title: Relative strengths of NH..O and CH..O hydrogen bonds between polypeptide chain segments.
abstract: Correlated ab initio calculations are used to compare the energetics when the CH and NH groups of the model dipeptide CHONHCH2CONH2 are each allowed to form a H-bond with the proton acceptor O of a peptide group. When the dipeptide is in its C7 conformation, the NH..O H-bond energy is found to be 7.4 kcal/mol, as compared to only 2.8 kcal/mol for the CH..O interaction. On the other hand, the situation reverses, and the CH..O H-bond becomes stronger than NH..O, when the dipeptide adopts a C5 structure. This reversal is important as C5 is nearly equal in stability to C7 for the dipeptide, and is representative of the commonly observed beta-sheet structure in a protein. Immersing the dipeptide-peptide pair in a model solvent weakens both sorts of H-bonds, and in a fairly uniform manner. Consequently, the trends observed in the in vacuo situation retain their validity in either aqueous solution or the protein interior. Likewise, the desolvation penalty, suffered by removing a H-bonded complex from water and placing it in the less polar interior of a protein, is quite similar for the NH..O and CH..O bonds.
authors.affiliation: Department of Chemistry & Biochemistry, Utah State University, Logan, Utah 84322-0300, USA. scheiner@cc.usu.edu
authors.forename: Steve
authors.initials: S
authors.lastname: Scheiner
mesh_terms: D004151:Dipeptides / Q000737:chemistry*; D006860:Hydrogen Bonding; D008956:Models, Chemical; D008958:Models, Molecular; D013816:Thermodynamics
chemical_list: D004151:Dipeptides