Issue 7, 2011

Infrared spectra of protonated neurotransmitters: dopamine

Abstract

The infrared (IR) spectrum of the isolated protonated neurotransmitter dopamine was recorded in the fingerprint range (570–1880 cm−1) by means of IR multiple photon dissociation (IRMPD) spectroscopy. The spectrum was obtained in a Fourier transform ion cyclotron resonance mass spectrometer equipped with an electrospray ionization source, which was coupled to a free electron laser (FEL). The spectroscopic studies are complemented by quantum chemical calculations at the B3LYP and MP2 levels of theory using the cc-pVDZ basis set. Several low-energy isomers with protonation occurring at the amino group are predicted in the energy range 0–50 kJ mol−1. Good agreement between the measured IRMPD spectrum and the calculated linear absorption spectra is observed for the two gauche conformers lowest in energy (ΔE) and free energy (ΔG) at both levels of theory, denoted g−1 and g+1. Minor contributions of higher lying gauche isomers cannot be ruled out spectroscopically but their calculated energies suggest only minor population in the sampled ion cloud. In all these gauche structures, one of the three protons of the ammonium group is pointing toward the catechol subunit, thereby maximizing the intramolecular NH–π interaction of the positive charge with the aromatic ring. In total, 16 distinct vibrational bands are observed in the IRMPD spectrum and assigned to individual normal modes of the energetically most stable g−1 conformer, with deviations of less than 24 cm−1 (average 11 cm−1) between measured and calculated frequencies. Comparison with neutral dopamine reveals the effects of protonation on the geometric and electronic structure.

Graphical abstract: Infrared spectra of protonated neurotransmitters: dopamine

Supplementary files

Article information

Article type
Paper
Submitted
12 Oct 2010
Accepted
16 Nov 2010
First published
13 Dec 2010

Phys. Chem. Chem. Phys., 2011,13, 2815-2823

Infrared spectra of protonated neurotransmitters: dopamine

A. Lagutschenkov, J. Langer, G. Berden, J. Oomens and O. Dopfer, Phys. Chem. Chem. Phys., 2011, 13, 2815 DOI: 10.1039/C0CP02133D

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Social activity

Spotlight

Advertisements