Isotachophoretic determination of stability constants of Ho and Y complexes with diethylenetriaminepentaacetic acid and 1,4,7,10-tetraazadodecane-N,N',N'',N'''-tetraacetic acid

The method of capillary isotachophoresis with conductivity detection was applied for the determination of the physico-chemical characteristics (conditional stability constants log beta') of holmium and yttrium complexes with DTPA (diethylenetriaminepentaacetic acid) and DOTA (1,4,7,10-tetraazadodecane-N,N',N',N'-tetraacetic acid). The log beta' determination is based on the linear relation between the stability constants of lanthanide-DTPA (lanthanide-DOTA) complexes and the reduction of the zone of the complex owing to the bleeding phenomena (liberating free metal ion). The stability constants calculated using this relationship are comparable with the literary data obtained by other methods for both holmium (log beta'(Ho-DTPA)=21.9, log beta'(Ho-DOTA)=24.5) and yttrium complexes (log beta'(Y-DTPA)=21.2, log beta'(Y-DOTA)=24.4). Capillary isotachophoresis was applied for the determination of the optimum composition of the reaction mixture (metal:ligand ratio) as well.     

Thermodynamics of Aqueous Diethylenetriaminepentaacetic Acid (DTPA) Systems: Apparent and Partial Molar Heat Capacities and Volumes of Aqueous H2DTPA3−, DTPA5−, CuDTPA3−, and Cu2DTPA− from 10 to 55°C

Apparent molar heat capacities and volumes have been determined for aqueous solutions of the mixed electrolytes Na₅DTPA + NaOH, Na₃CuDTPA + NaOH, and NaCu₂DTPA + NaOH, and the single electrolyte Na₃H₂DTPA (DTPA=diethylenetriaminepentaacetic acid) at temperatures from 10 to 55°C. The experimental results have been analyzed in terms of Young's rule with the Guggenheim form of the extended Debye–Hückel equation and the Pitzer ion-interaction model. These calculations led to standard partial molar heat capacities and volumes for the species H₂DTPA^3–(aq), DTPA^5–(aq), CuDTPA^3–(aq), and Cu₂DTPA^–(aq) at each temperature. The partial molar properties at 0.1 m ionic strength were also calculated. The standard partial molar properties were extrapolated to elevated temperatures with the revised Helgeson–Kirkham–Flowers (HKF) model. Values for the partial molar heat capacities from the HKF model have been combined with the literature data to estimate the ionization constants of H₂DTPA^3–(aq) and the formation constant of the CuDTPA^3–(aq) copper complex at temperatures up to 300°C.     

Conformational dependence of the intrinsic acidity of the aspartic acid residue sidechain in N-acetyl- -aspartic acid-N′-methylamide

The sidechain conformational potential energy hypersurfaces (PEHS) for the γ_L, β_L, α_L, and α_D backbone conformations of N-acetyl- -aspartate-N′-methylamide were generated. Of the 81 possible conformers initially expected for the aspartate residue, only seven were found after geometric optimizations at the B3LYP/6-31G(d) level of theory. No stable conformers could be located in the δ_L, _L, γ_D, δ_D, and _D backbone conformations. The ‘adiabatic’ deprotonation energies for the endo and exo forms of N-acetyl- -aspartic acid-N′-methylamide were calculated by comparing their optimized relative energies against those found for the seven stable conformers of N-acetyl- -aspartate-N′-methylamide. Sidechain conformational PEHSs were also generated for the estimation of ‘vertical’ deprotonation energies for both endo and exo forms of N-acetyl- -aspartic acid-N′-methylamide. All backbone–sidechain (N–H⁻O–C) and backbone–backbone (N–HO=C) hydrogen bond interactions were analyzed. A total of two backbone–backbone and four backbone–sidechain interactions were found for N-acetyl- -aspartate-N′-methylamide. The deprotonated sidechain of N-acetyl- -aspartate-N′-methylamide may allow the aspartyl residue to form strong hydrogen bond interactions (since it is negatively charged) which may be significant in such processes as protein–ligand recognition and ligand binding. As a primary example, the molecular geometry of the aspartyl residue may be important in peptide folding, such as that in the RGD tripeptide.     

Complexes of Bifunctional DO3A-N-(α-amino)propinate Ligands with Mg(II), Ca(II), Cu(II), Zn(II), and Lanthanide(III) Ions: Thermodynamic Stability,Formation and Dissociation Kinetics,and Solution Dynamic NMR Studies

The thermodynamic, kinetic, and structural properties of Ln³⁺ complexes with the bifunctional DO3A-ACE⁴⁻ ligand and its amide derivative DO3A-BACE⁴⁻ (modelling the case where DO3A-ACE⁴⁻ ligand binds to vector molecules) have been studied in order to confirm the usefulness of the corresponding Gd³⁺ complexes as relaxation labels of targeted MRI contrast agents. The stability constants of the Mg²⁺ and Ca²⁺ complexes of DO3A-ACE⁴⁻ and DO3A-BACE⁴⁻ complexes are lower than for DOTA⁴⁻ and DO3A³⁻, while the Zn²⁺ and Cu²⁺ complexes have similar and higher stability than for DOTA⁴⁻ and DO3A³⁻ complexes. The stability constants of the Ln(DO3A-BACE)⁻ complexes increase from Ce³⁺ to Gd³⁺ but remain practically constant for the late Ln³⁺ ions (represented by Yb³⁺). The stability constants of the Ln(DO3A-ACE)⁴⁻ and Ln(DO3A-BACE)⁴⁻ complexes are several orders of magnitude lower than those of the corresponding DOTA⁴⁻ and DO3A³⁻ complexes. The formation rate of Eu(DO3A-ACE)⁻ is one order of magnitude slower than for Eu(DOTA)⁻, due to the presence of the protonated amine group, which destabilizes the protonated intermediate complex. This protonated group causes the Ln(DO3A-ACE)⁻ complexes to dissociate several orders of magnitude faster than Ln(DOTA)⁻ and its absence in the Ln(DO3A-BACE)⁻ complexes results in inertness similar to Ln(DOTA)⁻ (as judged by the rate constants of acid assisted dissociation). The ¹H NMR spectra of the diamagnetic Y(DO3A-ACE)⁻ and Y(DO3A-BACE)⁻ reflect the slow dynamics at low temperatures of the intramolecular isomerization process between the SA pair of enantiomers, R-Λ(λλλλ) and S-Δ(δδδδ). The conformation of the C_α-substituted pendant arm is different in the two complexes, where the bulky substituent is further away from the macrocyclic ring in Y(DO3A-BACE)⁻ than the amino group in Y(DO3A-ACE)⁻ to minimize steric hindrance. The temperature dependence of the spectra reflects slower ring motions than pendant arms rearrangements in both complexes. Although losing some thermodynamic stability relative to Gd(DOTA)⁻, Gd(DO3A-BACE)⁻ is still quite inert, indicating the usefulness of the bifunctional DO3A-ACE⁴⁻ in the design of GBCAs and Ln³⁺-based tags for protein structural NMR analysis.     

Protonation equilibria of nitrilotris(methylenephosphonato)-and ethylenediamine-tetrakis(methylenephosphonato)-complexes of scandium,yttrium, and lanthanoids

The protonation equilibria of nitrilotris(methylenephosphonic acid) (NTMP, H₆L) and ethylenediaminetetrakis(methylenephosphonic acid) (EDTMP, H₈L) complexes of scandium, yttrium, and lanthanoids have been studied potentiometrically at 25°C and at an ionic strength of 0.1 mol-dm^–3 KNO₃. The first protonation constants of NTMP complexes of lanthanoids, K _MHL , decrease with decreasing of the ionic radius of the lanthanoid [log K _MHL =7.82 (La³⁺) –6.90 (Lu³⁺)] and show a so-called Tetrad effect. The second protonation constants, K _{MH 2}L, change very little with the lanthanoid metal ions (logK _{MH 2}L=5.3–5.7). These results suggest that, in the first protonation process in ML, the proton attacks the nitrogen of NTMP rupturing the M-N of M(ntmp)^3–. The pattern of the change in the protonation constants of the EDTMP complexes with the atomic number of the lanthanoid is quite different from that of the NTMP complexes. This fact indicates that the manner of protonation of the EDTMP complexes differs from that of NTMP complexes. The protonation constants of yttrium complexes of NTMP and EDTMP agree with those of lanthanoid complexes, whereas those of scandium complexes deviate from the values predicted from its ionic radius.     

The d metal-sulfosalicylate complexes: Herring-bone, ladder and double-stranded chain frameworks with green luminescences

Assembly of 5-sulfosalicylic acid (H₃L) and d¹⁰ transition metal ions (Cd^II, Ag^I) with the neutral N-donor ligands produces five new complexes: [Cd₂(HL)₂(4,4′-bipy)₃]_n·2nH₂O (1), {[Cd₂(μ₂-HCO₂)₂(4,4′-bipy)₂(H₂O)₄][Cd(HL)₂(4,4′-bipy)(H₂O)₂]}_n (2), {[Cd(4,4′-bipy)(H₂O)₄][HL]·H₂O}_n (3), [Cd(HL)(dpp)₂(H₂O)]_n·4nH₂O (4), {[Ag(4,4′-bipy)][Hhbs]}_n (5) (4,4′-bipy=4,4′-bipyridine, dpp=1,3-di(pyridin-4-yl)propane, H₂hbs=4-hydroxybenzenesulfonic acid, the decarboxylation product of H₃L). Complex 1 adopts a 5-connected 3D bilayer topology. Complex 2 has the herring-bone and ladder chain, which are extended to a 3D network via hydrogen bonding. In 3–4 complexes, 3 is a 3D supermolecular structure formed by polymeric chains and 2D network of HL²⁻, while 4 gives the double-stranded chains. In 5, ladder arrays are stacked with the 2D networks of Hhbs⁻ anions in an –ABAB– sequence. Complexes 1–4 display green luminescences in solid state at room temperature, while emission spectra of 3 and 4 show obvious blue-shifts at low temperature.     

The Complexes of Holmium with Methylenediphosphonate and 1-Hydroxyethylidenephosphonate

The composition and stability of holmium methylenediphosphonate (MDP) and 1-hydroxyethylidenephosphonate (HEDP) complexes were studied by potentiometric titration methods in 0.1M NaCl at 25 °C. It was found that besides L^4– anions the protonated H _n L^(4–n)– species (n = 1–3 for MDP and n = 1–4 for HEDP) are present in the pH region 3 to 10. The presence of the undissociated acids (H₄L) has not been unambiguously proved for MDP. The complexes of the composition HoH _n L (n varies from 1 to –2 for MDP and from 1 to –1 for HEDP) have been found if the concentration of the ligand is higher than the concentration of holmium. The protonation constants of both acids and the stability constants of the complexes discussed were determined and the comparison with literature data of analogical complexes of other lanthanides was performed.     

Synthesis, reactions and X-ray crystal structures of metallacrown ethers with unsymmetrical bis(phosphinite) and bis(phosphite) ligands derived from 2-hydroxy-2′-(1,4-bisoxo-6-hexanol)-1,1′-biphenyl

Chlorodiphenylphosphine and 2,2′-biphenylylenephosphorochloridite react with 2-hydroxy-2′-(1,4-bisoxo-6-hexanol)-1,1′-biphenyl to yield the new α,ω-bis(phosphorus-donor)-polyether ligands, 2-Ph₂PO(CH₂CH₂O)₂–C₁₂H₈-2′-OPPh₂ (1) and 2-(2,2′-O₂C₁₂H₈)P(CH₂CH₂O)₂–C₁₂H₈-2′-P(2,2′-O₂C₁₂H₈) (2). These ligands react with Mo(CO)₄(nbd) to form the monomeric metallacrown ethers, cis-Mo(CO)₄{2-Ph₂PO(CH₂CH₂O)₂–C₁₂H₈-2′-OPPh₂} (cis-3) and cis-Mo(CO)₄{2-(2,2′-O₂C₁₂H₈)P(CH₂CH₂O)₂–C₁₂H₈-2′-P(2,2′-O₂C₁₂H₈)} (cis-4), in good yields. The X-ray crystal structures of cis-3 and cis-4 are significantly different, especially in the conformation of the metal center and the adjacent ethylene group. The very different ¹³C-NMR coordination chemical shifts of this ethylene group in cis-3 and cis-4 suggest that the solution conformations of these metallacrown ethers are also quite different. Both metallacrown ethers undergo cis–trans isomerization in the presence of HgCl₂. Although the cis–trans equilibrium constants for the isomerization reactions are nearly identical, the isomerization of cis-3 is more rapid. Phenyl lithium reacts with cis-3 to form the corresponding benzoyl complexes but does not react with either trans-3 or cis-4. Both the slower rate of cis–trans isomerization of cis-4 and its lack of reaction with PhLi are consistent with weaker interactions between the hard metal cations and the carbonyl oxygens in both trans-3 and cis-4.     

Experimental and calculated complex formation curves for mixed, dynamic and semi-dynamic, metal–ligand systems.: A differential pulse polarographic study of Cu–sarcosine–OH and Cd–MIDA–OH systems at a fixed ligand to metal ratio and varied pH

The Cu–sarcosine–OH and Cd–MIDA–OH systems have been studied by differential pulse polarography (DPP) at a fixed total ligand to total metal concentration ratio and varied pH at 298 K and μ=0.5 mol dm⁻³ in the background of NaNO₃. Both the metal–ligand systems show initially dynamic (labile), followed by semi-dynamic behaviour on the DPP time scale. It has been shown that the experimental and calculated DPP complex formation curves used previously only for labile metal–ligand systems can be employed for the modelling of all species formed in a solution and optimisation of their stability constants. The stability constants of ML and ML₂ complexes as log β were estimated for Cu^II and Cd^II as 7.75±0.02, 14.49±0.01 and 6.67 ±0.02, 12.00±0.02, respectively (all known hydroxide species of copper and cadmium, including polynuclear species, were incorporated into the metal–ligand–OH systems). The formation of the complex CuL₂(OH) is suggested also and its stability constant as log β has been estimated to be 16.2±0.2. Results reported here seem to be reasonable when compared with the literature data reported at 298 K and different ionic strengths.     

Extraction behavior of trivalent lanthanoids and yttrium with bis (2,4,4-trimethylpentyl)octylphosphine oxide

The extraction behavior of yttrium and trivalent lanthanoids has been investigated from thiocyanate solutions using bis(2,4,4-trimethylpentyl)octylphosphine oxide (CYANEX 925) in xylene as an extractant by tracer techniques. The results demonstrate that these trivalent metal ions are extracted as M(SCN)₃•3CYANEX 925. The equalibrium constants of the extracted complexes have been deduced by non-linear regression analysis. The extraction behavior of trivalent lanthanoids and yttrium was found to be ambiguous since the distribution ratios of these metal ions are nonmonotinic function of atomic number (La<Y<Pm<Tm<Ho<Eu<Yb<Lu). The separation factors between these trivalent metal ions have been calculated and compared with commercially important extraction systems like tributylphosphate (TBP), trioctylphosphine oxide (TOPO), octy(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO) and di-2-ethylhexyl phosphoric acid (DEHPA). The possibilities for separating yttrium from trivalent lanthanoids has also been discussed.     

2-Benzothiazolylthioacetic acid and 4,4′-bipyridine as ligands in designing low-dimensional coordination polymers: Synthesis, architectures and magnetic properties

The combined use of 4,4′-bipyridine (4,4′-bipy) and 2-benzothiazolylthioacetic acid (HBTTAA) as ligands with Mn(II), Cd(II), Co(II) and Cu(II) ions afforded six polymeric complexes, namely {[Mn₃(BTTAA)₄(4,4′-bipy)₄](ClO₄)₂ · 2H₂O}_n (1), [Mn(BTTAA)₂(4,4′-bipy)₂]_n (2), [Cd(BTTAA)₂(4,4′-bipy)₂]_n (3), [Cd(BTTAA)(4,4′-bipy)(NO₃)(H₂O)]_n (4), [Co(BTTAA)₂(4,4′-bipy)(H₂O)₂]_n (5) and [Cu(BTTAA)₂(4,4′-bipy)]_n (6). All these complexes have been characterized by a combination of analytical, spectroscopic and crystallographic methods. Complex 1 is a novel 2D network formed by two different 4⁴ grid networks, whereas isomorphous complexes 2 and 3 exhibit a 2Dl coordination architecture formed by the same 4⁴ grid network. In 4–6, extended 1D chains are formed, with the 4,4′-bipy molecules acting as rigid rod-like links between adjacent metal centers. The carboxylato groups of BTTAA in these complexes exhibit four different coordination modes, namely monodentate, chelating, bridging and bridging-chelating modes. The magnetic properties of 1, 2, 5 and 6 were investigated in the temperature range 2.0–300.0 K. Variable temperature magnetic susceptibility measurements show weak antiferromagnetic interactions in these complexes.     

Equilibrium Studies of Schiff Bases and Their Complexes with Ni(II), Cu(II) and Zn(II) derived from Salicylaldehyde and Some α-Amino Acids

The acid-base equilibria of Schiff bases derived from salicylaldehyde, glycine, alanine, serine, tyrosine, and phenylalanine, and their Ni(II), Cu(II) and Zn(II) complex formation equilibria were investigated by a potentiometric method in aqueous solution (t = 25^∘C, μ = 0.1 M, KCl). The data from the potentiometric titrations were evaluated by means of the BEST computer program. The order of the formation constant values of the Schiff bases was Sal-Ala > Sal-Gly > Sal-Ser > Sal-Phe > Sal-Tyr, which is the same order as the increasing log K₁ values of amino acids (and the log K₂ values of tyrosine) with the exception of an inversion between serine and phenylalanine. Also, it was seen that the stability constants, log β₁ and log β₂, of Schiff base–metal complexes vary for all the metal ions investigated, viz., Sal-Gly > Sal-Ala > Sal-Ser > Sal-Tyr > Sal-Phe with the exception of Sal-Gly in the copper complex. The effect of the nature of the amino acids on their formation, protonation and stability constants was also discussed.     

Cu-superconductors in organic catalysis, II. The conversion of benzyl alcohol on various Cu-catalysts

The catalytic conversion of benzyl alcohol to toluene and benzaldehyde was performed on YBa₂Cu₃O_7–x (Y–Ba–Cu–O) in the presence of hydrogen at 250–400°C. The catalytic characteristics of Y–Ba–Cu–O were compared with those of CuO, Cu/SiO₂ and Y₂BaCuO₅. The structural changes in the catalysts during the reaction were measured by means of XRD and SEM. It was found that the oxidation state of the copper in Y–Ba–Cu–O was a considerable factor in the conversion of benzyl alcohol.Part I:React. Kinet. Catal. Lett. 51, 61 (1993).     

Molecular Structure of PrBr3 and HoBr3 According to Simultaneous Electron Diffraction and Mass Spectrometry Experiment

The saturated vapors of praseodymium and holmium tribromides were investigated for the first time by electron diffraction with mass spectral monitoring at 1100(10) and 991(10) K. It is established that the molecules have a pyramidal effective configuration with bond angles Br–Pr–Br = 114.7(10)° and Br–Ho–Br = 115.3(11)°. Given the low deformation vibration frequencies of lanthanide tribromide molecules, the insignificant pyramidality of the r_g configuration may correspond to the planar equilibrium geometry of D_3h symmetry for the molecules. The internuclear distances r_g(Pr–Br) = 2.696(6) and r_g(Ho–Br) = 2.594(5) point to the lanthanide compression effect. The vibration frequencies of PrBr₃ and HoBr₃ molecules were estimated from electron diffraction data.     

Rotational analysis of the v7,v11 (a′,a″) pair of bands of the infrared spectrum of the deuterium substituted propynal molecule C2H-CDO

The mid-infrared spectrum of the v₇,v₁₁ (a′,a″) pair of bands of the deuterium substituted propynal molecule C₂H-CDO was recorded at a resolution of about 0.08 cm⁻¹. An analysis of the pair of bands was completed using the method of simulation of the observed bands with synthetic spectra taking into account the effects of second order Coriolis interactions between the energy levels of the two bands. Best fit values for the changes in the rotational constants (A″ − A′), (B″ − B′) and (C″ − C′), the second order Coriolis constant ζ_7,11 and the δ_7,11 = v₁₁ − v₇ constant have been derived.     

Vibronic interactions in {6} and {18}hetero(A,B)annulenes

The vibronic (vibrational–electronic) interactions and the Jahn–Teller effects in the monoanions and trianions of {6}hetero(B,N), (C,N), and (B,O)annulenes and {18}hetero(B,N), (C,N), and (B,O)annulenes are discussed. All the heteroannulenes have threefold axis of symmetry and the twofold degenerate lowest unoccupied molecular orbital (LUMOs), and the E^′ or E vibrational modes can cause Jahn–Teller distortions in their monoanions and trianions. State vibronic coupling constants of the monoanions and trianions and orbital vibronic coupling constants concerning the LUMOs are calculated for each Jahn–Teller active vibrational mode at the B3LYP/6-31G* level of theory. Vibrational modes near 1500 cm⁻¹ of the {6}hetero(A,B)annulenes and low-frequency modes (<500 cm⁻¹) of the {18}hetero(A,B)annulenes give large coupling constants, and therefore, these modes are essential in the Jahn–Teller distortions and the vibronic interactions. The coupling constants are qualitatively analyzed by looking at the nuclear motions of the Jahn–Teller active modes and the shapes of the LUMOs on the basis of one-electron approximation.     

Synthesis, structure and thermal analysis of the gallium complex of 1,4,7,10-tetraazacyclo-dodecane-N,N′,N″,N-tetraacetic acid (DOTA)

As part of our efforts to synthesize gallium bioconjugates based on folic acid and thiamin we have utilized 1,4,7,10-tetraazacyclo-dodecane-N,N′,N″,N-tetraacetic acid (DOTA) as the chelating ligand for gallium(III). The reaction of gallium chloride with DOTA at room temperature in aqueous solution affords the complex [Ga(HDOTA) · 5.5H₂O] (1), which is characterized by single-crystal X-ray spectroscopy, electrospray mass spectrometry and thermal gravimetric analysis. Gallium displays 6-coordinate distorted octahedral geometry within a puckered macrocyclic DOTA framework. The equatorial plane comprises two nitrogens of the DOTA ring and two oxygens from two of the four pendant carboxylic acid groups. The axial positions are comprised of the remaining two transannular nitrogens of the DOTA ring.     

Solubility and Hydrolysis of La, Pr, Eu, Er, and Lu in 1 M NaCl Ionic Strength at 303 K

The pLn-pC _H diagrams obtained by a radiometric technique were used for the determination of the solubility and the first hydrolysis constants for La, Pr, Eu, Er, and Lu in 1 M NaCl ionic strength at 303 K. The saturation and unsaturation zones, and the borderline of precipitation were determined from these diagrams. The first hydrolysis constants were determined from pH titrations where no precipitation was found; these data were treated with the SUPERQUAD program. Fitting methods involving pLn versus pC _H and the average ligand number vs. pC _H were used to calculate both the first hydrolysis constants and the solubility products. The log K _sp values obtained for La, Pr, Eu, Er, and Lu were –19.53, –20.92, –22.24, –22.62, and –23.05 and the log* ₁ average values obtained were –8.87 ± 0.05, –8.54 ± 0.04, –8.34 ± 0.03, –8.16 ± 0.04, and –8.11 ± 0.03, respectively, under CO₂ free conditions. Finally, the results were compared with those found in the literature.     

A potentiometric and calorimetric study of the polynuclear and mononuclear complexes of nickel(II) with thioglycolic acid

The complex formation between nickel(II) and thioglycolic acid was studied by a potentiometric method at 25°C and in 0.5 M KN0₃. In solution two polynuclear complexes, B₃A₄ and B₄A₆, and one mononuclear complex, BA₂, were detected, and the following stability constants were determined: log β_3.4=32.219; log β_4.6=49.157; log β_1.2=12.759. The enthalpies of formation of the double (Ni-S-Ni) and single (Ni-S) bond were determined by calorimetric titration, and were found to be -5 kcal mol^-1 and -1.5 kcal mol^-1, respectively. It was shown that the stability of the polynuclear complexes is due to the enthalpy term, whereas the stability of the mononuclear complexes can be ascribed principally to the entropy term.