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Elucidating the multiple structures of pipecolic acid by rotational spectroscopy
1Grupo de Espectrocopía Molecular (GEM), Edificio Quifima, Laboratorios de Espectroscopia y Bioespectroscopia, Unidad Asociada CSIC, Parque Científico UVa, Universidad de Valladolid, 47011, Valladolid, Spain. jlalonso@qf.uva.es.
Physical Chemistry Chemical Physics : PCCP
|December 7, 2018
Summary
This study reveals the diverse structures of pipecolic acid conformers in the gas phase using microwave spectroscopy. Differences in its structure compared to proline are due to increased steric hindrance in the larger ring.
Area of Science:
- * Physical Chemistry: Investigating molecular structures and interactions in the gas phase.
- * Spectroscopy: Utilizing advanced microwave techniques for molecular analysis.
Background:
- * Pipecolic acid, a non-proteinogenic cyclic amino acid, has a complex conformational landscape.
- * Understanding its structure is crucial for various chemical and biological applications.
Purpose of the Study:
- * To explore the gas-phase conformational space of pipecolic acid for the first time.
- * To identify and characterize different conformers using spectroscopic methods.
- * To compare the conformational behavior of pipecolic acid with proline.
Main Methods:
- * Laser ablation vaporization of solid pipecolic acid samples.
- * Supersonic jet expansion for cooling and isolating molecular species.
- * Fourier transform microwave spectroscopy to record rotational spectra.
- * Comparison of experimental data with theoretical predictions for identification.
Main Results:
- * Observation and identification of nine distinct pipecolic acid conformers in the gas phase.
- * Experimental rotational and nuclear quadrupole coupling constants were determined.
- * Type-III conformers were observed, differing from proline's behavior.
- * Increased steric hindrance in the six-membered ring of pipecolic acid was identified as a key factor.
Conclusions:
- * The study provides the first comprehensive gas-phase conformational analysis of pipecolic acid.
- * The observed conformers and their structural characteristics were elucidated.
- * The conformational differences between pipecolic acid and proline were explained by steric effects.
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