title: Direct observation of intermolecular interactions mediated by hydrogen bonding.
abstract: Although intermolecular interactions are ubiquitous in physicochemical phenomena, their dynamics have proven difficult to observe directly, and most experiments rely on indirect measurements. Using broadband two-dimensional infrared spectroscopy (2DIR), we have measured the influence of hydrogen bonding on the intermolecular vibrational coupling between dimerized N-methylacetamide molecules. In addition to strong intramolecular coupling between N-H and C=O oscillators, cross-peaks in the broadband 2DIR spectrum appearing upon dimerization reveal strong intermolecular coupling that changes the character of the vibrations. In addition, dimerization changes the effects of intramolecular coupling, resulting in Fermi resonances between high and low-frequency modes. These results illustrate how hydrogen bonding influences the interplay of inter- and intramolecular vibrations, giving rise to correlated nuclear motions and significant changes in the vibrational structure of the amide group. These observations have direct impact on modeling and interpreting the IR spectra of proteins. In addition, they illustrate a general approach to direct molecular characterization of intermolecular interactions.
authors: Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, Massachusetts 02139, USA.
authors: Luigi
authors: L
authors: De Marco
authors: Department of Chemistry, James Frank Institute and The Institute for Biophysical Dynamics, The University of Chicago, 929 E 57th Street, Chicago, Illinois 60637, USA.
authors: Martin
authors: M
authors: Thämer
authors: Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, Massachusetts 02139, USA.
authors: Mike
authors: M
authors: Reppert
authors: Department of Chemistry, James Frank Institute and The Institute for Biophysical Dynamics, The University of Chicago, 929 E 57th Street, Chicago, Illinois 60637, USA.
authors: Andrei
authors: A
authors: Tokmakoff
mesh_terms: D000081:Acetamides / Q000737:chemistry*; D019281:Dimerization; D006860:Hydrogen Bonding; D013055:Spectrophotometry, Infrared
chemical_list: D000081:Acetamides; C018595:N-methylacetamide