Journal
CHEMPHYSCHEM
Volume 12, Issue 10, Pages 1816-1821Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/cphc.201100212
Keywords
density functional calculations; gramicidin; IR spectroscopy; protein folding; structural analysis
Funding
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic [Z40550506]
- Ministry of Education, Youth and Sports, Czech Republic [LC512]
- Grant Agency of the Academy of Sciences of the Czech Republic [IAA400550808]
- National Science Foundation [CHE-0911564]
- Borchard Foundation
- Direct For Mathematical & Physical Scien [0911564] Funding Source: National Science Foundation
- Division Of Chemistry [0911564] Funding Source: National Science Foundation
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We report double-resonant IR/UV ion-dip spectroscopy of neutral gramicidin peptides in the gas phase. The IR spectra of gramicidin A and C, recorded in both the 1000 cm(-1) to 1800 cm(-1) and the 2700 to 3750 cm(-1) region, allow structural analysis. By studying this broad IR range, various local intramolecular interactions are probed, and complementary IR modes can be accessed. Ab initio quantum chemical calculations are used to support the interpretation of the experimental IR spectra. The comparison of the calculated frequencies with the experimental IR spectrum probed via the strong infrared absorptions of all the amide groups (NH stretch, C=O stretch and NH bend), shows evidence for a helical structure in the gas phase, which is similar to that in the condensed phase. Additionally, we show that to improve the spectral resolution when studying large neutral molecular structures of the size of gramicidin, the use of heavier carrier gas could be advantageous.
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