Irikura K K, Tidor B, Brooks B R, Karplus M
Science. 1985 Aug 9;229(4713):571-2. doi: 10.1126/science.3839596.
The internal motions of the double-stranded DNA oligomer (dCdG)3 (dC, deoxycytidylate; dG, deoxyguanylate) in the B and Z forms have been calculated in the harmonic approximation. A complete vibrational analysis has been made, and the resulting normal mode frequencies have been used to evaluate the vibrational entropy of B and Z DNA. The greater flexibility of the B DNA hexamer leads to an entropic stabilization relative to the stiffer Z DNA hexamer of 22 calories per mole per kelvin at 300 K. The calculated value is of the same order as that (21 to 27 calories per mole per kelvin) obtained from nuclear magnetic resonance measurements on the methylated duplexes (m5dCdG)3 and (dCdGm5dCdGdCdG). This result demonstrates the importance of internal motions, which have been neglected in earlier studies of the transition from B to Z DNA, in the stability of different nucleic acid conformers.
双链DNA低聚物（dCdG）3（dC，脱氧胞苷酸；dG，脱氧鸟苷酸）处于B型和Z型时的内部运动已在简谐近似下进行了计算。已进行了完整的振动分析，所得的简正模式频率已用于评估B型和Z型DNA的振动熵。B型DNA六聚体更大的柔韧性导致在300 K时相对于更僵硬的Z型DNA六聚体每摩尔每开尔文有22卡路里的熵稳定化。计算值与通过对甲基化双链体（m5dCdG）3和（dCdGm5dCdGdCdG）进行核磁共振测量得到的值（每摩尔每开尔文21至27卡路里）处于同一数量级。这一结果证明了内部运动在不同核酸构象体稳定性中的重要性，而在早期关于从B型到Z型DNA转变的研究中内部运动一直被忽视。
