Dynamics of oligo(phenylene-ethynylene) self-assembled monolayers on Au(111)

Oligo(phenylene-ethynylene), self-assembled monolayers on Au(1 1 1) have been studied with scanning tunneling microscopy. The oligo(phenylene-ethynylene) molecules are adsorbed in a flat-lying orientation. Time-resolved scanning tunneling microscopy measurements reveal that the molecules continuously switch back and forth between two nearly degenerate configurations. The energy difference between the two configurations is 22 ± 5 meV and the activation barrier for the transition from the low-energy configuration to the high-energy configuration is 0.65 ± 0.03 eV. A statistical analysis of the residence times revealed that the switching process is stochastic. We propose that the two level switching is due to a torsional mode of the central phenyl ring

Synthesis and biophysical study of disassembling nanohybrid bioconjugates with a cubic octasilsesquioxane core

Polyhedral oligosilsesquioxanes (POSS) have recently attracted attention as scaffolds for the synthesis of multivalent bioconjugates. The synthesis of glycosyl-octasilsesquioxanes (glyco-POSS) using a copper(I)-catalyzed azide-alkyne 1,3-dipolar cycloaddition approach is reported. The problems associated with the use of bases or aqueous media in their preparation are investigated and a comprehensive study of the multivalent interaction between the mannosyl-octasilsesquioxanes and a model lectin, concanavalin A (Con A), using an array of complementary biophysical techniques is presented. The possibility to modulate the half-life of POSS conjugates in aqueous solution and the low toxicity of their constituent monomeric organosilanes offers an advantage over other scaffolds in vivo, preventing bioaccumulation and saturation of complementary receptors (lectins). Despite the hydrolysis in water, the octamannosyl-POSS studied shows a 50-fold higher binding affinity to Con A than methyl α-D-mannopyranoside. These experiments suggest that the novel glyco-POSS are attractive compounds for in vivo applications that require multivalent display of glycans.The authors thank the Spanish Ministerio de Ciencia e Innovación (projects CTQ-2006-15515-C02-02/BQU, CTQ2009-14551-C02-02, MAT2010-20646-C04-03, SAF2010-15670, and CTQ2010-15848), the Comunidad de Madrid (project S2009/PPQ-1634 “AVANCAT”), the Junta de Andalucía, and the European Union (FEDER and FSE) for fi nancial support. The authors also thank Ministerio de Ciencia e Innovación for FPU predoctoral contracts to B.T. and A.M.-A., and C.S.I.C. for a JAEPREDOC contract to M.E.P.-O.Peer Reviewe