Effects of Alkyl Groups on Excess-Electron Binding to Small-Sized Secondary Amide Clusters: A Combined Experimental and Computational Study

Abstract

Excess-electron binding to dimers and trimers of secondary amide molecules was studied by a combination of photoelectron spectroscopy and theoretical calculations. Vertical detachment energies (VDEs) of the cluster anions were measured in the range of a few hundred millielectronvolts. We found a tendency for VDE to decline with extension of alkyl side chains. It was fairly reproduced by results of quantum chemical calculations based on density functional theory. For the optimized structures of the cluster anions, the excess electron is located diffusively around the dangling NH group of the hydrogen-bond acceptor molecule. Dipole moment values calculated for the vertically detached neutrals are consistent with the motif of dipole-bound anions. Alkyl groups are likely to inhibit a close interaction between the excess electron and amide groups. It appears to be incompatible with a previously reported trend that the yield of the trimer anions is enhanced with extension of the side chains.

Schwingungsspektroskopische Untersuchung der Aggregation und Isomerisierung von Modellpeptiden in der Jet-Expansion am Beispiel kleiner sekundärer Amide

“…Die Thermodynamik der cis-/trans-Isomerisierung und die intermolekularen Wechselwirkungen in Form von Clusterbildung für kleine sekundäre Amide als Peptidmodellverbindungen sind Gegenstand der aktuellen Forschung [20][21][22] und stehen in Form einer experimentellen Abschätzung der Enthalpiedifferenz zwischen cisund trans-Konformeren für verschiedene sekundäre Amide und dem spektroskopischen Nachweis kleinster Molekülaggregate, wie Dimer und Trimer, im Zentrum dieser Arbeit.…”