Dual coordination modes of ethylene-linked NP2 ligands in cobalt(II) and nickel(II) iodides

Here we report the syntheses and crystal structures of a series of cobalt(II) and nickel(II) complexes derived from (R)NP2 ligands (where R = OMe(Bz), H(Bz), Br(Bz), Ph) bearing ethylene linkers between a single N and two P donors. The Co(II) complexes generally adopt a tetrahedral configuration of general formula [(NP2)Co(I)(2)], wherein the two phosphorus donors are bound to the metal center but the central N-donor remains unbound. We have found one case of structural isomerism within a single crystal structure. The Co(II) complex derived from (Bz)NP2 displays dual coordination modes: one in the tetrahedral complex [((Bz)NP2)Co(I)(2)]; and the other in a square pyramidal variant, [((Bz)NP2)Co(I)(2)]. In contrast, the Ni(II) complexes adopt a square planar geometry in which the P(Et)N(Et)P donors in the ligand backbone are coordinated to the metal center, resulting in cationic species of formula [((R)NP2)Ni(I)](+) with iodide as counterion. All Ni(II) complexes exhibit sharp (1)H and (31)P spectra in the diamagnetic region. The Co(II) complexes are high-spin (S = 3/2) in the solid state as determined by SQUID measurements from 4 to 300 K. Solution electron paramagnetic resonance (EPR) experiments reveal a high-spin/low-spin Co(II) equilibrium that is dependent on solvent and ligand substituent.     

Electronic structures of Group 9 metallocorroles with axial ammines

The electronic structures of metallocorroles (tpfc)M(NH(3))(2) and (tfc)M(NH(3))(2) (tpfc is the trianion of 5,10,15-(tris)pentafluorophenylcorrole, tfc is the trianion of 5,10,15-trifluorocorrole, and M = Co, Rh, Ir) have been computed using first principles quantum mechanics [B3LYP flavor of Density Functional Theory (DFT) with Poisson-Boltzmann continuum solvation]. The geometry was optimized for both the neutral systems (formal M(III) oxidation state) and the one-electron oxidized systems (formally M(IV)). As expected, the M(III) systems have a closed shell d(6) configuration; for all three metals, the one-electron oxidation was calculated to occur from a ligand-based orbital (highest occupied molecular orbital (HOMO) of B(1) symmetry). The ground state of the formal M(IV) system has M(III)-Cπ character, indicating that the metal remains d(6), with the hole in the corrole π system. As a result the calculated M(IV/III) reduction potentials are quite similar (0.64, 0.67, and 0.56 V vs SCE for M = Ir, Rh and Co, respectively), whereas the differences would have been large for purely metal-based oxidations. Vertically excited states with substantial metal character are well separated from the ground state in one-electron-oxidized cobalt (0.27 eV) and rhodium (0.24 eV) corroles, but become closer in energy in the iridium (0.15 eV) analogues. The exact splittings depend on the chosen functional and basis set combination and vary by ~0.1 eV.     

Nanocelluloses: a new family of nature-based materials

Cellulose fibrils with widths in the nanometer range are nature-based materials with unique and potentially useful features. Most importantly, these novel nanocelluloses open up the strongly expanding fields of sustainable materials and nanocomposites, as well as medical and life-science devices, to the natural polymer cellulose. The nanodimensions of the structural elements result in a high surface area and hence the powerful interaction of these celluloses with surrounding species, such as water, organic and polymeric compounds, nanoparticles, and living cells. This Review assembles the current knowledge on the isolation of microfibrillated cellulose from wood and its application in nanocomposites; the preparation of nanocrystalline cellulose and its use as a reinforcing agent; and the biofabrication of bacterial nanocellulose, as well as its evaluation as a biomaterial for medical implants.     

Electronic spectra of mono-substituted chromates

The electronic spectra of monosubstituted chromate ion derivatives, CrO₃X^-, where X^-=F^-, Cl^-, Br^- and IO₃ ^-, have been measured at liquid helium temperature, employing a variety of sample forms. The observed electronic transitions correlate simply and directly with those of CrO₄ ^2-, the lowest-lying transitions being only very weakly perturbed. Of particular interest is that the lowest excited state ¹ E^a retains the peculiarities of the ¹ T ₁ parent state of CrO₄ ^2-. The sharp line spectrum observed in Cr₂O₇ ^2- between 18 000 and 19 000 cm^-1 is identified as ¹ E^a (¹ T ₁ in T _d) ←¹ A ₁ in a single O₃CrO⁼ chromophore. It is suggested that the observed features of the low-lying absorption bands can be explained by assuming that two spin-triplet states [³ E, ³ A ₂] are located a few hundred wave numbers above the sharp 0-0 line of ¹ E^a ←¹ A ₁.     

The mean squared torque in pure and mixed dense fluids

The mean squared torque on a molecule can be obtained from infra-red or Raman band moments, and provides a direct measure of the strength of the anisotropic intermolecular forces. The expression for the mean squared torque on a molecule of species α in a fluid mixture is given in terms of the intermolecular potential and the angular pair correlation functions. This relation is made tractable by introducing a perturbation expansion in powers of the anisotropic potential strength for the angular pair correlation functions. Monte Carlo calculations of the mean squared torque are presented for a liquid of linear molecules having dipolar, quadrupolar and anisotropic overlap interactions. Comparison of the perturbation expansion to second order with these ‘exact’ results shows good agreement for μ*=μ/(εσ³)^1/2 and Q*=Q/(εσ⁵)^1/2 values less than about 0·5, and for values of the dimensionless overlap constant |δ| less than about 0·2. Finally, experimental values of the mean squared torque for both pure and mixed liquids are compared to the Monte Carlo and to the perturbation theory results.     

Impaired pulmonary blood flow distribution in congestive heart failure assessed using synchrotron radiation microangiography

Synchrotron radiation microangiography is a powerful tool for assessing adverse changes in pulmonary vessel density associated with primary pulmonary hypertension (PH). Congestive heart failure (CHF) leads to a `secondary' onset of PH, yet it is unknown whether secondary PH is also associated with reduced vessel density. This study utilized synchrotron radiation to assess both pulmonary vessel density and endothelial function in a Dahl rat model of CHF with secondary PH. High salt‐fed Dahl salt‐sensitive (Dahl‐S) and salt‐resistant (Dahl‐R) rats were anesthetized and microangiography was performed to assess the pulmonary vessel density and vascular responses to (i) sodium nitroprusside (5.0 µg kg^?1 min^?1), (ii) acetylcholine (3.0 µg kg^?1 min^?1) and (iii) ET‐1_A receptor blockade, BQ‐123 (1 mg kg^?1). Dahl‐S rats developed CHF and secondary PH as evident by endothelial dysfunction, impaired vasodilatory responses to acetylcholine, enhanced vasodilatory responses to BQ‐123 and extensive pulmonary vascular remodeling. Consequently, the pulmonary vessel density was adversely reduced. Interestingly, the etiology of secondary PH manifests with structural and functional changes that are comparable with that previously reported for primary PH. One important discrepancy, however, is that ET‐1 modulation of pulmonary vessels is most striking in vessels with a diameter range of 100–200 µm in secondary PH, in contrast to a range of 200–300 µm in primary PH. Such discrepancies should be considered in future studies investigating primary and secondary forms of PH.     

The influence of a zirconia environment on the melt processing of YBa2Cu3O7−x

In the self-flux growth of YBa₂Cu₃O_7−x single crystals in zirconia crucibles a large proportion of the boule consists of secondary phases, from which the YBa₂Cu₃O_7−x crystals are then mechanically separated. The same secondary phases also occur in thick films melt processed on zirconia substrates. The nature and relative proportions of the phases depend on the starting composition, the use of crucible or substrate and growth conditions. However, there are a number of common features, which are the subject of this paper. Scanning electron microscopy EDX analysis of crystal growth boules and thick films are reported. Considerable amounts of Zr are found in the flux phases, even at relatively large distances from the crucible or substrate interface. However, large Zr-doping of the 123 phases does not occur and the superconducting properties are not adversely affected by the presence of these small amounts of Zr.     

Sparse anti-magic squares and vertex-magic labelings of bipartite graphs

A sparse anti-magic square is an n×n array whose non-zero entries are the consecutive integers 1,…,m for some m?n² and whose row-sums and column-sums form a set of consecutive integers. We derive some basic properties of these arrays and provide constructions for several infinite families of them. Our main interest in these arrays is their application to constructing vertex-magic labelings for bipartite graphs.