Ab initio molecular orbital methods are used to calculate potential energy surfaces for proton transfers between water molecules in the linear hydrogen-bonded systems H+(H20),, n = 2, 3, 4, and 5. The split valence-shell 4-31G basis set used is shown to provide results in excellent agreement with more sophisticated treatments which include correlation energy contributions. Geometry optimizations and inclusion of two additional water molecules have little effect upon the energy barriers to proton transfer in H+(H20)2. Linear and angular deformations of the hydrogen bond increase proton-transfer barriers in a nonlinear fashion. Predictive power of group charges and overlap populations are demonstrated as they correlate quite well with calculated proton-transfer barriers. Potentials calculated for H+(HzO)3 are found to be subject to substantial end effects while the H+(HzO), system is more representative of the situation in long hydrogen-bonded chains. The barriers to single- and double-proton transfers in the pentamer are approximately the same as those for single transfer in the dimer and tetramer. These results are discussed with particular regard to a proposed model of proton transport through biomembranes.
Proton Transfers in Hydrogen Bonded Systems. Cationic Oligomers of WaterJournal of the American Chemical Society
PublisherAmerican Chemical Society
Citation InformationProton Transfers in Hydrogen Bonded Systems. Cationic Oligomers of Water S. Scheiner J. Am. Chem. Soc., 1981 103 (2), 315-320.