Lanthanide(III) complexes are more active inhibitors of the Fenton reaction than pure ligands

OBJECTIVES: This study is an extension to our finding of direct anti-oxidant activities of lanthanide(III) complexes with the heterocyclic compound, 5-aminoorotic acid (AOA). In this experiment, we used AOA and coumarin-3-carboxylic acid as the two heterocyclic compounds with anti-oxidant potential, to produce the complexes with different lanthanides. METHODS: Lanthanide(III) complexes were tested on the iron-driven Fenton reaction. The product of this reaction, the hydroxyl radical, was detected by HPLC. RESULTS: All complexes as well as their ligands had positive or neutral effect on the Fenton reaction but their behavior was different. Both pure ligands in low concentration ratio to iron were inefficient in contrast to some of their complexes. Complexes of neodymium, samarium, gadolinium, and partly of cerium blocked the Fenton reaction at very low ratios (in relation to iron) but the effect disappeared at higher ratios. In contrast, lanthanum complexes appeared to be the most promising. Both blocked the Fenton reaction in a dose-dependent manner. CONCLUSION: Lanthanide(III) complexes were proven to block the iron-driven production of the hydroxyl radical. Second, the lanthanide(III) element appears to be crucial for the anti-oxidant effect. Overall, lanthanum complexes may be promising direct anti-oxidants for future testing

Using remote substituents to control solution structure and anion binding in lanthanide complexes.

A study of the anion-binding properties of three structurally related lanthanide complexes, which all contain chemically identical anion-binding motifs, has revealed dramatic differences in their anion affinity. These arise as a consequence of changes in the substitution pattern on the periphery of the molecule, at a substantial distance from the binding pocket. Herein, we explore these remote substituent effects and explain the observed behaviour through discussion of the way in which remote substituents can influence and control the global structure of a molecule through their demands upon conformational space. Peripheral modifications to a binuclear lanthanide motif derived from α,α′-bis(DO3 Ayl)-m-xylene are shown to result in dramatic changes to the binding constant for isophthalate. In this system, the parent compound displays considerable conformational flexibility, yet can be assumed to bind to isophthalate through a well-defined conformer. Addition of steric bulk remote from the binding site restricts conformational mobility, giving rise to an increase in binding constant on entropic grounds as long as the ideal binding conformation is not excluded from the available range of conformers

r-Process Lanthanide Production and Heating Rates in Kilonovae

r-Process nucleosynthesis in material ejected during neutron star mergers may lead to radioactively powered transients called kilonovae. The timescale and peak luminosity of these transients depend on the composition of the ejecta, which determines the local heating rate from nuclear decays and the opacity. Kasen et al. (2013, ApJ, 774, 25) and Tanaka & Hotokezaka (2013, ApJ, 775, 113) pointed out that lanthanides can drastically increase the opacity in these outflows. We use the new general-purpose nuclear reaction network SkyNet to carry out a parameter study of r-process nucleosynthesis for a range of initial electron fractions $Y_e$, initial specific entropies $s$, and expansion timescales $\tau$. We find that the ejecta is lanthanide-free for $Y_e \gtrsim 0.22 - 0.30$, depending on $s$ and $\tau$. The heating rate is insensitive to $s$ and $\tau$, but certain, larger values of $Y_e$ lead to reduced heating rates, due to individual nuclides dominating the heating. We calculate approximate light curves with a simplified gray radiative transport scheme. The light curves peak at about a day (week) in the lanthanide-free (-rich) cases. The heating rate does not change much as the ejecta becomes lanthanide-free with increasing $Y_e$, but the light curve peak becomes about an order of magnitude brighter because it peaks much earlier when the heating rate is larger. We also provide parametric fits for the heating rates between 0.1 and $100\,\text{days}$, and we provide a simple fit in $Y_e$, $s$, and $\tau$ to estimate whether the ejecta is lanthanide-rich or not.Comment: 19 pages, 9 figure

Engineered ferritin for lanthanide binding

Ferritin H-homopolymers have been extensively used as nanocarriers for diverse applications in the targeted delivery of drugs and imaging agents, due to their unique ability to bind the transferrin receptor (CD71), highly overexpressed in most tumor cells. In order to incorporate novel fluorescence imaging properties, we have fused a lanthanide binding tag (LBT) to the C-terminal end of mouse H-chain ferritin, HFt. The HFt-LBT possesses one high affinity Terbium binding site per each of the 24 subunits provided by six coordinating aminoacid side chains and a tryptophan residue in its close proximity and is thus endowed with strong FRET sensitization properties. Accordingly, the characteristic Terbium emission band at 544 nm for the HFt-LBT Tb(III) complex was detectable upon excitation of the tag enclosed at two order of magnitude higher intensity with respect to the wtHFt protein. X-ray data at 2.9 Å and cryo-EM at 7 Å resolution demonstrated that HFt-LBT is correctly assembled as a 24-mer both in crystal and in solution. On the basis of the intrinsic Tb(III) binding properties of the wt protein, 32 additional Tb(III) binding sites, located within the natural iron binding sites of the protein, were identified besides the 24 Tb(III) ions coordinated to the LBTs. HFt-LBT Tb(III) was demonstrated to be actively uptaken by selected tumor cell lines by confocal microscopy and FACS analysis of their FITC derivatives, although direct fluorescence from Terbium emission could not be singled out with conventional, 295–375 nm, fluorescence excitation

Synthesis and Characterization of Luminescent Lanthanide Nano-Rings

It is not uncommon for inorganic chemistry classes to gloss over the chemistry of the lanthanides. Because most inorganic chemists work closely with the d -electrons of the transition metals, the shielded and inert f -electrons of the lanthanides may at first glance seem monotone or even boring. However, to truly appreciate the lanthanides and the complexes they produce, one must come to embrace their chemical simplicity and understand their much more interesting electronic properties that lead to extremely interesting luminescent and magnetic molecules. Furthermore, though the lanthanides generally only form 3+ ions, it is important to consider that their high coordination number can lead to some very large and unusual molecular structures. Additionally, lanthanide complexes are known for their photophysical properties, specifi cally their sharp emission peaks. This, along with the fact that they don't photobleach and are relatively nontoxic, make them ideal for biological probes. If the ligand in the complex can be functionalized to couple with an antibody, the complex should then be able to follow the antibody wherever it goes, for example, to a cancerous tumor, and the probes would then aggregate in the area, causing localized luminescence, aiding in early detection of cancer. This thesis reports the synthesis of a 42-nuclear lanthanide nano-ring: likely the highest nuclearity lanthanide complex ever produced. This complex, referred to as Ln 42, is produced by reacting an ortho-vanillin based ligand with lanthanide acetate, the suitable lanthanides being gadolinium, terbium, dysprosium, and holmium. The complex self-assembles, interestingly, fi rst hydrolyzing the ligand such that the only portion that remains in the final complex is deprotonated ortho-vanillin. Acetate and hydroxyl groups also remain in the final complex, in addition to the lanthanide centers. The structure in the crystalline solid state was determined using single crystal X-ray diffraction.Chemistr

Complex magnetism of lanthanide intermetallics unravelled

We explain a profound complexity of magnetic interactions of some technologically relevant gadolinium intermetallics using an ab-initio electronic structure theory which includes disordered local moments and strong $f$-electron correlations. The theory correctly finds GdZn and GdCd to be simple ferromagnets and predicts a remarkably large increase of Curie temperature with pressure of +1.5 K kbar$^{-1}$ for GdCd confirmed by our experimental measurements of +1.6 K kbar$^{-1}$. Moreover we find the origin of a ferromagnetic-antiferromagnetic competition in GdMg manifested by non-collinear, canted magnetic order at low temperatures. Replacing 35\% of the Mg atoms with Zn removes this transition in excellent agreement with longstanding experimental data.Comment: 11 pages, 4 figure