4,7,10,13-Tetrakis(carboxymethyl)-1-oxa-4,7,10,13-tetraazacyclopentadecane and properties of its metal complexes

A new N-carboxymethyl derivative of the oxa-tetraaza macrocyle, 4,7,10,13-tetrakis-(carboxymethyl)-1-oxa-4,7,10,13-tetraazacyclopentadecane, has been synthesised. The protonation constants of this compound and the stability constants of its complexes with several di- and trivalent metal ions were determined by potentiometric or spectrophotometric methods, at 25°C and ionic strength 0.10 M in tetramethyl ammonium nitrate. The ligand exhibits two high or fairly high values of protonation constants and two low ones, and its overall basicity is about 27 in log units. Mono- and dinuclear complexes were found. The stability constant values of the 1:1 complexes with most of the metal ions studied are lower than expected, but not those of the dinuclear complexes. This was interpreted, in the case of mononuclear complexes, as the non-involvement in the co-ordination to these metal ions of two nitrogen atoms of the macrocycle backbone and, probably also, of one or two carboxylate groups. The Cu²⁺ ion has an exceptional behaviour, its 1:1 complex exhibits a high stability constant value. Spectroscopic data have indicated, for the last complex, the presence of two octahedral isomers in solution, one of them having only two nitrogens in the co-ordination sphere, while in the other three nitrogen donor atoms of the macrocyclic framework are co-ordinated in the equatorial plane. A third species appears at pH values higher than 7. These features suggest that the presence of four carboxymethyl arms and the relatively large size of the macrocycle severely constrains the geometric arrangement of the nitrogen donor atoms of the macrocyclic backbone around the metal centre decreasing the co-ordination number or leading to a preferred co-ordination with oxygen atoms. Another consequence of these structural features, is their easy ability to form dinuclear complexes, as found in the equilibria studies in solution and also by EPR spectroscopy of the Cu²⁺ complexes where the presence of two types of signals in the ΔM_s=1 and ΔM_s=2 regions, clearly reveals the presence of the dinuclear complex.     

Ion-Pair High-Performance Liquid Chromatographic Retention Behavior of Copper(II)–1-Oxa-4,7,10,13- tetraazacyclopentadecane Complex

The ion-pair high-performance liquid chromatographic retention behavior of copper(II)–1-oxa-4,7,10,13-tetraazacyclopentadecane (Cu(II)–OTACP) complex is discussed with data from indirect spectrophotometric detection on the μBondapak CN column. The mobile phase was acetonitrile solution (MeCN:H₂O 20:80) containing sodium dodecyl sulfate (SDS) as ion-pairing reagent and sodium 1-naphthalenesulfonate (SNS) as detection reagent. The effects of the concentration of SDS and OTACP added to the sample solution to form the Cu(II)–OTACP complex on the capacity factor of the complex, k′, are illustrated. As a consequence of the study, it was found that two peaks anticipated for the 1:1 and 1:2 mole ratio complexes appeared, and the peak anticipated for the 1:2 mole ratio complex could be used to determine the Cu(II) ion. The method has been applied in the determination of Cu(II) ion in waste water and serum.     

Metal Complexes of Pentadentate Macrocyclic Ligands Containing Oxygen and Nitrogen as Donor Atoms

Four macrocyclic ligands have been synthesized: 1-oxa-4,7,10,13-tetraazacyclopentadecane ( 1 ), 1,4-dioxa-7,10,13-triazacyclopentadecane ( 2 ), 1,4-dioxa-7,11,14-triazacyclohexadecane ( 3 ), 1,4-dioxa-7,11,15-triazacycloheptadecane ( 4 ), one of them 3 , for the first time. The protonation constants of the ligands and the stability constants of the complexes formed by the four ligands with some divalent first-series transition-metal ions, Cd²⁺ and Pb²⁺, were determined by potentiometric methods, in aqueous solution, at 25° and I = 0.10M (KNO₃). The sequence of protonation of ligand 1 was studied by ¹H-NMR spectroscopy. The Irving-Williams' order of stability is obeyed for the complexes of all the ligands, and the metal complexes of 1 present the higher values of stability. A drop in the stability of all the metal complexes studied is observed when the metal complexes of 1 are compared with the corresponding complexes of 2 . The effect of the increase of the ring size of the macrocycle can be observed for metal complexes of the series of ligands 2 4 , where, in spite of the slight increase of the overall basicity of the ligands (20.28, 22.25, and 24.96 for 2, 3 , and 4 respectively), small differences in stability are found for the corresponding complexes of 2 and 3 , but a significant drop occurs for all the metal complexes formed with the 17-membered ligand, specially for the larger metal ions like Mn²⁺ and Pb²⁺.     

Spectrophotometric and Potentiometric Studies on the Binding Abilities of Two Novel Tripodal Imine-Phenol Ligands Towards Al(III) and Ga(III)

The aqueous coordination behavior of two novel tripodal imine-phenol ligands, cis,cis-1,3,5-tris{(2-hydroxybenzilidene)aminomethyl}cyclohexane (TMACHSAL, L¹) and cis,cis-1,3,5-tris{[(2-hydroxyphenyl)ethylidene]aminomethyl}cyclohexane (Me₃- TMACHSAL, L²) with Al³⁺ and Ga³⁺ has been investigated at an ionic strength of 0.1 mol⋅dm⁻³ KCl and 25±1 °C by potentiometric and spectrophotometric methods. Both ligands formed various monomeric metal complex species MLH₃, MLH₂, MLH, ML and MLH₋₁ with Ga(III); and MLH₃, ML and MLH₋₁ with Al(III). The Ga(III) complexes showed higher thermodynamic stability than the Al(III) complexes. Semi-empirical PM6 calculations along with TDDFT/B3LYP/3-21G calculations have been performed to complement the experimental measurements. The calculated structure of the metal complexes predicted a distorted octahedral geometry where favorable ring-flipping from the equatorial conformation in uncomplexed ligands to the axial conformation was observed upon chelation.     

Interaction of Co(II), Ni(II), Cu(II), and Zn(II) with 12- and 14-membered macrocycles containing O2N2 donors

The 12- and 14-membered diazadioxo macrocyclic ligands, 1,2?:?7,8-diphenyl-6,9-diaza-3,12-dioxocyclododecane (L¹) and 1,2?:?8,9-diphenyl-7,10-diaza-3,14-dioxocyclotetradecane (L²), were synthesized by condensation between o-phenylenediamine, 1,2-dibromoethane/1,3-dibromopropane, and catechol. Metal complexes [ML¹Cl₂] and [ML²Cl₂] [M?=?Co(II), Ni(II), Cu(II), and Zn(II)] were prepared by interaction of L¹ or L² with metal(II) chlorides. The ligands and their complexes were characterized by elemental analyses, IR, ¹H, and ¹³C NMR, EPR, UV-Vis spectroscopy, magnetic susceptibility, conductivity measurements, and Electrospray ionization-mass spectral (ESI-MS) studies. The results of elemental analyses, ESI-MS, Job's method, and conductivity measurements confirmed the stoichiometry of ligands and their complexes while absorption bands and resonance peaks in IR and NMR spectra confirmed the formation of ligand framework around the metal ions. Stereochemistry was inferred from the UV-Vis, EPR, and magnetic moment studies.     

Synthesis,Spectroscopic Characterization,and Antifungal Activity of Some Mixed Ligand Complexes of Zn(II), Cd(II), and Hg(II)

A series of new mixed ligand complexes of Zn(II), Cd(II), and Hg(II) with citronellal thiosemicarbazone [3,7-dimethyl-6-octene-1-a1 thiosemicarbazone (LH)] and N-phthaloyl amino acids (AH) have been synthesized by the reaction of metal(II) chloride with ligands citronellal thiosemicarbazone (DOTSC) and N-phthaloyl glycine [1,3-dihydro-1,3-dioxo-2H-isoindole-2-acetic acid (A₁H)] or N-phthaloyl alanine [1,3-dihydro-1,3-dioxo-α(methyl)-2H-isoindole-2-acetic acid (A₂H)] in 1:1:1 molar ratio in dry refluxing ethanol. All the complexes have been characterized by elemental analyses, molar conductance measurement, molecular weight measurement, IR, and multinuclear NMR (¹H and ¹³C{¹H}) spectral studies. IR, ¹H, and ¹³C{¹H} NMR spectral studies suggest the involvement of azomethine-N, thiol-S atoms of the thiosemicarbazone moiety and both carboxylate-O of N-phthaloyl amino acid moiety in coordination with central metal(II) ion, and four coordinated geometries have been assigned to these complexes. The free ligands and metal complexes have been screened for their antifungal activity against two fungal strains, Fusarium moniliformae and Macrophomina phaseolina, using the the radial growth method. The results of antifungal activity show that metal complexes show enhanced higher activity than the free ligands.

Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.     

Thermodynamic and spectroscopic study of the interaction of Cu(II), Ni(II), Zn(II) and Ca(II) ions with 2-amino-N-(2-oxo-2-(2-(pyridin-2-yl)ethyl amino)ethyl)acetamide,a pseudo-mimic of human serum albumin

The protonation equilibria of 2-amino-N-(2-oxo-2-(2-(pyridin-2-yl)ethyl amino)ethyl)acetamide ([H₂(556)–N]) and the complexation of this ligand with Cu(II) Ca(II), Zn(II) and Ni(II) have been studied by glass electrode potentiometry and UV–visible spectrophotometry. From pH ∼2.00–11.00, five models for Cu(II) with the following complexes; MLH, ML, MLH₋₁, MLH₋₂ and MLH₋₃ were generated and observed to describe the experimental data equally well as far as the statistical criteria were concerned. The MLH₋₂ complex predominates at physiological pH in all five models, while the MLH₋₁ complex species exists only at low concentration in two models. The coordination in the MLH₋₂ complex suggested the involvement of one amino, two deprotonated peptides and one pyridyl nitrogen atoms. Molecular mechanics (MM) calculations confirmed the MLH₋₂ complex as the most stable species. Speciation calculations, using a blood plasma model, predicted that the Cu(II)–[H₂(556)–N] complex is able to mobilize Cu(II). Octanol/water partition of CuLH₋₂ showed that 30% of the complex went into the octanol phase, hence promoting percutaneous absorption of copper. The complex is a poor mimic of native copper–zinc superoxide dismutase.     

Mixed ligand complexes of palladium(II) and platinum(II) with methionine and 2,4-disubstituted pyrimidines

Summary Mixed ligand complexes ofcis-[M(MetH)Cl₂] (M=Pd²⁺ and Pt²⁺; MetH=methionine) with 2,4-disubstituted pyrimidines were prepared and characterised. Thecis-[Pd(MetH)Cl₂] complex reacted with cytosine (2-hydroxy-4-aminopyrimidine), isocytosine (2-amino-4-hydroxypyrimidine) and thiocytosine (2-thio-4-amino-pyrimidine) to form ternary complexes.cis-[Pt(MetH)Cl₂] however reacted with cytosine, uracil (2,4-pyrimidine dione or 2,4-dihydroxypyrimidine) to yield the corresponding mixed ligand complexes. The primary ligand, methionine, binds to the metal ion through sulphur and amino nitrogenvia a six membered chelate ring. The secondary ligands (substituted pyrimidines) bind to the Pd²⁺ or Pt²⁺ metal ion through the ring nitrogen (N₃), as monodentate ligand. Thiocytosine however acts as a bidentate ligand, coordinating to the metal ion through-SH and ring nitrogen (N₃). All complexes are 11 electrolytes, except the thiocytosine complex, which is a 12 electrolyte.     

Thermochemical and spectrophotometrical study of Ni(II) Complexes with Thiadiamines

Ni(II) complexes of some linear tridentates with one sulphur and two nitrogen donors have been studied in aqueous solution at 25°C in 0.5 M (K)NO₃ medium by means of the calorimetric and spectrophotometric technique. It is shown that the percentage facial isomer in the NiL²⁺ complexes becomes more important with increasing substitution on the nitrogen or sulphur donor atoms. The NiL₂²⁺ complexes most probably have a trans-facial tetragonally distorted structure with four equatorially bound nitrogen donors and in axial position the sulphide donors. The same {Ni-(N₄S₂)}²⁺ cation was also present in the NiL₂(NO₃)₂ solid state compounds.     

Synthesis and characterization of copper(II) and nickel(II) complexes of a di-N-carboxymethylated tetraaza macrocycle

The reaction of 3,14-dimethyl-2,6,13,17-tetraazatricyclo[14,4,0^1.18,0^7.12]docosane (L¹) with bromoacetic acid produced the macrocycle (L²=2,13-bis(2-carboxymethyl)-3,14-dimethyl-2,6,13,17-tetraazatricyclo[14,4,0^1.18,0^7.12]docosane) in which two carboxymethyl groups are appended. The complexes [NiL²]·4H₂O (2) and [CuL²]·4H₂O (3) have been prepared and characterized. The two pendant carboxymethyl groups of the macrocyclic ligand are trans to each other, and the absolute configuration is a trans-III in the solid state. The crystal structures of 2 and 3 revealed an axially elongated octahedral geometry with four nitrogen atoms of the macrocycle and two oxygen atoms of the pendant arms at the axial positions. The nickel(II) and copper(II) ions are located at an inversion center. Macrocycle L² reacts more rapidly with metal (II) ions than does L¹. Spectra and electrochemical behaviors of the complexes are also discussed.     

Complexation of a tripodal amine-catechol ligand tris((2,3-dihydroxybenzylamino)ethyl)amine towards Al(III), Ga(III), and In(III)

Abstract  

The complexation of a tripodal amine-catechol ligand tris((2,3-dihydroxybenzylamino)ethyl)amine (TRENCAT, L) with group-13 metal ions, viz., Al(III), Ga(III), and In(III), were investigated by means of potentiometric titrations and spectrophotometric measurements in an aqueous medium of 0.1 M KCl at 25 ± 1 °C. The ligand shows the potential to form various monomeric complexes of the types MLH₃, MLH₂, MLH, and ML. At low pH, the ligand is coordinated through three more acidic ortho-catecholic O-atoms to give MLH₃ species. With the rise in pH, the species MLH₃ releases three protons in steps from the meta-catecholic O-atoms to form MLH₂, MLH, and ML. The order of stability Ga(III) > Al(III) > In(III) for the species MLH₃ and MLH₂ is changed into Al(III) > Ga(III) > In(III) for the species MLH and ML. The coordination modes, binding ability, selectivity, and the change in stability order were explained with the help of experimental evidence, molecular modeling calculations, and available literature.     

Nickel(II) and cobalt(II) complexes of rhodanine

Summary Nickel(II) and cobalt(II) complexes of rhodanine (Hrd) were prepared from the metal chloride or acetate and the ligand. With an excess of NH3, the octahedral [Ni(NH₃)₆](Rd)₂ and [Co(NH₃)₅Rd]Rd complexes are ob-tained; use of only two NH₃ equivalents per metal ion yields the Ni(Rd)₂ sd HRd · NH₃ and [Co(Rd)₂ ] · 1.5 H₂O complexes, the first with tetragonally distorted hexacoordination and the second with polymeric octahedral coordination. By using two equivalents of NaOH per metal ion, the binuclear [Ni(Rd)₂][Ni(Rd)₂ · (HRd)₂] · 2 H₂O complex is formed having one diamagnetic planar and one high spin octahedral chromophore. Rhodanine is coordinated through the thiocarbonylic sulphur in the neutral form and through the thiocarbonylic sulphur and the deprotanated nitrogen atoms in the rhodanidato anionic form.     

Hg(II) and Cd(II) complexes with mixed donor macrocyclic thioethers: The oxophobicity of mercury(II)

A series of Hg(II) and Cd(II) homoleptic complexes with mixed donor (O,S and N,S) macrocycles is reported. The macrocyclic oxa thiacrowns 9S2O (1-oxa-4,7-dithiacyclononane) and 18S4O2 (1,10-dioxa-4,7,13,16-tetrathiacyclooctadecane) bind to Hg(II) to form distorted tetrahedral S4 geometries without coordination of the oxygen atoms. In contrast, the two macrocycles coordinate to Cd(II) through all ligand donors to form S4O2 environments. We also report the structure of bis(9N2S (1,4-diaza-7-thiacyclononane))cadmium(II), [Cd(9N2S)₂]²⁺ which shows octahedral coordination in a trans N4S2 environment. Furthermore, two new homoleptic Cd(II) complexes with the related hexadentate macrocycles 18N6 (1,4,7,10,13,16-hexaazacyclooctadecane) and 18S6 (1,4,7,10,13,16-hexathiayclooctadecane) are described. Among the Cd(II) complexes, we highlight a trend in ¹¹³Cd NMR that shows progressive upfield chemical shifts as secondary amine donors replace thioether S donors.     

One-dimensional hydrogen-bonded infinite chains composed of nickel(II) and copper(II) tetraaza macrocyclic complexes with cyclopropane-1-carboxylic acid-1-carboxylate ligand

The reaction of [M(L)]Cl₂ · 2H₂O (M = Ni²⁺ and Cu²⁺, L = 3,14-dimethyl-2,6,13,17-tetraazatricyclo[14,4,0^1.18,0^7.12]docosane) with 1,1-cyclopropanedicarboxylic acid (H₂-cpdc) generates one-dimensional hydrogen-bonded infinite chains [Ni(L)(H-cpdc)₂] (1) and [Cu(L)(H-cpdc)₂] (2) (H-cpdc = cyclopropane-1-carboxylic acid-1-carboxylate). These complexes have been characterized by X-ray crystallography, spectroscopy, and cyclic voltammetry. The crystal structures of (1) and (2) show a distorted octahedral coordination geometry around the metal ion, with four secondary amines and two oxygen atoms of the H-cpdc ligand at the trans position. Complexes (1) and (2) display the one-dimensional hydrogen-bonded infinite chains. The cyclic voltammogram of the complexes display two one-electron waves corresponding to M^II/M^III and M^II/M^I processes. The electronic spectra and electrochemical behavior of the complexes are significantly affected by the nature of the axial H-cpdc ligand.     

Copper(II) complexes of pentadentate 17‐membered macrocyclic di­amido­diamines with N,O or S as additional donors

The crystal structures of (2,6‐dioxo‐1,4,7,11,14‐penta­aza­cyclo­heptadecanato)copper(II) tetrahydrate, [Cu(C₁₂H₂₃N₅O₂)]·4H₂O, (I), (3,16‐dioxo‐1‐oxa‐4,8,11,15‐tetra­aza­cyclo­heptadecanato)copper(II) pentahydrate, [Cu(C₁₂H₂₂N₄O₃)]·5H₂O, (II), and (3,16‐dioxo‐1‐thia‐4,8,11,15‐tetra­aza­cyclo­heptadecanato)copper(II) trihydrate, [Cu(C₁₂H₂₂N₄O₂S)]·3H₂O, (III), are reported. The coordination geometry in each case is approximately square pyramidal with two amine groups and two deprotonated amide groups in the basal plane. The apical position is occupied by an amine group, an ether O atom or a thio S atom. Trigonal distortion increases in the sequence S < O < N as apical donor. The relation between the distortion in the basal plane of the complexes and the maxima in their electronic spectra is discussed.     

Infrared spectra of o-toluidine and m-toluidine complexes of Co(II), Ni(II), Cu(II) and Zn(II) halides

The infrared spectra of eighteen metal complexes of empirical formula [ML₂X₂] (M = Co, Ni, Cu or Zn; L = o^? or m-toluidine; X = Cl, Br or I) have been determined over the range 4000-150 cm^?1. Assignments of the internal vibrations of the amino group are based on the band shifts induced by ¹⁵N-labelling of the nitrogen donors. Bands within the range 400–600 cm^?1 are assigned to the metal-nitrogen stretching frequency (vM-N) on the grounds of their sensitivity to ¹⁵N-labelling and metal ion substitution and their absence of sensitivity to halide substitution. Bands within the range 350–150 cm^?1 are assigned to the metal-halogen stretching frequency (vM-X) on the basis of their sensitivity to halide and metal ion substitution and their insensitivity to ¹⁵N-labelling. Structural aspects of the spectra are discussed and the present assignments are compared with those previously reported.     

Kinetics and equilibrium study of nickel(II) complexation by pterin

The kinetics of complexation of Ni(II) by pterin was studied in aqueous solutions with a stopped‐flow apparatus under conditions of pseudo‐first order in the temperature range 5–45°C, pH between 4.0 and 6.5, and ionic strength 0.4 M. The equilibrium constants, stoichiometry, and pK_a of the ligand and complex were also determined using a spectrophotometric technique. The results are consistent with the formation of a 1:1 complex between the metal ion and pterin. The first‐order experimental rate constant k_app is pH independent and shows the following dependence with the ion metal concentration at 25°C: k_app/s⁻¹ = 3.8 × 10⁻³ + 1.6 × 10⁻⁴ × [Ni(II)]⁻¹. A global activation energy of 57 ± 2 kJ/mol associated with the formation of a 1:1 chelate was measured. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 231–237, 2000     

Complexation of a tripodal amine-catechol ligand tris((2,3-dihydroxybenzylamino)ethyl)amine towards Al(III), Ga(III), and In(III)

Abstract  The complexation of a tripodal amine-catechol ligand tris((2,3-dihydroxybenzylamino)ethyl)amine (TRENCAT, L) with group-13 metal ions, viz., Al(III), Ga(III), and In(III), were investigated by means of potentiometric titrations and spectrophotometric measurements in an aqueous medium of 0.1 M KCl at 25 ± 1 °C. The ligand shows the potential to form various monomeric complexes of the types MLH₃, MLH₂, MLH, and ML. At low pH, the ligand is coordinated through three more acidic ortho-catecholic O-atoms to give MLH₃ species. With the rise in pH, the species MLH₃ releases three protons in steps from the meta-catecholic O-atoms to form MLH₂, MLH, and ML. The order of stability Ga(III) > Al(III) > In(III) for the species MLH₃ and MLH₂ is changed into Al(III) > Ga(III) > In(III) for the species MLH and ML. The coordination modes, binding ability, selectivity, and the change in stability order were explained with the help of experimental evidence, molecular modeling calculations, and available literature. Graphical Abstract        

Complexation of poly(ethyleneimine) with copper(II) and nickel(II) ions in 0.5 M KNO3 solution

Complexation of poly(ethyleneimine) (PEI) with copper(II) and nickel(II) ions was studied in a 0.5M aqueous KNO₃ solution. The potentiometrically determined logarithm of the three successive formation constants (log k_J) were 8.14, 7.96, and 7.37 for Cu⁺²-PEI complexation and 6.74, 6.52, and 6.23 for Ni⁺²–PEI complexation at 25°C, according to Bjerrum's modified method. The maximum average coordination number was 3.2 for the Cu⁺²–PEI system and 3.7 for the Ni⁺²–PEI system. An entropy effect was observed in the third coordination. The wavelengths of maximum absorption of the complexes and the continuous variation method showed that at least two coordination sites of Cu⁺² ion and three coordination sites of Ni⁺² ion were occupied immediately by PEI as the solutions of PEI and the metal ions were mixed.     

Investigation of Cd(II), Pb(II) and Cu(I) complexation by glutathione and its component amino acids by ESI-MS and size exclusion chromatography coupled to ICP-MS and ESI-MS

The elucidation of structures of glutathione (GSH) complexes play an important role in the fundamental understanding of biochemical pathways of metal ion deactivation in plants. This article attempts to feature key studies for stoichiometry of metal complexes with glutathione and its constituent amino acids to obtain a better understanding of the different metal affinities of the complexation sites of glutathione. The SEC-ICP-MS experiments have indicated that oxidation process of glutathione was accelerated by metal ion presence in following order Cu⁺, Pb²⁺ and Cd²⁺. The redox activity of metal ions was confirmed by ESI-MS experiments, which allowed to observe formation of glutathione disulphide (GSSG) in time. The stoichiometry of Cd²⁺, Cu⁺ and Pb²⁺ complexes with GSH was defined by observing the isotope pattern of investigated metals and hydrogen loss or transfer during binding. The complexes with metal bound to sulphur of 1:1 and 1:2 stoichiometry were found in case of cadmium and lead. The number of hydrogen atoms lost during metal binding and the SEC-ESI-MS results allowed to elucidate that copper is bound by GSSG in ratio 1:1 and 1:2. Additionally, size exclusion chromatography coupled to electrospray MS allowed to differentiate more stable complexes from weak ones that could be created in the gas phase.