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Effect of Hydrogen Bonding on Barrier‐Free Proton Transfer in Anionic Complexes of Uracil with Weak Acids: (U…HCN) − versus (U…H 2 S) −
Author(s) -
Harańczyk Maciej,
Rak Janusz,
Gutowski Maciej,
Radisic Dunja,
Stokes Sarah T.,
Bowen Kit H.
Publication year - 2004
Publication title -
israel journal of chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.908
H-Index - 54
eISSN - 1869-5868
pISSN - 0021-2148
DOI - 10.1560/pbm0-cm9l-7ybh-w719
Subject(s) - chemistry , deprotonation , uracil , proton , hydrogen bond , crystallography , proton affinity , spectral line , computational chemistry , molecule , protonation , organic chemistry , astronomy , ion , dna , biochemistry , physics , quantum mechanics
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 2 S, respectively. The experimental deprotonation enthalpies are 15.217 ± 0.009 and 15.212 ± 0.126 eV for HCN and H 2 S, respectively. Hence, HCN and H 2 S have very indeed similar deprotonation enthalpies. The photoelectron spectra of anionic complexes of uracil with HCN and H 2 S are, however, very different. The (UHCN) − spectrum reveals a broad feature with a maximum between 1.2–1.4 eV, whereas the main feature of the (UH 2 S) − spectrum has a maximum between 1.7 and 2.1 eV. We suggest that barrier‐free proton transfer (BFPT) occurs in the (UH 2 S) − complex, but not in (UHCN) − . Critical factors for the occurrence of BFPT have been analyzed. The difference between the (UHCN) − and (UH 2 S) − complexes is attributed to differences in hydrogen bonds formed by HCN and H 2 S with uracil.