Methodological effects in Fourier transform infrared (FTIR) spectroscopy: Implications for structural analyses of biomacromolecular samples

• Published in: Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy Vol. 193; pp. 558 - 564
• Main Authors: Kamnev, Alexander A., Tugarova, Anna V., Dyatlova, Yulia A., Tarantilis, Petros A., Grigoryeva, Olga P., Fainleib, Alexander M., De Luca, Stefania
• Format: Journal Article
• Language: English
• Published: England Elsevier B.V 15.03.2018
• Subjects: Bacterial biomass; Chemically modified pectin; Diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy; Fourier transform infrared (FTIR) spectroscopy; Pectin; Poly-3-hydroxybutyrate; Bacterial biomass; Pectin; Chemically modified pectin; Diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy; Poly-3-hydroxybutyrate; Fourier transform infrared (FTIR) spectroscopy
• ISSN: 1386-1425; 1873-3557
• DOI: 10.1016/j.saa.2017.12.051

A set of experimental data obtained by Fourier transform infrared (FTIR) spectroscopy (involving the use of samples ground and pressed with KBr, i.e. in a polar halide matrix) and by matrix-free transmission FTIR or diffuse reflectance infrared Fourier transform (DRIFT) spectroscopic methodologies (involving measurements of thin films or pure powdered samples, respectively) were compared for several different biomacromolecular substances. The samples under study included poly-3-hydroxybutyrate (PHB) isolated from cell biomass of the rhizobacterium Azospirillum brasilense; dry PHB-containing A. brasilense biomass; pectin (natural carboxylated heteropolysaccharide of plant origin; obtained from apple peel) as well as its chemically modified derivatives obtained by partial esterification of its galacturonide-chain hydroxyl moieties with palmitic, oleic and linoleic acids. Significant shifts of some FTIR vibrational bands related to polar functional groups of all the biomacromolecules under study, induced by the halide matrix used for preparing the samples for spectroscopic measurements, were shown and discussed. A polar halide matrix used for preparing samples for FTIR measurements was shown to be likely to affect band positions not only per se, by affecting band energies or via ion exchange (e.g., with carboxylate moieties), but also by inducing crystallisation of metastable amorphous biopolymers (e.g., PHB of microbial origin). The results obtained have important implications for correct structural analyses of polar, H-bonded and/or amphiphilic biomacromolecular systems using different methodologies of FTIR spectroscopy. [Display omitted] •FTIR and DRIFT measurements were compared with and without using KBr in samples.•Biopolyester (PHB), PHB-containing biomass, pectin and its derivatives were studied.•Spectra in KBr matrices showed band shifts for polar and H-bonded functional groups.•Native amorphous biopolyesters may crystallise during sample preparation with KBr.•Matrix-free DRIFT or FTIR measurements are preferable for native biological samples.