Thermodynamic and spectroscopic studies of copper (II) complexes with three bis(amide) ligands derived from L-tartaric acid

The interactions of three bis(amide) ligands derived from tartaric acid with copper (II) were investigated in aqueous solution by a combination of potentiometry, UV-vis spectrophotometry, electron paramagnetic resonance (EPR), and mass spectrometry. The formation constants of the complexes were measured and their relative structures were reported. The sites of complexation of these ligands are investigated based mostly on their electronic and EPR spectra and on the comparison with the behaviour of some analog compounds.     

Kinetics and equilibria for the formation of a new DNA metal-intercalator: the cyclic polyamine Neotrien/copper(II) complex

A study has been performed of the kinetics and equilibria involved in complex formation between the macrocyclic polyamine 2,5,8,11-tetraaza[12]-[12](2,9)[1,10]-phenanthrolinophane (Neotrien) and Cu(II) in acidic aqueous solution and ionic strength 0.5 M (NaCl), by means of the stopped-flow method and UV spectrophotometry. Spectrophotometric titrations and kinetic experiments revealed that the binding of Cu(II) to Neotrien gives rise to several 1:1 complexes differing in their degree of protonation. Under the experimental hydrogen ion concentration range investigated, complexation occurs by two parallel paths: (a) M2+ + (H4L)4+ <==> (MH4L)6+ and (b) M2+ + (H3L)3+ <==> (MH3L)5+. The rate constants values found for complex formation, by paths (a) and (b), are much lower than the values expected from water exchange at copper(II) and other amine/Cu(II) complexation kinetic constants. Kinetic experiments at different NaCl concentrations indicated that this finding was not due to chloride ion competition in complex formation with Neotrien, but it was related to a ring rigidity effect. As the phenanthroline moiety could, in principle, interact with nucleic acids by intercalation or external binding, some preliminary measurements concerned with the possible interactions occurring between the Cu(II)/Neotrien complex and calf thymus DNA (CT-DNA) have also been carried out. The absorption spectra of the Cu(II)/Neotrien complex change upon addition of CT-DNA at pH 7.0, revealing the occurrence of complex-nucleic acid interactions. Moreover, fluorescence titrations, carried out by adding the Cu(II)/Neotrien complex to CT-DNA, previously saturated with ethidium bromide (EB), show that the Cu(II)/Neotrien complex is able to displace EB from DNA, suggesting the complex is able to intercalate into the polynucleotide and then to cleave the phosphodiester bond of DNA.     

Solvent effects on the stability of nifuroxazide complexes with cobalt(II), nickel(II) and copper(II) in alcohols

A spectrophotometric study of the complexation of nifuroxazide with cobalt(II), nickel(II) and copper(II) was carried out in different alcohols. The formation of a complex in each case is reported and their stability constants have been calculated. For a given solvent, the stability of the complexes increases from cobalt to copper. In the case of copper(II), the stability varies as an inverse function of the dielectric constant of the solvent. A possible structure of the complex is proposed.     

Co-ordination of transition metal ions by galactaric acid: a potentiometric and spectroscopic study

A solution study on the ability of galactaric acid [GalaH(2), HOOC(CH)(4)COOH] in the complexation of biological metal ions such as Co(II) and Ni(II) and toxic metal ions such as Cd(II), Pb(II) and Hg(II), is reported. The stability constants of the complex species are determined by means of potentiometric measurements. Galactaric acid behaves as chelate ligand through carboxylic oxygen and alpha-hydroxy group towards Co(II) and Ni(II), while in the Pb(II) and Cd(II) containing system it co-ordinates the metal ion with carboxylic oxygen and two alcoholic hydroxy groups. The prevailing species at acidic or neutral pH is [MGala] which is also isolated in the solid state and characterized by means of IR spectroscopy. On increasing pH, the [MGalaH(-1)](-) species is also formed where the co-ordinated OH group undergoes deprotonation in all metal ion complexes except those with Hg(II), where the co-ordination of hydroxide ion is suggested as the precipitation of the metal hydroxide occurs at pH 7.     

Bioavailability and speciation—the case of inorganic compounds

Abstract

The stability constants of binary complexes of 2,4-dichlorophenoxyacetic acid (2,4-D), (4-chloro-2-methylphenoxy)acetic acid (2,4-MCPA) and (4-chloro-2-methylphenoxy) propionic acid (2,4-MCPP) with Hg(II), Pb(II) have been calculated at 298 K and at ionic strength μ = 0.1 (NaNO₃). Potentiometric measurements display two hydroxide complexes for Hg(II): HgH_?1A and HgH_?2A₂ whereas for Pb(II) we observe the formation of three species PbH_?1A, PbH_?1A₂ and PbH_?2A₂. With regard to the successive complexes, no other system represents this type of complexes under our experimental conditions. The order of capacity of complexation compared to metal for the three ligands is Hg(II)4Pb(II). Finally, the study in solution has been completed by a quantum examination of the structures of the complex of Hg(II) by the AM1 method.     

Free metal ion depletion by "Good's" buffers. III. N-(2-acetamido)iminodiacetic acid, 2:1 complexes with zinc(II), cobalt(II), nickel(II), and copper(II); amide deprotonation by Zn(II), Co(II), and Cu(II)

Potentiometric, visible, infrared, electron spin, and nuclear magnetic resonance studies of the complexation of N-(2-acetamido)iminodiacetic acid (H2ADA) by Ca(II), Mg(II), Mn(II), Zn(II), Co(II), Ni(II), and Cu(II) are reported. Ca(II) and Mg(II) were found not to form 2:1 ADA2- to M(II) complexes, while Mn(II), Cu(II), Ni(II), Zn(II), and Co(II) did form 2:1 metal chelates at or below physiological pH values. Co(II) and Zn(II), but not Cu(II), were found to induce stepwise deprotonation of the amide groups to form [M(H-1ADA)4-(2)]. Formation (affinity) constants for the various metal complexes are reported, and the probable structures of the various metal chelates in solution are discussed on the basis of various spectral data.     

Complexes of zinc, copper, and nickel with the nonprotein amino acid L-alpha-amino-beta-methylaminopropionic acid: a naturally occurring neurotoxin

The non-protein amino acid L-alpha-amino-beta-methylaminopropionic acid (L-MeDAP) causes motor neuron dysfunction in macaques. The amino acid is a potent chelator of divalent metal ions such as copper and zinc. Binding constants nickel(II) for copper(II) and zinc(II) with L-MeDAP have been measured. Some copper(II) complexes of L-MeDAP have been synthesized and characterized by their electronic, infrared, and epr spectra. These results are used to comment on the possibility that metal ion complexation in the central nervous system is involved in the expression of the meurotoxicity of L-MeDAP.     

DNA gyrase (Topoisomerase II) from Pseudomonas aeruginosa

DNA gyrase (Topoisomerase II) has been purified from Pseudomonas aeruginosa strain PAO. This enzyme is inhibited by novobiocin and nalidixic acid. DNA gyrase from P. aeruginosa is resistant to a much higher level of nalidixic acid than is Escherichia coli DNA gyrase. This increased level of resistance may explain, at least in part, the higher levels of natural resistance exhibited by P. aeruginosa toward nalidixic acid.     

Equilibrium studies on the binding of cadmium(II) to human serum transferrin

The binding of cadmium(II) to human serum transferrin in 0.01 M N-(2-hydroxyethyl)-piperazine-N'-2-ethanesulfonic acid with 5 mM bicarbonate at 25 degrees C has been evaluated by difference ultraviolet spectroscopy. Equilibrium constants were determined by competition versus three different low molecular weight chelating agents: nitrilotriacetic acid, ethylenediamine-N,N'-diacetic acid, and triethylenetetramine. Conditional equilibrium constants for the sequential binding of two cadmium ions to transferrin under the stated experimental conditions are log K1 = 5.95 +/- 0.10 and log K2 = 4.86 +/- 0.13. A linear free energy relationship for the complexation of cadmium and zinc has been prepared by using equilibrium data on 243 complexes of these metal ions with low molecular weight ligands. The transferrin binding constants for cadmium and zinc are in good agreement with this linear free energy relationship. This indicates that the larger size of the cadmium(II) ion does not significantly hinder its binding to the protein.     

Thermodynamic and spectroscopic studies of Cu(II) and Ni(II) complexes with a new proline-threonine dipeptide ligand

The interactions between a new proline-threonine dipeptide ligand with two metallic cations were investigated in aqueous solution. The metallic cations studied were the copper(II) and the nickel(II), which are involved in many biological processes. The combination of potentiometry, UV-visible spectrophotometry, EPR, and mass spectrometry was used to determine the formation constants of the complexes and their structure in solution. The complexation sites were identified using electronic absorption and EPR spectroscopies. Copper complexes were obtained as square planar or square pyramidal mononuclear species, whereas nickel complexes were obtained as dinuclear species with an octahedral geometry.     

Effect of Nalidixic Acid and Hydroxyurea on Division Ability of Escherichia coli fil+ and lon− Strains

Short periods of incubation in medium containing nalidixic acid or hydroxyurea, followed by a return to normal growth conditions, induced filament formation in Escherichia coli B (fil(+)) and AB1899NM (lon(-)) but not in B/r (fil(-)) and AB1157 (lon(+)). These drugs reversibly stopped deoxyribonucleic acid (DNA) synthesis with little or no effect on ribonucleic acid (RNA) synthesis or mass increase. The initial imbalance caused by incubation in these drugs was the same for B and B/r as was macromolecular synthesis following a return to normal growth conditions. DNA degradation caused by nalidixic acid was measured and found to be the same for B and B/r. Hydroxyurea caused no DNA degradation in these two strains. Survival curves as determined under various conditions by colony formation suggested that the property of filament formation was responsible for the extrasensitivity of fil(+) and lon(-) strains to either nalidixic acid or hydroxyurea. E. coli B was more sensitive to either drug than was B/r or B(s-1). Pantoyl lactone or liquid holding treatment aided division and colony formation of nalidixic acid-treated B but had no effect on B/r. Likewise, the filament-former AB1899NM was more sensitive to nalidixic acid than was the non-filament-former AB1157. The sensitivity of B/r and B(s-1) to nalidixic acid was nearly the same except at longer times in nalidixic acid, when B(s-1) appeared more resistant. Even though nalidixic acid, hydroxyurea, and ultraviolet light may produce quite different molecular alterations in E. coli, they all cause a metabolic imbalance resulting in a lowered ratio of DNA to RNA and protein. We propose that it is this imbalance per se rather than any specific primary chemical or photochemical alterations which leads to filament formation by some genetically susceptible bacterial strains such as lon(-) and fil(+).     

Investigation of the reaction of magnesium with p-nitro-o-carboxylazochromotropic acid and the determination of magnesium in plants and in water

The formation of a novel complex between magnesium and p-nitro-o-carboxylazochromotropic acid (NCBAC) has been observed which is sensitive and selective at pH 10.4 in the presence of ethylenediamine and fluoride. The constants of formation of this complex have been determined by a spectral correction technique, and the complexation reaction has been applied to the spectrophotometric determination of trace magnesium in plants and in water with satisfactory results.     

Fluorescence quenching and bonding properties of some hydroxamic acid derivatives by iron(III) and manganese(II)

Spectrophotometric investigations of highly fluorescent metal chelating molecules are of relevance due to their potential application in novel, selective fluorescence‐based sensors. Benzene and naphthalene chromophores are highly fluorescent while hydroxamic acids are widely used as ligands for complexation of transition metals. In order to develop fluorescence probes, several phenyl derivatives of N‐phenylbenzohydroxamic acid and an aminodihydroxamic acid linked with a naphthalene chromophore were synthesized and their selective ionophoric properties towards iron(III) and manganese(II) ions were investigated using fluorescence and absorption spectroscopy. Both methods confirm the formation of 1:1 and 1:2 complexes for iron(III) and a 1:1 complex for manganese(II). The complex that is formed depends on the concentration of the ligand and pH of the medium. The amino dihydroxamic acid exhibits a prominent selectivity towards iron(III) with a two‐step 1:1 and 1:2 quenching mechanism at pH 3 and towards manganese(II) with a 1:1 quenching mechanism at a probe concentration of 1 × 10^?5 mol dm^?3 at pH 9.5 The logarithm of overall formation constants of 1:1 and 1:2 complexes of iron(III) were estimated as 3.30 and 9.05, respectively. Copyright © 2008 John Wiley & Sons, Ltd.     

Free metal ion depletion by “good's” buffers: II. N-(2-acetamido)-2-aminoethanesulfonic acid (ACESH): Complexes with Calcium(II), Magnesium(II), Manganese(II), Cobalt(II), Zinc(II), Nickel(II), and Cooper(II)

Potentiometric, visible, and infrared studies of the complexation of N-(2-acetamido)-2-aminoethanesulfonic acid (ACESH) by Ca(II), Mg(II), Mn(II), Co(II), Zn(II), Ni(II), and Cu(II) are reported. Ca(II), Mg(II), and Mn(II) were found not to complex with ACES^?, while Co(II), Zn(II), Ni(II), and Cu(II) were found to form 2:1, ACES^? to M²⁺, complexes, and [Cu(ACES)₂] was found to undergo stepwise deprotonation of the amide groups to form [Cu(H_?1ACES)₂^2?]. Formation (affinity) constants for the various metal complexes are reported, and the probable structures of the various metal chelates in solution are discussed.     

Kinetics of Ni(II) and Co(II) monocomplex formation with O-phospho-dl-serine

The complexation reactions of O-phospho-DL-serine with Ni(II) or Co(II) were studied at 25°C and ionic strength 0.2 M (KNO₃) by temperature-jump. The observed rate constants for formation of the Ni²⁺ and Co⁺² monocomplexes were (1.32 ± 0.09) × 10⁵ and (1.73 ± 0.33) × 10⁷ M^?1 sec^?1, respectively. Complexation is postulated to involve formation of a monocoordinated steady state intermediate followed by rate-determining chelate ring closure.     

The binding of metal ions by captopril (SQ 14225). Part II. Complexation of copper(II)

Formation constants for the interaction of copper(II) with captopril have been measured using (i) histidine and (ii) 2,3-diaminopropionic acid monohydrochloride as competing ligands to prevent redoxing. The main species present in both the binary and ternary experimental systems are reported. Blood plasma models based upon these new formation constants indicate that captopril at high doses may mobilise copper(II) from blood plasma.     

Complexing capacity scales and “energy-rich” bonds

Stability constants for equilibria between copper(II) and chelating ligands are analyzed for comparison with equilibria involving “energy-rich” bonds in biochemical reactions. Equilibria between copper(II) and α-aminoacids and between copper(II) and aminoethanols give a consistent explanation of the experimental behavior only if both processes of deprotonation and complexation are considered at the same time. At pH = 7 the free-energy changes are close to the free energy for hydrolysis of ATP to ADP. The same holds for free-energy changes for equilibria between copper(II), proton, and oligopeptides. It is also shown that the free-energy changes for equilibria between nickel(II), proton, and oligopeptides are near the value of the free energy of hydrolysis of glycerol-3-phosphate.     

Effect of anionic micelles on speciation of L-glutamine in presence/absence of metals

Abstract

Protonation equilibria of L-glutamine and speciation of its complexes with Co(II), Ni(II) and Cu(II) have been studied in 0–2.5% w/v SLS–water media using pH-metric method. The protonation constants and binary stability constants have been calculated with the computer program MINIQUAD75. Selection of the best fit chemical models is based on standard deviation in stability constants and residual analysis using crystallographic R-factor and sum of squares of residuals in all mass-balance equations. The trend in the variation of stability constants of the complexes with mole fraction of the medium is attributed to the compartmentalisation of complexation equilibria. Distribution of species and effect of influential parameters on chemical speciation have also been presented.     

Interaction between iron(II) and hydroxamic acids: oxidation of iron(II) to iron(III) by desferrioxamine B under anaerobic conditions

Interaction between iron(II) and acetohydroxamic acid (Aha), alpha-alaninehydroxamic acid (alpha-Alaha), beta-alaninehydroxamic acid (beta-Alaha), hexanedioic acid bis(3-hydroxycarbamoyl-methyl)amide (Dha) or desferrioxamine B (DFB) under anaerobic conditions was studied by pH-metric and UV-Visible spectrophotometric methods. The stability constants of complexes formed with Aha, alpha-Alaha, beta-Alaha and Dha were calculated and turned out to be much lower than those of the corresponding iron(II) complexes. Stability constants of the iron(II)-hydroxamate complexes are compared with those of other divalent 3d-block metal ions and the Irving-Williams series of stabilities was found to be observed. Above pH 4, in the reactions between iron(II) and desferrioxamine B, the oxidation of the metal ion to iron(III) by the ligand was found. The overall reaction that resulted in the formation of the tris-hydroxamato complex [Fe(HDFB)]+ and monoamide derivative of DFB at pH 6 is: 2Fe2+ + 3H4DFB+ = 2[Fe(HDFB)]+ + H3DFB-monoamide+ + H2O + 4H+. Based on these results, the conclusion is that desferrioxamine B can uptake iron in iron(III) form under anaerobic conditions.     

Free metal ion depletion by "Good's" buffers. I. N-(2-acetamido)iminodiacetic acid 1:1 complexes with calcium(ii). magnesium(II), zinc(II), manganese(II), cobalt(II), nickel(II), and copper(II).

Formation (affinity) constants for 1:1 complexes of N-(2-acetamido)iminodiacetic acid (ADAH₂) with Ca(II), Mg(II), Mn(II), Zn(II), Co(II), Ni(II), and Cu(II) have been determined. Probable structures of the various metal chelates existing in solution are discussed. Values for the deprotonation of the amide group in [Cu(ADA)] and subsequent hydroxo complex formation are also reported. The use of ADA as a buffer is considered in terms of metal buffers complexes which can be formed at physiological pH, i.e., at pH 7.0 there is essentially no free metal ion in 1:1 M²⁺ to ADA solutions.