Oxygen-promoted synthesis of armchair graphene nanoribbons on Cu(111)

We report the systematic investigation of the effects of oxygen on the synthesis of 3 p sub-family armchair graphene nanoribbons(3 p-AGNRs),which revealed a strong catalytic effect with a reduction in the reaction temperature by approximately 180 K without degradation of the AGNRs.Poly(para-phenylene)(3-AGNR)was generated through Ullmann-type coupling of4,4’’-dibromo-p-terphenyl on Cu(111),which was then converted into wider 3 p-AGNRs via lateral fusion.Scanning tunneling microscopy(STM)and X-ray photoelectron spectroscopy demonstrated the formation of different ribbons up to 12-AGNR,which contained regions exhibiting increased STM contrast that we attribute to the intercalation of Br atoms during lateral fusion.     

Spatio-temporal perturbation of the dynamics of the ferroin catalyzed Belousov-Zhabotinsky reaction in a batch reactor caused by sodium dodecyl sulfate micelles

The effects of the anionic surfactant sodium dodecyl sulfate (SDS) on the spatio-temporal and temporal dynamics of the ferroin-catalyzed Belousov-Zhabotinsky (BZ) reaction have been studied over a wide surfactant concentration range. For the first time, investigations were performed also for unstirred systems. The presence of SDS in the reaction mixture influences the oscillatory parameters to an extent that significantly depends on the surfactant concentration. The trend of the wave speed v upon the increasing amount of SDS was found to have a maximum at [SDS] = 0.075 mol dm (-3) ( v = 0.071 mm s (-1)), after which the speed decreased to 0.043 mm s (-1) at [SDS] = 0.5 mol dm (-3), which is below the value found in the absence of the surfactant ( v = 0.055 mm s (-1)). The response of the oscillatory BZ system to the addition of SDS has been ascribed to two different causes: (a) the peculiar capability of the organized surfactant assemblies to affect the reactivity by selectively sequestering some key reacting species and (b) the modifications induced by SDS on the physical properties of the medium. These hypotheses have been corroborated by performing spectrophotometric investigations on the stirred BZ system. Complementary viscosity measurements gave useful hints for the clarification of the surfactant role.     

Hybrid niosome complexation in the presence of oppositely charged polyions

We have investigated the formation of complexes between negatively charged niosomal vesicles (hybrid niosomes), built up by dicethylphosphate [DCP], Tween 20 and Cholesterol, and three linear differently charged cationic polyions, such as alpha-polylysine, epsilon-polylysine, and polyethylvinylpyridinium bromide [PEVP], with two different substitution degrees. Our aim is to investigate the interaction mechanism between anionic-nonionic vesicles (hybrid niosomes) and linear polycations, characterizing the resulting aggregates in view of possible applications of these composite colloidal particles as vectors for multidrug delivery. In order to explore the aggregation behavior of the complexes and to gain information on the stability of the single niosomal vesicles within the aggregates, we employed dynamic light scattering (DLS), laser Doppler electrophoretic measurements, and fluorescence measurement techniques. The overall phenomenology is well described in terms of the re-entrant condensation and charge inversion behavior, observed in different colloidal systems. The aggregate size and overall charge depend on the charge ratio between vesicles and polyions, and the aggregates reach their maximum size at the point of charge inversion (re-entrant condensation). While the overall phenomenology is similar for all three polycations investigated, the stability and the integrity of the hybrid niosomal vesicles forming the aggregates strongly depend on the chemical structure of the polycations. The role of the polycations in the aggregation process is discussed by identifying specific interactions with the niosomal membrane, pointing out their importance for possible applications as drug delivery vectors.     

Heterocirculenes as a new class of organic semiconductors

We report a fabrication of field-effect transistors using the new organic semiconductors octathio[8]circulene and tetrathiotetraseleno[8]circulene . The maximum hole mobility of 9 x 10(-3) cm(2) V(-1) s(-1) is, most likely, limited by one-dimensional growth of and in thin films.     

Synthesis and characterization of diazonium functionalized nanoparticles for deposition on metal surfaces

Silica nanoparticles were surface-functionalized with diazonium groups. The reaction steps leading to the formation of the diazonium functionality were followed with IR and XPS, and the structure of the diazonium-functionalized nanoparticle was confirmed with solid state NMR. Nanoparticle size distribution was determined with DLS, SEM, and TEM. The nanoparticles were then covalently bonded to gold and iron surfaces. Their spatial distribution over the metal surface was analyzed by SEM. Diazonium modification of nanoparticles represents a new method for the covalent attachment of nanoparticles to metal surfaces.     

Interface engineering of synthetic pores: towards hypersensitive biosensors

Hydrophilic anchoring is introduced as a promising strategy to constructively control the various interactions of synthetic pore sensors with the surrounding biphasic environment. Artificial rigid-rod beta barrels are selected as classical synthetic multifunctional pores and random-coil tetralysines are attached as hydrophilic anchors. The synthesis of this advanced pore is accomplished in 32 steps from commercially available starting materials. With regard to pore activity as such, the key impact of hydrophilic anchoring is a change from a Hill coefficient n<1 to n=4. This change confirms successful suppression of the competing self-assembly with precipitation from the aqueous phase as the origin of the accomplished increase in pore activity. The hydrophilic anchors do not interfere with the blockage of the synthetic pore sensors by anionic analytes. In the case of stoichiometric binding of blockers (K(D)=EC(50) of the pore; EC(50)=concentration needed to observe 50 % pore activity), however, the increase in pore activity achieved by hydrophilic anchoring results in improved pore blockage under high dilution conditions. Controls confirm that this increase does not occur with analytes that do not exhibit stoichiometric binding (K(D)>EC(50)). These results not only reveal stoichiometric binding as the expected origin of the sensitivity limit of synthetic pore sensors, they also provide promising solutions for this problem. The combination of hydrophilic anchoring with targeted pore formation emerges as a particularly promising strategy to further reduce effective pore concentrations. The scope and limitations of this approach are exemplified with pertinent analyte pairs that are essential for the sensing of sucrose, lactose, acetate, and glutamate with synthetic pores in samples from the supermarket.     

Mass spectrometry and hydrogen/deuterium exchange measurements of alcohol-induced structural changes in cellular retinol-binding protein type I

To bind and release its ligand, cellular retinol-binding protein type I (CRBP) needs to undergo conformational and dynamic changes to connect the inner, solvent-shielded cavity, where retinol is found to bind, and the outside medium. Retinol dissociation in vitro is favoured by water/alcohol mixtures whose moderately low dielectric constants mimic a property characteristic of the membrane microenvironment where this process occurs in vivo. Apo- and holo-CRBP, in either water/methanol or water/trifluoroethanol (TFE) mixtures, were analyzed at equilibrium by electrospray ionization with orthogonal quadrupole time-of-flight mass spectrometry (ESI-Q-TOFMS) to identify the alcohol-induced species. The questions were asked whether the presence of alcohols affects protein dynamics, as reflected by hydrogen/deuterium (H/D) exchange monitored by continuous-labelling experiments, and to which extent retinol dissociation influences the process. With increasing methanol, at pH near neutrality, apo-CRBP exhibits a progressively more compact conformation, resulting in reduced H/D exchange with respect to the native protein in water. Retinol dissociation from the holo-protein did not promote hydrogen replacement. Similarly, in the presence of the low TFE concentration sufficient to cause retinol dissociation, the hydrogen exchange of the resulting apo-protein was not exalted. However, in contrast with the alkanol, higher TFE concentrations induced a transition of apo-CRBP to a new alpha-helix conformation capable of exchanging all available hydrogen atoms.     

Preparation of a set of 4,5-dihydro-3H-pyrrolo[3,2-d]pyrimidin-4-ones as potential Hsp90 ligands

A synthetic route for the preparation of 4,5-dihydro-3H-pyrrolo[3,2-d]pyrimidin-4-ones characterized by a decorated benzyl moiety at different positions of the five-membered ring has been developed, and some compounds have been tested as Hsp90 ligands. One of them displayed IC₅₀ = 50 μM representing an interesting starting point for further investigations.     

Sur les idéaux stables dans certains anneaux différentiels de formes quasi-modulaires de Hilbert

Nesterenko (Sb. Math. 187:1319–1348, [1996]) proved, among other results, the algebraic independence over ℚ of the numbers π and e ^π . A very important feature of his proof is a multiplicity estimate for quasi-modular forms associated to SL ₂(ℤ) which involves differential properties of certain non-linear differential systems. The aim of this article is to begin the study of the corresponding properties for Hilbert modular and quasi-modular forms, especially those which are associated with the number field . We show that the differential structure of these functions has several analogies with the differential structure of the quasi-modular forms associated to SL ₂(ℤ).      

Heterogeneous Photocatalytic Recycling of FeX2/FeX3 for Efficient Halogenation of C−H Bonds Using NaX

Environmental-friendly halogenation of C−H bonds using abundant, non-toxic halogen salts is in high demand in various chemical industries, yet the efficiency and selectivity of laboratory available protocols are far behind the conventional photolytic halogenation process which uses hazardous halogen sources. Here we report an FeX₂ (X=Br, Cl) coupled semiconductor system for efficient, selective, and continuous photocatalytic halogenation using NaX as halogen source under mild conditions. Herein, FeX₂ catalyzes the reduction of molecular oxygen and the consumption of generated oxygen radicals, thus boosting the generation of halogen radicals and elemental halogen for direct halogenation and indirect halogenation via the formation of FeX₃. Recycling of FeX₂ and FeX₃ during the photocatalytic process enables the halogenation of a wide range of hydrocarbons in a continuous flow, rendering it a promising method for applications.