Borer等人对核酸碱基的’H化学位移变化用环流各向异性作了解释。Cheng等人采用嘌呤作为简单的重叠模型化物,作了~1H和~13C实验与计算的比较。这些结果表明芳环重叠后的环流屏蔽引起环原子位移的变化。我们将NAD~+和∈NAD~+作了比较。对它们的烟酰胺~1H和~13C化学位移随pH的变化作对应相减时,其差值在pH4以下,在实验误差范围内;在pH4以上,∈NAD的~1H谱的2、4和5位质子较相应NAD~+的向高场最大位 Borer et al. Interpret the ’H shift in nucleic acid bases as a circular anisotropy. Cheng et al. Used purines as a simple overlay model and compared ~ 1H and ~ 13C experiments and calculations. These results show that the circulation barrier after aromatic rings overlap causes the displacement of ring atoms. We compare NAD ~ + with ∈NAD ~ +. Their chemical shifts of ~ 1H and ~ 13C of nicotinamide decrease correspondingly with the change of pH, the difference is below pH4, which is within the experimental error range. At pH4 and above, The position of the 5th proton is higher than the corresponding NAD ~ +