title: Dynamics in Supercooled Secondary Amide Mixtures: Dielectric and Hydrogen Bond Specific Spectroscopies.
abstract: Alkylacetamide-based model peptides display an intense Debye-type dielectric relaxation. In order to explore the extent to which this feature has to be regarded analogous to that in other supramolecular liquids, notably the monohydroxy alcohols, we applied broadband dielectric, time-dependent solvation, and near-infrared spectroscopies as well as shear rheology and various nuclear magnetic resonance techniques to mixtures of N-methylacetamide (NMA) or N-ethylacetamide (NEA) with N-methylformamide. Compared in the modulus format, dielectric relaxation, solvation dynamics, and mechanical response indicate a common global and local dynamics. The present spin-relaxation measurements reflect motional processes which are significantly faster than the dominant Debye dielectric response, and a similar conclusion is drawn from measurements of the shear viscosity. The NH overtone stretching vibrations reveal a temperature-dependent hydrogen-bond equilibrium that changes its characteristics near temperatures of 325 K. Finally, dielectric low-temperature data recorded for (NEA)0.4(NMF)0.6 mixed with 2-picoline indicate the existence of a critical concentration akin to the situation in various monohydroxy alcohol mixtures.
authors.affiliation: Fakultät Physik, Technische Universität Dortmund , 44221 Dortmund, Germany.
authors.forename: C
authors.initials: C
authors.lastname: Gainaru
authors.affiliation: Fakultät Physik, Technische Universität Dortmund , 44221 Dortmund, Germany.
authors.forename: S
authors.initials: S
authors.lastname: Bauer
authors.affiliation: Fakultät Physik, Technische Universität Dortmund , 44221 Dortmund, Germany.
authors.forename: E
authors.initials: E
authors.lastname: Vynokur
authors.affiliation: Fakultät Physik, Technische Universität Dortmund , 44221 Dortmund, Germany.
authors.forename: H
authors.initials: H
authors.lastname: Wittkamp
authors.affiliation: Fakultät für Chemie und Chemische Biologie, Technische Universität Dortmund , 44221 Dortmund, Germany.
authors.forename: W
authors.initials: W
authors.lastname: Hiller
authors.affiliation: School of Molecular Sciences, Arizona State University , Tempe, Arizona 85287-1604, United States.
authors.forename: R
authors.initials: R
authors.lastname: Richert
authors.affiliation: Fakultät Physik, Technische Universität Dortmund , 44221 Dortmund, Germany.
authors.forename: R
authors.initials: R
authors.lastname: Böhmer