Stability of a fluid-fluid interface in a biconical pore segment

Pore networks that include biconical pore segments are frequently used to model two-phase flow. In this work, we describe in detail the displacement of a fluid-fluid interface in such a pore segment. We assume sharp edges in the throat, inlet, and outlet of the pore segment to be the limiting cases of round edges, the radii of which vanish. We account for interfacial and lineal tensions that cause nonconstant contact angles. For zero lineal tension, we provide analytical solutions for flow induced by changing infinitesimally slowly either capillary pressure or the volume of one fluid. In diverging and converging cones, the common line among the two fluids and the solid phase slides while it is pinned in the throat, inlet, and outlet. We observe hysteresis within the pore segment, and drainage entry pressures deviate from prior work.     

Primary amido substituted diborane4 compounds and imidodiborate4 anions

Treatment of the diborane(4) compound B(2)(NMe(2))(4) with aniline or 2,6-dimethylaniline results in the primary amido compounds B(2)(NHR)(4)(R = Ph, 2,6-Me(2)C(6)H(3)); subsequent treatment with n-BuLi in toluene in each case affords the first examples of anionic imidodiborates namely Li(4)(thf)(6)B(2)(NPh)(4) and Li(4)(thf)(4)B(2)(N-2,6-Me(2)C(6)H(3))(4); all complexes have been characterised crystallographically.     

Selective, controllable, and reversible aggregation of polystyrene latex microspheres via DNA hybridization

The directed three-dimensional self-assembly of microstructures and nanostructures through the selective hybridization of DNA is the focus of great interest toward the fabrication of new materials. Single-stranded DNA is covalently attached to polystyrene latex microspheres. Single-stranded DNA can function as a sequence-selective Velcro by only bonding to another strand of DNA that has a complementary sequence. The attachment of the DNA increases the charge stabilization of the microspheres and allows controllable aggregation of microspheres by hybridization of complementary DNA sequences. In a mixture of microspheres derivatized with different sequences of DNA, microspheres with complementary DNA form aggregates, while microspheres with noncomplementary sequences remain suspended. The process is reversible by heating, with a characteristic "aggregate dissociation temperature" that is predictably dependent on salt concentration, and the evolution of aggregate dissociation with temperature is observed with optical microscopy.     

Preparation and properties of some α-aza-amino-acid derivatives,their possible use in peptide synthesis

Some derivatives of azaglycine and azaphenylalanine are described. Esters of acetyl- and benzoyl-aza-amino-acids rapidly cyclise to stable oxadiazolones and it is concluded that similar derivatives would be unsuitable for aza-peptide synthesis. t-Butyloxycarbonyl-azaglycine azide was too unreactive for use in peptide synthesis. Benzoyl-azaglycylphenylalanine ethyl ester and acetyl-azaphenylalanylphenylalanine ethyl ester were prepared by coupling benzoyl hydrazide and N-acetyl-N'-benzylhydrazide respectively with 2,4-dinitrophenyloxycarbonyl-phenylalanine ethyl ester.     

X-ray magnetic circular dichroism of Pseudomonas aeruginosa nickel(II) azurin

We show that X-ray magnetic circular dichroism (XMCD) can be employed to probe the oxidation states and other electronic structural features of nickel active sites in proteins. As a calibration standard, we have measured XMCD and X-ray absorption (XAS) spectra for the nickel(II) derivative of Pseudomonas aeruginosa azurin (NiAz). Our analysis of these spectra confirms that the electronic ground state of NiAz is high-spin (S = 1); we also find that the L(3)-centroid energy is 853.1(1) eV, the branching ratio is 0.722(4), and the magnetic moment is 1.9(4) mu(B). Density functional theory (DFT) calculations on model NiAz structures establish that orbitals 3d(x2-y2) and 3d(z2) are the two valence holes in the high-spin Ni(II) ground state, and in accord with the experimentally determined orbital magnetic moment, the DFT results also demonstrate that both holes are highly delocalized, with 3d(x2-y2) having much greater ligand character.     

Inner-sphere electron-transfer reorganization energies of zinc porphyrins

Inner-sphere electron-transfer reorganization energies of Zn(protoporphyrin IX) and Zn(octaethylporphyrin) are determined from band-shape analyses of the first ionization obtained by gas-phase valence photoelectron spectroscopy. The experimentally determined total inner-sphere reorganization energies for self-exchange (120-140 meV) indicate that structural changes upon oxidation are largely confined to the porphyrin ring, and substituents on the ring or solvent and other environmental factors make smaller contributions. Computational estimates by different models vary over a wide range and are sensitive to numerical precision factors for these low reorganization energies. Of current computational models that are widely available and practical for molecules of this size, functionals that contain a mixture of Hartree-Fock exchange and DFT exchange-correlation appear to be the most applicable.     

Mixed-metal cluster chemistry. 26 . Proclivity for “all-terminal” or “plane-of-bridging-carbonyls” ligand disposition in tungsten-triiridium clusters

Reaction of WH(CO)₃(η-C₅Me₅) with IrCl(CO)₂(4-H₂NC₆H₄Me) affords WIr₃(μ-CO)₃(CO)₈(η-C₅Me₅) in low yield. A structural study reveals a WIr₂-centred plane of bridging carbonyls, in contrast to the crystal structure of WIr₃(CO)₁₁(η-C₅H₅) (all-terminal carbonyl distribution). DFT calculations reveal an increasing proclivity to adopt an all-terminal CO disposition for clusters MIr₃(CO)₁₁(η-C₅H₅) in the gas phase on proceeding from M=Cr to Mo and then W, consistent with structural studies in the solid state for which the tungsten-containing cluster is the only all-terminal example. Increasing electron donation from the ligands in the tungsten system (either from phosphine substitution or cyclopentadienyl permethylation) suffices to impose a plane of bridging carbonyls in the ground state structure. ¹³C NMR fluxionality studies reveal that CO exchange mechanism(s) for WIr₃(CO)₁₁(η-C₅H₅) and the related tetrahedral cluster W₂Ir₂(CO)₁₀(η-C₅H₅)₂ are very fast and involve all carbonyls on the clusters. DFT calculations on MIr₃(CO)₁₁(η-C₅H₅) (M=Cr, Mo) substantiate a ‘merry-go-round’ mechanism for carbonyl scrambling in these systems, a result which is consistent with the scrambling behaviour seen in the NMR fluxionality studies on the W-containing congener.     

Synthesis, structure, and kinetics and stereochemistry of base-catalyzed hydrolysis of meso- and rac-[Co2(tmpdtne)Cl2]4+, bis(pentaamine) complexes devoid of deprotonatable NH centers

The bis(pentadentate) ligand tmpdtne binds two Co(II) centers, and the entity is readily oxidized to the dicobalt(III) derivative [Co(2)(tmpdtne)Cl(2)](4+) which has been separated into two isomeric forms. NMR studies establish these as meso and rac isomers arising from the different or same absolute configurations for the asym configuration about each Co(III) center. Each dinuclear ion base hydrolyses to the dihydroxo derivative [Co(2)(tmpdtne)(OH)(2)](4+) with retained asym configurations about each metal ion and also retained rac or meso configurations. The kinetics for the stepwise loss of the two Cl(-) ligands is uniphasic, and data are presented to show that the loss of the first chloride is rate determining and is followed by very rapid intramolecular and loss of the second Cl(-) via a hydroxo-bridged species to yield the observed dihydroxo derivative. Meso and rac forms of the latter have been crystallized. The X-ray crystal structure of the rac-dihydroxo complex is reported, and it establishes the configurations of all the complexes reported. The (1)H NMR spectra for the hydroxo ions show very high field Co-OH resonances (ca. delta-0.5 ppm) not observed previously for such ions, and this result is discussed in the context of published (1)H NMR data for bridged Co-OH-Co species. The base hydrolysis kinetics for the dichloro ions are first order in [OH(-)], and deprotonation at an alpha-CH(2) center (alpha to a pyridyl) is identified as the source of the catalysis, since there is no NH center available for deprotonation on the ligand. These data further support the new pseudoaminate base hydrolysis mechanism first reported in 2003. The values of k(OH) for the second-order base-catalyzed reaction are ca. 4.0 M(-1) s(-1) for both the rac and meso isomers, and these results are discussed in terms of the increased acidities of these 4+ cations compared to their 2+ ion counterparts.     

The role of covariance in the analysis of gamma-ray spectra

When a gamma-ray spectrum contains a number of photopeaks originating from the same nuclide, the calculation of nuclide activity depends not only on the values of, and uncertainties in, the photopeak areas, photopeak efficiencies, gamma-ray emission probabilities and peak area correction factors, but also on the correlations that exist between these quantities. When photopeaks corresponding to a group of nuclides overlap or are unresolved, simultaneous estimation of the activities of all the nuclides present in the group is necessary if the information contained in the spectrum is to be used efficiently — a procedure which can prove important when the only prominent photopeak associated with a nuclide of interest overlaps with the photopeak of another nuclide. Two procedures for activity estimation are described: both procedures take correlations into account; one procedure deals with the special case of activity estimation for a single nuclide, where unresolved photopeaks are absent or neglected; the other procedure deals with simultaneous activity estimation using all the photopeaks associated with an interrelated group of nuclides.