Nanoscopic morphological effect on the optical properties of polymer-grafted gold polyhedra.

Plasmonic nanoparticles show highly sensitive optical properties upon local dielectric environment changes. Hybridisation of plasmonic nanoparticles with active polymeric materials can allow stimuli-responsive and multiplex sensing over conventional monotonic sensing capacity. Such heterogeneous adlayers around the plasmonic core component, however, are likely to perturb the local refractive index in the nanometre regime and lead to uncertainty in its intrinsic sensitivity. Herein we prepare a series of polystyrene-grafted polyhedral gold nanoparticles, cubic and concave cubic cores, with different edge lengths and polymer thicknesses with precise synthesis control. Their localised surface plasmon resonance (LSPR) spectral changes are monitored to understand the effect of core morphological details in the interplay of nanoscale polymeric shells. Quantitative image analysis of changes in the core and shell shape contours and finite-difference time-domain simulations of the corresponding LSPR spectra and electric field distributions reveal that the magnitude of the LSPR spectral shift is closely dependent on the core morphology, polymer shell thickness and electric field intensity. We also demonstrate that the polystyrene-grafted gold concave cube displays higher sensitivity for nanoscale refractive index change in the polymer shell than the polystyrene-grafted gold cube at different temperatures. Our systematic investigation will help design polymer-composited plasmonic nanosensors for desirable applications.

Controllable coating and reshaping of gold nanorods with tetracyanoquinodimethane.

Various nanoparticle surface layers allow unique functionalities. We developed a coating method with tetracyanoquinodimethane that forms solid layers through π stacking on gold nanorod surfaces. Its reaction mechanism was investigated with reaction time, aging time and surfactant concentration. Our method could be generalizable to different nanoparticle shapes and crystal facets.

Morita-Baylis-Hillman reaction of a chiral aziridine aldehyde.

The Morita-Baylis-Hillman reaction of (R)-1-((R)-1-phenylethyl)aziridine-2-carbaldehyde with alkyl acrylate was carried out under various conditions by changing solvents, bases, and alcohol additives. The reaction at room temperature under neat conditions (no solvent) with quinuclidine as an amine nucleophile, in the presence of benzyl alcohol as an additive, afforded a product, γ-(aziridin-2-yl)-ß-hydroxy-α-methylene butanoate, in 97% yield with a diastereomeric ratio of anti and syn as 86 : 14.

Highly stereoselective directed reactions and an efficient synthesis of azafuranoses from a chiral aziridine.

Polyhydroxylated pyrrolidines, such as biologically important azafuranoses represented by the natural product (+)-2,5-imino-2,5,6-trideoxy-gulo-heptitol and its C(3)-epimer, were elaborated from a commercially available enantiomerically pure (2R)-hydroxymethylaziridine by highly stereoselective directed reactions in more than 61% overall yield. At first, the nucleophile 2-trimethylsilyloxyfuran was directed to (2R)-aziridine-2-carboxaldehyde by ZnBr2 to yield the unusual anti-addition product as a single isomer via the chelation-controlled transition. The ring opening of aziridine was followed by conjugate addition to give a cis-fused bicycle, which was converted to the target molecule after the required reductive operations.