435 research outputs found
High spin Fe(III)-doped nanostructures as T1 MR imaging probes
Magnetic Resonance Imaging (MRI) T1 contrast agents based on Fe(III) as an alternative to Gd-based compounds have been under intense scrutiny in the last 6-8 years and a number of nanostructures have been designed and proposed for in vivo diagnostic and theranostic applications. Excluding the large family of superparamagnetic iron oxides widely used as T2 -MR imaging agents that will not be covered by this review, a considerable number and type of nanoparticles (NPs) have been employed, ranging from amphiphilic polymer-based NPs, NPs containing polyphenolic binding units such as melanin-like or polycatechols, mixed metals such as Fe/Gd or Fe/Au NPs and perfluorocarbon nanoemulsions. Iron(III) exhibits several favorable magnetic properties, high biocompatibility and improved toxicity profile that place it as the paramagnetic ion of choice for the next generation of nanosized MRI and theranostic contrast agents. An analysis of the examples reported in the last decade will show the opportunities for relaxivity and MR-contrast enhancement optimization that could bring Fe(III)-doped NPs to really compete with Gd(III)-based nanosystems. This article is categorized under: Diagnostic Tools > In Vivo Nanodiagnostics and Imaging Diagnostic Tools > Diagnostic Nanodevices Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease
Comparison of Crystal Field Dependent and Independent Methods to Analyse Lanthanide Induced NMR Shifts in Axially Symmetric Complexes. Part II: Systems with a C4 Symmetry Axis
Analysis of the LIS data for several series of Ln3+ complexes of C4 symmetry in terms of structural
changes, crystal-field effects and/or variation of hyperfine constants along the lanthanide series was
undertaken using a combination of the two-nuclei and three-nuclei techniques together with the classical onenucleus
technique. Isostructurality of whole series of complexes, with changes of the Fi, and B02 parameters,
was clearly defined for the complexes of L by the combination of the two first methods. Small changes,
involving the three Fi, Gi and B02 parameters, are observed for the series of complexes of L-L4, using the
three data plotting methods. Some of the plots according to the two- and three-nuclei methods are
accidentally linear, without necessarily implying isostructurality of the complexes, as they involve
parameters, which may be insensitive to any small structural changes occurring in these systems. These
parameter variations could result from a magnification, by the present graphical analysis, of the breaks
expected from the gradual structural changes along the series due to the lanthanide contraction. The α and β
parameters of the three-nuclei method are not diagnostic of the type of structures the complexes have in
solution, due to their very indirect dependence on the geometric factors
Quantitation of absolute 2H enrichment of plasma glucose by 2H NMR analysis of its monoacetone derivative
A simple 2H NMR method for quantifying absolute 2H-enrichments in all seven aliphatic positions of glucose following its derivatization to monoacetone glucose is presented. The method is based on the addition of a small quantity of 2H-enriched formate to the NMR sample. When the method was applied to [2-2H]monoacetone glucose samples prepared from [2-2H]glucose standards of known enrichments in the range of 0.2-2.5%, enrichment estimates derived by the NMR method were in good agreement with the real enrichment values of the [2-2H]glucose precursors. The measurement was also applied to monoacetone glucose derived from human plasma glucose samples following administration of 2H2O and attainment of isotopic steady state, where glucose H2 and body water enrichment are equivalent. In these studies, the absolute H2 enrichment of plasma glucose estimated by the formate method was in good agreement with the 2H-enrichment of body water measured by an independent method. Magn Reson Med 48:535-539, 2002. © 2002 Wiley-Liss, Inc
NMR conformational study of diamagnetic complexes of some triazatriacetate macrocycles
The conformational properties of the diamagnetic complexes formed by five triazatriacetic macrocyclic ligands with monovalent (alkaline) and divalent (alkaline-earth, Zn2+ and Cd2+) cations have been studied by proton nuclear magnetic resonance spectroscopy (1H NMR) in aqueous solution as a function of pH and temperature. These structurally related triazatriacetic ligands, 1,4,7-triazacyclononane-N,N',N''-triacetic acid (NOTA), 1,4,7-triazacyclodecane-N,N',N''-triacetic acid (DETA), 1,4,8-triazacycloundecane-N,N',N''-triacetic acid (UNTA), 1,5,9-triazacyclododecane-N,N',N''-triacetic acid (DOTRA), and 9,10-benzylidene-1,4,7-triazacyclotridecane-N,N',N''-triacetic acid, (BUNTA) have triazamacrocyclic rings with different sizes and flexibilities, bearing three pendant acetate arms. In the case of the alkaline-earth, Zn2+ and Cd2+ cations, only one complex form (1:1) has been detected for all the ligands studied. In most cases the metal ion is coordinated to all the ligand ring nitrogens and to all or some of the carboxylate groups of the pendant arms, except when a poor fit of the cations into the macrocyclic hole occurs, such as for the Ba2+ complexes of DETA, UNTA and DOTRA and the Ca2+ and Sr2+ complexes of BUNTA. The resonance patterns of the ring proton resonances, determined by the long lifetime of the metal-nitrogen bonds, indicate that the six-membered rings formed upon chelation are conformationally rigid and the five-membered rings are conformationally flexible. The multiplicity of the acetate proton resonances shows that the metal-oxygen bonds are long-lived or short lived depending whether the acetates are bound to nitrogens involved in two ring bridges of equal or unequal sizes.http://www.sciencedirect.com/science/article/B6TG5-3T829PD-1D/1/7651a74d4d83a8b051a5d0b9286244e
An annotated checklist of freshwater copepoda (crustacea, hexanauplia) from continental Ecuador and the Galapagos archipelago
An annotated checklist of the free-living freshwater Copepoda recorded in different regions in Ecuador (including the Amazon, the Andes, the coastal region, and the Galapagos Islands) is here provided. We revised all published records, critically evaluated the validity of each taxon and provided short taxonomic and biogeographical remarks for each one. A total of 27 taxa have been reported, including species and records at the generic level only. The species and taxa identified only up to the generic level belong to five families and 14 genera. The Cyclopoida is the most diverse group with 16 records belonging to species (or identified to the generic level only) and eight genera, followed by the Harpacticoida with six species, one identification to the generic level only, and four genera, and Calanoida with four species belonging to two genera. A total of 18 taxa are recorded for the Andes. Six have been recorded in the Amazon, two are recorded for the coastal region, and six for the Galapagos. One species is shared between the Amazon and the Andes. One species is shared between the coastal region and the Amazon. Seventeen are only reported from the Andes and four are only reported from the Amazon. At the current status of the knowledge, any attempt to analyze and generalize distributional patterns of copepods in Ecuador is premature due to the scarcity of available information, and evidently there is an urgent need for more extensive field collections. A few working hypothesis for future studies are identified
Gd(III) chelates as NMR probes of protein-protein interactions. Case study: rubredoxin and cytochrome c3
Inorganic Chemistry 50(21):10600-7Two cyclen-derived Gd probes, [Gd-DOTAM](3+) and [Gd-DOTP](5-) (DOTAM = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetamide; DOTP = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrakis(methylenephosphonate)), were assessed as paramagnetic relaxation enhancement (PRE)-inducing probes for characterization of protein-protein interactions. Two proteins, Desulfovibrio gigas rubredoxin and Desulfovibrio gigas cytochrome c(3), were used as model partners. In a (1)H NMR titration it was shown that [Gd-DOTP](5-) binds to cytochrome c(3) near heme IV, causing pronounced PREs, characterized by line width broadenings of the heme methyl resonances at ratios as low as 0.08. A K(d) of 23 ± 1 μM was calculated based on chemical shift perturbation of selected heme methyl resonances belonging to three different heme groups, caused by allosteric effects upon [Gd-DOTP](5-) binding to cytochrome c(3) at a molar ratio of 2. The other probe, [Gd-DOTAM](3+), caused PREs on a well-defined patch near the metal center of rubredoxin (especially the patch constituted by residues D19-G23 and W37-S45, which broaden beyond detection). This effect was partially reversed for some resonances (C6-Y11, in particular) when cytochrome c(3) was added to this system. Both probes were successful in causing reversible PREs at the partner binding site, thus showing to be good probes to identify partners' binding sites and since the interaction is reversible to structurally characterize protein complexes by better defining the complex interface
The chemical consequences of the gradual decrease of the ionic radius along the Ln-series
[Abstract] In the periodical system, the lanthanides (the 15 elements in the periodic table between barium and hafnium) are unique in the sense that their trivalent cations have their valence electrons hidden behind the 5s and 5p electrons. They show a gradual decrease in ionic radius with increasing atomic number (also known as the lanthanide contraction). The resulting steric effects determine to a large extent the geometries of complexes of these ions. Here, we discuss these effects, particularly upon the properties of the complexes in aqueous solution, for selected families of Ln3+-complexes of oxycarboxylate and aminocarboxylate ligands. The physical properties of the cations are very different, which is very useful for the elucidation of the configuration, conformation and the dynamics of the complexes by X-ray techniques, NMR spectroscopy, and optical techniques. Often the structural analysis is assisted by computational methods
Quantification and Localization of Intracellular Free Mg2+ in Bovine Chromaffin Cells
Magnesium is an essential element for all living systems. The quantification of free intracellular Mg2+ concentration ([Mg2+]i) is of utmost importance since changes in its basal value may be an indication of
different pathologies due to abnormalities of Mg2+ metabolism. In this work we used 31P NMR and
fluorescence spectroscopy to determine the resting [Mg2+]i in bovine chromaffin cells, a neuron-like cellular
model, as well as confocal laser scanning microscopy to study the free Mg2+ spatial distribution in these cells.
31P NMR spectroscopy did not prove to be effective for the determination of [Mg2+]i in this particular case due to some special morphological and physiological properties of this cell type. A basal [Mg2+]i value of
0.551 ± 0.008 mM was found for these cells using fluorescence spectroscopy and the Mg2+-sensitive probe
furaptra; this value falls in the concentration range reported in the literature for neurons from different
sources. This technique proved to be an accurate and sensitive tool to determine the [Mg2+]i
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