Interaction Of Lanthanide Ions Research Articles

(Invited) New Developments in Single Molecule Magnetism of Endohedral Metallofullerenes

Encapsulation of metal clusters within the fullerene cage has multiple structural and physical consequences for the properties of endohedral metallofullerenes (EMFs). In particular, when encapsulated metals are lanthanides, unusual magnetic properties can be achieved. Interaction of lanthanide ions with negatively-charged non-metals (nitride, carbide) create large magnetic anisotropy of the former, which facilitates single molecule magnetism in EMFs. At the same time, carbon cage protects the endohedral species from the environment allowing formation of rather exotic combinations of metal and non-metal ions. Exchange and dipolar interaction between endohedral lanthanides also dramatically affects the magnetism of EMFs. This contribution will present an overview of the recent developments in the single molecule magnetism of EMFs.

The interface makes a difference: lanthanide ion coated vesicles hydrolyze phosphodiesters.

Lanthanide ions are strong Lewis acids. Their complexation to a variety of ligands can further enhance their Lewis acidity allowing the hydrolysis of phosphoesters and even DNA. We show that the interaction of lanthanide ions with vesicles from zwitterionic phosphatidylcholine lipids gives supramolecular structures in which the metal ion is loosely coordinated to the surface. This assembly provides a high density of Lewis-acidic metal centres, which hydrolyze phosphodiesters with enhanced rates.

Humic and hymatomelanic acids interaction with lanthanide ions

The interactions of lanthanide ions, REE(III), with semiquinone radicals naturally occurring in humic (HA) and hymatomelanic (HY) acids of different origin were studied mainly by EPR spectroscopy. Quantitative EPR analysis proved that only the semiquinone free radical concentration in both, HA and HY, was affected by interaction with some of the lanthanide ions, whereas the EPR g parameters of the formed radical–REE(III) complexes remained unchanged. The radical concentration was practically unaffected by the REE(III) ions with 4f1–4f6 electron configurations and in some degree increased by REE(III) ions with 4f8–4f14 configuration. The lanthanide playing an exceptional role was Gd(III) (4f7), which diminished strongly the free radicals concentration. The quenching ability of Gd(III) was stronger towards the radicals provided by HA than by HY, what was assigned to higher content in HA of both, oxygen-containing functional groups and conjugated aromatic rings, leading to more efficient Gd(III)–radical interaction. The semiquinone free radicals of HA and HY originated from the compost were more reactive than those from peat, as the humic acids from mature compost with less bulk density have more accessible functional groups.

Microcalorimetric studies on the interactions of lanthanide ions with bovine serum albumin

The interactions of lanthanide ions (Ln3+) with bovine serum albumin (BSA) under mimetic physiological conditions (310.15 K, pH 6.7, 0.1MNaCl) were studied by microcalorimetry. For the first time, based on Two Sets of Independent Sites Model, molar enthalpies (Δr H m1, Δr H m2) and coordination number (n 1, n 2) of the two sets of binding sites with different affinity were obtained directly from the microcalorimetric results. It was shown that the interactions are endothermic and entropy-driving processes. By combining with fluorescence spectroscopy, other thermodynamic parameters (Δr G m1, Δr S m1) were determined for high-affinity specific sites.

Study of the interaction between lanthanide ions and a supported bilayer lipid membrane by cyclic voltammetry and ac impedance

The interaction of lanthanide ions with a supported bilayer lipid (1,2-dimyristoyl- sn-glycero-3-phosphatidylcholine) membrane (sBLM) was investigated by cyclic voltammetry and ac impedance spectroscopy in this paper. Lanthanide can affect the conformation of the supported bilayer lipid membrane and cause pore formation. Through the pores, Fe(CN) 6 3−/4− can reach the electrode surface and show its redox behaviour. Furthermore the redox currents of Fe(CN) 6 3−/4− increased with increasing concentration of lanthanides and leveled off at 1.2 μM for Eu 3+. The interaction ability of three lanthanides with sBLM follows the sequence: Eu 3+>Tb 3+>La 3+.

The reaction of lanthanide ions with n-doxyl stearic acids and its utilization for the ESR study on the permeability of lipid-bilayer of erythrocyte membrane to gadolinium ions

The reaction of lanthanide ions with n-doxyl stearic acid ( nDS) spin labels ( n=5,7,12,16) was investigated by the electron spin resonance technique in aqueous solution. Among the lanthanides, the Gd 3+, Tb 3+, Tm 3+ and Ce 3+ ions strongly quenched the ESR signal of spin labels, but the effects of La 3+, Eu 3+ and Lu 3+ are very weak. The quenching effects are featured by: (1) the dependence on the concentration of lanthanide ions; (2) no obvious changes of the ESR line shape in the presence of lanthanide ions; (3) the quenching constant decreases in the order: Gd 3+ > Tb 3+ > Tm 3+ > Ce 3+; (4) the quenching effects of lanthanide ions are found to strikingly correlate with their magnetic properties. These findings indicate that the interaction of lanthanide ions with nitroxide oxygen leading to the reduction of ESR signal amplitude is dominated by their magnetic characteristics rather than the coordination effect. By labeling erythrocyte membrane with nDS, n=5,7,12,16 at different depths, we studied the diffusion of Gd 3+ into the lipid-bilayer of erythrocyte membrane by monitoring the reduction processes of the ESR signals of nitroxide spin labels located at different depths of membrane lipid-bilayer after addition of Gd 3+. These results revealed that the Gd 3+ ions can penetrate into the lipid-bilayer, though the entry rate is slow. It was shown that the Gd 3+ ions bind to the membrane and enhance the permeability of extracellular ascorbate into erythrocyte membrane. The transport mechanism of Gd 3+ ions through the lipid-bilayer might be involved in the Gd 3+ cation-induced pore formation in the surface of membrane.

NMR and FT-Raman Studies on the Interaction of Lanthanide Ions with Sphingomyelin Bilayers

Abstract The interactions of lanthanide ions with sphingomyelin bilayers have been studied by using 2D NOESY spectroscopy and FT-Raman spectroscopy methods. The results indicate that lanthanide ions, as well as divalent calcium, combine mainly to the phosphate group in the polar headgroup and do not change the conformation of O-C-C-N+ backbone in the choline group of sphingomyelin bilayers. The polar headgroup is still extending parallel to the bilayer surface and O-C-C-N+ group is still in its gauche conformer.

2D NMR and FT-Raman Spectroscopic Studies on the Interaction of Lanthanide Ions and Ln-DTPA with Phospholipid Bilayers

The interactions of lanthanide ions and the Ln-DTPA (DTPA = diethylenetriaminepentaacetate) complex with di palmitoylphosphatidylcholine (DPPC) and dipalmitoylphosphatidylethanolamine (DPPE) bilayers are studied by 2D NOESY and FT-Raman spectroscopy. Proton NMR spectroscopic results show that lanthanide ions combine with phosphate groups in the polar region of the outer layer of DPPC liposomes, leading to the separation in chemical shift of the proton signal of N(CH3)(3) The conformational change of the O-C-C-N+ backbone from the gauche conformer to the trans one is not found; i.e., the orientation of the polar headgroup is still parallel to the surface of the bilayers. The Ln-DTPA complex at low concentration in a pH 7.4 solution localizes far away from bilayers and thereby has little effect on the structure of bilayers. The FT-Raman spectroscopic results indicate that lanthanide ions affect strongly the fluidity of acyl chains of DPPE bilayers while the Ln-DTPA complex affects it slightly.

Luminescence and multinuclear N.M.R. study of the interaction of lanthanide ions with glycerophosphates

Luminescence and multinuclear N.M.R. study of the interaction of lanthanide ions with glycerophosphates

Interaction of lanthanide ions with Panulirus interruptus hemocyanin: Evidence for vicinity of some of the cation binding sites

The interaction of a number of lanthanide ions (namely terbium, praseodymium, erbium, lanthanum, gadolinium and europium) with Panulirus interruptus hemocyanin has been studied. Results from O 2-binding experiments indicate that all these ions may substitute for calcium as allosteric effectors of hemocyanin. Addition of the lanthanides to deoxygenated Panulirus hemocyanin saturated with Tb 3+ results in a quenching of the terbium luminescence. The highly efficient quenching observed in the case of Eu 3+ may indicate energy-transfer between Tb 3+ and Eu 3+. Since energy-transfer between lanthanides is only effective over very short distances, the data suggest that some of the cation binding sites of Panulirus hemocyanin are clustered.

Interaction of lanthanide ions with glutamic acid and γ-carboxyglutamic acid

Interactions of lanthanide ions with glutamic acid and γ-carboxyglutamic acid has been studied by the NMR method. These investigations made it possible to determine the coordination mode of aminoacids with lanthanide ions. The results are also of biological interest, since the lanthanides are often used as probes in calcium biochemistry. From our earlier studies on interaction of La(III), Lu(III) and Nd(III) ions with aspartic acid and asparagine it follows that light and heavy lanthanide ions interact in different ways with the carboxylic groups of aminoacids. In order to confirm this suggestion we extended our studies to glutamic acid and γ-carboxyglutamic acid. 1H, 13C NMR and electron spectra were recorded. Correlation of NMR chemical shifts with hypersensitive band intensity changes of lanthanide ions allows the determination of the coordination mode of the discussed aminoacids. Obtained results were confirmed by the Eu(III) luminescence spectra.

Interaction of lanthanide ions with bovine factor X and their use in the affinity chromatography of the venom coagulant protein of Vipera russelli

The substitution of trivalent lanthanide ions for Ca(II) in the Ca(II)-DEPENDENT ACTIVATION OF BOVINE Factor X by the coagulant protein of Russell's viper venom was studied at pH 6.8. Factor X contains two high affinity metal binding sites which bind Gd(III), Sm(III), and Yb(III) with a Kd of about 4 X 10-7 M and four to six lower affinity metal binding sites which bind Gd(III), Sm(III) with a Kd of about 1.5 X 10-5M. In comparison, 1 mol of Factor X binds 2 mol of Ca(II) with a Kd of 3 X 10-4M and weakly binds many additional Ca(II) ions. No binding of Gd(III) to the venom protein was observed. Dy(III), Yb(III), Tb(III), Gd(III), Eu(III), La(III), AND Nd(III) cannot substitute for Ca(II) in the Ca(II)-dependent activation of Factor X by the venom protein at pH 6.8. Kinetic data consistent with the models of competitive inhibition of Ca(II) by Nd(III) yielded a Ki of 1 to 4 X 10-6M. The substitution of lanthanide ions for Ca(II) to promote protein complex formation of Factor X-metal-venom protein without the activation of Factor X facilitated the purification of the coagulant protein from crude venom by affinity chromatography. Using a column containing Factor X covalently bound to agarose which was equilibrated in 10 mM Nd(III), Tb(III), Gd(III), or La(III), the coagulant protein was purified 10-fold in 40% yield from crude venom and migrated as a single band on gel electrophoresis in sodium dodecyl sulfate. These data suggest that lanthanide ions complete with Ca(II) for the metal binding sites of Factor X and facilitate the formation of a nonproductive ternary complex of venom protein-Factor X-metal. Tb(III) fluorescence, with emission maxima at 490 and 545 nm, is enhanced 10,000-fold in the presence of Factor X. The study of the participation of an energy donor intrinsic to Factor X in energy transfer to Tb(III) may be useful in the characterization of the metal binding sites of Factor X.