title: Base-pair interactions in the gas-phase proton-bonded complexes of C+G and C+GC.
abstract: Interactions involved in the formation of gas-phase proton-bonded molecular complexes of cytosine (C) and guanine (G) were theoretically investigated for the case of C(+)G and C(+)GC using B3LYP density functional theory. In this study, particular focus was on the dimeric interaction of proton-bonded C(+)G, where a proton bond and a hydrogen bond are cooperatively involved. The dimer interaction energy in terms of dissociation energy (D(e)) was predicted to be 41.8 kcal/mol. The lowest (frozen) energy structure for the C(+)G dimeric complex was found to be CH(+)...G rather than C...H(+)G in spite of the lower proton affinity of the cytosine moiety, which was more stable by 3.3 kcal/mol. The predicted harmonic vibrational frequencies and bond lengths suggest that the combined contributions of proton and hydrogen bonding may determine the resultant stability of each complex structure. In contrast to the dimer case, in the case of the isolated C(+)GC triplet, the two minimum energy structures of CH(+)...GC and C...H(+)GC were predicted to be almost equivalent in total energy. The dissociation energy (D(e)) for the C(+)G pairing in the C(+)GC triplet was 43.7 kcal/mol. Other energetics are also reported. As for the proton-transfer reaction in the proton-bond axis, the forward proton-transfer barriers for the dimer and trimer complexes were also predicted to be very low, 3.6 and 1.5 kcal/mol (DeltaE(e)(PT)), respectively.
authors.affiliation: Nanobio Fusion Research Center, Korea Research Institute of Standards and Science, Daejeon 305-340, Republic of Korea. sanghan@kriss.re.kr
authors.forename: Sang Yun
authors.initials: SY
authors.lastname: Han
authors.forename: Sang Hak
authors.initials: SH
authors.lastname: Lee
authors.forename: Jayong
authors.initials: J
authors.lastname: Chung
authors.forename: Han Bin
authors.initials: HB
authors.lastname: Oh
mesh_terms: D020029:Base Pairing; D003596:Cytosine / Q000737:chemistry*; D004735:Energy Transfer; D005740:Gases / Q000737:chemistry; D006147:Guanine / Q000737:chemistry*; D006860:Hydrogen Bonding; D008958:Models, Molecular; D011522:Protons; D013816:Thermodynamics
chemical_list: D005740:Gases; D011522:Protons; D006147:Guanine; D003596:Cytosine