Synthesis of polymer dielectric layers for organic thin film transistors via surface-initiated ring-opening metathesis polymerization

The use of surface-initiated ring-opening metathesis polymerization (SI-ROMP) for producing polymer dielectric layers is reported. Surface tethering of the catalyst to Au or Si/SiO2 surfaces is accomplished via self-assembled monolayers of thiols or silanes containing reactive olefins. Subsequent SI-ROMP of norbornene can be conducted under mild conditions. Pentacene semiconducting layers and gold drain/source electrodes are deposited over these polymer dielectric films. The resulting field effect transistors display promising device characteristics, demonstrating for the first time that SI-ROMP can be used in the construction of organic thin-film electronic devices.     

Synthesis of new cationic lipids from an unsaturated glycoside scaffold

[see structure]. We report the synthesis of new cationic lipids. These amphiphiles present a hydrophobic domain connected to a guanidinium entity by an unsaturated glycoside scaffold. The synthetic strategy using amide or acetal linkage led to various mono- and bicatenar derivatives. Investigation of their physicochemical properties indicated that these new compounds compact DNA.     

Characterization of monohydroxylated derivatives of the anticancer agent flavone-8-acetic acid by liquid chromatography with on-line UV and mass spectrometry

The experimental anticancer agent flavone-8-acetic acid (FAA) is metabolized into several monohydroxylated derivatives using mouse microsomes. Because these metabolites could be involved in the biological effects of FAA, the aim of this study was to characterize all its possible monohydroxylated derivatives. To do so, we have developed a methodology using reversed-phase high-performance liquid chromatography (RP-HPLC) coupled with ultraviolet (UV) detection and mass spectrometry (MS) to analyze and identify FAA derivatives hydroxylated at the 2', 3', 4', 3, 5, 6, or 7 position. In RP-HPLC, 4'-, 3'-, 2'-, 6-, and 7-OH-FAA eluted before FAA, whereas 3- and 5-OH-FAA eluted after FAA. UV spectra showed a bathochromic shift of band I for all derivatives and of band II for 5- and 6-OH-FAA. In addition, the position of the OH group could be determined by the presence of certain product ions in MS. Ions at m/z 133 and 151 were specific for 2'-, 3'-, 4'-, and 3-OH-FAA, whereas the ion at m/z 177 was specific for 3-OH-FAA only. The ions m/z 133, 151 and 167 were specific for 2'-OH-FAA. Ions at m/z 149 were specific for the presence of the OH group on cycle A only (i.e., 5-, 6- or 7-OH-FAA). The presence of both product ions m/z 149 and 179 were specific for 7-OH-FAA. Finally, ions at m/z 149 and several product ions of even m/z values were specific for 5-OH-FAA. In conclusion, the methodology described can be used to identify all possible monohydroxylated FAA derivatives.     

The reverse block copolymer Pluronic 25R2 promotes DNA transfection of skeletal muscle

Muscle is an important and attractive target for gene therapy. Recent findings have shown that neutral amphiphilic triblock copolymers with a PEO-PPO-PEO arrangement significantly increase muscle transfection as compared to naked DNA. We were interested in evaluating whether reverse Pluronics (PPO-PEO-PPO) also possess transfection properties. Therefore, we measured the in vitro and in vivo transfection activity of 25R2 and 25R4, two copolymers that differ by their hydrophilic/hydrophobic balance. The results show that 25R2 significantly increases the transfection level in muscle compared to naked DNA. Taken together, this work demonstrates that the reverse Pluronic 25R2 possesses interesting properties for in vivo transfection.     

"On-demand" control of thermoresponsive properties of poly(N-isopropylacrylamide) with cucurbit[8]uril host-guest complexes

The chain end complexation of a functional PNIPAM by a cucurbit[8]uril-viologen complex causes a shift in its lower critical solution temperature (LCST) by over 5 °C. An instantaneous phase change of the thermally responsive polymer beyond its LCST can be induced by addition of the aqueous cucurbituril host-guest complex. Subsequent decomplexation upon addition of a competitive guest releases the PNIPAM terminus and triggers complete reversibility.     

Supramolecular Polymerization Promoted and Controlled through Self‐Sorting

A new method in which supramolecular polymerization is promoted and controlled through self‐sorting is reported. The bifunctional monomer containing p‐phenylene and naphthalene moieties was prepared. Supramolecular polymerization is promoted by selective recognition between the p‐phenylene group and cucurbit[7]uril (CB[7]), and 2:1 complexation of the naphthalene groups with cucurbit[8]uril (CB[8]). The process can be controlled by tuning the CB[7] content. This development will enrich the field of supramolecular polymers with important advances towards the realization of molecular‐weight and structural control.     

Activation Energies Control the Macroscopic Properties of Physically Cross‐Linked Materials

Here we show the preparation of a series of water‐based physically cross‐linked polymeric materials utilizing cucurbit[8]uril (CB[8]) ternary complexes displaying a range of binding, and therefore cross‐linking, dynamics. We determined that the mechanical strength of these materials is correlated directly with a high energetic barrier for the dissociation of the CB[8] ternary complex cross‐links, whereas facile and rapid self‐healing requires a low energetic barrier to ternary complex association. The versatile CB[8] ternary complex has, therefore, proven to be a powerful asset for improving our understanding of challenging property–structure relationships in supramolecular systems and their associated influence on the bulk behavior of dynamically cross‐linked materials.     

Imidazolium-modification enhances photocatalytic CO2 reduction on ZnSe quantum dots

Colloidal photocatalysts can utilize solar light for the conversion of CO₂ to carbon-based fuels, but controlling the product selectivity for CO₂ reduction remains challenging, in particular in aqueous solution. Here, we present an organic surface modification strategy to tune the product selectivity of colloidal ZnSe quantum dots (QDs) towards photocatalytic CO₂ reduction even in the absence of transition metal co-catalysts. Besides H₂, imidazolium-modified ZnSe QDs evolve up to 2.4 mmol_CO g_ZnSe⁻¹ (TON_QD > 370) after 10 h of visible light irradiation (AM 1.5G, λ > 400 nm) in aqueous ascorbate solution with a CO-selectivity of up to 20%. This represents a four-fold increase in CO-formation yield and 13-fold increase in CO-selectivity compared to non-functionalized ZnSe QDs. The binding of the thiolated imidazolium ligand to the QD surface is characterized quantitatively using ¹H-NMR spectroscopy and isothermal titration calorimetry, revealing that a subset of 12 to 17 ligands interacts strongly with the QDs. Transient absorption spectroscopy reveals an influence of the ligand on the intrinsic charge carrier dynamics through passivating Zn surface sites. Density functional theory calculations indicate that the imidazolium capping ligand plays a key role in stabilizing the surface-bound *CO₂⁻ intermediate, increasing the yield and selectivity toward CO production. Overall, this work unveils a powerful tool of using organic capping ligands to modify the chemical environment on colloids, thus enabling control over the product selectivity within photocatalyzed CO₂ reduction.

A photocatalyst system consisting of ZnSe quantum dots modified with a thiolated imidazolium capping ligand for visible light-driven reduction of aqueous CO₂ to CO is reported without the need for a metal complex co-catalyst.     

Probing the stability of multicomponent self-assembled architectures based on cucurbit[8]uril in the gas phase

Aqueous supramolecular chemistry and highly controlled self-assembly of multi-component architectures are novel tools for investigating and answering questions with different biological implications. Among other self-assembly motifs the barrel-shaped host molecule cucurbit[8]uril (CB[8]) is of particular interest due to its capability of incorporating two guest molecules simultaneously in its hydrophobic cavity. This allows for its use as a supramolecular linking unit to conjugate two different entities such as polymers, peptides, and proteins as well as conjugation of various species to surfaces, colloids and nanoparticles. This study aims to improve our understanding of CB[8] ternary complex formation and stability. A series of CB[8] architectures of different size and chemistry have been analyzed in the gas phase to obtain information about their stability in the absence of solvent effects. While hydrophobic effects and solvation energies play a crucial role for host-guest affinities in solution, gas phase stabilities are determined by the guest's ability to form hydrogen bonding and electrostatic interactions. Increasing the size of the second guest resulted in an increase of gas phase stability, likely due to additional non-covalent interactions.