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Abstract Covalent attachment of thiols to the tyrosine residues of silk fibroin is accomplished with a high degree of functionalization through the reaction of a pyridyldithiol‐containing N‐hydroxysuccinimidal‐ester and an amino‐tyrosine silk intermediate. The extent of thiol modification is characterized by¹H NMR and UV–vis spectroscopy. Further modification of the thiol groups is probed by reacting with an iodoacetamide‐containing small molecule resulting in a novel fluorescent silk derivative. Last, the ability of the thiolated silk to form hydrogels in situ is investigated. 

Abstract Here, a reaction sequence that can be used to quantitatively modify the tyrosine residues in silk protein fromB. morisilkworms is demonstrated. A primary amine is installed ortho to the hydroxyl group on the tyrosine ring using a diazonium coupling reaction followed by reduction of the azo bond. The resulting amine is then acylated using carboxylic acid or NHS‐ester derivatives at room temperature and neutral pH conditions. The silk derivatives are characterized using¹H NMR, UV–vis spectroscopy, ATR‐FTIR, and a unique method to follow this reaction sequence using isotopically labeled reagents and 2D NMR spectroscopy is also used. This study further demonstrates that this sequence can be used to install alkyne or azide functional groups which can undergo further bio‐orthogonal cycloaddition reactions under mild conditions. Finally, methods to carry out these modifications on solid silk microparticles and electrospun mats are also described.