Rigid NON- and NSN-ligand complexes of tetravalent and trivalent uranium: comparison of U-OAr2 and U-SAr2 bonding

A rigid NSN-donor proligand, 4,5-bis(2,6-diisopropylanilino)-2,7-di-tert-butyl-9,9-dimethylthioxanthene (H(2)[TXA(2)], 1) was prepared by palladium-catalyzed coupling of 2,6-diisopropylaniline with 4,5-dibromo-2,7-di-tert-butyl-9,9-dimethylthioxanthene. Deprotonation of 1 using (n)BuLi provided Li(2)(DME)(2)[TXA(2)] (2), and subsequent reaction with UCl(4) afforded [Li(DME)(3)][(TXA(2))UCl(3)] (4). The analogous NON-donor ligated complex [(XA(2))UCl(3)K(DME)(3)] [3; XA(2) = 4,5-bis(2,6-diisopropylanilino)-2,7-di-tert-butyl-9,9-dimethylxanthene] was prepared by the reaction of K(2)(DME)(x)[XA(2)] with UCl(4). A cyclic voltammogram (CV) of 3 in THF/[NBu(4)][B(C(6)F(5))(4)] at 200 mV s(-1) showed an irreversible reduction to uranium(III) at E(pc) = -2.46 V versus FeCp(2)(0/+1), followed by a product wave at E(1/2) = -1.83 V. Complex 4 also underwent irreversible reduction to uranium(iii) [E(pc) = -2.56 V], resulting in an irreversible product peak at E(pa) = -1.83 V. One-electron reduction of complexes 3 and 4 using K(naphthalenide) under an argon atmosphere in DME yielded 6-coordinate [(XA(2))UCl(DME)] (5) and the thermally unstable 7-coordinate [(TXA(2))U(DME)Cl(2)Li(DME)(2)] (6), respectively. The U-S distances in 4 and 6 are uncommonly short, the C-S-U angles are unusually acute, and the thioxanthene backbone of the TXA(2) ligand is significantly bent. By contrast, the xanthene backbone in XA(2) complexes 3 and 5 is planar. However, κ(3)-coordination and an approximately meridional arrangement of the ancillary ligand donor atoms is maintained in all complexes. DFT and Atoms in Molecules (AIM) calculations were carried out on 3, 4, 5, 6, [(XA(2))UCl(3)](-) (3B), [(TXA(2))UCl(2)(DME)](-) (6B) and [(TXA(2))UCl(DME)] (6C) to probe the extent of covalency in U-SAr(2) bonding relative to U-OAr(2) bonding.     

Surface-initiated synthesis of poly(3-methylthiophene) from indium tin oxide and its electrochemical properties

Poly(3-methylthiophene) (P3MT) was synthesized directly from indium tin oxide (ITO) electrodes modified with a phosphonic acid initiator, using Kumada catalyst transfer polymerization (KCTP). This work represents the first time that polymer thickness has been controlled in a surface initiated KCTP reaction, highlighting the utility of KCTP in achieving controlled polymerizations. Polymer film thicknesses were regulated by the variation of the solution monomer concentration and ranged from 30 to 265 nm. Electrochemical oxidative doping of these films was used to manipulate their near surface composition and effective work function. Doped states of the P3MT film are maintained even after the sample is removed from solution and potential control confirming the robustness of the films. Such materials with controllable thicknesses and electronic properties have the potential to be useful as interlayer materials for organic electronic applications.     

Single-ion heat capacities, C(p)(298)ion, of solids: with a novel route to heat-capacity estimation of complex anions

Single-ion heat capacities, C(p)(298)(ion), are additive values for the estimation of room-temperature (298 K) heat capacities of ionic solids. They may be used for inferring the heat capacities of ionic solids for which values are unavailable and for checking reported values, thus complementing our independent method of estimation from formula unit volumes (termed volume-based thermodynamics, VBT). Analysis of the reported heat-capacity data presented here provides a new self-consistent set of heat capacities for both cations and anions that is compatible (and thus may be combined) with an extensive set developed by Spencer. The addition of a large range of silicate species permits the estimation of the heat capacities of many silicate minerals. The single-ion heat capacities of individual silicate anions are observed to be strictly proportional to the total number of atoms (Si plus O), n, contained within the silicate anion complex itself (e.g., for the anion Si(2)O(7)(2-), n = 9, for SiO(4)(2-), n = 5), C(p)(silicate anion)/J K(-1) mol(-1) = 13.8n, in a new rule that is an extension of the Neumann-Kopp relationship. The same linear relationship applies to other homologous anion series (for example, oxygenated heavy-metal anion complexes such as niobates, bismuthates, and tantalates), although with a different proportionality constant. A similar proportionality, C(p)(complex anion)/J K(-1) mol(-1) ≈ 17.5n, which may be regarded as a convenient "rule of thumb", also applies, although less strictly, to complex anions in general. The proportionality constants reflect the rigidity of the complex anion, being always less than the Dulong-Petit value of 25 J K(-1) mol(-1). An emergent feature of our VBT and single-ion approaches to an estimation of the thermodynamic properties is the identification of anomalies in measured values, as is illustrated in this paper.     

Gut microbiota, diet, and heart disease

Modulation of the gut microbiota is an area of growing interest, particularly for its link to improving and maintaining the systemic health of the host. It has been suggested to have potential to reduce risk factors associated with chronic diseases, such as elevated cholesterol levels in coronary heart disease (CHD). Diets of our evolutionary ancestors were largely based on plant foods, high in dietary fiber and fermentable substrate, and our gut microbiota has evolved against a background of such diets. Therapeutic diets that mimic plant-based diets from the early phases of human evolution may result in drug-like cholesterol reductions. In contrast, typical Western diets low in dietary fiber and fermentable substrate, and high in saturated and trans fatty acids, are likely contributors to the increased need for pharmacological agents for cholesterol reduction. The gut microbiota of those consuming a Western diet are likely underutilized and depleted of metabolic fuels, resulting in a less than optimal gut microbial profile. As a result, this diet is mismatched to our archaic gut microbiota and, therefore, to our genome, which has changed relatively little since humans first appeared. While the exact mechanism by which the gut microbiota may modulate cholesterol levels still remains uncertain, end products of bacterial fermentation, particularly the short chain fatty acids (i.e., propionate), have been suggested as potential candidates. While more research is required to clarify the potential link between gut microbiota and CHD risk reduction, consuming a therapeutic diet rich in plant foods, dietary fiber, and fermentable substrate would be a useful strategy for improving systemic health, possibly by altering the gut microbiota.     

Determination of crack spacing and penetration due to shrinkage of a solidifying layer

A method based on energy minimisation is used to determine the spacing and penetration of a regular array of cracks in a layer of material whose thickness is increasing as it solidifies from a liquid. After solidification, the slab shrinks and subsequently cracks due to internal stresses. A simple Stefan solidification model is used to determine the thickness of the slab as time progresses as well as the temperature profile in the slab. The key feature of the results is that a minimum crack spacing occurs early in the solidification process and this minimum defines a basic spacing for the crack array. The minimum spacing occurs for a range of constraints (boundary conditions) and thermal profiles in the material, indicating the robustness of the phenomenon. Cracks propagating with the unique minimum spacing are subject to a period doubling instability that acts to coarsen the crack pattern, which brings the crack spacing close to the minimum energy state for later time. Good numerical comparison between the crack spacings predicted by energy minimisation and those observed in basalt columns is demonstrated.     

Fusion around the barrier for 7Li+12C

Fusion cross-sections for the ⁷Li + ¹²C reaction have been measured at energies above the Coulomb barrier by the direct detection of evaporation residues. The heavy evaporation residues with energies below 3 MeV could not be separated out from the α-particles in the spectrum and hence their contribution was estimated using statistical model calculations. The present work indicates that suppression of fusion cross-sections due to the breakup of ⁷Li may not be significant for ⁷Li + ¹²C reaction at energies around the barrier.     

K1±(892) Production in π−N interactions at 200 GeV/c

K^1±(892) production is studied in the reaction π^?N → K_S⁰K_S⁰ + X where X includes up to five observed charged particles. An excess of K^1? over K¹⁺ is observed for Feynman-x > 0.1. The ratio of K¹⁺ to K^1? decreases with x as predicted by QCD counting rules. K_S⁰ and K¹ production are compared to recent D and D¹ data from other experiments.     

Correlation Analysis of the Alternating Step Generator

The alternating step generator is a well-known keystream generator consisting of two stop/go clocked LFSRs, LFSR₁ and LFSR₂, whose clocks are controlled by another LFSR, LFSR₃, which is clocked regularly. A probabilistic analysis of this generator is conducted which shows that the posterior probabilites of individual bits of the first derivatives of the regularly clocked LFSR₁ and LFSR₂ sequences, when conditioned on a given segment of the first derivative of the keystream sequence, can be computed efficiently in a number of probabilistic models of interest. The expected values of these probabilities, for a random keystream sequence, are derived by an approximate theoretical analysis and are also verified by systematic computer experiments. It is pointed out that these posterior probabilities can be enhanced in a resynchronization scenario and thus used for a low-complexity fast correlation attack on the two LFSRs. More generally, it is argued that even without resynchronization these probabilities may be significantly different from one half for fast correlation attacks based on iterative decoding algorithms to be successful, although with incresead complexity. A related method for computing the posterior probabilities of individual bits of the LFSR₃ sequence, when conditioned on both the keystream sequence and the LFSR₁ and LFSR₂ sequences, is also developed. As these posterior probabilities are much more different from one half, they can be used for a low-complexity fast correlation attack on LFSR₃, provided that the initial states of LFSR₁ and LFSR₂ are previously reconstructed.     

Vector-valued,rational interpolants III

In 1963, Wynn proposed a method for rational interpolation of vector-valued quantities given on a set of distinct interpolation points. He used continued fractions, and generalized inverses for the reciprocals of vector-valued quantities. In this paper, we present an axiomatic approach to vector-valued rational interpolation. Uniquely defined interpolants are constructed for vector-valued data so that the components of the resulting vector-valued rational interpolant share a common denominator polynomial. An explicit determinantal formula is given for the denominator polynomial for the cases of (i) vector-valued rational interpolation on distinct real or complex points and (ii) vector-valued Padé approximation. We derive the connection with theε-algorithm of Wynn and Claessens, and we establish a five-term recurrence relation for the denominator polynomials.