A diosgenin-containing water-soluble polymer as model for the controlled release of brassinosteroids

Abstract

Novel water-soluble polymers containing diosgenin moieties have been synthesized in order to study the proper conditions for the design of phytoactive formulations carrying brassinosteroid analogs. Samples are obtained by radical copolymerization between acrylamide (AM) and diosgenin monomaleate (DMM) at different initial feed compositions. The resulting copolymers present variable steroidal molar fractions ranging from 0.01 to 0.12, as calculated by means of ¹H NMR spectroscopy. Mao–Huglin method is employed for the estimation of monomer reactivity ratios, which renders 16.884 and 0.0024 for AM and DMM, respectively. Surface tension measurements evidence that copolymers with steroidal content below 0.1 exhibit aqueous stability with micelle formation. Controlled release of diosgenin moieties is achieved through alkaline hydrolysis of the monomaleate ester and followed by conductometry. The process displays second order kinetics with a suitable rate constant value for agricultural applications (0.061 L mol⁻¹ s⁻¹). The proposed formulation can also be extended for other applications of steroidal compounds.

Graphical Abstract

Keywords:

• Brassinosteroid analog
• controlled release system
• diosgenin
• phytoactive polymer
• polyacrylamide

Acknowledgments

We thank Dr. Reiner Jordan for providing facilities and equipment for carrying out an important part of this work. Also, we thank Dr. Fabienne Barroso Bujans for her valuable criticism.