title: Arginine increases the solubility of coumarin: comparison with salting-in and salting-out additives.
abstract: Poor aqueous solubility of low molecular weight drug substances hampers their development as pharmacological agents. Here, we have examined the effects of arginine on the solubility of organic compounds, coumarin, caffeine and benzyl alcohol, in aqueous solution. Arginine increased the solubility of aromatic coumarin, but not non-aromatic caffeine, concentration dependently, suggesting the favourable interaction of arginine with the aromatic structure. Consistent with this, arginine also increased the solubility of aromatic benzyl alcohol. Guanidine hydrochloride, urea and salting-in salts increased both coumarin and caffeine solubilities, while salting-out salts decreased them. These results suggest the specific interaction of arginine with aromatic groups, leading to increased solubility of coumarin. However, the effect of 1 M arginine on coumarin solubility was at most approximately 2-fold, which may limit its applications as a solubility enhancing agent.
authors.affiliation: Institute of Applied Physics, University of Tsukuba, Tsukuba, Ibaraki 305-8573, Japan.
authors.forename: Atsushi
authors.initials: A
authors.lastname: Hirano
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Arakawa
authors.forename: Kentaro
authors.initials: K
authors.lastname: Shiraki
mesh_terms: D001120:Arginine / Q000737:chemistry*; D001592:Benzyl Alcohols / Q000737:chemistry; D001671:Biochemistry / Q000379:methods*; D002110:Caffeine / Q000737:chemistry / Q000494:pharmacology; D003374:Coumarins / Q000737:chemistry* / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D019791:Guanidine / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D008954:Models, Biological; D012492:Salts / Q000494:pharmacology*; D012995:Solubility; D013499:Surface Properties; D014508:Urea / Q000494:pharmacology; D014867:Water / Q000737:chemistry
chemical_list: D001592:Benzyl Alcohols; D003374:Coumarins; D012492:Salts; D014867:Water; D002110:Caffeine; D014508:Urea; D001120:Arginine; C030123:coumarin; D019791:Guanidine