Irving-Williams Order Research Articles

Thermodynamic parameters of phenylglycine interaction with UO22+, La3+ and Zr4+

Phenylglycine interactions with (UO22+, La3+ and Zr4+) transition metal ions were studied at different ionic strengths and different temperature degrees applying Bjerrum’s method. The work determine and discuss both the thermodynamic stabilities and the degree of interactions left(acute{{text{n}}}right). Also the work calculate and discuss the thermodynamic parameters of interactions of phenylglycine with (UO22+, La3+ and Zr4+). The variables that govern the interaction between phenylglycine and the metal ions under investigation were related to the nature of the amino acid reactive species as well as to the nature of M+ such as the valence and radius of the ion. It was observed that reactions between the M+ and L− were the most likely to occur. It was determined that the pH values affect the degree of complex formation overline{{text{n}}} as well as the production of various reactive spices. When the range of degree of interaction was more than 0.5 and less than 1.15, forming 1:1 stoichiometric complex. Additionally, it was shown that the stability of the complexes produced between phenylglycine and MZ+ increased in the subsequent order, which was in good accord with the Irving–Williams order.

Desorption of Ammonia Adsorbed on Prussian Blue Analogs by Washing with Saturated Ammonium Hydrogen Carbonate Solution

Prussian blue analogs (PBAs) have been reported as promising ammonia (NH3) adsorbents with a high capacity compared to activated carbon, zeolite, and ion exchange resins. The adsorbed NH3 was desorbed by heating and washing with water or acid. Recently, we demonstrated that desorption was also possible by washing with a saturated ammonium hydrogen carbonate solution (sat. NH4HCO3aq) and recovered NH3 as an NH4HCO3 solid by introducing CO2 into the washing liquid after desorption. However, this has only been proven for copper ferrocyanide and the relationship between the adsorption/desorption behavior and metal ions in PBAs has not been identified. In this study, we investigated the adsorption/desorption behavior of PBAs that are complexes of first row transition metals with hexacyanometalate anions. Six types of PBAs were tested in this study and copper ferricyanide exhibited the highest desorption/adsorption ratio. X-ray diffraction results revealed high structural stability for cobalt hexacyanocobaltate (CoHCC) and nickel ferricyanide (NiHCF). The Fourier transform infrared spectroscopy results showed that the NH3 adsorbed on the vacancy sites tended to desorb compared to the NH3 adsorbed on the interstitial sites as ammonium ions. Interestingly, the desorption/adsorption ratio exhibited the Irving-Williams order.

Potentiometric determination of stability constants of ternary complexes of first row transition metal ions with ditopic azelaic acid dihydrazide and aspartic acid in aqueous medium

A Chemical speciation study of ternary complexes containing transition metal ions (Mn2+,Co2+,Ni2+, Cu2+ and Zn2+) with a ditopic novel ligand L ​= ​Azelaic acid dihydrazide (AZDH) and X ​= ​l-Aspartic acid of type [MmLlX xHh], (where m ​= ​1, 2; l ​= ​1; x ​= ​1, 2 and h ​= ​−2 to 5) in different ratios of M:L:X ​= ​1:1:1, 1:2:1, 2:1:1and 2:1:2 was carried out using pH -potentiometric method of data acquisition and applied to chemometric modelling methods of analysis. MINIQUAD-75 program was used for the resolution of the plausible species and their corresponding formation constants at 303 ​± ​0.1 ​K, and 0.01 ​M ionic strength. Species concentration distribution diagrams were generated using HySS program. Best-fit chemical models were selected on the basis of statistical parameters like Standard deviation (SD), U (sum of the squares of the residuals in mass balance equations), and chi-square test etc. Relatively stable ternary complexes were evaluated quantitatively using Δlog K formulation. All the formation constants for the species were compared for Irving-Williams order of stability.

Equilibrium Studies of Binary and Ternary Complexes Involving 2-Hydroxy-1- Naphthoic Acid and Amino Acids in Dioxane–Water Mixture

Complex formation equilibria of 2-hydroxy-1-naphthoic acid with Cu2+, Ni2+, Co2+ and Mn2+ and the ternary complexes involving Cu2+, 2-hydroxy-1-naphthoic acid and some amino acids containing different functional groups are investigated. Stoichiometry and stability constants for the complexes are estimated at 25 oC and 0.1M ionic strength in 50% dioxane-water mixture. The stability of the complexes follows the trend Cu2+ > Ni2+ > Co2+ > Mn2+, which is in agreement with the Irving–Williams order of the metal ions. Ternary complexes of amino acids are formed by a simultaneous mechanism. The stabilities of ternary complexes are quantitatively compared with their corresponding binary complexes. The concentration distribution diagrams of the complexes were evaluated.

New sulfonamide complexes with essential metal ions [Cu (II), Co (II), Ni (II) and Zn (II)]. Effect of the geometry and the metal ion on DNA binding and nuclease activity. BSA protein interaction

Mixed divalent Cu, Co, Ni and Zn complexes containing the new sulfonamide ligand N–(2–(pyridin–2–yl)ethyl)quinoline–8–sulfonamide (HQSEP) were prepared and characterized by physico-chemical techniques. The tetracoordinate [Cu(QSEP)X] [X = Br (1), Cl (2)] compounds present a seesaw geometry (τ4 = 0.56 (1) and 0.50 (2)). The Cu(II) in the [Cu(QSEP)(NO3)(MeOH)] (3) complex is five coordinate with a slightly distorted SP geometry (τ = 0.11). The [M(QSEP)(benz)] [M = Cu(II) (4), Ni(II) (5), Co(II) (6) and Zn(II) (7); benz = benzoate] compounds are configurationally isotypic. The coordination geometries of the M(II) ions can be best described as distorted SP (τ = 0.29, 0.15, 0.34 and 0.18 for 4, 5, 6 and 7, respectively). The interaction of the compounds with CT–DNA was studied by different techniques. Notably, these studies indicated that the tetracoordinate complexes (1 and 2) present higher DNA affinity than pentacoordinate compounds (3–7). In line with the Irving–Williams order of stability, 5 presented higher propensity for DNA binding than 6. Interestingly, the cleavage activity of 1–4 in the presence of ascorbate/H2O2 follows the same trend as that found for DNA binding affinity, being the tetracoordinate 1 and 2 more effective as nucleases than the five coordinate 3 and 4. Also, the DNA cleavage reaction mechanism was investigated. DNA cleavage experiments upon irradiation indicated the important role of the aromatic nature of the coligand in the photocleavage activity of 1–4. Finally, the interaction of the compounds with bovine serum albumin (BSA) was studied and the binding constants were calculated.

Uptake of Ni2+ and Cu2+ by Zn–Al layered double hydroxide intercalated with carboxymethyl-modified cyclodextrin: Equilibrium and kinetic studies

Zn–Al layered double hydroxides (Zn–Al LDHs) intercalated with carboxymethyl-modified cyclodextrin (CMCD) ions (CMCD•Zn–Al LDHs) were prepared by the co-precipitation method. The adsorption of Ni2+ by CMCD•Zn–Al LDHs followed the Langmuir-type mechanism, as evident from the adsorption isotherm. ESI-TOF-MS results implied that the uptake of Ni2+ by CMCD•Zn–Al LDHs could be attributed to the formation of chelate complexes between Ni2+ and CMCD ions in the interlayers of the CMCD•Zn–Al LDH. Kinetic studies revealed that the reaction involved in the uptake of Ni2+ by CMCD•Zn–Al LDH proceeded under mass transfer control, suggesting that the CMCD ion in the interlayer of the CMCD•Zn–Al LDH quickly formed a chelate complex with Ni2+. The transfer rate of Ni2+ through the product layer was rate-limiting. Similar results were obtained for the uptake of Cu2+ by CM-β-CD•Zn–Al LDH. It was also found that the CM-β-CD•Zn–Al LDH was more selective toward Cu2+ uptake than Ni2+ in the mixed solution. This was attributed to the Irving-Williams order of stability of bivalent transition metal complexes; Cu2+ formed a more stable chelate complex with the CM-β-CD ion in the interlayer of CM-β-CD•Zn–Al LDH as compared to Ni2+.

Study the Effect of Magnetized Water on Some of the Chemical Parameters for EBT Complexes with Some of M2+ Ions

In this paper, the effect of magnetized water on the stability constant Kst, oscillation strength f, molar extinction coefficient εmax and Gibbs free energy ΔG for complexes was investigated. Complexes of Eriochrome black T (EBT) as a ligand with Ca2+, Mn2+, and Zn2+ ions were prepared for this purpos. The stability constant values of the complexes found to be decreased by using magnetic water in their preparation except for EBT-Ca complex. Both Ca2+ and Mn2+ ions showed deviation from Irving-Williams order. The oscillation strength shows the type of spectrum is absorption spectrum for all complexes and in both in magnetized and non-magnetized water. εmax found to be increased by using magnetized water over than non-magnetized water. The stability constants for the complexes calculate analytically by applying jobs method and Yoe and Jones method.

Stoichiometry, polarity, and organometallics in solid-phase extracted dissolved organic matter of the Elbe-Weser estuary.

Dissolved organic matter (DOM) is ubiquitous in natural waters and plays a central role in the biogeochemistry in riverine, estuarine and marine environments. This study quantifies and characterizes solid-phase extractable DOM and trace element complexation at different salinities in the Weser and Elbe River, northern Germany, and the North Sea. Dissolved organic carbon (DOC), total dissolved nitrogen (TDN), Co and Cu concentrations were analyzed in original water samples. Solid-phase extracted (SPE) water samples were analyzed for DOC (DOCSPE), dissolved organic nitrogen (DONSPE), sulfur (DOSSPE) and trace metal (51V, 52Cr, 59Co, 60Ni, 63Cu, 75As) concentrations. Additionally, different pre-treatment conditions (acidification vs. non-acidification prior to SPE) were tested. In agreement with previous studies, acidification led to generally higher recoveries for DOM and trace metals. Overall, higher DOM and trace metal concentrations and subsequently higher complexation of trace metals with carbon and sulfur-containing organic complexes were found in riverine compared to marine samples. With increasing salinity, the concentrations of DOM decreased due to estuarine mixing. However, the slightly lower relative decrease of both, DOCSPE and DONSPE (~77%) compared to DOSSPE (~86%) suggests slightly faster removal processes for DOSSPE. A similar distribution of trace metal and carbon and sulfur containing DOM concentrations with salinity indicates complexation of trace metals with organic ligands. This is further supported by an increase in Co and Cu concentration after oxidation of organic complexes by UV treatment. Additionally, the complexation of metals with organic ligands (analyzed by comparing metal/DOCSPE and metal/DOSSPE ratios) decreased in the order Cu > As > Ni > Cr > Co and thus followed the Irving-Williams order. Differences in riverine and marine trace metal containing DOMSPE are summarized by their average molar ratios of (C107N4P0.013S1)1000V0.05Cr0.33Co0.19Ni0.39Cu3.41As0.47 in the riverine endmember and (C163N7P0.055S1)1000V0.05Cr0.47Co0.16Ni0.07Cu4.05As0.58 in the marine endmember.

Remobilization of trace metals from contaminated marine sediment in a simulated dynamic environment.

In this study, release and redistribution of sediment bound trace metals due to resuspension were investigated by a lid-driven elongated annular flume (LEAF). The total suspended particulate matters (SPMs) increased significantly in quantity with the raised resuspension energies and varied distinctively in particle size and mineral composition. Except for Cu, Ni, Cd, Pb, and Zn showed an increase in dissolved phase as the resuspension energy increased. Relatively low Cu was observed in dissolved phase whereas it owned the highest original concentration in the sediment. This is primarily due to the very low solubility of Cu sulfide. In comparison to sediment, all metals were evidently enriched in SPMs which primarily contributed to the much more fine particles (silt/clay fraction) contained in the SPMs. Metals enrichment followed the Irving-Williams order of complex stability. However, metals content varied indistinctively in the SPMs among the three selected resuspension levels. The distribution coefficients (K d) exhibited opposite trend with the increasing resuspension level with the exception of Cu. It indicated that physical and chemical characters of sediment such as grain composition, Fe/Mn, and organic matter content may also act as major factors in the release of metals and control their phase distribution in the water column.

Reasons behind the relative abundances of heptacoordinate complexes along the late first-row transition metal series.

A series of transition metal complexes [ML(1)] (H2L(1) = 1,4,10-trioxa-7,13-diazacyclopentadecane-N,N'-diacetic acid, M = Co, Ni, Cu, or Zn) have been prepared and characterized. The X-ray structures of the [CoL(1)] and [CuL(1)] complexes reveal that the metal ions are seven-coordinated with a distorted pentagonal bipyramidal coordination. The five donor atoms of the macrocycle define the pentagonal plane of the bipyramid, while two oxygen atoms of the carboxylate groups coordinate apically. The [NiL(1)] complex presents a very distorted structure with long Ni-O distances involving two oxygen atoms of the crown moiety [2.544(3) Å]. This distortion is related to the Jahn-Teller effect that is expected to operate in d(8) pentagonal bipyramidal complexes. The spectroscopic characterization of the [ZnL(1)] and [CuL(1)] complexes using NMR and EPR and the theoretical calculation of the (13)C NMR shifts and g- and A-tensors using DFT confirm that these complexes retain the pentagonal bipyramidal coordination in aqueous solution. The stability trend of the [ML(1)] complexes (Co(2+) > Ni(2+) < Cu(2+) > Zn(2+)), which is in contradiction with the Irving-Williams order, has been analyzed using DFT calculations (TPSSh functional). The free energy values calculated in the gas phase for [CoL(1)](g) + [M(H2O)6](2+)(g) → [ML(1)](g) + [Co(H2O)6](2+)(g) (M = Ni, Cu, Zn) reproduce fairly well the stability trend observed experimentally, the agreement being improved significantly upon inclusion of solvent effects. Our results indicate that the pentagonal bipyramidal coordination is particularly unfavorable for Ni(2+), and thus preorganized ligands that favor this geometry such as L(1) are selective for Co(2+) over Ni(2+) cations.

Stabilities of the Divalent Metal Ion Complexes of a Short-Chain Polyphosphate Anion and Its Imino Derivative

The stability constants of ML-type complexes of the two linear triphosphate ligand anion analogues triphosphate ( {text{P}}_{ 3} {text{O}}_{10}^{5 - } ) and diimidotriphosphate ( {text{P}}_{ 3} {text{O}}_{ 8} ( {text{NH}})_{2}^{5 - } ) were investigated thermodynamically using potentiometric titrations according to Schwarzenbach’s procedure. The stability constants of the ML-type complexes of different divalent metal ions with {text{P}}_{ 3} {text{O}}_{ 8} ( {text{NH}})_{2}^{5 - } are larger than those of the corresponding complexes with {text{P}}_{ 3} {text{O}}_{10}^{5 - } because of the greater basicity of the imino group. The order of the stability constants for the ML-type complexes follows the Irving–Williams order, indicating that only non-bridging oxygen atoms are coordinated directly to the different metal ions in both ligands, and that the imino groups cannot participate in coordination to the metal ions. In the complexation reactions of the Ca2+, Sr2+, Ba2+– {text{P}}_{ 3} {text{O}}_{10}^{5 - } and Cu2+, Zn2+, Ni2+– {text{P}}_{ 3} {text{O}}_{ 8} ( {text{NH}})_{2}^{5 - } systems, each metal ion forms an enthalpically stable complex, and there was no suggestion of a conspicuous entropic effect based on the chelate effect. Monodentate complexes that are strongly coordinated with the ligands were therefore formed, whereas entropically stable bidentate complexes were formed in the complexation reactions of the Cu2+, Zn2+, Ni2+– {text{P}}_{ 3} {text{O}}_{10}^{5 - } and Ca2+, Ba2+, Sr2+– {text{P}}_{ 3} {text{O}}_{ 8} ( {text{NH}})_{2}^{5 - } systems. According to the HSAB concept, hard metal cations such as Ca2+, Ba2+ and Sr2+ should bind to the harder oxygen atoms rather than the softer nitrogen atoms of the imidopolyphosphate anions, preventing direct coordination to the imino nitrogen atom.Graphical Electronic supplementary materialThe online version of this article (doi:10.1007/s10953-013-0099-2) contains supplementary material, which is available to authorized users.

Potentiometric and Thermodynamic Studies of Binary and Ternary Transition Metal(II) Complexes of Imidazole-4-acetic Acid and Some Bio-relevant Ligands

Proton–ligand association constants of imidazole-4-acetic acid (IMA) were determined potentiometrically in aqueous solution at different temperatures in the range 15–35 °C. The stepwise stability constants of IMA with some selected bivalent transition metal ions were also determined in 0.1 mol·dm−3 NaNO3. The stability of the complexes follows the trend Cu2+ > Ni2+ > Co2+ > Mn2+, which is in agreement with the Irving–Williams order of the metal ions. The thermodynamic parameters for Cu(II)–IMA complex formation were derived and discussed. The ternary complexes Cu(IMA)L (IMA = imidazole-4-acetic acid, HL = amino acid, amides or DNA constituents) have been investigated. Ternary complexes of amino acids or amides are formed by a simultaneous mechanism. Amino acids form the complex Cu(IMA)L, whereas amides form two complex species Cu(IMA)L and Cu(IMA)(LH−1). The DNA constituents form both 1:1 and 1:2 complexes. The stabilities of ternary complexes are quantitatively compared with their corresponding binary complexes. The concentration distribution of the complexes in solution was evaluated as a function of pH.

Bivalent transition metal complexes of cetirizine: Spectroscopic, equilibrium studies and biological activity

Metal complexes of cetirizine⋅2HCl (CTZ=2-[2-[4-[(4-chlorophenyl)phenyl methyl]piperazine-1-yl]-ethoxy]acetic acid, dihydrochloride have been prepared and characterized by elemental analyses, IR, solid reflectance, magnetic moment, molar conductance, and UV–Vis spectra. The analytical data of the complexes show the formation of 1:2 [M:L] ratio, where M represents Ni(II), Co(II) and Cu(II) ions, while L represents the deprotonated CTZ ligand. IR spectra show that CTZ is coordinated to the metal ions in a monodentate manner through carboxylate-O atom. Protonation equilibria of CTZ and its metal complexation by some divalent metal ions were determined in aqueous solution at constant ionic strength (0.1M NaCl) using an automatic potentiometric technique. Thermodynamic parameters for the protonation equilibria of CTZ were calculated and discussed. The stability order of M(II)–CTZ complexes were found to obey Mn2+<Co2+<Ni2+<Cu2+, in accordance with the Irving–Williams order. The concentration distribution of the complexes in solution is evaluated as a function of pH. The CTZ ligand and its metal complexes were screened for their biological activity against bacterial species (Bacillus subtillis RCMB 010067, Staphylococcus aureus RCMB 010028, Pseudomonas aeuroginosa RCMB 010043, and Escherichia coli RCMB 010052) and fungi as (Aspergillus flavus RCMB 02568, Pencicillium italicum RCMB 03924, Candida albicans RCMB 05031 and Geotricum candidum RCMB 05097). The activity data show that the metal complexes have antibacterial and antifungal activity more than the parent CTZ ligand against one or more bacterial or fungi species. MIC was evaluated for the isolated complexes.

Metal ion interactions with drugs: Electrochemical study of complexation of various bivalent metal ions with nimesulide and ibuprofen

The present study reports the stability constants of complexes of two NSAIDs: nimesulide and ibuprofen with Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Sn2+, Hg2+ and Pb2+ ions in water–ethanol medium 50% v/v at three different temperatures (298K, 308K and 318K), keeping ionic strength constant (0.1M KNO3). Experiments were conducted in 1000mL jacketed glass reaction vessels under nitrogen atmosphere. Hydrogen ion concentrations were measured and the stability constants were calculated from the pH-metric titration curves. The order of the stability constants of the formed complexes decreases in the sequence Cu2+>Co2+>Cd2+>Zn2+>Ni2+>Sn2+>Pb2+≈Hg2+ for nimesulide (D1) and Cu2+>Co2+>Zn2+>Ni2+>Cd2+>Sn2+>Pb2+>Hg2+ for ibuprofen (D2). The effect of temperature was also studied and the corresponding thermodynamic functions ΔG, ΔH and ΔS were derived and discussed. The formation of metal complexes has been found to be spontaneous and entropically favorable. The method of Calvin and Bjerrum as adopted by Irving and Rossotti has been employed to determine log K1 values. This order is in good agreement with the Irving–Williams order of stability.

Mixed ligand complexation of some transition metal ions in solution and solid state: Spectral characterization, antimicrobial, antioxidant, DNA cleavage activities and molecular modeling

Equilibrium studies of Ni(II), Cu(II) and Zn(II) mixed ligand complexes involving a primary ligand 5-fluorouracil (5-FU; A) and imidazoles viz., imidazole (him), benzimidazole (bim), histamine (hist) and L–histidine (his) as co-ligands(B) were carried out pH-metrically in aqueous medium at 310±0.1K with I=0.15M (NaClO4). In solution state, the stoichiometry of MABH, MAB and MAB2 species have been detected. The primary ligand(A) binds the central M(II) ions in a monodentate manner whereas him, bim, hist and his co-ligands(B) bind in mono, mono, bi and tridentate modes respectively. The calculated ΔlogK, logX and logX′ values indicate higher stability of the mixed ligand complexes in comparison to binary species. Stability of the mixed ligand complex equilibria follows the Irving-Williams order of stability. In vitro biological evaluations of the free ligand(A) and their metal complexes by well diffusion technique show moderate activities against common bacterial and fungal strains. Oxidative cleavage interaction of ligand(A) and their copper complexes with CT DNA is also studied by gel electrophoresis method in the presence of oxidant. In vitro antioxidant evaluations of the primary ligand(A), CuA and CuAB complexes by DPPH free radical scavenging model were carried out. In solid, the MAB type of M(II)5-FU(A)his(B) complexes were isolated and characterized by various physico-chemical and spectral techniques. Both the magnetic susceptibility and electronic spectral analysis suggest distorted octahedral geometry. Thermal studies on the synthesized mixed ligand complexes show loss of coordinated water molecule in the first step followed by decomposition of the organic residues subsequently. XRD and SEM analysis suggest that the microcrystalline nature and homogeneous morphology of MAB complexes. Further, the 3D molecular modeling and analysis for the mixed ligand MAB complexes have also been carried out.

Speciation of binary complexes of Co(II), Ni(II) and Cu(II) with L-aspartic acid in propylene glycol–water mixtures

Speciation of binary complexes of Co(II), Ni(II) and Cu(II) with L-aspartic acid in (0-60% v/v) propylene glycol-water mixtures was studied pH metrically at 303.0±0.1 K and at an ionic strength of 0.16 mol L-1. The binary species refined were ML, ML2, ML2H2, ML2H3 and ML2H4. The stabilities of the complexes followed the Irving-Williams order i.e.Co(II) <Ni(II) < Cu(II). The linear variation of stability constants as a function of dielectric constant of the medium indicated the dominance of electrostatic forces over non-electrostatic forces. Some species were stabilised due to electrostatic interactions and some were destabilised due to the decreased dielectric constant. The order of ingredients influencing the magnitudes of stability constants due to incorporation of errors in their concentrations was alkali > acid > ligand > metal. Equilibria for the formation of binary complexes were proposed based on the forms of the ligand and their existence at different pH values.

Synthesis, characterization, biological activity and equilibrium studies of metal(II) ion complexes with tridentate hydrazone ligand derived from hydralazine

In the present study, a new hydrazone ligand (2-((2-phthalazin-1-yl)hydrazono)methyl)phenol) prepared by condensation of hydralazine (1-Hydralazinophthalazine) with salicylaldehyde (SAH). The synthesized SAH-hydrazone and its metal complexes have been characterized by elemental analyses, IR, 1H NMR, solid reflectance, magnetic moment, molar conductance, mass spectra, UV–vis and thermal analysis (TGA). The analytical data of the complexes show the formation of 1:1 [M:L] ratio, where M represents Ni(II), Co(II) and Cu(II) ions, while L represents the deprotonated hydrazone ligand. IR spectra show that SAH is coordinated to the metal ions in a tridentate manner through phthalazine-N, azomethine-N and phenolic-oxygen groups. The ligand and their metal chelates have been screened for their antimicrobial activities using the disc diffusion method against the selected bacteria and fungi. Proton-ligand association constants of (SAH) and the stepwise stability constants of its metal complexes are determined potentiometrically in 0.1M NaNO3 at different temperatures and the corresponding thermodynamic parameters were derived and discussed. The order of −ΔG° and −ΔH° were found to obey Mn2+<Co2+<Ni2+<Cu2+, in accordance with the Irving–Williams order. The complexes were stabilized by enthalpy changes and the results suggest that the complexation is an enthalpy-driven process. The concentration distribution diagrams of the complexes are evaluated.

Thermodynamic Investigation and Mixed Ligand Complex Formation of 1,4-Bis-(3-aminopropyl)-piperazine and Biorelevant Ligands

Thermodynamic parameters for protonation of 1,4-bis(3-aminopropyl)-piperazine (BAPP) and its metal complexation with some divalent metal ions were determined in aqueous solution at constant ionic strength (0.1 M NaNO3) using a potentiometric technique. The order of –ΔG0 and –ΔH0 was found to obey Co2+ < Ni2+ < Cu2+ > Zn2+, in accordance with the Irving-Williams order. The formation equilibria of zinc (II) complexes and the ternary complexes Zn(BAPP)L, where L = amino acid, amides, or DNA constituents), have been investigated. Ternary complexes are formed by a simultaneous mechanism. The concentration distribution of the complexes in solution was evaluated as a function of pH. Stoichiometry and stability constants for the complexes formed are reported and discussed. The stability of ternary complexes was quantitatively compared with their corresponding binary complexes in terms of the parameter Δlog K.

First row transition metal complexes of (E)-2-(2-(2-hydroxybenzylidene) hydrazinyl)-2-oxo-N-phenylacetamide complexes

Manganese(II), iron(II), cobalt(II), nickel(II), copper(II), and chromium(III) complexes of (E)-2-(2-(2-hydroxybenzylidene)hydrazinyl)-2-oxo-N-phenylacetamide were synthesized and characterized by elemental and thermal (TG and DTA) analyses, IR, UV–vis and 1H NMR spectra as well as magnetic moment. Mononuclear complexes are obtained with 1:1 molar ratio except [Mn(HOS) 2(H 2O) 2] and [Co(OS) 2](H 2O) 2 complexes which are obtained with 1:2 molar ratios. The IR spectra of ligand and metal complexes reveal various modes of chelation. The ligand behaves as a monobasic bidentate one and coordination occurs via the enolic oxygen atom and azomethine nitrogen atom. The ligand behaves also as a monobasic tridentate one and coordination occurs through the carbonyl oxygen atom, azomethine nitrogen atom and the hydroxyl oxygen. Moreover, the ligand behaves as a dibasic tridentate and coordination occurs via the enolic oxygen, azomethine nitrogen and the hydroxyl oxygen atoms. The electronic spectra and magnetic moment measurements reveal that all complexes possess octahedral geometry except the copper complexes possesses a square planar geometry. From the modeling studies, the bond length, bond angle, HOMO, LUMO and dipole moment had been calculated to confirm the geometry of the ligands and their investigated complexes. The thermal studies showed the type of water molecules involved in metal complexes as well as the thermal decomposition of some metal complexes. The protonation constant of the ligand and the stability constant of metal complexes were determined pH-metrically in 50% (v/v) dioxane–water mixture at 298 K and found to be consistent with Irving–Williams order. Moreover, the minimal inhibitory concentration (MIC) of these compounds against Staphylococcus aureus, Escherechia coli and Candida albicans were determined.

Solution Equilibria of Ni(II), Cu(II), and Zn(II) Complexes Involving Pyridoxine and Imidazole Containing Ligands: pH Metric, Spectral, Electrochemical, and Biological Studies

Solution equilibria and relevant stability constants for M(II)-pyridoxine (PN)(A) [M(II) = Cu(II), Ni(II), and Zn(II)], and M(II)-PN(A)-imidazole containing ligands (B) [B = imidazole (him), benzimidazole (bim), histamine (hist), and l-histidine (his)] in aqueous solution have been determined by a pH metric method at 310 K and I = 0.15 M NaClO4. The complexation model for each system has been established by the MINIQUAD-75 program. The probable binding mode in the binary and ternary species was discussed based upon the derived stability constants. The concentration distributions of various species formed in solution were evaluated. The stability of ternary complexes follows the Irving–Williams order of metal ions, which was quantitatively (Δ log K, log X, and % RS) compared with their corresponding binary complexes. In terms of the ligands (B), the stability of the complexes follows him > bim > hist > his. The molecular geometry of the complexes formed in solution between the ligands and M(II) was determi...