Synthesis and esterolytic reactions of linear and cross-linked asymmetric imidazole-containing polymers

Asymmetric linear and cross-linked imidazole-containing polymers were prepared from 1-[2(S)-methylbutyl]-4-vinylimidazole and 1-[2(S)-methylbutyl]-5-vinylimidazole. The esterolytic reactions of these linear and cross-linked asymmetric polymers with the enantiomeric substrates (R)- and (S)-4-(3-methylpentadecanoyl)-3-nitrobenzoic acid, (R)- and (S)-S, were studied by measuring the pseudo-first order kinetics of the solvolysis of these enantiomeric substrates in the presence of these asymmetric polymers. The linear homopolymers and copolymers of 1-[2(S)-methylbutyl]-4- and 5-vinylimidazole showed hydrophobic and electrostatic effects in the solvolysis of the enantiomeric substrates with these linear asymmetric polymers. Cross-links were introduced into these asymmetric polymers to increase the rigidity and reduce the number of conformations available to the polymer. The reduced conformational mobility was expected to enhance any enantioselectivity in the solvolysis of the enantiomeric substrates with these polymers. Using these cross-linked polymers, hydrophobic interactions were observed in the solvolysis of a series of substrates with increasing alkyl chain length. Also, on changing the polarity of the solvent, a bell-shaped rate profile was observed in the solvolysis of the long chain substrate S. This effect was attributed to a combination of the coiling of the cross-linked polymer chains and hydrophobic interactions with the substrate on changing solvent polarity. Even with the increased rigidity of these cross-linked polymers, no significant enantioselectivity in the solvolysis of the enantiomeric substrates was observed. So, neither the linear nor the cross-linked asymmetric polyvinylimidazoles showed enantioselectivity in the solvolysis of these enantiomeric substrates. In this case, the hydrophobic interactions and the reduced conformational mobility through crosslinking were not strong enough to bring about enantioselectivity in the solvolysis of these enantiomeric substrates.     

Photodecarboxylation and photohydration of pyrimidine derivatives

Thymine-1-acetic acid is shown to undergo photodecarboxylation while uracil-1-acetic acid is subject to photohydration and photodecarboxylation. In contrast, no photodecarboxylation was observed for thymine-1-propionic acid and uracil-1-propionic acid. With the esters and amides of these acids, only photohydration occurred. In no instance was lactonization or azalactone formation detected in these photoreactions. Irradiation of these compounds in the dry solid state resulted in little change; however, in frozen aqueous solutions cyclobutyl dimers were isolated without decarboxylation. Detailed mechanistic study revealed that photohydration and photodecarboxylation of these pyrimidines probably are simultaneous processes which may occur from the vibrationally excited levels of the ground state.     

Reconstruction and crosstalk of protein-protein interaction networks of Wnt and Hedgehog signaling in Drosophila melanogaster

In the last few years, researchers have an intense interest in the evolutionarily conserved signaling pathways which have crucial roles during embryonic development. The most intriguing factor of this interest is that malfunctioning of these signaling pathways (Hedgehog, Notch, Wnt etc.) leads to several human diseases, especially to cancer. This study deals with the β-catenin dependent branch of Wnt signaling and the Hedgehog signaling pathways which offer potential targeting points for cancer drug development. The identification of all proteins functioning in these signaling networks is crucial for the efforts of preventing tumor formation. Here, through integration of protein-protein interaction data and Gene Ontology annotations, Wnt/β-catenin and Hedgehog signaling networks consisting of proteins that have statistically high probability of being biologically related to these signaling pathways were reconstructed in Drosophila melanogaster. Next, by the structural network analyses, the crucial components functioning in these pathways were identified. The proteins Arm, Frizzled receptors (Fz and Fz2), Arr, Apc, Axn, Ci and Ptc were detected as the key proteins in these networks. Futhermore, the hub protein Mer having tumor suppressor function may be proposed as a putative drug target for cancer and deserves further investigation via experimental methods. Finally, the crosstalk analysis between the reconstructed networks reveals that these two signaling networks crosstalk to each other.     

Mode of action and biosynthesis of the azabicycle-containing natural products azinomycin and ficellomycin

Only a handful of aziridine-containing natural products have been identified out of the more than 100,000 natural products characterized to date. Among this class of compounds, only the azinomycins (azinomycin A and B) and ficellomycin contain an unusual 1-azabicyclo[3.1.0]hexane ring system, which has been reported to be the reason for theDNAcrosslinking abilities and cytotoxicity of these metabolites. Both families of natural products are produced by Streptomyces species, Streptomyces sahachiroi and Streptomyces ficellus, respectively. Up until recently, much of the work on these molecules has focused on the synthesis of these natural products or their corresponding analogs for in vitro investigations evaluating their DNA selectivity. While one of the most intriguing aspects of these natural products is their biosynthesis, progress made in this area was largely impeded by difficulties with obtaining a reliable culture method and securing a consistent source of these natural products. In this review, we will cover the discovery and biological activity of the azinomycins, their mode of action, related synthetic analogs and biosynthesis, and finish with a discussion on the less studied metabolite, ficellomycin.     

Calorimetric and structural investigation of the interaction of lysozyme and bovine serum albumin with poly(ethylene oxide) and its copolymers

This work reports investigations aiming at verifying the occurrence of specific interactions between lysozyme or bovine serum albumin (BSA) and poly(ethylene oxide) and its copolymers with poly(propylene oxide). Thermal stability of these proteins, followed by means of high sensitivity DSC, was found to be mostly unaffected by the presence of these polymers. Chromatographic experiments (reverse-phase HPLC and size exclusion chromatrography) did not reveal any sign of specific interaction for these mixtures, either. Isothermal titration calorimetry revealed an increase in enthalpy for the mixtures, represented by a positive enthalpy of transfer for these proteins from buffer to polymer solutions. Moreover, SAXS analyses confirmed that at ambient temperatures these polymers do not affect lysozyme structure. In summary, no evidence is found to support earlier suggestions that some kind of complex could be formed between these proteins and poly(ethylene oxide) or its copolymers, but the present results suggest the occurrence of entropically driven hydrophobic effects.     

Preparation and Properties,Reactions, and Applications of Radialenes

Radialenes are alicyclic compounds in which every ring atom is sp²-hybridized and carries an exocyclic C? C double bond. Because of their unusual topology and electronic structures these hydrocarbons have aroused the interest of both preparative chemists and theoreticians. Although considerable progress has been achieved recently, directed and efficient syntheses of these molecules remain a challenge. The study of their chemical behavior offers vast opportunities. Very recently materials scientists have become interested in these unusual compounds in their search for organic conductors and ferromagnets.     

二碘荧光素、荧光素稀土配合物的合成及性质的研究

本文报导了一种合成二碘荧光素、荧光素稀土配合物的新方法,得到了定组成的固体配合物,并对它们的一系列性质进行了研究。通过化学分析、元素分析确定了它们的组成。     

Computer simulations and analysis of structural and energetic features of some crystalline energetic materials

A database of 43 literature X-ray crystal structure determinations for compounds with known, or possible, energetic properties has been collected along with some sublimation enthalpies. A statistical study of these crystal structures, when compared to a sample of general organic crystals, reveals a population of anomalously short intermolecular oxygen-oxygen separations with an average crystal packing coefficient of 0.77 that differs significantly from 0.70 found for the general population. For the calculation of lattice energies, three atom-atom potential energy schemes and the semiempirical SCDS-PIXEL scheme are compared. The nature of the packing forces in these energetic materials is further analyzed by a study of the dispersive versus Coulombic contributions to overall lattice energies and to molecule-molecule energies in pairs of near neighbors in the crystals, a partitioning made possible by the unique features of the SCDS-PIXEL scheme. It is shown that dispersion forces are stronger than Coulombic forces, contrary to common belief. The low abundance of hydrogen atoms in these molecules, the close oxygen-oxygen contacts, and the high packing coefficients explain the observation that, for these energetic materials, crystal densities are anomalously high compared to those of most organic materials. However, an understanding, not to mention prediction or control, of the deeper mechanisms for the explosive power of these crystalline materials, such as the role of lattice defects, remains beyond present capabilities.     

Flow field-flow fractionation and characterization of ionic and neutral polysaccharides of vegetable and microbial origin

The flow field-flow fractionation (FlFFF) analysis of a variety of neutral as well as ionic polysaccharides from plants and micro-organisms shows the generally broad distribution in molecular size of these polymers. This result is also obtained on a commercial sample of pullulan whose size distribution appears much wider than that of any of five standard fractions of the same polymer. Clear evidence of some physico-chemical properties of the polysaccharides is given by the study of the effect of the carrier ionic strength on salep, oxidized salep and konjac, carboxymethylcellulose and hyaluronic acid. While neutral polysaccharides, regardless of their origin, only slightly change size distribution in the presence of a simple electrolyte in solution, charged polymers, either naturally charged or chemically ionized, consistently exhibit very low retention levels in water which dramatically increase even at low salt concentrations. Exclusion mechanisms, including steric effects, are shown to be responsible for the anticipated retention times in water of these species that assume the expected statistical coil behavior only when electric charges are screened by the added electrolyte. Under these conditions, higher retention levels are obtained because the volume adjacent to the accumulation wall becomes more accessible to the sample during relaxation. On the basis of these findings, the elution behavior of a number of polysaccharide samples in-laboratory obtained from the fungus Aureobasidium pullulans under different incubation conditions is attributed to the presence of species varying in physico-chemical properties and molecular size.     

Pulse reactions of methane, ethane and ethylene over Li-, La- and Sm-promoted MgO catalysts in the presence and absence of free oxygen

Pulse reaction of methane in the presence and absence of free (or gaseous) oxygen and that of ethane and ethylene in the absence of free oxygen over Li−MgO, La−MgO and Sm−MgO (Li or La or Sm/Mg ratio=0.1) have been investigated for elucidating the role of lattice and free oxygen in oxidative coupling of methane (OCM) over these catalysts. No significant role is played by the lattice oxygen from these catalysts in the OCM process. The presence of free oxygen is essential for all these catalysts to be active and selective in OCM process. However, lattice oxygen plays some role in ethane conversion but a very significant role in ethylene conversion over these catalysts.     

Raman spectroscopic characterisations and analytical discrimination between caffeine and demethylated analogues of pharmaceutical relevance

The FT Raman spectrum of caffeine was analysed along with that of its demethylated analogues, theobromine and theophylline. The similar but not identical structures of these three compounds allowed a more detailed assignment of the Raman bands. Noticeable differences in the Raman spectra of these compounds were apparent and key marker bands have been identified for the spectroscopic identification of these three compounds.     

Preparation and characterization of ceria‐zirconia composite for enrichment and identification of phosphopeptides

Ceria‐zirconia composites at different molar ratios were synthesized. Several methods were used to characterize these composites, including X‐ray photoelectron spectroscopy, surface area and surface acid‐base property detection. A one‐step method for isolation and identification of phosphopeptides from peptide mixture was created using these ceria‐zirconia composites. Using tryptic digest of standard phosphorylated protein, we have shown that these enrichment and dephosphorylation activities are effective. The adsorption capacity and catalytic property of ceria‐zirconia composites at different molar ratios and calcinated temperatures were studied. In combination with MALDI‐TOF‐based peptide mass finger printing technique, we have established a method to utilize the enrichment/dephosphorylation dual properties of these ceria‐zirconia composites for the analysis of phosphoprotein in nonfat milk successfully.     

Syntheses of ladder-type oligonaphthalene derivatives and their photophysical and electrochemical properties

Ladder-type oligophenylene derivatives are important compounds for light-emitting devices. However, the closely related ladder-type oligonaphthalene derivatives have received little attention due to the lack of synthetic accessibility. We hereby report the syntheses of these novel conjugated systems by means of an intramolecular cationic cyclization protocol. Utilizing a one-pot-multiple-component reaction, the acyclic precursors to these ladder-type oligomers up to pentamer can be synthesized from small fragments in just two or three steps. Photophysical and electrochemical studies revealed that the electron delocalization in these compounds is considerably enhanced relative to that found in the regular unplanarized oligonaphthalene derivatives. However, such an effect is much weaker than that found in fully planar rylene derivatives.     

Synthesis and characterization of novel alkoxy nonionic biosurfactants

A series of novel alkoxy nonionic biosurfactants were synthesized by ring-opening reaction of methoxy poly(ethylene glycols) and alkylene oxide. The chemical structures of these biosurfactants were confirmed by Fourier-transform infrared spectroscopy (FTIR) and ¹HNMR spectra. The surface tensions of these nonionic biosurfactants in the aqueous solutions were determined using a surface tensionmeter. The results showed that the critical micelle concentrations decreased with the increase of hydrophobic chain. However, due to the effect of intermolecular hydrogen bonding, the critical surface tensions of these nonionic biosurfactants increased with increasing the hydrophobic chain and were lower than those of conventional nonionic biosurfactants. Meanwhile, the effects of electrolytes on surface tension of these nonionic biosurfactants were slight. Due to the excellent surface activity, these alkoxy nonionic biosurfactants could have great potential in cleansing, oil recovery, and drug delivery.     

Cyclic imides. 16. Hydroxy and methoxy derivatives of aminophthalimide and phthalhydrazide

Treatment of N-alkyl derivatives of 3,6-dichlorophthalimide and 4,5-dichlorophthalimide with potassium nitrite gave 3-hydroxy-6-nitro- and 4-hydroxy-5-nitrophthalimides. The potassium salts of these phenols were alkylated by dialkyl sulfates. The products were reduced to the 3-amino-6-alkoxy- and 4-amino-5-alkoxyphthalimides, and the fluorescence emission spectra of these products were measured. Hydrazinolysis of the phthalimides in a toluene medium gave phthalhydrazides. The luminescence spectra of several aminophthalhydrazides were measured. The infrared and proton magnetic resonance spectra of these and of some nitrophthalhydrazides were measured and aspects of these spectra characteristic of phthalhydrazides were identified.     

Synthesis and biological properties of prostaglandin endoperoxides, thromboxanes and prostacyclins.

Prostaglandins continue to be a major and fast-developing area of research in the chemical and biological sciences. Increasing evidence has recently prompted some researchers to suggest that the important physiological actions of these hormones are exerted by their unstable arachidonic acid pathway intermediates, the endoperoxides, thromboxanes, and prostacyclin. The importance of these substances in physiology and medicine and the challenge they pose to synthetic chemistry place them in the forefront of chemical and biochemical investigation. Current biological research has greatly benefited by synthetic advances which have made available large quantities of some of these naturally occurring intermediates and several analogs with increased stabilities. Following a brief review of the primary prostaglandins, the present article describes recent biosynthetic developments, partial and total syntheses of prostaglandin endoperoxide analogs, thromboxane B₂, and prostacyclins, and the biological properties of these molecules.     

Mass spectrometric characterization and gas-phase chemistry of self-assembling supramolecular squares and triangles

A detailed mass spectrometric characterization of self-assembling polynuclear metal complexes is described. The complexes can only be ionized as intact species under a surprisingly narrow range of conditions by electrospray ionization. Comparison with the results from NMR experiments shows that several solution-phase features of these squares and triangles (such as trends in bond energies, ligand-exchange reactions, or square-triangle equilibria) are qualitatively reflected in the gas-phase data. Consequently, mass spectrometry represents a valuable method for the characterization of these compounds. Nevertheless, the formation of unspecific aggregates during the ionization process occurs and its implications are discussed. Beyond the chemistry in solution, the fragmentation pathways of these complexes in the gas phase have been studied by infrared multiphoton dissociation (IRMPD) experiments. The results of IRMPD studies allow us to draw conclusions with respect to the structure and energetics of fragmentation products. In this tandem MS experiment, reaction pathways can be observed directly which can hardly be analyzed in solution. According to these results, the equilibration of triangles and squares involves the supramolecular analogue of a neighboring-group effect.     

Chemical and semisynthesis of posttranslationally modified proteins

Posttranslational modifications of proteins play crucial roles in health and disease by affecting numerous aspects of protein structure, function, stability and sub cellular localization. Yet understanding the effects of these modifications on several of these processes at the molecular level has been hindered by the lack of homogeneously modified proteins obtained via traditional biochemical and molecular biology approaches. Moreover, the preparation of such bioconjugates at a workable level is highly demanding. Recent advances in protein chemistry applying chemical and semisynthetic approaches are becoming increasingly beneficial to overcome these challenges. These methods allow site-specific modifications of a desired protein and afford the product in large quantities for biochemical and structural analyses. In this review, we survey these efforts and their importance in dissecting the role of several posttranslational modifications in various proteins. Several examples are presented where glycosylated, phosphorylated, ubiquitinated, lipidated, acetylated and methylated proteins were prepared.     

铁电极上硫脲及衍生物的缓蚀作用研究

用极化曲线方法测定了硫酸溶液中硫脲及其衍生物的浓度变化对铁腐蚀电化学行为的影响，获得了腐蚀电位下缓蚀剂对阴极和阳极过程的作用系数，用ＥＨＭＯ方法对硫脲及其衍生物的结构参数进行了量化计算，分析表明，缓蚀剂对阴极和阳极过程作用系数的大小与这些参量有密切关系。     

Synthesis and Photochemistry of Novel 3,5-Diacetyl-1,4-dihydropyridines

 Some novel 3,5-diacetyl-1,4-dihydropyridine derivatives were synthesized; their photochemical behaviour was studied under oxygen or argon atmosphere. Irradiation of these compounds resulted in the aromatization of the ring and formation of 3,5-diacetylpyridine derivatives. The presence of oxygen plays an important role in the type, rate, or failure of oxidation. Irradiation of these compounds with of 2-furyl or 5-methyl-2-furyl substituents in position 4 under argon resulted in the formation of a pyridine ring with retention of these substituents, whereas loss of these substituents and ring aromatization was observed upon irradiation under oxygen.