The 1,3-dipolar cycloaddition of adamantine-derived nitrones with maleimides

Abstract

Adamantane-derived aldo- and ketonitrones react with maleimides giving corresponding isoxazolidines. In the case of aldonitrones reactions proceed giving the diastereomeric mixtures. The ratio of isomers is changing during the reaction process due to the reversibility of the cycloaddition reaction. The cytotoxic and virus-inhibiting activity against influenza virus was investigated for selected adducts.     

Chemical modification of nanocrystalline cellulose for improved interfacial compatibility with poly(lactic acid)

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Synthesis,Crystal Structure,and Colloidal Dispersions of Vanadium Tetrasulfide (VS4)

Although many of the layered metal chalcogenides, such as MoS₂, are well‐studied, some other chalcogenides have received less attention by comparison. In particular, there has been an emerging interest in vanadium tetrasulfide (VS₄), which displays useful properties as a component of hybrids. However, the synthetic methods and characteristics of individual VS₄ are not yet well defined, and there is no report on its solution processability. Here we have synthesized VS₄ by a simple and fast direct reaction between elements. Reinvestigation of the VS₄ crystal structure yielded more precise atomic coordinates and interatomic distances, thereby confirming the crystallization of VS₄ in the monoclinic C2/c group and its quasi‐1D chainlike structure. As the chains in VS₄ are only bonded by weak van der Waals forces, we further demonstrate that bulk VS₄ may be ultrasonically dispersed in appropriate solvents to form colloids, similarly to the layered chalcogenides. VS₄ particles in colloids retain their phase identity and rod‐shaped morphology with lengths in the range of hundreds of nanometers. Isopropanol dispersion exhibited the highest concentration and stability, which was achieved owing to the repulsion caused by high negative charges on the edges of the particles.     

Recent Advances in Mechanically Robust and Stretchable Bulk Heterojunction Polymer Solar Cells

Organic bulk heterojunction solar cells are promising candidates as future photovoltaic technologies for large‐scale and low‐cost energy production. It is, therefore, not surprising that research on the design and preparation of these types of organic photovoltaics has attracted a lot of attention since the last two decades, leading to constantly growing values of energy conversion and efficiency. Combined with the possibility of a large‐scale production via roll‐to‐roll printing techniques, bulk heterojunction solar cells enable the fabrication of conformable, light‐weight and flexible light‐harvesting devices for point‐of‐use applications. This perspective review will highlight the recent advances toward mechanically robust and intrinsically stretchable bulk heterojunction solar cells. Mechanically robust fullerene‐based and all‐polymer devices will be presented, as well as a comprehensive overview of the recent challenges and characterization techniques recently developed to overcome some of the challenges of this research area, which is still in its infancy.     

In Situ-Generated,Dispersed Cu Catalysts for the Catalytic Hydrogenolysis of Glycerol

The present study is dedicated to the experimental verification of a concept for the hydrogenolysis of glycerol over in situ-generated Cu dispersed particles (Cu-DP). The Cu-DP were generated by in situ reduction of a precursor salt (Cu(OAc)₂, CuSO₄, CuCl₂) in the presence of KOH and were active in glycerol conversion under hydrogen (T = 200–220 °C, p(H₂) = 1–4 MPa), where 1,2-propylene glycol (PG) and lactic acid (LA) were detected to be the main products. The influence of the reaction conditions (temperature, hydrogen pressure, reaction time, catalyst-to-feed ratio and the KOH/Cu ratio) on the yields of the products is described. It was shown that the selectivity between the PG and LA could be tuned by changing p(H₂) or by the KOH amount, i.e., higher yields of LA corresponded to lower p(H₂) and higher alkalinity of the reaction media. The activity of the in situ-generated Cu-DP was found to be comparable to that of an industrial Cu-Cr₂O₃ catalyst. The Cu-DP catalysts were characterized by XRD, XPS, HRTEM and SEM. During the reaction, the catalyst evolved by the sintering and recrystallization of the separate Cu-DP; the crystallite sizes after 1 and 15 h reaction times amounted to 35 and 49 nm, respectively.     

Desymmetrization of Perylenediimide Bay Regions Using Selective Suzuki–Miyaura Reactions from Dinitro Substituted Derivatives

Bay decoration of perylenediimide (PDI) is an attractive approach for tuning the optoelectronic properties of the dye as well as breaking backbone planarity, which provides the possibility of preventing the undesired formation of aggregates. This is usually performed through successive bis-bromination of PDI and pallado-catalyzed cross-coupling, which leads to symmetric triads. We now describe an efficient synthetic strategy for desymmetrization of the accepting PDI core by starting from its bis-nitration. To this end, Suzuki–Miyaura Couplings (SMC) were carried out on a mixture of 1,6- and 1,7-dinitroPDI regioisomers to add triphenylamine donating moieties and obtain donor–acceptor–donor triads. Investigation of the reactivity of dinitro PDI derivatives toward SMC has allowed us to access unprecedented asymmetric π-conjugated PDI-centered triads. These 1,6- and 1,7-PDI based triads, prepared as regioisomeric mixtures, were successfully separated and their spectroscopic, crystallographic and optoelectronic differences are reported.     

Trianionic 1,3,2-Dioxaborine-Containing Polymethines: Bright Near-Infrared Fluorophores

Trianionic polymethines of the A′-π-A-π-A-π-A′ type comprising dioxaborine rings (A) and different electron-accepting end groups (A′) have been synthesized. The obtained dyes absorb and emit light in the near-infrared region with remarkably high molar attenuation coefficients (ϵ up to 495 000 M⁻¹ cm⁻¹ in DMF) and fluorescence quantum yields (Φ_f up to 0.73 in DMF). Thus, the novel trianionic dyes stand among the brightest individual fluorophores known to date – with a magnitude of fluorescence brightness (ϵ⋅Φ_f) of 313 000 M⁻¹ cm⁻¹ in DMF. The synthesized dyes demonstrate a minor negative solvatochromism and small Stokes shifts. X-ray data reveal the nearly planar geometry of the trianionic chromophore. All the obtained compounds are stable in the solid state and in a solution, although the relative stability is much higher in polar aprotic than in protic solvents.     

2,3-unsubstituted chromones and their enaminone precursors as versatile reagents for the synthesis of fused pyridines

A divergent and regioselective approach to fused pyridines was developed through formal [3 + 3] cyclocondensations from simple 2,3-unsubstituted chromones or their enaminone precursors.     

Modulation of Living Cell Behavior with Ultra‐Low Fouling Polymer Brush Interfaces

Ultra‐low fouling and functionalizable coatings represent emerging surface platforms for various analytical and biomedical applications such as those involving examination of cellular interactions in their native environments. Ultra‐low fouling surface platforms as advanced interfaces enabling modulation of behavior of living cells via tuning surface physicochemical properties are presented and studied. The state‐of‐art ultra‐low fouling surface‐grafted polymer brushes of zwitterionic poly(carboxybetaine acrylamide), nonionic poly(N‐(2‐hydroxypropyl)methacrylamide), and random copolymers of carboxybetaine methacrylamide (CBMAA) and HPMAA [p(CBMAA‐co‐HPMAA)] with tunable molar contents of CBMAA and HPMAA are employed. Using a model Huh7 cell line, a systematic study of surface wettability, swelling, and charge effects on the cell growth, shape, and cytoskeleton distribution is performed. This study reveals that ultra‐low fouling interfaces with a high content of zwitterionic moieties (>65 mol%) modulate cell behavior in a distinctly different way compared to coatings with a high content of nonionic HPMAA. These differences are attributed mostly to the surface hydration capabilities. The results demonstrate a high potential of carboxybetaine‐rich ultra‐low fouling surfaces with high hydration capabilities and minimum background signal interferences to create next‐generation bioresponsive interfaces for advanced studies of living objects.