KINETICS OF FORMATION AND STABILITY CONSTANTS OF MONO AND BIS l-TYROSINE COMPLEXES OF Cu(II), Co(II), AND Ni(II)

Abstract

The kinetics and stability constants of l-tyrosine complexation with copper(II), cobalt(II) and nickel(II) have been studied in aqueous solution at 25° and ionic strength 0.1 M. The reactions are of the type M(HL)^(3-n)+ _n-1 + HL- ? M(HL)^(2-n)+_n(k_n, forward rate constant; k_-n, reverse rate constant); where M=Cu, Co or Ni, HL^? refers to the anionic form of the ligand in which the hydroxyl group is protonated, and n=1 or 2. The stability constants (K_n=k_n/k_-n) of the mono and bis complexes of Cu²⁺, Co²⁺ and Ni²⁺ with l-tyrosine, determined by potentiometric pH titration are: Cu²⁺, log K₁=7.90 ± 0.02, log K₂=7.27 ± 0.03; Co²⁺, log K₁=4.05 ± 0.02, log K₂=3.78 ± 0.04; Ni²⁺, log K₁=5.14 ± 0.02, log K₂=4.41 ± 0.01. Kinetic measurements were made using the temperature-jump relaxation technique. The rate constants are: Cu²⁺, k₁=(1.1 ± 0.1) × 10⁹ M ^?1 sec^?1, k_-1=(14 ± 3) sec^?1, k₂=(3.1 ± 0.6) × 10⁸ M ^?1 sec^?1, k^?2=(16 ± 4) sec^?1; Co²⁺, k₁=(1.3 ± 0.2) × 10⁶ M ^?1 sec^?1, k_-1=(1.1 ± 0.2) × 10² sec^?1, k₂=(1.5 ± 0.2) × 10⁶ M ^?1 sec^?1, k_-2=(2.5 ± 0.6) × 10² sec^?1; Ni²⁺, k₁=(1.4 ± 0.2) × 10⁴ M ^?1 sec^?1, k_-1=(0.10 ± 0.02) sec^?1, k₂=(2.4 ± 0.3) × 10⁴ M ^?1 sec^?1, k_-2=(0.94 ± 0.17) sec^?1. It is concluded that l-tyrosine substitution reactions are normal. The presence of the phenyl hydroxyl group in l-tyrosine has no primary detectable influence on the forward rate constant, while its influence on the reverse rate constant is partially attributed to substituent effects on the basicity of the amine terminus.     

Studies on copper(II) complexes of some polyaza macrocycles derived from 1,2-diaminoethane

Syntheses of copper(II) complexes of 20-membered and 15-membered aza macrocycles 1,3,6,8,11,13,16,18-octaaza-2,7,12,17-tetrachlorocycloeicosane (OTCE, [20]-N₈) and 1,3,6,8, 11,13-hexaazacyclopentadecane (HCPD, [15]-N₆) involving metal template condensation between 1,2-diaminoethane, trichloromethane and dichloromethane, respectively, are reported. Formulation of [Cu₄(OTCE)(H₂O)₈]Cl₈ and [Cu₃(HCPD)(H₂O)₆]Cl₆ · 2H₂O and the ligand hydrochlorides OTCE · 8HCl and HCPD · 6HCl are supported by elemental analyses, conductivity measurements, and spectral studies. For a comparative cavity size effect on the stability constant, potentiometric measurements on the copper complexes of the generated macrocycles [15]-N₆ and [20]-N₈ and the structurally related larger macrocycle 1,3,6,8,11,13,16,18,21,23-decaaza-2,2,7,7,12,12,17,17,22,22-decachlorocyclopentacosane (DDCP, [25]-N₁₀, prepared recently) have been performed in aqueous solution at 25°C (μ = 0.1 M KNO₃). Very high stability constants obtained for reaction Cu²⁺ + A ? CuA²⁺ (A = ligand, log K = 20.51 and 25.87, respectively, for OTCE and DDCP systems) are a reflection on the folding of the ligand to provide a small cavity suitable for fitting of the copper ion. Further, a high equilibrium constant value for CuA²⁺ + Cu²⁺ ? Cu₂A⁴⁺ (OTCE system, log K = 14.59) or Cu₂A⁴⁺ + Cu²⁺ ? Cu₃A⁶⁺ (DDCP system, log K = 16.69) is due to suitable fitting of two and three copper ions in the 20-membered and 25-membered ring cavity of OTCE and DDCP, respectively.     

Complexation Properties of a Carbon-Bridged Cryptand with Metal Ions in Aqueous Solution at 25°C

Abstract

Thermodynamic quantities (log K, ΔH, and ΔS) for the interactions of a carbon-bridged cryptand with Li⁺, Na⁺, K⁺, Ca²⁺, Sr²⁺, Ba²⁺, and Pb²⁺ were determined at 25° C by calorimetric titration in aqueous solution. The cryptand forms complexes with Na⁺, Sr²⁺, Ba²⁺, and Pb²⁺ with log K ≤ 2. Complexation was not detected for Li⁺, K⁺, and Ca²⁺. Weak interactions with Li⁺ and K⁺ and a log K value of 2.4 for Na⁺ suggest that the cavity size of the cryptand is close to that of Na⁺ but too small for K⁺ and too large for Li⁺. The carbon-bridged cryptand selectively binds Sr²⁺ (log K = 3.2) over Ca²⁺ and Ba²⁺ by more than one order of magnitude.     

Homo- and heterometallic complexes based on polytopic carboxylic acid: synthesis,characterization, and property

Two heterometallic [K₄M₄(HL)₄(H₂O)₁₂] (M=Co (1), Ni (2)) and two homometallic [M₂L(H₂O)₇]?·?2H₂O ((M=Co (3), Ni (4)) (H₄L?=?(2-(bis(carboxymethyl)amino) terephthalic acid) have been synthesized and characterized by elemental analysis, FT-IR spectrum, and single-crystal X-ray diffraction. The isomorphous 1 and 2 contain K⁺ and M²⁺, in which K⁺ were bridged with M²⁺ through μ-HL^3? and μ-H₂O, leading to 2-D layer structures. The isomorphous 3 and 4 show homometallic binuclear complexes with μ-HL^3? as the bridging ligand. Various H-bonds including different H-bond helical chains form, by which 3 and 4 assemble into 3-D supramolecular frameworks. TG analysis indicates that the decomposition temperatures are [K₄M₄(HL)₄(H₂O)₁₂] (1)?>?[M₂L(H₂O)₇]?·?2H₂O (3)?>?H₄L.     

Extraction and <Emphasis Type="Italic">ab initio</Emphasis> calculation studies on the complexation of Ca<Superscript>2+</Superscript> with valinomycin

From extraction experiments and γ-activity measurements, the exchange extraction constant corresponding to the equilibrium Ca²⁺ (aq)+1·Sr²⁺ (nb) ⇆ 1·Ca²⁺ (nb) + Sr²⁺ (aq) taking place in the two-phase water-nitrobenzene system (1 = valinomycin; aq = aqueous phase, nb = nitrobenzene phase) was evaluated as log K _ex (Ca²⁺, 1·Sr²⁺) = 2.4±0.1. Further, the stability constant of the valinomycin-calcium complex (abbrev. 1·Ca²⁺) in nitrobenzene saturated with water was calculated for a temperature of 25 °C: log β _nb (1·Ca²⁺) = 8.3±0.1. By using quantum mechanical DFT calculations, the most probable structure of the 1·Ca²⁺·2H₂O complex species was predicted. In this complex, the “central” Ca²⁺ cation is bound by strong bonds to two oxygen atoms of the respective water molecules and to four ester carbonyl oxygens of the parent valinomycin ligand 1. Finally, the calculated binding energy of the considered complex 1·Ca²⁺·2H₂O is −319.2 kcal/mol, which confirms the relatively high stability of this cationic complex species.     

Experimental Evidence for a Calix[4]arene-Proton Complex

Summary. From extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium H⁺(aq) + 1 ·Na⁺(nb) ⇆ 1 ·H⁺(nb) + Na⁺(aq) taking place in the two-phase water-nitrobenzene system (1 = p-tert-butylcalix[4]arene-tetrakis(N, N-diethylacetamide); aq = aqueous phase, nb = nitrobenzene phase) was evaluated as log K _ex(H⁺, 1 ·Na⁺) = −1.4 ± 0.1. Further, the stability constant of the p-tert-butylcalix[4]arene-tetrakis(N,N-diethylacetamide)-H⁺ complex in water saturated nitrobenzene was calculated for a temperature of 25°C as log β_nb(1 · H⁺) = 8.1 ± 0.1.     

Stability of the Ion Pair Between Ca<Superscript>2+</Superscript> and 2-(Hydroxymethyl)-3-Deoxy-D-<Emphasis Type="Italic">erythro</Emphasis>-Pentonate (α-Isosaccharinate)

Ion-pair formation between Ca²⁺ and -isosaccharinate, Ca²⁺ + ISA^-CaISA⁺, was studied by two independent methods: an ion-exchange and a potentiometric method (Ca-selective electrode). The two methods gave similar values for the complexation constant, log K_CaISA+^o at I = 0, (22 ± 1)°C. The ion-exchange method gave a value of log K_o^CaISA+ = (1.8 ± 0.1) and the potentiometric method resulted in logK_CaISA+^o = (1.78 ± 0.04). These values are in good agreement with the estimated value, log K_CaISA+^o = 1.7, based on the formation of a Ca-gluconate ion pair.     

Experimental Evidence for a Calix[4]arene-Proton Complex

From extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium H⁺(aq) + 1 ·Na⁺(nb) ⇆ 1 ·H⁺(nb) + Na⁺(aq) taking place in the two-phase water-nitrobenzene system (1 = p-tert-butylcalix[4]arene-tetrakis(N, N-diethylacetamide); aq = aqueous phase, nb = nitrobenzene phase) was evaluated as log K _ex(H⁺, 1 ·Na⁺) = −1.4 ± 0.1. Further, the stability constant of the p-tert-butylcalix[4]arene-tetrakis(N,N-diethylacetamide)-H⁺ complex in water saturated nitrobenzene was calculated for a temperature of 25°C as log β_nb(1 · H⁺) = 8.1 ± 0.1.     

Azothia- and Azoxythiacrown Ethers as Ion Carriers. Part I. Cationic Response of Membrane Electrodes

13-Membered azothia- and azoxythiacrown ethers have been applied as ion carriers in ion-selective membrane electrodes. Their sensitivity and selectivity were studied towards alkali, alkaline earth, transition and heavy metal cations. It was found that membranes doped with the azoxythiacrown ether (A) show higher affinity towards Pb²⁺ than Cu²⁺ (log K_Cu,Pb ^pot = 1.7), whereas membranes with the azothiacrown ether (B) are more selective towards Cu²⁺ than Pb²⁺ (log K_Cu,Pb ^pot = -2.4). The discrimination of alkali and alkaline earth cations was found to be greater for B than for A. Electrodes with both ionophores suffered from strong interference by Ag⁺ and Hg²⁺. The relation between the carrier structure and electrode properties has been discussed.     

Synthesis and metal-ion binding properties of new N2S4- and N2S5-donor macrocycles

Synthetic procedures for new N₂S₄- and N₂S₅-donor macrocycles (2 and 4) were given. The ligands were prepared by the reaction of NaBH₄ with the appropriate macrocyclic diamide in the presence of boron trifluoride ethyl etherate in dry tetrahydrofuran (THF). Solvent extraction method was used to evaluate metal-ion binding properties of the new ligands. The solvent extraction experiments suggested that the reduced macrocycles have Ag⁺ and Hg²⁺ selectivities compared to Pb²⁺, Co²⁺, Zn²⁺, Ni²⁺, Cu²⁺, Mn²⁺ and Cd²⁺ ions. The extraction constants (log K _ex) and complex compositions were determined for Ag⁺ and Hg²⁺ complex of compound (4).     

Zur Stabilität der Metallkomplexe von Methantriessigsäure und cis,cis-1,3,5-Cyclohexantricarbonsäure

The stabilities of the Mn²⁺-, Co²⁺-, Ni²⁺-, Cu²⁺- and Zn²⁺-complexes with 2-(carboxymethyl)glutaric acid ( 2 ) and cis,cis-1,3,5-cyclohexanetricarboxylic acid ( 3 ) were measured potentiometrically at 25° and I = 0.5 (KNO₃). Beside the complexes ML^? protonated species MLH and MLH are also formed. Their stability constants are given in Table 1. A comparison between the stabilities of 2 or 3 and those of acetate, as a model for a monocarboxylate, or succinate and glutarate, as examples for dicarboxylates, indicates that in all species only one carboxylate is strongly bound whereas the second and third ones are probably not. The observation that Δlog K₁ = log K ? log K as well as Δlog K₂ = log K ? log K are practically constants with values of 0.34 ± 0.05 and 0.49 ± 0.07, respectively, for both ligands and the five metal ions studied is also in line with the proposed monodentate structures of the complexes ML^?, MLH and MLH.     

Vanadium(V) 8-quinolinolate—monomer or dimer?

Extraction of vanadium(V) with 8-quinolinol into chlorobenzene is discussed. Three dimeric species are shown to be responsible for the extraction: 2VO₃^- + 4(HOx)_o α (V₂O₃Ox₄)_o + 2OH^-; log K_ex,1 = -1.60 ± 0.10 2VO₃^- + 4(HOx)_o + H⁺ + ClO₄^- α (V₂O₃H(Ox)₄ · ClO₄)_o + 2OH^-; log K_ex,2 = 1.55 ± 0.10 2VO₃^- + 4(HOx)_o + 2H⁺ + 2ClO₄^- α (V₂O₂Ox₄ · 2ClO₄)_o + 2OH^-; log K_ex,3 = 2.65 ± 0.10 The vanadium(V) complex of 8-quinolinol has also been studied by thermogravimetry and i.r. and visible spectroscopy; an oxo-bridged dimeric structure is postulated. In contrast to 8-quinolinol, 2-methyl-8-quinolinol gives a monomeric vanadium(V) complex under the usual experimental conditions.     

Influence of Water on the Equilibria of Protonation of Mesoporphyrin IX Dimethyl Ether in Acetonitrile

The equilibria of protonation of mesoporphyrin IX dimethyl ether (H₂MP), namely, H₂MP + H⁺ H₃MP⁺ and H₃MP⁺ + H⁺ H₄MP²⁺, in the H₂MP(1.4 × 10^–5 mol/l)–HClO₄(0–0.01 mol/l)–H₂O(0.01–1.65 mol/l)–CH₃CN system at 298 K were studied using the spectropotentiometry method. It was established that the first-step equilibrium (logK ₁ = 11.95) is not affected by water. The dication forms two hydrates (H₂O)H₄MP²⁺ and (H₂O)₂H₄MP²⁺ with the step formation constants K _{h 1} = 8.50 and K _{h 2} = 1.39. The conventional constant of the second protonation step is related to the water concentration through the equation logK ₂ ^" = logK ₂ + log(1 + K _{h 1}[H₂O] + K _{h 1} K _{h 2}[H₂O]²). In anhydrous acetonitrile, logK ₂ = 7.51. The electronic absorption spectra of H₄MP²⁺ and of its hydrates are identical; therefore, K ₁ and K ₂ ^" cannot be distinguished in photometric determination of [H₄MP²⁺] in the presence of water.     

A Novel QSAR Approach for Estimating Toxicity of Phenols

Abstract

Toxicity values (log IGC^?1 ₅₀) for 60 phenols tested in the 2-d static population growth inhibition assay with the ciliate Tetrahymena pyriformis were tabulated. Each chemical was selected so the series formed uniform coverage of the hydrophobicity/ionization surface. A high quality hydrophobicity-dependent (log K _ow) structure-toxicity relationship (log IGC^?1 ₅₀ = 0.741 (log K_ow) ?1.433; n = 17; r² = 0.970; s = 0.134; F = 486.55; Pr > F = 0.0001) was developed for phenols with pK_a values > 9.8. Similarly, separate hydrophobicity-dependent relationships were developed for phenols with pK_a values of 4.0, 5.1, 6.3, 7.5, and 8.7. Comparisons of intercepts and slopes, respectively, revealed phenols with pK_a values of 6.3 to be the most toxic and the least influenced by hydrophobicity. These relationships were reversed for the more acidic and basic phenols. Plots of toxicity versus pK_a for nitro-substituted phenols and phenols with log K_ow values of either 1.75 or 2.50 further demonstrated bilinearity between toxicity and ionization. In an effort to more accurately model the relationship between toxicity and ionization, the absolute value function |6.3-pK_a| was used to model ionization affects for derivatives with pK_a values between 0 and 9.8. For derivatives with pK_a value > 9.8, a value of 3.50 was used to quantitate ionization effects. The use of log K_ow in conjunction with this modified pK_a (ΔpK_a) resulted in the structure-toxicity relationship (log IGC^?1 ₅₀ = 0.567 (log K_ow)-0.226 (ΔpK_a-0.079; n = 54; r² = 0.926; s = 0.215; F = 321.06; Pr > F = 0.0001). Derivatives with a nitro group in the 4-position typically did not model well with the above equation.     

Copper Catalysed Oxygenation of Bis (2-pyridyl) methane and 6-Methyl-bis (2-pyridyl)methane to the Corresponding Ketones

The ligands (L) bis (2-pyridyl) methane (BPM) and 6-methyl-bis (2-pyridyl)methane (MBPM) form the three complexes CuL²⁺, CuL, and Cu₂L₂H with Cu²⁺. Stability constants are log K₁ = 6.23 ± 0.06, log K₂ = 4.83 ± 0.01, and log K (Cu₂L₂H + 2H²⁺ ? 2 CuL²⁺) = ?10.99 ± 0.03 for BPM and 4.56 ± 0.02, 2.64 ± 0.02, and ?11.17 ± 0.03 for MBPM, respectively. In the presence of catalytic amounts of Cu²⁺, the ligands are oxygenated to the corresponding ketones at room temperature and neutral pH. With BPM and 2,4,6-trimethylpyridine (TMP) as the substrate and the buffer base, respectively, the kinetics of the oxygenation can be described by the rate law with k₁ = (5.9 ± 0.2) · 10^?13 mol l^?1 s^?1, k₂ = (4.0 ± 0.6) · 10^?4 mol^?1 ls^?1, k₃ = (1.1 ± 0.1) · 10^?12 mol l^?1 s^?1, and k₄ = (9 ± 2) · 10^?14 mol l^?1 s^?1.     

Complex Formation of PdII Ion with the Tripodal Ligand Tris[2-(dimethylamino)ethyl]amine

The complex formation of Pd^II with tris[2-(dimethylamino)ethyl]amine (N(CH₂CH₂N(CH₃)₂)₃, Me₆tren) was investigated at 25° and ionic strength I = 1, using UV/VIS, potentiometric, and NMR measurements. Chloride, bromide, and thiocyanate were used as auxiliary ligands. The stability constant of [Pd(Me₆tren)]²⁺ in various ionic media was obtained: log β([Pd(Me₆tren)] = 30.5 (I = 1(NaCl)) and 30.8 (I = 1(NaBr)), as well as the formation constants of the mixed complexes [Pd(HMe₆tren)X]²⁺ from [Pd(HMe₆tren)(H₂O)]³⁺:log K = 3.50 = Cl^?) and 3.64 (X^? = Br^?) and [Pd(Me₆tren)X]⁺ from [Pd(Me₆tren)(H₂O)]²⁺: log K = 2.6 (X^? = Cl^?), 2.8(Br^?) and 5.57 (SCN^?) at I = 1 (NaClO₃). The above data, as well as the NMR measurements do not provide any evidence for the penta-coordination of Pd^II, proposed in some papers.     

The Association Constants of H<Superscript><Emphasis Type="Italic">+</Emphasis></Superscript> and Ca<Superscript><Emphasis Type="Italic">2 +</Emphasis></Superscript> with 2-Keto-D-Gluconate in Aqueous Solutions

2-Keto-D-gluconate (kG) is naturally produced in soils, sediments and rock faces through the microbial oxidation of glucose. Studies have qualitatively shown kG to enhance the dissolution of soil minerals. However, quantitative information, such as the log K values for the formation of metal–kG complexes, are not available. This paper presents the results of potentiometric titration studies that employ H⁺ and Ca²⁺ ion selective electrodes (ISEs) to determine the conditional ion association constants (log Q values) for the protonation and deprotonation of kG and the formation of Ca–kG complexes. The experimentally-determined log Q values were then converted to the corresponding ion association constants (the zero ionic strength condition; log K values) by employing a modified Davies equation for charged species and the Setchenów equation for neutral species. The log K values were determined by potentiometric titrations at constant kG concentration, varied ionic strengths, 25 or 22 ^∘C, and in the absence of CO₂. The computer model GEOCHEM-PC was used to determine the aqueous speciation of ions other than kG and the computer model FITEQL was used to estimate conditional log Q values for reactions in the various chemical models. Based on our evaluations, equilibrium constants for the following reactions were determined: H⁺+ kG^– ⇌ HkG⁰, log K_a1 = (3.00 ± 0.06), kG^–⇌ H_–1kG^2–+ H⁺, log K_a–1 = –(11.97 ± 0.41), and Ca²⁺+ kG^–⇌ CakG⁺, log K₁₀₁ = (1.74 ± 0.04).     

Complexing tendencies of UO 22+ and Th4+ in their mixed ligand complexes with aminopolycarboxylates and resorcinol or its derivatives

Formation contants (log K _MAL ^MA ) of mixed ligand complexes MAL, where M = UO ₂ ²⁺ or Th⁴⁺, A = IMDA, NTA, HEDTA, EDTA, CDTA or DTPA, and L = resorcinol (res), 2-methyl resorcinol (2-Me-res), 5-methyl resorcinol (5-Me-res) or 4-chloro resorcinol (4-Cl-res), have been determined pH-metrically by the Irving-Rossotti approach at 25°C and at an ionic strength,I = 0.2(moldm⁻³KNO₃). The observed stability sequences are IMDA > NTA > HEDTA > EDTA > CDTA > DTPA, and 4-Cl-res > 5-Me-res > 2-Me-res > res with respect to primary and secondary ligands, respectively. Th⁴⁺ forms more stable mixed complexes than UO ₂ ²⁺ . The A ΔlogK values are negative due mainly to the charge repulsion involved in the complexation MA + L⇋MAL.