Related Experiment Video
Updated: Jun 25, 2026

A Novel Technique for Raman Analysis of Highly Radioactive Samples Using Any Standard Micro-Raman Spectrometer
Published on: April 12, 2017
Enthalpies of hydrogen-bonds in alpha-helical peptides. An ONIOM DFT/AM1 study
Robert Wieczorek1, J J Dannenberg
1Department of Chemistry, City University of New York-Hunter College, New York, New York 10021, USA.
Abstract:
We report the enthalpy differences between alpha-helical and extended beta-strand conformations of acetyl(Ala)nNH2, for n = 8, 10, 12-17, calculated using molecular (MO) orbital theory from complete vibrational analyses of the optimized species. The calculations used the ONIOM method with B3LYP/D95(d.p) as the high and AM1 as the low levels. The incremental change in enthalpy upon addition of one Ala to a growing beta-strand defined using the hypothetical polycondensation reaction, n Ala + CH3COOH + NH3 --> acetyl(Ala)nNH2 + n H2O, reaches its asymptotic limit of -1.4 kcal/mol at n = 10, while that for the alpha-helix continues to increase in magnitude at n = 17. The asymptotic limit of the enthalpic preference of the alpha-helix over beta-strand is estimated to be about 3 kcal/mol, while that for n = 17 is 11.99 kcal/mol or about 0.8 kcal/mol/H-bond, which is similar to measured values for polyalanines of this size in aqueous solution.
Related Concept Videos
¹H NMR: Complex Splitting
Splitting diagrams or splitting tree diagrams are routinely used to depict such complex couplings. While drawing splitting diagrams, the splitting with the larger coupling constant is usually applied first.
IR Spectrum Peak Splitting: Symmetric vs Asymmetric Vibrations
Cooperative Allosteric Transitions
Atomic Nuclei: Magnetic Resonance
Atomic Force Microscopy
The AFM Probe
The probe is regarded as the heart of any AFM setup and comprises the...
NMR Spectroscopy Of Amines

