Charge transport parameters of the pentathienoacene crystal

Pentathienoacene, the thiophene equivalent of pentacene, is one of the latest additions to the family of organic crystal semiconductors with a great potential for use in thin film transistors. By using density functional theory and gas-phase ultraviolet photoelectron spectroscopy, we investigate the microscopic charge transport parameters of the pentathienoacene crystal. We find that the valence band exhibits a stronger dispersion than those in the pentacene and rubrene single crystals with marked uniaxial characteristics within the molecular layer due to the presence of one-dimensional pi-stacks; a small hole effective mass is also found along the direction perpendicular to the molecular layers. In the conduction band, strong intermolecular sulfur-sulfur interactions give rise to a significant interstack electronic coupling whereas the intrastack dispersion is greatly reduced. The intramolecular vibronic coupling (reorganization energy) is stronger than that in pentacene but comparable to that in sexithiophene; it is larger for holes than for electrons, as a result of low-frequency modes induced by the sulfur atoms. The polarization energy is large, but its effect on the vibronic coupling remains small. Charge transport is discussed in the framework of both band and hopping models.     

On the Local Time of Random Walks Associated with Gegenbauer Polynomials

The local time of random walks associated with Gegenbauer polynomials \(P_{n}^{(\alpha)}(x)\), x∈[?1,1], is studied in the recurrent case: \(\alpha\in [-\frac{1}{2},0]\). When α is nonzero, the limit distribution is given in terms of a Mittag-Leffler distribution. The proof is based on a local limit theorem for the random walk associated with Gegenbauer polynomials. As a by-product, we derive the limit distribution of the local time of some particular birth-and-death Markov chains on ?.     

Effects of partial anion substitution on the thermoelectric properties of silver(I) chalcogenide halides in the system Ag5Q2X with Q=Te, Se and S and X=Br and Cl

A selection of mixed conducting silver chalcogenide halides of the general formula Ag₅Q₂X with Q=sulfur, selenium and tellurium and X=chlorine and bromine has been investigated due to their thermoelectric properties. Recently, the ternary counterpart Ag₅Te₂Cl showed a defined d¹⁰-d¹⁰ interaction in the disordered cation substructure at elevated temperatures where Ag₅Te₂Cl is present in its high temperature α-phase. A significant drop of the thermal diffusivity has been observed during the β−α phase transition reducing the values from 0.12 close to 0.08 mm² s⁻¹. At the same transition the thermopower reacts on the increasing silver mobility and jumps towards less negative values.Thermal conductivities, thermopower and thermal diffusivity of selected compounds with various grades of anion substitution in Ag₅Q₂X were determined around the silver-order/disorder β−α phase transition. A formation of attractive interactions could be observed for selenium substituted phases while no effect was detected for bromide and sulfide samples. Depending on the grade and type of substitution the thermopower changes significantly at and after the β−α phase transition. Thermal conductivities are low reaching values around 0.2-0.3 W m⁻¹ K⁻¹ at 299 K. Partial anion exchange can substantially tune the thermoelectric properties in Ag₅Q₂X phases.     

Functional Polymer‐Opals from Core–Shell Colloids

Colloidal photonic crystals were prepared from monodisperse core–shell particles. The shell is hereby formed from a functional monomer, such as glycidylmethacrylate or different reactive ester monomers, which can perform chemical reactions and the core from a standard monomer, which yields highly monodisperse colloids. It was possible to crystallize the core–shell particles into artificial opals with excellent optical properties. Reactions on the functional surface of the colloids were carried out, which lead to a dramatic rise in the mechanical stability or to a functionalization of His‐tagged silicatein, which acts as nanoreactor to synthesize and immobilize gold nanoparticles from auric acid onto the core–shell colloids.

     

Biocatalytic Reduction of 2‐Monosubstituted 3‐Thiazolines Using Imine Reductases

The application of a straightforward biocatalytic technology for the reduction of racemic 2‐monosubstituted 3‐thiazolines, which are easily prepared via Asinger‐multicomponent reaction, is reported. The biocatalytic reduction yields racemic 2‐monosubstituted 3‐thiazolidines, which are difficult to be prepared by means of classic chemical routes, in moderate to high yields. Moreover, our study clarifies the stereochemical reaction course of the biocatalytic reduction. Furthermore, the efficiency of this biocatalytic technology is demonstrated in an experiment at an elevated substrate concentration of 60 mM leading to 96% conversion.     

New advances in the synthesis of tripyridinophane macrocycles suitable to enhance the luminescence of Ln(III) ions in aqueous solution

A series of four new 18-membered hexaaza macrocyclic ligands bearing three endocyclic pyridine units and acetate or methylenephosphonate pendant arms has been prepared. The new synthetic procedure is based on the use of amine and diamine precursors incorporating masked carboxylate or phosphonate functions and on an efficient sodium template effect which controls the crucial macrocyclization step (yields of macrocyclization reactions: 62–88%). This procedure appears as a suitable alternative compared to the classical Richman-Atkins methodology generally used for the preparation of this class of macrocycles. As demonstrated with the Eu^III and Tb^III complexes derived from two ligands, these tripyridinophane chelators form luminescent and stable mononuclear Ln^III complexes in aqueous solution at physiological pH. In such a medium, Tb^III complexes exhibit a brightness of 1700 (λ_exc?=?279?nm) and 3000 (λ_exc?=?268?nm)?M^?1?cm^?1.     

Carbon nanotubes as intracellular protein transporters: generality and biological functionality

Various proteins adsorb spontaneously on the sidewalls of acid-oxidized single-walled carbon nanotubes. This simple nonspecific binding scheme can be used to afford noncovalent protein-nanotube conjugates. The proteins are found to be readily transported inside various mammalian cells with nanotubes acting as the transporter via the endocytosis pathway. Once released from the endosomes, the internalized protein-nanotube conjugates can enter into the cytoplasm of cells and perform biological functions, evidenced by apoptosis induction by transported cytochrome c. Carbon nanotubes represent a new class of molecular transporters potentially useful for future in vitro and in vivo protein delivery applications.     

On the determination of the stereochemistry of semisynthetic natural product analogues using chiroptical spectroscopy: desulfurization of epidithiodioxopiperazine fungal metabolites

Isolation and semisynthetic modification of the fungal metabolite chaetocin gave access to a desulfurized analogue of this natural product. Detailed chiroptical studies, comparing experimentally obtained optical rotation values, electronic circular dichroism spectra, and vibrational circular dichroism spectra to computationally simulated ones, reveal the desulfurization of chaetocin to unambiguously proceed with retention of configuration. Consideration of the plausible mechanisms for this process highlighted inconsistencies in the stereochemical assignment of related molecules in the literature. This in turn allowed the stereochemical reassignment of the natural product analogue dethiodehydrogliotoxin.     

Bulk-modified modified screen-printing carbon electrodes with both lactate oxidase (LOD) and horseradish peroxide (HRP) for the determination of L-lactate in flow injection analysis mode

A screen-printed carbon electrode modified with both HRP and LOD (SPCE–HRP/LOD) has been developed for the determination of l-lactate concentration in real samples. The resulting SPCE–HRP/LOD was prepared in a one-step procedure, and was then optimised as an amperometric biosensor operating at [0, −100] mV versus Ag/AgCl for l-lactate determination in flow injection mode. A significant improvement in the reproducibility (coefficient variation of about 10%) of the preparation of the biosensors was obtained when graphite powder was modified with LOD in the presence of HRP previously oxidised by periodate ion (IO₄⁻). Optimisation studies were performed by examining the effects of LOD loading, periodation step and rate of the binder on analytical performances of SPCE–HRP/LOD. The sensitivity of the optimised SPCE–HRP/LOD to l-lactate was 0.84 nA L μmol⁻¹ in a detection range between 10 and 180 μMol. The possibility of using the developed biosensor to determine l-lactate concentrations in various dairy products was also evaluated.