Preparation and Structure of Amino-Acid Films Based on Vacuum Deposition Processing with and without an Irradiation of Inductively Coupled Plasma

Abstract

Amino acids are capable of constructing supramlecular networks through the multiple hydrogen bonds. Dry processing can produce amino-acid films without the influence of polar solvents, which are usually used for dissolving amino acids in wet processing. In this study, D-phenylalanine (D-Phe) films are prepared by vacuum vaporization methods with and without the assistance of irradiation of inductively coupled plasma (ICP). The vaporized film without ICP irradiation (Vap film) consists of round sponge-like masses (2- to 6-μm diameter) and the content of raw material D-Phe is 72%. Infrared and X-ray photoelectron spectroscopies clarified that there exists little differences between the raw D-Phe and the Vap film. ICP irradiation during vaporization of D-Phe flattened the resultant film surface extremely well and reduced the content of D-Phe to 1.7%. The ICP-treated films have the unpaired electrons at their concentrations of several 10⁴ spins/cm³. Slight reduction of atomic ratios of oxygen in these vaporized films may have been caused by the dehydration and decarboxylation reactions. However, the differences in atomic ratios between these vaporized films and the raw D-Phe are quite small.