Patel D J, Shen C
Proc Natl Acad Sci U S A. 1976 Jun;73(6):1786-90. doi: 10.1073/pnas.73.6.1786.
The ionophore lasalocid A (X537A) and its metal salts have been investigated by high resolution (270 MHz and 360 MHz) proton nuclear magnetic resonance spectroscopy to obtain structural and kinetic information in nonpolar solution. The proton resonances were assigned from double resonance studies on lasalocid A and on its salts, homologs, isomers, and chemically modified derivatives. Studies of proton and carbon longitudinal relaxation time suggest that lasalocid A exists as a monomer, whereas the sodium and barium salts exist as dimers in nonpolar solvents. A study of the magnitude of the vicinal proton coupling constants and the chemical shifts and linewidths of the hydroxyl resonances suggest that the backbone conformation and intramolecular hydrogen bonds are similar for lasalocid A and its sodium and barium salts in nonpolar solvents. Nuclear magnetic resonance studies on the role of bound solvent molecules suggest a tightly bound water molecule in the barium complex dimer (crystallized from water-ethanol) and a weakly bound ethanol molecule in the lasalocid A monomer (crystallized from ethanol) in cyclohexane. The selective changes in proton chemical shift on complexation [where the polar faces of two lasalocid anions coordinate the metal cation(s) in nonpolar solvents have been analyzed in terms of the proximity of the resonances to the cation, their linkage to the coordinating oxygen atoms, and the magnetic anisotropy effects of the polar groups of one ligand on the resonances of its partner in the dimer. The nuclear magnetic resonance studies in solution are compared with earlier observations on lasalocid A and its salts in the crystalline state. Thus, the short Ag-C5 distance in the crystal structure of silver complex dimer is also observed in the solution structure. The kinetic parameters associated with the exchange between lasalocid A and its barium complex in chloroform have been measured from an analysis of the resonance line shapes as a function of temperature.
已通过高分辨率（270兆赫兹和360兆赫兹）质子核磁共振光谱法对离子载体拉沙洛西A（X537A）及其金属盐进行了研究，以获取非极性溶液中的结构和动力学信息。通过对拉沙洛西A及其盐、同系物、异构体和化学修饰衍生物进行双共振研究，确定了质子共振峰。对质子和碳纵向弛豫时间的研究表明，拉沙洛西A在非极性溶剂中以单体形式存在，而钠盐和钡盐则以二聚体形式存在。对邻位质子耦合常数的大小以及羟基共振峰的化学位移和线宽的研究表明，拉沙洛西A及其钠盐和钡盐在非极性溶剂中的主链构象和分子内氢键相似。对结合溶剂分子作用的核磁共振研究表明，在环己烷中，钡络合物二聚体（由水 - 乙醇结晶而成）中有一个紧密结合的水分子，而拉沙洛西A单体（由乙醇结晶而成）中有一个弱结合的乙醇分子。根据共振峰与阳离子的接近程度、它们与配位氧原子的连接以及二聚体中一个配体的极性基团对其伙伴共振峰的磁各向异性效应，分析了络合过程中质子化学位移的选择性变化（其中两个拉沙洛西阴离子的极性面在非极性溶剂中配位金属阳离子）。将溶液中的核磁共振研究结果与早期对拉沙洛西A及其盐的晶体状态的观察结果进行了比较。因此，在溶液结构中也观察到了银络合物二聚体晶体结构中较短的Ag - C5距离。通过分析共振线形状随温度的变化，测量了氯仿中拉沙洛西A与其钡络合物之间交换的动力学参数。
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