Self-association of nicotinamide in aqueous solution: light-scattering and vapor pressure osmometry studies.
Nicotinamide is a hydrotropic agent that has been reported to self-associate in aqueous solution. The objective of this study is to characterize the self-association of nicotinamide with regard to the extent of self-association as well as association constants using light-scattering and vapor pressure osmometry. Both methods allow calculation of association constants; however, while light-scattering measurements depend on the size of particles in solution, vapor pressure osmometry depends on the number of particles in solution. Using light-scattering, nicotinamide was found to associate primarily as dimers and trimers. Higher order aggregates can be characterized by an average aggregation number of 4.37. The association constants were 9.99 L/mol and 13.1 L/mol for dimerization and trimerization, respectively. From vapor pressure osmometry data were calculated a dimerization constant of 0.203 L/mol and a trimerization constant of 14.1 L/mol. In comparison, the trimerization constants are in good agreement, while the dimerization constants differ by an order of magnitude. Since light-scattering measurements are less reliable for small molecules like nicotinamide at low concentrations, it is felt that the dimerization constant calculated from vapor pressure osmometry is the more accurate.
Coffman
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Department of Industrial and Physical Pharmacy, School of Pharmacy, Purdue University, West Lafayette, IN 47907, USA.
Kildsig
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D008027:Light; D009536:Niacinamide / Q000737:chemistry*; D009994:Osmolar Concentration; D012542:Scattering, Radiation; D012996:Solutions; D014867:Water
D012996:Solutions; D014867:Water; D009536:Niacinamide