Fig. 3: Polypeptide and protein functionalization with 1.

Yield determined by UV absorption (λ_max = 328 nm); yields and ratios of 11 and 13 were determined by UV absorption at 328 nm and deconvoluted zero-charge mass spectra analysis (Supplementary Information, pages 101–102, 113). The numbers in brackets indicate the molecular weight of unmodified proteins. ^aMgCl₂ (0.1 M) was used in the reaction. ^bTFA (100 mM) was used as buffer. The reaction was conducted at 25 °C for 2.5 h to prevent the aggregation of insulin. ^cMgCl₂ (50 mM) and urea (2.4 M) were used for denaturation. The reaction was conducted at 37 °C for 12 h. ^dThe reaction was conducted at 37 °C for 16 h; Na₂SO₄ (200 mM) was used to stabilize the protein. ^eThe reaction was conducted for 16 h. NaPi, sodium-phosphate buffer; TFA, trifluoroacetic acid; Y, tyrosine residue. Blue background, major modified residue as opposed to red background.