Prediction of vibrational frequencies of UO2(2+) at the CCSD(T) level

Electronic structure calculations at the coupled cluster (CCSD(T)) and density functional theory levels with relativistic effective core potentials and large basis sets were used to predict the isolated uranyl ion frequencies. The effects of anharmonicity and spin-orbit corrections on the harmonic frequencies were calculated. The anharmonic effects are larger than the spin-orbit corrections, but both are small. The anharmonic effects decreased all the frequencies, whereas the spin-orbit corrections increased the stretches and decreased the bend. Overall, these two corrections decreased the harmonic asymmetric stretch frequency by 6 cm-1, the symmetric stretch by 3 cm-1, and the bend by 3 cm-1. The best calculated values for UO22+ for the asymmetric stretch, symmetric stretch, and bend were 1113, 1032, and 174 cm-1, respectively. The separation between the asymmetric and the symmetric stretch band origins was predicted to be 81 cm-1, which is consistent with experimental trends for substituted uranyls in solution and in the solid state. The anharmonic vibrational frequencies of the isoelectronic ThO2 molecule also were calculated and compared to experiment to calibrate the UO22+ results.     

Helical pores self-assembled from homochiral dendritic dipeptides based on L-Tyr and nonpolar alpha-amino acids

The synthesis of dendritic dipeptides (4-3,4-3,5)12G2-CH2-Boc-L-Tyr-X-OMe where X = Gly, L-Val, L-Leu, L-Ile, L-Phe, and L-Pro is reported. Their self-assembly in bulk and in solution and the structural and retrostructural analysis of their periodic assemblies were compared to those of the previously reported and currently reinvestigated dendritic dipeptides with X = L-Ala. All dendritic dipeptides containing as X nonpolar alpha-amino acids self-assemble into helical porous columns. The substituent of X programs the structure of the helical pore and the resulting periodic array, in spite of the fact that its molar mass represents only between 0.05 and 4.77% from the molar mass of the dendritic dipeptide. In addition to the various 2-D columnar lattices, the dendritic dipeptides based on L-Ala, L-Leu, and L-Phe self-organize into 3-D hexagonal columnar crystals while those based on L-Val and L-Ile into an unknown columnar crystal. The principles via which the aliphatic and aromatic substituents of X program the structure of the helical pores indicate synthetic pathways to helical pores with bioinspired functions based on artificial nonpolar alpha-amino acids.     

Cyclic Alkyl Amino Carbene (CAAC) Ruthenium Complexes as Remarkably Active Catalysts for Ethenolysis

An expanded family of ruthenium‐based metathesis catalysts bearing cyclic alkyl amino carbene (CAAC) ligands was prepared. These catalysts exhibited exceptional activity in the ethenolysis of the seed‐oil derivative methyl oleate. In many cases, catalyst turnover numbers (TONs) of more than 100 000 were achieved, at a catalyst loading of only 3 ppm. Remarkably, the most active catalyst system was able to achieve a TON of 340 000, at a catalyst loading of only 1 ppm. This is the first time a series of metathesis catalysts has exhibited such high performance in cross‐metathesis reactions employing ethylene gas, with activities sufficient to render ethenolysis applicable to the industrial‐scale production of linear α‐olefins (LAOs) and other terminal‐olefin products.     

A catalytic, asymmetric formal synthesis of (+)-hamigeran B

A concise asymmetric, formal synthesis of (+)-hamigeran B is reported. A Pd-catalyzed, decarboxylative allylic alkylation, employing a trifluoromethylated derivative of t-BuPHOX, is utilized as the enantioselective step to form the critical quaternary carbon center in excellent yield and enantioselectivity. The product is converted in three steps to a late-stage intermediate previously used in the synthesis of hamigeran B.     

Ni(COD)2/PCy3 catalyzed cross-coupling of aryl and heteroaryl neopentylglycolboronates with aryl and heteroaryl mesylates and sulfamates in THF at room temperature

Reaction conditions for the Ni(COD)(2)/PCy(3) catalyzed cross-coupling of aryl neopentylglycolboronates with aryl mesylates were developed. By using optimized reaction conditions, Ni(COD)(2)/PCy(3) was shown to be a versatile catalyst for the cross-coupling of a diversity of aryl neopentylglycolboronates with aryl and heteroaryl mesylates and sulfamates containing both electron-donating and electron-withdrawing substituents in their para, ortho, and meta positions in THF at room temperature. This Ni-catalyzed cross-coupling of aryl neopentylglycolboronates is also effective for the synthesis of heterobiaryls and biaryls containing electrophilic functionalities sensitive to organolithium and organomagnesium derivatives. In combination with the recently developed Ni-catalyzed neopentylglycolborylation, all Ni-catalyzed routes to functional biaryls and heterobiaryls are now easily accessible.     

Acid dissolution of copper oxides as a method for the activation of Cu(0) wire catalyst for SET‐LRP

Here we reported the acid dissolution of copper oxides as a methodology for the activation of Cu(0) wire used as catalyst in single‐electron transfer living radical polymerization (SET‐LRP). In this method, the oxide layer on the surface of commercial Cu(0) wire was removed by dissolution in a concentrated acid such as nitric acid, glacial acetic acid and hydrochloric acid. SET‐LRP of methyl acrylate catalyzed with Cu(0) wire activated with acids showed comparable k value to that of the nonactivated Cu(0) wire‐catalyzed counterpart. However, the polymerizations catalyzed with activated Cu(0) wire proceeded with no initial induction period, predictable molecular weight evolution with conversion, and narrow molecular weight distribution. Regardless of the activation method, the chain end functionality of α,ω‐di(bromo) poly(methyl acrylate) (PMA) prepared from SET‐LRP initiated with a bifunctional initiator is extremely high, maintaining a 100% chain end functionality at ～90% monomer conversion. The degree of bimolecular termination increased as the polymerization exceeds 92% conversion. However, for binfunctional initiators this small amount of bimolecular termination at high conversion maintains a perfectly bifunctional polymer. Structural analysis by MALDI‐TOF upon thioetherification of α,ω‐di(bromo) PMA with thiophenol and 4‐fluorothiophenol confirmed the high fidelity of bromide chain ends. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Modeling of metamagnetism in metallic-based materials with first-order transitions

During the past decade, the magnetic properties of metallic-based materials with first-order transitions have been extensively studied, motivated in part by the observation of large magnetocaloric effect (MCE) peaks displayed by these materials near room temperature. These large peaks are believed to be the result of the materials' magnetic properties at the metamagnetic region, characterized by (i) the thermal-induced transition from the ferromagnetic state (FM) to the paramagnetic state (PM) near the Curie temperature (T_C) and (ii) the field-induced transition from PM state to FM state above T_C. We developed a phenomenological model that utilizes the materials' mixed-state probability function to model the materials' complex hysteretic and properties at metamagnetic region. The approximate probability functions are obtained from the first and second derivatives of the magnetization curve. The probability functions are used to separate the materials' magnetization into a FM state component and a PM state component. The applicability of the model is demonstrated for a metallic-based metamagnetic material, Gd₅Si₂Ge₂ compound, where the modeled behaviors show remarkable agreement with the experimental data at the metamagnetic region and provide new physical insights in this mixed-state region. Specifically, in the region of metamagnetic transition, the PM state component is non-reversible and is a function of the FM state component.     

Influence of acceptor functionality on charge transfer interactions in mixtures of poly(9-vinylcarbazole) with nitroaromatic compounds

Charge transfer interactions in mixtures of poly(9-vinylcarbazole) with three nitro compounds (4,4′dinitrodibenzyl, ethyl 3,5-dinitrobenzoate and 2,2′,4,4′-tetranitrodibenzyl) were examined.     

Transport Properties of Alkali Fluoride High Temperature Ionic Liquids and Application of Theories of Viscous Flow

The transport properties of several alkali fluoride high temperature ionic liquids(LiF, NaF, KF, RbF and CsF) were studied in a range of 980-1400 K and the temperature dependences of the viscosity and density were interpreted, in agreement with the classical equations characterizing the viscous flow(Arrhenius, Batchinski, Eyring and Frenkel). The experimental results reveal the validity of these equations even at high temperatures, suggesting that no significant structural changes of alkali fluorides occurred in the studied temperature range. Our results clearly demonstrate that the mentioned thermo-physical properties can be used as powerful tools in the further investigations of the ionic interactions governing the alkali fluoride molten salts.