Critical role of water content in the formation and reactivity of uranium, neptunium, and plutonium iodates under hydrothermal conditions: implications for the oxidative dissolution of spent nuclear fuel

The reactions of 237NpO2 with excess iodate under acidic hydrothermal conditions result in the isolation of the neptunium(IV), neptunium(V), and neptunium(VI) iodates, Np(IO3)4, Np(IO3)4.nH2O.nHIO3, NpO2(IO3), NpO2(IO3)2(H2O), and NpO2(IO3)2.H2O, depending on both the pH and the amount of water present in the reactions. Reactions with less water and lower pH favor reduced products. Although the initial redox processes involved in the reactions between 237NpO2 or 242PuO2 and iodate are similar, the low solubility of Pu(IO3)4 dominates product formation in plutonium iodate reactions to a much greater extent than does Np(IO3)4 in the neptunium iodate system. UO2 reacts with iodate under these conditions to yield uranium(VI) iodates solely. The isotypic structures of the actinide(IV) iodates, An(IO3)4 (An=Np, Pu), are reported and consist of one-dimensional chains of dodecahedral An(IV) cations bridged by iodate anions. The structure of Np(IO3)4.nH2O.nHIO3 is constructed from NpO9 tricapped-trigonal prisms that are bridged by iodate into a polar three-dimensional framework structure. Second-harmonic-generation measurements on a polycrystalline sample of the Th analogue of Np(IO3)4.nH2O.nHIO3 reveal a response of approximately 12x that of alpha-SiO2. Single-crystal magnetic susceptibility measurements of Np(IO3)4 show magnetically isolated Np(IV) ions.     

Hydrothermal preparation,structures, and NLO properties of the rare earth molybdenyl iodates,RE(MoO2)(IO3)4(OH) [RE = Nd,Sm, Eu

The reactions of RE(IO3)3 [RE = Nd, Sm, Eu] with I2O5 and MoO3 in a 1:2:2 molar ratio at 200 degrees C in aqueous media provide access to RE(MoO2)(IO3)4(OH) [RE = Nd (1), Sm (2), Eu (3)] as pure phases as determined from powder X-ray diffraction data. Single crystal X-ray diffraction experiments demonstrate that these compounds are isostructural and crystallize in the chiral and polar space group P2(1). The structures are composed of three-dimensional networks formed from eight-coordinate, square antiprismatic RE3+ cations and MoO2(OH)+ moieties that are bound by bridging iodate anions. The Mo(VI) centers are present in distorted octahedral environments composed of two cis-oxo atoms, a hydroxo group, and three bridging iodate anions arranged in a fac geometry. There are four crystallographically unique iodate anions in the structures of 1-3, one of these is actually present in the form of a IO3+1 polyhedron where a short interaction of 2.285(4) A is formed between the iodate anion and the hydroxo group bound to the Mo(VI) center. This interaction results in significant distortions of the iodate anion similar to those found in tellurites with TeO3+1 units. Two of the four iodate anions are aligned along the polar b-axis, imparting the required polarity to these compounds. Second-harmonic generation (SHG) measurements on sieved powders of 1 show a response of 350 x alpha-quartz. Crystallographic data: 1, monoclinic, space group P2(1), a = 6.9383(5) A, b = 14.0279(9) A, c = 7.0397(5) A, beta = 114.890(1) degrees, Z = 2; 2, monoclinic, space group P2(1), a = 6.9243(6) A, b = 13.963(1) A, c = 7.0229(6) A, beta = 114.681(1) degrees, Z = 2; 3, monoclinic, space group P2(1), a = 6.9169(6) A, b = 13.943(1) A, c = 7.0170(6) A, beta = 114.542(1) degrees, Z = 2.     

多谱线耦合系统辐射束缚问题的理论处理

提出一种处理多荧光谱线耦合系统辐射束缚问题的理论方法．这里的耦合包括激发态间的碰撞传能和当谱线重叠时对荧光的交叉吸收．首先将描述辐射束缚的Ｈｏｌｓｔｅｉｎ方程扩展为适用于描述多个激发能级且包括交叉耦合项的微分积分方程组，并将其纳入矢量、矩阵的形式．然后直接通过算符运算求解，给出按算符展开的级数解式．最后对级数解进行约化，导出一个只用有限项便可对系统行为进行完整描述的、远较简单截断近似优越的结果．还给出了一个双激发能级系统的计算实例     

New quasi-one-dimensional tetracyanidoplatinate,Cs4[Pt(CN)4](CF3SO3)2: Synthesis,structure, and physical characterization

The synthesis and some physical properties of a new quasi-one-dimensional tetracyanidoplatinate, Cs₄[Pt(CN)₄](CF₃SO₃)₂ (CsCP(OTf)) are reported and described in comparison to the well-known K₂[Pt(CN)₄]Br_0.30·3.2H₂O (KCP). Single-crystal X-ray diffraction reveals Pt–Pt spacings to be greater than those of KCP by 5% longitudinal and 38% transverse, but much shorter than comparable spacings in other non-partially oxidized platinates. Anomalies are observed between temperatures 100 K and 200 K: (1) Longitudinal DC conductivity is two orders of magnitude higher and is non-monotonic with temperature, showing a minimum at around 170 K. (2) Nuclear magnetic resonance (NMR) longitudinal relaxation time T₁ is at least three orders of magnitude higher than that of KCP, and is also non-monotonic with temperature, showing a sharp peak at around 120 K. Since X-ray diffraction reveals no structural transition at 120 K, these suggest a possible lattice freezing or stiffening at around 120 K.     

Analytical approach to the quantum-phase transition in the one-dimensional spinless Holstein model

We study the one-dimensional Holstein model of spinless fermions interacting with dispersion-less phonons by using a recently developed projector-based renormalization method (PRM). At half-filling the system shows a metal-insulator transition to a Peierls distorted state at a critical electron-phonon coupling where both phases are described within the same theoretical framework. The transition is accompanied by a phonon softening at the Brillouin zone boundary and a gap in the electronic spectrum. For different filling, the phonon softening appears away from the Brillouin zone boundary and thus reflects a different type of broken symmetry state.     

Association of biotin with silver (I) in solution: a circular dichroism study

A strong polymeric helical complex of Ag(I) with biotin, a water-soluble vitamin also called vitamin H or B₇, has been described in the crystal phase, yet with missing spatial characteristic of its solution structure. In this work, the complexation of d-(+)-biotin with Ag⁺ in aqueous solution has been studied by means of circular dichroism spectroscopy and mass spectrometry with electrospray ionization in positive mode (MS-ESI+). For comparison, the spectra of the Nujol suspension of studied systems in the solid state were also measured. The results indicate that the Ag(I)–biotin complex has a helical arrangement of the biotin molecules in solution. Our results show that the binding process involves the thioether sulfur atom and ureido carbonyl oxygen atom, while the carboxylate side group is not coordinated with the silver. The MS-ESI experiments have revealed the composite structures of Ag⁺ with biotin of various constitutions, which represent the products of the polymeric helical Ag(I)–biotin complex.     

Hydrogen-bonding interactions in the active sites of cytochrome P450cam and its site-directed mutants.

Resonance Raman spectroscopy is applied to the cyanide adducts of cytochrome P450cam and its T252A and D251N site-directed mutants, both in their substrate-free and camphor-bound forms, to probe active-site heme structure and, in particular, interactions of the FeCN fragment with potential active-site H-bond donors. In contrast to the ferrous CO and ferric NO adducts, which form only essentially linear (slightly distorted) FeXY fragments, the spectra of the ferric CN(-) adducts provide clear evidence the for the existence of an additional, rather highly bent, conformer; that is, the cyanide complexes form both linear and bent conformers in both the substrate-free and substrate-bound forms. Formation of this bent conformer is most reasonably attributed to the presence of off-axis H-bond donors, which induce distortion on the FeCN fragment but not the FeCO and FeNO fragments, which are poorer H-bond acceptors. For all three proteins, the substrate-free form exhibits a complex spectral pattern which arises because one of the modes associated with the FeCN fragment is coupled with two heme macrocycle deformation modes. Significantly, no evidence for such coupling is observed in the spectra of the camphor-bound forms. While various unknown factors may possibly give rise to selective activation of such coupling in the substrate-free derivative, given the known facts about the active-site architecture of this enzyme, a plausible explanation is that the bent conformer is oriented toward the water-filled substrate-binding site in the substrate-free form, but oppositely, toward the proposed proton delivery shuttle, in the substrate-bound form. Sensitivity of the FeCN modes to H(2)O/D(2)O exchange in the two camphor-bound mutants, which is apparently absent for the camphor-bound native protein, is most reasonably attributed to the known presence of extra water in the active sites of these mutants.     

Using Peptide Arrays to Profile Phosphatase Activity in Cell Lysates

Phosphorylation is an important post-translational modification on proteins involved in many cellular processes; however, understanding of the regulation and mechanisms of global phosphorylation remains limited. Herein, we utilize self-assembled monolayers on gold for matrix-assisted laser desorption/ionization mass spectrometry (SAMDI-MS) with three phosphorylated peptide arrays to profile global phosphatase activity in cell lysates derived from five mammalian cell lines. Our results reveal significant differences in the activities of protein phosphatases on phospho- serine, threonine, and tyrosine substrates and suggest that phosphatases play a much larger role in the regulation of global phosphorylation on proteins than previously understood.