Highly conducting transmembrane pores formed by aromatic oligoamide macrocycles

Oligoamide macrocycles 1d and 1e, which carry membrane-compatible side chains and contain a hydrophilic, noncollapsible cavity, were found to mediate high ion flux across a lipid bilayer, as demonstrated by results from (23)Na NMR and planar bilayer conductance measurements. The measured transmembrane single channel currents are very high, rivaling those typically associated with pore-forming protein toxins. The obtained results have demonstrated the promise of developing large, highly conducting channels based on nanopores formed by oligoamide macrocycles.     

Cd(II) binding by particulate low-rank coals in aqueous media: sorption characteristics and NICA-Donnan models

An experimental investigation of Cd(II) sorption onto two Australian coals was carried out in 0.1 M NaNO3 at 298.2 K. The initial concentration of Cd(II) was varied from 0.133 to 2.000 mmol/g in a series of batch adsorption experiments with an initial coal concentration of 3.75 g/L of Loy Yang (brown) or of Collie (sub-bituminous) coals in the p[H+] range 2-8. Adsorption edges were typical of metal ion adsorption onto negatively charged organic substrates, starting at p[H+] approximately 3 and increasing with increasing pH. The largest measured Cd(II) uptake capacities from these experiments were of 1.2 mmol/g for Loy Yang and 0.7 mmol/g for Collie coals. This difference is ascribed to the larger concentrations of carboxyl groups in Loy Yang coal (2.78 mmol/g) compared to Collie coal (1.34 mmol/g). An adsorption isotherm for Loy Yang coal at p[H+] 6 was collected up to a surface loading of 1.7 mmol/g of adsorbed Cd(II). These experiments also revealed a release of about 1.5-1.6 protons per adsorbed Cd(II). Zeta potentials of Loy Yang coal suspensions were not affected by Cd(II) adsorption, suggesting that the coal particles efficiently neutralize the charge of Cd(II). Collie coal, on the other hand, exhibited a zeta potential increase that may indicate a modification of the surface potentials of the coal particles. Cd(II) uptake data obtained from both batch experiments and proton balance data have been combined with p[H+] stat data for the same experimentally covered Cd(II)/coal ratios to model adsorption using the NICA-Donnan model. The modeling results suggest that both coals possess identical affinities and reaction stoichiometries. Loy Yang coal, however, possessed a narrower distribution of affinities.     

Simulation of organic monolayers as templates for the nucleation of calcite crystals

Living organisms can control the size, shape, and structure of minerals. Attempts to reproduce this biological control in the laboratory often use Langmuir monolayers of long-chain carboxylic acids. We use large-scale molecular dynamics simulations to calculate the interfacial energies of calcite crystals grown on stearic (octadecanoic) acid monolayers. In light of these simulations we discuss the argument that the orientation of the growing mineral is controlled by the organic substrate acting as a template which the mineral must fit in order to grow.     

Mapping the OH + CO-->HOCO reaction pathway through IR spectroscopy of the OH-CO reactant complex

A hydrogen-bonded complex composed of the OH and CO reactants has been identified along the OH + CO-->HOCO reaction pathway. IR action spectroscopy in the OH overtone region has been used to examine the vibrational modes of the linear OH-CO complex, including intermolecular bending modes that probe portions of the reaction path leading to HOCO. The spectroscopic measurements have accessed highly excited intermolecular levels, with energies up to 250 cm-1 above the zero-point level, which lie in close proximity to the transition state for reaction. The OH-CO binding energy, D0 < or = 430 cm-1, has also been established from the quantum state distribution of the OH fragments following vibrational predissociation of the OH-CO complex. Complementary electronic structure calculations have been performed to characterize the OH-CO and OH-OC complexes, the transition state for HOCO formation, and the direct reaction path that connects the experimentally observed OH-CO complex to the HOCO intermediate.     

Structural consequences of the one-electron reduction of d4 [Mo(CO)2(eta-PhC[triple bond]CPh)Tp']+ and the electronic structure of the d5 radicals [M(CO)L(eta-MeC[triple bond]CMe)Tp'] {L = CO and P(OCH2)3CEt}

Reduction of [M(CO)2(eta-RC[triple bond]CR')Tp']X {Tp' = hydrotris(3,5-dimethylpyrazolyl)borate, M = Mo, X = [PF6]-, R = R' = Ph, C6H4OMe-4 or Me; R = Ph, R' = H; M = W, X = [BF4]-, R = R' = Ph or Me; R = Ph, R' = H} with [Co(eta-C5H5)2] gave paramagnetic [M(CO)2(eta-RC[triple bond]CR')Tp'], characterised by IR and ESR spectroscopy. X-Ray structural studies on the redox pair [Mo(CO)2(eta-PhC[triple bond]CPh)Tp'] and [Mo(CO)2(eta-PhC[triple bond]CPh)Tp'][PF6] showed that oxidation is accompanied by a lengthening of the C[triple bond]C bond and shortening of the Mo-C(alkyne) bonds, consistent with removal of an electron from an orbital antibonding with respect to the Mo-alkyne bond, and with conversion of the alkyne from a three- to a four-electron donor. Reduction of [Mo(CO)(NCMe)(eta-MeC[triple bond]CMe)Tp'][PF6] with [Co(eta-C5H5)2] in CH2Cl2 gives [MoCl(CO)(eta-MeC[triple bond]CMe)Tp'], via nitrile substitution in [Mo(CO)(NCMe)(eta-MeC[triple bond]CMe)Tp'], whereas a similar reaction with [M(CO){P(OCH2)3CEt}(eta-MeC[triple bond]CMe)Tp']+ (M = Mo or W) gives the phosphite-containing radicals [M(CO){P(OCH2)3CEt}(eta-MeC[triple bond]CMe)Tp']. ESR spectroscopic studies and DFT calculations on [M(CO)L(eta-MeC[triple bond]CMe)Tp'] {M = Mo or W, L = CO or P(OCH2)3CEt} show the SOMO of the neutral d5 species (the LUMO of the d4 cations) to be largely d(yz) in character although much more delocalised in the W complexes. Non-coincidence effects between the g and metal hyperfine matrices in the Mo spectra indicate hybridisation of the metal d-orbitals in the SOMO, consistent with a rotation of the coordinated alkyne about the M-C2 axis.     

On the combination reactions of hydrogen atoms with resonance-stabilized hydrocarbon radicals

Procedures for accurately predicting the kinetics of H atom associations with resonance stabilized hydrocarbon radicals are described and applied to a series of reactions. The approach is based on direct CASPT2/cc-pvdz evaluations of the orientation dependent interaction energies within variable reaction coordinate transition state theory. One-dimensional corrections to the interaction energies are estimated from a CASPT2/aug-cc-pvdz minimum energy path (MEP) on the specific reaction of interest and a CASPT2/aug-cc-pvtz MEP for the H + CH3 reaction. A dynamical correction factor of 0.9 is also applied. For the H + propargyl, allyl, cyclopentadienyl, and benzyl reactions, where the experimental values appear to be quite well determined, theory and experiment agree to within their error bars. Predictions are also made for the combinations with triplet propargylene, CH2CCCH, CH3CCCH2, CH2CHCCH2, CH3CHCCH, cyclic-C4H5, CH2CCCCH, and CHCCHCCH.     

Orthomodularity of Decompositions in a Categorical Setting

We provide a method to construct a type of orthomodular structure known as an orthoalgebra from the direct product decompositions of an object in a category that has finite products and whose ternary product diagrams give rise to certain pushouts. This generalizes a method to construct an orthomodular poset from the direct product decompositions of familiar mathematical structures such as non-empty sets, groups, and topological spaces, as well as a method to construct an orthomodular poset from the complementary pairs of elements of a bounded modular lattice. Mathematics Subject Classifications (2000): 06C15, 81P10, 03G12, 18A30     

Differential Many‐Body Cooperativity in Electronic Spectra of Oligonuclear Transition‐Metal Complexes

In computational chemistry, non‐additive and cooperative effects can be defined in terms of a (differential) many‐body expansion of the energy or any other physical property of the molecular system of interest. One‐body terms describe energies or properties of the subsystems, two‐body terms describe non‐additive but pairwise contributions and three‐body as well as higher‐order terms can be interpreted as a measure for cooperativity. In the present article, this concept is applied to the analysis of ultraviolet/visible (UV/Vis) spectra of homotrinuclear transition‐metal complexes by means of a many‐body expansion of the change in the spectrum induced by replacing each of the three transition‐metal ions by another transition‐metal ion to yield a different homotrinuclear transition‐metal complex. Computed spectra for the triangulo‐complexes [M₃{Si(mt^Me)₃}₂] (M=Pd/Pt, mt^Me=methimazole) and tritopic triphenylene‐based N‐heterocyclic carbene Rh/Ir complexes illustrate the concept, showing large and small differential three‐body cooperativity, respectively.