MRI contrast agents based on supramolecular assemblies of DTPA-derivatives

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Heterobimetallic gadolinium(III)-iron(III) complex of DTPA-bis(3-hydroxytyramide)

A derivative of diethylenetriamine-N,N,N',N",N"-pentaacetic acid (DTPA), carrying two catechol functional groups has been synthesised by the reaction between DTPA-bis(anhydride) and 3-hydroxytyramine (dopamine). The ligand DTPA-bis(3-hydroxytyramide), [DTPA(HTA)(2)], is able to form stable heterobimetallic complexes with gadolinium(III) and iron(III) ions. The gadolinium(III) occupies the internal coordination cage of DTPA formed by three nitrogens, two carboxylate and two amide oxygens, while the [Fe(NTA)(H2O)(2)] (nitrilotri acetic acid, NTA) binds to catechol units by the substitution of two water ligands. The formation of polymeric species was avoided by using the tripodal NTA ligand. The heterobimetallic complex was characterised by means of visible absorption spectroscopy, electron spray ionisation-mass spectrometry (ESI-MS), and nuclear magnetic resonance (NMR) spectroscopy.status: publishe

Contraststoffen voor magnetische resonantie beeldvorming (MRI)

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Direct determination of Pd, Pt and Rh in fire assay lead buttons by laser ablation-ICP-OES : automotive exhaust catalysts as an example

The increasing use of Pd, Pt and Rh as catalysts in industrial applications results in the necessity of fast and accurate methods for the determination of these elements, not only in natural sources, but also in recyclable materials, such as spent automotive exhaust catalysts. Because of the low Pd, Pt and Rh contents in the samples typically analyzed and in order to avoid the influence of matrix components and sample heterogeneity, trace/matrix separation by means of lead fire assay usually precedes the actual analysis. This article concentrates on the determination of Pd, Pt and Rh in lead buttons obtained via fire assay using laser ablation-optical emission spectrometry. A 266 nm Nd:YAG-based laser ablation unit offering a maximum laser beam diameter of 780 mm was coupled to an ICP-OES instrument permitting simultaneous monitoring of the entire spectrum owing to the use of linear CCD detectors mounted on a Rowland circle of a spectrometer in Paschen-Runge mounting. Matrix-matched standards were applied for the construction of calibration curves, which were subsequently used for analysis of some real-life samples. The three different acquisition methods available were evaluated, but turned out to be quite similar in terms of linearity, accuracy and detection power. All but two of the resulting regression coefficients of the calibration curves were >= 0.999, while, taking into account their uncertainty, the experimental results are in good agreement with the reference values (obtained via wet chemical analysis) for the real-life samples analyzed, Pb buttons prepared by fire assay of an automotive exhaust catalyst. Limits of detection vary between 2.5 and 12 mu g g(-1) in the Pb button and the method precision was shown to be typically better than 5%

Synthesis of 1,4-oxazepane-2,5-diones via cyclization of rotationally restricted amino acid precursors and structural reassignment of serratin

Several natural products containing a 1,4-oxazepane-2,5-dione-core are known. One example is serratin, isolated from Serratia marcescens. Because of the presence of a carboxylic amide, which has a preference for a trans conformation, and the presence of a labile lactone in this core, many synthetic methodologies commonly used for the cyclization toward medium-sized heterocycles cannot be applied. As N-acyl amino acids lacking a third substituent at nitrogen failed to undergo ring-closure, several N-protecting groups were evaluated. With the use of the removable PMB-group, an N-unsubstituted 1,4-oxazepane-2,5-dione was synthesized. Via the application of pseudoprolines (i.e. serine-derived oxazolidines as another type of protecting group), a compound with the presumed structure of the natural product serratin was obtained. As a result of the differences in spectral data, the incorrect structural assignment of the natural product serratin was identified. Instead of the predicted seven-membered heterocycle, a symmetrical serratamolide analogue is proposed to be the correct structure of serratin

Selective synthesis of functionalized trifluoromethylated pyrrolidines, piperidines, and azepanes starting from 1-tosyl-2-(trifluoromethyl)aziridine

This paper reports on the generation and alkylation of the 1-tosyl-2-(trifluoromethyl)aziridin-2-yl anion with omega,omega'-dihaloalkanes, followed by a novel ring-expansion protocol toward 2-CF3-pyrrolidines, 2-CF3-piperidines, and 3-CF3-azepanes. A variety of halogen, oxygen, nitrogen, sulfur, and carbon nucleophiles was used to trigger this ring rearrangement, resulting in CF3-azaheterocycles bearing different types of functionalized side chains

Bis(phenylethylamide) derivatives of Gd-DTPA as potential receptor-specific MRI contrast agents

DTPA-bis(amide) derivatives bearing phenyl, phenol or catechol groups that mimic side chains of naturally occurring amino acids, such as phenylatanine, tyrosine or dopamine, were synthesized and characterized by elemental analysis, electrospray mass spectrometry, NMR spectroscopy and IR spectroscopy. The gadolinium(III) complexes of the ligands DTPA-bis(tyramide) [DTPA-(TA)(2)], DTPA-bis(3-hydroxytyramide) [DTPA-(HTA)(2)] and DTPA-bis(phenylalanine ethyl ester) [DTPA-(PAE)(2)], were prepared and then studied in vitro by O-17 NMR spectroscopy and by nuclear magnetic relaxation dispersion (NMRD) measurements. The residence time of the coordinated water in gadolinium(III) complexes was obtained from O-17 NMR relaxometric T-2 measurements. At 310 K, the following tau(M) values were obtained: Gd-DTPA(TA)(2) 582 ns, Gd-DTPA-(HTA)(2) 372 ns and Gd-DTPA-(PAE)(2) 809 ns. As shown by the analysis of the proton NMRD profiles, the larger proton relaxivities of the gadolinium(III) complexes at 310 K relative to that of the parent Gd-DTPA complex are mainly because of the increase in the rotational correlation time.status: publishe