Abstract
The molecular conformation of the carboxyl group can be crucial for its chemical properties and intermolecular interactions, especially in complex molecular environments such as polypeptides. Here, we study the conformational behaviour of the model amino acid N-acetylproline in solution at room temperature with two-dimensional infrared spectroscopy. We find that the carboxyl group of N-acetylproline adopts two distinct conformations, syn- and anti-. In the syn-conformer the O–H group is oriented at ~60∘ with respect to the C=O and in the anti-conformer the O–H is anti-parallel to the C=O. In hydrogen-bond accepting solvents such as dimethyl sulfoxide or water, we observe that, similar to simple carboxylic acids, around 20% of the -COOH groups adopt an anti-conformation. However, when N-acetylproline is dissolved in a weakly hydrogen-bond accepting solvent (acetonitrile), we observe the formation of a strong intramolecular hydrogen bond between the carboxyl group in the anti-conformation and the amide group, which stabilizes the anti-conformer, increasing its relative abundance to ~60%.
Highlights
The molecular conformation of the carboxyl group can be crucial for its chemical properties and intermolecular interactions, especially in complex molecular environments such as polypeptides
We study the conformational isomerism of the carboxyl group of the model acetylated amino acid N-acetylproline in weakly and strongly interacting solvents with polarizationresolved two-dimensional infrared spectroscopy (2DIR)
We observe that the maximum frequency of the carboxyl C=O stretch absorption shifts from 1752 cm−1 in acetonitrile to ~1720 cm−1 in dimethyl sulfoxide (DMSO) and water
Summary
The molecular conformation of the carboxyl group can be crucial for its chemical properties and intermolecular interactions, especially in complex molecular environments such as polypeptides. We study the conformational behaviour of the model amino acid Nacetylproline in solution at room temperature with two-dimensional infrared spectroscopy. In hydrogen-bond accepting solvents such as dimethyl sulfoxide or water, we observe that, similar to simple carboxylic acids, around 20% of the -COOH groups adopt an anti-conformation. We showed that the carboxyl group of simple carboxylic acids in room temperature solution adopts two distinct nearly planar conformations, syn- (70–80% fraction) and anti- (20–30%)[9]. We study the conformational isomerism of the carboxyl group of the model acetylated amino acid N-acetylproline in weakly and strongly interacting solvents with polarizationresolved two-dimensional infrared spectroscopy (2DIR). In the presence of an intra-molecular hydrogen-bond, the two molecular groups are interacting, and, the two molecular vibrations can be coupled leading to the observation of cross-peak signatures
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
