Absence Of Promoters Research Articles

One-dimensional copper bromide based inorganic-organic hybrids as fuels for hypergolic bipropellants with hydrogen peroxide as oxidizer

In this work, a series of unprecedented one-dimensional (1D) copper bromide-based inorganic–organic hybrids were synthesized as hypergolic fuels. In the absence of promoters, all 1D hybrids exhibited good hypergolic activity toward oxidant HTP (H2O2 with concentration of >95 %). Among the hybrids, the 1-propargyl-3-methylimidazolium bromide-based complex achieved the shortest ignition delay (ID) of 12 ms. The structure-performance relationships revealed that the abundant copper alkynyl bonds distributed in the 1D infinite Cu-Br chain functioned as interconnecting hotspots, which greatly promote the hypergolic efficiency. This work demonstrates that the hybrids combined with HTP have potential applications as green hypergolic bipropellants for rocket.

ChemInform Abstract: Homologation Reaction of Ketones with Diazo Compounds

AbstractReview: 314 refs.

Homologation Reaction of Ketones with Diazo Compounds.

This review covers the addition of diazo compounds to ketones to afford homologated ketones, either in the presence or in the absence of promoters or catalysts. Reactions with diazoalkanes, aryldiazomethanes, trimethylsilyldiazomethane, α-diazo esters, and disubstituted diazo compounds are covered, commenting on the complex regiochemistry of the reaction and the nature of the catalysts and promoters. The recent reports on the enantioselective version of ketone homologation reactions are gathered in one section, followed by reports on the use of cyclic ketones ring expansion in total synthesis. Although the first reports of this reaction appeared in the literature almost one century ago, the recent achievements, in particular, for the asymmetric version, forecast the development of new breakthroughs in the synthetically valuable field of diazo chemistry.

Fabrication of Fischer–Tropsch Catalysts by Deposition of Iron Nanocrystals on Carbon Nanotubes

The fabrication of supported catalysts consisting of colloidal iron oxide nanocrystals with tunable size, geometry, and loading—homogeneously dispersed on carbon nanotube (CNT) supports—is described herein. The catalyst synthesis is performed in a two‐step approach. First, colloidal iron and iron oxide nanocrystals with a narrow size distribution are produced. Second, the nanocrystals are attached to CNT grains serving as support structure. Important features, like iron loading and nanocrystal density on the CNT support, are controlled by changing the nanocrystal concentration and ligand concentration, respectively. The Fischer–Tropsch performance reveals these new materials to be active, selective toward lower olefins (60% C of hydrocarbons produced in the absence of promoters), and remarkably stable against particle growth.

The clustering of CpG islands may constitute an important determinant of the 3D organization of interphase chromosomes

We used the 4C-Seq technique to characterize the genome-wide patterns of spatial contacts of several CpG islands located on chromosome 14 in cultured chicken lymphoid and erythroid cells. We observed a clear tendency for the spatial clustering of CpG islands present on the same and different chromosomes, regardless of the presence or absence of promoters within these CpG islands. Accordingly, we observed preferential spatial contacts between Sp1 binding motifs and other GC-rich genomic elements, including the DNA sequence motifs capable of forming G-quadruplexes. However, an anchor placed in a gene/CpG island-poor area formed spatial contacts with other gene/CpG island-poor areas on chromosome 14 and other chromosomes. These results corroborate the two-compartment model of the spatial organization of interphase chromosomes and suggest that the clustering of CpG islands constitutes an important determinant of the 3D organization of the eukaryotic genome in the cell nucleus. Using the ChIP-Seq technique, we mapped the genome-wide CTCF deposition sites in the chicken lymphoid and erythroid cells that were used for the 4C analysis. We observed a good correlation between the density of CTCF deposition sites and the level of 4C signals for the anchors located in CpG islands but not for an anchor located in a gene desert. It is thus possible that CTCF contributes to the clustering of CpG islands observed in our experiments.

Poly(Vinylpyrrolidone)-Anchored Iridium Nanoparticles Supported on Al<sub>2</sub>O<sub>3</sub> as Ultra-Selective Catalyst for the Hydrogenation of <i>p</i>-Chloronitrobenzene

Poly (vinylpyrrolidone)-anchored iridium nanoparticles (PVP-Ir) were prepared via the reduction of H2IrCl6·nH2O in ethanol/water mixtures. The catalytic properties of the colloidal nanoparticles that dispersed on Al2O3(PVP-Ir/Al2O3) were investigated in the selective hydrogenation ofp-chloronitrobenzene (p-CNB) top-chloroaniline (p-CAN). The results indicated that the selectivity top-CAN remained on the level of 100 % at complete conversion ofp-CNB at lower temperature of 288 K. Moreover, the side reaction of hydrogenolysis of the carbon-halogen bond was completely inhibited in the absence of promoters and inhibitors. The great improvement on activity and selectivity of PVP-Ir/Al2O3was attributed to the highly and homogeneously dispersion of the iridium nanoparticles on the support Al2O3and the addition of appropriate amount of water in organic solvents

Suitable combination of promoter and micellar catalyst for kilo fold rate acceleration on propanol to propionaldehyde conversion in aqueous media

Oxidation of propanol by chromic acid produces propionaldehyde under kinetic condition [propanol]T≫[Cr(VI)]T. This oxidation reaction is performed also in presence of micellar catalysts (anionic, cationic and neutral) and hetero-aromatic nitrogen bases promoters (picolinic acid, 2,2′-bipyridine, 1,10-phenanthroline) in aqueous media. The product is confirmed by 2,4-DNP test and 1H NMR spectroscopy. Anionic surfactant sodium dodecyl sulphate (SDS), neutral surfactant triton X-100 (TX-100) accelerated the reaction both in presence and absence of promoters whereas cationic surfactant N-cetyl pyridinium chloride (CPC) inhibited the reaction. Combination of SDS and bipy is found to be the most efficient for this oxidation.

Aromatic nitration with bismuth nitrate in ionic liquids and in molecular solvents: a comparative study of Bi(NO3)3·5H2O/[bmim][PF6] and Bi(NO3)3·5H2O/1,2-DCE systems

A suspension of bismuth nitrate pentahydrate (BN) in [bmim][PF6] or [bmim][BF4] imidazolium ionic liquid (IL) is an effective reagent for ring nitration of activated aromatics under mild conditions without the need for external promoters. Nitration can also be effected in 1,2-DCE, MeCN, or MeNO2 without additives. Nitration of activated arenes (anisole, toluene, ethylbenzene, cumene, p-xylene, mesitylene, durene, and 1,3-dimethoxybenzene) is considerably faster (time to completion) in BN/[bmim][PF6] relative to BN/1,2-DCE and there are also differences in isomer distributions (for anisole, toluene, and ethylbenzene). With introduction of strongly deactivating substituents (–CHO; –MeCO; –NO2) the BN/IL system is no longer active but reactions still proceed with BN/1,2-DCE in reasonable yields. The ready availability and low cost of BN, simple operation, and absence of promoters, coupled to recycling and reuse of the IL, provide an attractive alternative to classical nitration methods for activated arenes. Switching from Bi(NO3)3·5H2O/[bmim][PF6] to Bi(NO3)3·5H2O/1,2-DCE increases the scope of the substrates that can be nitrated.

Synthesis of S- and C-galactofuranosides via a galactofuranosyl iodide. Isolable 1-galactofuranosylthiol derivative as a new glycosyl donor

The use of the easily available persilylated derivative 1 for the synthesis of C- and S-Galf derivatives has been investigated. By anomeric iodination of 1 with TMSI, followed by in situ coupling with C- and S-nucleophiles under very mild conditions and in the absence of promoters, derivatives with value as glycomimetics or as precursors of glycobiological tools were synthesized. Among them, the synthesis of the isolable 1-galactofuranosylthiol 15 is remarkable, as it paves the way for alternative approaches for S-galactofuranosyl derivatives.

Choice of a suitable hetero-aromatic nitrogen base as promoter for chromic acid oxidation of dl-mandelic acid in aqueous media at room temperature

Chromic acid oxidation of dl-mandelic acid in the presence and absence of different promoters has been studied in aqueous media under the kinetic conditions [mandelic acid]T ≫ [Cr(VI)]T and [promoter]T ≫ [Cr(VI)]T at 30 °C. The promoters used in this oxidation reaction, picolinic acid (PA), 2,2′-bipyridine (bpy), and 1,10-phenanthroline (phen), are strong chelating ligands which form complexes with most transition metal ions. The reaction is first-order with regard to [H+], [mandelic acid]T, and [Cr(VI)]T and also has first-order dependence on [promoter]T. HCrO4 − was found to be kinetically active in the absence of promoters; in the presence of promoters the Cr(VI)–promoter complexes were believed to be the active oxidants. In this path the Cr(VI)-promoter complex in each case undergoes nucleophilic attack by the mandelic acid to form a ternary complex which subsequently undergoes redox decomposition involving 3e transfer as the rate-determining step. Among the three promoters oxidation is much faster with 1,10-phenanthroline.

Abstract 200: A transcribed BRCA1 pseudogene regulates gene expression and promotes breast cancer cell proliferation.

Abstract Background: Pseudogenes, originally derived from protein coding genes, have generally been considered to represent non-functional artifacts of evolutionary processes due to degenerative features such as the absence of promoters or the presence of premature stop codons. Pseudogenes, however, account for a significant fraction of the human genome with an estimated number of ∼20,000 comparable to the number of protein-coding genes (∼27,000). Mounting evidence indicates potential biological functions for pseudogenes as regulators of gene expression by generating siRNA, sequestering microRNAs, or regulating RNA stability. Despite the abundance of pseudogenes in the human genome, the pathophysiological roles of pseudogenes remain poorly understood. Methods: qRT-PCR was performed in 15 breast cancer cell lines with custom-designed SYBR assays. Somatic copy number alterations (SCNAs) were measured in 44 normal and breast tumour tissues from patients recruited from the U of Chicago Breast SPORE using custom-designed TaqMan CNV assays. Cell proliferation and invasion assays were performed in bioengineered breast cancer cells with BRCA1P1 over-expression. Affymetrix GeneChip U133 and miRNA 2.0 microarrays were utilized for gene and microRNA profiling. Results: We analyzed the structure of a pseudogene of breast cancer susceptibility protein1 (BRCA1P1) duplicated from the functional gene (BRCA1) with only three exons (exon 1a, 1b & 2). Comparison of DNA sequences revealed that BRCA1P1 is a fusion pseudogene with 343 bp sequences of 60S acidic ribosomal protein (RPLP1) inserted in the exon 1a. Because of a point mutation in the translation start site of exon 2, BRCA1P1 expresses noncoding RNAs (ncRNA) that accumulate in nuclei. BRCA1P1 is ubiquitously transcribed in human normal tissues and highly expressed in breast cancer cell lines. Frequent BRCA1P1 amplification events (44%) were observed in breast tumor DNAs whereas no amplification occurred in normal breast tissues. The data indicate a potential contribution of BRCA1P1 amplification to an increase in BRCA1P1 expression in breast cancer. A significant increase in cell proliferation was observed in cells with BRCA1P1 over-expression (2.82 ± 0.32 fold) compared to cells transfected with control vectors. We are currently performing microarray as well as investigating the pseudogene interaction with BRCA1, RPLP1, or other miRNAs to elucidate mechanisms of cell proliferation regulation by BRCA1P1. Conclusion: This novel study of BRCA1P1 suggests that pseudogenes may play critical roles in neoplastic processes of human cancer. A better understanding of the function of pseudogenes and elucidation of pathways driven by BRCA1P1 pseudogene may advance the field of cancer biology and could provide novel targets for preventive and therapeutic intervention of human breast cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 200. doi:1538-7445.AM2012-200

CpG islands influence chromatin structure via the CpG-binding protein Cfp1

CpG islands (CGIs) are prominent in the mammalian genome owing to their GC-rich base composition and high density of CpG dinucleotides. Most human gene promoters are embedded within CGIs that lack DNA methylation and coincide with sites of histone H3 lysine 4 trimethylation (H3K4me3), irrespective of transcriptional activity. In spite of these intriguing correlations, the functional significance of non-methylated CGI sequences with respect to chromatin structure and transcription is unknown. By performing a search for proteins that are common to all CGIs, here we show high enrichment for Cfp1, which selectively binds to non-methylated CpGs in vitro. Chromatin immunoprecipitation of a mono-allelically methylated CGI confirmed that Cfp1 specifically associates with non-methylated CpG sites in vivo. High throughput sequencing of Cfp1-bound chromatin identified a notable concordance with non-methylated CGIs and sites of H3K4me3 in the mouse brain. Levels of H3K4me3 at CGIs were markedly reduced in Cfp1-depleted cells, consistent with the finding that Cfp1 associates with the H3K4 methyltransferase Setd1 (refs 7, 8). To test whether non-methylated CpG-dense sequences are sufficient to establish domains of H3K4me3, we analysed artificial CpG clusters that were integrated into the mouse genome. Despite the absence of promoters, the insertions recruited Cfp1 and created new peaks of H3K4me3. The data indicate that a primary function of non-methylated CGIs is to genetically influence the local chromatin modification state by interaction with Cfp1 and perhaps other CpG-binding proteins.

The Chloroplast trnT–trnF Region in the Seed Plant Lineage Gnetales

The trnT-trnF region is located in the large single-copy region of the chloroplast genome. It consists of the trnL intron, a group I intron, and the trnT-trnL and trnL-trnF intergenic spacers. We analyzed the evolution of the region in the three genera of the gymnosperm lineage Gnetales (Gnetum, Welwitschia, and Ephedra), with especially dense sampling in Gnetum for which we sequenced 41 accessions, representing most of the 25-35 species. The trnL intron has a conserved secondary structure and contains elements that are homologous across land plants, while the spacers are so variable in length and composition that homology cannot be found even among the three genera. Palindromic sequences that form hairpin structures were detected in the trnL-trnF spacer, but neither spacer contained promoter elements for the tRNA genes. The absence of promoters, presence of hairpin structures in the trnL-trnF spacer, and high sequence variation in both spacers together suggest that trnT and trnF are independently transcribed. Our model for the expression and processing of the genes tRNA(Thr)(UGU), tRNA(Leu)(UAA), and tRNA(Phe) (GAA) therefore attributes the seemingly neutral evolution of the two spacers to their escape from functional constraints.

Conversion of N‐Acetylneuraminic Acid Glycosyl Chloride into Dibenzyl Glycosyl Phosphate: O‐Glycosylation in the Absence of a Promoter.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Grignard reagent formation

It is likely that reactions of magnesium metal with organic halides RX in ether solvents are typical metallic corrosions in which the stabilization of Mg 2+ , substantially through its coordination by the solvent, drives its loss from the metal and consequently the reductions of RX and reaction intermediates such as R at the metal surface. Although alkyl halides form Grignard reagents through non-chain mechanisms in which intermediate radicals diffuse in solution, very small amounts of radical isomerization occur in Grignard reactions of certain vinyl and aryl halides, even when intermediate radicals R would isomerize very rapidly. This suggests a dominant non-radical mechanism for these vinyl and aryl halides or a mechanism in which intermediate radicals R have extremely short lifetimes. Since the former seems more likely, a dianion mechanism, through a transition state [RX 2− ] ‡ , is proposed. Surface studies of polycrystalline Mg show that the “oxide” layer is mostly Mg(OH) 2 and that it is mechanically passivating. In the absence of promoters, Grignard reactions occur very slowly until enough RX has seeped to the magnesium surface and reacted there to undercut and cause the Mg(OH) 2 layer to flake off.

Conversion of N-acetylneuraminic acid glycosyl chloride into dibenzyl glycosyl phosphate: O-glycosylation in the absence of a promoter

Readily accessible N-acetylneuraminic acid (Neu5Ac) glycosyl chloride, which was regarded to be a poor glycosyl donor, was shown to react with dibenzyl phosphoric acid salts in the absence of glycosylation promoters to give the corresponding β-Neu5Ac dibenzyl glycosyl phosphate in high yield.

Direct voltammetry of cytochrome c at trace concentrations with nanoelectrode ensembles

Gold nanoelectrode ensembles (NEEs) are prepared by electroless plating of Au nanoelectrode elements within the pores of a microporous polycarbonate template membrane. The surfaces of these NEEs and also the inner morphology of the gold nanofibers inside the membrane pores are imaged by scanning and transmission electron microscopy. The use of NEEs in micromolar cytochrome c (cyt c) solutions reveals the possibility of observing the direct electrochemistry of the protein, without the need of any promoter or mediator. Cyt c detection limits at NEEs are 1.0 μM by cyclic voltammetry and 0.03 μM by differential pulse voltammetry. The main difference between the voltammetric signals recorded at NEEs in the absence and in the presence of the promoter 4,4 ′-bipyridyl is the more extended dynamic range obtained in the latter case. Quartz crystal microbalance measurements at gold-coated quartz crystals show that, in the absence of promoter, adsorption problems are responsible for the poisoning of the electrode surface. Such adsorption is, however, concentration dependent, so that in diluted solutions (cyt c concentration ⩽20 μM) it becomes negligible. Experimental evidence indicates that the capability of NEEs to detect the direct electrochemistry of cyt c even in the absence of promoters is related to their peculiar property of furnishing well-resolved voltammetric signals in diluted solutions, where this unwanted adsorption is eliminated.

Promoter-induced synthesis of MCM-41 type mesoporous materials including Ti- and V-MCM-41 and their catalytic properties in oxidation reactions

The addition of small amounts of certain oxyanions of group VA, VIA and VIIA (such as nitrate, phosphate, arsenate, sulfate, bromate, iodate etc.) to the synthesis gel mixture of MCM-41 type mesoporous materials reduces the synthesis time considerably. The hydrothermal syntheses of Si-MCM-41, Al-MCM-41, Ti-MCM-41 and V-MCM-41 were carried out in the presence and absence of promoters by refluxing the gel mixture at atmospheric pressure. Studies on the effect of different promoters in the synthesis of Si-MCM-41 show different degrees of enhancement in the long-range ordering process. It has been observed that the higher the charge/radius ratio ( Z/ r, Å −1) of the central cation of the promoter, the higher is the ability of the promoter to speed up the synthesis. The concept of promoter-induced synthesis of MCM-41 type mesoporous materials is applicable not only to Si-MCM-41 but also to Al-MCM-41, Ti-MCM-41 and V-MCM-41. The materials were characterized by XRD, N 2 adsorption, diffuse reflectance UV–vis spectroscopy, FTIR, solid state MAS NMR, SEM, EDX and TEM. The XRD patterns and the quite high BET surface areas with isotherms of type IV of all the samples are typical for hexagonal MCM-41 type ordered mesoporous materials. EDX analysis, solid state 27 Al and 51 V MAS NMR spectra and diffuse reflectance UV–vis spectra of the M-MCM-41 (M = Ti and V) samples confirm the incorporation of Al, Ti and V into the framework. The catalytic properties of the two Ti-MCM-41 samples and the two V-MCM-41 samples, prepared in the presence and absence of a promoter, were compared by means of the epoxidation of cyclohexene and the hydroxylation of 1-naphthol in the presence of different peroxide sources. Comparable catalytic properties indicate that the samples, prepared in the presence and absence of a promoter, are similar in nature and the metal ions are present in the framework, presumably in a tetrahedral coordination.

Unmediated heterogeneous electron transfer reaction of ascorbate oxidase and laccase at a gold electrode.

The unmediated electrochemistry of two large Cu-containing proteins, ascorbate oxidase and laccase, was investigated by direct-current cyclic voltammetry. Rapid heterogeneous electron transfer was achieved in the absence of promoters or mediators by trapping a small amount of protein within a solid, electrochemically inert, tributylmethyl phosphonium chloride membrane coating a gold electrode. The problems typical of proteins in solution, such as adsorption on the electrode surface, were avoided by this procedure. In anaerobic conditions, the cyclic voltammograms, run at a scan rate of up to 200 mV/s, showed the electron transfer process to be quasi-reversible and diffusion-controlled. The pH-dependent redox potentials (+360 mV and +400 mV against a normal hydrogen electrode at pH7.0 for ascorbate oxidase and laccase respectively and +390 mV and +410 mV at pH5.5) were similar to those of the free proteins. The same electrochemical behaviour was recorded for the type 2 Cu-depleted derivatives, which contain reduced type 3 Cu, whereas the apoproteins were electrochemically inactive. Under aerobic conditions the catalytic current intensity of holoprotein voltammograms increased up to approx. 2-fold at a low scanning rate, with unchanged redox potentials. The voltammograms of type 2 Cu-depleted proteins and of apoproteins were unaffected by the presence of oxygen. This suggests that electron uptake at the electrode surface involves type 1 Cu and that only in the presence of oxygen is the intramolecular electron transfer to other protein sites rapid enough to be observed. The analogy with available kinetic results is discussed.

THERMOLYSIS AND PHOTOLYSIS OF SOME SELECTED ARYL THIOESTERS

Abstract Aryl thioesters I and II were prepared and pyrolyzed in the absence of promoters either alone or in isoquinoline as solvent. Thermolysis of β-naphthyl thiobenzoate (I) on heating in air at 250°C gives benzil, benzophenone, benzoic acid, biphenyl, thio β-naphthol, 2,2′-binaphthyl, diphenyl sulfide, thian-threne, thiophenol, phenyl β-naphthyl sulfide and 2.2′-binaphthyl sulfide. Similar results were also obtained on heating p-tolyl thiobenzoate (11) under the same conditions in addition to thio p-cresol, p-bitolyl. p-ditolyl sulfide and phenyl p-tolyl sulfone. H2S and CO are also produced in all cases. Thermolysis of I and II in the presence of isoquinoline affords in addition to the above products, I-phenylisoquinoline. Photolysis of I and II in acetone gives similar products to those of the thermolysis. From these results a free radical mechanism has been postulated to take place through the initial homolysis of C—S bond. No isomer redistribution proceeds the coupling reactions.