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.

Structural and spectroscopic studies of transition metal nitrite complexes. II. Crystal structures of cis-Bis(ethane-1,2-diamine)(nitrito-O,O')zinc(II) nitrite and trans-Bis[N,N-dimethyl(ethane-1,2-diamine)]dinitritozinc(II)

1981 ◽  
Vol 34 (10) ◽  
pp. 2061 ◽  
Author(s):  
AJ Finney ◽  
MA Hitchman ◽  
CL Raston ◽  
GL Rowbottom ◽  
AH White
Keyword(s):  
Transition Metal ◽  
Metal Ions ◽  
Crystal Structures ◽  
Coordination Polyhedron ◽  
Metal Ion ◽  
Spectroscopic Studies ◽  
Bond Lengths ◽  
Coordination Sites ◽  
Metal Ligand ◽  
Ligand Bond

The crystal structures of the complexes cis-bis(ethane-1,2-diamine)(nitrito-O,O')zinc(II) nitrite and trans-bis[N,N-dimethyl(ethane-l,2-diamine)]dinitritozinc(II) are described. The former compound contains one chelating nitrite, the second group being present as a counter ion. In this complex the coordination polyhedron about the metal ion may be described either as a distorted trigonal bi-pyramid or an octahedron, depending upon whether the chelated nitrite is considered to occupy one or two coordination sites. The second compound is a trans nitrito complex, having an octahedral ligand geometry, though with three markedly different metal-ligand bond lengths. The structures of the complexes are compared with those of analogous nickel(II) nitrite complexes, and the differences are discussed in terms of the electron configurations of the two metal ions.

Metal ion catalysis in nucleophilic displacement reactions at carbon, phosphorus, and sulfur centers. I. Catalysis by metal ions in the reaction of p-nitrophenyl diphenylphosphinate with ethoxide

1989 ◽  
Vol 67 (9) ◽  
pp. 1440-1448 ◽  
Author(s):  
Edward J. Dunn ◽  
Erwin Buncel
Keyword(s):  
Crown Ether ◽  
Alkali Metal ◽  
Transition State ◽  
Metal Ions ◽  
Ground State ◽  
Metal Ion ◽  
Complexing Agents ◽  
Transition State Stabilization ◽  
Nucleophilic Displacement ◽  
Metal Ion Catalysis

The effect of macrocyclic crown ether and cryptand complexing agents on the rate of the nucleophilic displacement reaction of p-nitrophenyl diphenylphosphinate by alkali metal ethoxides in ethanol at 25 °C has been studied by spectrophotometric techniques. For the reactions of potassium ethoxide, sodium ethoxide, and lithium ethoxide, the observed rate constant increased in the order KOEt < NaOEt < LiOEt. Crown ether and cryptand cation-complexing agents have a retarding effect on the rate. Increasing the ratio of complexing agent to base results in a decrease in kobs to a minimum value corresponding to the rate of reaction of free ethoxide ion. In complementary experiments, alkali metal ions were added to these reaction systems in the form of unreactive salts, causing an increase in reaction rate. The kinetic data were analysed in terms of ion-pairing treatments, which allowed evaluation of rate coefficients due to free ethoxide ions and metal ion – ethoxide ion pairs. Possible roles of the metal cations are discussed in terms of ground state and transition state stabilization. Evaluation of the equilibrium constants for association of the metal ion with ground state (Ka) and the transition state (K′a) shows that catalysis occurs as a result of enhanced association between the metal ion and the transition state, with (K′a) values increasing in the order K+ < Na+ < Li+. A model is proposed in which transition state stabilization arises largely from chelation of the solvated metal ion to two charged oxygen centers. This appears to be the first reported instance of catalysis by alkali metal cations in nucleophilic displacement at phosphoryl centers. Keywords: nucleophilic displacement at phosphorus, alkali-metal-ion catalysis.

Syntheses, and Characterization of Complexes Containing Beta-lactam Group with some Transitional Elements and Study their Biological Activity

2021 ◽  
Vol 19 (11) ◽  
pp. 72-83
Author(s):  
N. Ghufran Kareem ◽  
Mohammed Hamid Said
Keyword(s):  
Biological Activity ◽  
Metal Ions ◽  
Atomic Absorption ◽  
1H Nmr ◽  
Inhibitory Activity ◽  
Negative Charge ◽  
Beta Lactam ◽  
Penicillanic Acid ◽  
Metal Ligand

In this study, a novel azo-azomethine ligand [6[2-hydroxy-4-((3-nitrophenyl)diazenyl)-1-phenyl]imine penicillanic acid] [HNDIP] is synthesized from [2-hydroxy-4-((3-nitrophenyl)diazenyl) benzaldehyde]. And reflux with 6-aminopenicillin acid, this ligand was identified by UV-Vis, FTIR, 1H-NMR, C13NMR, and mass, and it was used to prepare new complexes with [Cu(II), Ni(II), Co(II), Zn(II), and Fe(II)] metal ions. These complexes were identified by FTIR, UV-Vis, molar conduct, magnetic sensitivity, and atomic absorption for all complexes, the reaction ingredients were observed to be ratio 1:2 (metal: ligand). The ligand, a tridentate with a single negative charge, was coupled with metal ions to form claw complexes, resulting in an octahedral shape. Finally, antibacterial effectiveness was determined for the ligand and complexes against two distinct bacteria strains (Pseudomonas and klebsiella). It was discovered that the ligand and its complexes have high inhibitory activity against bacteria (Pseudomonas and Klebsiella). As a result, the chemicals created may be feasible substitutes for routinely used drugs.

scholarly journals Preparation of metallosupramolecular single-chain polymeric nanoparticles and their characterization by Taylor dispersion

2020 ◽  
Vol 11 (2) ◽  
pp. 586-592 ◽  
Author(s):  
Laura N. Neumann ◽  
Dominic A. Urban ◽  
Philipp Lemal ◽  
Sushila Ramani ◽  
Alke Petri-Fink ◽  
...  
Keyword(s):  
Complex Formation ◽  
Metal Ions ◽  
Polymeric Nanoparticles ◽  
Taylor Dispersion ◽  
Dispersion Analysis ◽  
Single Chain ◽  
Ligand Complex ◽  
Dispersed Particles ◽  
Metal Ligand

Polymers with pendant ligands furnish single-chain polymeric nanoparticles upon intramolecular metal–ligand complex formation with different metal-ions and Taylor dispersion analysis is employed to reliably characterize the dispersed particles.

scholarly journals Complexation equilibria of ambroxol hydrochloride in solution by potentiometric and conductometric methods

2018 ◽  
Vol 9 (1) ◽  
pp. 49-56
Author(s):  
Ahmed Hosny Naggar ◽  
Hammed Mohammed Al-Saidi ◽  
Othman Abd El-Moaty Farghaly ◽  
Taher Mohammed Hassan ◽  
Salma Zaidan Mohamed Bortata
Keyword(s):  
Ionic Strength ◽  
Metal Ions ◽  
Stability Constants ◽  
Formation Constants ◽  
Alkaline Media ◽  
Ligand Complex ◽  
Complex Species ◽  
The Stability ◽  
Ambroxol Hydrochloride ◽  
Metal Ligand

The formation constants of Li(I), Mg(II), Sr(II), Ca(II), Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Ba(II), Pb(II), Al(III), Cr(III), Fe(III) and Th(IV) ions with ambroxol hydrochloride (AMB) were calculated using the half-n value. In presence of 0.1 M NaNO3, metal ions such as Zn(II), Cd(II), Ni(II), Cr(III), Li(I), Mg(II) and Al(III) forms three types of metal-ligand complexes (1:1, 1:2 and/or 1:3), while Sr(II) and Co(II) tend to form two types of metal complexes 1:1 and 1:2 (M:L). For ligand protonation constants, two logarithmic association constant values were calculated by the half-n method and are 10.7 and 7.6, respectively. The effect of ionic strength on stability constant of AMP, with different metal ions viz. Fe(III), Th(IV), Al(III), Cr(III) and Cu(II) was studied. Based on relationship between the ionic strength studied values and the 1st stability constants (Log K1H), we can conclude that the stability constants of the formed metal-ligand complex (1:1) were decreased as the ionic strength increased. The stoichiometry of the formed complexes in solution were determined by conductometric method and it is found to be of 1:1, 1:2 and/or 1:3 (M:L) complex species is formed in alkaline media. Also, study the species distribution diagrams of AMP for the calculated mole fraction αML and αML2 were discussed.

scholarly journals Polyaniline Modified Natural Zeolite as Adsorbent for Chromium(III) Metal Ion

2019 ◽  
Vol 22 (6) ◽  
pp. 292-298
Author(s):  
Rina Nurianingsih ◽  
Sriatun Sriatun ◽  
Adi Darmawan
Keyword(s):  
Metal Ions ◽  
Natural Zeolite ◽  
Metal Ion ◽  
Alkali Metals ◽  
Inorganic Material ◽  
Negative Charge ◽  
Three Dimensional ◽  
Industrial Processes ◽  
Adsorption Ability ◽  
Cationic Compounds

Zeolite is an inorganic material whose surface has a permanent negative charge in its crystal structure. This material consists of tetrahedral [SiO4]-4 and [AlO4]-5, which are connected by oxygen atoms in such a way as to form an open three-dimensional framework containing canals and cavities, as well as alkali or alkali metals for balancing the negative charge. This structure makes zeolites have the ability to adsorb. The ability of natural zeolite adsorption can improve by modifying the surface by adding polyaniline cationic compounds (PANI), which have an amine group (: NH2). Moreover, environmental pollution by metals is the biggest problem in daily life, one of which is the metal ion Cr(III), which is a waste from industrial processes. Therefore, it is necessary to have an effort to reduce waste. This study aims to determine the effect of the addition of polyaniline on the adsorption ability of natural zeolites to metal ions Cr(III). The research was carried out in several stages, namely activation of natural zeolite using HF 1%, modification with polymer from aniline monomers, and ammonium peroxidisulphate (APS), and testing the ability of adsorption on Cr(III) metal ions. The study on the ability to adsorb Cr(III) metal ions by PANI-modified zeolites was carried out on variations in the concentration of Cr(III) metal ions and the system pH. The results showed that natural zeolite successfully modified with PANI. The FTIR absorption band at wavenumber 1303 -1319 cm-1 and 1597 cm-1 indicated the presence of NH functional groups. Meanwhile, adsorption capability test data showed that the best adsorbent for adsorption of Cr(III) metal ions was zeolite-PANI 0.01M. The best pH was 4, the initial concentration of Cr(III) metal ions was 1000 ppm, and the percentage of absorption is 48.13%.

Mixed ligand ion buffers for calibrating ion-selective electrodes at trace levels

1990 ◽  
Vol 333 (1628) ◽  
pp. 163-163 ◽  
Keyword(s):  
Metal Ions ◽  
Metal Ion ◽  
Concentration Ratio ◽  
Ph Value ◽  
Mixed Ligand ◽  
Ligand Concentration ◽  
Ion Selective Electrodes ◽  
Equivalence Point ◽  
Metal Ligand ◽  
Standard Solutions

The calibration of cation-selective electrodes has been facilitated by the use of ion buffers. Hitherto, calibration was made using solutions containing the metal ion and an appropriate complexing ligand, such as EDTA in an appropriate concentration ratio, or by changing the pH value of a solution with fixed metal-ligand concentration. To cover a wide calibration range, say from 10 -7 to 10 -3 m [Ca 2+ ], standard solutions involving at least two different ligands had to be prepared. These approaches were both cumbersome and lacked precision in the unbuffered region near the equivalence point of titration of ligand with metal ions.

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