Abstract: Degradable compounds that can be controlled to degrade and can be used for delivery of a cargo component. Cobalt (III) complexes have been exploited as vehicles for molecular complexes. This disclosure describes the use of such complexes as bioconjugation reagents in crosslinking proteins to form particles, PEGylation of proteins, and the synthesis of (bio)polymer-drug conjugates. The Co-based linkages can be designed to respond to internal stimuli, such as changes in pH and reduction potential, or external stimuli, such as applied electromagnetic radiation. Therapeutics are entrapped within these crosslinked particles, covalently attached to the polymer making up the matrix through additional stimuli-responsive linkages, or could comprise the matrix itself.