Related Experiment Video
Updated: Jul 29, 2026

Analyzing Protein Dynamics Using Hydrogen Exchange Mass Spectrometry
Published on: November 29, 2013
Effects of hydrogen-bond deletion on peptide helices: structural characterization of depsipeptides containing lactic
1Laboratory for the Structure of Matter, Naval Research Laboratory, Washington, DC, 20375-5341, USA.
Abstract:
The insertion of alpha-hydroxy acids into peptide chains provides a convenient means for investigating the effects of hydrogen bond deletion on polypeptide secondary structures. The crystal structures of three oligopeptides containing L-lactic acid (Lac) residue have been determined. Peptide 1, Boc-Val-Ala-Leu-Aib-Val-Lac-Leu-Aib-Val-Ala-Leu-OMe (Boc: tert-butyloxycarbonyl; Aib: alpha- aminoisobutyric acid; OMe: methyl ester), and peptide 2, Boc-Val-Ala-Leu-Aib-Val-Lac-Leu-Aib-Val-Leu-OMe, adopt completely helical conformations in the crystalline state with the Lac(6) residue comfortably accommodated in the center of a helix. The distance between the O atoms of Leu(3) CO group and the Lac(6) O (ester) in both the structures is 3.1-3.3 A. The NMR and CD studies of peptide 1 and its all-amide analogue 4, Boc-Val-Ala-Leu-Aib-Val-Ala-Leu-Aib-Val-Ala-Leu-OMe, provide firm evidence for a continuous helical conformation in solution in both the cases. In a 14-residue peptide 3, Boc-Val-Ala-Leu-Aib-Val-Ala-Leu-Val-Ala-Leu-Aib-Val-Lac-Leu-OMe, residues Val(1)-Leu(10) adopt a helical conformation. Aib(11) is the site of chiral reversal resulting in helix termination by formation of a Schellman motif. Residues 12-14 adopt nonhelical conformations. The loss of the hydrogen bond near the C-terminus appears to facilitate the chiral reversal at Aib(11). Published 2001 John Wiley & Sons, Inc. Biopolymers 59: 276-289, 2001
Related Concept Videos
Hydrolysis
Hydrolysis is a chemical reaction in which the addition of water breaks down a polymer into its simpler monomer units. For example, peptides break into amino acids, carbohydrates into simple sugars, and DNA into nucleotides. Enzymes often facilitate these processes.
Hydrolysis Reverses Dehydration Synthesis
Complex carbohydrates can be broken down by breaking the bonds between individual sugar units. The reaction breaks a glycosidic bond as water is added to the compound. The...
Amino acids
Peptide Bonds
¹³C NMR: Distortionless Enhancement by Polarization Transfer (DEPT)
Acid Halides to Carboxylic Acids: Hydrolysis
As shown below, the mechanism involves a nucleophilic attack by water at the carbonyl carbon to form a tetrahedral intermediate. This is followed by the reformation of the carbon–oxygen π bond along with the departure of a halide ion. A final proton transfer step yields carboxylic acid...
Amides to Carboxylic Acids: Hydrolysis
Acid-catalyzed hydrolysis:
Hydrolysis of amides under acidic conditions yields carboxylic acids. Since the reaction occurs slowly, hydrolysis requires the conditions of heat.
The mechanism begins with the protonation of the carbonyl oxygen by the acid catalyst. The protonation makes the amide carbonyl carbon more...

