Designing liquid-crystalline dendronised hexa-adducts of [60]fullerene via click chemistry

ABSTRACT

Liquid-crystalline [60]fullerodendrimers were constructed via click chemistry based on the reaction between hexa-adducts of [60]fullerene (C₆₀) bearing 12 azide groups and alkyne-terminated cyanobiphenyl dendrons of first- and second-generation. The structure of all the new compounds was confirmed by IR, UV, ¹H and ¹³C NMR spectroscopies and mass spectrometry. The mesomorphic properties were studied by polarised optical microscopy, differential scanning calorimetry and small-angle X-ray scattering. The hexa-adduct of C₆₀ functionalised with the first-generation dendrons gave rise to the formation of a smectic A phase and a rectangular columnar phase (c2mm symmetry) while the hexa-adduct of C₆₀ decorated with the second-generation dendrons displayed only a rectangular columnar phase (c2mm symmetry). Our results show that the hexa-adduct of C₆₀ is a unique synthetic platform for the design of fullerodendrimers and dendronised materials.     

Live Monitoring of Cargo Release From Peptide‐Based Hybrid Nanocapsules Induced by Enzyme Cleavage

The miniemulsion process is used as a new route for the preparation of enzyme‐responsive nanocapsules with payload‐release properties. Peptide‐based hybrid nanocapsules are prepared via interfacial polyaddition containing a water‐soluble dye that is efficiently encapsulated inside. The influence of the synthetic parameters as the functionality of the peptide and the nature of the dispersed phase on the structure of the nanocapsules were investigated. After redispersion in water, the enzymatic cleavage of the peptide sequence and the release of the fluorescent dye are both monitored in real time. This is evidenced because of the quenching FRET system framing the recognition site in the peptide sequence, and the fluorescence recovery of the self‐quenched encapsulated dye respectively.     

Intramolecular Homolytic Substitution of Sulfinates and Sulfinamides

A general and efficient method for the synthesis of cyclic sulfinates and sulfinamides based on intramolecular homolytic substitution (S_Hi) at the sulfur atom by aryl or alkyl radicals is described. Both alkyl and benzofused compounds can be accessed directly from easily prepared acyclic precursors. Enantiomerically enriched sulfur‐based heterocycles were formed through an S_Hi process with inversion of configuration at the sulfur atom. Cyclization of prochiral radicals proceeded with varying stereochemical outcomes, depending on the size of the incoming radical. 2‐Pyridyl and 2‐quinolyl radicals led to biaryl compounds, which result from attack onto the ortho position of the arylsulfinate rather than a thiophilic substitution.     

Mechanical properties of natural rubber nanocomposites reinforced with cellulosic nanoparticles obtained from combined mechanical shearing,and enzymatic and acid hydrolysis of sisal fibers

In a previous work (Siqueira et al. 2010b) the preparation of cellulosic nanoparticles from sisal fibers using different processing routes, viz. a combination of mechanical shearing, acid and enzymatic hydrolysis was reported. It was shown that the pre-enzymatic hydrolysis treatment of bleached sisal pulp helps the preparation of well individualized rod-like nanocrystals. An amorphous polymer (natural rubber—NR) was chosen as model matrix to investigate the effect of these nanoparticles on the thermo-mechanical properties of nanocomposites. Both tensile tests and dynamic mechanical analyses showed improved stiffness for all nanocomposites. The enzymatic treatment allowed production of a huge range of cellulosic nanoparticles which provided completely different mechanical properties to NR matrix.