Generation of AuPd22/Au2Pd21 analogues of the high-nuclearity Pd23(CO)20(PEt3)10 cluster containing 19-atom centered hexacapped-cuboctahedral (nu 2-octahedral) metal fragment: structural-to-synthesis approach concerning formation of Au2Pd21(CO)20(PEt3)10

Reactions of Pd(PEt(3))(2)Cl(2) and Au(PPh(3))Cl in DMF with NaOH under CO atmosphere gave rise to the unique capped three-shell homopalladium Pd(145)(CO)(x)(PEt(3))(30)(x approximately 60) and two neutral Au-Pd clusters: Au(2)Pd(21)(CO)(20)(PEt(3))(10) (1) and Au(2)Pd(41)(CO)(27)(PEt(3))(15)(following article). Similar reactions with Pd(PMe(3))(2)Cl(2) being used in place of Pd(PEt(3))(2)Cl(2) afforded Au(2)Pd(21)(CO)(20)(PMe(3))(10) (2), the trimethylphosphine analogue of, and the electronically equivalent [AuPd(22)(CO)(20)(PPh(3))(4)(PMe(3))(6)](-) monoanion (3) as the [PPh(4)](+) salt. Each of these three air-sensitive 23-atom heterometallic Au-Pd clusters was obtained in low yields (7-25%); however, their geometrical similarities with the known cuboctahedral-based homopalladium Pd(23)(CO)(20)(PEt(3))(10) (4), recently obtained in good yields from Pd(10)(CO)(12)(PEt(3))(6), suggested an alternative preparative route for obtaining. This "structure-to-synthesis" approach afforded 1 in 60-70% yields from reactions of Pd(10)(CO)(12)(PEt(3))(6) and Au(PPh(3))Cl in DMF with NaOH under N(2) atmosphere. Both the compositions and atomic arrangements for 1, 2 and 3 were unambiguously established from low-temperature single-crystal CCD X-ray crystallographic determinations in accordance with their nearly identical IR carbonyl frequencies. Cluster 1 was also characterized by (31)P[(1)H] NMR, cyclic voltammetry (CV) and elemental analysis. The virtually identical Au(2)Pd(21) core-architectures of 1 and 2 closely resemble that of 4, which consists of a centered hexa(square capped)-cuboctahedral Pd(19) fragment of pseudo-O(h) symmetry that alternatively may be viewed as a centered Pd(19)nu(2)-octahedron (where nu(n) designates (n + 1) equally spaced atoms along each edge). [AuPd(22)(CO)(20)(PPh(3))(4)(PMe(3))(6)](-) (3) in the crystalline state ([PPh(4)](+) salt) consists of two crystallographically independent monoanions 3A and 3B; a superposition analysis ascertained that their geometries are essentially equivalent. A CV indicates that reversibly undergoes two one-electron reductions and two one-electron oxidations; these reversible redox processes form the basis for an integrated structural/electronic picture that is compatible with the existence of the electronically-equivalent 1-3 along with the electronically-nonequivalent 4 (with two fewer CVEs) and other closely related species.     

Formation of cis-enediyne complexes from rhenium alkynylcarbene complexes

Dimerization of the alkynylcarbene complex Cp(CO)(2)Re=C(Tol)C(triple bond)CCH(3) (8) occurs at 100 degrees C to give a 1.2:1 mixture of enediyne complexes [Cp(CO)(2)Re](2)[eta(2),eta(2)-TolC(triple bond)CC(CH(3))=C(CH(3))C(triple bond)CTol] (10-Eand 10-Z), showing no intrinsic bias toward trans-enediyne complexes. The cyclopropyl-substituted alkynylcarbene complex Cp(CO)(2)Re=C(Tol)C(triple bond)CC(3)H(5) (11) dimerizes at 120 degrees C to give a 5:1 ratio of enediyne complexes [Cp(CO)(2)Re](2)[eta(2),eta(2)-TolC(triple bond)C(C(3)H(5))C=C(C(3)H(5))C(triple bond)CTol] (12-E and 12-Z); no ring expansion product was observed. This suggests that if intermediate A formed by a [1,1.5] Re shift and having carbene character at the remote alkynyl carbon is involved, then interaction of the neighboring Re with the carbene center greatly diminishes the carbene character as compared with that of free cyclopropyl carbenes. The tethered bis-(alkynylcarbene) complex Cp(CO)(2)Re=C(Tol)C(triple bond)CCH(2)CH(2)CH(2)C(triple bond)CC(Tol)= Re(CO)(2)Cp (13) dimerizes rapidly at 12 degrees C to give the cyclic cis-enediyne complex [Cp(CO)(2)Re](2)[eta(2),eta(2)-TolC(triple bond)CC(CH(2)CH(2)CH(2))=CC(triple bond)CTol] (15). Attempted synthesis of the 1,8-disubstituted naphthalene derivative 1,8-[Cp(CO)(2)Re=C(Tol)C(triple bond)C](2)C(10)H(6) (16), in which the alkynylcarbene units are constrained to a parallel geometry, leads to dimerization to [Cp(CO)(2)Re](2)(eta(2),eta(2)-1,2-(tolylethynyl)acenaphthylene] (17). The very rapid dimerizations of both 13 and 16 provide compelling evidence against mechanisms involving cyclopropene intermediates. A mechanism is proposed which involves rate-determining addition of the carbene center of A to the remote alkynyl carbon of a second alkynylcarbene complex to generate vinyl carbene intermediate C, and rearrangement of C to the enediyne complex by a [1,1.5] Re shift.     

In vitro mineral availability from digested tea: a rich dietary source of managanese

Tea is potentially a rich source of some dietary metals and approximately 70 l are drunk per capita per year in the UK. In particular, tea may be an important source of Mn, since leaf tea contains 350-900 micrograms g-1 of this essential element. However, the leaching and bioavailability of Mn from tea have been little studied, so a recently developed in vitro assay was applied to compare the bioavailability of Mn from tea infusions with that of other major and trace essential elements. Analysis of tea infusions before digestion showed that 1.0 l contained 115% of the average daily dietary intake of Mn but < 6% of all other minerals. Samples of these infusions were incubated with human gastric juice (37 degrees C, 1 h) and some were then adjusted to pH 6.5 to simulate intestinal pH. All were centrifuged through ultrafilters with molecular mass cut-offs of 3, 10 and 30 kDa. The percentages of ultrafilterable (< 3 kDa) elements following simulated gastrointestinal digestion were (n = 3; mean +/- s) Ca 47.7 +/- 10.7, Cu 45.3 (n = 1), Fe < 5, Mg 66.4 +/- 1.6, Mn 39.8 +/- 11.4, K 40.3 +/- 2.2, Na 100.0 +/- 5.3 and Zn 33.7 +/- 1.1. Hence the ultrafilterability of elements showed the general trend M+ > M2+ > M3+, which is probably the inverse of the order of their strengths of binding to tea polyphenols. However, Mn was the only element found in significant dietary amounts in tea, and under simulated intestinal conditions was still 40% bioavailable.     

Determination of adhesion in bitumen-mineral systems by heat-of-immersion calorimetry

Chemical factors influencing bitumen-mineral adhesion have been examined by heat-of-immersion calorimetry. Two chosen minerals (quartz and calcite) and bitumen derived from Venezuelan and Middle East crude oils were characterised and the energy released by the bitumen-mineral interaction measured. Heat-of-immersion data are correlated with the concentration of heteroatomic species present in the bitumen and the structure of the mineral surfaces. Bitumen-quartz bonding is promoted by the presence of basic species in the bitumen and bitumen-calcite adhesion is favoured by the presence of acidic groups. A mechanism is proposed to account for the observed bond energies.     

Titan

Ohne Zusammenfassung     

Kobalt

Analytical and Bioanalytical Chemistry -     

Modulating the stacking modes of nanosized metal–organic frameworks by morphology engineering for isomer separation

Modulating different stacking modes of nanoscale metal–organic frameworks (MOFs) introduces different properties and functionalities but remains a great challenge. Here, we describe a morphology engineering method to modulate the stacking modes of nanoscale NU-901. The nanoscale NU-901 is stacked through solvent removal after one-pot solvothermal synthesis, in which different morphologies from nanosheets (NS) to interpenetrated nanosheets (I-NS) and nanoparticles (NP) were obtained successfully. The stacked NU-901-NS, NU-901-I-NS, and NU-901-NP exhibited relatively aligned stacking, random stacking, and close packing, respectively. The three stacked nanoscale NU-901 exhibited different separation abilities and all showed better performance than bulk phase NU-901. Our work provides a new morphology engineering route for the modulation of the stacking modes of nano-sized MOFs and improves the separation abilities of MOFs.

A morphology engineering method was utilized to modulate the stacking modes of three nano-NU-901 materials, leading to different separation abilities for isomers.     

Zinn

Ohne Zusammenfassung     

Thermal treatment of dense polyimide membranes

A study has been conducted to clarify the relationship between polymer structure, annealing temperature, and the extent of plasticization by high‐pressure CO₂ for two typical polyimide membranes; BTDA‐DAPI (poly(3,3′‐4,4′‐benzophenone tetracarboxylic–dianhydride diaminophenylindane) and 6FDA‐TMPDA (poly(2,2′‐bis(3,4′‐dicasrboxyphenyl) hexafluoropropane dianhydride–2,3,5,6‐tetramethyl‐1,4‐phenylenediamine). Both membrane materials are exposed to varying levels of thermal annealing at 200 and 250 °C. The effect of this heat treatment on free volume is examined using positron annihilation lifetime spectroscopy (PALS), whereas fluorescence spectroscopy is used to monitor changes in electronic structure. Results show that thermal annealing causes a reduction in both the size and number of free volume elements. A strong relationship is found between the fluorescence peak intensity for 6FDA‐TMPDA and both the membrane gas permeability and plasticization pressure. This correlation is most likely the result of the formation of charge transfer complexes, particularly at 250 °C. However, the formation of covalent crosslinks at these temperatures cannot be discounted. No fluorescence is observed for BTDI‐DAPI. Although thermal annealing has a significant effect on the extent of plasticization in both polymers, it is found that the rate of plasticization is unaffected by the annealing temperature. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1879–1890, 2008