Effect of Water on the Molecular Mobility of Sucrose and Poly(vinylpyrrolidone) in a Colyophilized Formulation as Measured by ¹³C-NMR Relaxation Time

Abstract

Individual molecular mobility of sucrose and poly(vinylpyrrolidone) (PVP) in a colyophilized mixture of 1 : 1 by weight has been determined by ¹³C spin–lattice relaxation times in the laboratory frame (T₁) and in the rotating frame (T_1ρ) for systems containing absorbed water at various levels. The T₁ of the PVP pyrrolidone ring carbon increased with storage relative humidity (RH) in lyophilized PVP alone, indicating that the MHz-order motions of PVP side chain increased with storage RH. However, in the colyophilized mixture, the side chain motions of PVP did not change with storage RH, and showed similar mobility to sucrose. This may be caused by hydrogen bonding between the PVP ring carbonyl group and hydroxyl group of sucrose, as suggested by a previous FT-Raman study. The mid-kHz-order motions of sucrose in the sucrose–PVP mixture as determined by T_1ρ did not increase with storage RH as much as in lyophilized sucrose alone. This suggests that the molecular mobility of sucrose decreases in the presence of PVP due to hydrogen bonding between the hydroxyl group of sucrose and the carbonyl group of PVP. Inhibition of sucrose crystallization by PVP in the presence of water appears to be linked to the effect of PVP on the molecular mobility of sucrose.