Abstract Protamine, one of the nucleoproteins, is contained in the sperm of fishes and is a linear polypeptide with many arginine (Arg) residues. The basic polypeptide chain can behave as… Click to show full abstract
Abstract Protamine, one of the nucleoproteins, is contained in the sperm of fishes and is a linear polypeptide with many arginine (Arg) residues. The basic polypeptide chain can behave as the proton acceptor site in the acid-base composite material. Therefore, we prepared the composite material by the mixing of the basic protein, protamine, and the acidic molecule, methanediphosphonic acid (MP). The protamine-MP composite materials formed the acid-base complex by the electrostatic interaction between the protonated guanidino group in Arg residue and the deprotonated phosphonic acid group in the MP molecule. In addition, the protamine-MP composite material showed the anhydrous proton conductivity of 9.1 × 10−4 S cm−1 at 160 °C in the flowing dry nitrogen. The proton conducting mechanism in the protamine-MP composite material depended on the proton transfer to the proton defect site in the MP molecule without the need of diffusible molecules, such as the oxonium ion.
               
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