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CH ⃛ O hydrogen bonding in solutions of methylated nucleic acid base analogs as revealed by nmr
Author(s) -
Bruskov V. I.,
Bushuev V. N.,
Okon M. S.,
Shulyupi. V.,
Poltev V. I.
Publication year - 1989
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.360280205
Subject(s) - chemistry , hydrogen bond , chloroform , dimer , intermolecular force , hydrogen atom , acetone , molecule , chemical shift , proton nmr , crystallography , stereochemistry , medicinal chemistry , organic chemistry , alkyl
Abstract Formation and thermodynamic characteristics of CH ⃛ O hydrogen bonding of methylated uracils and caffeine have been studied by nmr along two lines. 1 The concentration and temperature dependencies of the PMR spectra of 1,3‐dimethyluracil (m 2 1,3 Ura), 1,3‐dimethylthymine (m 2 1,3 Thy), and 1,3,6‐trimethyluracil (m 3 1,3,6 Ura) in chloroform at high concentrations of base analogs indicated the self‐association of m 2 1,3 Ura and m 2 1,3 Thy via C(6)H ⃛ O hydrogen bonding and the competitive formation of CH ⃛ O bonds between carbonyl oxygens and chloroform. The intermolecular interaction energy and the arrangement of molecules in the local minima of various m 2 1,3 Ura dimers were calculated by the method of atom‐atom potentials. The deepest minimum for the m 2 1,3 Ura coplanar dimer corresponds to a C(6)H ⃛ O hydrogen‐bond formation. 2 At low concentration of m 2 1,3 Ura and caffeine in CCl 4 , C(6)H ⃛ O bonding for m 2 1,3 Ura and C(8)‐H ⃛ O bonding for caffeine with oxygens of dimethyl sulfoxide (DMSO) and acetone were observed. The association constants of these complexes were obtained at different temperatures. The enthalpies Δ H , of the m 2 1,3 Ura–DMSO, m 2 1,3 Ura–accetone, caffeine–DMSO, and caffeine–acetone complexes were −2 ⃛ 0.1 kcal/mol. The calculations showed that the deepest minimum of the caffeine‐acetone coplanar complex corresponds to C(8)H ⃛ O bonding with energy of −3.5 kcal/mol and that of the m 2 1,3 Ura‐acetone complexes corresponds to C(6)H ⃛ O bonding with energy of −3.4 kcal/mol. The approximate correction for the solvent effect provides good agreement of the experimental data with the calculations.