Electrodeposition of nanocrystalline zinc from acidic sulfate solutions containing thiourea and benzalacetone as additives

Nanocrystalline zinc coatings were produced by pulse electrodeposition in acid sulfate bath containing thiourea and benzalacetone additives and characterized by X-ray diffraction and scanning electron microscopy techniques. The influence of benzalacetone concentration and pulse peak current density on the grain size and crystallographic orientation of zinc deposits was investigated. Zinc electrodeposited from additive-free solutions or with one of the two additives is not composed of nanosized crystals. The mixture additives of thiourea and benzalacetone give rise to the formation of particle-like nanocrystalline zinc with a (10ī1) random orientation. A change in peak current density from 2 to 1 A/cm² only increases the grain size from 60 to 62 nm.     

Energy transfer rates and impact sensitivities of two classes nitramine explosives molecules

Some explosives are stable molecules with large energy barriers to chemical reaction, and in shock or impact initiation, a sizable amount of phonon energy must be converted to the molecular internal higher vibrations by multiphonon up pumping. To investigate the relationship between impact sensitivities and energy transfer rates, the number of doorway modes of explosive molecules is estimated by a simple theory in which the rate is proportional to the number of normal mode vibrations. We evaluated frequencies of normal mode vibrations of 13 explosive molecules which are CHNO nitramine-contained and have not been analyzed previously. The number of doorway modes in the regions of 200–700 cm⁻¹ was evaluated by the direct counting method. For more clear investigation of the relationship we have classified these 13 nitramine explosive molecules, by the number of nitramine group they contained, into two groups. There are eight molecules that contained one nitramine group and five molecules that contained poly-nitramine groups. It is found that the number of doorway modes shows a linearly correlation to the impact sensitivities derived from drop hammer tests. This result is in agreement with that of several previous works. Besides, it is also noted in our study that in those nitramine explosives molecules with similar molecular structure (similar number nitramine group they contained) and similar molecular weight, the correlation between the sensitivity and the number of doorway modes is higher. We found that the vibrational frequency of ω corresponds to nitro group motions of every molecule is contributed to the number of doorway modes in the regions of 200–700 cm⁻¹.     

Fully automated polymer-assisted synthesis of 1,5-biaryl pyrazoles

The polymer-assisted solution-phase (PASP) synthesis of a 192-member 2-D array of 1,5-biaryl pyrazoles 4[1-12,1-16] is reported. The synthesis was performed in a fully automated manner using a multiprobe top-filtration robot and incorporates a "catch and release" step to afford library compounds directly in high yield and purity.     

Photocatalytic synthesis of copper colloids from CuII by the ferrihydrite core of ferritin

The iron-storage protein ferritin encapsulates a nanoparticle of iron oxide. The size and properties of these nanoparticles can be adjusted by controlled oxidative hydrolysis reactions of Fe(II). This mineralized ferritin protein cage has previously been shown to act as an effective photocatalyst for reduction of Cr(VI). In the present work, we demonstrate that Fe(O)OH-mineralized ferritin catalyzes the photoreduction of Cu(II) to form a stable, air-sensitive, colloidal dispersion of Cu(0). In addition, the particle sizes of the Cu colloids can be controlled by varying the ratio of Cu(II) to ferritin. This illustrates an important principle, namely that the properties of one preformed material can be utilized for the specific synthesis of a second material, thus tailoring the desired physical properties of the final products. This procedure represents a multistep materials synthesis: the formation of a new nanomaterial from a catalytic precursor.     

Chiral base route to functionalised cyclopentenyl amines: formal synthesis of the cyclopentene core of nucleoside Q

A chiral base route to a range of highly functionalised amino cyclopentenes has been developed. The key asymmetric step involved the chiral lithium amide base-mediated rearrangement of a protected trans-4-hydroxy cyclopentene oxide to give an allylic alcohol (88% ee). Subsequent Overman rearrangement gave a protected trans-1,2-aminocyclopentenol whereas Mitsunobu substitution with BocNHNs gave a protected cis-amino cyclopentenol. Both are proven intermediates for natural product synthesis. The protected cis-aminocyclopentenol was transformed in a few steps into a precursor of the cyclopentene core of nucleoside Q, a natural product whose deficiency in animals is related to tumour growth.     

Tributylgermanium hydride as a replacement for tributyltin hydride in radical reactions

Tributylgermanium hydride (Bu(3)GeH) can be used as an alternative to tributyltin hydride (Bu(3)SnH) as a radical generating reagent with a wide range of radical substrates. Tributylgermanium hydride has several practical advantages over tributyltin hydride, e.g. low toxicity, good stability and much easier work-up of reactions. The reagent can be easily prepared in good yield and stored indefinitely. Suitable substrates include iodides, bromides, activated chlorides, phenyl selenides, tert-nitroalkanes, thiocarbonylimidazolides and Barton esters. Alkyl, vinyl and aryl radicals can be generated in radical reactions including reduction and cyclisation processes. Common radical initiators such as ACCN and triethylborane can be used. The slower rate of hydrogen abstraction by carbon-centred radicals from Bu(3)GeH as compared to Bu(3)SnH facilitates improved cyclisation yields. Polarity reversal catalysis (PRC) with phenylthiol can be used in reactions which generate stable radical intermediates which will not abstract hydrogen from Bu(3)GeH.     

A convenient, general synthesis of 1,1-dimethylallyl esters as protecting groups for carboxylic acids

[reaction: see text] Carboxylic acids were converted in high yield to their 1,1-dimethylallyl (DMA) esters in two steps. Palladium-catalyzed deprotection of DMA esters was shown to be compatible with tert-butyl, benzyl, and Fmoc protecting groups, and Fmoc deprotection could be carried out selectively in the presence of DMA esters. DMA esters were also shown to be resistant to nucleophilic attack, suggesting that they will serve as alternatives to tert-butyl esters when acidic deprotection conditions need to be avoided.     

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 and characterization of carbohydrate-based phospholipids

Novel carbohydrate-based phospholipids containing two saturated C(12) (dilauroyl ribo-phosphocholine) (DLRPC), C(14) (dimyristoyl ribo-phosphocholine) (DMRPC), and C(20) (diarachadonyl ribo-phosphocholine) (DARPC) carboxylic acid chains were synthesized. The physical properties of the supramolecular structures formed by these compounds were compared to those formed by their direct glycerol analogues dilauroyl phosphocholine (DLPC), dimyristoyl phosphocholine (DMPC), and diarachadonyl phosphocholine (DAPC). Modulated differential scanning calorimetry (MDSC) and X-ray diffraction data indicated that with chain lengths < or =14 carbons, the carbohydrate backbone increased the thermal stability of the bilayer below the phase-transition temperature (T(m)) as compared to the glycerol-based lipids. With longer chains (C(20)), the bilayer structure was destabilized as compared to glycerol-based lipids. NMR studies of a DMRPC vesicle dispersion reveal split choline headgroup signals and distinct magnetization transfer effects arising from the "inner" and "outer" surfaces of the bilayer vesicle. Modulated differential scanning calorimetry also demonstrated that glycerol- and carbohydrate-based lipids mix, as evidenced by a single intermediate T(m). In addition, carbohydrate-based lipid/cholesterol mixtures exhibited a decrease in enthalpy with an increase in cholesterol concentration. Unlike glycerol phospholipids, carbohydrate lipids were resistant to enzymatic degradation by phospholipase A(2) (PLA(2)).     

Comparison of lysis methods and preparation protocols for one- and two-dimensional electrophoresis of Aspergillus oryzae intracellular proteins

Filamentous fungal fermentations are used to produce billions of dollars of biochemical and pharmaceutical products annually, yet are plagued by a number of poorly understood problems that would benefit from proteomic analysis. Unfortunately, few publications are available which describe extraction of filamentous fungal proteins for two-dimensional electrophoresis. The goal here was to develop protocols for extraction of fungal proteins, from both wild-type and a recombinant strain of the industrially important filamentous fungi Aspergillus oryzae, to be used for both one- and two-dimensional electrophoresis (1-DE and 2-DE). Because fungal cell walls are exceptionally resistant to fragmentation, four lysis protocols were tested: (i) boiling in strong alkali solution, (ii) boiling in Sodium dodecyl surfate (SDS), (iii) chemical lysis in Y-PER(R) reagent, and (iv) mechanical lysis via rapid agitation with glass beads in a Mini-BeadBeater(R). For both 1-DE and 2-DE, rapid agitation with glass beads was found to be the most efficient extraction method, yielding both mini- and large-format gels with little streaking or spot tailing, and proteins comprising a broad range of molecular weights and pI values.