Modulation of small molecule solubility and protein binding by arginine

Abstract

We previously showed that arginine increases the aqueous solubility of the low molecular weight aromatic compounds octyl-gallate (OG) and coumarin. In this study, we focused on acycloguanosine (ACV), an antiherpic agent with moderate aqueous solubility, and examined the effects of arginine on its solubility at a neutral pH. The solubility of ACV increased by approximately 1.9- and 2.6-fold in the presence of 1 and 2 M arginine, respectively, while no solubility changes were observed at an arginine concentration below 0.1 M. These results were found to be consistent with observed changes in OG solubility in the presence of arginine. However, ACV and OG exhibited differential binding to bovine serum albumin (BSA): ACV showed no binding to BSA, while OG showed substantial BSA binding. In conclusion, Arginine partially blocked the protein binding of OG.