Photocatalytic Polymerization from Amino Acid to Protein by Carbon Dots at Room Temperature

The chemical origins of life have been widely accepted at the present stage. However, the idea that amino acids further react to produce peptides and proteins remains an unsatisfactory explanation, because producing polypeptides via spontaneous reaction of amino acids in solution is extremely difficult. It is also necessary to further answer whether amino acids can form longer peptide chains as well as specific chiral structures and so on under this same reaction mechanism. Carbon dots (CDs) have been intensively researched over the past years due to their unique chemical and physical properties. Here, we demonstrate the photocatalytic polymerization of amino acids into polypeptides and proteins using CDs as a photocatalyst, in which the synthetic conditions required are only room temperature (or as low as -20 °C) and aqueous conditions along with light irradiation, which are very mild and easy to satisfy. We even obtain a protein with tertiary structures, namely an artificial insulin with the biological function to reduce the blood sugar of the laboratory mice. The innovation of using CDs to initiate amino acids to condense into polypeptides is based on strong adsorption (e.g., hydrogen bonding), the acidity of the -OH surface functional groups, and the photogenerated protons/holes, which are the fundamental factors for polypeptide or even ternary structure protein formation by means of capturing and condensing the amino acids as well as forming the S-S bonds.