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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, 2010Vibrational Energy Transport in a Peptide Capping Layer overGold NanoparticlesMarco Schade 1 , Paul M. Donaldson 1 , Peter Hamm 1 ,Alessandro Moretto 2 , and Claudio Toniolo 21 Institute of Physical Chemistry, University of Zűrich, Zűrich, 8057, Switzerland; 2 ICB,Padova Unit, CNR, Department of Chemistry, University of Padova, Padova, 35131, ItalyIntroductionGold nanoparticles have found numerous applications in life sciences as labels, where theyare often covered by biocompatible capping agents [1-3]. Thermal relaxation processes [4]in metal nanoparticles and the subsequent energy transfer process into a solvent havereached considerable interest in current research.Results and DiscussionTo obtain site-selective information about different positions in a 3 10 -helical [5] peptidecapping layer, we used 13 C isotope labeling. The two peptides studied were HS-CH 2 CH 2 -O-CO-NH-Aib-Ala*-Aib 6 -OMe (1) and HS-CH 2 CH 2 -O-CO-NH-Aib 3 -Ala*-Aib 4 -OMe (2)(Figure 1). The N-terminal HS-groups of these peptides allow covalent attachment to thegold nanoparticles. Due to a difference in the metal core diameter (sample 1, 1.2 nm;sample 2, 2 nm) the plasmon resonance in the Vis spectrum of 2 is more pronounced.Because of the size-dependent surface/volume ratio, a higher absolute concentration of 2 isneeded to reach the same effective peptide concentration as that of 1.HSOH H HCHHCHH33 CHHCHH33 CHHN3 CHN3 CHN3 CH 3N N N N N OH C HO 3H COHO 3 O 3 C H C HO 3 O 3 C H HO 3 CO 3 CO*peptide 1HSOH H HCH 3 CH H3N NN CH H HCHH3CHH33 CH 3 CH 3NN NN CH 3NOH C H CO 3 O 3 H C HO 3 O * O H 3 C HO 3 C H HO 3 CO 3 COpeptide 2Fig. 1. The two capping agents used in this study are the 3 10 -helical octapeptides HS-(CH 2 ) 2 -O-CO-Aib-L-Ala*-(Aib) 6 -OMe (peptide 1) and HS-(CH 2 ) 2 -O-CO-(Aib) 3 -L-Ala*-(Aib) 4 -OMe (peptide 2), where Aib stands for α-aminoisobutyric acid and an asterisk (*)indicates a 13 C=O label. A urethane moiety was inserted between the linking group andthe actual peptide to have an intrinsically spectrally resolved C=O group at thebeginning of the helical chain.620