactions. Part 22.1 Cr(III)-catalyzed isotopic hydrogen exchange in methylimidazoles

2000 ◽  
Vol 78 (4) ◽  
pp. 474-486
Author(s):  
Omoshile Clement ◽  
Ikenna Onyido ◽  
Erwin Buncel
Keyword(s):  
Metal Ions ◽  
Kinetic Data ◽  
Metal Ion ◽  
Hydrogen Exchange ◽  
Careful Analysis ◽  
Order Rate Constant ◽  
Electronic Configuration ◽  
Exchange Reactions ◽  
Experimental Conditions ◽  
Isotopic Hydrogen

The detritiation kinetics of the Cr(III) complexes 1 and 3-6 have been studied in aqueous buffers at 35°C, using the liquid scintillation counting technique. Results for 5 and 6 provide benchmark kinetic data for N-T/N-H exchange under the experimental conditions of the study and have aided in the delineation of N-T/N-H from C-T/C-H exchange in the parallel reactions observed experimentally. Curved first-order plots obtained for 1, 3, and 4 were treated to yield rate constants for two parallel exchange reactions kobsA  and kobsB  for the "fast" and "slow" processes, respectively. The "fast" process has been assigned to C(2)-H exchange in 1, competing N-H and C(2)-H exchange in 3, and N-H exchange in 4. In all cases, the "slow" process is associated with C(4,5)-H exchange. Identification of exchange sites in 1, 3, and 4 was made possible by the consideration of the results of an IR spectroscopic study of hydrogen-deuterium exchange, comparison of the extent of 3H incorporatation in different complexes in the tritiation experiments, and a careful analysis of the exchange kinetic data. Analysis of the rate data indicates that Cr(III) significantly enhances C(2)-H exchange in 1 and 3, while C(4,5)-H exchange, hitherto reported in the literature only under drastic reaction conditions, was observed for 1, 3, and 4 under the mild conditions of the present study. Quantitation of the effect of Cr(III) coordination on 3H exchange in imidazole-type nuclei was achieved fully in 1; giving kM+ values of 6 × 103 and 7 × 102 M-1s-1 for C(2)-H and C(4,5)-H exchange, respectively. Using the literature value for kH+, the second-order rate constant for C(2)-H exchange under H+ catalysis, 2.9 × 102 M-1s-1, it follows that Cr(III) is ca. 20 times better as a catalyst for C(2)-H exchange in 1-methylimidazole than H+, providing the first example of a metal ion being more effective than a proton in these processes. Comparison of the results obtained with 1 with literature results for 2 shows a very large (ca. 3 × 105-fold) difference in the catalytic activities of Cr(III) and Co(III), favouring the former. The dichotomy in the effectiveness of the two metal ions in catalyzing 3H exchange in the imidazole nucleus has been ascribed to differences in (i) extent of Mn+—N bond polarization (and the consequent effect on ligand C-H acidity); (ii) electronic configuration; (iii) crystal field stabilization and activation energies; and (iv) importance of metal-ligand π back-bonding. The study highlights the diversity of factors and complexity of interactions involved in determining the role of metal ions in biological systems, especially where such processes involve complex formation between metal ions and heterocyclic fragments of biomolecules.Key words: metal ion-biomolecule interactions, methylimidazole, isotopic hydrogen exchange, catalysis by chromium.

Nonlinear Hammett Relationships in the Reaction of Peroxomonosulfate Anion (HOOSO3-) with meta- and para-Substituted Anilines in Alkaline Medium

2001 ◽  
Vol 66 (6) ◽  
pp. 897-911 ◽  
Author(s):  
Subbiah Meenakshisundaram ◽  
Ramanathan Sockalingam
Keyword(s):  
Nitrogen Atom ◽  
Equilibrium Constant ◽  
Rate Equation ◽  
Kinetic Data ◽  
Formation Constant ◽  
Order Rate Constant ◽  
Reactive Intermediate ◽  
Substituted Anilines ◽  
Experimental Conditions ◽  
First Order

The HOOSO3- oxidation of eleven meta- and para-substituted anilines to the corresponding nitrosobenzenes at pH ≈ 11 was characterized by the rate equation v = kK[OX][An]/(1 + K[An]). Formation constant of the reactive intermediate and its rate of decomposition were evaluated separately for ascertaining the structure-reactivity relationships. Under the experimental conditions the dianion, -O-O-SO3- is probably the effective electrophile. Kinetic data can be rationalized by a bimolecular process which involves the attack of nucleophilic nitrogen atom on the peroxidic oxygen. The highlight of the study is the opposite curvatures observed in the nonlinear Hammett plots of first-order rate constant k and the "equilibrium" constant K, being concave downward and upward, respectively.

Metal ion – biomolecule interactions. Part 16. C(2)-H isotopic exchange in Co(III)-coordinated imidazoles

1995 ◽  
Vol 73 (6) ◽  
pp. 772-780 ◽  
Author(s):  
Erwin Buncel ◽  
Fan Yang ◽  
Robert Y. Moir ◽  
Ikenna Onyido
Keyword(s):  
Metal Ions ◽  
Metal Ion ◽  
Hydrogen Exchange ◽  
Isotopic Exchange ◽  
Negative Charge ◽  
Ligand Complex ◽  
Transition State Stabilization ◽  
Anionic Species ◽  
Metal Ligand ◽  
Ligand Bond

Transition-metal-bound imidazoles are suitable models for evaluating the roles of metal ions in biomolecules having the imidazole moiety and similar heterocyclic residues as part of their structure. Such studies provide useful insights into metal–biomolecule interactions in biological systems, especially when the lability of the metal–ligand bond is substantially reduced, such that the identity of the metal–ligand complex is preserved during the course of the reaction under investigation. The present paper reports on a kinetic study of tritium exchange from the C(2) position of the imidazole moiety in the substitution-inert complex cations [Co(NH3)5[2-3H]-imidazole]3+ (1) and [Co(NH3)5-1-methyl-[2-3H]-imidazole]3+ (2). Rate–pH profiles have been determined in aqueous solution at 60 °C. Both substrates are believed to react through rate-determining attack of hydroxide ion (kM+ pathway) at C(2)-T. Dissection of the kinetic data reveals an additional pathway for 1 consequent upon deprotonation of its pyrrole-like N-H(T) to yield 3, which is then attacked by hydroxide at C(2) (kM pathway). The ratio kM+/kM = 103 that is obtained is in accord with the expected reduced reactivity of 3. Comparison of the present data with those reported for a variety of heterocyclic substrates shows that the order of reactivity, protonated [Formula: see text] metal ion coordinated [Formula: see text] neutral form of substrates, prevails. The superiority of the proton over metal ions in catalyzing isotopic hydrogen exchange is attributed to its larger ground state acidifying effect coupled with the greater transition state stabilization it affords, relative to metal ions. The exchange reaction of 3 via the kM pathway is the first example of a reactive anionic species in which the negative charge is located α to the exchanging C-H. Keywords: tritium exchange, cobalt (III)-coordinated imidazoles.

scholarly journals Adsorption and Separation of Crystal Violet, Cerium(III) and Lead(II) by Means of a Multi-Step Strategy Based on K10-Montmorillonite

Minerals ◽  
2020 ◽  
Vol 10 (5) ◽  
pp. 466 ◽  
Author(s):  
Filippo Parisi
Keyword(s):  
Metal Ions ◽  
Cation Exchange ◽  
Crystal Violet ◽  
Metal Ion ◽  
Complete Removal ◽  
Experimental Conditions ◽  
Factors Affecting ◽  
Adsorption Processes ◽  
Removal Of Metal Ions ◽  
Time Required

A multi-step procedure, based on the employment of K10-Montmorillonite, is proposed for the selective removal of metal ions and dyes from a multicomponent solution. The objective is twofold: decontaminate the effluents and separate and recover the valuable byproducts present in wastewaters. Three common contaminants, i.e., crystal violet dye (CV), Ce(III) and Pb(II) were chosen as “model” pollutants. The main factors affecting the pollutants’ sorption were investigated. The experimental data were correlated with adsorption isotherms and kinetic models to obtain a deeper insight into the adsorption processes. The affinity of the clay toward the pollutants is favored by an increasing pH and follows the order CV > Pb(II) > Ce(III). Whereas Ce(III) metal ions do not adsorb onto clay under strongly acidic conditions, both Pb(II) and CV can adsorb under all the investigated pH conditions. The analysis of isotherms and kinetic profiles revealed that CV adsorbs onto clay through a mechanism consisting of two parallel processes, namely cation exchange on the external mineral surface and in the interlayer and surface complexation at the edge sites, while metal ion uptake is due solely to cation exchange processes involving mineral surfaces. The time required for the complete removal of pollutants follows the order CV > Ce(III) >> Pb(II). The possibility to modulate the adsorption features by changing experimental conditions was successfully employed to propose the best strategy for the progressive removal of different components from aqueous solutions.

scholarly journals Anthracene coupled adenine for the selective sensing of copper ions

2010 ◽  
Vol 6 ◽  
Author(s):  
Kumaresh Ghosh ◽  
Tanushree Sen
Keyword(s):  
Metal Ions ◽  
Metal Ion ◽  
Copper Ions ◽  
The Other ◽  
Ion Recognition ◽  
Experimental Conditions

Anthracene-based adenines 1 and 2 have been designed and synthesized, and their metal ion recognition properties have been established fluorometrically. Both molecules exhibit Cu2+ induced ON-OFF type signaling patterns over the other representative metal ions studied. Compound 1 exhibits 97% quenching of emission in the presence of Cu2+ whilst derivative 2 shows 81% quenching under similar experimental conditions.

Deposition and dissolution of metal sulfide layers at the Hg electrode surface in seawater electrolyte conditions

2014 ◽  
Vol 11 (2) ◽  
pp. 167 ◽  
Author(s):  
Ivana Milanović ◽  
Damir Krznarić ◽  
Elvira Bura-Nakić ◽  
Irena Ciglenečki
Keyword(s):  
Metal Ions ◽  
Exchange Reaction ◽  
Metal Ion ◽  
Natural Waters ◽  
Metal Sulfide ◽  
Reduction Peak ◽  
Exchange Reactions ◽  
Dissolved Sulfide ◽  
Free Metal ◽  
Sulfide Species

Environmental context The electrochemical detection of many sulfur compounds in natural waters is based on the deposition of a HgS layer at the Hg electrode. In samples containing metal ions in excess of sulfide species, electrochemical exchange reactions between the HgS and the metal ion produce metal-sulfide voltammetric peaks. These peaks can easily be misinterpreted as dissolved sulfide species, and hence do not reflect the bulk state of the solution. Abstract Cyclic voltammetry on a Hg electrode was used to investigate the influence of metal ion (Zn, Cd, Cu, Fe, Pb, Co) on HgS deposition–dissolution in seawater conditions. Due to the exchange of electrons between Hg2+ from a HgS layer and free metal (M2+) from the solution (HgSlayer + M2+ + 2e– ↔ MSlayer + Hg0), the Hg electrode becomes the site for surface metal sulfide (MS) formation. The exchange reaction is reversible, and the surface-formed MS layer reduces at a more negative potential than HgS (MSlayer + 2e– + H+ → M0 + HS). The potentials of both electrode reactions, and the formation and reduction of the MS layer, are determined by the MS solubility product. In solutions containing excess of the free metal ions in comparison to the free sulfide, the exchange reaction produces MS voltammetric peaks, which can be misrepresented for the dissolved sulfide species. This research indirectly confirmed that the FeS electrochemical signal, usually recorded in an iron- and sulfide-rich environment at ~–1.1V v. Ag/AgCl, is not due to FeS reduction. The connection between the studied MS reduction peak potentials and the solubility products shows that the FeS layer formed by an electrochemical exchange reaction with HgS should be reduced at the Hg surface ~100mV more negative than free Fe2+.

ChemInform Abstract: Metal Ion Effects in Isotopic Hydrogen Exchange in Biologically Important Heterocycles

ChemInform ◽  
2000 ◽  
Vol 31 (52) ◽  
pp. no-no
Author(s):  
Erwin Buncel ◽  
Omoshile Clement ◽  
Ikenna Onyido
Keyword(s):  
Metal Ion ◽  
Hydrogen Exchange ◽  
Isotopic Hydrogen ◽  
Ion Effects ◽  
Metal Ion Effects

Investigation on the removal of bivalent cadmium ions from aqueous solution and treatment of industrial wastewater using new alumina interfaced biocarbon

2021 ◽  
Vol 6 (1) ◽  
pp. 1-9
Author(s):  
Sundaram R ◽  
Singanan M
Keyword(s):  
Metal Ions ◽  
Adsorption Capacity ◽  
Metal Ion ◽  
Health Concern ◽  
Activation Process ◽  
Lawsonia Inermis ◽  
Experimental Conditions ◽  
Cadmium Ions ◽  
Real Sample Analysis ◽  
Acute And Chronic Exposure

The presence of heavy metals in water and wastewater is becoming a severe environmental and public health concern. It may contribute variety of adverse environmental and human health effects due to their acute and chronic exposure through air, water and food chain. They are released into the aquatic environment from many industrial activities. The present research paper deals with the adsorption capacity of the biocarbon material produced from the leaves of Lawsonia inermis plant. The biocarbon was prepared by the H2SO4 activation process. The adsorption capacity of the biocarbon was evaluated by considering the effect of various parameters such as pH of the solution, biocarbon dose, contact time, and initial metal ions concentration and to optimize the conditions for maximum adsorption. The metal ion uptake capacity of the biocarbon was tested in the stimulated wastewater containing bivalent cadmium ions. The maximum uptake of 97.85% of the Cd (II) metal ions was observed at the equilibrium time of 3.0 hours at a dose of 3.0 g and at the pH of 4.5 in the stimulated wastewater. In the real sample analysis, electroplating industry wastewater is used for the removal of cadmium (II) ions. The results indicate that 95.16% of ions were effectively removed at the same experimental conditions. It is also further noted that the metal sorption capability of the adsorbent is higher with rising concentration of metal ions in the solution. The percentage of adsorption of the metal ions was also significantly increased with rise of temperature of the wastewater.

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