Concentration- and temperature-dependent conformation change of cyclohexyl isocyanide on gold nanoparticle surfaces

Abstract

The conformational changes of cyclohexyl isocyanide (CHNC) on gold nanoparticle surfaces were investigated by means of concentration- and temperature-dependent surf ace-enhanced Raman scattering (SERS). The equatorial chair conformer appeared to be dominant at high-bulk concentrations or low temperatures, whereas both the equatorial and axial chair conformers of CHNC were found to exist at low-bulk concentrations or high temperatures as in the previous reports of cyclohexanethiol (CHT). Depending on concentrations and temperatures, the spectral changes of the NC stretching vibration on gold nanoparticles appeared to be more conspicuous than those of the cyclohexyl ring modes. A density functional theory (DFT) calculation was performed at the level of B3LYP/6-31G++(d,p) to compare the energetic stability of the various conformers of CHT and CHNC. The energy differences between the equatorial and axial chair conformers were predicted to be smaller for CHNC than for CHT by similar to 3 kJ mol(-1) from the DFT calculation. Copyright (C) 2008 John Wiley & Sons, Ltd.