Dissociation Kinetics of Open‐Chain and Macrocyclic Gadolinium(III)‐Aminopolycarboxylate Complexes Related to Magnetic Resonance Imaging: Catalytic Effect of Endogenous Ligands

The kinetics of the metal exchange reactions between open‐chain Gd(DTPA)^2? and Gd(DTPA‐BMA), macrocyclic Gd(DOTA)^? and Gd(HP‐DO3A) complexes, and Cu²⁺ ions were investigated in the presence of endogenous citrate, phosphate, carbonate and histidinate ligands in the pH range 6–8 in NaCl (0.15 M ) at 25 °C. The rates of the exchange reactions of Gd(DTPA)^2? and Gd(DTPA‐BMA) are independent of the Cu²⁺ concentration in the presence of citrate and the reactions occur via the dissociation of Gd³⁺ complexes catalyzed by the citrate ions. The HCO₃^?/CO₃^2? and H₂PO₄^? ions also catalyze the dissociation of complexes. The rates of the dissociation of Gd(DTPA‐BMA), catalyzed by the endogenous ligands, are about two orders of magnitude higher than those of the Gd(DTPA)^2?. In fact near to physiological conditions the bicarbonate and carbonate ions show the largest catalytic effect, that significantly increase the dissociation rate of Gd(DTPA‐BMA) and make the higher pH values (when the carbonate ion concentration is higher) a risk‐factor for the dissociation of complexes in body fluids. The exchange reactions of Gd(DOTA)^? and Gd(HP‐DO3A) with Cu²⁺ occur through the proton assisted dissociation of complexes in the pH range 3.5–5 and the endogenous ligands do not affect the dissociation rates of complexes. More insights into the interaction scheme between Gd(DTPA‐BMA) and Gd(DTPA)^2? and endogenous ligands have been obtained by acquiring the ¹³C NMR spectra of the corresponding diamagnetic Y(III)‐complexes, indicating the increase of the rates of the intramolecular rearrangements in the presence of carbonate and citrate ions. The herein reported results may have implications in the understanding of the etiology of nephrogenic systemic fibrosis, a rare disease that has been associated to the administration of Gd‐containing agents to patients with impaired renal function.     

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.     

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.     

Complexation Properties of N,N′,N″,N′′′‐[1,4,7,10‐Tetraazacyclododecane‐1,4,7,10‐tetrayltetrakis(1‐oxoethane‐2,1‐diyl)]tetrakis[glycine] (H4dotagl). Equilibrium,Kinetic, and Relaxation Behavior of the Lanthanide(III) Complexes

Eu³⁺, Dy³⁺, and Yb³⁺ complexes of the dota‐derived tetramide N,N′,N″,N′′′‐[1,4,7,10‐tetraazacyclododecane‐1,4,7,10‐tetrayltetrakis(1‐oxoethane‐2,1‐diyl)]tetrakis[glycine] (H₄dotagl) are potential CEST contrast agents in MRI. In the [Ln(dotagl)] complexes, the Ln³⁺ ion is in the cage formed by the four ring N‐atoms and the amide O‐atom donor atoms, and a H₂O molecule occupies the ninth coordination site. The stability constants of the [Ln(dotagl)] complexes are ca. 10 orders of magnitude lower than those of the [Ln(dota)] analogues (H₄dota=1,4,7,10‐tetraazacyclododecane‐1,4,7,10‐tetraacetic acid). The free carboxylate groups in [Ln(dotagl)] are protonated in the pH range 1–5, resulting in mono‐, di‐, tri‐, and tetraprotonated species. Complexes with divalent metals (Mg²⁺, Ca²⁺, and Cu²⁺) are also of relatively low stability. At pH>8, Cu²⁺ forms a hydroxo complex; however, the amide H‐atom(s) does not dissociate due to the absence of anchor N‐atom(s), which is the result of the rigid structure of the ring. The relaxivities of [Gd(dotagl)] decrease from 10 to 25°, then increase between 30–50°. This unusual trend is interpreted with the low H₂O‐exchange rate. The [Ln(dotagl)] complexes form slowly, via the equilibrium formation of a monoprotonated intermediate, which deprotonates and rearranges to the product in a slow, OH^?‐catalyzed reaction. The formation rates are lower than those for the corresponding Ln(dota) complexes. The dissociation rate of [Eu(dotagl)] is directly proportional to [H⁺] (0.1–1.0M HClO₄); the proton‐assisted dissociation rate is lower for [Eu(H₄dotagl)] (k₁=8.1?10^?6 M ^?1 s^?1) than for [Eu(dota)] (k₁=1.4?10^?5 M ^?1 s^?1).     

Magnetocaloric Properties of Heterometallic 3d–Gd Complexes Based on the [Gd(oda)3]3− Metalloligand

A series of heterometallic 3d–Gd³⁺ complexes based on a lanthanide metalloligand, [M(H₂O)₆][Gd(oda)₃] ? 3 H₂O [M=Cr³⁺ ( 1‐Cr )] (H₂oda=2,2′‐oxydiacetic acid), [M(H₂O)₆][MGd(oda)₃]₂ ? 3 H₂O [M=Mn²⁺ ( 2‐Mn ), Fe²⁺ ( 2‐Fe ) and Co²⁺ ( 2‐Co )], and [M₃Gd₂(oda)₆(H₂O)₆] ? 12 H₂O [M=Ni²⁺ ( 3‐Ni ), Cu²⁺ ( 3‐Cu ), and Zn²⁺ ( 3‐Zn )], are reported. Magnetic and heat‐capacity studies revealed a significant impact on the magnetocaloric effect depending on the anisotropy of the 3d transition metal ions, as confirmed by comparison of the observed maximum values of ?ΔS_m between complexes 2‐Co and 1‐Cr . In these two complexes, the 3d metal ions have the same spin (S=3/2 for Co²⁺ and Cr³⁺ ions), and the theoretical calculation suggested a larger ?ΔS_m value for 2‐Co (47.8 J K^?1 kg^?1) than 1‐Cr (37.5 J K^?1 kg^?1); however, the significant anisotropy of Co²⁺ ions in 2‐Co , which can result in smaller effective spins, gives a smaller value of ?ΔS_m for 2‐Co (32.2 J K^?1 kg^?1) than for 1‐Cr (35.4 J K^?1 kg^?1) at ΔH=9 T.     

Approaching the Kinetic Inertness of Macrocyclic Gadolinium(III)‐Based MRI Contrast Agents with Highly Rigid Open‐Chain Derivatives

A highly rigid open‐chain octadentate ligand (H₄cddadpa) containing a diaminocylohexane unit to replace the ethylenediamine bridge of 6,6′‐[(ethane‐1,2 diylbis{(carboxymethyl)azanediyl})bis(methylene)]dipicolinic acid (H₄octapa) was synthesized. This structural modification improves the thermodynamic stability of the Gd³⁺ complex slightly (log K_GdL=20.68 vs. 20.23 for [Gd(octapa)]^?) while other MRI‐relevant parameters remain unaffected (one coordinated water molecule; relaxivity r₁=5.73 mm ^?1 s^?1 at 20 MHz and 295 K). Kinetic inertness is improved by the rigidifying effect of the diaminocylohexane unit in the ligand skeleton (half‐life of dissociation for physiological conditions is 6 orders of magnitude higher for [Gd(cddadpa)]^? (t_1/2=1.49×10⁵ h) than for [Gd(octapa)]^?. The kinetic inertness of this novel chelate is superior by 2–3 orders of magnitude compared to non‐macrocyclic MRI contrast agents approved for clinical use.     

Application of Cloud Point Extraction for Copper,Nickel, Zinc and Iron Ions in Environmental Samples

A cloud point extraction procedure was presented for the preconcentration of copper, nickel, zinc and iron ions in various samples. After complexation by 2‐(6‐(1H‐benzo[d]imidazol‐2‐yl)pyridin‐2‐yl)‐1H‐benzo[d]Imidazole (BIYPYBI), analyte ions are quantitatively extracted in Triton X‐114 following centrifugation. 1.0 mol L^?1 HNO₃ nitric acid in methanol was added to the surfactant‐rich phase prior to its analysis by flame atomic absorption spectrometry (FAAS). The adopted concentrations for BIYPYBI, Triton X‐114 and HNO₃ and bath temperature, centrifuge rate and time were optimized. Detection limits for Cu²⁺, Fe³⁺, Zn²⁺ and Ni²⁺ ions was 1.4, 2.2, 1.0 and 1.9 ng mL^?1, respectively. The preconcentration factors for all ions was 30, while the enrichment factor of Cu²⁺, Fe³⁺, Zn²⁺ and Ni²⁺ ions was 35, 25, 39 and 30, respectively. The proposed procedure was applied to the analysis of real samples.     

Metal complexes with macrocyclic ligands. Part XXXVI. Thermodynamic and kinetic studies of bivalent and trivalent metal ions with 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid

NMR, potentiometric, and UV/VIS measurements were run to study the protonation and the In³⁺ and Cu²⁺ stability constants of 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid (do3a, L). The protonation of do3a follows the typical scheme with two high and several low log K_H values. Between pH 11 and 13, the protonation mainly occurs at the N-atom, which is not substituted by an acetate side chain. The In³⁺ complex is not appreciably protonated even at low pH values (pH ? 1.7), whereas [CuL] can add up to three protons in acidic solution to give the species [CuLH], [CuLH₂], and [CuLH₃], the stability of which was determined. The formation rates of the Y³⁺, Gd³⁺, Ga³⁺, and In³⁺ complexes with do3a were measured using a pH-stat technique, whereas that of Cu²⁺, being faster, was followed on a stopped-flow spectrophotometer. In all cases, the reaction scheme implies the rapid formation of partially protonated intermediates, which rearrange themselves to the final product in the rate-determining process. ([MLH])_in, an intermediate, in which the metal ion probably is coordinated by two amino acetate groups, proved to be the reactive species for Y³⁺, Gd³⁺, and Ga³⁺. The formation of [Cu(do3a)] was interpreted by postulating that either ([CuLH])_in or ([CuLH])_in, and ([CuLH₂])_in are the reactive complexes. The rates of dissociation of the Y³⁺, Gd³⁺, and Cu²⁺ complexes with do3a were studied spectrophotometrically. For Y³⁺ and Gd³⁺, arsenazo III was used as a scavenger, whereas for Cu²⁺ the absorption associated with d-d* transition was followed. For [Y(do3a)] and [Gd(do3a)], the rate law follows the kinetic expression k_obsd ? k₀ + k₁[H⁺]. The dissociation of [Cu(do3a)] goes through the proton-independent dissociation of [CuLH₃], which is the main species at low pH.     

Bipyridinophane‐containing conjugated polymers modulated with an intramolecular aromatic C?H/π interaction

Bipyridinophane–fluorene conjugated copolymers have been synthesized via Suzuki and Heck coupling reactions from 5,8‐dibromo‐2,11‐dithia[3]paracyclo[3](4,4′)‐2,2′‐bipyridinophane and suitable fluorene precursors. Poly[2,7‐(9,9‐dihexylfluorene)‐co‐alt‐5,8‐(2,11‐dithia[3]paracyclo[3](4,4′)‐2,2′‐bipyridinophane)] ( P7 ) exhibits large absorption and emission redshifts of 20 and 34 nm, respectively, with respect to its planar reference polymer Poly[2,7‐(9,9‐dihexylfluorene)‐co‐alt‐1,4‐(2,5‐dimethylbenzene)] ( P11 ), which bears the same polymer backbone as P7 . These spectral shifts originate from intramolecular aromatic C? H/π interactions, which are evidenced by ultraviolet–visible and ¹H NMR spectra as well as X‐ray single‐crystal structural analysis. However, the effect of the intramolecular aromatic C? H/π interactions on the spectral shift in poly[9,9‐dihexylfluorene‐2,7‐yleneethynylene‐co‐alt‐5,8‐(2,11‐dithia[3]paracyclo[3](4,4′)‐2,2′‐bipyridinophane)] ( P10 ) is much weaker. Most interestingly, the quenching behaviors of these two conjugated polymers are largely dependent on the polymer backbone. For example, the fluorescence of P7 is efficiently quenched by Cu²⁺, Co²⁺, Ni²⁺, Zn²⁺, Mn²⁺, and Ag⁺ ions. In contrast, only Cu²⁺, Co²⁺, and Ni²⁺ ions can partially quench the fluorescence of P10 , but much less efficiently than the fluorescence of P7 . The static Stern–Volmer quenching constants of Cu²⁺, Co²⁺, and Ni²⁺ ions toward P7 are of the order of 10⁶ M^?1, being 1300, 2500, and 37,300 times larger than those of P10 , respectively. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4154–4164, 2006     

Electron capture dissociation and collision-induced dissociation of metal ion (Ag+, Cu2+, Zn2+, Fe2+, and Fe3+) complexes of polyamidoamine (PAMAM) dendrimers

The electron capture dissociation (ECD) and collision-induced dissociation (CID) of complexes of polyamidoamine (PAMAM) dendrimers with metal ions Ag⁺, Cu²⁺, Zn²⁺, Fe²⁺, and Fe³⁺ were determined by Fourier transform ion cyclotron resonance mass spectrometry. Complexes were of the form [PD + M + mH]⁵⁺ where PD = generation two PAMAM dendrimer with amidoethanol surface groups, M = metal ion, m = 2−4. Complementary information regarding the site and coordination chemistry of the metal ions can be obtained from the two techniques. The results suggest that complexes of Fe³⁺ and Cu²⁺ are coordinated via both core tertiary amines, whereas coordination of Ag⁺ involves a single core tertiary amine. The Zn²⁺ and Fe²⁺ complexes do not appear to involve coordination by the dendrimer core.     

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)].     

Silver(I)‐Selective PVC Membrane Potentiometric Sensor Based on a Recently Synthesized Calix[4]arene

A new PVC membrane potentiometric sensor for Ag(I) ion based on a recently synthesized calix[4]arene compound of 5,11,17,23‐tetra‐tert‐butyl‐25,27‐dihydroxy‐calix[4]arene‐thiacrown‐4 is developed. The electrode exhibits a Nernstian response for Ag(I) ions over a wide concentration range (1.0×10^?2?1.0×10^?6 M) with a slope of 53.8±1.6 mV per decade. It has a relatively fast response time (5–10 s) and can be used for at least 2 months without any considerable divergence in potentials. The proposed electrode shows high selectivity towards Ag⁺ ions over Pb²⁺, Cd²⁺, Co²⁺, Zn²⁺, Cu²⁺, Ni²⁺, Sr²⁺, Mg²⁺, Ca²⁺, Li⁺, K⁺, Na⁺, NH₄⁺ ions and can be used in a pH range of 2–6. Only interference of Hg²⁺ is found. It is successfully used as an indicator electrode in potentiometric titration of a mixture of chloride, bromide and iodide ions.     

Multiple‐Frequency and Variable‐Temperature EPR Study of Gadolinium(III) Complexes with Polyaminocarboxylates: Analysis and Comparison of the Magnetically Dilute Powder and the Frozen‐Solution Spectra

An electron paramagnetic resonance (EPR) study of glasses and magnetically dilute powders of [Gd(DTPA)(H₂O)]^2?, [Gd(DOTA)(H₂O)]^?, and macromolecular gadolinate(1?) complexes P792 was carried out at the X‐ and Q‐bands and at 240 GHz (DTPA=diethylenetriaminepentaacetato; DOTA=1,4,7,10‐tetraazacyclododecane‐1,4,7,10‐tetraacetato). The results show that the zero‐field splitting (ZFS) parameters for these complexes are quite different in a powder as compared to the frozen aqueous solution. In several complexes, an inversion of the sign of the axial component D of the zero field splitting is observed, indicating a significant structural change. In contrary to what was expected, powder samples obtained by lyophilization do not allow a more precise determination of the static ZFS parameters. The results obtained in glasses are more relevant to the problem of electron spin relaxation in aqueous solution than those obtained from powders.     

Effect of Toxic Metal Ions on Photosensitized Singlet Oxygen Generation for Photodegradation of Polyaromatic Hydrocarbon Derivatives and Inactivation of Escherichia coli

Here, we report an experimental study of the effect of toxic metal ions on photosensitized singlet oxygen generation for photodegradation of PAH derivatives, Anthracene‐9,10‐dipropionic acid disodium salt (ADPA) and 1,5‐dihydroxynapthalene (DHN) and photoinactivation of Escherichia coli bacteria by using cationic meso‐tetra(N‐methyl‐4‐pyridyl)porphine tetrachloride (TMPyP) as a singlet oxygen photosensitizer. Three s‐block metals ions, such as Na⁺, K⁺ and Ca²⁺ and five toxic metals such as Cd²⁺, Cu²⁺, Hg²⁺, Zn²⁺ and Pb²⁺ were studied. The s‐block metal ions showed no change in the rate of photodegradation of ADPA or DHN by TMPyP, whereas a dramatic change in the photodegradation of ADPA and DHN was observed in the presence of toxic metals. The maximum photodegradation rate constants of ADPA and DHN were observed for Cd²⁺ ions [(3.91 ± 0.20) × 10^?3 s^?1 and (7.18 ± 0.35) × 10^?4 s^?1, respectively]. Strikingly, the photodegradation of ADPA and DHN was almost completely inhibited in the presence of Hg²⁺ ions and Cu²⁺ ions. A complete inhibition of growth of E. coli was observed upon visible light irradiation of E. coli solutions with TMPyP and toxic metal ions particularly, Cd²⁺, Hg²⁺, Zn²⁺ and Pb²⁺ ions, except for Cu²⁺ ions where a significantly slow inhibition of E. coli's growth was observed.     

The rates of the exchange reactions between [Gd(DTPA)]2- and the endogenous ions Cu2+ and Zn2+: a kinetic model for the prediction of the in vivo stability of [Gd(DTPA)]2-, used as a contrast agent in magnetic resonance imaging

The kinetic stability of the complex [Gd(DTPA)]2- (H5DTPA = diethylenetriamine-N,N,N',N",N"-pentaacetic acid), used as a contrast-enhancing agent in magnetic resonance imaging (MRI), is characterised by the rates of the exchange reactions that take place with the endogenous ions Cu2+ and Zn2+. The reactions predominantly occur through the direct attack of Cu2+ and Zn2+ on the complex (rate constants are 0.93+/-0.17 M(-1) s(-1) and (5.6+/-0.4) x 10(-2)M(-1) S(-1), respectively). The proton-assisted dissociation of [Gd(DTPA)]2- is relatively slow (k1 = 0.58+/-0.22 M(-1) s(-1)), and under physiological conditions the release of Gd3+ predominantly occurs through the reactions of the complex with the Cu2+ and Zn2+ ions. To interpret the rate data, the rate-controlling role of a dinuclear intermediate was assumed in which a glycinate fragment of DTPA is coordinated to Cu2+ or Zn2+. In the exchange reactions between [Gd-(DTPA)]2- and Eu3+, smaller amounts of Cu2+ and Zn2+ and their complexes with the amino acids glycine and cysteine have a catalytic effect. In a model of the fate of the complex in the body fluids, the excretion and the "dissociation" of [Gd(DTPA)]2- are regarded as parallel first-order processes, and by 10 h after the intravenous administration the ratio of the amounts of "dissociated" and excreted [Gd(DTPA)]2- is constant. From about this time, 1.71% of the injected dose of [Gd(DTPA)]2- is "dissociated". The results of equilibrium calculations indicate that the Gd3+ released from the complex is in the form of Gd3+-citrate.     

Silver nanoparticle loaded on activated carbon and activated carbon modified with 2-(4-isopropylbenzylideneamino)thiophenol (IPBATP) as new sorbents for trace metal ions enrichment

The efficiencies and performances of silver nanoparticle loaded activated carbon modified with 2-(4-isopropylbenzylideneamino)thiophenol (IPBATP-Ag-NP-AC) and activated carbon modified with IPBATP (IPBATP-AC), as new sorbents, were evaluated for separation and preconcentration of Cu²⁺, Zn²⁺, Co²⁺, Cd²⁺ and Pb²⁺ ions from real environmental samples. The retained metals content was reversibly eluted using 5?mL of CH₃COOH (6.0?mol?L^?1) and/or 10?mL of 4.0?mol?L^?1 HNO₃ for IPBATP-Ag-NP-AC and IPBATP-AC, respectively. The experimental parameters influence the recoveries of metal ions including pH, amounts of ligand and supports, condition of eluents, sample and eluent flow rates of has been investigated. The preconcentration factors were found to be 100 for Zn²⁺, Cd²⁺, Co²⁺, Cu²⁺ and 50 for Pb²⁺ ions using IPBATP-Ag-NP-AC, and 50 for Zn²⁺, Cd²⁺, Co²⁺, Cu²⁺ and 25 for Pb²⁺ ions using IPBATP-AC. The detection limit of both SPE-based sorbents was between 1.6–2.5?ng?mL^?1 for IPBATP-AC and 1.3–2.5?ng?mL^?1 for IPBATP-Ag-NP-AC. The proposed methods have been successfully applied for the extraction and determination of the understudy metal ions content in some real samples with extraction efficiencies higher than 90% and relative standard deviations (RSD) lower than 2.4%.     

Transition metals as electron traps. II. Structures,energetics and electron transfer dissociations of ternary Co,Ni and Zn–peptide complexes in the gas phase

Transition metal cations Co²⁺, Ni²⁺ and Zn²⁺ form 1 : 1 : 1 ternary complexes with 2,2′‐bipyridine (bpy) and peptides in aqueous methanol solutions that have been studied for tripeptides GGG and GGL. Electrospray ionization of these solutions produced singly charged [Metal(bpy)(peptide ? H)]⁺ and doubly charged [Metal(bpy)(peptide)]²⁺ ions (Metal = metal ion) that underwent charge reduction by glancing collisions with Cs atoms at 50 and 100 keV collision energies. Electron transfer to [Metal(bpy)(peptide)]²⁺ ions was less than 4.2 eV exoergic and formed abundant fractions of non‐dissociated charge‐reduced intermediates. Charge‐reduced [Metal(bpy)(peptide)]⁺ ions dissociated by the loss of a hydrogen atom, ammonia, water and ligands that depended on the metal ion. The Ni and Co complexes mainly dissociated by the elimination of ammonia, water, and the peptide ligand. The Zn complex dissociated by the elimination of ammonia and bpy. A sequence‐specific fragment was observed only for the Co complex. Electron transfer to [Metal(bpy)(peptide ? H)]⁺ was 0.6–1.6 eV exoergic and formed intermediate radicals that were detected as stable anions after a second electron transfer from Cs. [Metal(bpy)(peptide ? H)] neutrals and their anions dissociated by the loss of bpy and peptide ligands with branching ratios that depended on the metal ion. Optimized structures for several spin states, electron transfer and dissociation energies were addressed by combined density functional theory and Møller–Plesset perturbational calculations to aid interpretation of experimental data. The experimentally observed ligand loss and backbone cleavage in charge‐reduced [Metal(bpy)(peptide)]⁺ complexes correlated with the dissociation energies at the present level of theory. The ligand loss in ⁺CR^? spectra showed overlap of dissociations in charge‐reduced [Metal(bpy)(peptide ? H)] complexes and their anionic counterparts which complicated spectra interpretation and correlation with calculated dissociation energies. Copyright © 2009 John Wiley & Sons, Ltd.     

Metal Complexes with Macrocyclic Ligands,V. Formation and dissociation kinetics of the pentaco-ordinated Ni2+, Cu2+, Co2+ and Zn2+ complexes with 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane

The formation and dissociation kinetics of the pentaco-ordinated Cu²⁺, Ni²⁺, Co²⁺ and Zn²⁺ complexes with 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane (4-MeCyclam-14) was studied by pH-stat techniques and spectrophotometrically. The rates of the reactions between 4-MeCyclam-14 and each of the four metal ions, although slower than normal complexations by a factor of 10³?10⁴, closely follow the order Cu²⁺ > Zn²⁺ > Co²⁺ > Ni²⁺, found for the rate of water exchange. This implies that beside water exchange an other constant factor plays an important role in the rate determing step. The dissociation of the pentaco-ordinated 4-MeCyclam-14 complexes is acid catalyzed. The limiting rate for acid dissociation is not reached even in 2.5M HNO₃ in the case of Ni(4-MeCyclam-14)²⁺. From the formation and dissociation rates stability constants have been calculated, which do not show any macrocyclic effect.     

A pyrophosphate-responsive gadolinium(III) MRI contrast agent

This study shows that the relaxivity and optical properties of functionalised lanthanide‐DTPA‐bis‐amide complexes (lanthanide=Gd³⁺ and Eu³⁺, DTPA=diethylene triamine pentaacetic acid) can be successfully modulated by addition of specific anions, without direct Ln³⁺/anion coordination. Zinc(II)‐dipicolylamine moieties, which are known to bind strongly to phosphates, were introduced in the amide “arms” of these ligands, and the interaction of the resulting Gd–Zn₂ complexes with a range of anions was screened by using indicator displacement assays (IDAs). Considerable selectivity for polyphosphorylated species (such as pyrophosphate and adenosine‐5′‐triphosphate (ATP)) over a range of other anions (including monophosphorylated anions) was apparent. In addition, we show that pyrophosphate modulates the relaxivity of the gadolinium(III) complex, this modulation being sufficiently large to be observed in imaging experiments. To establish the binding mode of the pyrophosphate and gain insight into the origin of the relaxometric modulation, a series of studies including UV/Vis and emission spectroscopy, luminescence lifetime measurements in H₂O and D₂O, ¹⁷O and ³¹P NMR spectroscopy and nuclear magnetic resonance dispersion (NMRD) studies were carried out.