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Mass Spectrometric Approaches to Study Protein Structure and Interactions in Lyophilized Powders
Published on: April 14, 2015
On the pH memory of lyophilized compounds containing protein functional groups
H R Costantino1, K Griebenow, R Langer
1Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
Biotechnology and Bioengineering
|February 5, 1997
Summary
Lyophilized proteins retain properties from their liquid state, a phenomenon known as "pH memory." This study confirms that model compounds also exhibit similar ionization states after freeze-drying, supporting this concept.
Area of Science:
- Biochemistry
- Physical Chemistry
- Spectroscopy
Background:
- Proteins exhibit "pH memory," retaining characteristics from their aqueous solution pH after lyophilization (freeze-drying).
- The underlying molecular basis for this pH memory, particularly the ionization state of functional groups, requires direct investigation.
Purpose of the Study:
- To investigate whether the ionization state of model organic compounds, mimicking protein functional groups, is retained after lyophilization.
- To quantify the similarity in ionization states and pK(a) values between aqueous and lyophilized forms of these model compounds.
Main Methods:
- Utilized infrared (IR) spectroscopy to analyze the ionization state of amino, carboxyl, and phenolic groups in model compounds.
- Compared the fraction of ionized species in both aqueous solutions and lyophilized powders.
- Determined and compared pK(a) values for each compound in both states.
Main Results:
- The ionization state of model organic compounds was found to be "remembered" after lyophilization.
- Infrared spectroscopy successfully quantitated the fraction of ionized species in both aqueous and lyophilized states.
- pK(a) values in the aqueous and lyophilized forms were highly similar, differing by no more than 0.3 units.
Conclusions:
- The "pH memory" phenomenon extends to the ionization state of key functional groups found in proteins.
- Lyophilization preserves the ionization characteristics of these model compounds, supporting the concept of solid-state behavior reflecting aqueous origins.
