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Updated: May 19, 2026

Proton Transfer and Protein Conformation Dynamics in Photosensitive Proteins by Time-resolved Step-scan Fourier-transform Infrared Spectroscopy
Published on: June 27, 2014
Crown complexation of protonated amino acids: influence on IRMPD spectra
Corey N Stedwell1, Johan F Galindo, Kerim Gulyuz
1Department of Chemistry and Center for Chemical Physics, University of Florida, Gainesville, P.O. Box 117200, Florida 32611-7200, USA.
Abstract:
We report infrared multiple photon dissociation (IRMPD) spectra for a series of crown-adducted, protonated amino acids, generated by electrospray ionization. The tight chelation of 18-crown-6 on the protonated NH(3)(+) moiety results in a considerable red shift of the NH(3)(+) stretch modes, notably the antisymmetric NH(3)(+) stretch. This is rationalized by a distortion of the NH(3)(+) normal mode potential energy surface, as verified by quantum chemical calculations. On the other hand, the local oscillator modes, such as the carboxylic acid OH stretch, indole NH stretch, and phenol OH stretches, remain well-resolved and are subject to minor and predictable blue shifts of 5-15 cm(-1). Other chemically diagnostic modes, such as the guanidine NH stretch and alcohol OH stretches, also have discernible band positions. Crucially, some of these diagnostic band positions have little to no overlap with one another and can hence be readily distinguished. In addition, the complexes are often found to efficiently photodissociate by neutral loss of 18-crown-6, particularly for higher-basicity amino acids. This in principle opens the door on multiplexing the IRMPD experiment, where the IR spectra of multiple precursors are recorded simultaneously.
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