The complexation behavior of the ligand 2,6-bis{3-[N,N-bis(carboxymethyl)aminomethyl]pyrazol-1-yl}-pyridine, L, toward lanthanide cations was investigated throughout the series. Potentiometric titration experiments on L (0.1 M KCl) revealed the presence of four protonation steps in the 2-12 pH domain, associated with the protonation of the two tertiary amine nitrogen atoms and with two of the four carboxylate functions. The stability constants for the formation of the [LnL](-) complexes (Ln = La, Nd, Eu, Ho, and Lu) were determined in water and evidenced a hill-shaped complexation trend along the series, with log K increasing from 14.56(9) (La) to 16.68(2) (Ho) and decreasing to 15.42(2) (Lu). Geometry optimizations showed the [LnL](-) complexes (Ln = La, Nd, Eu, Ho, Yb, and Lu) adopting a C(2) symmetry with the symmetry axis going through the metal atom and the nitrogen atom of the central pyridine ring, leading to the presence of Delta and Lambda helical enantiomers. Analysis of the calculated Ln-O and Ln-N bond lengths showed a marked deviation from the expected values at the end of the series, which accounts for the observed decreased complexation affinity. (1)H and (13)C NMR experiments in D(2)O (room temperature) showed the shortening of the bond distances in [LnL](-) complexes from La to Lu to be accompanied by a rigidification of the structure, leading to a decreased C(2) symmetry for the Lu complex compared to C(2v) for La. This decreased symmetry was attributed to a slow Delta <--> Lambda interconversion that was followed by variable-temperature (13)C NMR experiments on the Lu complex. The activation parameters determined by line broadening analysis for this interconversion process point to an associatively assisted interconversion process. The (1)H NMR spectrum of the paramagnetic [YbL](-) complex was investigated in D(2)O, and a lanthanide induced shift analysis showed good agreement between the observed paramagnetic chemical shifts and those calculated from the DFT optimized structures using a dipolar model, especially when solvent effects are taken into account. The UV-vis absorption and near-infrared luminescence spectra of the Pr, Nd, Er, and Yb complexes were measured in water and showed the complexation pocket provided by the ligand to be well-suited for the protection of the cations, all of them displaying typical Ln-centered emission spectra, the Yb complex having a relatively long lifetime of 3.0 micros in water.
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http://dx.doi.org/10.1021/ic801816p | DOI Listing |
Int J Biol Macromol
December 2024
Faculty of Chemistry and Mineralogy, Universität Leipzig, Johannisallee 29, Leipzig 04103, Germany.
Two octa-coordinated lanthanum (III) complexes of deprotonated azaphosphor β-diketon and diimine ligands, [LnLQ] (L = [ClCHC(O)NP(O)(NCH)], Q = Phen (C1) and Bipy (C2)), were synthesized and characterized by elemental analysis, IR, and NMR spectra. X-ray crystallography revealed a distorted tetragonal antiprism LaO6N2 coordination geometry around the lanthanum atom in both compounds. Nano-sized complexes (Ć1 and Ć2) were synthesized via a sonochemical process and analyzed using SEM and XRPD.
View Article and Find Full Text PDFInorg Chem
December 2024
Department of Chemistry, Lomonosov Moscow State University, Leninskie gory 1 bld. 3, Moscow 119991, Russia.
Hybrid N,O-donor ligands based on 1,10-phenanthroline are a promising class of compounds for processing high-level waste. Here, we synthesized novel phenanthroline-based diphosphonates containing electron-withdrawing fluorine atoms in alkyl substituents. We studied their extraction properties for Am(III) and, for the first time, for the entire series of lanthanides(III).
View Article and Find Full Text PDFEJNMMI Radiopharm Chem
August 2024
Department of Environmental and Prevention Sciences, University of Ferrara, Via L. Borsari, 46, 44121, Ferrara, Italy.
Background: The integration of positron emission tomography (PET) and magnetic resonance imaging (MRI) holds promise for advancing diagnostic imaging capabilities. The METRICS project aims to develop cyclotron-driven production of Mn for PET/MRI imaging.
Results: Using the Cr(p,n)Mn reaction, we designed chromium metal targets via Spark Plasma Sintering and developed a separation procedure for isolating Mn.
Nature
August 2024
Max-Planck-Institut für Kohlenforschung, Mülheim an der Ruhr, Germany.
Polyene cyclizations are among the most complex and challenging transformations in biology. In a single reaction step, multiple carbon-carbon bonds, ring systems and stereogenic centres are constituted from simple, acyclic precursors. Simultaneously achieving this kind of precise control over product distribution and stereochemistry poses a formidable task for chemists.
View Article and Find Full Text PDFCurr Neurol Neurosci Rep
September 2024
Sleep and Brain Plasticity Centre, Department of Neuroimaging, Institute of Psychiatry, Psychology and Neuroscience (IoPPN), King's College London, De Crespigny Park, London, SE5 8AF, UK.
Purpose Of Review: Sleep disturbances are amongst most frequent non-motor symptoms of Parkinson's Disease (PD), and they are similarly frequently reported in other alpha-syncleinopathies, such as Dementia with Lewy Bodies (DLB) and Multiple System Atrophy (MSA). More recently, the orexin system has been implicated in control of arousal based on salient environmental set points, and its dysregulation in sleep issues in alpha-synucleinopathies suggested by the findings from the translational animal models. However, its role in the patients with alpha-synucleinopathies remains unclear.
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