| Abstract
| - The surface molecular structure and adsorbed mass of a series of model amphiphilic peptides have beenstudied in situ with surface-specific sum frequency generation (SFG) vibrational spectroscopy and quartzcrystal microbalance (QCM) at the hydrophobic polystyrene and hydrophilic silica solid−water interface.The peptides are designed to form α-helical (XY14) and β-strand (XY7) secondary structures at an apolarinterface and contain hydrophobic (X) and charged (Y) amino acids with sequence Ac-XYYXXYXXYYXXYX-NH2 or Ac-XYXYXYX-NH2, respectively. The X and Y combinations are leucine (L) and lysine(K), alanine (A) and lysine (K), alanine (A) and arginine (R), and phenylalanine (F) and arginine (R). Oneadditional peptide with sequence Ac-LKKLLKL-NH2 (LK7 α) was synthesized. These peptides allow for thestudy of how chain length (LK14 vs LK7 α and LK7 β), amino acid side chain character (LK vs AK vs ARvs FR), and sequence (LK7 α-helix vs LK7 β-strand sequences) affect adsorption. The SFG spectra of adsorbedpeptides on polystyrene typically show CH resonances characteristic of the hydrophobic side chains orientedat the interface. On polystyrene, the molecular orientation the side chain of alanine is more sensitive to changesin peptide chain length and sequence than that of leucine or phenylalanine. The SFG spectra of adsorbedpeptides on silica show no distinct peptide modes, with the exception of the LK14 peptide, where an amideA NH mode is observed. The results demonstrate that SFG vibrational spectra can fingerprint specific aminoacid ordering occurring at the polystyrene interface and secondary structure ordering at the silica interface.QCM data indicates that all peptides except LK7 β adsorb onto both hydrophobic polystyrene and hydrophilicsilica surfaces, even when SFG active modes are not observed.
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