Fluorine and chlorine behavior in chlorine-rich volcanic rocks from White Island, New Zealand

Extraordinarily high chlorine-bearing volcanic bombs were erupted from White Island volcano on January 25, 1987. The concentrations of fluorine and chlorine were measured in these paralava bombs and their likely parent rocks. The paralavas contain glass with over 1.0 wt.% and up to 1.7% of chlorine. The F/Cl ratios and their relationship with other constituents show that the fluorine and chlorine in the bombs were derived from hydrothermal fluid, most likely concentrated brine in an active Crater Pool.     

Convergent assembly of highly potent analogues of bryostatin 1 via pyran annulation: bryostatin look-alikes that mimic phorbol ester function

Highly potent bryostatin analogues which contain the complete bryostatin core structure have been synthesized using a pyran annulation approach as a key strategic element. The A ring pyran was assembled using a pyran annulation reaction between a C1-C8 hydroxy allylsilane and an aldehyde comprising C9-C13. This pyran was transformed to a new hydroxy allylsilane and then coupled with a preformed C ring aldehyde subunit in a second pyran annulation, with concomitant formation of the B ring. This tricyclic intermediate was elaborated to bryostatin analogues which displayed nanomolar to subnanomolar affinity for PKC, but displayed properties indistinguishable from a phorbol ester in a proliferation/attachment assay.     

Thallium fractionation in polluted environmental samples using a modified BCR three-step sequential extraction procedure and its determination by electrothermal atomic absorption spectrometry

Determination of thallium in polluted environmental samples and their extracts obtained by a modified BCR three-step sequential extraction procedure was used to study thallium distribution and mobility in the monitored polluted area affected by acidification (Šobov, Central Slovakia). The results of fractionation applied to 5 soil certified reference materials and 14 environmental samples show that the vast majority of thallium occurred in the residual fraction. This means that highly toxic thallium is strongly entrapped in the parent rock materials remains immobile and its environmental toxicity is therefore reduced. The limit of detection for thallium in the studied fractions was lower than 0.050 mg kg⁻¹, the precision (RSD) of the ultratrace determination of thallium in the studied fractions was better than 17 % and the accuracy of the used method was verified by analyzing certified reference materials. Presented at the XVIIIth Slovak Spectroscopic Conference, Spišská Nová Ves, 15–18 October 2006.     

Molecular structure of 2-methylamino-5-[(5-methyl-2-benzoxazolinone-3-yl)methyl]-1,3,4-thiadiazole dihydrophosphate: a combined X-ray crystallographic and ab initio study

Crystal structure of the compound entitled 2-methylamino-5-[(5-methyl-2-benzoxazolinone-3-yl)methyl]-1,3,4-thiadiazole dihydrophosphate is determined using X-ray analysis and compared with the structure obtained from semiempirical and RHF methods at various levels of theory. RHF/6-31G(d) calculations offer the best conformity with X-ray results for bond lengths and bond angles. Moreover, at the result of the comparison of various combinations of basis sets and methods, it appears that there is not much gain in accuracy by using sophisticated methods.     

An ab initio molecular orbital study of the grignard reagents CH3MgCl and [CH3MgCl]2: The Schlenk equilibrium

Ab initio molecular orbital calculations are used to study the modified Schlenk equilibrium: 2RMgCl (RMgCl)² MgR₂ + MgCl₂ Mg(Cl₂)MgR₂ with R=H and CH₃. In the absence of any solvents, calculations indicate that the formation of the various possible bridged dimers (RMgCl)₂ is substantially exothermic. However, using dimethylether as a model solvent, we show that the formation of the dimer (Me₂O)(CH₃)Mg(Cl₂)Mg(CH₃)(OMe₂) is exothermic only when entropic effects are included.     

Towards a Sustainable Synthesis of Oxymethylene Dimethyl Ether by Homogeneous Catalysis and Uptake of Molecular Formaldehyde

Oxymethylene dimethyl ethers (OME_n; CH₃(‐OCH₂‐)_nO‐CH₃, n=3–5) are a novel class of sustainable synthetic fuels, which are of increasing interest due to their soot‐free combustion. Herein a novel anhydrous OME_n synthesis route is presented. Catalyzed by trimethyloxonium salts, dimethoxymethane takes up monomeric gaseous formaldehyde instantaneously and forms high purity OME_n at temperatures of 25–30 °C. This new anhydrous approach using molecular formaldehyde and catalytic amounts of highly active trimethyloxonium salts represents a promising new step towards a sustainable formation of OME_n emanating from CO₂ and H₂.     

Synthesis of chiral alkenyl epoxides: the sex pheromone of the elm spanworm Ennomus subsignaria (Hübner) (Lepidoptera: Geometridae)

The identification of the sex pheromone of the elm spanworm Ennomos subsignaria (Hübner), as the chiral alkenyl epoxide (6Z)-cis-9,10-epoxy-nonadecene has been accomplished. Both enantiomers of (6Z)-cis-9,10-epoxy-nonadecene have been synthesized via two routes. The key steps in the first route were to prepare both threo-epoxy tosylates and then to perform an alkylative rearrangement of these intermediates to obtain the target molecules. An alternative enantioenriched synthesis that took advantage of the Sharpless dihydroxylation reaction was developed so that a common starting material could be used to access both enantiomers. A field study and GC/EAD testing indicated that Z6-cis-9S,10R-epoxy-nonadecene was the sex pheromone of the elm spanworm E. subsignaria (Hübner).     

Systematic study of the formation of the lanthanoid cubane cluster motif mediated by steric modification of diketonate ligands

The treatment of ortho ring-functionalised 1-phenylbutane-1,3-dione ligands bearing nitro (Hnpd, Hnmc), methoxy (Hmmc) or fluoro (Hfpp) groups with hydrated lanthanoid salts has provided [Er(4)(μ(3)-OH)(4)(H(2)O)(2)(npd)(8)] (3), [Ln(4)(μ(3)-OH)(4)(nmc)(8)] (Ln = Gd (4), Tb (5), Dy (6) and Er (7)), [Er(4)(μ(3)-OH)(4)(mmc)(8)] (8) and [Er(4)(μ(3)-OH)(4)(H(2)O)(2)(fpp)(8)] (9), respectively. The products were all obtained as cubane clusters in the solid state, as distinct from previous diketonato clusters, with control over motif formation attributed to the steric influence of the ortho-positioned functional groups at the cluster periphery. This work highlights a means of targeting a specific lanthanoid cluster motif by the rational modification of ligands at key locations.     

Composite hydrogels with temperature sensitive heterogeneities: influence of gel matrix on the volume phase transition of embedded poly-(N-isopropylacrylamide) microgels

The thermo-responsive behaviour of poly-(N-isopropylacrylamide) (PNiPAM) microgels embedded in covalently cross-linked non-temperature-sensitive polyacrylamide (PAam) hydrogel matrixes with different compositions was investigated by using small angle neutron scattering (SANS). The composition of the composite hydrogel was varied by (a) increasing the cross-linker and acrylamide concentration leading to strong hydrogel matrixes and (b) by increasing the microgel concentration to obtain composite gels with an internal structure. Additionally we synthesized composite hydrogels by using γ-irradiation as initiation for the polymerisation. This leads to the formation of chemical bonds between the PNiPAM microgels and the surrounding polyacrylamide matrix. Thus it is possible to synthesize hydrogels without an additional cross-linker, as well as pure particle networks. Some samples were prepared at two different temperatures, below and above the volume phase transition temperature of PNiPAM, resulting in highly swollen or totally collapsed microgels during the incorporation step. The volume phase transition of microgels is not influenced by a hydrogel matrix with high acrylamide concentration independent of the preparation temperature. However, an increased cross-linker concentration leads to a corset like constraint on microgel swelling. Microgels, which are embedded in the collapsed state (at 50 °C), are not able to swell upon cooling, whereas microgels embedded in the swollen state can collapse upon heating. For samples with an increased microgel concentration, the close microgel packing was disturbed by the formation of the polyacrylamide matrix. The hydrogel matrix squeezes the microgels together and leads to partial aggregation. The experiments demonstrate how composite hydrogels with stimuli-sensitive heterogeneities can be prepared such that the full responsiveness of the embedded microgels is retained while the macroscopic dimensions of the gel are not affected by the volume phase transition of the microgels.