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Uranium trioxide, UO3, has a T-shaped structure with bent uranyl, UO22+, coordinated by an equatorial oxo, O2-. The structure of cation UO3+ is similar but with an equatorial oxyl, O•-. Neutral and cationic uranium trioxide coordinated by nitrates were characterized by collision induced dissociation (CID), infrared multiple-photon dissociation (IRMPD) spectroscopy, and density functional theory. CID of uranyl nitrate, [UO2(NO3)3]- (complex A1), eliminates NO2 to produce nitrate-coordinated UO3+, [UO2(O•)(NO3)2]- (B1), which ejects NO3 to yield UO3 in [UO2(O)(NO3)]- (C1). Finally, C1 associates with H2O to afford uranyl hydroxide in [UO2(OH)2(NO3)]- (D1). IRMPD of B1, C1, and D1 confirms uranyl equatorially coordinated by nitrate(s) along with the following ligands: (B1) radical oxyl O•-; (C1) oxo O2-; and (D1) two hydroxyls, OH-. As the nitrates are bidentate, the equatorial coordination is six in A1, five in B1, four in D1, and three in C1. Ligand congestion in low-coordinate C1 suggests orbital-directed bonding. Hydrolysis of the equatorial oxo in C1 epitomizes the inverse trans influence in UO3, which is uranyl with inert axial oxos and a reactive equatorial oxo. The uranyl ν3 IR frequencies indicate the following donor ordering: O2-[best donor] ≫ O•-> OH-> NO3-.

The chemistry of linear uranyl(V/VI) dioxo cations, [Oyl–U–Oyl]+/2+, is dominated by coordination of uranium in the equatorial plane. Effects of this constraint were evaluated by experiment and theory for gas-phase mixed-valence UV/VI coordination dimers in which uranyl moieties are linked by alkyl dicarboxylates, [(UO2+)(UO22+)(OOC-(CH2)n-2-COO2–)2]– (n = 3–12). Faster O2-addition to dimers with short linkers n = 3 and 4, vs. n ≥ 5, suggests a structural difference. Computed structures with the shortest linkers have bridging dicarboxylates and nearly parallel, non-interacting uranyls. Longer linkers, n = 5–7, accommodate uranyl orientations with distinct UV–UVI end-on cation-cation interactions (CCIs), whereby Lewis base Oyl from UV coordinates to the acid UVI, denoted as UVOyl···UVI. The dimer structure for n = 8 has a UV–UVI side-on diamond-shape CCI, with UVOyl···UVI and UVIOyl···UV interactions. Addition of O2 to the n = 4 and 5 dimers yields [(UO22+)2(OOC-(CH2)n-2-COO2–)2(O2–)]–, with UV oxidized to UVI and O2 reduced to O2–. Whereas O2 can associate to and oxidize the exposed UV center for dimers with n = 3 and 4, the more crowded UV site in the CCI structures inhibits O2 addition. The results demonstrate rational structural control of uranyl-uranyl bonding and reactivity in small coordination complexes.

The bond distance is the simplest and most obvious indicator of the nature of a given chemical bond. However, for rare chemistry, it may happen that it is not yet firmly established. In this communication, we will show that the formally-triple protactinium(V) mono-oxo bond is predicted to be longer than what was previously reported in the solid state and in solution, based on robust quantum mechanical calculations, supported by an extensive methodological study. Furthermore, additional calculations are used to demonstrate that the Pa–Ooxo bond of interest is more sensitive to complexation than the supposedly analogous U–Oyl ones, not only in terms of bond distance but also of finer bond descriptors associated with the effective bond multiplicity. [ABSTRACT FROM AUTHOR]

A central goal of chemistry is to achieve ultimate oxidation states, including in gas-phase complexes with no condensed phase perturbations. In the case of the actinide elements, the highest established oxidation states are labile Pu(VII) and somewhat more stable Np(VII). We have synthesized and characterized gas-phase AnO3(NO3)2- complexes for An = U, Np, and Pu by endothermic NO2 elimination from AnO2(NO3)3-. It was previously demonstrated that the PuO3+ core of PuO3(NO3)2- has a Pu-O• radical bond such that the oxidation state is Pu(VI); it follows that in UO3(NO3)2- it is the stable U(VI) oxidation state. On the basis of the relatively more facile synthesis of NpO3(NO3)2-, a Np(VII) oxidation state is inferred. This interpretation is substantiated by reactivity of the three complexes: NO2 spontaneously adds to UO3(NO3)2- and PuO3(NO3)2- but not to NpO3(NO3)2-. This unreactive character is attributed to a Np(VII)O3+ core with three stable Np═O bonds, this in contrast to reactive U-O• and Pu-O• radical bonds. The computed structures and reaction energies for the three AnO3(NO3)2- support the conclusion that the oxidation states are U(VI), Np(VII), and Pu(VI). The results establish the extreme Np(VII) oxidation state in a gas-phase complex, and demonstrate the inherently greater stability of Np(VII) versus Pu(VII).

A central goal of chemistry is to achieve ultimate oxidation states, including in gas-phase complexes with no condensed phase perturbations. In the case of the actinide elements, the highest established oxidation states are labile Pu(VII) and somewhat more stable Np(VII). We have synthesized and characterized gas-phase AnO3(NO3)2- complexes for An = U, Np, and Pu by endothermic NO2 elimination from AnO2(NO3)3-. It was previously demonstrated that the PuO3+ core of PuO3(NO3)2- has a Pu-O• radical bond such that the oxidation state is Pu(VI); it follows that in UO3(NO3)2- it is the stable U(VI) oxidation state. On the basis of the relatively more facile synthesis of NpO3(NO3)2-, a Np(VII) oxidation state is inferred. This interpretation is substantiated by reactivity of the three complexes: NO2 spontaneously adds to UO3(NO3)2- and PuO3(NO3)2- but not to NpO3(NO3)2-. This unreactive character is attributed to a Np(VII)O3+ core with three stable Np═O bonds, this in contrast to reactive U-O• and Pu-O• radical bonds. The computed structures and reaction energies for the three AnO3(NO3)2- support the conclusion that the oxidation states are U(VI), Np(VII), and Pu(VI). The results establish the extreme Np(VII) oxidation state in a gas-phase complex, and demonstrate the inherently greater stability of Np(VII) versus Pu(VII).

We develop an arbitrage pricing theory framework extension to study the pricing of squared returns/volatilities. We analyze the interplay between factors at the return level and those in idiosyncratic variances. We confirm the presence of a common idiosyncratic variance factor, but do not find evidence that this represents a missing risk factor at the (linear) return level. Thereby, we consistently identify idiosyncratic returns. The price of the idiosyncratic variance factor identified by squared returns is small relative to the price of market variance risk. The quadratic pricing kernels induced by our model are in line with standard economic intuition. [ABSTRACT FROM AUTHOR]

Polonium (Po, Z = 84) is a main-block element with poorly known physico-chemical properties. Not much information has been firmly acquired since its discovery by Marie and Pierre Curie in 1898, especially regarding its speciation in aqueous solution and spectroscopy. In this work, we revisit the absorption properties of two complexes, [PoCl5]− and [PoCl6]2−, using quantum mechanical calculations. These complexes have the potential to exhibit a maximum absorption at 418 nm in HCl medium (for concentrations of 0.5 mol L−1 and above). Initially, we examine the electronic spectra of the Po4+ free ion and of its isoelectronic analogue, Bi3+, in the spin–orbit configuration interaction (SOCI) framework. Our findings demonstrate that the SOCI matrix should be dressed with correlated electronic energies and that the quality of the spectra is largely improved by decontracting the reference states at the complete active space plus singles (CAS + S) level. Subsequently, we investigate the absorption properties of the [PoCl5]− and [PoCl6]2− complexes in two stages. Firstly, we perform methodological tests at the MP2/def2-TZVP gas phase geometries, indicating that the decontraction of the reference states can be skipped without compromising the accuracy significantly. Secondly, we study the solution absorption properties by means of single-point calculations performed at the solvated geometries, obtained by an implicit solvation treatment or a combination of implicit and explicit solvation. Our results highlight the importance of saturating the first coordination sphere of the PoIV ion to obtain a qualitatively correct picture. Finally, we conclude that the known-for-decades 418 nm peak could be attributed to a mixture of both the [PoCl5(H2O)]− and [PoCl6]2− complexes. This finding not only aligns with the behaviour of the analogous BiIII ion under similar conditions but also potentially provides an explanation for previous discrepancies in the literature. [ABSTRACT FROM AUTHOR]

Protactinium (Z = 91) is a very rare actinide with peculiar physico-chemical properties. Indeed, although one may naively think that it behaves similarly to either thorium or uranium by its position in the periodic table, it may in fact follow its own rules. Because of the quite small energy gap between its valence shells (in particular the 5f and 6d ones) and also the strong influence of relativistic effects on its properties, it is actually a challenging element for theoretical chemists. In this article, we combine experimental information, chemical arguments and standard first-principle calculations, complemented by implicit and explicit solvation, to revisit the stepwise complexation of aqueous protactinium(V) with sulfate and oxalate dianionic ligands (SO42− and C2O42−, respectively). From a methodological viewpoint, we notably conclude that it is necessary to at least saturate the coordination sphere of protactinium(V) to reach converged equilibrium constant values. Furthermore, in the case of single complexations (i.e. with one sulfate or oxalate ligand bound in the bidentate fashion), we show that it is necessary to maintain the coordination of one hydroxyl group, present in the supposed [PaO(OH)]2+ precursor, to obtain coherent complexation constants. Therefore, we predict that this hydroxyl group is maintained in the formation of 1 : 1 complexes while we confirm that it is withdrawn when coordinating three sulfate or oxalate ligands. Finally, we stress that this work is a first step toward the future use of theoretical predictions to elucidate the enigmatic chemistry of protactinium in solution. [ABSTRACT FROM AUTHOR]

We revisit in-sample asymptotic analysis extensively used in the realized volatility literature. We show that there are gains to be made in estimating current realized volatility from considering realizations in prior periods. The weighting schemes also relate to Kalman-Bucy filters, although our approach is non-Gaussian and model-free. We derive theoretical results for a broad class of processes pertaining to volatility, higher moments, and leverage. The paper also contains a Monte Carlo simulation study showing the benefits of across-sample combinations. [ABSTRACT FROM AUTHOR]

A number of information-theoretic alternatives to GMM have recently been proposed in the literature, For practical use and general interpretation, the main drawback of these alternatives, particularly in the case of conditional moment restrictions, is that they give up the computational and interpretational simplicity of quadratic optimization. The main contribution of this paper is to analyze the informational content of estimating equations within the unified framework of Chisquare distance. Improved inference by control variables, closed form formula for implied probabilities and information-theoretic interpretations of continuously updated GMM are discussed in the two cases of unconditional and conditional moment restrictions. JEL classification: C13; C14; C31 Keywords: Information-based inference; Generalized method of moments; Continuous updating; Empirical likelihood; Control variates

We advocate in this paper the use of a sequential partial indirect inference (SPII) approach, in order to account for calibration practice where dynamic stochastic general equilibrium models (DGSE) are studied only through their ability to reproduce some well-chosen moments. We stress that, despite a lack of statistical formalization, the controversial calibration methodology addresses a genuine issue on the consequences of misspecification in highly nonlinear and dynamic structural macro-models. We argue that a well-driven SPII strategy might be seen as a rigorous calibrationnist approach, that captures both the advantages of this approach (accounting for structural 'a-statistical' ideas) and of the inferential approach (precise appraisal of loss functions and conditions of validity). This methodology should be useful for the empirical assessment of structural models such as those stemming from the real business cycle theory or the asset pricing literature. JEL classification: C52; C51; C15 Keywords: Calibration; Indirect inference; Structural models; Real business cycle; Asset pricing

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jeconom.2005.02.003 Byline: Jean-Marie Dufour (a), Denis Pelletier (b), Eric Renault (c) Abstract: We propose methods for testing hypothesis of non-causality at various horizons, as defined in Dufour and Renault (Econometrica 66, (1998) 1099-1125). We study in detail the case of VAR models and we propose linear methods based on running vector autoregressions at different horizons. While the hypotheses considered are nonlinear, the proposed methods only require linear regression techniques as well as standard Gaussian asymptotic distributional theory. Bootstrap procedures are also considered. For the case of integrated processes, we propose extended regression methods that avoid nonstandard asymptotics. The methods are applied to a VAR model of the US economy. Author Affiliation: (a) CIRANO, CIREQ, and Departement de sciences economiques, Universite de Montreal, C.P. 6128 succursale Centre-ville, Montreal, Que., Canada H3C 3J7 (b) CIRANO, CIREQ, Universite de Montreal, and Department of Economics, North Carolina State University, Campus Box 8110, Raleigh, NC 27695-8110, USA (c) CIRANO, CIREQ, and Departement de sciences economiques, Universite de Montreal, C.P. 6128 succursale Centre-ville, Montreal, Que., Canada H3C 3J7

Investigation of the relative hydrogen-bond (HB) properties of sulfoxides was conducted using data from the Cambridge structural database and theoretically through density functional calculations at the B3LYP/6-311++G(3df,3pd)//B3LYP/6-311++G(3df,3pd) level. It was found that selenoxides are better HB acceptors than sulfoxides.

In this paper, we consider temporal aggregation of volatility models. We introduce semiparametric volatility models, termed square-root stochastic autoregressive volatility (SR-SARV), which are characterized by autoregressive dynamics of the stochastic variance. Our class encompasses the usual GARCH models and various asymmetric GARCH models. Moreover, our stochastic volatility models are characterized by multiperiod conditional moment restrictions in terms of observables. The SR-SARV class is a natural extension of the class of weak GARCH models. This extension has four advantages: (i) we do not assume that fourth moments are finite; (ii) we allow for asymmetries (skewness, leverage effect) that are excluded from weak GARCH models; (iii) we derive conditional moment restrictions and (iv) our framework allows us to study temporal aggregation of IGARCH models. JEL classification: C22; C43; C50; C51 Keywords: GARCH; Stochastic volatility; State-space; SR-SARV; Temporal aggregation; Asset returns; Diffusion processes

This paper assesses the empirical performance of an intertemporal option pricing model with latent variables which generalizes the Black-Scholes and the stochastic volatility formulas. We derive a closed-form formula for an equilibrium model with recursive preferences where the fundamentals follow a Markov switching process. In a simulation experiment based on the model, show that option prices are more informative about preference parameters than stock returns. When we estimate the preference parameters implicit in S&P 500 call option prices given our model, we find quite reasonable values for the coefficient of relative risk aversion and the intertemporal elasticity of substitution. JEL classification: C1; C5; G1 Keywords: Stochastic volatility; Black-Scholes implied volatility; Smile effect; Equilibrium option pricing; Recursive utility

The DNA Methylation Database (MethDB; http://www.methdb.net) is a public database dedicated to DNA methylation. It attempts to store all data about DNA methylation in a common source. MethDB can be searched in different ways, ranging from a simple browse mode to detailed queries for sequence-specific DNA methylation profiles and patterns, total methylation content data or environmental conditions that can influence the methylation state of DNA. Currently, the database contains 2570 values for methylation content and 5278 methylation patterns and profiles for a total of 83 genes or loci. MethDB is an annotated database, and the scientific community is invited to submit their own data (submit@methdb.de). KEY WORDS: * DNA methylation * MethDB * epigenetics * database * cancer * 5-methylcytosine