Hydroxyl deformation frequencies as a probe of hydrogen bonding in lasalocid A (X-537A) and its sodium complex.

The hydroxyl deformation frequencies (900-1 500 cm-l) of lasalocid A, its sodium complex, and their deuterated derivatives were studied with Raman spectroscopy. The secondary and tertiary hydroxyl groups of lasalocid A give rise to spectral lines near 1425, 1303, 1172, and 738 cm-’, typical of hydrogen-bonded hydroxyl groups. In the lasalocid A-sodium complex, these are replaced by peaks at 1382, 1200-1250 cm-’, which are not typical of either free or hydrogen-bonded secondary or tertiary hydroxyl residues. The lack of splitting of the 1382-cm-l line is interpreted to indicate the absence of hydrogen bonding of the aliphatic hydroxyl groups in the lasalocid A-sodium complex, implying that cation-oxygen interactions rather than hydrogen bonds are primarily responsible for stabilizing the observed molecular conformations. This result is not consistent with the conventional interpretation of x-ray diffraction data of Johnson et al. on the Ag+ and Ba2+ complexes of lasalocid A, which have been interpreted as indicating that in these complexes the lasalocid A hydroxyl groups are hydrogen bonded.