title: Photo-stability of peptide-bond aggregates: N-methylformamide dimers.
abstract: The formation of weakly-bound dimers of N-methylformamide (NMF) and the photochemistry of these dimers after irradiation at 248 nm were explored using matrix-isolation spectroscopy. Calculations were used to characterize the diverse isomers and assign their IR spectra; non-adiabatic dynamics was simulated to understand their photo-deactivation mechanism. The most stable dimers, and , were obtained by trans-trans aggregation (N-HO[double bond, length as m-dash]C interactions) and could be identified in the matrix. The main products formed after irradiation are the trans-cis dimers ( and ), also stabilized by N-HO[double bond, length as m-dash]C interactions. In contrast to the photochemistry of the monomers, no dissociative products were observed after 248 nm irradiation of the dimers. The absence of dissociative products can be explained by a proton-transfer mechanism in the excited state that is faster than the photo-dissociative mechanism. The fact that hydrogen bonding has such a significant effect on the photochemical stability of NMF has important implications to understand the stability of peptide-bonded systems to UV irradiation.
authors: Max-Planck-Institut für Kohlenforschung, Kaiser-Wilheim-Platz 1, 45470 Mülheim an der Ruhr, Germany. barbatti@kofo.mpg.de.
authors: Rachel
authors: R
authors: Crespo-Otero
authors: Artur
authors: A
authors: Mardykov
authors: Elsa
authors: E
authors: Sanchez-Garcia
authors: Wolfram
authors: W
authors: Sander
authors: Mario
authors: M
authors: Barbatti
mesh_terms: D019281:Dimerization; D005559:Formamides / Q000737:chemistry*; D006860:Hydrogen Bonding; D007536:Isomerism; D008968:Molecular Conformation; D009584:Nitrogen / Q000737:chemistry; D010455:Peptides / Q000737:chemistry* / Q000378:metabolism; D013055:Spectrophotometry, Infrared; D013816:Thermodynamics; D014466:Ultraviolet Rays
chemical_list: D005559:Formamides; D010455:Peptides; D009584:Nitrogen; C002950:methylformamide