Sankaram M B, Easwaran K R
Int J Pept Protein Res. 1985 Jun;25(6):585-93. doi: 10.1111/j.1399-3011.1985.tb02214.x.
The solution conformations of complexes of valinomycin with magnesium and strontium were investigated by circular dichroism, nuclear magnetic resonance and infrared techniques. The results were compared with our earlier results on lithium, calcium, manganese and barium complexes. All these cations, except lithium, form 2:1 ion sandwich and 1:1 carrier-cation complexes with valinomycin. The 1:1 complex has a conformation different from that of the valinomycin-potassium complex. Lithium forms only the 1:1 complex. Strontium and barium form a large number of 1:2 complexes with open conformations rapidly interconverting in solution in addition to the above 2:1 and 1:1 complexes. These observations are rationalized taking into account the ionic radii and coordination numbers of the cations and the conformational restraints of valinomycin molecules. It is suggested that cations with co-ordination numbers of about six (magnesium and calcium) form the 2:1 and 1:1 complexes whereas those with higher co-ordination numbers (strontium and barium) form 1:2 complexes also.
通过圆二色性、核磁共振和红外技术研究了缬氨霉素与镁和锶配合物的溶液构象。将结果与我们早期关于锂、钙、锰和钡配合物的结果进行了比较。除锂外，所有这些阳离子都与缬氨霉素形成2:1离子夹心配合物和1:1载体-阳离子配合物。1:1配合物的构象与缬氨霉素-钾配合物不同。锂仅形成1:1配合物。除上述2:1和1:1配合物外，锶和钡还形成大量具有开放构象的1:2配合物，这些构象在溶液中迅速相互转化。考虑到阳离子的离子半径和配位数以及缬氨霉素分子的构象限制，对这些观察结果进行了合理的解释。建议配位数约为六的阳离子（镁和钙）形成2:1和1:1配合物，而配位数较高的阳离子（锶和钡）也形成1:2配合物。
