La Analog Research Articles

Intermediate valence state of Ce in the novel quaternary compound CeRu2Sn2Zn18

A novel quaternary compound CeRu2Sn2Zn18 has been synthesized by a self-flux method. The structural, magnetic, and transport properties have been studied using single crystal X-ray structural analysis and measurements of the electrical resistivity ρ, specific heat C, and magnetic susceptibility χ. The X-ray structural analysis reveals that CeRu2Sn2Zn18 is an ordered variant of the CeCr2Al20- and ZrZn22-types, as found in the isostructural RT2Sn2Zn18 (R = La, Ce, Pr, Nd, T = Fe, Co, Ru). ρ shows no sign of a phase transition down to 2 K and is proportional to T2 below 50 K. χ exhibits a broad peak near 100 K, and the values are on the order of 10−3 emu/mol over a temperature range of 2–300 K. The electronic specific heat coefficient γ is found to be 69 mJ/K2 mol, which is approximately seven-fold larger than that of the La analog. These findings indicate that CeRu2Sn2Zn18 is in the intermediate valence state.

The disulfide compound α-lipoic acid and its derivatives: A novel class of anticancer agents targeting mitochondria

The endogenous disulfide α-lipoic acid (LA) is an essential mitochondrial co-factor. In addition, LA and its reduced counterpart dihydro lipoic acid form a potent redox couple with antioxidative functions, for which it is used as dietary supplement and therapeutic. Recently, it has gained attention due to its cytotoxic effects in cancer cells, which is the key aspect of this review. We initially recapitulate the dietary occurrence, gastrointestinal absorption and pharmacokinetics of LA, illustrating its diverse antioxidative mechanisms. We then focus on its mode of action in cancer cells, in which it triggers primarily the mitochondrial pathway of apoptosis, whereas non-transformed primary cells are hardly affected. Furthermore, LA impairs oncogenic signaling and displays anti-metastatic potential. Novel LA derivatives such as CPI-613, which target mitochondrial energy metabolism, are described and recent pre-clinical studies are presented, which demonstrate that LA and its derivatives exert antitumor activity in vivo. Finally, we highlight clinical studies currently performed with the LA analog CPI-613. In summary, LA and its derivatives are promising candidates to complement the arsenal of established anticancer drugs due to their mitochondria-targeted mode of action and non-genotoxic properties.

11B and 195Pt NMR study ofheavy-fermion compound CePt2B2C

We report 11B and 195Pt NMR Knight shiftK and spin–latticerelaxation rate 1/T1 in CePt2B2C in the range 4–315 K. The quadrupolar coupling constant,νQ for boron nuclei is790 ± 10 kHz. The change ofhyperfine field, Hhf, is observedbelow 30 K in the K versussusceptibility, χ, plot.The calculated value of Hhf at the 11B (195Pt) is 0.156 (6.86)kOe/μB in the range30–300 K and ∼0 (0.22) kOe/μB below30 K. The 1/T1 versus T curve shows some exotic behavior. The Ce 4f spin contribution to the nuclear relaxation rate (1/T1f) in each case is obtained by subtracting theT1K−1 estimated fromits La analog, i.e. LaPt2B2C. In the case of 11B resonance, in the temperature range of 300–100 K, (1/T1f) isindependent of T, suggesting a Curie–Weiss behavior of the imaginary part of the dynamicsusceptibility. It then shows a slow but continuous increment in therange 100–70 K, indicating a signature of the development of short-rangemagnetic correlation among the Ce 4f spins. Below 70 K, this enhancement of1/T1f is completely suppressed and it decreases sharply, indicating a suppression of the effect ofmagnetic correlation, due to the dominance of the Kondo effect over the RKKY interaction.1/T1f, follows∼Tα, with an exponentα∼0.7 in the range 4–30 Kfor 195Pt and in therange 8–30 K for 11B resonance. This is a characteristics of a non-Fermi-liquid like behavior. However, in the case of 11B, there is again a clear change in the slope of the1/T1f versusT curve below 8 K,with the value of α = 1.0, as if the behavior of the conduction electrons approaches towards a Fermi liquid, when probed nearthe 11B site.

Thermopower of CeNi5 with strong f-electron instability: Band effects

Numerical calculations of the thermopower component Sd that is associated with the fine structure of the density of d states near the Fermi level are carried out for CeNi5 and its La analog. The estimates, together with earlier experimental data on the transport coefficients in Ce(MxNi1−x)5 solid solutions with M=Ga, Cu (0≤x≤0.4)), are used to analyze the behavior of the thermopower component Sf originating from the Ce valence instability. It is shown that as Ce crosses over from the state of its usual intermediate valence to the saturated-valence state, the feature near the Fermi energy, which represents a Lorentzian-shaped peak of the density of f states, transforms to a double-humped structure. The possibility of formation of a strongly correlated band of f states in Ce(MxNi1−x)5 in the crossover to the Ce saturated-valence state, accompanied by the opening of a quasi-gap Δ ∼ 400 K, is discussed.

Unique crown thioether complexes of f elements: the crystal structure of U(III) and La(III) complexes of 1,4,7-trithiacyclononane.

The crystal structures of the first U(III) complex of a crown thioether and of its La(III) analog have been determined; a stronger M-S interaction is observed for U(III) with respect to La(III) and Ce(III) in solution and in the solid state.

Deuterium NMR study of the MP-2269: albumin interaction — a step forward to the dynamics of non-covalent binding

MP-2269, the Gd(III) complex of 4-pentylbicyclo[2.2.2]octane-1-carboxyl-di-L-aspartyl-lysine-derived-DTPA, is a small Gd-agent that binds non-covalently to serum albumin in vivo to assume the enhanced relaxivities associated with macromolecular agents, (due in part to increased rotational correlation time, tau(R)). To further explore the fundamental parameters that govern the dynamics of water proton relaxation enhancement by this prototypical albumin-binding agent, the rotational correlation time (tau(R)) for the deuterated La(III) analog of MP-2269 has been independently measured in the presence and absence of 4% albumin using 2H-NMR approaches. The diamagnetic La(III) analog of MP-2269 was deuterated at the alpha-position of the carbonyl groups. 2H-NMR studies were conducted at 7.05T (46 MHz) and 310 degrees K on a Bruker NMR spectrometer. Spectral deconvolution permitted calculation of transverse relaxation rates, 1/T(2), from the NMR linewidths and subsequently, tau(R). The results yielded a tau(R) of the albumin bound complex of approximately 8 ns. This value is intermediate between those earlier estimated by 17O-NMR ( approximately 1 ns) and 1H-NMRD ( approximately 20-50 ns) and significantly shorter than that of albumin. The 2H-NMR study results also indicate that the exchange between free and albumin-bound forms of the La(III) analog is slow (exchange lifetimes >1 ms). This slow exchange does not affect the water residence lifetimes (tau(M) 140-280 ns).

Solution and solid state spectroscopy of tetrakis complexes of 2,2′-bipyridine-1,1′-dioxide with europium(III)

Previous studies on the crystal structure of a complex formed with 2,2′-bipyridine-1,1′-dioxide (bpyO 2) and La(III) ions have shown the existence of an tetrakis eight coordinate complex in which the metal ion sits in a site of approximate D 4 symmetry. In this paper we describe high-resolution luminescence and circularly polarized luminescence results on Eu(bpyO 2) 4 3+. The appearance of several crystal-field transitions in the emission for the Eu(III) complex are interpreted in terms of distortions from the D 4 symmetry seen for the La(III) analog. Extraordinarily large absorption and emission intensities for the hypersensitive transitions of Nd(bpyO 2) 4 3+ and Eu(bpyO 2) 4 3+ are observed and discussed. Large circularly polarized luminescence is observed from Eu(bpyO 2) 4 3+ dissolved in acetonitrile following circularly polarized laser excitation. This result suggests that the complex occurs in solution as a racemic complex that does not racemize on the emission time scale.

Magnetic-susceptibility and heat-capacity measurements on PrRhSb.

Magnetic-susceptibility (ac and dc) and heat-capacity measurements have been carried out on the compound PrRhSb. These measurements reveal two magnetic transitions in this compound---one at about 18 K and the other around 6 K. In the dc susceptibility the 18-K transition is evident as the temperature below which a magnetic correlation sets in and the susceptibility is found to be field dependent. The lower transition manifests as a peak in the susceptibility of zero-field-cooled samples which were measured in low applied fields. The electronic-specific-heat coefficient, \ensuremath{\gamma}, is found to be 33 mJ/mol ${\mathrm{K}}^{2}$ between 40 and 70 K after correcting for the lattice contribution taken to be the same as in its La analog. The \ensuremath{\gamma} value is fairly large for a Pr compound and may be indicative of moderately heavy quasiparticles. A Kondo-type interaction of the Pr 4f electrons with the conduction electrons may be responsible for high-magnetic-ordering temperatures and the moderately large \ensuremath{\gamma} value in this compound.

Neutron diffraction study of the “brown phase” BaNd 2CuO 5

A neutron Rietveld refinement study of the “brown phase” BaNd 2CuO 5 shows that this material is isostructural with the La analog, but adopts a totally different structure from that of the “green phase” BaR 2CuO 5 formed for R = Y and most lanthanide elements. BaNd 2CuO 5 is tetragonal, space group P4/mbm(126), with Z=2 and refined cell parameters a = 6.7015(1) and c=5.8211 (1) Å. The BaNd 2CuO 5 framework is built from edge- and face-sharing BaO 10 and NdO 8 polyhedra, while in the green phase structure the smaller R 3+ ion is surrounded by seven oxygen atoms. The square-planar CuO 4 groups are isolated in the structure.

Low temperature magnetic hardness due to Co in CaCu 5 type bulk materials

The coercive force at 4.2 K of bulk specimens YCo 5− x Ni x and LaCo 5− x Ni x increases from negligible values (of order H c < 1 kOe) for x = 0 to values of H c of 11 and 27 kOe for the Y and La analog compounds with x = 3. This indicates that a transition metal alone can be responsible for the phenomenon of strong low temperature magnetic hardness in bulk specimens formerly found in various systems with anisotropic and magnetic rare earths. The coercive force of SmCo 2Ni 3 is larger than 50 kOe at 4.2 K while the analogous compound on the basis of Tb does not show coercive forces begond 0.5 kOe. The origins of the phenomenon are discussed briefly.