title: The influence of residual water on the secondary structure and crystallinity of freeze-dried fibrinogen.
abstract: The purpose of this work was to investigate the influence of water content on the secondary structure of a freeze-dried protein (fibrinogen) after a storage period of two weeks. To that end, attenuated reflectance Fourier transformed infrared (ATR-FTIR) and Raman spectra were generated and evaluated and the crystalline state of the fibrinogen bulks was determined via X-ray diffraction. First, a PCA (principal component analysis) of the spectral data was performed. While the α-helix and β-turn contents were increasing with the increasing water content, the β-sheet content was decreasing. A partial least squares (PLS) model was developed to correlate the mid-infrared and Raman spectral changes with the degree of crystallinity. The obtained R(2) value of 0.953 confirmed a correlation between changes in the secondary structure and crystallinity of the samples. The results demonstrated that the combined ATR-FTIR and Raman approach could be used to predict the crystalline state in freeze-dried fibrinogen products.
authors.affiliation: Research Center Pharmaceutical Engineering, Graz, Austria; Institute for Process and Particle Engineering, Graz University of Technology, Austria.
authors.forename: Verena
authors.initials: V
authors.lastname: Wahl
authors.affiliation: Research Center Pharmaceutical Engineering, Graz, Austria.
authors.forename: Otto
authors.initials: O
authors.lastname: Scheibelhofer
authors.affiliation: Research Center Pharmaceutical Engineering, Graz, Austria; Institute for Biotechnology and Biochemical Engineering, Graz University of Technology, Austria.
authors.forename: Ulrich
authors.initials: U
authors.lastname: Roessl
authors.affiliation: Research Center Pharmaceutical Engineering, Graz, Austria.
authors.forename: Stefan
authors.initials: S
authors.lastname: Leitgeb
authors.affiliation: Laboratory of Pharmaceutical Process Analytical Technology, Ghent University, Belgium.
authors.forename: Thomas
authors.initials: T
authors.lastname: De Beer
authors.affiliation: Research Center Pharmaceutical Engineering, Graz, Austria; Institute for Process and Particle Engineering, Graz University of Technology, Austria. Electronic address: khinast@tugraz.at.
authors.forename: Johannes
authors.initials: J
authors.lastname: Khinast
mesh_terms: D003460:Crystallization; D005340:Fibrinogen / Q000737:chemistry*; D005612:Freeze Drying / Q000379:methods; D017433:Protein Structure, Secondary; D017550:Spectroscopy, Fourier Transform Infrared / Q000379:methods; D014867:Water / Q000737:chemistry*
chemical_list: D014867:Water; D005340:Fibrinogen
keywords: ATR-FTIR spectroscopy; PLS; Raman spectroscopy; Relative crystallinity; Secondary structure; Solid-state protein