Voltammetric studies on composition and stabilities of complexes of tetracycline and oxytetracycline with some metal ions in aqueous medium

Summary The composition and stability of complexes of tetracycline and oxytetracycline with Cu(II), Cd(II), Pb(II) and UO₂(II) have been studied polarographically (direct current and differential pulse polarographic techniques) at 25±0.1°C. Differential pulse polarographic studies have been particularly helpful in deciding the nature of metal-drug interactions at low concentrations. The reduction of Cu(II)-tetracycline has been found to be irreversible and diffusion controlled with the presence of an adsorption component. In the system uranyl(II)-tetracycline the complex formed has a stoichiometry of 1:1 and logK _ox=4.04 which is very close to that obtained by potentiometric measurements. The peak half widthW _1/2 of the Pb(II)-OTC system is 60 – 70mV indicating that the process is reversible and two electrons are consumed. The log is 10.30 in 0.1 mol dm^–3 NaClO₄. In the Cu(II)-OTC system two complexes were formed with log ₁=8.50 and log ₂=14.10. Cyclic voltammograms were recorded using a hanging dropping mercury electrode for the systems Cu(II), Cd(II), Pb(II) and UO₂(II)-OTC to examine the irregularities in both peak potentials and peak currents during the polarographic investigations.

---

Voltammetrische Untersuchungen zur Zusammensetzung und Stabilität von Komplexen von Tetracyclin und Oxytetracyclin mit einigen Metallionen in wäßrigem Medium

Zusammenfassung Es wurden Zusammensetzung und Stabilität von Tetracyclin- und Oxytetracyclin-Komplexen mit Cu(II), Cd(II), Pb(II) und UO₂(II) polarographisch mittels Direktstrom- und differentieller Pulspolarographie-Technik bei 25±0.1°C bestimmt. Zur Aufklärung der Metall-Substrat-Wechselwirkungen bei geringen Konzentrationen waren insbesonders differentielle Pulspolarographie-Untersuchungen erfolgreich. Es wurde festgestellt, daß die Reduktion von Cu(II)-Tetracyclin irreversibel und diffusionskontrolliert verläuft. Im System Uranyl(II)-Tetracyclin hat der Komplex eine Stöchiometrie von 1:1 und ein logK _oxvon 4.04; dieser Wert ist dem aus potentiometrischen Messungen erhaltenen sehr ähnlich. Die Peak-Halbwertsbreite des Pb(II)-OTC-Systems ist 60 – 70 mV und zeigt damit einen reversiblen Prozess bei Verbrauch von zwei Elektronen an. In 0.1 mol dm^–3 NaClO₄ ist log 10.30. Im Cu(II)-OTC-System werden zwei Komplexe mit log ₁=8.50 und log ₂=14.10 gebildet. Die cyclischen Voltammogramme wurden unter Verwendung einer hängenden tropfenden Quecksilberelektrode für die Systeme Cu(II), Cd(II), Pb(II) und UO₂(II)-OTC aufgenommen, um die Unregelmäßigkeiten der Peak-Potentiale und der Peak-Ströme während der polarographischen Untersuchung zu überprüfen.

     

Ternary complexes of some phenoxyacetic acid herbicides and pyridines with metal ions of biological interest

Ternary complexes of Co(II), Ni(II) and Cu(II) with pyridine (Py) or 2-methyl pyridine (2-MePy) (primary ligand) and some phenoxyacetic acid herbicides, such as phenoxyacetic acid (PAA), 2-chlorophenoxyacetic acid (2-CPA), 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) (secondary ligands) have been studied in solution using a potentiometricpH-titration technique in order to test a complexation hypothesis of plant growth regulating activities of these herbicides. From stability constant data, the species distribution have been computed and it was found that the percentage of ternary complex (MAL) is about 60% of the totalM ²⁺ present at highpH indicating greater stability of these ternary complexes. TheMA ⁺ species (M ²⁺-Py andM ²⁺-2-MePy) have shown discriminating behaviour towards the next incoming secondary ligand containing O as donor atoms. Since the stabilities of biologically active (2-CPA, 2,4-D and2,4,5-T) and inactive (PAA) phenoxyacetic acid herbicides in binary (ML ₂) and ternary (MAL) metal complexes were found approximately of the same magnitude, chelation may not thus be the probable mode of action of these plant growth regulators.

---

Ternäre Komplexe einiger Phenoxyessigsäure-Herbizide mit Pyridin und Metallionen von biologischer Bedeutung

Zusammenfassung Ternäre Komplexe von Co(II), Ni(II) und Cu(II) mit Pyridin (Py) oder 2-Methylpyridin (2-Me Py) als Primärliganden und einigen Herbiziden vom Phenoxyessigsäure-Typ [Phenoxyessigsäure (PAA), 2-Chlor-PAA (2-CPA), 2,4-Dichlor-PAA (2,4-D) und 2,4,5-Trichlor-PAA (2,4,5-T)] als Sekundärliganden wurden im Hinblick auf eine Komplexierungshypothese der pflanzenwuchssteuernden Wirkung dieser Herbizide mittels potentiometrischerpH-Titration untersucht. Aus den Stabilitätskonstanten wurden die Anteile der einzelnen Spezien in Lösung berechnet. Dabei wurden 60% an ternärem Komplex (MAL) — bezogen auf die totaleM ^2–-Menge — bei hohenpH-Werten festgestellt und damit die größere Stabilität dieser Komplexe gezeigt. DieMA ⁺-Spezies (M ²⁺-Py undM ²⁺-MePy) zeigte ein unterschiedliches Verhalten gegenüber dem nächsten chelierenden Liganden mit O als Donor. Da die Stabilitäten der biologisch aktiven (2-CPA, 2,4-D und2,4,5,-T) und inaktiven (PAA) Liganden in binären (ML ₂) und ternären (MAL) Metallkomplexen in der gleichen Größenordnung liegen, scheint die Komplexierung bei der Regulierung des Pflanzenwuchses bei diesen Herbiziden kein entscheidender Faktor zu sein.

     

Potentiometric and conductometric studies of malonyl bis(salicyloylhydrazone) and divalent metal complexes

A series of complexes of divalent transition metal ions with malonyl bis(salicyloylhydrazone) (H₄MSH) have been prepared and characterized with the help of conductometric, potentiometric methods. The proton–ligand and metal–ligand stability constants were obtained pH-metrically. The electrical conductivity of solid complexes was measured at 289 K. The low molar conductance values observed for these complexes indicate that, they are non-electrolytes. They are soluble to a limited extent in DMF and DMSO. The elemental analyses of the complexes indicate that the complexes have 1:1 and 2:1 (M:L) stoichiometry with the existence of water, chloride, acetone molecules inside the coordination sphere as evidence from the IR spectral studies. Further, the complexes have been formulated by comparing C, H, N & metal analysis data, and UV–visible spectra of the complexes have been discussed. The protonation constants of the ligand and the stability constants of their metal complexes will be evaluated potentiometrically. The stoichiometric ratios of the complexes formed in solution will be evaluated applying the molar ratio (spectrophotometric) method and confirmed conductometrically.     

New Colorimetric Method for Determination of Tetracycline and Oxytetracycline Via Charge Transfer Complex Formation

Abstract

A colorimetric method for the determination of tetracycline and oxytetracycline is developed. It depends on nitration and reaction of the nitroderivatives with acetone in the presence of potassium hydroxide. A highly colored complex is produced. Variables such as temperature) time of heating, volume of nitrating mixture, acetone and potassium hydroxide have been evaluated to permit the selection of the most advantageous technique. Beer's Law is obeyed over the concentration range from 0.004 – 0.04 mg ml for tetracycline and oxytetracycline.     

Ligand exchange separation of metal ions on tetracycline hydrochloride sorbed on alumina

Summary The high sorption capacity of basic alumina for tetracycline hydrochloride is utilized for the separation of metal ions on the basis of ligand exchange. Tetracyclines are powerful chelating agents. Break-through capacity and rate of sorption have been studied. The distribution coefficients of 11 metal ions have been determined in demineralised water and in five different pH systems. On the basis of differences in Kd values some quantitative separations of metal ions have been achieved.     

Spectroscopic and potentiometric studies of the interaction of adenine with trivalent metal ions

Potentiometric titration was used to determine the potentiometric diagrams of complexes of adenine with Al³⁺, Cr³⁺, and Fe³⁺. IR and Raman spectra of solids show that the interaction of adenine with Cr³⁺ is not as strong as the other metals. Fe³⁺ binds to adenine at low and medium pH values at an Fe³⁺–adenine ratio of 6, while Al³⁺ binds to adenine at all pH values at an Al³⁺–adenine ratio of 8. The IR band associated with N-9–H is split into two components at high and low wavenumbers; IR band splitting has been observed for groups with a large dipole moment such as carbonyl and phosphate. To the best of our knowledge, this is the first time to see the splitting of IR bands involving a nitrogen. We also obtained potentiometric titration plots for adenine with Al³⁺, Cr³⁺, and Fe³⁺, independently, in various molar ratios which showed an interaction with adenine, consistent with the IR and Raman findings. Metal–adenine-hydroxo complexes were formed.     

Polymer complexes XXXIV. Potentiometric and thermodynamic studies of monomeric and polymeric complexes containing 2-acrylamidosulphadiazine

2-Acrylamidosulphadiazine (ASD) was synthesized and characterized by elemental analyses, IR and 1H NMR spectra. Proton-monomeric ligand dissociation and metal-monomeric ligand stability constants of ASD with some metal ions were determined potentiometrically in 0.1 M KCl and 40% (v/v) ethanol-water mixture. In the presence of 2,2^′-azobisisobutyronitrile as initiator, the dissociation and stability constants of ASD were determined in polymeric form (PASD). The influence of temperature on the dissociation of ASD and the stability constants of their complexes in monomeric and polymeric forms were critically studied. The pK₂^H value of PASD was found to be higher than ASD, this means that the vinyl group in the monomeric form decreases the electron density and hence reduces the N-H bond strength. The stability constants of the metal complexes in polymeric form are higher than those of the monomeric form. This is quite reasonable because the ligand in a polymeric form is considered as a better complexing agent.     

Potentiometric and spectroscopic studies on aluminium(III) complexes of some catechol derivatives

The interactions of aluminium(III) ion with the triprotic catechol derivatives (H3L), 2,3-dihydroxybenzoic acid (2,3-DHBA), 3,4-dihydroxyphenylacetic acid (3,4-DHPA), 3,4-dihydroxybenzoic acid (3,4-DHBA), and 3,4-dihydroxyhydrocinnamic acid (3,4-DHHCA) were investigated in aqueous solution at 25.0 degrees C. The Calvin-Bjerrum titration method was adopted for the determination of formation constants of proton-ligand and aluminium(III)-ligand complexes. Potentiometric and spectroscopic results indicated that these catechol derivatives exhibit a true bidentate character. The chelation occurs via their catecholate sites, with the exception of 2,3-DHBA. In the case of 2,3-DHBA complexes, the dominant species are either the salicylate type (COO-, O-) or catecholate type (O-, O-) complex. The protonation constants of ligands and their formation constants of Al(III) complexes were also correlated. The order of decreasing stabilities of complexes is: 3,4-DHPA>3,4-DHBA>3,4-DHHCA>2,3-DHBA.     

Solution and solid studies of some metal complexes with cytosine and its derivatives

Stability constants for the binary (1?:?1) complexes of CoII, NiII, CuII, ZnII, CdII, CaII, SrII and BaII with cytosine, cytidine, 5-bromocytosine, 5-azacytosine and 5-fluorocytosine were determined in aqueous solution (Ionic strength, μ = 0.1?mol?dm^?3 NaNO₃) potentiometrically at 25, 35 and 45°C. Experimental pH titration data were analyzed using the BEST computer program in order to evaluate formation constants of various intermediate species formed in the above binary systems. Enthalpy and entropy changes for the formation of binary complexes were calculated. On the basis of solution studies, efforts were made to prepare the binary complexes with 5-azacytosine ligand. Isolated solid complexes were characterized by different techniques and spectroscopic studies suggested a polymeric nature for the complexes, with OH and 5-azacytosine acting as bridging ligands.     

Thermodynamics of the complexation of some transition metal ions with trithiocarbodiglycolic acid. Potentiometric and voltammetric studies

Summary Proton-ligand dissociation and metal-ligand stability constants of trithiocarbodiglycolic acid (TCGA) with some transition metal ions were calculated potentiometrically. The order of stability constants was found to be Fe³⁺ > Cu²⁺ > Ni²⁺ > Co²⁺. The effect of temperature on the stability of the complexes formed was studied and the corresponding thermodynamic functions were derived and discussed. Polarographic and cyclic voltammetric behaviours ofTCGA were investigated in B.R. buffer solutions ofpH 2–12. In solutions ofpH<8, the polarograms and cyclo-voltammograms exhibited a single 2-electron diffusion-controlled irreversible step, corresponding to the reduction of the C=S. The mechanism of the reduction process was postulated and the kinetic parameters of the electrode process were evaluated.

---

Thermodynamik der Komplexierung einiger Übergangsmetallionen mit Trithiocarbodiglykolsäure. Potentiometrische und voltammetrische Untersuchungen

Zusammenfassung Die Protonendissoziation vom Liganden und die Metall-Ligand-Stabilitätskonstanten von Trithiocarbodiglykolsäure (TCGA) mit einigen Übergangsmetallionen wurden potentiometrisch bestimmt. Die Reihung der Stabilitäten ist Fe³⁺ > Cu²⁺ > Ni²⁺ > Co²⁺. Die Temperaturabhängigkeit der Stabilitäten wurde gemessen und die entsprechenden thermodynamischen Funktionen abgeleitet. Das polarographische und cyclovoltammetrische Verhalten vonTCGA wurde in B.R.-Puffer beipH 2–12 ermittelt. In Lösungen vonpH<8 zeigten die Polarogramme und Cyclovoltagramme eine einzelne diffusionskontrollierte irreversible 2-Elektronen-Stufe, die der Reduktion von C=S entspricht. Es wurde ein Mechanismus postuliert und die kinetischen Parameter des Elektrodenprozesses wurden bestimmt.

     

Synthesis,characterization and biological activity of triaminoxime and its metal complexes

Mn(II), Fe(III), Co(II), Ni(II), Cu(II) and Zn(II) complexes of multifunctional triaminoxime have been synthesized and characterized by elemental analyses, IR, UV–Vis spectra, magnetic moments, ¹H- and ¹³C-NMR spectra for ligand and its Ni(II) complex, mass spectra, molar conductances, thermal analyses (DTA, DTG and TG) and ESR measurements. The IR spectral data show that the ligand is bi-basic or tri-basic tetradentate towards the metals. Molar conductances in DMF indicate that the complexes are non-electrolytes. The ESR spectra of solid copper(II) complexes [(HL)(Cu)₂(Cl)₂] · 2H₂O (2) and [(L)(Cu)₃(OH)₃(H₂O)₆] · 7H₂O (6) show axial symmetry of a d _{x²???y ²} ground state; however, [(HL)(Co)] (4) shows an axial type with d _Z ² ground state and manganese(II) complex [(L)(Mn)₃(OH)₃(H₂O)6] · 4H₂O (10) shows an isotropic type. The biological activity of the ligand and its metal complexes are discussed.     

Detection of tetracycline and oxytetracycline residues in pig and calf hair by ultra-high-performance liquid chromatography tandem mass spectrometry

An ultra-high-performance liquid chromatography tandem mass spectrometry method to detect residues of tetracycline (TC), epi-tetracycline (eTC) and oxytetracycline (OTC) in animal hair was developed. Hair samples were washed with water, extracted with NH₄OH 0.1 M, purified by SPE-C₁₈ cartridge and analyzed by tandem mass spectrometry (ESI⁺, MRM mode) with satisfactory results. For the first time, accumulation of TC, eTC and OTC was confirmed in livestock hairs after a therapeutic treatment with TC and OTC, respectively. Administered drug residues were detectable in hair samples up to 2 months after the last treatment, providing a retrospective evidence of TC and OTC administration. Hair analysis seems to offer a wider window of detection than edible tissues.     

Synthesis and spectroscopic studies on 3-isonicotinamidorhodanine complexes of some bivalent metal ions

Summary 3-Isonicotinamido-rhodanine (HINRd) reacts with metal ions to yield complexes of the types M(INRd)OH·nH₂O (where M=Co^II, Ni^II, Zn^II or Cd^II and n=1 or 2), Cu(HINRd)X·2H₂O (where X=Cl or Br), Pd(HINRd)Cl₂ and Cd(HINRd)X₂·H₂O (where X=Cl or Br), depending on the metal salt used and the reaction conditions. The metal complexes have been characterized by elemental analysis, molar conductivities, molecular weights, magnetic susceptibility, visible, and i.r. studies. The i.r. spectra show that HINRd binds in a bidentate or monodentate manner. The spectral and magnetic studies suggest a tetrahedral arrangement for Co^II, octahedral for Ni^II and square-planar for Pd^II. HINRd behaves as a reducing agent towards Cu^II chloride or bromide forming diamagnetic Cu^I complexes.     

Equilibrium and spectral studies of putrescine complexes with copper(II)

Summary It has been found that in the putrescine-copper system several types of complex compounds (MHL,ML,ML ₂,ML ₂OH) are formed. In thepH range of 7–9, despite a multiple excess of ligand, a precipitation occurs. When adenosine is introduced to the system, the ability to observe the complexation reaction in solution is largely increased, because the additional ligand prevents precipitation. On the basis of computer analysis of potentiometric titration data the stability constants of the compounds have been determined. The coordination mode of the complexes is discussed.

---

Gleichgewichte und spektroskopische Untersuchungen an Putrescin-Komplexen mit Kupfer(II)

Zusammenfassung Es wurde festgestellt, daß sich im Putrescin-Kupfer System einige Typen von Komplexen bilden (MHL,ML,ML ₂ andML ₂OH). ImpH-Bereich von 7–9 tritt trotz eines mehrfachen Ligandenüberschusses ein Niederschlag auf. Bei Einführung von Adenosin in das System wird die Beobachtbarkeit der Komplexreaktion verbessert, da der zusätzliche Ligand die Niederschlagsbildung verhindert. Mittels Computeranalyse der potentiometrischen Titrationsdaten wurden die Stabilitätskonstanten der Verbindungen ermittelt. Die Art der Komplexierung wird ebenfalls diskutiert.

     

Complex formation equilibria between aluminum(III), gadolinium(III) and yttrium(III) ions and some fluoroquinolone ligands. Potentiometric and spectroscopic study

Complex formation equilibria of aluminum(III), gadolinium(III), and yttrium(III) ions with the fluoroquinolone antibacterials moxifloxacin, ofloxacin, fleroxacin, lomefloxacin, levofloxacin, and ciprofloxacin were studied in aqueous solution by potentiometric and spectroscopic methods. The identity and stability of metal–fluoroquinolone complexes were determined by analyzing potentiometric titration curves (310 K, μ = 0.15 M NaCl, pH range = 2–11, C_L/C_M = 1?:?1 to 3?:?1, C_M = 1.0 mM) with the aid of Hyperquad2006 program. The main species formed in the system may be formulated as M_pH_qL_r (p = 1, q = ?2 to 2, r = 1–3, L = fluoroquinolone anion, logarithm of overall stability constant, log β_p,q,r = in the range ca. ?10 to 45). The stability of complexes is mostly influenced by metal ion properties (ionization potential, ionic radius) indicating partial ionic character of the coordination bond. The complexes were also characterized by spectroscopic measurements: spectrofluorimetry, ¹H-NMR, and ESI-MS. Fluorimetric data were evaluated with the aid of HypSpec2014 and indicated the formation of ML_r (r = 1–3) complexes with cumulative conditional stability constants significantly lower than the thermodynamic ones. NMR and MS data corroborate potentiometrically determined speciation. Calculated plasma mobilizing capacity of the ligands generally follows the order levofloxacin > moxifloxacin > ciprofloxacin at concentration levels of the ligands higher or equal to ca. 10^?4 M.     

Potentiometric studies on the complexation equilibria between some trivalent lanthanide metal ions and biologically active 2-hydroxy-1-naphthaldehyde thiosemicarbazone (HNATS)

Summary The chelation behaviour of some trivalent lanthanide and yttrium metal ion with biologically active 2-hydroxy-1-naphthaldehyde thiosemicarbazone (HNATS) has been investigated by potentiomotric measurements at 20±0.5°C in 75% (v/v) dioxane-water medium at various ionic strengths of sodium perchlorate. The method of Bjerrum and Calvin, as modified by Irving and Rossotti has been used to find out the values of (average number of ligand bound per metal ion) andpL (free ligand exponent). The formation constants of metal chelates have been computed on a PC-XT computer, using a program patterned after that of Sullivan et al. to give _n values using weighted least squares method. TheS _min values (S _min =²) have been calculated. The order of formation constants of chelates was found to be: La³⁺3+3+3+3+3+3+3+3+3+. The formation constants of the chelates formed have been correlated to size and ionization potentials of the metal ions.

---

Potentiometrische Untersuchungen der Komplexierungsgleichgewichte zwischen einigen trivalenten Metallionen und biologisch aktivem 2-Hydroxy-1-naphthaldehyd-thiosemicarbazon (HNATS)

Zusammenfassung Es wurde das Chelierungsverhalten einiger trivalenter Lanthanidenionen mit biologisch aktivem 2-Hydroxy-1-naphthaldehyd-thiosemicarbazon (HNATS) mittels potentiometrischer Messungen bei 20±0.5°C in 75% (v/v) Dioxan-Wasser bei verschiedener Ionenstärke an Natriumperchlorat untersucht. Die Methode nach Bjerrum und Calvin in der Modifikation nach Irving und Rossotti wurde zur Ermittlung der Werte (mittlere Anzahl an Liganden pro Metallion) undpL (Exponent an freiem Liganden) verwendet. Die Komplexbildungskonstanten wurden in Anlehnung an Sullivan et al. an einem PC-XT Computer errechnet. DieS _min-Werte (S _min=²) wurden ebenfalls bestimmt. Die Reihung der Chelatbildungskonstanten war: La³⁺3+3+3+3+3+3+3+3+3+. Die Bildungskonstanten sind mit der Größe und dem Ionisierungspotential der Metallionen zu korrelieren.

     

Equilibrium studies of some divalent metal ions complexes with pyridoxol,pyridoxal and pyridoxamine

The interaction of vitamin B₆ compounds, pyridoxol, pyridoxal and pyridoxamine with metal ions Mn²⁺, Co²⁺, Ni²⁺ and Hg²⁺ are studied. Values for stability constants are evaluated and the reaction stiochiometries are investigated in aqueous 0.50 M KCl at 25°C. It is shown that only pyridoxamine possesses a fairly good affinity to interact with metal ions. A linear relation holds between the stability constants of the first complex and the ionization potential of the divalent metal ions.     

On-line dialysis of some metal ions and metal complexes

The effect of ionic strength, pH and complexing ligands on the dialysis of metal ions, particularly zinc(II), through cellulose acetate membranes, was studied under flow conditions. The dialysis factor, which depends on both the mass transfer and the membrane permeability, was found to be independence of ionic strength in the interaval 0.05–0.3 M and to increase only slightly with pH 4.6 and 7.0. Some common buffer constituents had no effect, but chloride and calcium ions affected the transfer rates. The rate of transfer of the ligands histidine, NTA and EDTA was of the same order of magnitude as that of the metal ions. The transfer rate of the Ni(II)-EDTA complex was the same as that of a mixture of Ni(II) and EDTA. Generally, addition of the chelating agents decreased the metal-ion transfer rates. Partition coefficients between the membrane polymer and the buffers were evaluated and compared with the dialysis factors and there were significant differences with regard to the range of variation, effect of concentration and pH-dependence. The time scale of uptake or release of metal ions by the polymer is much longer than that of a steady-state transfer in dialysis. Partition and dialysis may not be directly related to each other.     

Studies on complexes of 4-(2-thiazolyl)thiosemicarbazide with some bivalent metal ions

Summary The 4-(2-thiazolyl)thiosemicarbazide HTTSC, reacts with metal ions to yield two types of complex M(HTTSC)₂ Cl₂ [M=cobalt(II), nickel(II) copper(II), cadmium(II), or mercury(II)] and [M(TTSC)₂] [M=cobalt(II), nickel(II) or copper(II)]. These complexes have been characterized by elemental analyses and studied by magnetic and spectroscopic techniques. Tetrahedral coordination around cadmium(II) and mercury(II), square planar geometry around cobalt(II) and nickel(II) in [Co(TTSC)₂] and [Ni(HTTSC)₂]Cl₂, respectively, and octahedral stereochemistry for the remaining complexes is proposed.