Low-barrier hydrogen bonds:Abinitio and DFT investigation

✍ Scribed by Kumar, Ganesh A.; Pan, Yongping; Smallwood, C. Jay; McAllister, Michael A.

• Book ID: 101220902
• Publisher: John Wiley and Sons
• Year: 1998
• Tongue: English
• Weight: 193 KB
• Volume: 19
• Category: Article
• ISSN: 0192-8651
• DOI: 10.1002/(sici)1096-987x(199809)19:12<1345::aid-jcc3>3.0.co;2-i

✦ Synopsis

High-level ab initio and DFT molecular orbital calculations have been used to investigate the physical properties of a model low-barrier hydrogen Ž . bond LBHB system: formic acid᎐formate anion. In the gas phase, it is found w that the hydrogen bond formed is extraordinarily short and strong ca. 27 Ž .x kcalrmol at B3LYPr6-31qqG d, p , with a calculated enthalpy of activation for proton transfer from donor to acceptor that is less than the zero-point vibrational energy available to the system. Several perturbations to this system were studied. Forcing a mismatch of p K s between donor and acceptor, via the a use of substituents, causes the strength of the hydrogen bond to decrease. Microsolvation of the hydrogen-bonded complex does not affect the strength of the low-barrier hydrogen bond very much. Small variations in the structure of the LBHB results in a decrease in hydrogen-bond strength. Increasing the effective polarity of the cavity surrounding the LBHB was found to have a significant impact on the strength of the hydrogen bond. Implications for enzyme catalysis are discussed.