Graphite furnace atomic absorption spectrometric determination of ruthenium in iron meteorites

A procedure for the determination of ruthenium in iron meteorites involves its oxidation to RuO₄ by sodium periodate in hydrochloric acid and extraction of the tetroxide into chloroform. Various parameters of the method were studied: sample dissolution, optimum amount of oxidant, shaking time, distribution ratio and stability of the complex. The relative standard deviation assessed from replicate analyses of the North Chile iron meteorite was 6.6%. There are no certified standards for iron meteorites, but the value of 20.0 μg g^? obtained for this meteorite compares well with a reported abundance of 19.3 μg g^?1 obtained by radiometric neutron-activation analysis (RNAA). The analysis of 15 meteorites that had previously been analysed by RNAA gave values averaging 11% below those reported by the latter method, but within the standard deviation of the RNAA data. It is considered that the present method is a more practical alternative to RNAA for the determination of ruthenium in iron meteorites.     

Stereochemical assignment of the C1-C6 fragment of psymberin by synthesis and natural product degradation

[reaction: see text] Psymberin is a sponge-derived natural product that shows striking selectivity as a cytotoxic agent. Conformational mobility has precluded stereochemical assignment for the acyl fragment of this molecule (psymberic acid) by NMR. Herein we report stereoselective syntheses of all four stereoisomers of psymberic acid. A comparison of the acid-mediated cyclization products of these compounds to the product of psymberin's acidic methanolysis showed the stereochemical configuration of this fragment to be 4S,5S.     

Photosensitization of nanocrystalline TiO2 by self-assembled layers of CdS quantum dots

CdS quantum dots can be self-assembled on high surface area nanocrystalline TiO2 electrodes; spectroscopic and photoelectrochemical studies indicate that the size, and hence the absorption edge, of the CdS particles can be controlled; efficient photosensitization of the TiO2 electrode by the Q-particles has been achieved.     

Generation of 3-pyridyl biaryl systems via palladium-catalyzed Suzuki cross-couplings of aryl halides with 3-pyridylboroxin

The synthesis of 3-pyridyl biaryl systems can be readily achieved by means of palladium-catalyzed Suzuki cross-coupling reactions between aryl halides and 3-pyridylboroxin. A series of cross-couplings were conducted in order to investigate the scope and limitations of this protocol.     

Nature's protection racket

(2S)-4-amino-2-hydroxybutyrate (AHBA) is a side chain that is important for the antibiotic activities of aminoglycosides. The elucidation of the biosynthetic pathway to AHBA, by Spencer et al. in this issue of Chemistry & Biology [1], reveals several surprises and will facilitate biosynthetic engineering of new improved aminoglycoside antibiotics.     

A computational study of the reactions of a beta-diketiminatoaluminium(I) complex with the hydrogen atom and the electron

A computational study has been performed to examine the reactions of a model beta-diketiminatoaluminium (I) complex with the hydrogen atom and with the electron. It was found that the hydrogen atom adds to the metal centre exothermically (DeltaH(rxn)=-202 kJ mol(-1)), and the spin density in the resulting radical resides entirely on the beta-diketiminato ligand. The spin density of the corresponding radical anion is very similar to the H-adduct.     

Synthesis of indaphyrins: meso-tetraarylsecochlorin-based porphyrinoids containing direct o-phenyl-to-beta-linkages

The synthesis of indaphyrins, novel meso-tetraarylsecochlorin-derived chromophores incorporating o-phenyl-to-beta-linkages, is described. Oxidative diol cleavage of meso-tetraaryl-2,3-dihydroxy-2,3-chlorins results in the formation of a secochlorin bisaldehyde. Depending on the reaction conditions during the ring cleavage reaction, one or two of the aldehyde groups react with the adjacent o-phenyl positions, leading to an intramolecular electrophilic aromatic substitution of the o-phenyl proton, and the establishment of a direct o-phenyl-to-beta-linkage. The initially formed carbinol is spontaneously oxidized to the corresponding ketone. This modification forces the aryl groups into co-planarity with the macrocycle, allowing for interactions between the pi-electrons of the aryl groups, the ketone linkage, and those of the chromophore, resulting in a significant electronic modulation of the porphyrinic pi-system. The UV-vis spectroscopic properties of the free base, CuII, NiII, and ZnII indaphyrins are discussed.     

Self-assembly of phosphate fluorosurfactants in carbon dioxide

Anionic phosphodiester surfactants, possessing either two fluorinated chains (F/F) or one hydrocarbon chain and one fluorinated chain (H/F), were synthesized and evaluated for solubility and self-assembly in liquid and supercritical carbon dioxide. Several surfactants, of both F/F and H/F types and having varied counterions, were found to be capable of solubilizing water-in-CO2 (W/C), via the formation of microemulsions, expanding upon the family of phosphate fluorosurfactants already found to stabilize W/C microemulsions. Small-angle neutron scatteringwas used to directly characterize the microemulsion particles at varied temperatures, pressures, and water loadings, revealing behavior consistent with previous results on W/C microemulsions.     

Rapid method for the determination of alachlor, atrazine and metolachlor in groundwater by solid-phase extraction

A solid-phase extraction method is described for the separation of alachlor, atrazine and metolachlor from groundwater using solid-phase disposable columns. The method is rapid, reproducible and uses considerably fewer reagents than classical liquid-liquid methods. The average recoveries were greater than 90% for all three compounds.     

Covalent Schiff base catalysis and turnover by a DNAzyme: a M2+ -independent AP-endonuclease mimic

A DNAzyme, synthetically modified with both primary amines and imidazoles, is found to act as a M2+ -independent AP lyase-endonuclease. In the course of the cleavage reaction, this DNAzyme forms a covalent Schiff base intermediate with an abasic site on a complementary oligodeoxyribonucleotide. This intermediate, which is inferred from NaCNBH3 trapping as well as cyanide inhibition, does not evidently accumulate because the second step, dehydrophosphorylative elimination, is fast compared to Schiff base formation. The 5'-product that remains linked to the catalyst hydrolyzes slowly to regenerate free catalyst. The use of duly modified DNAzymes to perform Schiff base catalysis demonstrates the value of modified nucleotides for enhancing the catalytic repertoire of nucleic acids. This work suggests that DNAzymes will be capable of catalyzing aldol condensation reactions.