Conformational and Cs+ complexation properties of norbadione-A: a molecular modeling study.
Conformational and Cs+ complexation properties of norbadione-A: a molecular modeling study.
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降巴二酮-A 的构象和 Cs 络合特性：分子建模研究。
DOI：
10.1039/b712836c
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发表时间：
2008
期刊：
影响因子：
--
通讯作者：
G. Wipff
中科院分区：
文献类型：
--
作者：
R. Schurhammer;R. Diss;B. Spiess;G. Wipff
用量子力学(QM)和经典分子动力学(MD)研究了去甲二酮-A(NBA)的构象和络合性质，它是蘑菇与Cs+络合的关键色素。比较了中性(Pulv_0)、单-(Pulv(-1))和二去质子化(Pulv(-2))状态下的Z和E异构体，并从头算计算了~1H化学位移。PULV(-1)被发现通过内部COOH(-)O(烯)氢键以E形式稳定。没有发现相应的COO(-)Ho(Enol)态的能量极小值，这表明Pulv0的共轭烯醇函数比COOH函数更酸性。进一步的去质子化导致了PULV(-2)的Z和E形式，这两种形式在能量上接近，并且都解释了邻位-H8质子的显著下场位移增量。当Pulv0的酯类似物的烯醇功能去质子化时，也发现了类似的移位。因此，与之前的假设相反(参见7：P.KUAD等人，J.Am化学。Soc.，2005,127,1323)，当NBA或鼠脑酸去质子化时，在pH 9.5附近的增量(H8)的大移位不能被视为E-Z构象转换的指示器，而仅仅反映了pH诱导的(H8)-环附近的羧酸基的构象变化。对NBA(2-)和NBA(4-)的量子化学和分子动力学研究支持这样的观点，即这两个物种在气相和溶液中都倾向于具有两个分子内COOH(-)O(烯醇基)氢键的E/E形式。最后，我们用分子动力学方法模拟了Cs+与NBA(2-)和NBA(4-)的单核和双核配合物，结果表明，只有在高pH值下填充的NBA(4-)态才能与两个Cs+离子结合，并具有E和Z构象。
We report a quantum mechanical (QM) and classical molecular dynamics (MD) study of the conformational and complexation properties of norbadione-A (NBA), a key pigment involved in the Cs+ complexation by mushrooms. The Z versus E isomers of its pulvinic moieties are compared in their neutral (Pulv0), mono- (Pulv(-1)) and di-deprotonated (Pulv(-2)) states, and the 1H chemical shifts are calculated ab initio. Pulv(-1) is found to be stabilized in the E form by an internal COOH(-)O(enolate) hydrogen-bond. No energy minimum is found for the corresponding COO(-)HO(enol) state, indicating that the conjugated enol function of Pulv0 is more acidic than the COOH function. Further deprotonation leads to the Z and E forms of Pulv(-2) that are close in energy and both account for a marked downfield shift delta of ortho-H8 protons. A similar shift is found upon deprotonation of the enol function of an ester analogue of Pulv0. Therefore, contrary to previous assumptions (ref. 7: P. Kuad, et al., J. Am. Chem. Soc., 2005, 127, 1323), the large shift of delta(H8) around pH 9.5 upon deprotonation of NBA or of pulvinic acid cannot be taken as an indicator of an E-to-Z conformational switch, but merely reflects the pH-induced conformational change of the carboxylate group adjacent to the (H8)-ring. The QM and MD studies on NBA(2-) and NBA(4-) support the view that both species prefer the E/E form with two intramolecular COOH(-)O(enolate) hydrogen-bonds in the gas phase and in solution. Finally, we simulated mono- and di-nuclear complexes of Cs+ with NBA(2-) and NBA(4-) by MD, showing that only the NBA(4-) state populated at high pH values can bind two Cs+ cations, with both E and Z conformations of the pulvinic arms.
影响因子：
1.7
作者：
Toyota, M;Omatsu, I;Asakawa, Y
通讯作者：
Asakawa, Y