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Stability Constants (stability + constant)
Selected AbstractsVoltammetry as a Virtual Potentiometric Sensor in Modeling of a Metal-Ligand System and Refinement of Stability Constants.ELECTROANALYSIS, Issue 8 2004Part 1. Abstract A mathematical conversion of data coming from nonequilibrium and dynamic voltammetric techniques (a direct current sampled (DC) and differential pulse (DP) polarography) into potentiometric sensor type of data is described and tested on a dynamic metal-ligand system. A combined experiment involving DCP, DPP and glass electrode potentiometry (GEP) was performed on a single solution sample containing a fixed [LT],:,[MT] ratio (acid-base titration). Dedicated potentiometric software ESTA was successfully employed in the refinement operations performed on virtual potentiometric (VP) data obtained from DC and DP polarography. It was possible to refine stability constants either separately, from VP-DC or VP-DP, or simultaneously from any combination of VP-DC, VP-DP and GEP. The concept of VP-DC or VP-DP is reported for the first time and numerous documented and possible advantages are discussed. The proposed procedure can be easily utilized also by nonelectrochemists who are interested in, e.g., the ligand design strategies. [source] Stability Constants and Dissociation Rates of the EDTMP Complexes of Samarium(III) and Yttrium(III)EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 30 2008Ferenc Krisztián Kálmán Abstract The stability constants of Sm(EDTMP) (log,KML = 20.71) and Y(EDTMP) (log,KML = 19.19) were determined by a competition reaction between the Ln3+ ion (Ln3+ = Sm3+ or Y3+) and Cu2+ for the EDTMP ligand by spectrophotometry at pH , 10, in the presence of an excess amount of citrate (0.15 M NaCl, 25 °C). For determining the stability constants of Cu(EDTMP) (log,KML = 19.36) and Ca(EDTMP) (log,KML = 8.71) pH,potentiometry was used. In the pH range 4,9 the EDTMP complexes are present in the form of nonprotonated and mono-, di- and triprotonated species. The Ca2+ ion forms a dinuclear complex with Ln(EDTMP). In a simplified blood plasma model consisting of Sm3+, Ca2+ and Zn2+ metal ions, EDTMP, citrate, cysteine and histidine ligands, Sm3+ is practically present in the form of [Sm(HEDTMP)Ca]2,, whereas Zn2+ predominantly forms [Zn(HEDTMP)]5, and [Zn(H2EDTMP)]4, complexes. For studying the dissociation rates of the complexes, the kinetics of the metal exchange (transmetallation) reactions between the Ln(EDTMP) complexes and Cu2+,citrate were investigated in the pH range 7,9 by the stopped-flow method. The rates of the exchange reactions are independent of the Cu2+ concentration and increase with the H+ concentration. The rate constants, characterizing the proton-assisted dissociation of the Ln(EDTMP) complexes, are several orders of magnitude higher than those of the similar Ln(EDTA) complexes, because the protonation constants of Ln(EDTMP) are high and the protonated Ln(HEDTMP) and Ln(H2EDTMP) species are present in higher concentration. The half-times of dissociation of Sm(EDTMP) and Y(EDTMP) at pH = 7.4 and 25 °C are 4.9 and 7.5 s, respectively. These relatively short dissociation half-time values do not predict the deposition of Ln3+ ions in bones in the form of intact Ln(EDTMP) complexes. It is more probable that sorption of the EDTMP ligand and Sm3+ or Y3+ ions occurs independently after the dissociation of complexes.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Electronic Interactions in Ferrocene- and Ruthenocene-Functionalized Tetraazamacrcocyclic Ligand Complexes of FeII/III, CoII, NiII, CuII and ZnIIEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 2 2005Peter Comba Abstract The syntheses of ferrocene- and ruthenocene-functionalized tetraazamacrocyclic ligands and their corresponding transition metal complexes are described. Reaction of N,N, -bis(2-aminoethyl)-1,3-propanediamine (2,3,2-tet) with 1,1,-diformylferrocene and 1,1,-diformylruthenocene produces the ligands fcmac and rcmac in 81,85% yield. Examination of their CuII, NiII, CoII, ZnII and FeII/III complexes by IR, UV/Vis, EPR and Mössbauer spectroscopy as well as by electrochemical studies suggests electronic communication between the two metal centers of each complex. The molecular structure of [CuII(fcmac)(FBF3)]BF4, determined by X-ray structure analysis, is reported and shows that the distance between the two metals is 4.54 Ĺ. Stability constants, determined by potentiometric titration, indicate that the copper(II) complexes are of similar stability as those with unfunctionalized tetraazamacrocyclic ligands (e.g. cyclam = 1,4,8,11-tetraazacyclotetradecane); stability constants of cobalt(II) complexes are about 2 log units smaller, those of nickel(II) and zinc(II) complexes are reduced by more than 10 log units. This selectivity is discussed on the basis of the structural studies. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Expanding Sapphyrin: Towards Selective Phosphate BindingCHEMISTRY - A EUROPEAN JOURNAL, Issue 29 2008Evgeny Abstract The anion-templated syntheses and binding properties of novel macrocyclic oligopyrrole receptors in which pyrrole rings are linked through amide or imine bonds are described. The efficient synthesis was accomplished by anion-templated [1+1] Schiff-base condensation and acylation macrocyclization reactions. Free receptors and their host,guest complexes with hydrochloric acid, acetic acid, tetrabutylammonium chloride, and hydrogen sulfate were analyzed by single-crystal X-ray diffraction analysis. Stability constants with different tetrabutylammonium salts of inorganic acids were determined by standard 1H,NMR and UV/Vis titration techniques in [D6]DMSO/0.5,% water solution. According to the titration data, receptors containing three pyrrole rings (10 and 12) exhibit high affinity (log,Ka=5,7) for bifluoride, acetate, and dihydrogen phosphate, and interact weakly with chloride and hydrogen sulfate. The amido-bipyrrole receptors 11 and 13 with four pyrrole rings exhibit 104 - and 102 -fold selectivity for dihydrogen phosphate, respectively, as inferred from competitive titrations in the presence of tetrabutylammonium acetate. [source] Nanosized Ball Joints Constructed from C60 and Tribenzotriquinacene Sockets: Synthesis, Component Self-Assembly and Structural InvestigationsCHEMISTRY - A EUROPEAN JOURNAL, Issue 35 2007Björn Bredenkötter Dr. Abstract The formation of supramolecular host,guest complexes of fullerene (C60) and two novel tribenzotriquinacene based hosts (5,a and 5,b) was investigated in solution and in the solid state. Stability constants for 1:1 and 2:1 complexes were obtained from spectroscopic (UV/Vis, 1H,NMR) titration experiments. Association constants of K1=(2908±360),L,mol,1 and K2=(2076±300),L,mol,1 for C60/5,a, and K1=(5608±220),L,mol,1 and K2=(673±160),L,mol,1 for C60/5,b were obtained. Single crystal X-ray structural analysis of compound C60,5,b,3,toluene revealed that a molecule of C60 was located at short van der Waals contact distances in the open pre-organised cavity of the rigid host. The supramolecular complex created resembles an engineered nanosized ball joint and represents the first member for a future nanomechanics construction kit. [source] Adding magnesium to the silver-gill binding model for rainbow trout (Oncorhynchus mykiss)ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 3 2001Melissa L. Schwartz Abstract Rainbow trout (Oncorhynchus mykiss; 2,17 g) were exposed to approximately 0.1 ,M silver as AgNO3 for 3 to 4 h in synthetic, ion-poor water (20 ,M Ca, 100 ,M Na, 150 ,M Cl, pH 7) to which was added Mg, Ca, or thiosulfate (S2O3). Gills were extracted and assayed for Ag using graphite furnace atomic absorption spectrophotometry. Up to 210 mM Mg (four fold the concentration of Mg in seawater) did not reduce accumulation of Ag by trout gills. The conditional equilibrium stability constant (K) for Mg at silver-binding sites on the gills was calculated to be log KMg-gillAg = 3.0, or approximately half-as-strong binding as for Ca at these sites. The inclusion of the Mg-gill stability constant into the original Ag-gill binding model increases the flexibility of the model, although the competitive effects of Mg are only important in sodium-poor systems. [source] Equilibrium and kinetic investigation of the interaction of model palladium(II) complex with biorelevant ligandsINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 10 2010Mohamed M. Shoukry Pd(DME)Cl2 complex was synthesized and characterized, where DME is 2-{[2-(dimethylamino)ethyl]-methylamino}ethanol. Stoichiometry and stability constants of the complexes formed between various biologically relevant ligands (amino acids, peptides, DNA constituents, and dicarboxylic acids) and [Pd(DME)(H2O)2]2+ are investigated at 25°C and at constant 0.1 M ionic strength. The effect of dielectric constant of the medium on the stability constant of Pd(DME)-CBDCA complex, where CBDCA is cyclobutanedicarboxylate, is also reported. The concentration distribution diagrams of the various species formed are evaluated. The kinetics of base hydrolysis of amino acid esters coordinated to Pd(DME)2+ complex is investigated. The effect of the temperature on the kinetics of base hydrolysis of glycine methyl ester complex is studied. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 608,618, 2010 [source] Determination of the binding constant between alprostadil and alpha-cyclodextrin by capillary electrophoresis: Implications for a freeze-dried formulationJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 7 2005Benjamin R. Schipper Abstract The binding constant between alprostadil (PGE1) and ,-cyclodextrin (,-CD) was determined at three temperatures by capillary electrophoresis. ,-CD is an excipient material in Caverject Dual Chamber Syringe (DCS), added to enhance stability. The binding constant was used to calculate the amount of PGE1 free upon reconstitution and injection, the latter of which is critical to product performance. Measurement was made in a pH 7.2 separation buffer to ensure a negative charge on PGE1. The concentration of PGE1 was fixed while the concentration of ,-CD was varied over a suitable range. As the amount of PGE1 bound to ,-CD increases, the weighted average of the resultant mobility decreases, thereby allowing a binding isotherm to be generated from which the stability constant was extracted via nonlinear regression analysis. A value of 708,±,64 M,1 was obtained at 27°C, while at physiological temperature (37°C) the value was 537,±,27 M,1. These results compare favorably to values previously obtained by NMR. Calculation of the percent PGE1 free upon reconstitution and injection show it to be near the desired outcome of 100%. Hence, we were able to conclude that the amount of free drug delivered by Caverject DCS is nominally the same as for Caverject S. Po., an earlier-developed product that contains no ,-CD. © 2005 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 94:1528,1537, 2005 [source] Bile acid sequestrants based on cationic dextran hydrogel microspheres.JOURNAL OF PHARMACEUTICAL SCIENCES, Issue 6 2001Abstract Cationic dextran hydrogel microspheres with pendant quaternary ammonium groups having alkyl substituents (C2,C12) at quaternary nitrogen were synthesized. The in vitro sorption of sodium salts of four bile acids (glycocholic, cholic, taurocholic, and deoxycholic acids) with these hydrogels was studied as a function of substituent alkyl chain length and bile acid hydrophobicity. Sorption experiments were performed in phosphate buffer solutions (pH 7.4) containing one bile salt (individual sorption) or mixtures of several bile salts (competitive sorption). Parameters for individual sorption were calculated taking into consideration the stoichiometric and cooperative binding of bile salts to oppositely charged polymer hydrogels. The results show that the increase in the length of the alkyl chain of the substituent leads to an increase in both ionization constant K0 and overall stability constant of binding K, but decreases the cooperativity parameter u. The competitive sorption studies indicate that the hydrogels display a good affinity for both dihydroxylic and trihydroxylic bile salts. The molar ratio of maximum amounts bound for the two types of bile acid is 2 to 1, which is much lower than those reported for other cationic polymers recommended as bile acid sequestrants. The binding constants for the sorption of bile salts by some dextran hydrogels are 20,30 times higher than those obtained for cholestyramine under similar sorption conditions. © 2001 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 90:681,689, 2001 [source] Enhanced solubility and dissolution rate of lamotrigine by inclusion complexation and solid dispersion techniqueJOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 9 2008Vikram R. Shinde ABSTRACT The solid-state properties and dissolution behaviour of lamotrigine in its inclusion complex with ,-cyclodextrin (,CD) and solid dispersions with polyvinylpyrrolidone K30 (PVP K30) and polyethyl-eneglycol 6000 were investigated. The phase solubility profile of lamotrigine with ,CD was classified as AL -type, indicating formation of a 1:1 stoichiometry inclusion complex, with a stability constant of 369.96 ± 2.26 M,1. Solvent evaporation and kneading methods were used to prepare solid dispersions and inclusion complexes, respectively. The interaction of lamotrigine with these hydrophilic carriers was evaluated by powder X-ray diffractometry, Fourier transform infrared spectroscopy and differential scanning calorimetry. These studies revealed that the drug was no longer present in crystalline state but was converted to an amorphous form. Among the binary systems tested, PVP K30 (1:5) showed greatest enhancement of the solubility and dissolution of lamotrigine. [source] Structural compatibility of novel nucleotide modifications with shortened linkages designed for antigene/antisense therapyJOURNAL OF RAMAN SPECTROSCOPY, Issue 5 2004J. Hanu Abstract The impact of isopolar shortened internucleotide linkage modification on the hybridization properties of potential antisense or antigene oligonucleotides was studied by using a model molecular system consisting of polyuridylic acid (PolyU) and analogs of diadenosine monophosphate with the modified linkage. Raman spectra of mixed aqueous solutions were measured at various temperatures and compositions of the mixtures for four types of modified linkage and natural ApA (3,,5,) as a reference. Analysis of the spectral sets provided amounts of formed complexes and their Raman spectra. It has been found that as in the case of ApA (3,,5,), the studied ApA analogs form with PolyU triplex-like complexes containing a central pseudo-chain of closely arranged adenosine dimers. In the case of S - and R -configured 2,,5, and 3,,5, ApCOH A analogs, respectively, the amounts of complexes formed even exceed the ApA. This hybridization effectiveness is reached, however, by a more feasible prolongation of the pseudo-chain, while the stability constant for the initiation step is significantly lower. Raman spectra of the complexes showed that for both of the above analogs the structural compatibility with the natural nucleic acid chain is decreased, because of the distorted position of one adenine residue. This distortion influences the Watson,Crick hydrogen bonds. The two types of linkages may be suitable just for construction of longer antigene or antisense oligonucleotides with alternating lengthened and shortened linkages. There is, however, a warning of possible decreased binding specificity. Copyright © 2004 John Wiley & Sons, Ltd. [source] Recovering Ga(III) from coordination complexes using pyridine 2,6-dicarboxylic acid chelation ion chromatographyBIOMEDICAL CHROMATOGRAPHY, Issue 9 2010K. Staff Abstract Ion exchange chelation chromatography is an effective means to extract metals from coordination complexes and biological samples; however there is a lack of data to verify the nature of metal complexes that can be successfully analysed using such a procedure. The aim of this study was to assess the capability of pyridine 2,6-dicarboxylic acid (PDCA) to extract and quantify Ga(III) from a range of environments using standard liquid chromatography apparatus. The PDCA chelation method generated a single Ga(III) peak with a retention time of 2.55 ± 0.02 min, a precision of <2% and a limit of detection of 110 ,M. Ga(III) hydroxide complexes (highest stability constant 15.66) were used to successfully cross-validate the chelation method with inductively coupled plasma mass spectrometry. The PDCA assay extracted 96.9 ± 1.2% of the spiked Ga(III) from porcine mucus and 100.7 ± 2.7% from a citrate complex (stability constant 10.02), but only ca 50% from an EDTA complex (stability constant 22.01). These data suggest that PDCA chelation can be considered a suitable alternative to inductively coupled plasma mass spectrometry for Ga(III) quantification from all but the most strongly bound coordinated complexes i.e. a stability constant of <15. Copyright © 2010 John Wiley & Sons, Ltd. [source] A Novel Synthesis of 2-Amino-2-deoxy- D -gluconic Acid and Its Complexation with Cu(II) in Alkaline MediumCHINESE JOURNAL OF CHEMISTRY, Issue 10 2006Wen-Xiu Gu Abstract A novel synthesis of the functional carbohydrate 2-amino-2-deoxy- D -gluconic acid was introduced and its complex formation with Cu(II) was investigated to obtain the stability constant for its further applications to the food and pharmaceutical industries. The equilibrium was investigated by spectrophotometric measurements and processed by dual-series linear regression method. Results:the yield of 2-amino-2-deoxy- D -gluconic acid is 70%. The complexation molar ratio is 1:2, the molar apsorptivity of the complex is 39.906 L·mol,1·cm,1 at 630 nm, and the stability constant ,nis 6.24×105. [source] Electrochemical study on interaction of vincristine with tubulinCHINESE JOURNAL OF CHEMISTRY, Issue 11 2001Yong Yu Abstract In Tris (0.005 mol/L)-NaCl (0.05 mol/L) buffer solution (pH = 7.10), keeping temperature at 37°C, a highly sensitive reduction peak of the antitumor agent was obtained by linear sweep voltammetry. The peak potential is-1.56 V (vs. SCE). The peak current is proportional to the concentration of vincristine over the range of 2.1 ± 10,7 -4.2 ± 10,6 mol/L with the detection limit of 1.0 ± 10,7 mol/L. The behavior of the binding of vincristine to tubulin was studied. The results showed that the reaction of tubulin dimer with vincristine formed an electrochemically active complex to be 1:2. Its stability constant is 2.5 ± 1014. The reduction process of the complex is irreversible with adsorptive characteristics. [source] Complex Formation in the Region of Metal Hydrolysis and M(OH)2 Precipitation.ELECTROANALYSIS, Issue 7 2006(AMPSO)x, (OH)y, (OH)y Systems, A Glass Electrode Potentiometric, Polarographic Study of Cd Abstract The interaction between cadmium or zinc and AMPSO was investigated by DCP and GEP, at fixed total ligand to total metal concentration ratios and various pH values, at 25.0,°C and 0.1,M KNO3 ionic strength. For Cd,(AMPSO)x,(OH)y system, CdL and CdL(OH) species, were identified, with stability constants values set to (as log,,): 2.1±0.1 and 6.2±0.2, respectively. For Zn,(AMPSO)x,(OH)y system, the proposed final model with stability constants set to (as log,,) is: ZnL=2.5±0.1 and ZnL(OH)2=12.9±0.2. For both systems, the fact that AMPSO deprotonation occurs in the metal hydrolysis and M(OH)2 precipitation and the complexes formed are not too strong added a real challenge to data interpretation. [source] Voltammetry as a Virtual Potentiometric Sensor in Modeling of a Metal-Ligand System and Refinement of Stability Constants.ELECTROANALYSIS, Issue 8 2004Part 1. Abstract A mathematical conversion of data coming from nonequilibrium and dynamic voltammetric techniques (a direct current sampled (DC) and differential pulse (DP) polarography) into potentiometric sensor type of data is described and tested on a dynamic metal-ligand system. A combined experiment involving DCP, DPP and glass electrode potentiometry (GEP) was performed on a single solution sample containing a fixed [LT],:,[MT] ratio (acid-base titration). Dedicated potentiometric software ESTA was successfully employed in the refinement operations performed on virtual potentiometric (VP) data obtained from DC and DP polarography. It was possible to refine stability constants either separately, from VP-DC or VP-DP, or simultaneously from any combination of VP-DC, VP-DP and GEP. The concept of VP-DC or VP-DP is reported for the first time and numerous documented and possible advantages are discussed. The proposed procedure can be easily utilized also by nonelectrochemists who are interested in, e.g., the ligand design strategies. [source] Comparative Solution Equilibrium Study of the Interactions of Copper(II), Iron(II) and Zinc(II) with Triapine (3-Aminopyridine-2-carbaldehyde Thiosemicarbazone) and Related LigandsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 11 2010Éva A. Enyedy Abstract The interactions of CuII, ZnII and FeII with Triapine (3-aminopyridine-2-carbaldehyde thiosemicarbazone), which is currently undergoing phase II clinical trials as a chemotherapeutic antitumour agent, were investigated in a water/DMSO mixture. The proton-dissociation constants of the ligands, the stability constants and the coordination modes of the metal complexes formed were determined by pH-potentiometric, UV/Vis spectrophotometric, EPR, 1H NMR spectroscopic and ESI-MS methods. Two N-terminally dimethylated derivatives of Triapine were also studied. Mono- and bis-ligand complexes in different protonation states were identified. Furthermore, the formation of the dinuclear species [Cu2L3]+ was confirmed for all ligands by EPR spectroscopy and ESI-MS measurements. The results showed that the N-terminally dimethylated ligands are much more potent chelators than Triapine for the divalent metal ions studied. All three ligands formed the least stable complexes with ZnII, whereas the FeII complexes were somewhat more stable than the corresponding CuII species. [source] Synthesis, Protonation and CuII Complexes of Two Novel Isomeric Pentaazacyclophane Ligands: Potentiometric, DFT, Kinetic and AMP Recognition StudiesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 1 2009Andrés G. Algarra Abstract The synthesis and coordination chemistry of two novel ligands, 2,6,9,12,16-pentaaza[17]metacyclophane (L1) and 2,6,9,12,16-pentaaza[17]paracyclophane (L2), is described. Potentiometric studies indicate that L1 and L2 form a variety of mononuclear complexes the stability constants of which reveal a change in the denticity of the ligand when moving from L1 to L2, a behaviour that can be qualitatively explained by the inability of the paracyclophanes to simultaneously use both benzylic nitrogen atoms for coordination to a single metal centre. In contrast, the formation of dinuclear hydroxylated complexes is more favoured for the paraL2 ligand. DFT calculations have been carried out to compare the geometries and relative energies of isomeric forms of the [CuL]2+ complexes of L1 and L2 in which the cyclophane acts either as tri- or tetradentate. The results indicate that the energy cost associated with a change in the coordination mode of the cyclophane from tri- to tetradentate is moderate for both ligands so that the actual coordination mode can be determined not only by the characteristics of the first coordination sphere but also by the specific interactions with additional nearby water molecules. The kinetics of the acid promoted decomposition of the mono- and dinuclear CuII complexes of both cyclophanes have also been studied. For both ligands, dinuclear complexes convert rapidly to mononuclear species upon addition of excess acid, the release of the first metal ion occurring within the mixing time of the stopped-flow instrument. Decomposition of the mononuclear [CuL2]2+ and [CuHL2]3+ species occurs with the same kinetics, thus showing that protonation of [CuL2]2+ occurs at an uncoordinated amine group. In contrast, the [CuL1]2+ and [CuHL1]3+ species show different decomposition kinetics indicating the existence of significant structural reorganisation upon protonation of the [CuL1]2+ species. The interaction of AMP with the protonated forms of the cyclophanes and the formation of mixed complexes in the systems Cu,L1 -AMP, Cu,L2 -AMP, and Cu,L3 -AMP, where L3 is the related pyridinophane containing the same polyamine chain and 2,6-dimethylpyridine as a spacer, is also reported. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Stability Constants and Dissociation Rates of the EDTMP Complexes of Samarium(III) and Yttrium(III)EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 30 2008Ferenc Krisztián Kálmán Abstract The stability constants of Sm(EDTMP) (log,KML = 20.71) and Y(EDTMP) (log,KML = 19.19) were determined by a competition reaction between the Ln3+ ion (Ln3+ = Sm3+ or Y3+) and Cu2+ for the EDTMP ligand by spectrophotometry at pH , 10, in the presence of an excess amount of citrate (0.15 M NaCl, 25 °C). For determining the stability constants of Cu(EDTMP) (log,KML = 19.36) and Ca(EDTMP) (log,KML = 8.71) pH,potentiometry was used. In the pH range 4,9 the EDTMP complexes are present in the form of nonprotonated and mono-, di- and triprotonated species. The Ca2+ ion forms a dinuclear complex with Ln(EDTMP). In a simplified blood plasma model consisting of Sm3+, Ca2+ and Zn2+ metal ions, EDTMP, citrate, cysteine and histidine ligands, Sm3+ is practically present in the form of [Sm(HEDTMP)Ca]2,, whereas Zn2+ predominantly forms [Zn(HEDTMP)]5, and [Zn(H2EDTMP)]4, complexes. For studying the dissociation rates of the complexes, the kinetics of the metal exchange (transmetallation) reactions between the Ln(EDTMP) complexes and Cu2+,citrate were investigated in the pH range 7,9 by the stopped-flow method. The rates of the exchange reactions are independent of the Cu2+ concentration and increase with the H+ concentration. The rate constants, characterizing the proton-assisted dissociation of the Ln(EDTMP) complexes, are several orders of magnitude higher than those of the similar Ln(EDTA) complexes, because the protonation constants of Ln(EDTMP) are high and the protonated Ln(HEDTMP) and Ln(H2EDTMP) species are present in higher concentration. The half-times of dissociation of Sm(EDTMP) and Y(EDTMP) at pH = 7.4 and 25 °C are 4.9 and 7.5 s, respectively. These relatively short dissociation half-time values do not predict the deposition of Ln3+ ions in bones in the form of intact Ln(EDTMP) complexes. It is more probable that sorption of the EDTMP ligand and Sm3+ or Y3+ ions occurs independently after the dissociation of complexes.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] (Benzimidazolylmethyl)cyclen: A Potential Sensitive Fluorescent PET Chemosensor for ZincEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 32 2007Abir El Majzoub Abstract A new fluorescent probe for Zn2+, methylbenzimidazole-pendant cyclen [LH: 1-(benzimidazol-2-ylmethyl)-1,4,7,10-tetraazacyclododecane] was designed and synthesized. The protonation constants of (benzimidazolylmethyl)cyclen and the stability constants of the corresponding zinc complex were determined by potentiometric titrations. The single-crystal X-ray diffraction analysis showed that LH and Zn2+ form a 1:1 complex [ZnLH]2+. The results of potentiometric, 1H NMR and UV titrations indicated that above pH 8, [ZnLH]2+ mainly deprotonates into [ZnL]+. On addition of successive amounts of Zn2+ at pH 10.4 (2,×,10,2 mol,L,1 CAPS, 25 °C), the fluorescence emission of cyclen(methylbenzimidazole) increases linearly by a factor of 3.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Thermodynamic Study of the Binding of Methyltrioxorhenium with Pyridine and Its Derivatives in Benzene SolutionEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 12 2005S. Masoud Nabavizadeh Abstract A spectrophotometric study of the interaction of methyltrioxorhenium (MTO) with pyridine and its derivatives in benzene solution has been carried out at various temperatures. The stability constants of the resulting 1:1 complexes were determined by analysis of spectrophotometric data and found to vary in the order 3,4-Me2Py > 4- tBuPy > 4-MePy > 3-MePy > 4-BenzylPy > Py > 3-PhPy > 3-C(O)OMePy > 3-ClPy. The enthalpy and entropy of adduct formation were determined from the temperature dependence of the stability constants. All complexes formed were enthalpy stabilized but entropy destabilized. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Electronic Interactions in Ferrocene- and Ruthenocene-Functionalized Tetraazamacrcocyclic Ligand Complexes of FeII/III, CoII, NiII, CuII and ZnIIEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 2 2005Peter Comba Abstract The syntheses of ferrocene- and ruthenocene-functionalized tetraazamacrocyclic ligands and their corresponding transition metal complexes are described. Reaction of N,N, -bis(2-aminoethyl)-1,3-propanediamine (2,3,2-tet) with 1,1,-diformylferrocene and 1,1,-diformylruthenocene produces the ligands fcmac and rcmac in 81,85% yield. Examination of their CuII, NiII, CoII, ZnII and FeII/III complexes by IR, UV/Vis, EPR and Mössbauer spectroscopy as well as by electrochemical studies suggests electronic communication between the two metal centers of each complex. The molecular structure of [CuII(fcmac)(FBF3)]BF4, determined by X-ray structure analysis, is reported and shows that the distance between the two metals is 4.54 Ĺ. Stability constants, determined by potentiometric titration, indicate that the copper(II) complexes are of similar stability as those with unfunctionalized tetraazamacrocyclic ligands (e.g. cyclam = 1,4,8,11-tetraazacyclotetradecane); stability constants of cobalt(II) complexes are about 2 log units smaller, those of nickel(II) and zinc(II) complexes are reduced by more than 10 log units. This selectivity is discussed on the basis of the structural studies. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Configuration of Octahedral Metal Compounds , Equilibrium, Crystal and Molecular Structure of Nickel(II) Complexes of Linear N2O4, N4S2 or N6 Donors Set Atoms LigandsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 6 2004Aminou Mohamadou Abstract Two new nickel(II) complexes of symmetric hexadentate mixed-ligand N,O [1,12-bis(2-pyridyl)-5,8-dioxa-2,11-diazadodecane (pydado)] and N,S [1,12-bis(2-pyridyl)-5,8-dithia-2,11-diazadodecane (pydadt)] donor atoms have been synthesised as perchlorate salts and characterised by X-ray crystallography and ligand-field spectroscopy. In both complexes the Ni2+ ion is hexacoordinate. The cation [Ni(pydado)]2+ is pseudo-octahedral with the two pyridyl groups in trans position; all Ni,N and Ni,O bond lengths are practically equivalent. In [Ni(pydadt)]2+ complex, however, the size of the thioether sulfur atoms imposes a C2v symmetry; the pyridyl groups and the sulfur atoms are in trans positions and all Ni,N bond lengths are equivalent. The comparison of these structures with those of octahedral cobalt, copper and zinc complexes with the same ligands shows that their configurations depend not only on the nature of the two central donor atoms of the ligand, but also on the nature of the metallic ion. In aqueous solution, the stability constants of the NiII chelates with these two ligands, determined by potentiometry, show the formation of [Ni(LH)]3+ and [NiL]2+ species in all cases. The chelating power of the pydadt ligand is slightly greater than that of pydado. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Structural, Photophysical and Chiro-Optical Properties of Lanthanide Complexes with a Bis(benzimidazole)pyridine-Based Chiral LigandEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 22 2003Gilles Muller Abstract The neutral LnIII 1:1 nitrato complexes with the chiral ligand 2,6-bis(1- S -neopentylbenzimidazol-2-yl)pyridine (L11) have been synthesised and their stability constants measured in acetonitrile (log K1 = 4.0,6.4). The crystal and molecular structure of [Eu(NO3)3(L11)(MeCN)] shows the typical meridional planar coordination of L11 to the metal ion and low symmetry of the coordination polyhedron. The influence of the steric hindrance generated by the substituent at R2 on the crystal packing and bond lengths is discussed. Photophysical measurements show that ligand L11 induces a 3,,*-to-Ln energy-transfer process in the EuIII complex, while the TbIII compound is ten times less luminescent. Addition of a second molecule of L11 to give [Ln(ClO4)2(L11)2]+ leads to a large quenching of the EuIII luminescence (140-fold) due to several factors: a less efficient 1,,*,3,,* transfer (ca. fourfold), a smaller intrinsic quantum yield QEu (ca. threefold), and a substantially less efficient ligand-to-metal transfer (ca. 12-fold). In the case of the TbIII complex, the decrease in the energy of the triplet state reduces further the TbIII emission through increased back transfer. The specific rotary dispersion of the 1:1 and 1:2 complexes points to the chirality of the complexes arising mainly from the ligand, while the circularly polarized luminescence of these complexes with EuIII and TbIII displays a weak effect, pointing to a small diastereomeric excess in solution. Altogether, this study demonstrates that electronic, thermodynamic and photophysical properties of lanthanide complexes with aromatic terdentate ligands can be tuned by modifying the number and the arrangement of the ligands, as well as their substituents, particularly those in the R2 and R3 positions. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Lanthanide Chelates Based on Diethylenetriamine Fitted with O -Benzoic Acid Pendant ArmsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 7 2003Daniel Imbert Abstract A new polycarboxylate ligand H5L has been synthesized by the attachment of five benzoate subunits onto a diethylenetriamine framework. Seven pKa values have been determined by potentiometry, spectrophotometry and NMR spectroscopy as 1.9(2), 2.8(2), 3.87(5), 4.58(6), 4.87(6), 9.19(6) and 11.68(5), the first four corresponding to the carboxylic functions and the last three to amine sites. The interaction between H5L and LnIII ions in dilute aqueous solution has been examined by UV/Vis absorption and emission spectrometries, and has been found to result in monometallic complexes that are moderately stable in the pH range 3.7,7.5. Conditional stability constants at pH 5.3 are logK11 = 5.3(2), 6.6(1), 6.5(1) and 7.2(3) for La, Eu, Tb and Lu, respectively. In the case of TbIII, the stability constants for [Tb(HL)], and [Tb(H2L)] are log,111 = 22.0(2) and log,121 = 29.8(1), giving a pTb of 10.0. In the pH range 4,7, more than 90% of the TbIII ions are in the form of the neutral species [Tb(H2L)]. Lifetime determinations of the Eu(5D0) and Tb(5D4) excited levels in both H2O and D2O at pH 5.3 indicate 4.8 ± 0.5 (Eu) and 4.5 ± 0.5 (Tb) water molecules being bound in the inner coordination sphere of the LnIII. The triplet state of the ligand in water lies at around 26000 cm,1, resulting in a sizeable sensitisation of the Tb-centred luminescence (absolute quantum yield: ,abs = 10.3%), while the luminescence of EuIII is only poorly sensitised (,abs = 1.5%). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Enantioselective Recognition of Aliphatic Amino Acids by ,-Cyclodextrin Derivatives Bearing Aromatic Organoselenium Moieties on the Primary or Secondary SideEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 8 2003Yu Liu Abstract Spectrophotometric titrations have been performed in order to determine the stability constants of inclusion complexation of some aliphatic amino acids with four structurally related organoselenium-modified ,-cyclodextrins: mono(6-phenylseleno-6-deoxy)-,-cyclodextrin (1a), mono[6-(p -methoxyphenylseleno)-6-deoxy]-,-cyclodextrin (1b), mono(2-phenylseleno-2-deoxy)-,-cyclodextrin (2a), and mono[2-(p -methoxyphenylseleno)-2-deoxy]-,-cyclodextrin (2b). Conformation analysis by circular dichroism and 2D NMR spectroscopic studies revealed that the aryl-substituted ,-cyclodextrins gave self-inclusion intramolecular complexes in aqueous solution, while the extent of penetration depended both on the positions and on the structures of substituents. Quantitative investigation on the binding ability of the hosts with amino acids showed that they were able to recognize the size and the shape of guests, affording supramolecular complexes with quite small stability constants ranging from 24 to 355 M,1. The molecular recognition abilities are discussed from the viewpoints of induced-fitting mechanisms, geometric complementary, and cooperative binding processes. Furthermore, these ,-cyclodextrin derivatives displayed considerable enantioselectivity towards L/D -amino acid isomers, giving the highest L -enantioselectivity (up to 8.4) for inclusion complexation between leucine and 2a. The binding modes of L/D -leucine with 1b were elucidated from NOESY studies and the chiral recognition phenomena were interpreted accordingly. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Effects of Zinc(II) on the Luminescence of Europium(III) in Complexes Containing , -Diketone and Schiff BasesHELVETICA CHIMICA ACTA, Issue 11 2009Yuko Hasegawa Abstract The UV, excitation, and luminescence spectra of tris(pivaloyltrifluoroacetonato)europium(III) ([Eu(pta)3]; Hpta=1,1,1-trifluoro-5,5-dimethylhexane-2,4-dione=HA) were measured in the presence of bis(salicylidene)trimethylenediamine (H2saltn), bis[5-(tert- butyl)salicylidene]trimethylenediamine (H2(tBu)saltn), or bis(salicylidene)cyclohexane-1,2-diyldiamine (H2salchn), and the corresponding ZnII complexes [ZnB] (B=Schiff base). The excitation and luminescence spectra of the solution containing [Eu(pta)3] and [Zn(salchn)] exhibited much stronger intensities than those of solutions containing the other [ZnB] complexes. The introduction of a tBu group into the Schiff base was not effective in sensitizing the luminescence of [Eu(pta)3]. The luminescence spectrum of [ZnB] showed a band around 450,nm. The intensity decreased in the presence of [Eu(pta)3], reflecting complexation between [Eu(pta)3] and [ZnB]. On the basis of the change in intensity against the concentration of [ZnB], stability constants were determined for [Eu(pta)3Zn(saltn)], [Eu(pta)3Zn{(tBu)saltn}], and [Eu(pta)3Zn(salchn)] as 4.13, 4.9 and 5.56, respectively (log,, where =[[Eu(pta)3ZnB]]([[Eu(pta)3]][[ZnB]]),1). The quantum yields of these binuclear complexes were determined as 0.15, 0.11, and 0.035, although [Eu(pta)3Zn(salchn)] revealed the strongest luminescence at 613,nm. The results of X-ray diffraction analysis for [Eu(pta)3Zn(saltn)] showed that ZnII had a coordination number of five and was bridged with EuIII by three donor O-atoms, i.e., two from the salicylidene moieties and one from the ketonato group pta. [source] Influence of Decreasing Solvent Polarity (1,4-Dioxane/Water Mixtures) on the Acid,Base and Copper(II)-Binding Properties of Guanosine 5,-Diphosphate,HELVETICA CHIMICA ACTA, Issue 3 2005Emanuela The acidity constants of twofold protonated guanosine 5,-diphosphate, H2(GDP),, and the stability constants of the [Cu(H;GDP)] and [Cu(GDP)], complexes were determined in H2O as well as in 30 or 50% (v/v) 1,4-dioxane/H2O by potentiometric pH titrations (25°; I=0.1M, NaNO3). The results showed that in H2O one of the two protons of H2(GDP), is located mainly at the N(7) site and the other one at the terminal , -phosphate group. In contrast, for 50% 1,4-dioxane/H2O solutions, a micro acidity-constant evaluation evidenced that ca. 75% of the H2(GDP), species have both protons phosphate-bound, because the basicity of pyridine-type N sites decreases with decreasing solvent polarity whereas the one of phosphate groups increases. In the [Cu(H;GDP)] complex, the proton and the metal ion are in all three solvents overwhelmingly phosphate-bound, and the release of this proton is inhibited by decreasing polarity of the solvent. Based on previously determined straight-line plots of log,Kvs. pK (where R represents a non-interacting residue in simple diphosphate monoesters ROP(O,)(O)OP(O)(O,)2, RDP3,), which were now extended to mixed solvents (based on analogies), it is concluded that, in all three solvents, the [Cu(GDP)], complex is more stable than expected based on the basicity of the diphosphate residue. This increased stability is attributed to macrochelate formation of the phosphate-coordinated Cu2+ with N(7) of the guanine residue. The formation degree of this macrochelate amounts in aqueous solution to ca. 75% (being thus higher than that of the Cu2+ complex of adenosine 5,-diphosphate) and in 50% (v/v) 1,4-dioxane/H2O to ca. 60%, i.e., the formation degree of the macrochelate is only relatively little affected by the change in solvent, though it needs to be emphasized that the overall stability of the [Cu(GDP)], complex increases with decreasing solvent polarity. By including previously studied systems in the considerations, the biological implications are shortly discussed, and it is concluded that Nature has here a tool to alter the structure of complexes by shifting them on a protein surface from a polar to an apolar region and vice versa. [source] Equilibrium and kinetic investigation of the interaction of model palladium(II) complex with biorelevant ligandsINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 10 2010Mohamed M. Shoukry Pd(DME)Cl2 complex was synthesized and characterized, where DME is 2-{[2-(dimethylamino)ethyl]-methylamino}ethanol. Stoichiometry and stability constants of the complexes formed between various biologically relevant ligands (amino acids, peptides, DNA constituents, and dicarboxylic acids) and [Pd(DME)(H2O)2]2+ are investigated at 25°C and at constant 0.1 M ionic strength. The effect of dielectric constant of the medium on the stability constant of Pd(DME)-CBDCA complex, where CBDCA is cyclobutanedicarboxylate, is also reported. The concentration distribution diagrams of the various species formed are evaluated. The kinetics of base hydrolysis of amino acid esters coordinated to Pd(DME)2+ complex is investigated. The effect of the temperature on the kinetics of base hydrolysis of glycine methyl ester complex is studied. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 608,618, 2010 [source] Kinetics of the simultaneous oxidation of nickel(II) and sulfur(IV) by oxygen in alkaline medium in Ni(II),sulfur(IV),O2 systemINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 8 2010Anil Kumar Sharma In the Ni(II),S(IV),O2 system in the region of pH > 8.4, both Ni(II) and S(IV) are simultaneously autoxidized, and when sulfur is consumed fully NiOOH precipitates. At pH > 8.4, ethanol has no effect on the rate, whereas ammonia strongly inhibits the reaction when pH > 7.0. The kinetics of the reaction, in both the presence and the absence of ethanol, is defined by the rate law where k is the rate constant, KO is the equilibrium constant for the adsorption of O2 on Ni(OH)2 particle surface. In ammonia buffer, the factor F is defined by where K, KOH, K1, K2, K3, and K4 are the stability constants of NiSO3, NiOH+, Ni(NH3)2+, Ni(NH3), Ni(NH3), and Ni(NH3), respectively. In unbuffered medium, the factor F reduces to The values of k and Ksp were found to be (1.3 ± 0.08) × 10,1 s,1 and (4.2 ± 3.5) × 10,16, respectively, at 30°C. A nonradical mechanism that assumes the adsorption of both SO32, and O2 on the Ni(OH)2 particle surface has been proposed. At pH , 8.2, Ni(II) displays no catalytic activity for sulfur(IV)-autoxidation and it is also not oxidized to NiOOH. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 464,478, 2010 [source] | ||||||||||||||||||||||||||||