The kinetics of acid-catalyzed dissociation of the copper(II) complex with 7-methyl-3,7,11,17-tetraazabicyclo[11.3.1]heptadeca-1(17),13,15-triene-3,11-diacetic acid (ac2Me[14]pyN4) at [H+] = 0.05-0.25 mol l-1, I = 0.25 mol l-1 (Na, H)ClO4, and T = 298.16 K was studied with conventional and stopped-flow UV/VIS spectroscopy. Three steps of consecutive complex reaction were observed. The very fast first and second steps characterized by k1 = 70 ± 10 and k2 = 0.23 ± 0.01 l mol-1 s-1 depend on the H+ concentration. The third step is very slow, k3 = (1.08 ± 0.03) × 10-3 s-1, and does not depend on the H+ concentration. Latter rate-determining step involves an isomerisation process forcing the copper(II) ion to leave rapidly the macrocyclic cavity. The reaction mechanism of the complex dissociation has been proposed, taking into account the results obtained for related systems by independent methods: potentiometry, UV/VIS and EPR spectroscopies, X-ray diffraction analysis, and molecular mechanics calculations.

• MeSH
• Kinetics MeSH
• Ligands MeSH
• Copper MeSH
• Organometallic Compounds chemical synthesis   MeSH
• Radiopharmaceuticals chemical synthesis   MeSH

A symmetrical flexible bis(phosphinoferrocene) derivative, viz. bis[1'-(diphenylphosphino)ferrocenyl]methane (1), was prepared and studied as a ligand in Pd(II) and Au(I) complexes. The reactions of 1 with [PdCl₂(cod)] (cod = cycloocta-1,5-diene) and [Pd(μ-Cl)(LNC)]₂ (LNC = [2-(dimethylamino-κN)methyl]phenyl-κC¹) produced bis(phosphine) complex trans-[PdCl₂(1-κ²P,P')] (4), wherein the ligand spans trans positions in the square-planar coordination sphere of Pd(II) and the tetranuclear, P,P-bridged complex [(μ(P,P')-1){PdCl(LNC)}₂] (5), respectively. In reactions with the Au(I) precursors [AuCl(tht)] and [Au(tht)₂][SbF₆] (tht = tetrahydrothiophene), ligand 1 gave rise to tetranuclear Au₂Fe₂ complex [(μ(P,P')-1)(AuCl)₂] (6) and to symmetrical macrocyclic tetramer [Au₄(μ(P,P')-1)₄][SbF₆]₄ (7). All compounds were characterized by spectroscopic methods. In addition, the structures of compound 1, its synthetic precursor bis[1'-(diphenylphosphino)ferrocenyl]methanone (3), and all aforementioned Pd(II) and Au(I) complexes were determined by single-crystal X-ray diffraction analysis (some in solvated form).

• MeSH
• Phosphines chemistry   MeSH
• Coordination Complexes chemical synthesis   MeSH
• Crystallography, X-Ray MeSH
• Ligands MeSH
• Metallocenes chemistry   MeSH
• Molecular Structure MeSH
• Palladium chemistry   MeSH
• Iron chemistry   MeSH
• Gold chemistry   MeSH
• Publication type
• Journal Article MeSH

The complexes of Fe(II), Mn(II) and Ni(II) with a combination of a Schiff base, nitrogen-donor ligand or macrocyclic ligand and trithiocyanuric acid (ttcH3) were prepared and characterized by elemental analysis and spectroscopies. Crystal and molecular structures of the iron complex of composition [Fe(L1)](ttcH2)(ClO4)·EtOH·H2O (1), where L1 is Schiff base derived from tris(2-aminoethyl)amine and 2-pyridinecarboxaldehyde, were solved. It was found that the Schiff base is coordinated to the central iron atom by six nitrogens forming deformed octahedral arrangement, whereas trithiocyanurate(1-) anion, perchlorate and solvent molecules are not coordinated. The X-ray structure of the Schiff base sodium salt is also presented and compared with the iron complex. The anticholinesterase activity of the complexes was also studied.

• MeSH
• Cholinesterase Inhibitors chemical synthesis   chemistry   pharmacology   MeSH
• Cholinesterases metabolism   MeSH
• Enzyme Assays MeSH
• Ethylenediamines chemistry   MeSH
• Coordination Complexes chemical synthesis   chemistry   pharmacology   MeSH
• Complex Mixtures chemistry   MeSH
• Rats MeSH
• Crystallography, X-Ray MeSH
• Ligands MeSH
• Manganese chemistry   MeSH
• Brain drug effects   enzymology   MeSH
• Nickel chemistry   MeSH
• Pyridines chemistry   MeSH
• Schiff Bases chemistry   MeSH
• Triazines chemistry   MeSH
• Iron chemistry   MeSH
• Animals MeSH
• Check Tag
• Rats MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH

Lanthanide(III) complexes of 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid (H(3)DO3A) are suggested as sensors for sensitive luminescence-based determination of a carbonate anion. Thermodynamic study of association of [Eu(H(2)O)(2)(DO3A)] with bidentate anionic ligands using luminescence spectroscopy reveals an affinity order CO(3)(2-) > oxalate(2-) > picolinate(-) > phthalate(2-) ≈ citrate(3-); presumably as a consequence of an increasing chelate ring size. The ternary [Eu(DO3A)(picolinate)](-) and [Tb(DO3A)(picolinate)](-) complexes show improved photophysical properties due to the antenna effect of the picolinate anion. High quenching effect of carbonate anion and, to a lesser extent also oxalate, enables construction of a linear calibration plot utilizing optimized experimental conditions (e.g. c(LnL) = 0.1 mM, c(picolinate) = 2-5 mM, pH = 7.4, λ(exc) = 286 nm, etc.) for carbonate determination in solution. Both sensors show a comparable sensitivity and the detection limit of about 0.4 mM. In order to improve the photophysical properties of Ln(III) sensor by shift of excitation wavelength about 40 nm to VIS range, the isoquinoline-3-carboxylic acid (IQCA) as antenna ligand was employed instead of picolinic acid. The analysis of commercial samples of European mineral waters was carried out and they were compared to the results obtained by capillary isotachophoresis to confirm there is no inherent (systematic) error to the present analysis. The Ln(III) sensor with IQCA is recommended since it has a better robustness than that with picolinate. The present analytical method is simple and rapid, and it is useful for sensitive determination of bicarbonate/carbonate concentration in water samples under aerobic conditions.

• MeSH
• Chemistry Techniques, Analytical instrumentation   MeSH
• Europium chemistry   MeSH
• Heterocyclic Compounds, 1-Ring chemistry   MeSH
• Ligands MeSH
• Luminescent Measurements MeSH
• Macrocyclic Compounds chemistry   MeSH
• Organometallic Compounds chemistry   MeSH
• Terbium chemistry   MeSH
• Thermodynamics MeSH
• Carbonates analysis   chemistry   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH

RATIONALE: Heavy metals are both a problem for the environment and an important resource for industry. Their selective extraction by means of organic ligands therefore is an attractive topic. The coordination of three thiacrown ethers to late 3d-metal ions was investigated by a combination of electrospray ionization mass spectrometry (ESI-MS) and electron paramagnetic resonance (EPR). METHODS: The mass spectrometric experiments were carried out in an ion trap mass spectrometer with an ESI source. Absolute binding constants were estimated by comparison with data for 18-crown-6/Na(+). EPR spectroscopy was used as a complementary method for investigating the Cu(I) /Cu(II) redox couple. RESULTS: The study found that thiacrown ethers preferentially bind traces of copper even at an excess of other metal ions (Co(II), Ni(II), and Zn(II)). The absolute association constants of the Cu(I) complexes were about 10(8) M(-1), and about two orders of magnitude lower for the other 3d-metal cations. The EPR spectra demonstrated that the reduction from Cu(II) to Cu(I) upon formation of the [(thiacrown)Cu](+) species takes place in solution. CONCLUSIONS: ESI-MS demonstrated that the three thiacrown ligands examined had high binding constants as well as good selectivities for copper(I) at low concentrations, and in the presence of other metal ions. By a combination of ESI-MS and EPR spectrometry it was shown that the reduction from Cu(II) to Cu(I) occurred in solution.

• Publication type
• Journal Article MeSH

The interactions of valinomycin, macrocyclic depsipeptide antibiotic ionophore, with ammonium cation NH4+ have been investigated. Using quantum mechanical density functional theory (DFT) calculations, the most probable structure of the valinomycin-NH4+ complex species was predicted. In this complex, the ammonium cation is bound partly by three strong hydrogen bonds to three ester carbonyl oxygen atoms of valinomycin and partly by somewhat weaker hydrogen bonds to the remaining three ester carbonyl groups of the valinomycin ligand. The strength of the valinomycin-NH4+ complex was evaluated experimentally by capillary affinity electrophoresis. From the dependence of valinomycin effective electrophoretic mobility on the ammonium ion concentration in the background electrolyte, the apparent binding (association, stability) constant (Kb) of the valinomycin-NH4+ complex in methanol was evaluated as log Kb = 1.52 +/- 0.22.

• MeSH
• Anti-Bacterial Agents chemistry   MeSH
• Financing, Organized MeSH
• Cations chemistry   MeSH
• Quantum Theory MeSH
• Quaternary Ammonium Compounds chemistry   MeSH
• Molecular Conformation MeSH
• Models, Molecular MeSH
• Valinomycin chemistry   MeSH

In a combined experimental and theoretical approach, the interactions of valinomycin (Val), macrocyclic depsipeptide antibiotic ionophore, with sodium cation Na(+ )have been investigated. The strength of the Val-Na(+ )complex was evaluated experimentally by means of capillary affinity electrophoresis. From the dependence of valinomycin effective electrophoretic mobility on the sodium ion concentration in the BGE (methanolic solution of 20 mM chloroacetic acid, 10 mM Tris, 0-40 mM NaCl), the apparent binding (stability) constant (K(b)) of the Val-Na(+ )complex in methanol was evaluated as log K(b) = 1.71 +/- 0.16. Besides, using quantum mechanical density functional theory (DFT) calculations, the most probable structures of the nonhydrated Val-Na(+) as well as hydrated Val-Na(+).H(2)O complex species were proposed. Compared to Val-Na(+), the optimized structure of Val-Na(+).H(2)O complex appears to be more realistic as follows from the substantially higher binding energy (118.4 kcal/mol) of the hydrated complex than that of the nonhydrated complex (102.8 kcal/mol). In the hydrated complex, the central Na(+) cation is bound by strong bonds to one oxygen atom of the respective water molecule and to four oxygens of the corresponding C=O groups of the parent valinomycin ligand.

• MeSH
• Electrophoresis, Capillary methods   instrumentation   MeSH
• Financing, Organized MeSH
• Cations chemistry   MeSH
• Models, Molecular MeSH
• Molecular Structure MeSH
• Osmolar Concentration MeSH
• Computer Simulation MeSH
• Sodium chemistry   MeSH
• Temperature MeSH
• Valinomycin analysis   chemistry   MeSH

Magnesium complexes of phthalocyanines (Pcs) and their aza-analogues have a great potential in medical applications or fluorescence detection. They are known to demetallate to metal-free ligands in acidic environments, however, detailed investigation of this process and its possible prevention is lacking. In this work, a conversion of lipophilic and water-soluble magnesium complexes of Pcs and tetrapyrazinoporphyrazines (TPyzPzs) to metal-free ligands was studied in relation to the acidity of the environment (organic solvent, water) including the investigation of the role of delivery systems (microemulsion or liposomes) in improvement in their acido-stability. The mechanism of the demetallation in organic solvents was based on an acidoprotolytic mechanism with the protonation of the azomethine nitrogen as the first step and a subsequent conversion to non-protonated metal-free ligands. In water, the mechanism seemed to be solvoprotolytic without any protonated intermediate. The water-soluble magnesium complexes were stable in a buffer with a physiological pH 7.4 while a time-dependent demetallation was observed in acidic pH. The demetallation was immediate at pH < 2 while the full conversion to metal-free ligand was done within 10 min and 45 min for TPyzPzs at pH 3 and pH 4, respectively. Incorporation of lipophilic magnesium complexes into microemulsion or liposomes substantially decreased the rate of the demetallation with the latter delivery system being much more efficient in the protection from the acidic environment. A comparison of two different macrocyclic cores revealed significantly higher kinetic inertness of magnesium TPyzPz complexes than their Pc analogues.

• Publication type
• Journal Article MeSH

In magnetic resonance imaging (MRI), paramagnetic complexes are utilized as contrast agents. Much attention has been paid to the development of new contrast agents responsive to pH, temperature or concentration of various components of body liquids. We report a new type of MRI probe sensing the concentrations of calcium and magnesium in biological media. The ligand do3ap(BP) combines a dota-like chelator with a bisphosphonate group. In the complex, the Gd(III) ion is entrapped in the macrocyclic cavity whereas the bisphosphonate group is not coordinated and therefore is available for coordination with endogenous metal ions. In the presence of metal ions, Gd-do3ap(BP) appears to show formation of coordination oligomers leading to an unprecedented increase in r(1) up to 200-500%. The extremely high relaxivity response makes this type of compound interesting for further studies as MRI ion-responsive probes for biomedical research.

• MeSH
• Diphosphonates chemistry   MeSH
• Gadolinium chemistry   MeSH
• Magnesium chemistry   MeSH
• Contrast Media chemistry   MeSH
• Magnetic Resonance Imaging methods   MeSH
• Calcium chemistry   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH

Radiolabeled bisphosphonates are commonly used in the diagnosis and therapy of bone metastases. Blood clearance of bisphosphonates is usually fast and only 30%-50% of the injected activity is retained in the skeleton, while most of the activity is excreted by the urinary tract. A longer blood circulation may enhance accumulation of bisphosphonate compounds in bone metastases. Therefore, a chemically modified macrocyclic bisphosphonate derivative with an additional human albumin binding entity was synthesized and pharmacokinetics of its complex was evaluated. The DOTA-bisphosphonate conjugate BPAMD was compared against the novel DOTAGA-derived albumin-binding bisphosphonate DOTAGA(428-d-Lys)M(BP) (L1). The ligands were labeled with (68)Ga(III) and were evaluated in in vitro binding studies to hydroxyapatite (HA) as well as to human serum albumin. The compounds were finally compared in in vivo PET and ex vivo organ distribution studies in small animals over 6h. Binding studies revealed a consistent affinity of both bisphosphonate tracers to HA. Small animal PET and ex vivo organ distribution studies showed longer blood retention of [(68)Ga]L1. [(68)Ga]BPAMD is initially more efficiently bound to the bone but skeletal accumulation of the modified compound and [(68)Ga]BPAMD equalized at 6h p.i. Ratios of femur epiphyseal plate to ordinary bone showed to be more favorable for [(68)Ga]L1 than for [(68)Ga]BPAMD due to the longer circulation time of the new tracer. Thus, the chemical modification of BPAMD toward an albumin-binding bisphosphonate, L1, resulted in a novel PET tracer which conserves advantages of both functional groups within one and the same molecule. The properties of this new diagnostic tracer are expected to be preserved in (177)Lu therapeutic agent with the same ligand (a theranostic pair).

• MeSH
• Adsorption MeSH
• Diphosphonates chemistry   metabolism   pharmacokinetics   MeSH
• Heterocyclic Compounds, 1-Ring chemistry   MeSH
• Durapatite chemistry   MeSH
• Bone and Bones diagnostic imaging   metabolism   MeSH
• Rats MeSH
• Humans MeSH
• Rats, Wistar MeSH
• Positron-Emission Tomography MeSH
• Gallium Radioisotopes MeSH
• Serum Albumin metabolism   MeSH
• Tissue Distribution MeSH
• Animals MeSH
• Check Tag
• Rats MeSH
• Humans MeSH
• Male MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH