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Proceedings of the 31 st European Peptide SymposiumMichal Lebl, Morten Meldal, Knud J. Jensen, Thomas Hoeg-Jensen (Editors)European Peptide Society, 2010Au 25 Nanoclusters Capped by PhotoactiveAib-based AzopeptidesIvan Guryanov, Sabrina Antonello, Mahdi Hesari, Martina Zamuner,and Flavio MaranDepartment of Chemistry, University of Padova, Padova, 35131, ItalyIntroductionThe study of novel phenomena and processes at the molecular level provides usefulknowledge for designing a wide range of tools, materials, devices, and systems withspecific characteristics. Monolayer-protected gold nanoclusters (MPC) of small size (< 1.5nm) are of particular interest because they are rather complex hybrid systems but stilldisplay quasi-molecular features, such as the presence of a well-defined HOMO-LUMOgap [1,2]. The introduction of different ligands into the nanoparticle-capping monolayercan significantly affect the properties of the nanoparticle, such as the redox or opticalbehavior. For this purpose, rigid 3 10 -helical peptides based on the α-aminoisobutyric (Aib)acid unit are very interesting molecules because they are stiff, possess a strong dipolemoment, and are capable of mediating electron tunneling very efficiently [3,4]. In thiswork, we used the ligand place-exchange approach to introduce a thiolated Aib-peptide,containing an azo-fragment, into the monolayer of preformed phenylethanthiolate-protectedgold nanoclusters Au 25 (SCH 2 CH 2 Ph) 18 . Upon irradiation at 366 nm, trans→cisisomerization of the –N=N– bond was expected to change the spatial orientation of thepeptide dipole moment as well as the distance between the peptide and the nanoparticlecore (Figure 1).Results and DiscussionTwo azo-group containing ligands were synthesized, one with the peptide fragment(compound 1) and the other with a methyl ester group (compound 2) (Figure 2A). Bystudying the optical behavior of the free trityl (Trt) protected ligands (trans form), weFig. 1. Ligand exchange reaction with thiolated azopeptides.Fig.2. Ligands used for nanoparticle modification (A) and trans→cis isomerization of 1 (B) orthe 20% substituted Au nanoparticle (C) at 366 nm.616