IRMPD Spectroscopy Shows That AGG Forms an Oxazolone b2+ Ion

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• 作者：Sung Hwan Yoon ; Julia Chamot-Rooke ; Brittany R. Perkins ; Amy E. Hilderbrand ; John C. Poutsma ; Vicki H. Wysocki
• 刊名：Journal of the American Chemical Society
• 出版年：2008
• 出版时间：December 31, 2008
• 年：2008
• 卷：130
• 期：52
• 页码：17644-17645
• 全文大小：157K
• 年卷期：v.130,no.52(December 31, 2008)
• ISSN：1520-5126

文摘

Infrared multiple photon dissociation (IRMPD) spectroscopy combined with theoretical vibrational spectra provides a powerful tool for probing structure. This technique has been used to probe the structure of protonated cyclic AG and the b₂⁺ ion from AGG. The experimental spectrum for protonated cyclo AG compares very well with the theoretical spectra for a diketopiperazine. The spectrum corresponds best to a combination of two structures protonation at the alanine and glycine amide oxygens. The experimental spectrum for the b₂⁺ ion from protonated AGG matches best to the theoretical spectrum for an oxazolone structure protonated on the ring nitrogen. In particular, the carbonyl stretching band at 1970 cm⁻¹ is blue-shifted by 200 cm⁻¹ compared to the experimental spectrum for protonated cAG, indicating that these two structures are distinct. This is the first time that an IRPD spectrum of a b₂⁺ ion has been obtained and, for this ion, the oxazolone structure proposed based on prior calculations and experiments is confirmed by the spectroscopic method.