This research program uses modern methods of electronic structure theory to understand the fundamental nature of interactions between molecules. Chief among the concerns are hydrogen bonds which are so important to structure and function of biomolecules like proteins.
When considering a H-bond, the thoughts of most would ordinarily turn to OH··O or OH··N interactions that pair electronegative atoms like O and N. Indeed, such bonds are quite common in proteins and act as a strong glue, cementing one part of the molecule to another. On the other hand, clues have turned up over the years that even less electronegative atoms like C can participate in H-bonds, albeit weaker ones. Most of these clues have been of the structural variety, wherein a CH group might lie in close proximity to an O atom, and the geometry of the contact might be reminiscent of a H-bond, i.e. the putative bridging H could lie along the direction of one of the lone electron pairs of the oxygen acceptor. Yet structural information of this sort is incapable of distinguishing a "coincidental" contact, where the two groups happen to lie close together for the sake of the structure of the entire molecule, from a true CH··O H-bond. The latter would be accompanied by an attractive interaction, a "fingerprint" electron redistribution pattern, and a number of characteristic spectroscopic features.
Our group makes use of state-of-the-art ab initio quantum chemical methods to probe the underlying nature of the CH··O interaction, paying particular attention to the above properties, extracting information that is inaccessible to experimental measurements. We have learned that under certain conditions, the CH··O interaction is indeed a true H-bond, with an attractive force that can rival the more conventional OH··O bond. And even though the C-H stretching frequency may shift to the blue rather than to lower frequencies, this property is typical of certain weak H-bonds.
The work has demonstrated that these weak H-bonds, commonly overlooked, can play a very important structural role in some of the most important and widely occurring protein structural motifs, such as beta sheets. We have immersed these systems in environments that are characteristic of aqueous solvent or the interior of a protein, and found that many of our findings in the gas phase remain valid. By comparing H-bond strengths in solvents of varying polarizability, it has been possible to estimate the magnitude of the so-called “desolvation penalty” which characterizes the weakening suffered by a H-bond upon transferring from aqueous solvent to the interior of the protein.
And with particular regard to conventional H-bonds, of the NH··O sort that connects a pair of peptide units within a protein, calculations have shown that the strength with which such a bond can form is surprisingly dependent upon the specific conformation of the polypeptide chain on which the bond occurs. For example, the NH··O bond within a stretched polypeptide, as in a β-sheet, is considerably weaker than if the same bond were to occur within a helical portion of the protein.
Journal of Molecular Structure, Theochem
International Journal of Quantum Chemistry
S. Scheiner, Ed., Molecular Interactions. From van der Waals to Strongly Bound Complexes. Wiley Press, 1997.
S. Scheiner, Hydrogen Bonding. A Theoretical Perspective, Oxford University Press, 1997.
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Cooperativity of Conventional and Unconventional Hydrogen Bonds involving Imidazole
T. Kar, S. Scheiner Int. J. Quantum Chem. 2006 106 843-851
Stabilities and Properties of Complexes Pairing Hydroperoxyl Radical with Monohalomethanes
M. Solimannejad, S. Scheiner J. Phys. Chem. A 2006 110 5948-5951.
Weak Hydrogen Bonds in Complexes Pairing Monohalomethanes with Neutral Formic Acid
M. Solimannejad, S. Scheiner Chem. Phys. Lett. 2006 424 1-6
Hydrogen Bonding of Radicals: Interaction of Dimethyl Ether with OOH, HOOH, and OOH-
M. Solimannejad, S. Scheiner Chem. Phys. Lett. 2006 429 38-42
Contributions of NH··O and CH··O H-Bonds to the Stability of β-Sheets in Proteins
S. Scheiner J. Phys. Chem. B 2006 110 18670-18679
Theoretical Evidence for a NH··XC Blue Shifting Hydrogen Bond: Complexes Pairing Monohalomethanes with HNO
M. Solimannejad, S. Scheiner J. Phys. Chem. A 2007 111 4431-4435
Minimum Energy Pathways for Proton-Transfer between Adjacent Sites Exposed to Water
R. Friedman, S. Fischer, E. Nachliel, S. Scheiner, M. Gutman J. Phys. Chem. B 2007 111 6059-6070
The Strength with Which a Peptide Group Can Form a Hydrogen Bond Varies with the Internal Conformation of the Polypeptide Chain
S. Scheiner J. Phys. Chem. B 2007 111 11312-11317
Underlying Source of the Relation between Polypeptide Conformation and Strength of NH··O Hydrogen Bonds
S. Scheiner, T. Kar J. Mol. Struct. 2007 844-845 166-172
Periodicity in Proton Conduction along a H-bonded Chain. Application to Biomolecules
A. Isaev, T. Kar, S. Scheiner Int. J. Quantum Chem. 2007 108 607-616
Analysis of Complexes Pairing Hydroperoxyl Radical with Peroxyformic Acid
M. Solimannejad, S. Gh. Shirazi, S. Scheiner J. Phys. Chem. A 2007 111 10717-10721
Bonding Rearrangements of Hydrogen Bonded Complexes involving Alkynes
E. S. Kryachko, S. Scheiner J. Phys. Chem. A 2008 112 1940-1945
Theoretical Investigation of the Mechanism of LiH + NH3 → LiNH2 + H2
T. Kar, S. Scheiner, L. Li J. Mol. Struct. Theochem 2008 857 111-114
Complexes Pairing Hypohalous Acids with Nitrosyl Hydride. Blue Shift of a NH Bond that is Uninvolved in a H-bond
M. Solimannejad, S. Scheiner J. Phys. Chem. A 2008 112 4120-4124
Analysis of Catalytic Mechanism of Serine Proteases. Viability of Ring-Flip Hypothesis
S. Scheiner J. Phys. Chem. B 2008 112 6837-6846
The Effect on Acidity of Size and Shape of Carboxylated Single-Wall Carbon Nanotubes. A DFT-SLDB Study
T.Kar, S. Scheiner, A.K. Roy Chem. Phys. Lett. 2008 460 225-229
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This page last edited September 10, 2008