ON THE PH MEMORY OF LYOPHILIZED COMPOUNDS CONTAINING PROTEIN FUNCTIONAL-GROUPS

Lyophilized proteins exhibit ''pH memory,'' i.e., their behavior in th e solid form corresponds to the pH of the aqueous solution from which they were freeze dried. Herein, we directly tested whether the ionizat ion state is ''remembered'' by model organic compounds containing vari ous protein functional groups (amino, carboxyl, and phenolic). The fra ction of ionized species was quantitated from the infrared spectra of both the aqueous and lyophilized states. The pK(a) values in the aqueo us and lyophilized forms for each compound were found to be quite simi lar, within 0.3 units from each other. (C) 1997 John Wiley & Sons, Inc .