Fingerprint Vibrational Spectra of Protonated Methyl Esters of Amino Acids in the Gas Phase

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• 作者：Aude Simon ; Luke MacAleese ; Philippe Ma&icirc ; tre ; Joë ; l Lemaire ; Terrance B. McMahon
• 刊名：Journal of the American Chemical Society
• 出版年：2007
• 出版时间：March 14, 2007
• 年：2007
• 卷：129
• 期：10
• 页码：2829 - 2840
• 全文大小：275K
• 年卷期：v.129,no.10(March 14, 2007)
• ISSN：1520-5126

文摘

Infrared spectra of the protonated monomers of glycine, alanine, valine, and leucine methyl estersare presented. These protonated species are generated in the gas phase via matrix assisted laser desorptionionization (MALDI) within the cell of a Fourier transform ion cyclotron resonance spectrometer (FTICR)where they are subsequently mass selected as the only species trapped in the FTICR cell. Alternatively,they have also been generated by electrospray ionization and transferred to a Paul ion-trap massspectrometer where they are similarly isolated. In both cases IR spectra are then derived from the frequencydependence of the infrared multiple photon dissociation (IRMPD) in the mid-infrared region (1000-2200cm^-1), using the free electron laser facility Centre de Laser Infrarouge d'Orsay (CLIO). IR bands are assignedby comparison with the calculated vibrational spectra of the lowest energy isomers using density functionaltheory (DFT) calculations. There is in general good agreement between experimental IRMPD spectra andcalculated IR absorption spectra for the lowest energy conformer which provides evidence for conformationalpreferences. The two different approaches to ion generation and trapping yield IRMPD spectra that are inexcellent agreement.