Now, Molly M. Stevens and co-workers report the design of a system with two different communicating polymersome nanoreactors, which can be externally manipulated by light without requiring continuous addition of external chemical fuel. The experimental setup involves an esterase enzyme encapsulated in a polymersome nanoreactor, whose permeability for small molecules can be turned on and off by a donor–acceptor Stenhouse adduct (DASA) photoswitch and a constantly semipermeable polymersome nanoreactor that contains urease as a pH-sensitive enzyme. When the DASA–esterase nanoreactor is irradiated with green light, it becomes permeable for the substrate ethyl acetate, which is consequently transformed to acetic acid by the entrapped esterase (pictured). The system also contains the pH-sensitive pigment methyl red (MR). Lowering the pH by acetic acid formation protonates MR, turning it into a green-light-absorbing species (protonated MR (MRH)). MRH competes with the DASA–esterase nanoreactor for the absorption of light resulting in a negative feedback loop. In addition, the more acidic conditions activate urease to transform urea into ammonia. The formation of this base drives the deprotonation of the pigment back to its non-green-light-absorbing state, providing a positive feedback loop. As such, the two enzymes in this system act in an antagonistic manner.
Importantly, the system was responsive to several dark and light cycles. Moreover, the researchers demonstrated that this light-mediated out-of-equilibrium nanoreactor network can be used to control the swelling of a hydrogel containing tertiary amines. Light-promoted production of acid provokes the protonation of the tertiary amine-containing hydrogel leading to swelling, which was subsequently reversed by accumulation of base under dark conditions.
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