Homoleptic pnictogen-chalcogen coordination complexes

The synthesis and structural characterization of dicationic selenium and tellurium analogues of the carbodiphosphorane and triphosphenium families of compounds are reported. These complexes, [Ch(dppe)][OTf](2) [Ch = Se, Te; dppe = 1,2-bis(diphenylphosphino)ethane; OTf = trifluoromethanesulfonate], are formed using [Ch](2+) reagents via a ligand-exchange protocol and represent extremely rare examples of homoleptic pnictogen → chalcogen coordination complexes. The corresponding arsenic compounds were also prepared, [Ch(dpAse)][OTf](2) [Ch = Se, Te; dpAse = 1,2-bis(diphenylarsino)ethane], exhibiting the first instance of an arsenic → chalcogen dative bond. The electronic structures of these unique compounds were determined and compared to previously reported chalcogen dications.     

The reactivity of air-stable pyridine- and pyrimidine-containing diarylamine antioxidants

We recently reported a preliminary account of our efforts to develop novel diarylamine radical-trapping antioxidants (Hanthorn et al. J. Am. Chem. Soc.2012, 134, 8306-8309), wherein we demonstrated that the incorporation of ring nitrogens into diphenylamines affords compounds that display a compromise between H-atom transfer reactivity to peroxyl radicals and stability to one-electron oxidation. Herein, we report the results of thermochemical and kinetic experiments on an expanded set of diarylamines (see the accompanying paper, DOI: 10.1021/jo301013c ), which provide a more complete picture of the structure-reactivity relationships of these compounds as antioxidants. Nitrogen incoporation into a series of alkyl-, alkoxyl-, and dialkylamino-substituted diphenylamines raises their oxidation potentials systematically with the number of nitrogen atoms, resulting in overall increases of 0.3-0.5 V on going from the diphenylamines to the dipyrimidylamines. At the same time, the effect of nitrogen incorporation on their reactivity toward peroxyl radicals was comparatively small (a decrease of only 6-fold at most), which is also reflected in their N-H bond dissociation enthalpies. Rate constants for reactions of dialkylamino-substituted diarylamines with peroxyl radicals were found to be >10(7) M(-1) s(-1), which correspond to the pre-exponential factors that we obtained for a representative trio of compounds (log A ～ 7), indicating that the activation energies (E(a)) are negligible for these reactions. Comparison of our thermokinetic data for reactions of the diarylamines with peroxyl radicals with literature data for reactions of phenols with peroxyl radicals clearly reveals that diarylamines have higher inherent reactivities, which can be explained by a proton-coupled electron-transfer mechanism for these reactions, which is supported by theoretical calculations. A similar comparison of the reactivities of diarylamines and phenols with alkyl radicals, which must take place by a H-atom transfer mechanism, clearly reveals the importance of the polar effect in the reactions of the more acidic phenols, which makes phenols comparatively more reactive.     

A therapeutically viable photo-activated manganese-based CO-releasing molecule (photo-CO-RM)

A new class of photochemically-activated CO-releasing molecule (photo-CO-RM), based on a Mn(CO)(4)(C^N) system, is reported in this study. Three CO molecules are released per CO-RM molecule. Complex 3 is a fast releaser, thermally stable in the dark and a viable therapeutic agent.     

Theoretical exploration of uranyl complexes of a designed polypyrrolic macrocycle: structure/property effects of hinge size on Pacman-shaped complexes

A polypyrrolic macrocycle with naphthalenyl linkers between the N(4)-donor compartments (L(2)) was designed theoretically according to its experimentally-known analogues with phenylenyl (L(1)) and anthracenyl (L(3)) linkers. The uranyl and bis(uranyl) complexes formed by this L(2) ligand have been examined using scalar-relativistic density functional theory. The calculated structural properties of the mononuclear uranyl-L(2) complexes are similar to those of their L(1) counterparts. The binuclear L(2) complexes exhibit a butterfly-like bis(uranyl) core in which a linear uranyl is coordinated in a side-by-side fashion to a cis-uranyl unit. The calculated U[double bond, length as m-dash]O bond orders in the uranyl-L(2) complexes indicate partial triple bonding character with the only exceptions being the U-O(endo) bonds in the U(2)O(4) core of the butterfly-shaped binuclear complexes. Overall, the bond orders agree with the trends in the calculated U[double bond, length as m-dash]O stretching vibrational frequencies. Regarding the bis(uranyl) L(1), L(2) and L(3) complexes, the phenylenyl-hinge L(1) complexes adopt a butterfly-like and a T-shaped isomer in the oxidation state of U(vi), but only a butterfly-like one in the U(v), which differs from that of the naphthalenyl-hinge L(2) complexes as well as the lateral twisted structure of the anthracenyl-hinge L(3) complexes. The intramolecular cation-cation interactions are found in the L(1) and L(2) complexes, but are absent in the L(3) complexes. Finally, using model uranyl transfer reactions from the L(1) complexes, the formation of the mononuclear L(2) complexes is calculated to be a slightly endothermic process. This suggests that it should be possible to synthesize the L(2) complexes using similar protocols as employed for the L(1) complexes.     

Stochastic sensing of IP(3) has far-reaching consequences

Hagan Bayley's group at Texas A&M University has devised a stochastic sensing methodology for the quantitation of the second messenger inositol 1,4,5-trisphosphate. The unique sensing scheme is very selective and has the potential to measure cytosolic concentrations of IP(3).     

ChemInform Abstract: Synthesis of [(SnSe)1.15]m(TaSe2)n Ferecrystals: Structurally Tunable Metallic Compounds.

The title ferecrystals (fere: Latin, almost) with 1 ≤ n,m ≤ 6 and n and m varied independently are prepared by physical vapor deposition of the elements followed by annealing at 400 °C for 30 min.     

Surface nitridation induced high electrochemical performance of Li4Ti5O12 using urea as a nitrogen source

Surface nitridation of the Li₄Ti₅O₁₂ particles was carried out by thermal treatment with urea as the nitrogen source in a controllable manner. The titanium nitride (TiN) was formed in the well-dispersed zones on the surface of the Li₄Ti₅O₁₂ particles, depending on the coverage of the nitride. The surface TiN formed led to a great improvement of the conductivity of the oxide. The extent of the surface nitridation exhibited a large effect on electrochemical behaviors of the Li₄Ti₅O₁₂ particles, with the Li₄Ti₅O₁₂/TiN composite (prepared using 6 % urea) providing the best initial capacity and rate capability. Thus, the electrochemical performance of the Li₄Ti₅O₁₂ particles can be achieved by optimizing surface nitridation of the oxide. The chemically inert TiN occupied the surface sites of the Li₄Ti₅O₁₂ particles which may have prevented the electrolyte from decomposition and stabilized the surface structure of the Li₄Ti₅O₁₂ particles, endowing the oxide with excellent cycleability     

Nonlinear Bound States on Weakly Homogeneous Spaces

We prove the existence of ground state solutions for a class of nonlinear elliptic equations, arising in the production of standing wave solutions to an associated family of nonlinear Schrödinger equations. We examine two constrained minimization problems, which give rise to such solutions. One yields what we call F _λ-minimizers, the other energy minimizers. We produce such ground state solutions on a class of Riemannian manifolds called weakly homogeneous spaces, and establish smoothness, positivity, and decay properties. We also identify classes of Riemannian manifolds with no such minimizers, and classes for which essential uniqueness of positive solutions to the associated elliptic PDE fails.     

Pullbacks of Arithmetical Rings

We give necessary and sufficient conditions that the pullback of a conductor square be a chain ring (i.e., a ring whose ideals are totally ordered by inclusion). We also give necessary and sufficient conditions that the pullback of a conductor square be an arithmetical ring (i.e., a ring which is locally a chain ring at every maximal ideal). For any integral domain D with field of fractions K, we characterize all Prüfer domains R between D[X] and K[X] such that the conductor C of K[X] into R is nonzero. As an application, we show that for n ≥ 2, such a ring R has the n-generator property (every finitely generated ideal can be generated by n elements) if and only if R/C has the same property.