title: N-methyl-trimethylacetamide in thin films displays infrared spectra of π-helices, with visible static and dynamic growth phases, and then a β-sheet.
abstract: The simplest (minimal) peptide model is HCONHCH3. An increase in the π-helix content with increased substitution in the acyl portion suggested the examination of N-methyl-trimethylacetamide) (NMT). NMT displays spectra, in which there is evolution of a set of helices defined by their amide I maxima near 1686 (3(10)), 1655 (first π), and, most importantly, at 1637 cm(-1) (π). Expanded thin-film infrared spectroscopy (XTFIS) shows pauses or slow stages, which are identified as static phases followed by dynamic phases with the incremental gain or loss of a helix turn. In addition, absorbance at 1637 cm(-1) suddenly increases at 82.1 s (30% over 0.3 s), indicating a phase change and crystallization of the π-helix, along with a coincidental decrease in the absorbance for the first π-helix. A sharp peak occurs at the maximum of the phase change at 82.5 s, representing a pure NMT π-helix. The spectra then undergo a decreasing general absorption loss over 150 s, with the π-helix evolving further to an antiparallel β-sheet fragment. The spectral quality arises from the immobilization of polar molecules on polar surfaces. The crystal structure is that of an antiparallel β-sheet.
authors.affiliation: School of Chemistry, Tel-Aviv University, Ramat-Aviv, Tel-Aviv 69978 (Israel). kosower@post.tau.ac.il.
authors.forename: Edward M
authors.initials: EM
authors.lastname: Kosower
authors.forename: Galina
authors.initials: G
authors.lastname: Borz
authors.forename: Israel
authors.initials: I
authors.lastname: Goldberg
authors.forename: Natalya
authors.initials: N
authors.lastname: Ermakov
mesh_terms: D000081:Acetamides / Q000737:chemistry*; D006860:Hydrogen Bonding; D010455:Peptides / Q000737:chemistry*; D017433:Protein Structure, Secondary; D013055:Spectrophotometry, Infrared
chemical_list: D000081:Acetamides; D010455:Peptides; C018595:N-methylacetamide
keywords: IR spectroscopy; N-methyl-trimethylacetamide; helical structures; hydrogen-bonded peptides; planar fibers