Arginine is widely used in refolding, purification, analysis and formulation of proteins, primarily because of its ability to suppress protein-protein and protein-surface interactions. Such a property of arginine is at least partially attributable to its affinity for the aromatic groups present in proteins. Herein, we have extended its study further to characterize arginine in terms of its affinity for heteroaromatic compounds, using nucleobases as a model compound. Arginine increased the solubility of all nucleobases tested when these nucleobases were electrically neutral, indicating that arginine interacts favorably with these heteroaromatics. The observed effects of arginine on the solubility of nucleobases suggest that arginine should stabilize the melted state of nucleic acids, in which the nucleobases are more solvent-exposed. In an acidic solution, to our surprise, arginine decreased the solubility of positively charged nucleobases.
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