1,721,718 research outputs found
Gas-phase ultraviolet photoelectron spectra of [{Ni(η-C5H5)}2(μ-C2R2)] (R = H or CF3) complexes
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Lanthanides-based catalysis in eukaryotes
No full textRare earth elements play a pivotal role in high-technology devices, are used as contrast agents for magnetic resonance imaging in clinical settings, are explored as drug carriers for tumor photodynamic therapy, and are used as fertilizers. From the biochemical viewpoint, they act not only as antagonists of Ca2+ but have been proposed as alternative to Ca2+ in metallo-enzymes, in particular in Ce3+-based methanol dehydrogenases (MDHs). Up to now, the analysis of protein sequence databases identified Ce3+-based MHDs only in Archea and Bacteria. Here, we report evidence that Ce3+-based MDHs are also present in higher organisms. These enzymes, identified in the parasite Plasmodium yoelii yoelii, in the spider Nephila clavipes, in the Tibetan antelope Pantholops hodgsonii, and in Homo sapiens, are encoded by intronless genes, thus representing a case of multiple, independent lateral gene transfer from Prokaryotes to Eukaryotes. The conservation of residues involved in the Ce3+ coordination, pyrroquinoline quinone cofactor recognition and in the structure stabilization suggests that these enzymes belong to the Ce3+-dependent MDH family, hitherto considered as exclusive of Prokaryotes. © 2018 IUBMB Life, 70(11):1067–1075, 2018
Modifying LnHPDO3A Chelates for Improved T 1 and CEST MRI Applications
No full textThe new ligand HPDO3MA [(R,R,R,R)-10-(2-hydroxypropyl)-a,a’,a’’-trimethyl-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid] was designed to combine and optimize the chemical properties of the macrocyclic ligands HPDO3A and DOTMA. The presence of the methyl groups on the acetic pendant arms of HPDO3A is expected to rigidify the structure of the ligand and favor an increase of the kinetic inertness of the Ln complexes. 1H NMR spectra of Eu(HPDO3MA) displayed the presence of two pairs of diastereoisomers: SAP (square antiprismatic) and TSAP (twisted square
antiprismatic) isomers (56 and 44%, respectively). In addition, 1H and 17O relaxometric NMR studies of Gd(HPDO3MA) showed approximately a 10% increase in relaxivity and a faster water exchange rate with respect to Gd(HPDO3A). Moreover, a detailed chemical exchange saturation transfer (CEST) characterization of Yb(HPDO3MA) displayed a sensitivity about two times larger than that of Yb(HPDO3A) both in phantom and in cell labeling experiments. Finally, the kinetic inertness of Yb(HPDO3MA) was measured to be twice as high as that of Yb(HPDO3A), with a dissociation half-life at physiological pH of about 2500 years
High kinetic inertness of a bis-hydrated Gd-complex with a constrained AAZTA-like ligand
No full textKinetic inertness is a key property for a Gd-based contrast agent. The Gd-III complex of a cyclohexyl-fused AAZTA derivative shows the highest kinetic inertness for non-macrocyclic bis hydrated (q = 2) Gd-III-complexes with a dissociation half-life of 91 years under physiological conditions, very close to that of macrocyclic clinically approved contrast agents. It also shows optimal relaxometric performance (r(1) = 8.3 mM(-1) s(-1) at 20 MHz and 25 degrees C) due to the presence of two inner sphere water molecules in fast exchange with bulk water and not displaced by endogenous anions
Metodo a risonanza magnetica, prodotto di programma per computer e macchina per a risonanza magnetica
No full textL'invenzione è relativa ad un metodo innovativo a
risonanza magnetica per analizzare processi metabolici, in
particolare processi enzimatici, per diagnostica tumorale senza l'utilizzo di agenti di contrasto
Seeking for Innovation with Magnetic Resonance Imaging Paramagnetic Contrast Agents: Relaxation Enhancement via Weak and Dynamic Electrostatic Interactions with Positively Charged Groups on Endogenous Macromolecules
Full text linkA paramagnetic probe to localize residues next to carboxylates on protein surfaces
No full textIt is shown that the paramagnetic properties of lanthanides can be exploited to obtain information on specific parts of a protein surface. Owing to the high affinity of coordinatively unsaturated lanthanide complexes for oxygen donors, carboxylate groups can be used as preferential targets for the interaction. The DO3A ligand is particularly useful in these studies, as it coordinates lanthanides in a heptadentate fashion, leaving two sites available for exogenous donors. A solution of a N-15-labeled sample protein, calbindin D-9k (75 residues), was titrated with up to 200% of Gd(III)-DO3A complex, and an inversion recovery N-15-H-1 HSQC experiment was used to measure the paramagnetic contributions to the longitudinal relaxation rates of the amide protons. Relaxation data were used as distance constraints to estimate the number of interacting complexes and the occupancies of their binding sites. Four preferential interaction sites on the protein surface are found. Inspection of the various carboxylate side chains on the surface of the protein indicates that Gd(III)-DO3A interacts preferentially with carboxylate-rich regions, rather than with isolated carboxylates, suggesting the possibility of chelation of one Gd(III)-DO3A molecule by two carboxylate groups. Gd(III)-DO3A is thus a valuable semi-selective probe for clusters of negative charges on the protein surface
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