N-methylformamide, a hyperplectic model for peptides in thin film infrared spectroscopy on planar AgX

J Phys Chem B. 2009 Apr 23;113(16):5622-32. doi: 10.1021/jp809920c.

Abstract

N-methylformamide (NMF), the simplest model for peptides, exhibits hyperplectic (both simple and complex) behavior as revealed by thin film infrared spectroscopy on planar AgX [AgCl:AgBr] fiber. IR spectra (0.1 s scans) of 10 microg NMF/dichloromethane(DCM) under N(2) flow first show NMF monomer, dimers, and trimers, which then form surface-organized NMF oligomers as pseudocrystals (P(n)) of increasing length and intensity to P(12). After 4 s, P(12) decays in 1.5 to 4 s steps via P(11), P(10), P(9), P(8), P(7), P(6), and P(5) to P(4) and P(3). The nature of P(n) (n = 5-12) is explained using a model based on the crystal structure of NMF and consisting of a matrix of 7 x 7 helices, alternating R(ight) and L(eft) with TDC (transition dipole coupling) in groups with 2, 3, or 4 neighbors. The total (10) dipolar couplings are matched to the 10 maxima of P(n) and prove the value of the model. P(4) (spectrum 325) fits a 5 x 5 matrix without corners. P(3) is transformed into the very weakly absorbing cyclic hexamer, shown to be very stable and swelling in DCM with increased intensity but without wavelength changes.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bromides / chemistry*
  • Formamides / chemistry*
  • Membranes, Artificial*
  • Models, Chemical*
  • Nitrogen / chemistry
  • Peptides / chemistry*
  • Silver Compounds / chemistry*
  • Spectroscopy, Fourier Transform Infrared / methods

Substances

  • Bromides
  • Formamides
  • Membranes, Artificial
  • Peptides
  • Silver Compounds
  • silver chloride
  • Nitrogen
  • silver bromide
  • methylformamide