Physicochemical Characterization of Four Gadolinium(III) DTPA‐like Complexes

The analysis of ¹⁷O NMR transverse relaxation rates and EPR transverse electronic relaxation rates for aqueous solutions of the four DTPA‐like (DTPA = diethylenetriamine‐N,N,N′,N″,N″‐pentaacetic acid) complexes, [Gd(DTPA‐PY)(H₂O)]^? (DTPA‐PY = N′‐(2‐pyridylmethyl)), [Gd(DTPA‐HP)(H₂O)₂]^? (DTPA‐HP = N′‐(2‐hydroxypropyl)), [Gd(DTPA‐H1P)(H₂O)₂]^? (DTPA‐H1P = N′‐(2‐hydroxy‐1‐phenylethyl)) and [Gd(DTPA‐H2P)(H₂O)₂] (DTPA‐H2P = N′‐(2‐hydroxy‐2‐phenylethyl)), at various temperatures allows us to understand the water exchange dynamics of these four complexes. The water‐exchange lifetime (τM) parameters for [Gd(DTPA‐PY)(H₂O)]^?, [Gd(DTPA‐HP)(H₂O)₂]^?, [Gd(DTPA‐H1P)(H₂O)₂]^? and [Gd(DTPA‐H2P)(H₂O)₂] are of 585, 98, 163, and 69 ns, respectively. Compared with [Gd(DTPA)(H₂O)]^2? (τM = 303 ns), the τM value of [Gd(DTPA‐PY)(H₂O)]^? is slightly higher, but the other three complexes values are significantly lower than those of [Gd(DTPA)(H₂O)]^2?. This difference is explained by the fact that the gadolinium(III) complexes of DTPA‐HP, DTPA‐H1P, and DTPA‐H2P have two inner‐sphere waters. The ²H longitudinal relaxation rates of the labeled diamagnetic lanthanum complex allow the calculation of its rotational correlation time (τR). The τR values calculated for DTPA‐PY, DTPA‐HP, DTPA‐H1P, and DTPA‐H2P are of 127, 110, 142 and 147 ps, respectively. These four values are higher than the value of [La(DTPA)]^2? (τR = 103 ps), because the rotational correlation time is related to the magnitude of its molecular weight.     

NMR Characterization of Lanthanide(3+) Complexes of Tetraazatetrakisphosphinato and Tetraazatetra­kisphosphonato Ligands

The three‐dimensional structures in aqueous solution of the entire series of the Ln³⁺ complexes [Ln(DOTP*‐Et)]^? (formed from the free ligand P,P′,P″,P′′′‐[1,4,7,10‐tetraazacyclododecane‐1,4,7,10‐tetrayltetrakis(methylene)]tetrakis[P‐ethylphosphinic acid] (H₄DOTP*‐Et) were studied by NMR techniques to rationalize the parameters governing the relaxivity of the Gd³⁺ complex and evaluate its potential as MRI contrast agent. From the ¹H‐ and ³¹P‐NMR lanthanide‐induced‐shift (LIS) values, especially of the [Yb(DOTP*‐Et)]^? complex, it was concluded that the [Ln(DOTP*‐Et)]^? complexes adopt in solution twisted square antiprismatic coordination geometries which change gradually their coordination‐cage structure along the lanthanide series. These complexes have no inner‐sphere‐H₂O coordination, and preferentially have the (R,R,R,R) configuration of the P‐atoms in the pendant arms. Self‐association was observed in aqueous solution for the tetraazatetrakisphosphonic acid ester complexes [Ln(DOTP*‐OEt)]^? (=[Ln(DOTP‐Et)]^?) and [Ln(DOTP*‐OBu)]^? (=[Ln(DOTP‐Bu)]^?) at and above 5 mM concentration, through analysis of ³¹P‐NMR, EPR, vapor‐pressure‐osmometry, and luminescence‐spectroscopic data. The presence of the cationic detergent cetylpyridinium chloride (CPC; but not of neutral surfactants) shifts the isomer equilibrium of [Eu(DOTP*‐OBu)]^? to the (S,S,S,S) form which selectively binds to the cationic micelle surface.     

Synthesis and Physicochemical Characterization of New C‐Functionalized Derivatives of the Gadolinium(III) Complex with 3,6,10‐Tris(carboxymethyl)‐3,6,10‐triazadodecanedioic Acid (H5ttda) Exhibiting Fast Water Exchange – Potential Paramagnetic Reporters for Molecular Imaging

To confirm the observation that [Gd(ttda)] derivatives have a significantly shorter residence time τ_M of the coordinated H₂O molecule than [Gd(dtpa)], four new C‐functionalized [Gd(ttda)] complexes, [Gd(4‐Me‐ttda)] ( 1 ), [Gd(4‐Ph‐ttda)] ( 2 ), [Gd(9‐Me‐ttda)] ( 3 ), and [Gd(9‐Ph‐ttda)] ( 4 ), were prepared and characterized (H₅ttda=3,6,10‐tris(carboxymethyl)‐3,6,10‐triazadodecanedioic acid; H₅dtpa=3,6,9‐tris(carboxymethyl)‐3,6,9‐triazaundecanedioic acid). The temperature dependence of the proton relaxivity for these complexes at 0.47 T and of the ¹⁷O transverse relaxation rate of H₂¹⁷O at 7.05 T confirm that the proton relaxivity is not limited by the H₂O‐exchange rate. The residence time of the H₂O molecules in the first coordination sphere of the gadolinium complexes at 310 K, as calculated from ¹⁷O‐NMR data, is 13, 43, 2.9, and 56 ns for 1, 2, 3 , and 4 , respectively. At 310 K, the longitudinal relaxivity of 2 is higher than for the parent compound [Gd(ttda)] and the other complexes of the series. The stability of the new compounds was studied by transmetallation with Zn²⁺ ions. All the new complexes are more stable than the parent compound [Gd(ttda)].     

Synthesis and Relaxometric Properties of Gadolinium(III) Complexes of New Triazine‐Based Polydentate Ligands

Two new derivatives based on an s‐triazine structural motif were synthesized by attaching two 2,2′‐hydrazinylidenebis[acetic acid] moieties to the triazine ring to reach an overall heptadenticity for the complexation of lanthanide(III) cations. The remaining reactive site was exploited for the substitution with a functionizable amino group (see H₄ L1 ) and a lipophilic moiety (see H₄ L2 ). Luminescence‐lifetime determinations revealed the presence of a single H₂O molecule coordinated for [Eu( L1 )]. A complete ¹H‐NMR relaxometric study was carried out for the octacoordinated [Gd( L1 )] and [Gd( L2 )] complexes. A remarkably long H₂O residence lifetime (²⁹⁸τ_M =5.2 μs) was found by ¹⁷O‐NMR in the case of [Gd( L1 )]. Micelle formation of the lipophilic complex [Gd( L2 )] was evidenced, the critical micellization concentration (cmc) determined, and relaxometric properties of the system investigated.     

Synthesis,Relaxivity and MRI Enhancement of Linear Oligo‐Gd(III) Complexes with Poly (DTPA‐ester) Ligands Derived from Amino Acids

Six linear oligo‐DTPA‐ester Gd(III) complexes being used for potential MRI contrast agents were synthesized from amino adds and characterized. Their longitudinal relaxation rates were measured. One of them, die phenylalanine derivative, with high relaxivity, was chosen for the acute toxicity and T₁,‐weighted imaging test. The results indicated that there was no obvious toxicity for this new oligomeric Gd(III) complex, and it exhibits the highly enhanced MRI signal intensity and the increasing signal duration in the liver tissue compared to Gd‐DTPA.     

Iron(III)‐Complexes Engaged in the Biochemical Processes in Seawater. II. Voltammetry of Fe(III)‐Malate Complexes in Model Aqueous Solution

Characteristics of iron(III) complexes with malic acid in 0.55 mol L^?1 NaCl were investigated by voltammetric techniques. Three iron(III)‐malate redox processes were detected in the pH range from 4.5 to 11: first one at ?0.11 V, second at ?0.35 V and third at ?0.60 V. First process was reversible, so stability constants of iron(III) and iron(II) complexes were calculated: log K₁(Fe^III(mal))=12.66±0.33, log β₂(Fe^III(mal)₂)=15.21±0.25, log K₁(Fe^II(mal))=2.25±0.36, and log β₂(Fe^II(mal)₂)=3.18±0.32. In the case of second and third reduction process, conditional cumulative stability constants of the involved complexes were determined using the competition method: log β(Fe(mal)₂(OH)_x)=15.28±0.10 and log β(Fe(mal)₂(OH)_y)=27.20±0.09.     

Synthesis of Two N,N′-bis(N,N-dialkylamide) Derivatives of Diethylenetriaminepentaacetic Acid and the Stabilities of Their Complexes with Gd3+, Ca2+, Cu2+, and Zn2+

Two bis(N,N-dialkylamide) derivatives of DTPA [(carboxymethyl)iminobis (ethylenenitrilo) tetraacetic acid], DTPA-BDMA = the bis(N,N-dimethylamide) and DTPA-BDEA = the bis(N,N-diethylamide) were synthesized. Their protonation constants were determined by potentiometric titration in 0.10 M Me₄NNO₃ and by NMR pH titration at 25.0 ± 0.1 °C. Stability and selectivity constants were measured to evaluate the possibility of using the corresponding gadolinium(III) complexes for magnetic resonance imaging contrast agents. The stability constants of gadolinium(III), copper(II), zinc(II), and calcium(II) complexes with DTPA-BDMA and DTPA-BDEA were investigated quantitatively by potentiometry. The stability constant for gadolinium(III) complexes is larger than those for Ca(II), Zn(II), and Cu(II) complexes. The selectivity constants and modified selectivity constants of the amides for Gd³⁺ over endogenously available metal ions were calculated. Effectiveness of these two ligands in binding divalent and trivalent metal ions in biological media is assessed by comparing pM values at physiological pH 7.4. Spin-lattice relaxivity values R₁ for Gd(III) complexes were also determined. The observed relaxivity values were found to decrease with increasing pH in the acid range below pH 4 and relaxivity values became invariant with respect to pH changes over the range of 4–10. ¹⁷O NMR shifts showed that the [Dy(DTPA-BDMA)] and [Dy(DTPA-BDEA)] complexes had one inner-sphere water molecule. Water proton spin-lattice relaxation rates for the [Gd(DTPA-BDMA)] and [Gd(DTPA-BDEA)] complexes were also consistent with one inner-sphere gadolinium(III) coordination position.     

EPR Spectra of Copper(II) Complexes with N,N-Dialkyl Amino Acids. The Influence of Water dissolved in Organic Solvents on the Copper(II) Coordination Sphere

EPR spectra of four bis(N,N-dialkyl-L-α-aminoacidato) copper(II) complexes were studied with the aim to determine the effect of the water molecules dissolved in organic solvents on the electronic states of copper(II). It was shown that water dissolved in methylene chloride or dioxan influence the copper(II) electronic states. If the amino acid side chains are long enough to form the aliphatic intramolecular van der Waals contacts, the water molecules will induce the change in the conformation of the whole complex.     

Study of the EFG tensor at 75As nuclei in Ge‐As‐Se chalcogenide glasses

Asymmetry parameters of the electric field gradient tensor at ⁷⁵As nuclei were determined for chalcogenide glassy semiconductors (CGS) of the Ge‐As‐Se system by comparing the experimental and simulated ⁷⁵As nuclear quadrupole resonance nutation interferograms. The electric field gradient asymmetry in CGS was analyzed, and it is believed that a structural change in these glassy semiconductors takes place at = 2.425. Electron paramagnetic resonance spectra of the Ge‐As‐Se system were obtained for the first time. A comparison was made between the results of analysis of the Ge‐As‐Se system by nuclear quadrupole resonance and electron paramagnetic resonance methods, and this allowed us to make the supposition that a structural phase transition occurs at = 2.4 from two‐dimensional to three‐dimensional CGS structure. Copyright © 2013 John Wiley & Sons, Ltd.     

Crystal Structure and Magnetic Characteristics of a New 3‐Methylisoquinolinium Tetrachloridoferrate(III)

The crystal structure of a new 3‐methylisoquinolinium[3‐Me(IsoQH)] salt, [3‐Me(IsoQH)][FeCl₄], was determined. The iron cation is tetracoordinated by chlorine anions, and it adopts a slightly distorted tetrahedral coordination. In the crystal structure, there are π ··· π stacking interactions between the 3‐methylisoquinolinium cations in an ABAB infinite arrangement, N–H ··· Cl hydrogen bonds, and C–H ··· Cl intermolecular interactions. Magnetic measurements of a powdered sample were carried out. A negative Weiss constant as well as the intermolecular exchange parameter for [3‐Me(IsoQH)][FeCl₄] indicate the occurrence of antiferromagnetic interactions transmitted in the crystal lattice.     

Synthesis of Two Derivatives of 3,6,9‐tri(carboxymethyl)‐3,6,9‐triazaundecanedioic Acid and the Stabilities of Their Complexes with Ca2+, Cu2+, Zn2+, Dy3+ and Gd3+

Two N‐2‐hydroxy‐1‐phenylethyl and N‐2‐hydroxy‐2‐phenylethyl derivatives of DTPA (3,6,9‐tri(carboxymethyl)‐3,6,9‐triazaundecanedioic acid), DTPA‐H1P = 3,9‐di(carboxymethyl)‐6‐2‐hydroxy‐1‐phenylethyl‐3,6,9‐triazaundecanedioic acid, and DTPA‐H2P = 3,9‐di(carboxymethyl)‐6‐2‐hydroxy‐2‐phenylethyl‐3,6,9‐triazaundecanedioic acid were synthesized. Their protonation constants were determined by Potentiometric titration in 0.10 M Me₄NNO₃ and by NMR pH titration at 25.0 ± 0.1°C. The formations of lanthanide(III), copper(II), zinc(II) and calcium(II) complexes were investigated quantitatively by potentiometry. The stability constant for Gd(III) complex is larger than those for Ca(II), Zn(II) and Cu(II) complexes with these two ligands. The selectivity constants and modified selectivity constants of the DTPA‐H1P and DTPA‐H2P for Gd(III) over endogenously available metal ions were calculated. Comparing pM values at physiological pH 7.4 assesses effectiveness of these two ligands in binding divalent and trivalent metal ions in biological media. The observed water proton relaxivity values of [Gd(DTPA‐H1P)]^? and [Gd(DTPA‐H2P)]^? became constant with respect to pH changes over the range of 4‐10. ¹⁷O NMR shifts showed that the [Dy(DTPA‐H1P)]^? and [Dy(DTPA‐H2P)]^? complexes at pH 6.30 had 1.91 and 2.28 inner‐sphere water molecules, respectively. Water proton spin‐lattice relaxation rates of [Gd(DTPA‐H1P)]^? and [Gd(DTPA‐H2P)]^? complexes were also consistent with the inner‐sphere Gd(III) coordination.     

Eu3+,Tb3+混配配合物的激光诱导荧光

利用激光诱导荧光技术研究了两种三价稀土金属离子的β－二酮与有机配体混配络合物中金属离子的寿命及其能级结构，得到了Ｅｕ＾３＋的能级常数。     

Dating Sediments by EPR Using Al-h Centre: A Comparison between the Properties of Fine (4–11 µm) and Coarse (>63 µm) Quartz Grains

The possibility of EPR dating for sediments using Al-h signals of fine (4–11 μm) grains of quartz has not been previously discussed. Here, the Al-h and peroxy EPR spectra of fine (4–11 μm) and coarse (63–90, 125–180 μm) sedimentary quartz from thoroughly investigated loess sites in Eastern Europe were examined. By comparing experimental spectra with a simulated signal, we evaluated the overestimation observed when using the standard approach established by Toyoda and Falguères to measure Al-h intensity for different doses of radiation, up to 40,000 Gy. This overestimation, caused by the presence of peroxy signals, was much more pronounced for fine grains. Fine grains exhibited some additional dose-dependent signals, which, for some samples, caused a complete distortion of the Al-h spectra at high doses, making it impossible to measure the standard amplitude. We propose a new approach to measuring Al-h signal intensity, focusing on the peak-to-baseline amplitude of the part of the signal at g ≈ 2.0603, which is not affected by the peroxy signals and therefore has the potential of providing more accurate results. The shapes of dose response curves constructed for coarse and fine grains using the new approach show considerable similarity, suggesting that Al-h centre formation in fine and coarse grains upon artificial radiation at room temperature follows the same pattern.     

Iron(III)‐Complexes Engaged in the Biochemical Processes in Seawater. I. Voltammetry of Fe(III)‐Succinate Complexes in Model Aqueous Solution

Fe³⁺ complexes with succinic acid, a ligand naturally present in seawater, were investigated in aqueous solutions by square‐wave and cyclic voltammetry. [Fe(suc)₂(OH)₂] and [Fe(suc)₃] were detected at potentials ?0.22 and ?0.37 V, depending on C_suc in the ranges from 0.01 to 0.07 and 0.1 to 0.5 mol L^?1, respectively. Redox processes were irreversible, first with reactant adsorption and second diffusion controlled, both accompanied by chemical step. By UV/Vis spectra formation of these complexes was confirmed and equilibrium constant Fe(suc)₂(OH)₂?Fe(suc)₃ calculated (logK_2?3=(1.14±0.15) mol^?1 L), as well as their perceptible stoichiometry. With NTA as competing ligand, conditional stability constant of [Fe(suc)₂(OH)₂] complex was calculated (β^cond=(3.1±1.3)×10²² mol^?1 L).     

Synthesis and Photophysical and Electrochemical Study of Tyrosine Covalently Linked to High‐Valent Copper(III) and Manganese(IV) Complexes

As bio‐inspired chemical model of the oxygen‐evolving complex (OEC) in photosystem II, a new tyrosine‐modified corrole ligand 3 and its high‐valent copper and manganese complexes 3a and 3b were synthesized and characterized. The copper complexes 1a and 2a of corrole 1 and 2 were also prepared for comparison. The emission property indicates that the emission of ligands 2 and 3 is located at 670 nm, but no emission is observed for their metal complexes due to its suppression by the metal center. The electrochemical study shows that 3a might dimerize at the first two reversible oxidations, a behavior which was not observed in the case of 1a and 2a . The corrolato manganese(IV) complex 3b shows one reversible reduction and one quasireversible oxidation at ?0.17 and 0.77 V vs. Ag/Ag⁺, respectively.     

Synthesis,Characterization and Magnetic Studies of μ‐Oxamido Copper (II) ‐ Chromium (III) Heterodinuclear Complexes

Three new μ‐oxamido‐bridged heterodinuclear copper (II)‐chromium (III) complexes formulated [Cu(Me₂oxpn)Cr‐(L)₂](NO₃)₃, where Me₂oxpn denotes N,N'‐bis(3‐amino‐2, 2‐dimethylpropyl)oxamido dianion and L represents 5‐methyl‐1,10‐phenanthroline (Mephen), 4,7‐diphenyl‐1,10‐phenanthroline (Ph₂phen) or 2,2′‐bipyridine (bpy), have been synthesized and characterized by elemental analyses, IR and electronic spectral studies, magnetic moments of room‐temperature and molar conductivity measurements. It is proposed that these complexes have oxamido‐bridged structures consisting of planar copper (II) and octahedral chromium (III) ions. The variable temperature magnetic susceptibilities (4.2–300 K) of complexes [Cu(Me₂oxpn)Cr(Ph₂phen)₂](NO₃)₃ (1) and [Cu(Me₂oxpn)Cr(Mephen)₂] (NO₃)₃ (2) were further measured and studied, demonstrating the ferromagnetic interaction between the adjacent chromium (III) and copper (II) ions through the oxamido‐bridge in both complexes 1 and 2. Based on the spin Hamiltonian, ? = ‐ 2J?₁ · ?₂, the exchange integrals J were evaluated as + 21.5 an^?1 for 1 and + 22.8 cm^?1 for 2.     

Synthesis,characterization and magnetism of copper(II)‐lanthanide(III) heterobimetalic complexes with N,N'‐oxamidobis‐(benzoato)cuprate (II)

Seven new μ‐oxamido copper(II)‐lanthanide(III) heterobimetalic complexes described by the formula Cu(obbz) Ln‐(Ph‐phen)₂NO₃(Ln = La, Nd, Eu, Gd, Tb, Ho, Er), where obbz denotes the oxamidobis(benzoato) and Ph‐phen represents 5‐phenyl‐1, 10‐phenanthroline, have been synthesized and characterized by the elemental analyses, spectroscopic (IR, UV, ESR) studies, magnetic moments (at room temperature) and molar conductivity measurement. The temperature dependence of the magnetic susceptibility of Cu(obbz)Gd(Ph‐phen)₂NO₃ complex has been measured over the range 4.2–300 K. The least‐squares fit of the experimental susceptibilities based on the spin Hamiltonian operator, ? = ?2 J?₁·?₂, yielded J= +1.28 cm^?1, a weak ferromagnetic coupling, A plausible mechanism for a ferromagnetic coupling between Gd(III)‐Cu(II) is discussed in terms of spin‐polarization.     

Mono‐ and Binuclear Dimethylthallium(III) Complexes with o‐Benzoquinone‐TTF‐o‐Benzoquinone Ligand; Synthesis,Spectroscopy and X‐ray Study

The new mono‐ and binuclear semiquinonato dimethylthallium complexes (Q‐TTF‐SQ)TlMe₂ ( 1 ) and Me₂Tl(SQ‐TTF‐SQ)TlMe₂ ( 2 ) based on di‐o‐quinone with tetrathiafulvalene (TTF) bridge, 4,4′,7,7′‐tetra‐tert‐butyl‐2,2′‐bis‐1,3‐benzodithiol‐5,5′,6,6′‐tetraone Q‐TTF‐Q, were synthesized by the reaction between corresponding mono‐ and di‐sodium semiquinonates (Q‐TTF‐SQ)Na and Na(SQ‐TTF‐SQ)Na and one or two equivalents of Me₂TlCl, respectively. The same products could be obtained by the interaction of Q‐TTF‐Q with one or two equivalents of Me₃Tl. Complexes 1 and 2 were characterized by IR and electronic absorption spectroscopy, EPR, and magnetic measurements. The molecular structures of 1 and 2 were determined by single‐crystal X‐ray diffraction. It was found that mono‐semiquinonato derivative 1 partially disproportionates into Q‐TTF‐Q and binuclear complex 2 in THF solution. According to variable temperature magnetic susceptibility measurements and EPR data, compound 1 reveals paramagnetic behavior with an S = 1/2 state in the range 50–300 K, whereas compound 2 has an S = 0 ground state as the consequence of antiferromagnetic coupling between semiquinonato moieties realized through the TTF‐bridge.     

Theoretical studies of the EPR parameters and local structures for the two Cu2+ centers in Cd(HCOO)2·2H2O

Based on the studies of the electron paramagnetic resonance parameters for two types of the Cu²⁺ centers in Cd(HCOO)₂·2H₂O by using the high‐order perturbation formulas for a 3d⁹ ion in a rhombically elongated octahedron, local structure of the doped copper ion is determined. Research suggests that the impurity Cu²⁺ replaces the host Cd²⁺ and undergoes the local rhombic elongation distortion, characterized by the axial elongation ratios of 4.1%, and 3.8% along the z‐axis and the planar bond length variation ratios of 3.8%, and 3.1% along the x‐axis and y‐axis, for Cu²⁺ Centers, I and II, respectively. The above slightly different axial elongation ratios and planar bond length variation ratios may suitably account for the slightly dissimilar axial g anisotropies Δg (≈0.351 and 0.339) and perpendicular g anisotropies δg (≈0.028 and 0.022) of the two centers, respectively.