FTIR analysis of natural and synthetic collagen

Infrared spectroscopy is one of the oldest and well established experimental techniques for the analysis of secondary structure of polypeptides and proteins. It is convenient, non-destructive, requires less sample preparation, and can be used under a wide variety of conditions. This review introduces the recent developments in Fourier transform infrared (FTIR) spectroscopy technique and its applications to protein structural studies. The experimental skills, data analysis, and correlations between the FTIR spectroscopic bands and protein secondary structure components are discussed. The applications of FTIR to the secondary structure analysis, conformational changes, structural dynamics and stability studies of proteins are also discussed.

This study investigates alginate-chitosan polyelectrolyte complexes (PECs) in the form of a film, a precipitate, as well as a layer-by-layer (LbL) assembly. The focus of this study is to fully characterize, using the complementary techniques of Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) in combination with solution stability evaluation, the interactions between alginate and chitosan in the PECs. In the FTIR spectra, no significant change in the band position of the two carbonyl vibrations from alginate occurs upon interaction with different ionic species. However, protonation of the carboxylate group causes a new band to appear at 1710 cm(-1), as anticipated. Partial protonation of the amine group of chitosan causes the appearance of one new band ( approximately 1530 cm(-1)) due to one of the -NH3+ vibrational modes (the other mode overlaps the amide I band). Importantly, the position of the two main bands in the spectral region of interest in partly protonated chitosan films is not dependent on the extent of protonation. XPS N 1s narrow scans can, however, be used to assess the degree of amine protonation. In our alginate-chitosan film, precipitate, and LbL assembly, the bands observed in the FTIR correspond to the species -COO- and -NH3+, but their position is not different from each of the single components. Thus, the conclusion of the study is that FTIR cannot be used directly to identify the presence of PECs. However, in combination with XPS (survey and narrow N 1s scans) and solution stability evaluation, a more complete description of the structure can be obtained. This conclusion challenges the assignment of FTIR spectra in the literature.

UV irradiation acts as a broad activator of cell surface growth factor and cytokine receptors. This ligand-independent receptor activation induces multiple downstream signaling pathways that regulate expression of multiple genes. These signaling pathways converge to stimulate transcription factor AP-1. Among genes whose expression is regulated by AP-1 are several matrix-metalloproteinase (MMP) family members and type I procollagen. UV-enhanced matrix degradation is accompanied with decreased collagen production mediated not only by activation of AP-1, but also by inhibition of transforming growth factor (TGF)-beta signaling. Several alterations to skin connective tissue that occur during aging are mediated by mechanisms that are similar to those that occur in response to UV irradiation. Thus, skin aging is associated with increased AP-1 activity, increased MMP expression, impaired TGF-beta signaling, enhanced collagen degradation, and decreased collagen synthesis. Knowledge gained from examining molecular responses of human skin to UV irradiation provides not only a framework for understanding mechanisms involved in skin aging, but also may help in development of new clinical strategies to impede chronological and UV-induced skin aging.