Effect of Hydrogen Bonding on Barrier-Free Proton Transfer in Anionic Complexes of Uracil with Weak Acids: (U...HCN){sup -} versus (U...H{sub 2}S){sup -}
A photoelectron spectrum is reported for an anionic complex of uracil (U) with HCN. The effects of electron attachment to a complex of U with HA (A = CN, NC) have been studied at the density functional theory level with 6-31++G** basis sets and the B3LYP and MPW1K exchange correlation functionals. Critical anionic structures have been reexamined at the MP2/6-31++G** level. The B3LYP gas phase deprotonation enthalpies are equal to 14.56, 15.13, and 15.12 eV for HNC, HCN, and H{sub 2}S, respectively. The experimental deprotonation enthalpies are 15.100 {+-} 0.008 and 15.214 {+-}0.125 eV for HCN and H{sub 2}S, respectively. Hence, HCN and H{sub 2}S have very similar deprotonation enthalpies. The photoelectron spectra of anionic complexes of uracil with HCN and H{sub 2}S are, however, very different. The (UHCN){sup -} spectrum reveals a broad feature with a maximum between 1.2-1.4 eV, whereas the main feature of the (UH{sub 2}S){sup -} spectrum has a maximum between 1.7 and 2.1 eV. We suggest that barrier-free proton transfer (BFPT) [Eur. Phys. J. D 2002, 20, 431-439; J. Phys. Chem. B 2003, 107, 7889-7895] occurs in the (UH{sub 2}S){sup -} complex but not in (UHCN){sup -}. Critical factors for the occurrence of BFPT have been analyzed. The difference between the (UHCN){sup -} and (UH{sub 2}S){sup -} complexes is attributed to differences in hydrogen bonds formed by HCN and H{sub 2}S with uracil.
- Research Organization:
- Pacific Northwest National Lab., Richland, WA (US)
- Sponsoring Organization:
- US Department of Energy (US)
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 15011379
- Report Number(s):
- PNNL-SA-43146; ISJCAT; KP1102020; TRN: US200506%%485
- Journal Information:
- Israel Journal of Chemistry, Vol. 44, Issue 1-3; Other Information: PBD: 26 Oct 2004; ISSN 0021-2148
- Country of Publication:
- United States
- Language:
- English
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