Simultaneous separation of actinides and technetium from large volumes of natural water for their determination

Journal of Radioanalytical and Nuclear Chemistry - Monitoring of radionuclide concentration in natural samples is important for assessing environmental safety. The low concentration of long-lived...     

Energy characteristics of carbon spheres

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A Novel Metastable Pentavalent Plutonium Solid Phase on the Pathway from Aqueous Plutonium(VI) to PuO2 Nanoparticles

Here we provide evidence that the formation of PuO₂ nanoparticles from oxidized Pu^VI under alkaline conditions proceeds through the formation of an intermediate Pu^V solid phase, similar to NH₄PuO₂CO₃, which is stable over a period of several months. For the first time, state‐of‐the‐art experiments at Pu M₄ and at L₃ absorption edges combined with theoretical calculations unambiguously allow to determine the oxidation state and the local structure of this intermediate phase.     

Universal scaling relations in strongly anisotropic materials

We consider the critical temperature in strongly anisotropic antiferromagnetic materials, with weak coupling between stacked planes, in order to determine the interplane coupling constant from experimentally measured susceptibilities. We present theoretical arguments for a universal relation between interplane coupling and susceptibility shown numerically by Yasuda et al. [Phys. Rev. Lett. 94, 217201 (2005)10.1103/PhysRevLett.94.217201]. We predict a more general scaling function if the system is close to a quantum critical point, a similar relation for other susceptibilities than considered in Yasuda et al., and the validity of these relations for more general phase transitions.     

Quantum Hall effect of massless dirac fermions in a vanishing magnetic field

The effect of strong long-range disorder on the quantization of the Hall conductivity sigma{xy} in graphene is studied numerically. It is shown that increasing Landau-level mixing progressively destroys all plateaus in sigma{xy} except the plateaus at sigma{xy}=-/+e{2}/2h (per valley and per spin). The critical state at the Dirac point is robust to strong disorder and belongs to the universality class of the conventional plateau transitions in the integer quantum Hall effect. We propose that the breaking of time-reversal symmetry by ripples in graphene can realize this quantum critical point in a vanishing magnetic field.     

Hyperfine interactions of muonium and hydrogen in silicon and diamond: Quantum chemical calculations

The electronic structure of a hydrogen-like atom located at interstitial sites of the silicon and diamond crystals is calculated by the intermediate neglect of differential overlap (INDO) method. Calculations of the electronic g- and hyperfine interaction tensors of the impurity atom are performed. The results obtained are compared with the experimental properties of both “anomalous” muonium and hydrogen centers. It is shown that the most likely model for these centers in silicon and diamond is that in which interstitial neutral hydrogen-like atom locates at the bond-center site.     

Catalytic mechanism of yeast cytosine deaminase: an ONIOM computational study

The complete path for the deamination reaction catalyzed by yeast cytosine deaminase (yCD), a zinc metalloenzyme of significant biomedical interest, has been investigated using the ONIOM method. Cytosine deamination proceeds via a sequential mechanism involving the protonation of N(3), the nucleophilic attack of C(4) by the zinc-coordinated hydroxide, and the cleavage of the C(4)-N(4) bond. The last step is the rate determining step for the generation of the zinc bound uracil. Uracil is liberated from the Zn atom by an oxygen exchange mechanism that involves the formation of a gem-diol intermediate from the Zn bound uracil and a water molecule, the C(4)-O(Zn) cleavage, and the regeneration of the Zn-coordinated water. The rate determining step in the oxygen exchange is the formation of the gem-diol intermediate, which is also the rate determining step for the overall yCD-catalyzed deamination reaction.     

Highly regiocontrolled Pd-catalyzed cross-coupling reaction of terminal alkynes and allenylphosphine oxides

The cross-coupling of a variety of terminal alkynes 1 with allenylphosphine oxides 2 catalyzed by a Pd(OAc)(2)-TDMPP system provided conjugated endo-enynes 3 solely, while the TCPC-catalyzed reaction of the same regents led to the exclusive formation of exo-isomers 4. The mechanistic rationale for these selective transformations was proposed. Synthetic usefulness of the prepared exo-enyne 4 was demonstrated in the synthesis of multisubstituted diarylbenzylphosphine oxides 5 via the Pd-catalyzed [4+2]-benzannulation reaction.