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Fig. 2. FTIR and UV-vis (inset) spectra in acetonitrile-d 3 recorded for nanoparticlescoated with peptide 1 (black line) and peptide 2 (gray line) at equal effective peptideconcentration. The spectrally resolved C=O bands are labeled according to theirpositions in the peptide chain. Bands 1: urethane C=O; bands 3 and 5: labeled amide13 C=O; bands 9: methyl ester C=O; main band: amide C=O. Inset: in the UV-vis spectrathe plasmon resonance appearing around 520 nm is more pronounced for thenanoparticles coated with peptide 2 (gray line) due to the bigger diameter of its goldcore.In a VIS pump /IR probe experiment we deposited vibrational excess energy in the goldnanoparticles by exciting their plasmon resonance and monitored the responses ofspectrally resolved C=O thermometers in the backbone of the helical peptides. Thesequential appearance of the bleach maxima of the different C=O reporter units nicelyshowed the propagation of vibrational energy trough the capping layer: the further areporter unit is away from the heated gold nanoparticle, the later and the less vibrationalenergy arrives (Figure 2). We observed that the cooling behavior depends on the particlesize: due to a lower surface/volume ratio, bigger particles cool slower. To analyze thestructural distribution and its dynamics, we recorded the 2D-IR spectra of the cappinglayer. From the distinct tilt of the 2D-IR peaks, in particular that of the isotope labelled one,we concluded that the transitions are strongly inhomogenously broadened. The increasedinhomogeneous broadening, compared to that of the isolated peptides in solution, suggestsstrong interactions among the aligned peptides in the capping layer or between the peptidesand the gold nanoparticles.References1. Giljohann, D.A., Seferos, D.S., Daniel, W.L., Massich, M.D., Patel, P.C., Mirkin, C.A. Angew.Chem. Int. Edit. 49, 3280-3294 (2010).2. Bunz, U.H.F., Rotello, V.M. Angew. Chem. Int. Edit. 49, 3268-3279 (2010).3. Klajn, R., Fraser Stoddart, J., Grzybowski, B.A. Chem. Soc. Rev. 39, 2203-2237 (2010).4. Backus, E.H.G., Bloem, R., Moretto, A., Crisma, M., Toniolo, C., Hamm, P. J. Phys. Chem. B113,13405-13409 (2009).5. Toniolo, C., Benedetti, E. Trends Biochem. Sci. 16, 350-353 (1991).621