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.     

A Modular Tubular Flow System with Replaceable Photocatalyst Membranes for Scalable Coupling and Hydrogenation

Heterogeneous photocatalysis is effective for the selective synthesis of value-added chemicals at lab-scale, yet falls short of requirements for mass production (low cost and user friendliness). Here we report the design and fabrication of a modular tubular flow system embedded with replaceable photocatalyst membranes for scalable photocatalytic C−C, C−N homocoupling and hydrogenation reactions, which can be operated in either circular and continuous flow mode with high performance. The photocatalyst membranes almost fully occupy the volume of the reactor, thus enabling optimal absorption of the incident light. Additionally, the porous structured photocatalyst membranes facilitate the mass transfer of the reactants to efficiently use the active sites, resulting in 0^th-order reaction kinetics and a high space-time yield compared to the batch reaction system at practical application levels and prolonged reaction times.     

Kinetic and Product Study of the S-oxidation vs HAT Chemoselectivity in Reactions Promoted by Nonheme Iron(IV)-oxo Complex/NHPI Mediator System

The chemoselectivity between S-oxidation and hydrogen atom transfer (HAT) from C−H bonds has been investigated in the oxidations of a series of aryl sulfides, alkyl aromatic compounds and benzylic alcohols promoted by the iron(IV)-oxo complex [(N4Py)Fe^IV(O)]²⁺ (N4Py: N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)-methylamine) either alone or in the presence of the N-hydroxyphthalimide (NHPI) mediator via kinetic and product studies. Kinetic analyses indicate a generally higher reactivity of [(N4Py)Fe^IV(O)]²⁺ for S-oxidation process while HAT is favored in the reactions promoted by phthalimide-N-oxyl radical (PINO) deriving from NHPI oxidation. Product analysis in intermolecular competitive oxidations confirms the kinetic results with sulfoxides obtained as major products in the oxidation promoted by [(N4Py)Fe^IV(O)]²⁺. Conversely, when NHPI is employed as a mediator, significant differences in terms of chemoselectivity are observed, and HAT-derived products are obtained in higher yields which translate into an inversion of selectivity in the case of the substrates containing activated C−H bonds like diphenylmethane, triphenylmethane and benzylic alcohols. A similar change of chemoselectivity is also observed in the oxidation of aromatic substrates containing both a sulfur atom and α to OH benzylic C−H bonds, with the sulfoxide product more abundant in the absence of NHPI and carbonyl products prevailing with the [(N4Py)Fe^IV(O)]²⁺/NHPI system.     

Probabilistic Study of the Speed of Approach to Equilibrium for an Inelastic Kac Model

This paper deals with a one-dimensional model for granular materials, which boils down to an inelastic version of the Kac kinetic equation, with inelasticity parameter p>0. In particular, the paper provides bounds for certain distances—such as specific weighted χ-distances and the Kolmogorov distance—between the solution of that equation and the limit. It is assumed that the even part of the initial datum (which determines the asymptotic properties of the solution) belongs to the domain of normal attraction of a symmetric stable distribution with characteristic exponent α=2/(1+p). With such initial data, it turns out that the limit exists and is just the aforementioned stable distribution. A necessary condition for the relaxation to equilibrium is also proved. Some bounds are obtained without introducing any extra condition. Sharper bounds, of an exponential type, are exhibited in the presence of additional assumptions concerning either the behaviour, close to the origin, of the initial characteristic function, or the behaviour, at infinity, of the initial probability distribution function. Research partially supported by Ministero dell’Istruzione, dell’Università e della Ricerca (MIUR grant 2006/134526).