Intramolecular Hydrogen Bonding and Conformation of Small Peptides:  Variable-Temperature FTIR Study on N-Acetyl-l-Pro-l-Leu-Gly-NH₂ and Related Compounds

Abstract

Intramolecular hydrogen bonding and conformation of tripeptide amides in CDCl3 solutions have been examined by variable-temperature FTIR spectroscopy. Absorption in the NH stretching region of N-acetyl-l-Pro-l-Leu-Gly-NH2 was decomposed into some component bands by least-squares fitting. Two broad bands at around 3350 and 3290 cm-1 were assigned to intramolecularly hydrogen-bonded NH groups in different conformers. The other relatively sharp bands were assigned to hydrogen-bond-free NHs of the three different amide groups by referring to spectra of analogous amide compounds. From temperature dependence of the band intensities, it is concluded that the C-terminal amide group takes part in the hydrogen bonding in both hydrogen-bonded conformers. From comparison with spectra of N-trifluoroacetyl-l-Pro-l-Leu-Gly-NH2 and l-Pro-l-Leu-Gly-NH2, the 3290-cm-1 band has been assigned to a 13-membered ring with the hydrogen bond between NH of the C-terminal amide group and CO of the N-terminal acetyl group. The 3350-cm-1 band, on the other hand, has been assigned to a 10-membered hydrogen-bonded ring between the C-terminal amide NH and a prolyl carbonyl group. A van't Hoff analysis shows that the 13-membered hydrogen-bonded ring is enthalpically more favorable but entropically less favorable than the 10-membered hydrogen-bonded ring.

Luffa cylindrica sponges as a thermally and chemically stable support for Aspergillus niger lipase

“…It should also be noted that the absorption maxima of the bands in the spectra of the products after lipase immobilization are shifted to higher wavenumbers compared with the spectra for pure sponges and native lipase, which may suggest that the enzyme particles are bound to the support surface via hydrogen bonds …”

Novel layer-by-layer self-assembled peptide nanocarriers for siRNA delivery

“…It is well established that the non-hydrogen bonded N-H is due to higher energy bands, while the lower energy bands correspond to intramolecularly hydrogen bonded N-H. 37,41 Large absorption peaks seen at amide A and B regions of FFA dimers and FFANP and low-frequency shoulders indicates the presence of hydrogen bonding of the N-H group. 35,42 Urea (CO(NH 2 ) 2 ), as a strong H-bonding donor, is commonly used as a hydrogen bonding inhibitor and protein denaturing agent. 43,44 FFANPs were incubated with urea to determine the driving force for the self-assembly mechanism.…”

Temperature and pressure effects on conformational equilibria of alanine dipeptide in aqueous solution

“…They estimated the enthalpy change accompanying the rupture of their intramolecular hydrogen bond, ⌬H (free3 HBd) , at Ϫ8.4 Ϯ 0.2 kJ/mol. Tonan and Ikawa 18 have also reported the temperature dependence of the conformational equilibria of N-acetyl-L-Pro-L-Leu-L-Gly-NH 2 (Ac-PLG-NH 2 ) in chloroform solution using the NOH stretching mode of infrared spectroscopy. They found that this peptide adopts two types of intramolecular hydrogen bonded conformations.…”