Polypeptide Ultrathin Films by Vacuum Deposition: Preparation and Characterization
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POLYPEPTIDE ULTRATHIN FILMS BY VACUUM DEPOSITION: PREPARATION AND CHARACTERIZATION Timothy M. Fulghum1, Hiroyuki Yamagami2, Kuniaki Tanaka2, Hiroaki Usui2, Kiyotaka Shigehara2 and Rigoberto C. Advincula1. 1 University of Alabama at Birmingham, Chemistry Department, Birmingham, AL, USA. 2 Tokyo University of Agriculture and Technology, Chemistry Department, Tokyo, Japan. ABSTRACT Polypeptide ultrathin films covalently grafted on solid substrates have attracted considerable attention in the interfacial polymer science community over the past couple of years. The potential applications of these films ranges from applications in liquid crystal displays, biosensors, optical devices, etc.. Their study may address important biocompatibility issues. We have synthesized polypeptide ultrathin films through the use of the physical vapor deposition technique. We expect to gain better insight into the polymerization process of the NCA monomers, as well as, possible control of the secondary structure. Through use of the vapor deposition technique and the amino acid n-carboxy anhydride (NCA) benzyl serine we have been able to prepare polymeric amino acids for analysis. Benzyl serine NCA was evaporated in high vacuum at a temperature of 95-130°C. Different substrates have been used to examine the effects of chemical binding sites on polymerization and secondary structure formation. From IR-spectroscopy and optical microscopy it was evident that without a free amine initiator on the surface of the substrate, polymerization would not occur. Analysis of the films with IR and optical microscopy were used to determine optimum deposition and polymerization conditions. The methyl peak around 3000 cm-1, amide peak at 1650 cm-1 and the carbonyl stretching at 1750 cm-1 evidence of the monomer are greatly reduced or disappear in the deposition range of 40-100nm/min. Analysis of the films with attenuated total reflectance (ATR) Infrared spectroscopy was used to examine the secondary structure. Values of amide 1 peak at 1632 cm-1, representing the carbonyl stretching, and the peak at 1530 cm-1, representing the carbon nitrogen stretching, match with literature values of beta sheet conformation. INTRODUCTION The formation of polypeptides from aminoacid n-carboxy anhydrides (NCA) has been known for a long time. Recently, aminoacid NCAs have become popular materials for preparing thin film polypeptide materials [1-5]. These materials have potential applications in liquid crystal displays, biosensors, optical devices, and their study may address important biocompatibility issues. They are easy to polymerize as homopolymers and copolymers compared to direct stepcondensation methods of amino acid residues. Amine initiator species can be utilized to form high molecular weight polymers through a ring opening polymerization mechanism. The polypeptide films have been prepared in solution or by surface grafting reactions in solution [13]. Recently, Frank and Chang have demonstrated the preparation of these films via a vapor phase deposition from amine fun
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