FT-IR Spectroscopy and Density Functional Theory Calculations of 13C Isotopologues of the Helical Peptide Z-Aib6-OtBu

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• 作者：Timothy Zeko ; Steven F. Hannigan ; Timothy Jacisin ; Matthew J. Guberman-Pfeffer ; Eric R. Falcone ; Melissa J. Guildford ; Christopher Szabo ; Kathryn E. Cole ; Jessica Placido ; Erin Daly ; Matthew A. Kubasik
• 刊名：Journal of Physical Chemistry B
• 出版年：2014
• 出版时间：January 9, 2014
• 年：2014
• 卷：118
• 期：1
• 页码：58-68
• 全文大小：537K
• ISSN：1520-5207

文摘

Isotope-edited FT-IR spectroscopy is a combined synthetic and spectroscopic method used to characterize local (e.g., residue-level) vibrational environments of biomolecules. We have prepared the 3₁₀ helical peptide Z-Aib₆-OtBu and seven ¹³C-enriched analogues that vary only in the number and position(s) of ¹³C鈺怬 isotopic enrichment. FT-IR spectra of these eight peptides solvated in the nonpolar aprotic solvent dichloromethane have been collected and compared to frequency, intensity, and normal mode results of DFT calculations. Single ¹³C enrichment of amide functional groups tends to localize amide I vibrational eigenmodes, providing residue-specific information regarding the local environment (e.g., hydrogen bonding or solvent exposure) of the peptide bond. Double ¹³C enrichment of Z-Aib₆-OtBu allows for examination of interamide coupling between two labeled amide functional groups, providing experimental evidence of interamide coupling in the context of 3₁₀ helical structure. Although the calculated and observed interamide couplings of Z-Aib₆-OtBu are a few cm^鈥? and less, the eight peptides exhibit distinct infrared spectra, revealing details of interamide coupling and residue level vibrational environments.