What is Aromaphilicity?

Proteins and peptides have the ability to interact with various substances such as biological molecules and artificial objects. In principle, these interactions are attributed to the interplays of amino acid residues and peptide bonds with target substances and are often described in physical terms, including electrostatic interaction, hydrogen bond, and van der Waals interaction. However, in some practical cases, conceptual scales and indices for describing the nature of amino acids, such as the hydrophilicity scale and the hydropathy index, are more useful for understanding the interactions. In recent years, I have investigated the affinity of proteins and peptides for aromatic carbon materials, such as carbon nanotubes (CNTs) and graphene, and realized that this affinity is barely described by conventional scales and indices. After speculating whether a more suitable index for describing the affinity of amino acids for aromatic carbon materials is available in such a situation, I recognized the need for a new concept that describes such an affinity. Upon establishing this concept, I named the affinity for aromatic carbon material surfaces “aromaphilicity,” meaning an aromatic-loving nature. In this Commentary and Perspective, I summarized my recent works with my collaborators regarding physical interactions between amino acids (or amino acid residues) and aromatic carbon material surfaces and introduced a new index— aromaphilicity index—of amino acids. The aromaphilicity index is unique and distinct from conventional indices for amino acids, offering prospective applications as a universal index for describing the properties of amino acids.