Spectrophotometric study of the reaction of iron(iii) with methylthymol blue

The reaction between iron(III) and Methylthymol Blue (MTB or H(6)A) has been investigated by spectrophotometry. It has been established that iron(III) and MTB form two complexes with compositions iron(III): MTB = 1:1 and 1:2. The 1:1 complex is stable in acidic medium containing excess of iron, and the 1:2 complex is stable in slightly acidic or alkaline media containing excess of MTB. The absorption maxima are at 610 mmu (1:1) and 515 mmu (1:2), the molar absorptivities being 1.73 +/- 0.01 x 10(4) and 3.21 +/- 0.05 x 10(3) respectively. The nature of the two complexes at pH 6 and the stability constants have been determined: log beta(11) = 20.56 +/- 0.07, log beta(112) = 43.29 +/- 0.09, log beta(12) = 6.66 +/- 0.05.     

Spectrophotometric study of the reaction of bismuth(III) with Xylenol Orange

The reaction between bismuth(III) and Xylenol Orange (XO) has been investigated by spectrophotometry. It has been established that bismuth(III) and Xylenol Orange form complex compounds with compositions Bi(III):XO = 1:1 (up to pH 1) and Bi(III):XO = 1:2 (above pH 1) which have absorption maxima at 550 and 500 nm respectively. The formula of the 1:1 complex is [Bi(H(3)R)] whereas the 1:2 complex can take one of the following forms: [Bi(H(4)R)(2)](1-), [Bi(H(4)R)(H(3)R)](2-) and [Bi(H(3)R)(2)](3-). If the values for pK(Bi(H(3)R)) and pK(Bi(H(3)R)(2)) respectively are 9.80 +/- 0.03 and 15.53 +/- 0.03 at a constant ionic strength of 1.0.     

Highly specific spectrophotometric method for palladium(II) determination with 3-(5'-tetrazolylazo)-2,6-Diaminotoluene in the presence of chlorides. Kinetic and equilibrium study of reactions

3-(5'-tetrazolylazo)-2,6-Diaminotoluene (TEADAT, H(3)L(2+)) forms stable 1:1 and 1:2 (metal:ligand) pink-red complexes (lambda(max) 506 and 536 nm) with palladium(II). The apparent molar absorptivity of 1:2 complex is 5.2 x 10(4) 1.mol(-1). cm(-1) at 536 nm. Equilibrium constants beta*(nl) for reactions PdCl(2-)(4) + nH(3)L(2+) right harpoon over left harpoonright harpoon over left harpoon PdCl(4-n) (H(2)L)(2n-2)(n) + n Cl(-) + n H(+) were determined: logbeta*(1) = 4.09 +/- 0.05, logbeta*(2) = 8.40 +/- 0.02, corresponding stability conditional constants of PdCl(3)(H(2)L) and PdCl(2)(H(2)L)(2+)(2) were log beta(1) = 19.03, log beta(2) = 26.74. The formation of complexes was rather slow but could be speeded up considerably by the catalytic effect of trace amounts of thiocyanate. Constant absorbance values were thus reached in 2-5 min. A rapid, sensitive and highly specific method for the determination of palladium(II) at pH 1.42 in 0.25M NACl has been worked out with a detection limit of 0.54 mug. Interference of precious and common metal ions have been studied and the method has been applied for the determination of palladium in Pd asbestos, oakay alloys and various catalysts and for the determination of palladium in precious metals.     

Mixed hydroxide complex formation and solubility of bismuth in nitrate and perchlorate medium

From the precipitation borderlines in the pBi'-pH diagram, determined experimentally under CO(2)-free conditions, the stability constants of bismuth hydroxide, bismuthoxynitrate and bismuthoxyperchlorate have been established. The following values have been found Nitrate-medium: Perchlorate-medium: log *K(SO)(OH) = 5.2, log *K(SO)(OH) = 5.2; log *K(SO)(NO(3)) = -1.2, log*K(SO)(ClO(4)) = -0.9; log *beta(2) = -4.0, log *beta(2) = -4.1; log *beta(3) = -10.0, log *beta(3)= -9.9; log *beta(4) = -21.5, log *beta(4) = -21.5; log *beta(1,0,1) = 1.2, log *beta(1,0,1) = 3.5. The constants refer to precipitates equilibrated for 30 min, prepared at room temperature (23 +/- 0.5 degrees) in sodium perchlorate or sodium nitrate medium with an ionic strength of 1.00 +/- 0.01. Concerning error propagation it is stated that pBi' values calculated with these constants will have a standard deviation of about 0.1 log unit.     

The stabilization of managese(III) by azide ions in aqueous solution

The evidences of spontaneous oxidation of Mn(II) by the dissolved oxygen in azide buffer medium, which is dependent on the N (-)(3)HN (3) concentration, suggested a formation of stable Mn(III) complexes due to marked colour changes. Spectrophotometric studies combined with coulometric generation of Mn(III), in presence of large excess of Mn(II), showed a maximum absorbance peak at 432 nm. The molar absorptivity increases with azide concentration (0.44-3.9 mol 1(-1)) from 3100 to 6300 mol(-1) 1 cm(-1), showing a stepwise complex formation. Potential measurements of the Mn(III) Mn(II) system in several azide aqueous buffers solutions: 1.0 x 10(-2) mol 1(-1) HN(3), (0.50-2.0 mol 1(-1)) N(-)(3) and 5.0 x 10(-2) mol 1(-1) Mn(II) and constant ionic strength 2.0 mol 1(-1), kept with sodium perchlorate, leads to the conditional potential, E(0')x, in several azide concentrations at 25.0 +/- 0.1 degrees C. Considering the overall formation constants of Mn(II) N (-)(3), from former studies, and the potential, E(0')s = 1.063 V versus SCE, for Mn(III) Mn(II) system in non-complexing media, it was possible to calculate the Fronaeus function, F(0)(L), and the following overall formation constants: beta(1) = 1.2 x 10(5) M(-1), beta(2) = 6.0 x 10(8) M(-2), beta(3) = (2.4 +/- 0.7) x 10(11) M(-3), beta(4) = (1.5 +/- 0.5) x 10(11) M(-4) and beta(5) = (9.6 +/- 0.8) x 10(11) M(-5) for the Mn(III) N (-)(3) complexes. These data give important support to understand the importance of Mn(II) and Mn(III) synergistic effect on the analytical method of S(IV) determination based on the Co(II) autoxidation.     

Use of a bismuth ion-selective electrode for investigation of bismuth complexes of citric and malic acids

A bismuth ion-selective electrode has been used to determine the nature and stability of the complexes formed by bismuth with citric acid and malic acid, by measurement of the response of the electrode to different total bismuth concentrations at various combinations of pH and total ligand concentration. The values found were beta(2) = 3 x 10(13) for Bi(Cit)(2)(3-) and beta(3) = 8 x 10(9) for Bi(Mal)(2)(3-).     

Use of electrospray mass spectrometry (ESI-MS) for the study of europium(III) complexation with bis(dialkyltriazinyl)pyridines and its implications in the design of new extracting agents

ESI mass spectrometry was used to investigate the europium complexation by tridentate ligands L identical with 2,6-bis(5,6-dialkyl-1,2,4-triazin-3-yl)-pyridines (DATP) that have shown unique separation properties of actinides(III) from lanthanides(III) in nitric acid solutions. Complexes of three ligands, namely methyl (DMTP), n-propyl (DnPTP), and iso-propyl (DiPTP), have been investigated in acidic solutions to check the aqueous-phase stability of Eu(L)(3)(3+) ions identified previously in the solid state. The data obtained show, first, the presence of stable Eu(L)(3)(3+) ions with DnPTP (log beta(3)(app) = 12.0 +/- 0.5) and DiPTP (log beta(3)(app) = 14.0 +/- 0.6) in methanol/water (1:1 v/v) solutions under pH range 2.8-4.6 and, second, a mechanism whereby alkyl moieties contribute to a self-assembling process leading to the formation of Eu(L)(3)(3+) ions. Other complexes such as Eu(L)(2)(3+) ions are only observed for DnPTP (log beta(2)(app) = 6.7 +/- 0.5) and DMTP (log beta(2)(app) = 6.3 +/- 0.1) and Eu(L)(3+) only for DMTP (log beta(1)(app) = 2.9 +/- 0.2). The log beta(n)(app) values for the Eu(L)(n)(3+) (n = 1-3) complexes were determined at pH 2.8. Better insight was given in this study concerning the role of the hydrophobic exterior of the ligands for the design of a new range of extracting agents.     

Spectrophotometric investigation of the reaction of eriochrome cyanin RC and magnesium and aluminium

The reaction of magnesium or aluminium ions with Eriochrome Cyanin RC in alkaline medium leads to formation of a complex of type ML. The molar absorptivities of the complexes are 1.90 +/- 0.14 x 10(3)1. mole(-1).cm(-1) at 570 nm for the magnesium complex and 3.87 +/- 0.04 x 10(4) at 555 nm for the aluminium complex. The conditional stability constants of the complexes were determined at various pH values, and hence the overall formation constants, which were found to be log beta(111) = 8.65 +/- 0.06 for MgOHL, log beta(121) = 22.29 +/- 0.05 for AlH(2)L, log beta(111) = 18.25 +/- 0.14 for AlHL, and log beta(101) = 13.66 +/- 0.01 for AlL.     

Preparation and characterization of novel inorganic-organic hybrid materials containing rare, mixed-halide anions of bismuth(III)

Three new hybrid inorganic-organic salts containing novel mixed haloanions of bismuth were synthesized by the solvothermal reaction of bismuth iodide with a haloacid, HX (X = Cl or Br), and the alkylamine 4,4'-trimethylenedipiperidine (TMDP). All three compounds were structurally characterized by single-crystal X-ray diffraction. Reaction of TMDP and BiI(3) with HCl yielded two crystalline products: [H(2)TMDP](2)[(Bi(2)I(9))(BiCl(2)I(2))] (1, major yield) and [H(2)TMDP](2)[Bi(2)Cl(10-x)I(x)] (2, x = 3.83, minor yield). Compound 1 crystallizes in the monoclinic space group Cc (a = 22.8586(11) A, b = 15.5878(7) A, c = 17.6793(9) A, beta = 118.7010(10) degrees , Z = 4) and contains the mononuclear mixed-halide anion BiCl(2)I(2)(-) in addition to a face-sharing bioctahedral Bi(2)I(9)(3)(-) anion and two independent H(2)TMDP(2+) cations. The BiCl(2)I(2)(-) anion has a sawhorse geometry (equatorially vacant trigonal bipyramidal geometry) that is not commonly observed in bismuth chemistry. Compound 2 crystallizes in the monoclinic space group P2(1)/c (a = 14.9471(7) A, b = 12.7622(6) A, c = 13.3381(7) A, beta = 116.1030(10) degrees , Z = 2) and contains an edge-sharing bioctahedral mixed-halide anion in which iodide occupies one and chloride occupies two of the five crystallographically independent halide sites. The remaining two sites have mixed-chloride and -iodide occupancy. Reaction of TMDP and BiI(3) with HBr yielded the crystalline product [H(2)TMDP][BiBr(5-x)I(x)] (3, x = 0.99), which contains, in addition to the organic cation, a polymeric, mixed-haloanion of bismuth(III). Compound 3 crystallizes in the chiral, orthorhombic space group P2(1)2(1)2(1) (a = 8.5189(5) A, b = 14.8988(9) A, c = 17.9984(11) A, Z = 4) and consists of an H(2)TMDP(2+) cation in addition to the anion, which is built up of corner-sharing BiX(6) octahedra. Of the five crystallographically independent halide sites in this anion, two are occupied solely by Br and the remaining three have mixed-bromide and -iodide occupancy. Other anion stoichiometries have been observed crystallographically for 3, as the specific stoichiometry is dependent on the relative concentration of the haloacid starting material used.     

Complex formation constants for the aqueous copper(I)-acetonitrile system by a simple general method

A simple spectrophotometric method for the evaluation of formation constants for aqueous copper(I) has been developed, based on the kinetics of reduction of Co(III)(NH(3))(5)X complexes. The method has been applied to the aqueous copper(I)-acetonitrile system to determine the successive formation constants beta(1), beta(2), and beta(3) as 4.3 x 10(2) M(-)(1), 1.0 x 10(4) M(-)(2), and 2.0 x 10(4) M(-)(3), respectively, in 0.14 M NaClO(4)/HClO(4) at 21 +/- 1 degrees C.     

Spectrophotometric determination of phosphate ions with the system cerium(III)Arsenazo III

A new method for the spectrophotometric determination of PO(3-)(4), based on the conversion of the complex of cerium(III) with arsenazo III (CeH(4)R(-)) into CePO(4) is proposed and used for the indirect spectrophotometric determination of phosphorus in ferro-silicon. The reaction between Ce(III) and arsenazo III has been studied spectrophotometrically and the stability constants of the complex CeH(4)R(-) have been determined: log beta(1) = 6.42 +/- 0.10 (for pH 1-3) and log beta(1) = 6.11 +/- 0.02 (for pH 5.5-7).     

Formation constants of zinc(II) complexes with Semi-Xylenol Orange

A potentiometric and spectrophotometric investigation on the formation of zinc(II) complexes with Semi-Xylenol Orange (SXO or H(4)L) is reported. In an aqueous solution (mu = 0.1), three 1:1 complex species, MH(2)L, MHL(-), ML(2-), and a 1:2 complex, ML(6-)(2), seem to exist. In a strongly alkaline medium (above pH 12.5) the complexes may dissociate to give zinc hydroxide and L(4-). The formation of a hydroxy complex is not observed. The absorption maxima are at 445 nm (MH(2)L), 466 nm (MHL(-)) and 561 nm (ML(2-)), the molar absorptivities being 2.34 x 10(4), 2.42 x 10(4) and 3.14 x 10(4) 1.mole(-1) .cm(-1) respectively. The formation constants are (at 25 +/- 0.1 degrees ) log K(M)(ML) = 11.84, log K(M)(MHL) = 7.13, log K(M)(MH(2)L) = 2.70, log K(M)(ML(2)) = 16.60.     

Kinetics and mechanism of iron(III)-nitrilotriacetate complex reactions with phosphate and acetohydroxamic acid

The kinetics and mechanism of the substitution of coordinated water in nitrilotriacetate complexes of iron(III) (Fe(NTA)(OH(2))(2) and Fe(NTA)(OH(2))(OH)(-)) by phosphate (H(2)PO(4)(-) and HPO(4)(2)(-)) and acetohydroxamic acid (CH(3)C(O)N(OH)H) were investigated. The phosphate reactions were found to be pH dependent in the range of 4-8. Phosphate substitution rates are independent of the degree of phosphate protonation, and pH dependence is due to the difference in reactivity of Fe(NTA)(OH(2))(2) (k = 3.6 x 10(5) M(-)(1) s(-)(1)) and Fe(NTA)(OH(2))(OH)(-) (k = 2.4 x 10(4) M(-)(1) s(-)(1)). Substitution by acetohydroxamic acid is insensitive to pH in the range of 4-5.2, and Fe(NTA)(OH(2))(2) and Fe(NTA)(OH(2))(OH)(-) react at equivalent rates (k = 4.2 x 10(4) and 3.8 x 10(4) M(-)(1) s(-)(1), respectively). Evidence for acid-dependent and acid-independent back-reactions was obtained for both the phosphate and acetohydroxamate complexes. Reactivity patterns were analyzed in the context of NTA labilization of coordinated water, and outer-sphere electrostatic and H-bonding influences were analyzed in the precursor complex (K(os)).     

Potentiometric studies of indium(III) azide complexes in aqueous medium

The stability constants of indium-azide complexes were determined by the potentiometric method (glass electrode). The effect monitored was the change in pH of a solution of azide and hydrazoic acid (N(-)(3)/HN(3)) when indium(III) cations were added. The azide concentration was varied from close to zero to 90mM, the ionic strength being kept at 2.000 M with sodium perchlorate and the temperature at 25.0 degrees . Evaluation of experimental data showed only mononuclear species, and the global constants found were beta(1) = (2.0 +/- 0.1) x 10(3), beta(2) = (7 +/- 2) x 10(5), beta(3) = (5 +/- 1) x 10(7) and beta(4) = (7 +/- 3) x 10(8).     

Thermodynamics, kinetics, and mechanism of the stepwise dissociation and formation of Tris(L-lysinehydroxamato)iron(III) in aqueous acid

pK(a) values for the hydroxamic acid, alpha-NH(3)(+), and epsilon-NH(3)(+) groups of L-lysinehydroxamic acid (LyHA, H(3)L(2+)) were found to be 6.87, 8.89, and 10.76, respectively, in aqueous solution (I = 0.1 M, NaClO(4)) at 25 degrees C. O,O coordination to Fe(III) by LyHA is supported by H(+) stoichiometry, UV-vis spectral shifts, and a shift in nu(CO) from 1648 to 1592 cm(-1) upon formation of mono(L-lysinehydroxamato)tetra(aquo)iron(III) (Fe(H(2)L)(H(2)O)(4)(4+)). The stepwise formation of tris(L-lysinehydroxamato)iron(III) from Fe(H(2)O)(6)(3+) and H(3)L(2+) was characterized by spectrophotometric titration, and the values for log beta(1), log beta(2), and log beta(3) are 6.80(9), 12.4(2), and 16.1(2), respectively, at 25 degrees C and I = 2.0 M (NaClO(4)). Stopped-flow spectrophotometry was used to study the proton-driven stepwise ligand dissociation kinetics of tris(L-lysinehydroxamato)iron(III) at 25 degrees C and I = 2.0 M (HClO(4)/NaClO(4)). Defining k(n) and k(-n) as the stepwise ligand dissociation and association rate constants and n as the number of bound LyHA ligands, k(3), k(-3), k(2), k(-2), k(1), and k(-1) are 3.0 x 10(4), 2.4 x 10(1), 3.9 x 10(2), 1.9 x 10(1), 1.4 x 10(-1), and 1.2 x 10(-1) M(-1) s(-1), respectively. These rate and equilibrium constants are compared with corresponding constants for Fe(III) complexes of acetohydroxamic acid (AHA) and N-methylacetohydroxamic acid (NMAHA) in the form of a linear free energy relationship. The role of electrostatics in these complexation reactions to form the highly charged Fe(LyHA)(3)(6+) species is discussed, and an interchange mechanism mediated by charge repulsion is presented. The reduction potential for tris(L-lysinehydroxamato)iron(III) is -214 mV (vs. NHE), and a comparison to other hydroxamic acid complexes of Fe(III) is made through a correlation between E(1/2) and pFe.     

The impact of tripodal chelates on water exchange kinetics and mechanisms: a variable temperature and pressure 17O NMR study to clarify the structure-reactivity relationship in [Fe(II)(L)(H2O2](-) complexes

The effect of temperature and pressure on the water exchange reaction of [Fe(II)(NTA)(H2O)2](-) and [Fe(II)(BADA)(H2O)2](-) (NTA = nitrilotriacetate; BADA = beta-alanindiacetate) was studied by 17O NMR spectroscopy. The [Fe(II)(NTA)(H2O)2](-) complex showed a water exchange rate constant, k(ex), of (3.1 +/- 0.4) x 10(6) s(-1) at 298.2 K and ambient pressure. The activation parameters DeltaH( not equal), DeltaS( not equal) and DeltaV( not equal) for the observed reaction are 43.4 +/- 2.6 kJ mol(-1), + 25 +/- 9 J K(-1) mol(-1) and + 13.2 +/- 0.6 cm(3) mol(-1), respectively. For [Fe(II)(BADA)(H2O)2](-), the water exchange reaction is faster than for the [Fe(II)(NTA)(H2O)2](-) complex with k(ex) = (7.4 +/- 0.4) x 10(6) s(-1) at 298.2 K and ambient pressure. The activation parameters DeltaH( not equal), DeltaS( not equal) and DeltaV( not equal) for the water exchange reaction are 40.3 +/- 2.5 kJ mol(-1), + 22 +/- 9 J K(-1) mol(-1) and + 13.3 +/- 0.8 cm(3) mol(-1), respectively. The effect of pressure on the exchange rate constant is large and very similar for both systems, and the numerical values for DeltaV( not equal) suggest in both cases a limiting dissociative (D) mechanism for the water exchange process.     

On the formation of iron(III) hydroxo acetate complexes

The formation of hydroxo acetate complexes of iron (III) ion has been studied at 25 degrees C in 3 M (Na)ClO4 ionic medium by measuring with a glass electrode the hydrogen ion concentration in Fe(ClO4)3-HClO4-NaAc mixtures (Ac = acetate ion). The acetate/metal ratio ranged from 0 to 6, the metal concentration varied from 0.005 to 0.06 M, whereas [H+] was stepwise decreased from 0.1 M to initial precipitation of hydroxo-acetates. This occurred, depending on the acetate/metal ratio, in the -log[H+] range 1.85-2.7. The potentiometric data are consistent with the presence of Fe3(OH)3Ac3(3+), Fe2(OH)2(4+), Fe3(OH)4(5+), Fe3(OH)5(4+) and, as minor species, of Fe3(OH)2Ac6+, FeAc2+, FeAc2+, FeOH2+ and Fe(OH)2+. Previously published EMF measurements with redox and glass half-cells were recalculated to refine the stability constants of FeAc2+, FeAc2+ and Fe3(OH)2Ac6+. Formation constants *beta pqr for pFe(3+)+(q-r)H2O + rHAc reversible Fep(OH)(q-r)(Ac)r3p-q + qH+ (in parenthesis the infinite dilution value): log*beta 111 = -1.85 +/- 0.02 (-0.67 +/- 0.15), log*beta 122 = -3.43 +/- 0.02 (-1.45 +/- 0.15); log*beta 363 = -5.66 +/- 0.03 (-2.85 +/- 0.40), log*beta 386 = -8.016 +/- 0.006 (-4.06 +/- 0.15), log*beta 220 = -2.88 +/- 0.02 (-2.84 +/- 0.05), log*beta 340 = -6.14 +/- 0.18 (-6.9 +/- 0.4), log*beta 350 = -8.44 +/- 0.09 (-7.65 +/- 0.15).     

Structure of sodium bis(N-methyl-iminodiacetato)iron(III): trans-meridional N-coordination in the solid state and in solution

The results of a detailed solid state and solution structural study of the Fe(III) bis-mida complex [Fe(III)(mida)(2)]- (mida = N-methyl-iminodiacetate) are reported. The structure of the sodium salt Na[Fe(mida)2][NaClO4]2.3H2O (1) was determined by single-crystal X-ray analysis. The complex anion in 1 contains a six-coordinate Fe(III) centre bound to two tridentate mida ligands arranged in the meridional configuration, and the mer Fe(III)N2O4 chromophore shows a high degree of distortion from regular octahedral symmetry. Raman- and UV/VIS/NIR spectroscopic measurements showed that no gross changes take place in the Fe(III) coordination sphere upon redissolution in water. Quantum chemical calculations of all three possible configurations of the [Fe(mida)2]- complex ion in the gas phase support the finding that the mer isomer is more stable than the u-fac (cis) and s-fac (trans) isomers. Redox potential measurements of the Fe(III/II)(mida) couple in dependence of pH led to the following values for the equilibrium contants: log beta(III)(101) = 11.98 +/- 0.05, log beta(III)(102) = 20.49 +/- 0.01, pK(III)(a1 OH) = 7.81; log beta(II)(101) = 6.17 +/- 0.01, log beta(II)(102) = 11.39 +/- 0.01.     

Structural characterization and formation kinetics of sitting-atop (SAT) complexes of some porphyrins with copper(II) ion in aqueous acetonitrile relevant to porphyrin metalation mechanism. Structures of aquacopper(II) and cu(II)-SAT complexes as determined by XAFS spectroscopy

The formation of the sitting-atop (SAT) complexes of 5,10,15,20-tetraphenylporphyrin (H(2)tpp), 5,10,15,20-tetrakis(4-chlorophenyl)porphyrin (H(2)t(4-Clp)p), 5,10,15,20-tetramesitylporphyrin (H(2)tmp), and 2,3,7,8,12,13,17,18-octaethylporphyrin (H(2)oep) with the Cu(II) ion was spectrophotometrically confirmed in aqueous acetonitrile (AN), and the formation rates were determined as a function of the water concentration (C(W)). The decrease in the conditional first-order rate constants with the increasing C(W) was reproduced by taking into consideration the contribution of [Cu(H(2)O)(an)(5)](2+) in addition to [Cu(an)(6)](2+) to form the Cu(II)-SAT complexes. The second-order rate constants for the reaction of [Cu(an)(6)](2+) and [Cu(H(2)O)(an)(5)](2+) at 298 K were respectively determined as follows: (4.1 +/- 0.2) x 10(5) and (3.6 +/- 0.2) x 10(4) M(-1) s(-1) for H(2)tpp, (1.15 +/- 0.06) x 10(5) M(-1) s(-1) and negligible for H(2)t(4-Clp)p, and (4.8 +/- 0.3) x 10(3) and (1.3 +/- 0.3) x 10(2) M(-1) s(-1) for H(2)tmp. Since the reaction of H(2)oep was too fast to observe the reaction trace due to the dead time of 2 ms for the present stopped-flow technique, the rate constant was estimated to be greater than 1.5 x 10(6) M(-1) s(-1). According to the structure of the Cu(II)-SAT complexes determined by the fluorescent XAFS measurements, two pyrrolenine nitrogens of the meso-substituted porphyrins (H(2)tpp and H(2)tmp) bind to the Cu(II) ion with a Cu-N(pyr) distance of ca. 2.04 A, while those of the beta-pyrrole-substituted porphyrin (H(2)oep) coordinate with the corresponding bond distance of 1.97 A. The shorter distance of H(2)oep is ascribed to the flexibility of the porphyrin ring, and the much greater rate for the formation of the Cu(II)-SAT complex of H(2)oep than those for the meso-substituted porphyrins is interpreted as due to a small energetic loss at the porphyrin deformation step during the formation of the Cu(II)-SAT complex. The overall formation constants, beta(n), of [Cu(H(2)O)(n)()(an)(6)(-)(n)](2+) for the water addition in aqueous AN were spectrophotometrically determined at 298 K as follows: log(beta(1)/M(-1)) = 1.19 +/- 0.18, log(beta(2)/M(-2)) = 1.86 +/- 0.35, and log(beta(3)/M(-3)) = 2.12 +/- 0.57. The structure parameters around the Cu(II) ion in [Cu(H(2)O)(n)(an)(6-n)](2+) were determined using XAFS spectroscopy.     

A new zinc(II) fluorophore 2-(9-anthrylmethylamino)ethyl-appended 1,4,7,10-tetraazacyclododecane

A new 2-(9-anthrylmethylamino)ethyl-appended cyclen, L(3) (1-(2-(9-anthrylmethylamino)ethyl)-1,4,7,10-tetraazacyclododecane) (cyclen = 1,4,7,10-tetraazacyclododecane), was synthesized and characterized for a new Zn(2+) chelation-enhanced fluorophore, in comparison with previously reported 9-anthrylmethylcyclen L(1) (1-(9-anthrylmethyl)-1,4,7,10-tetraazacyclododecane) and dansylamide cyclen L(2). L(3) showed protonation constants log K(a)(i)() of 10.57 +/- 0.02, 9.10 +/- 0.02, 7.15 +/- 0.02, <2, and <2. The log K(a3) value of 7.15 was assigned to the pendant 2-(9-anthrylmethylamino)ethyl on the basis of the pH-dependent (1)H NMR and fluorescence spectroscopic measurements. The potentiometric pH titration study indicated extremely stable 1:1 Zn(2+)-L(3) complexation with a stability constant log K(s)(ZnL(3)) (where K(s)(ZnL(3)) = [ZnL(3)]/[Zn(2+)][L(3)] (M(-)(1))) of 17.6 at 25 degrees C with I = 0.1 (NaNO(3)), which is translated into the much smaller apparent dissociation constant K(d) (=[Zn(2+)](free)[L(3)](free)/[ZnL(3)]) of 2 x 10(-)(11) M with respect to 5 x 10(-)(8) M for L(1) at pH 7.4. The quantum yield (Phi = 0.14) in the fluorescent emission of L(3) increased to Phi = 0.44 upon complexation with zinc(II) ion at pH 7.4 (excitation at 368 nm). The fluorescence of 5 microM L(3) at pH 7.4 linearly increased with a 0.1-5 microM concentration of zinc(II). By comparison, the fluorescent emission of the free ligand L(1) decreased upon binding to Zn(2+) (from Phi = 0.27 to Phi = 0.19) at pH 7.4 (excitation at 368 nm). The Zn(2+) complexation with L(3) occurred more rapidly (the second-order rate constant k(2) is 4.6 x 10(2) M(-)(1) s(-)(1)) at pH 7.4 than that with L(1) (k(2) = 5.6 x 10 M(-)(1) s(-)(1)) and L(2) (k(2) = 1.4 x 10(2) M(-)(1) s(-)(1)). With an additionally inserted ethylamine in the pendant group, the macrocyclic ligand L(3) is a more effective and practical zinc(II) fluorophore than L(1).