Intermolecular complexation of low-molecular-weight succinoglycans directs solubility enhancement of pindolol

• Low-molecular-weight succinoglycans from Sinorhizobium meliloti complexed with pindolol.
• Complex formation was confirmed by various instrumental methods.
• Linear succinoglycans enhanced pindolol solubility much better than cyclodextrin.
• Low-molecular-weight succinoglycans were suggested as the best solubilizer for pindolol.

The low-molecular-weight succinoglycans isolated from Sinorhizobium meliloti are repeating octasaccharide units consisting of monomers, dimers, and trimers. Pindolol is a beta-blocker used to treat cardiovascular disorders. We investigated the formation of complexes between pindolol and low-molecular-weight succinoglycan monomers (SGs). Even though SGs have a linear structure, the solubility of pindolol in the presence of SGs was increased up to 7-fold compared with methyl-β-cyclodextrin reported as the best solubilizer of pindolol. Complexation of SGs with pindolol was confirmed by nuclear magnetic resonance, Fourier-transform infrared spectroscopy, differential scanning calorimetry, and scanning electron microscopy. Formation constants of complexes were determined from phase solubility diagrams. Conformation of complex was suggested based on a molecular docking study. The present study indicated that formation of pindolol/SGs complexes not only resulted in increased pindolol solubility but also could be useful for improving its clinical application as it did not affect cell viability.