Structural Selection by Microsolvation:  Conformational Locking of Tryptamine

Abstract

The conformational space of tryptamine has been thoroughly investigated using rotationally resolved laser-induced fluorescence spectroscopy. Six conformers could be identified on the basis of the inertial parameters of several deuterated isotopomers. Upon attaching a single water molecule, the conformational space collapses into a single conformer. For the hydrogen-bonded water cluster, this conformer is identified unambiguously as tryptamine A. In the complex, the water molecule acts as proton donor with respect to the amino group. An additional interaction with one of the aromatic C-H bonds selectively stabilizes the observed conformer more than all other conformers. Ab initio calculations confirm much larger energy differences between the conformers of the water complex than between those of the monomers.

Electronically excited states of tryptamine and its microhydrated complex

“…Schmitt et al 19 found only six conformers. The "missing" conformer in the latter study can be identified as the C2 band of Philips and Levy.…”

“…19 While high quality structure calculations for the electronic ground state are straightforward and bear in general no problems, electronically excited states are much harder to describe with an accuracy comparable to the experiment. Rotationally resolved electronic spectroscopy yields rotational constants which are related to the moments of inertia as primary structural information.…”

“…16 In this study no further conformers could be found. Recently, Nguyen et al 18 and Schmitt et al 19 independently presented the results of high resolution rotationally resolved spectroscopy on the conformers of tryptamine, which differ in the number of conformers which were observed and in two assignments. In the study of Nguyen et al 18 seven different conformers were identified, while…”

“…20 Complexation of tryptamine with one solvent molecule such water, methanol, or ethanol leads to a selective stabilization of only one conformer. 23,24 The rotational constants of the water cluster were determined by Felker 25 and Connell et al 26 using rotational coherence spectroscopy, and by Schmitt et al 19 using rotationally resolved electronic spectroscopy. A bridged structure, which connects the amino group and the acidic CH group at the pyrrole ring, was found for this cluster, selectively stabilizing the A ͓Gpy͑out͔͒ conformer.…”

Structural motifs of 2-(2-fluoro-phenyl)-ethylamine conformers

“…Therefore, the conformation of the flexible key, which is recognized by the usually more rigid lock, must be quite limited to achieve high selectivity. 6 Indeed, the conformational topography of representative NTs appearing in the gas phase as neutral, [7][8][9][10][11][12][13][14][15][16][17][18][19][20] fluorinated, 21,22 protonated 23,24 and cluster 10,25,26 species was explored by various spectroscopic methods, assisted by quantum chemical calculations. In these studies, comparison of the measured spectral signatures with the calculated spectra enabled one to find the corresponding structures and to unravel their intrinsic properties at the most fundamental level.…”