Effect of counterions on the physical properties of l-arginine in frozen solutions and freeze-dried solids.
The objective of this study was to elucidate the physical properties of L-arginine and various counterion combinations in frozen aqueous solutions and in freeze-dried solids. L-Arginine remains amorphous in the highly concentrated non-ice phase in frozen solutions with a Tg (glass transition temperature of maximally freeze-concentrated solutes) of -41.4 degrees C. Some acids and salts (e.g., H3PO4, H2SO4, HNO3, and NaH2PO4) raised the Tg , whereas others (e.g., HCl, CH3COOH, HCOOH, Na2HPO4, and NaCl) had little effect or lowered the L-arginine Tg . Co-lyophilization with phosphoric acid also raised the glass transition temperature (Tg) of amorphous freeze-dried L-arginine solids. Arginine-H3PO4 combinations exhibited properties that led to either the stabilization or destabilization of a model protein (lactate dehydrogenase: LDH) during freeze-drying, depending on their concentration ratios. Fourier-transform infrared (FT-IR) and diffusion reflectance near-infrared (NIR) spectra indicated the presence of interactions between the amino and/or guanidyl groups of L-arginine and phosphate ions in the amorphous freeze-dried cakes. It was postulated that the interaction between L-arginine and the multivalent counterions, as well as an increase in hydrogen bonding network, reduced the mobility of molecules in the frozen solutions and freeze-dried solids.
Izutsu
Ken-Ichi
K
National Institute of Health Sciences, 1-18-1 Kamiyoga, Setagaya, Tokyo 158-8501, Japan. izutsu@nihs.go.jp
Fujimaki
Yasuto
Y
Kuwabara
Akiko
A
Aoyagi
Nobuo
N
D000818:Animals; D001120:Arginine / Q000737:chemistry*; D002850:Chromatography, Gel; D004055:Differential Thermal Analysis; D005612:Freeze Drying; D005615:Freezing; D007770:L-Lactate Dehydrogenase / Q000737:chemistry / Q000378:metabolism; D010756:Phosphoric Acids / Q000737:chemistry; D011817:Rabbits; D012996:Solutions; D017550:Spectroscopy, Fourier Transform Infrared; D019265:Spectroscopy, Near-Infrared
D010756:Phosphoric Acids; D012996:Solutions; D001120:Arginine; D007770:L-Lactate Dehydrogenase