Ionic Hydrogen Bonds in Bioenergetics. 3. Proton Transport in Membranes, Modeled by Ketone/Water Clusters

Authors

Michael Meot-Ner, University of Canterbury and the National Institue of Standards and Technology
Steve Scheiner, Utah State UniversityFollow
Wa On Yu, Southern Illinois University Carbondale

Document Type

Article

Journal/Book Title

Journal of the American Chemical Society

Publication Date

7-1998

Publisher

American Chemical Society

Volume

120

Abstract

Hydrogen bond networks in protonated acetone/water clusters are stabilized by H₃O⁺(Me₂CO)₂ centers, and the stabilizaton increases with further acetone content. For example, proton transfer from neat water (H₂O)₆H⁺ clusters to form mixed (Me₂CO)₃(H₂O)₃H⁺ clusters is exothermic by 80 kJ/mol (19 kcal/mol), due to strong hydrogen bonding of the carbonyl groups; in a series of mixed clusters B3(H₂O)₃H⁺, the stability of the hydrogen bond network correlates with the proton affinities PA(B). In diketone models of adjacent peptide links, the proton is stabilized by internal hydrogen bonds between the carbonyl groups. The internal bonds can be significant, for example, 31 kJ/mol (7 kcal/mol) in (MeCOCH₂CH₂COMe)H⁺, but proton transfer through the internal bond has a high barrier. However, water molecules can bridge between the CO groups. In these bridges, the proton remains on an H₃O⁺ center, in both acetone/water and diketone/water systems. With a further H₂O molecule, the diketone/water cluster (MeCOCH₂CH₂COMe)(H₂O)₂H⁺ and diamide/water clusters form two-water H₃O^+_...H₂O bridges, which allow proton transfer between the CO groups with a small barrier of /mol (/mol). The cluster models suggest several roles for hydrogen bonds in proton transport through membranes. (1) Ionic hydrogen bonds involving polar amide groups stabilize ions by up to 135 kJ/mol (32 kcal/mol) in clusters and can similarly stabilize ions in membrane water chains and enzyme centers. (2) The proton can remain on an H₃O⁺ center and, therefore, remain delocalized and mobile in water chains, despite the stronger basicities of the surrounding amide groups. This effect results from electrostatic balancing of opposing peptide amide dipoles. (3) In the water chains, H₃O^+_...H₂O bridges between peptide amide groups can provide low-energy pathways for proton transport.

Comments

Originally published in the Journal of the American Chemical Society by the American Chemical Society . Publisher’s PDF available through remote link. DOI: 10.1021/ja971663s

Recommended Citation

Ionic Hydrogen Bonds in Bioenergetics. 3. Proton Transport in Membranes, Modeled by Ketone/Water Clusters M. Meot-Ner, S. Scheiner, W. O. Yu J. Am. Chem. Soc. 1998 120 (28), 6980-6990.