Dependence of the molecular mobility and protein stability of freeze-dried gamma-globulin formulations on the molecular weight of dextran

Purpose. The effect of the molecular weight of dextran on the molecular mobility and protein stability of freeze-dried serum gamma-globulin (BGG) formulations was studied. The stabilizing effect of higher molecular weight dextran is discussed in relation to the molecular mobility of the formulations. Methods. The molecular mobility of freeze-dried BGG formulations containing dextrans of various molecular weights was determined based on the free induction decay of dextran and water protons measured by proton NMR. The protein stability of the formulations was determined at temperatures ranging from 20 to 70 degrees C by size exclusion chromatography. Results. Changes in the molecular mobility of freeze-dried formulations that occurred at temperatures below the glass transition temperature could be detected as the molecular mobility-changing temperature (T-mc), at which dextran protons started to exhibit a Lorentzian relaxation decay due to higher mobility in addition to a Gaussian relaxation decay. T-mc increased as the molecular weight of dextran increased. The proportion of dextran protons which exhibited the higher mobility relaxation process (Phm) at temperatures above T-mc decreased as the molecular weight of dextran increased. Protein stability was closely related to molecular mobility. The temperature dependence of the denaturation rate changed at around T-mc, and denaturation in the microscopi cally liquidized state decreased as P-hm decreased with increasing molecular weight of dextran. Conclusions. The effect of the molecular weight of dextran on the protein stability of freeze-dried BGG formulations could be explained in terms of the parameters obtained by H-1-NMR such as T-mc and P-hm. These parameters appear to be useful in preformulation and stability prediction of freeze-dried formulations.