Abstract
Stable chitosan thin films can be promising substrates for creating nanometric peptide-bound polyglucosamine layers. Those are of scientific interest since they can have certain structural similarities to bacterial peptidoglycans. Such films were deposited by spin coating from chitosan solutions and modified by acetylation and N-protected amino acids. The masses of deposited materials and their stability in aqueous solutions at different pH values and water interaction were determined with a quartz crystal microbalance with dissipation (QCM-D). The evolution of the surface composition was followed by X-ray photoelectron (XPS) and attenuated total reflectance infrared (ATR-IR) spectroscopy. Morphological changes were measured by atomic force microscopy (AFM), while the surface wettability was monitored by by static water contact angle measurements. The combination of the characterization techniques enabled an insight into the surface chemistry for each treatment step and confirmed the acetylation and coupling of N-protected glycine peptides. The developed procedures are seen as first steps toward preparing thin layers of acetylated chitin, potentially imitating the nanometric peptide substituted glycan layers found in bacterial cell walls.
Highlights
The backbone of peptidoglycans is an alternating copolymer of β-1-4 linked N-acetyl-D-glycosamine (GlcNAc) and N-acetyl D-muramic acid (MurNAc) and comprises the main dry mass of most bacterial cell walls arranged in nanometric layers.[1,2] Peptidoglycans can be viewed as a type of chitin derivative, or poly β-1−4 N-acetyl D-glucosamine
Direct acetylation of thin films with, for example, acetic anhydride, could not be encountered to the best of our knowledge in the literature.[29−32] Regarding the immobilization of peptides, Neugebauer et al developed a method for the solid-phase peptide synthesis (SPPS) on chitin powders in organic solvents followed by capping of unreacted groups by acetic anhydride and cleavage of the peptide.[33]
Stable and smooth chitosan thin films can be prepared on silicon wafers and gold-coated quartz crystal microbalance with dissipation (QCM-D) sensors by spin coating form aqueous hydrochloric acid solutions
Summary
The backbone of peptidoglycans is an alternating copolymer of β-1-4 linked N-acetyl-D-glycosamine (GlcNAc) and N-acetyl D-muramic acid (MurNAc) and comprises the main dry mass of most bacterial cell walls arranged in nanometric layers.[1,2] Peptidoglycans can be viewed as a type of chitin derivative, or poly β-1−4 N-acetyl D-glucosamine. Deacetylated chitin or chitosan could be a potential precursor if one attempts to semisynthetically mimic the structure of peptidoglycans.[3] Such mimetics can be of interest for studying phenomena at interfaces such as adsorption,[4] enzymatic digestion,[5] live-cell adhesion,[6] or lithography.[7,8] A defined semisynthetic peptidoglycan coating could contribute to insights into biological pattern recognition,[9] cell−cell communication,[10,11] or immune response[12] and can increase our understanding of bacteria.[13] Peptidoglycans are very complex, and bacterial cell walls do consist of polysaccharides and peptides. The first steps toward a potential mimetic based on chitosan would rely on investigating conditions for preparing thin coatings, followed by acetylation into some form of chitin, and derivatization with suitable peptides.
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