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Main Title: Weak hydrogen bonding motifs of ethylamino neurotransmitter radical cations in a hydrophobic environment: infrared spectra of tryptamine(+)-(N-2)(n) clusters (n <= 6)
Author(s): Sakota, Kenji
Schütz, Markus
Schmies, Matthias
Moritz, Raphael
Bouchet, Aude
Ikeda, Takamasa
Kouno, Yuuki
Sekiya, Hiroshi
Dopfer, Otto
Type: Article
Language Code: en
Abstract: Size-selected clusters of the tryptamine cation with N2 ligands, TRA+–(N2)n with n = 1–6, are investigated by infrared photodissociation (IRPD) spectroscopy in the hydride stretch range and quantum chemical calculations at the ωB97X-D/cc-pVTZ level to characterize the microsolvation of this prototypical aromatic ethylamino neurotransmitter radical cation in a nonpolar solvent. Two types of structural isomers exhibiting different interaction motifs are identified for the TRA+–N2 dimer, namely the TRA+–N2(H) global minimum, in which N2 forms a linear hydrogen bond (H-bond) to the indolic NH group, and the less stable TRA+–N2(π) local minima, in which N2 binds to the aromatic π electron system of the indolic pyrrole ring. The IRPD spectrum of TRA+–(N2)2 is consistent with contributions from two structural H-bound isomers with similar calculated stabilization energies. The first isomer, denoted as TRA+–(N2)2(2H), exhibits an asymmetric bifurcated planar H-bonding motif, in which both N2 ligands are attached to the indolic NH group in the aromatic plane via H-bonding and charge–quadrupole interactions. The second isomer, denoted as TRA+–(N2)2(H/π), has a single and nearly linear H-bond of the first N2 ligand to the indolic NH group, whereas the second ligand is π-bonded to the pyrrole ring. The natural bond orbital analysis of TRA+–(N2)2 reveals that the total stability of these types of clusters is not only controlled by the local H-bond strengths between the indolic NH group and the N2 ligands but also by a subtle balance between various contributing intermolecular interactions, including local H-bonds, charge–quadrupole and induction interactions, dispersion, and exchange repulsion. The systematic spectral shifts as a function of cluster size suggest that the larger TRA+–(N2)n clusters with n = 3–6 are composed of the strongly bound TRA+–(N2)2(2H) core ion to which further N2 ligands are weakly attached to either the π electron system or the indolic NH proton by stacking and charge–quadrupole forces.
Issue Date: 2014
Date Available: 23-Jun-2016
DDC Class: 540 Chemie und zugeordnete Wissenschaften
Journal Title: Physical chemistry, chemical physics
Publisher: Royal Society of Chemistry
Publisher Place: Cambridge
Volume: 16
Issue: 8
Publisher DOI: 10.1039/c3cp54127d
Page Start: 3798
Page End: 3806
EISSN: 1463-9076
Notes: Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.
This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.
Appears in Collections:Inst. Optik und Atomare Physik » Publications

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